Subwoofers and Phase Question For You Sub Experts

     Okay, I'm back and have more time now, so I'll just pick up where I left off in my last post.
     However, I realize you already own two good quality subs which I also know should work well if the subs are properly located and configured and you're mainly concerned with just good bass response at your listening seat and not throughout your entire room, which would require a 4-sub DBA system.  I recommend you use the crawl method to optimally locate each sub around the perimeter of your room. Here's how to perform the crawl method:


1.  Disconnect your 3C speakers, hook up one of your HSU subs and place it at your listening seat position.

2.  On the HSU sub, set the volume control at 50%, the crossover frequency at 60 Hz and the phase at 0 (in-phase).  Play some music with good and repetitive bass.

3.  Beginning at the right front corner of your room, slowly begin walking in a counter-clockwise direction around the perimeter of your room, listening carefully for the exact spot at which the bass sounds best to you (solid, powerful, accurate, detailed, dynamic and natural).  Take your time, walk or crawl on your hands and knees very slowly, listen very closely and repeat if necessary until you identify the exact spot.

4.  Once the spot is identified, move the HSU sub to this exact position.
5.  Repeat this process for your second HSU sub but just begin searching slowly for the next exact room perimeter spot the bass sounds best to you, from where the first sub was located.

6. Once the second spot is identified, move the second HSU sub to this exact position. 

7.  Replay the same music, sit at your listening seat and verify the bass sounds very good to you.  If it does, proceed to step#8.  If it does not, you need to redo the entire procedure starting at step#1. 
8.  Reconnect your 3C main speakers but reverse the polarity on each speaker by connecting the pos. wire to the neg. speaker terminal and the neg. wire to the pos. speaker terminal.  NOTE: Make sure you reverse polarity only on the speakers and not on the amps.  Play the same music and set the phase control on both subs to the position at which the bass sounds the worst to you (the least solid, powerful, accurate, detailed, dynamic and natural).  The reason the polarities are reversed on the main speakers for this step is because it's normally easier to identify the worst bass response in a room than it is to identify the best, it's just a useful trick.  Reconnect your 3C speakers as normal and in-phase, pos. wire to pos. speaker terminal and neg. speaker wire to neg. speaker terminal.
9.  The final step is to fine tune both of your subs by optimally setting the volume and crossover frequency controls on each sub, one at a time. For best results, I recommend setting both controls as low as possible with the caveat that the bass overall still sounding very good to you at your listening seat. It's very useful to recruit a volunteer for this final step, who can slowly adjust the controls at your direction from your listening seat.  Of course, you're free to set these controls at whatever settings you prefer but, based on my knowledge and experience, setting each of them as low as possible typically provides the best results in terms of seamless integration, accuracy, details and a general sense of ease and naturalness on all bass content.  

     Strictly following this procedure should ensure that your listening seat is not located at a bass peak, dip or null in your room and vastly improve the overall perception of bass response performance from your listening seat. I believe your previous sub positioning arrangements likely resulted in your listening seat being positioned at a bass dip or null in your room.  It's very important that you position each sub at the exact position each sounds best from your listening seat, even if that means rearranging your room décor a bit to accommodate optimum positioning.  
     Poor bass response performance is often the result of individuals, or their significant others, wanting to position the subs where they look the best, are the most convenient or are the most out of the way, rather than where they perform best.  It's just like everything else in audio, a matter of choices and compromises.


I hope this will help you,
       Tim

Rooze:
"Just to describe the problem a little more fully -

I have my mains about 75 inches from the front wall and with the mains only I get an excellent perspective, sense of depth and space, and very focused imaging. By perspective I mean that the soundscape is almost entirely behind the front plane of the speakers and extends through the front wall and beyond the outside boundaries of the speakers. The bass from the Dunlavy, in my room, is poor in two ways. Using a test CD and SPL meter, the extension from the sealed box speakers is good into the 45hz range then rolls off quickly. There are dips around 70-130Hz, again at 150-170Hz. I can clearly hear those on certain tracks.

Adding a pair of subs on the outsides of the mains, about an inch or so forward, helps to flesh out the bottom end and mid-bass, but the subs are obviously affected in the same way as the mains by the room modes and the frequency response anomalies.
So it's still far from ideal, but - the attractive imaging and soundstage properties are maintained. There's no negative effect. There's a positive effect but it isn't 'problem solved'.

So moving the subs and placing them by ear/test to get the best and smoothest response at the listening position I end up with the right channel sub about 2 feet behind the right main and the left channel about 5 feet in front of the left main, both up against side walls, both well away from corners and neither firing directly into a wall!

In this way I get a smoother response all the way through the frequency range. Not perfect but better. However, the depth and width of stage is diminished and I lose the laser-like focus of images in the soundscape. There's almost a smearing affect where the air and space around images diminishes and that's what I'm referring to as a 'phase anomaly'.

I've moved the mains to and fro ad nauseam, as we do. I can get a little better response closer to the front wall but the perspective and depth is diminished and I don't want that.
I've tried different listening seat positions, obviously.
I've tried sub placement all over the room and messed with phase toggles (0 or 180) and right now I seem to have the best compromise. But I'm not entirely happy with it.

So if the above is something other than a phase issue I'm happy to stick a new label on it and I'm all over any ways to fix it that don't involve bringing in more gear!

Since posting this thread I've written to a couple sub manufacturers to see if they'd come up with some comments and perhaps even loan out a quad of subs so I can set up the DBA and write the process up as a review. I doubt that will go anywhere but plan B is to go out and buy two or four subs on the used market.
All of your comments are helping and my trigger finger is twitching, but I'm not quite ready to buy more subs just yet."


Hello Rooze,
    I think your comments above are a very good summary of your concerns and goals. Basically, you'd like the already very good soundstage illusion created at your listening seat by your Dunlavy 3C main speakers in the midrange and treble regions, what you call "perspective", to be equally good in the bass region. You've been attempting to achieve this by incorporating two good quality HSU subs in your system and room, at various positions and configurations, with less than desired results.   I believe this is the crux of your matter, but please correct me if I've misunderstood.
    If not, my opinion is also that your issues are not phase related. I believe they are instead sub positioning and configuration related. I'm not surprised that you're having bass issues since it's highly unlikely that the optimum positions of your pair of 3C speakers, in relation to your listening seat, for midrange/treble and imaging performance are the exact same optimum positions of your pair of 3C speakers, in relation to your listening seat, for bass performance. The real problem is that the position of your system's bass drivers (woofers) in your room are restricted to being located directly below your system's midrange and treble drivers in your room.
    As I stated earlier, bass frequency soundwaves behave very differently than the much higher midrange and treble frequency soundwaves in any given room. This is mainly due to the fact that full cycle bass frequency soundwaves are very long and have omnidirectional radiation patterns while full cycle midrange/treble frequency soundwaves are much shorter and have very directional radiation patterns. As a result, the perception of bass and midrange/treble at one's listening seat is facilitated and can be optimized when the positions of their corresponding drivers are independent of each other and can be located in the room separately.
    The above is why I prefer to treat my systems as two systems: a bass system and an everything else system. I typically begin by optimizing the bass in the room first because I think it's usually the hardest to get sounding right in most rooms and then optimize the everything else, which includes midrange/treble and imaging performance, afterward because it's relatively much simpler. I suggest you may want to try doing the same.
    In your case, this would entail a couple of possible options as solutions. Based on my knowledge and experience, I know that utilizing either an Audio Kinesis or a custom 4-sub DBA (distributed bass array) system would provide the highest quality bass response and integration in virtually any room and with any pair of main speakers. I believe this is the ideal solution for you because it will work extremely well for your system now as well as if you ever change rooms or main speakers.
    However, I realize you already own two good quality subs which I also know should work well if the subs are properly located and configured. I recommend you use the crawl method to optimally locate each sub around the perimeter of your room.  I can describe this, as well as how to optimally set the volume, crossover frequency and phase controls on each, later if you're interested.  Sorry I don't have time right now.


    

Playing with phase settings has little impact on the problem since there’s just a toggle for 0 and 180

This is not phase. This is polarity.

Some of the more upmarket subs have 360 degree control

This is phase. This basically helps to achieve maximum output level of the subs.

but the subs are obviously affected in the same way as the mains by the room modes and the frequency response anomalies.

 Multiple subs helps with this issue.

There's almost a smearing affect where the air and space around images diminishes and that's what I'm referring to as a 'phase anomaly'.

 This could be caused by an overlap in frequencies being produced by your mains and your subs. This is an issue that a crossover or speaker management system can eliminate. If you do not want to do an external crossover set the low pass filter on your subs to the low end cutoff point of your mains. Plugging any ports should also help.

@audiokinesis Duke I emailed you a cool video of constructive and destructive interference and the nodal pattern , reflection matter :-) as I know you know

Hello Duke,

    I'm just glad you were following this thread and willing to give such a detailed and informative answer to my question. It all makes perfect sense to me.....Again..... and I'm sorry you needed to repeat your excellent explanation just for that dim-witted knucklehead. Thank you, again and the knucklehead did take notes this time.
    There's a lot of interesting and useful things to know about attaining very good bass reproduction in a domestic sized room and I'm very appreciative for your and James Romeyn's help in sharing the knowledge and experience both of you have gained over the years. It's definitely been of great value to me in my journey that has finally led to attaining near sota bass performance in my room and system.
    I've learned a lot and gained valuable first hand experience along the way. For example, I discovered that class D amp bass can initially sound very good on one's main speakers; very quick, impactful, dynamic and taut. However, I've learned the very high damping factors of many of these class D amps is a likely cause of the bass sounding somewhat unnatural, although still enjoyable, with the leading edge of the bass notes being emphasized and the trailing edges being underemphasized and the decay even being truncated. 
     I only realized this after I installed the AK Debra 4-sub DBA system powered by a Dayton class AB amp and continued to run my main speakers full range driven by my high powered class D mono-blocks (D-Sonic M3-600-M with 1,200 watts and damping factors > 1,000) originally into my 4 ohm Magnepan 2.7QR and now into my 4 ohm 3.7i main speakers.  Suddenly, the bass sounded much more natural, still with powerful and dynamic leading edge bass but also with easily discerned trailing edges and natural sounding decays.  
    I was wondering if you noticed the same thing with class D high damping factor amps versus class AB lower damping factor amps driving your speakers and subs?  If so, is this why you use a class AB amp instead of a class D amp on the Swarm and Debra systems?

Thanks for all your help Duke,
              Tim

A very illuminating study was conducted in which short-duration low frequency signals - including mere fractions of a cycle - were digitally created and played over headphones (to avoid room effects). Listeners were UNABLE to even DETECT the presence of bass energy from less than one full wavelength. Consider how long wavelengths are at low frequencies and you’ll see that, unless your room is very large, by the time you BEGIN to hear the deep lows, that energy has already reflected off of multiple room surfaces. In this context, a difference in subwoofer arrival times which amounts to a tiny fraction of a wavelength is inconsequential.

Herein also explains why high damping factors are overrated! The ear cannot detect instantaneous starts and stops if less than one waveform; it is the ability to stop a woofer that is trotted out in the discussions about damping, which goes something like 'Imagine a pulse which starts and stops...' and of course you can't hear that, and further doesn't exist in the real world.


Not meant to derail the topic!

@noble100 wrote: "... I’m still having difficulty recalling exactly why it’s not important that the timing of the bass soundwaves reaching our ears matches the timing of the midrange and treble soundwaves reaching our ears.... Hopefully, Duke will chime in again and explain it again. I’ll write it down someplace this time if he does."

The short answer is, the ear doesn’t hear small differences in arrival times at low frequencies.

Here’s a much longer answer:

It makes intuitive sense to line up everything up so that the arrival time for the sub(s) is the same as for the mains, but the real world is more complicated. What we overlook is, the effect of the phase response.

Let me give a fairly simple example: Suppose we have a 4th order crossover at 80 Hz (maybe 4th order lowpass filter on the subs, maybe 2nd order acoustic rolloff + 2nd order highpass filter on the mains). With a 4th order crossover the lowpass and highpass sections are theoretically "in phase" at the crossover frequency, but the lowpass section (the subwoofer) is lagging the highpass section (the mains) by 360 degrees... one full wavelength. In order to align their arrival times, the subwoofers would need to be one wavelength at 80 Hz closer to the ears. That’s fourteen feet! (This same principle holds up for shallower slope crossovers and for asymmetrical crossovers, the fraction of a wavelength is less but more math is involved which is why I picked 4th order for this example.)

The ear’s poor time-domain resolution at low frequencies comes to our rescue. We don’t notice that the output from the subs is arriving one wavelength (fourteen feet) later than it should. I’m not saying there would be no subjective improvement from correcting that, but it’s not "what matters most"... which is a topic I’ll come back to later.

It also makes intuitive sense for the output of all of the subs to arrive at exactly the same instant. This is inherently accomplished if you only have one sub, and can be accomplished at one listening position if you have more than one sub. However if arrival time was what mattered the most in the bass region, then one sub would be what sounds the best, especially outside of the sweet spot.

The reason arrival time isn’t what matters most is, the ear has very poor time-domain resolution at low frequencies. This is why we are so poor at hearing the direction of very low frequency sine waves in a room - we cannot separate the first arrival from the reflections. But this makes the ear very forgiving of small timing errors at low frequencies.

A very illuminating study was conducted in which short-duration low frequency signals - including mere fractions of a cycle - were digitally created and played over headphones (to avoid room effects). Listeners were UNABLE to even DETECT the presence of bass energy from less than one full wavelength. Consider how long wavelengths are at low frequencies and you’ll see that, unless your room is very large, by the time you BEGIN to hear the deep lows, that energy has already reflected off of multiple room surfaces. In this context, a difference in subwoofer arrival times which amounts to a tiny fraction of a wavelength is inconsequential.

(Something which to the best of my knowledge has not been studied is what the time-domain resolution is for the tactile -"felt" with the body rather than heard with the ears - perception of bass energy. I would guess that the time window for "perceptually simultaneous" impact is related to receptor nerve and/or neuron firing rates, which I have not studied.)

Of far greater perceptual consequence is what’s happening to the trailing edge of the bass tones... how smoothly do they fade away? (The first time I encountered a designer giving precedence to the trailing edge over the leading edge was Jon Dahlquist. Jon wrote that, in the course of designing the legendary DQ-10, he had to choose between aligning the leading edges of waveforms, or aligning the trailing edges of waveforms. Listening tests led him to the counter-intuitive conclusion that the trailing edge of the notes mattered more. So this concept is applicable elsewhere in the spectrum, but it is especially applicable at low frequencies in the size listening rooms we have in our homes.)

Well it turns out that speakers + room = a minimum phase system at low frequencies (this according to multiple researchers, including Floyd Toole and Earl Geddes), which means that the time-domain response tracks the frequency response. So where there is a frequency response peak, that’s where the energy takes longer to decay into inaudibility (not that it necessarily decays slower; but because it starts out louder, it takes longer to finish decaying).

I said I’d come back to "what matters most" in the bass region, and imo it's the in-room frequency response. This is predicted by equal-loudness curves, which bunch up south of 100 Hz. They tell us that a 5 dB difference at 40 Hz or so is perceptually comparable to a 10 dB difference at 1 kHz! No wonder big in-room peaks in the bass region are so detrimental to sound quality.

So to recap, the ear has very poor time-domain resolution in the bass region, but has exaggerated sensitivity to frequency response errors in the bass region.

The good news is, the ear really appreciates any improvements we can make in the bass region, whether they be by way of EQ, bass trapping, a distributed multi-sub system, or just working with positioning... or any combination thereof. The information I’ve seen leads me to believe that a distributed multisub system usually makes a bigger improvement than these other techniques in an already competent system, but I’m hardly a disinterested observer.

Sorry this is probably a much longer answer than anyone was looking for.

Duke

And a nice Fluke DMM

Vandertones are a free download, everyone should have them and an SPL meter in toolbox

So your subs are crossed over too high and mucking up image, 

what is the filter set at and what slope?

download Vandertones and get an analog SPL meter, pm me for process 

the vandertones are not built using 1/3 octaves like most RTA or DSP, based on typical nodes in listening roomed, RV is a practical dude, and he read and agreed w Geddes paper and work many many many years ago

@m-db 

Rooze, way off topic questions.
What model phono cartridge are you using and what did the Zesto Audio Andros bring to your setup?

m

Using a ZYX Ultimate and the Zesto is great!! Actually just posted a brief review of it earlier today... maybe you saw that?

Rooze, way off topic questions.
What model phono cartridge are you using and what did the Zesto Audio Andros bring to your setup?

m

Used a Lyngrof DPA-1 to delay my main speakers as suggested by JL Audio 10 years ago.
It did work and I listened for several weeks after which I went back to my original set up and removed the Lyngrof processor which yielded time delay, room correction and preamp.
I found the music in my system was artificial enough that it bored me, the excitement and physical sensation was not truly present.
Perhaps after 10 years technology has leaped forward and I am willing try some other devices as suggested by JL Audio eg DEQX.

Wow this has turned into a great thread. I was a little concerned about it going off the rails early on, but it hasn't.

Thanks to everyone who has chimed in so far and keep the ideas coming.

My take away so far is mostly derived from an earlier post from Audiokinesis:

1 - Get the room as 'tuned' as possible using conventional bass traps and treatments.

2 - Then, utilize one or both of EQ/DSP and DSA to dial-in the best response. As Duke says, smooth bass = fast bass.

Then things get a little more subjective around the following:

1 - Time-alignment is a non issue due to low frequency wavelengths. I can see the physics of this argument yet there are others in the know who disagree. Lyngdorf for example (The TACT spinoff) factor for sub positions and have a delay factor for the mains built into their DSP or 'Room Perfect'. Perhaps that's a novelty or selling point and nothing more. I don't know.

2 - Phase control. Is it an issue or isn't it an issue? In my OP I was asking whether or not DSP factors for phase alignment and the consensus has been that it does not. Some of the more upmarket subs have 360 degree control where others simply have a 0-180 toggle. REL, known for their 2-channel prowess offer neither on their T/7i, which is aimed at the 2-channel market. So what gives? I suppose their answer would be to flip the leads on the amp binding posts. (high level)

My choice of the word 'phase' when describing a specific issue was perhaps misleading. Maybe it's a phase issue maybe it's something else.

Just to describe the problem a little more fully -

I have my mains about 75 inches from the front wall and with the mains only I get an excellent perspective, sense of depth and space, and very focused imaging. By perspective I mean that the soundscape is almost entirely behind the front plane of the speakers and extends through the front wall and beyond the outside boundaries of the speakers. The bass from the Dunlavy, in my room, is poor in two ways. Using a test CD and SPL meter, the extension from the sealed box speakers is good into the 45hz range then rolls off quickly. There are dips around 70-130Hz, again at 150-170Hz. I can clearly hear those on certain tracks.

Adding a pair of subs on the outsides of the mains, about an inch or so forward, helps to flesh out the bottom end and mid-bass, but the subs are obviously affected in the same way as the mains by the room modes and the frequency response anomalies.
So it's still far from ideal, but - the attractive imaging and soundstage properties are maintained. There's no negative effect. There's a positive effect but it isn't 'problem solved'.

So moving the subs and placing them by ear/test to get the best and smoothest response at the listening position I end up with the right channel sub about 2 feet behind the right main and the left channel about 5 feet in front of the left main, both up against side walls, both well away from corners and neither firing directly into a wall!

In this way I get a smoother response all the way through the frequency range. Not perfect but better. However, the depth and width of stage is diminished and I lose the laser-like focus of images in the soundscape. There's almost a smearing affect where the air and space around images diminishes and that's what I'm referring to as a 'phase anomaly'.

I've moved the mains to and fro ad nauseam, as we do. I can get a little better response closer to the front wall but the perspective and depth is diminished and I don't want that.
I've tried different listening seat positions, obviously. 
I've tried sub placement all over the room and messed with phase toggles (0 or 180) and right now I seem to have the best compromise. But I'm not entirely happy with it.

So if the above is something other than a phase issue I'm happy to stick a new label on it and I'm all over any ways to fix it that don't involve bringing in more gear!

Since posting this thread I've written to a couple sub manufacturers to see if they'd come up with some comments and perhaps even loan out a quad of subs so I can set up the DBA and write the process up as a review. I doubt that will go anywhere but plan B is to go out and buy two or four subs on the used market.
All of your comments are helping and my trigger finger is twitching, but I'm not quite ready to buy more subs just yet.

millercarbon:
"Exactly. Two completely different animals. This may be one of the hardest parts of the whole thing to understand. Though granted, the whole DBA approach relies on a number of hard to understand concepts. No one of them really so much hard as different. At least I feel it must be something like that. Else why so many have explained so clearly and yet so few seem to get it?"

Hello millercarbon,

     Besides Duke, I think we're both aware that we are probably the biggest believers and proponents of the 4/5-sub DBA concept on these forums.  There are several other members that are strong believers in the DBA concept but you and I are likely the most prominent and vocal advocates.  I believe this is due to us both doing a lot of research on the sound bass principles underpinning the DBA concept, being relatively early adopters of the concept and having years of practical experience actually using the concept in our own systems/ rooms and knowing first hand how consistently, reliably and exceptionally well the concept performs.
     I think I have a fairly good grasp of most of the dynamics afoot in the behavior of bass soundwaves in any given room that enables the 4-sub DBA concept to deliver near state of the art bass reproduction in any room and seamless bass integration with any pair of main speakers. 
     I understand that bass radiates in a omnidirectional pattern, the length of soundwaves are inversely proportional to their frequency, the length of deep bass soundwaves can often exceed any of a room's dimensions, humans require the entire full cycle soundwave to be present in the room to even perceive a sound, we require 3 complete soundwaves to perceive a change in pitch, we cannot localize bass soundwaves at or below about 80 Hz, soundwaves continue to reflect off of room boundaries (floor, ceiling and walls) until they are absorbed, diffused or run out of energy, the multiple soundwaves reflecting around the room will typically collide with each other causing frequency peaks, dips and nulls.  
     Utilizing multiple subs will actually increase the number of bass peaks, dips and nulls in the room but our amazing brains are able to process these multiple peaks, dips and nulls by summing the bass by frequency and averaging it out and creating a perception that the bass is smoother, faster and more detailed.  As a bonus, this excellent bass response perception is created no matter where in the room one's head is actually positioned. All quite amazing and very beneficial to music lovers desiring excellent bass reproduction throughout their entire room.
     I understand all of the above but I'm still having difficulty recalling exactly why it's not important that the timing of the bass soundwaves reaching our ears matches the timing of the midrange and treble soundwaves reaching our ears.  I know it's unimportant just by listening to my system, bass from 20-40 Hz reproduced by the 4 distributed subs and midrange/treble reproduced by a pair of carefully positioned Magnepan 3.7i main speakers.  The bass deep, powerful, smooth, fast, detailed, dynamic and natural seamlessly integrated with the main speakers.  
    I know there's a logical and reasonable explanation but I can't, for the life of me, recall it.  Hopefully, Duke will chime in again and explain it again. I'll write it down someplace this time if he does.

Tim

I should say image shift for poorly integrated systems

Also for students of the bass, yes I am a hack but I can get around a fretless, the wave is BIG, bigger than most rooms....so reality is the wave is folded and truncated anyway, which IF ya think about it absolutely F the phase...

IF you like math, get Olsons excellent and of course still very relevant text: Elements of Acoustical Engineering

but you also need a reference for accurate bass, two that I use are Ray Brown - Soular Energy and JD Souther - Silver Blue off of Black Rose ( Stanley Clarke, man that cat can play )

both of these recordings will reveal image shift at between 80-150 HZ 

you can figure out the notes ;-)

First for the OP - great choice of main speakers, wish he was still alive along with Jim T
( yes I owned and sold both ) and have Vandersteen to this day , time and phase do matter and most importantly above 120 HZ) the Vandersteen sub 9 is a swarm with analog 11 band EQ for each of the 4 subs to fix room issues below 120 and w aysemetic cut vs boost. 
Swarm fixes freq response issues caused by room, analog EQ fixes bass at listening position

dsp probably screws up time and phase above 120

have fun, Tori Amos beackons....

I just wanted to add a bit of information to readers about concerns with a somewhat related topic: aligning arrival times of midrange /treble soundwaves with bass soundwaves at our ears. Briefly stated: don't even bother to be concerned with it.  
    Midrange/treble complete cycle soundwaves are very directional and short compared to bass complete cycle soundwaves that are omnidirectional and very long.

Exactly. Two completely different animals. This may be one of the hardest parts of the whole thing to understand. Though granted, the whole DBA approach relies on a number of hard to understand concepts. No one of them really so much hard as different. At least I feel it must be something like that. Else why so many have explained so clearly and yet so few seem to get it?

This one though I give top honors because if there's one thing we all know for sure its that timing matters a lot. With full range speakers everything must be done just right or you will get poor if any imaging, and it will be obvious where the sound is coming from. With subs, and especially with a swarm, you can plop them down just about anywhere and never know. The first few weeks with mine I lost count how many times I walked right up to one and finally wound up putting my hand on it just to be sure it was working.

But then this should be obvious, if for no other reason than a lot of us run these things pointed at the wall. Hello! At. The. Wall.

How much more different you can get than that, I just don't know.

danvignau,

    I know you're referring to phase alignment of the woofers.  But I just wanted to add a bit of information to readers about concerns with a somewhat related topic: aligning arrival times of midrange /treble soundwaves with bass soundwaves at our ears. Briefly stated: don't even bother to be concerned with it.  
    Midrange/treble complete cycle soundwaves are very directional and short compared to bass complete cycle soundwaves that are omnidirectional and very long.  A 20 Hz deep bass soundwave is 56 feet long and a 20,000 Hz high treble soundwave is a fraction of an inch long.  Because of this, midrange/treble soundwaves behave very differently than bass soundwaves do in any given room.  
    With the main speakers pointed directly at your listening seat, the short and highly directional midrange/treble soundwaves are going to take a direct path and reach our ears first and fairly quickly, before the omnidirectional bass soundwaves that take an indirect path and typically bounce off multiple room boundaries (floors, walls and ceiling) on their way, before arriving at our ears  a bit subsequently.  One would think this results in the bass being perceived as somewhat lagging behind but it does not; the arrival times of the bass, midrange and treble are perceived as properly time aligned.  
     There's an explanation for this that I believe is important to understand but I don't recall what the explanation is.  Can anyone explain why the arrival times of bass soundwaves slightly after midrange and treble soundwaves at our ears doesn't appear to be important?

Thanks,
  Tim

I certainly do not claim to be an expert, but I can add this; Take a sub driver and main woofer out and measure the distance  from the mounting surface to the center of the magnet, and not at an angle from one to the other.  Make certain the sub cabinets and mains cabinets are positioned from the front to of the cabinet,  exactly the distance as the difference between the two measurements. Allow for the thicknesses of the two cabinets, if necessary.   This will phase align all your woofs. It really works. 

We humans may not hear directionality from the woofage, but the laws of physics are not waived because of that fact.   

@rooze 

I have a REL S5 and the sense of space that it creates with my PSB T3's in my listening area is amazing. Both on music and home theater. The REL mission statement is all about doing exactly what you want. The S5 was just replaced in the REL lineup 2 months ago by the S812.

GLHF!

@noble 100:
Ii have two Krell EV-600 monoblocks and two JL Fathom 13’s.  I have not had to increase the subs volume, or turn up my preamps volume since utilizing the dbx unit.  It has a max output of +22 dBu through balanced outputs.  You can also delay the subs or main speakers output, to properly align the subs and main speakers, as well as adjust phase of both on the fly.

Hello handymann,

     Well, it seems like we now have a few contenders for high quality methods for integrating subs into one’s system; the distributed bass array, the line bass array and now, the DBX Venue 360 device. Since the DBX Venue 360 is basically an equalizer and room correction device, however, my main concern is that very high powered amps would also be required for it to operate effectively.
     I have little doubt this unit is able to correct all the frequency peaks it identifies in a room, since it merely needs to direct the amps to reduce power at the appropriate frequencies or filter out the excess energy.  But I do doubt this unit, without considerable amp power used in conjunction, is able to correct all the frequency dips it identifies in a room, since it needs to direct the amps to increase power at the appropriate frequencies. Correcting frequency response dips requires significant amp power, possibly even a doubling or more of power at bass frequencies.
So, the DBX Venue 360 could be performing its function perfectly but there’s insufficient amp power to correct all the room’s frequency dips it has identified.
     Handymann, how many amps and how much amp power do you utilize for your subs and main speakers? Do you have a sense of whether or not your system amp power is sufficient to correct all the frequency dips in your room identified by the DBX without straining these amps?

Thanks,
Tim

I have wrestled with sub integration for years, until I purchased a DBX Venue 360. You can control your main speaker delay or sub delay.  This unit is designed for live stage performance, but cured my subwoofer problem completely.  You should really look at the specs and try one.  It fixed my TT acoustic feedback, as well a a whole host of issues. I used to listen and worry about how I could make everything coherent. Now, I just listen and appreciate. 

     Audiologic's procedure for properly setting the phase control is the best I've found thus far.    
    With phase, it's usually easier to identify the setting that is most 'out of phase' ( the worst or least bass) than identifying the setting that is 'most in phase' (the best or most accurate bass). And all it takes is a simple phase inversion on a speaker. listening and setting the phase control accurately and the a simple reversal of the phase inversion back to normal.
    As I write this, I realize It is a bit confusing when written out.  
 I think audiologic better articulated the procedure than I did here.   I recommend rereading his post and striving for comprehension of the task at hand, it's easier than I make it out to be once you understand the goal. I'm going to shut up now.

Tim

@rooze 

If your HSU subs lack continuously variable phase adjustment, then integration is more difficult.  A simple method for integrating subs with mains is to disconnect one speaker and the sub residing closest to that speaker.  At a medium volume, play a test tone at the frequency you've chosen for crossing from mains to subs. While you sit in your listening position,  have a friend adjust the gain on the subwoofer amp until the output from sub and main is equal.  At that point change the polarity on the main speaker putting it 180 out of phase with the sub.  Again play the test tone and have the friend adjust the sub's phase control back and forth until you have maximum bass drop out, or a bass null if you will.  Reconnect the main to it's correct polarity and the main and sub will be in phase.  Do the same for the other channel.  I use that method in conjunction with Dirac Live and it works beautifully.

kenjit:"in other words we dont really know how all these things work so just do a bit of each and see what happens. "

Hello kenjit,

     That's not what Duke stated and I think you're aware of that. Most members already understand that he knows how all these things work and that he stated that utilizing bass trapping room treatments, EQ and multiple distributed subs in a room and system will all contribute to better in-room bass performance in most any given room.
     Bass trapping absorbs in-room bass energy which shortens the decay times and thereby reduces the magnitude of both the peaks and the dips everywhere in the room. (The in-room frequency response tracks the time domain response, and vice-versa, in the bass region.)
     EQ is very good at reducing peaks but not so good at filling in dips, which are caused by modal cancellation, and driving that cancellation harder can eat up a lot of power and excursion (a 6 dB boost to fill in a dip would call for a doubling of excursion and a quadrupling of power). EQ of a single subwoofer is most effective at a single location, because the room-interaction peaks-and-dips will be at different frequencies for different locations within the room. So EQ can be great in the sweet spot, but it usually make things worse elsewhere in the room. In general the larger the listening area we try to fix with EQ, the less improvement we are able to make at any specific location within that area. 
     A distributed multisub system results in a significantly improved peak-and-dip pattern. Each sub contributes its own unique peak-and-dip pattern, but each sub is only contributing maybe 1/4 of the total bass energy, so the net result is many small peaks and dips instead of a few large ones. This can have a non-obvious psychoacoustic benefit: When a peak and a dip are fairly close to one another (within about 1/3 octave), the ear/brain system averages them out. So the perceptual improvement tends to be greater than what we would infer from eyeballing before-and-after curves. And this improvement is not limited to a given location, but extends throughout the room.
     Duke is not recommending individuals do a little bit of bass trapping, a little bit of equalizing and a little bit of utilizing multiple subs and just see what happens.  He's stating that it's best to utilize all 3 approaches, bass trapping, EQ and multiple distributed subs, in a thorough and complete manner in order to realize the optimum bass response performance attainable in a given room.
      I know my intention, and I believe Duke's intention, of contributing our knowledge and experience on this thread is to save some time and effort for those interested in attaining exceptionally good bass performance in their rooms no matter their room details or the specific main speakers they utilize.  
     Of course, I realize that Duke has superior knowledge and experience on this stuff than I possess.  But I believe I also have relevant information to contribute based on my experiences using his AK 4-sub Debra DBA system for over 4 years thus far.
    You're more than welcome to take the long path I took in researching the distributed bass array concept via reading scientific White Papers on the subject written by Dr. Earl Geddes and Dr. Floyd Toole as well as other writings on the subject from Harman International's Todd Welti and Audio Kinesis's Duke Lejeune and James Romeyn before finally deciding to take a bit of a leap of faith and buying the $3K Debra and giving it a try in my medium sized room with Magnepan main speakers.  I just thought readers might appreciate the time saving gains resulting from summarizing the main dynamics involved in the DBA concept and my 4+ years of experience enjoying it.
     The reality is that I'm currently only using one of Duke's recommended three methods of attaining very good in-room bass performance, the use of the 4-sub DBA concept system, but I'm still achieving what I consider near state of the art bass performance throughout my entire room without the use of any EQ or bass trapping. 
    However, I respect and trust Duke's advice about bass trapping, EQ and using multiple distributed subs.  I also had a free room analysis done by GIK Acoustics that recommended bass trapping so I just ordered about $3,500 worth of room treatments that includes stacked bass traps in all four corners, two 5.25" thick 244 bass trap panels on the front and rear short walls and a 50/50  ratio of absorbing and diffusing treatments throughout my room for midrange and treble frequency control.  Once these are all installed, my plan is to listen to the results before deciding if EQ and any further room treatments would be worth trying.

Tim

bdp24, slipping in right at the wire taking the prize for top post of 2019:

"in other words we don't really know how all these things work so just do a bit of each and see what happens."

Now remember, this was posted after a number of posts from Duke, noble100, millercarbon, and others, in which they provided plenty of evidence that we DO know how all these things work.

Poor reading comprehension skills, slow learner, or just plain ol' duh?

Don't reply. Just read, and bask in its beauty.

Has anyone tried Rythmik subwoofers? They use servos to make them fast and clean. In my little room I use a sealed unit and I cound an out of the way place where it fits in with my Magnepans.

OP, if you think this is a phase problem, in the sense that you would hear out of phase L and R speakers, swap both of your main speaker cables.  See if that fixes what you are hearing.
If that's not it, then I have no idea why we are talking about phase problems in your particular situation. If that's not what you are hearing, then the issue is the usual complicated subwoofer problem of integrating to the room and main speakers.

My 2 cents.

 A pair of JL Fathom subs positioned near each SCIII and budget permitting a CR1 crossover.  Crossover the SCIII and the Fathoms at 80 Hz. bypass the crossover in the Fathom subs built in control.  Run the correction on each sub.  Then phase align them.

Play an 80 Hz tone. 

Disconnect the right speaker and subwoofer.

Reverse the polarity of the left speaker by connecting the positive speaker wire to the negative terminal and the negative speaker wire to the positive terminal.

With your head placed equidistant from the speaker and the subwoofer, slowly rotate the subwoofers phase control knob until you notice the bass drop off significantly, then begin to rise. With the speaker and subwoofer playing the test tone at the same level, but 180 degrees out of phase, a null point is created, and the bass cancellation should be easily discernible.

Set the subwoofers phase control at the position where the bass appears to have the least amplitude.

Reverse the polarity of the speaker again by connecting the positive speaker wire to the positive speaker terminal and the negative speaker wire to the negative speaker terminal.

Repeat for the right side.

>The CR1 has damping and and sub/sat balance controls for fine tuning.  Do a Google search and read the reviews.

EQ wont affect phase. Beauty of JL is the continuous phase adjustment.Barry Ober the support guy at JL has some excellent material on their site explaining foolproof phase set up. (reverse polarity on speaker cables, play test tone at crossover frequency, dial phase until you hear the signal null, reconnect cables correct polarity) Check out his stuff.

gosta:"Tried the "swarm" approach and moved four subs into the room but unfortunately found out that they all have about the same tops and dips wherever placed (+/- 20 db from 25 to 100 Hz). So not much of an improvement. Room eq necessary."

Hello gosta,

     As Duke mentioned, something is likely wrong in your positioning of the subs or configuration if you didn’t notice a dramatic bass improvement using a 4-sub DBA in your room. I suggest you may want to answer Duke’s questions to you on his reply if you’d like to figure things out, he knows more about attaining good bass than anybody I’m aware of.
     In the meantime, I thought I’d share how I setup my 4 subs just in case it might work well for you. I have the Audio Kinesis Debra 4-sub DBA system using a single sub amp/control unit. However, I don’t know which 4 subs you’re using, a complete AK Swarm or Debra bass system kit or 4 traditional self-amplified subs. Either should work well, it’s just that you’ll need to adjust the volume, crossover frequency and phase controls on each sub individually if you use traditional self-amplified subs. On the Swarm and Debra, you just need to adjust these controls once on the included amp/control unit for all 4 subs as a group.
     But either way, following my positioning method could be helpful to you:

1. Disconnect your main speakers and move them to another room.
2. Hookup sub#1 and place it at your listening position. If you’re using self-amplified subs, do the same thing but set the volume to 50%, the crossover frequency to 40 and the phase control to "0" (in-phase).
3. Play some music with good and repetitive bass.
4. Starting at the front right corner of your room, slowly begin walking in a counter-clockwise direction around the perimeter of your room listening for the first exact spot that the bass sounds best to you (solid, detailed, dynamic and natural). Take your time, listen carefully and repeat this step until you are certain you’ve found the exact spot.
5. Once you’ve identified the exact spot, move sub#1 from your listening position to this exact spot.
6. Hookup sub#2 and place it at your listening position. If you’re using self-amplified subs, do the same thing but set the volume to 50%, the crossover frequency to 40 and the phase control to "0" (in-phase).
7. Play some music with good and repetitive bass.
8. Starting at sub#1, slowly begin walking in a counter-clockwise direction around the perimeter of your room listening for the next exact spot that the bass sounds best to you (solid, detailed, dynamic and natural). Take your time, listen carefully and repeat this step until you are certain you’ve found the exact spot.

9. Once you’ve identified the exact spot, move sub#2 from your listening position to this exact spot.
10. Repeat this procedure for subs #3 and #4, beginning from sub#2 for placing sub#3 and from sub#3 for placing sub#4.
11. Bring your main speakers back into the room, hook them up and position them optimally in relation to your listening position for midrange/treble and imaging. You now have 2 systems: an independent powerful,fast, smooth,detailed and dynamic bass system as a solid foundation and an independent everything else system consisting of any main speakers you choose to use.

     Once all 4 subs have been positioned, the final step is to optimally set the volume, crossover frequency and phase controls. It’s much easier to do this if you sit at your listening seat and have an assistant adjust the settings at your direction. I achieved the best results by precisely setting the volume and crossover frequency as low as possible with the bass still sounding powerful, fast, smooth, detailed, dynamic and natural. I set the phase at the position at which the bass subjectively sounded the best to me.

     As I mentioned earlier, these 3 settings are set once, for all 4 subs as a group, on the Swarm/Debra amp/control unit but must be individually for each sub if traditional self-amplified subs are utilized.


Hope this helps,
Tim

Auto EQ is soooo variable.  

It is damn convenient and anyone can ise them, but I can understand why many dislike the results.  So, Dirac and JL have good results.

I love my miniDSP but what a PITA to set up right

The other things I love about the Vandersteen approach to subs is the way he his amps/x overs mimic the sound of the main amp.  If you spend money on a very expensive amp, his sub amps (AB type) mimic the sound so you don't have that fight either.  It does make a difference to my ears.  

I personally don't like any of the DSP I've heard as it takes away from the sound.  Some are bette than others, but even at the stores that sell DSP, most agree, but it's so easy to set up and most don't listen for the differences as they want it to sound better than analog EQ. ;) 

@bdp24 your statement makes sense, I don't completely understand the acoustics behind it, I understand physics and kind of grasp the concept but not entirely. Now the empirical evidence and testing of before and after proves me this solution is perfect, affordable and more importantly something people don't mention scalable, should you move to another bigger house or listening room just add 2 more little subs.

I concur, I lived the one sub then two subs scenario and yes I had deep bass from two big subs but did not sound like natural bass. Shopping for speakers I met Duke and got his speakers, I have to say the sub array was an extra on the purchase as I wasn't looking for subs I had doubts honestly the Dayton sub amps (because of the price) will integrate and control the subs properly, I looked into more complex sub integration like mini dsp, dspeaker, trinnov etc but with digital dsp comes a side effect within the digital world which is losses during conversion if you are using hires content, anyway the subs arrived, I installed the them and was very surprised how well Duke's approach worked, I sold my two big subs and never looked back. The sub array takes almost no space as a matter of fact less space than my previous 2 subs and I have 4 now, can be easily positioned anywhere and the sound is natural bass not boomy, the daytons will provide all the phase controls and analog corrections needed, the price for the entire 4 sub system is the same or maybe a little less than the 2 subs.

Keeping this on thread for the OP the 4 sub approach allows you to put the subs almost anywhere and makes the positioning simpler and more inline with the geometry, because of the reasons already explained above by Duke himself, some others here are using 6. The daytons allows you to change the phase gradually not only 0 and 180 that is something digital sub integration usually don't have and I think not because is hard to do but the manufacturers haven't seen a need for it, I say usually because the high end ones trinnov comes to mind have it but be ready to hurt your wallet.

I think duke hit it on the head. Multi sub systems with some EQ, phase and time alignment are best. 

noble100:

 The truth is that the 4-sub Distributed Bass Array (DBA) Concept actually works like a proverbial charm! There are no ifs ands or buts, no maybes, no under the right conditions, no excuses, no fear and loathing, no terms, no conditions, no stipulations, no hidden clauses, no fine print, no oils and no qualifiers whatsoever.  
      It's the cat's pajamas, the bee's knees, good as gold, tits, right as rain and too legit to quit. I believe it's the gold standard of sub systems that all others should be judged against.  
    Based on the 4-sub DBA's near state of the art bass quality, I actually continue to be amazed that it isn't more widely known, accepted and utilized, especially by fellow Audiogon members who are typically keenly aware and accepting of high quality audio related concepts, technology and methods they can utilize to increase the performance of their systems.  

Ain't it the truth.

I struggled for so many years looking at so many different things all of them ultimately running into the same fundamentally immutable physics problem. Well the thing is it really is a fundamentally immutable physics problem. So whattre you gonna do? Give up! And I did. Gave up all hope.

For years.

And yes of course I know all about all the wonderful different subs, including the magical REL, and EQ, and bass traps, and all that jazz.

What part of fundamentally immutable physics do these people not get?

I had come to view the situation as so hopeless that when first reading about this, right about a year ago now, I assumed it had to be just one more dead end. But you never know. So I read. And read. And read some more. Dang. This just might work. So I read a ton more. Read Toole, et al, read every post by Audiokinesis, read all the reviews, read the threads. 

All the physics, all the psycho-acoustics, the measurements, every single bit, it all made sense. Solid, compelling, logical sense.

So I decided to go for it. DIY. Might as well. And Duke is all thanking me for the leap of faith.

The what??!? So of course I had to tell Duke faith had nothing to do with it. No sane sensible man of science could look at this and come to any other conclusion than its gonna work. Just as surely as no other solution can possibly work, this solution cannot possibly fail to work. The laws of physics would have to be re-written. Something that is not happening any time soon.

That said, still it is hard to fathom just how well it does work. Last night listening to the 20th Anniversary 45 of Jennifer Warnes Famous Blue Raincoat it was absolutely freaking amazing the way the drums are no longer this thud thud thud that moves a bit left or right but actual 3D drums with skin and case and body and its not a dull thud but a clean impact that reverberates across the skin so that you feel and hear every up and down movement of the skin, and its not one sound or even one event its the wave moving out across the skin from where it was hit and then reverberating up and down and this is something you can see with your ears, its right there in the room which is completely mind blowing because as much as you know there are 5 subs plus the two speakers there is no sense of that, none whatsoever, its all just one seamless presentation, the drum and the skin and the room, the all-enveloping room that has erased the room you were in so completely its not the performers being there in your room its you being in theirs. And that's just the one whack. I could go on like this paragraph after paragraph on literally every track of every recording on the shelf.

The DBA approach is so superior to everything else that this one thing has transformed my system from where the bass was easily the worst weakest lamest thing about it to one where its the strongest most astounding aspect- and we're talking not because anything else is lacking but because the bass is just that crazy good. And not just because of any one thing like impact or extension or articulation or any of that but all of it together. We're talking play an absolutely average ordinary record and watch your guest move forward to the edge of the chair lean in fascinated and exclaim, "The bass!" 

And yet, as surprising as all that is its nothing compared to how stunned I am to stop and think this isn't some brand new thing just discovered last week. It wasn't even new when I first heard about it a year ago. Its like 20, 30 years, something like that, depending on how you want to count. From the PhD thesis or the commercial use or whatever. Not here to split hairs. We have people for that. All they do. Forest for the trees. 
 
Forest for the trees!

Everyone should be doing this. Or at the very least, everyone who has not tried it should maybe hold off until they do. Or if not that then at least take into consideration one or two of the dozens of compelling lines of evidence and reasoning behind this before spouting the usual irrelevant nonsense.

But no. Forest for the trees. Boggles the mind.

" Tried the "swarm" approach and moved four subs into the room but unfortunately found out that they all have about the same tops and dips wherever placed (+/- 20 db from 25 to 100 Hz). "

Did each sub have the same in-room frequency response curve regardless of where you placed it, or did each one have a different frequency response curve but with the same amount of variation? (+/- 20 dB... that’s a lot of variation.... I don't recall ever measuring worse than +/- 10.)

Did you measure with all four playing at the same time?

Can you tell us about your room and approximately where the subs were placed within it?

Thanks!

Duke

Tried the "swarm" approach and moved four subs into the room but unfortunately found out that they all have about the same tops and dips wherever placed (+/- 20 db from 25 to 100 Hz). So not much of an improvement. Room eq necessary.

Hi Rooze,
Rather than challenge other's assertions I will describe what has worked well for me in my room(s) and cars with various subwoofers over the years for getting the best integration.  
It really starts with the subwoofer- design, performance and controls.  
I have had the best results with sealed subwoofers that are designed to be corner loaded to yield their flattest response.  A sub that is easier to integrate will have a wide flat response when positioned properly.  
My last in home subwoofers were JL audio and they are sealed design with a very flat useable response.  These two aspects make them more musical rather than having peaks in the response that prevent them from disappearing.  
With a sealed design and a flat response the next thing is a continuously variable phase control- 0 to 360 on the dial. This is a requirement- more later.  I have never been able to satisfactorily integrate a subwoofer that only had a 0-180 deg. switch.  
When you have these fundamentals I had no need for DSP or room correction of any kind.  I have tuned subs with these assumptions with DSP and switching on the correction did not improve the sound.  
Tuning- get an app or RTA software and a microphone for a laptop for example.  Get a CD with full spectrum pink noise (the sheffield labs "my disk" for example.  
Now play the pink noise through your speakers (no subs) at moderate / high volume and measure their response from you listening seat.  
Note the frequency where the bass response drops off and is ~ 3db less than the midrange frequencies- e.g. 65 Hz.  
Place your subs at the room positions where they sound the best and most even at your spot.  
Turn on one sub at first and set the crossover for your measured frequency- e.g. 65hz.  
Turn the sub up higher than normal and take a system measurement with the pink noise track again.  
Look for the behavior at the crossover- peaks and valleys.  Back off on the crossover until you see a "valley" in the response, then slowly bring it back up again until the response is smooth. 
Then adjust the level until that is smooth. 
Here comes the fun part and the secret sauce for perfect integration. 
Play some music (loudly) with extended bass beats.  I use gnarls barkley "gone daddy gone" or new order "blue monday" 
Set the continuous phase to "0" and listen, take notes about the bass beats- tight, blurry, weak? etc.  now rotate the phase dial ~ 45 degrees, sit back and take more notes.  listen to where the bass is clearest and tightest.  You are trying to "time" the sub to your main speaker at the crossover frequency.  Once your notes say you have the best position - e.g. -45 degrees, from there rotate it 1/16 turn in either direction and see if it can sound any better.  
Once you have it dialed in the sub and mains are in perfect sync at the crossover frequency.  bass will be tight and powerful and there will be no muffling or cancelling.  It will sound impactful without effort.  Take note and log of all the settings. 
Now add in the second sub - you are now going to integrate the second sub into your "integrated system".  Repeat the same procedures changing only the settings on the second sub. 
Practice, be patient, take notes and have fun!  Once you nail this you will have the best sounding subs you can have !   

Hello Duke,

Thanks for clarifying the awards your AK Swarm system has received, all well deserved. If you don’t mind, it seems like a few things need clarifying about attaining good bass response performance using subs.

The first issue concerns the timing of the bass reaching our ears at the listening position. Mijostyn stated:"Ideally the sound from the sub should reach the listening position at exactly the same time and at exactly the same phase angle as the woofers in the satellite speakers."
It seems to me that some people are stating false information because they’re assuming that bass soundwaves behave and are perceived by us exactly the same as midrange and treble soundwaves in any given room, specifically as it relates to timing and arrival times. It’s my understanding that bass soundwaves behave differently than mid/treble soundwaves in any given room and that we perceive them differently, too. For phase, I understand I can optimize this by adjusting the continuously variable phase control on the amp as well as sequentially inverting the phase on each sub to determine whether or not the inversion of one specific sub’s phase improves overall bass performance. Would you mind clarifying?

The second issue concerns the use of bass room treatments and room correction software/hardware. I currently use the AK Debra 4-sub DBA system in my room without the use of bass room treatments or room correction and I consider the bass performance near state of the art both for 2-ch music and HT surround sound.
However, I recently had my room analyzed by GIK and they recommended that I place stacked versions of their bass traps (called TriTraps) in all 4 corners of my room along with 2 bass trapping 5.25" thick panels (called 244 panels) along both the front and rear short walls in my room. Their remaining suggestions were an even distribution in the room of absorbing and diffusing acoustic panels for the midrange and treble from my main speakers.
The total assortment of recommended room treatments is about $2,500 and I was initially going to not include any bass treatments to save money but also not to negatively effect the already very good bass performance in my room.
I’ve since reconsidered and decided to include all of the bass room treatments on my order. My current understanding is that these bass room treatments will only have positive effects on my perception of the bass response performance in my room, with no negative effects. I still have no desire to utilize room correction of any type but am under the impression that room correction is also completely optional and will have no negative effects on the bass performance of 4-sub DBA systems. Do you agree with this?

Thanks,
Tim

The speed of sound is actually closer to 1100 ft/sec than 1200 ft/sec at standard temperature pressure at sea level. Which brings me to my Pop Quiz. For a free prize explain why placing bowls of very cold water out in front of the speakers on the floor improves the sound from the listening position. First correct answer wins a set of 3 brand new Flying Saucers on Afterburners for Windows. 🛸 🛸 🛸

Um, the speed of sound in air at ground level is generally given to be approximately 1,200 feet per second.


https://en.wikipedia.org/wiki/Speed_of_sound

1 millisecond = 1/1000 of a second, so 1.2 feet per millisecond or 14.5".


So 1/10 of a millisecond would be about 1.45"

Thank you very much, ctsooner. I am honored that Richard Vandersteen thinks the distributed multi-sub approach (which is actually Earl Geddes’ idea that I’m using with his permission) has merit. 

Duke