There's a lot more bass in a 6.5" driver than most of you think

I use Mirage M290 two ways with 6.5 inch mid/woofers as computer speakers.  They produce a good sound with a balanced frequency response, but to compare the bass from ported 6.5s to the bass from good 15" woofers loaded in 25 Hz Bill Fitzmaurice designed corner horns in my main DIY speakers  would be as unfair as comparing a T Model Ford to a new Porsche Turbo S.  Also the bass from the 15 inch woofers is as tight and fast as any 6.5 inch woofer I have ever heard.

Some some very interesting comments here. I’ve always been a fan of multiple smaller drivers For producing bass. As a speaker builder hobbyist when I started out with lower cost drivers, one of my goals was to get quality bass from smaller drivers in a smaller cabinet.  One of the most frequent comments people made when hearing them was surprise at the amount of bass volume from the smaller drivers.  Yes, to get bass you need to move air, but you can do that with multiple smaller surface areas, each with their own motors. It just makes sense that the effect will be greater accuracy and definition, at least in what the drivers are producing. Once that’s in the room, a lot more comes into play, to Erik’s point.  But flabby bass from the get go only gets worse in a less than friendly environment.  What my experience has shown me is that my preference is sealed cabinets, with multiple smaller drivers.  For me, it’s well worth the trade offs. I find that longer slope of the sealed cabinet oh so satisfying!  
Thanks for the original post, it seems like a topic that doesn’t get visited enough. 
Dave

I don't usually draw conclusions before 100 hrs. of break-in, but at 3 hrs. there is not a single area in which the Purifi 6.5" mid/woofer doesn't surpass the stock doped Scanspeak 8545 in a Merlin VSM. 

The Purifi drivers with their unique surround will reduce a polarity of shear so it does  not return back down the cone and become a part of the next impulse. Tom

Just wanted to mention, I've taken a quick peek at the SS Ellipticor measurements on the same sight and the IM distortion is almost as good as the Purifi. :) 

A shootout of these high end mid-woofers would be fascinating.

Right out of the box and into the cabinet these Purfi drivers are clearly better than my very nice Seas..sound as if I installed 
a highly articulate 10..As I type it opens up.. fun to hear and watch.. Dave G installed his today in his Merlins and has several hours on those. Maybe we will hear from him..These maybe the new king. Tom

I have to agree the woofers in my beethovens are claimed 7” but are more like 5” and they’re tuned to play bass, limited spl for sure but clean and solid.

Hello mozartfan,

     I watched your YT video you attached on your post from yesterday. I liked your equipment, your choice of music tracks played and especially your cool cat Cleo. But c’mon man, your room is so bright we all need shades. I had listening fatigue by the end of your 34 minute video.
     I watched your video on my laptop but bypassed the computer’s inboard audio and listened via a combination of an external JDS Labs usb dac, Aune headphone amp and a pair of Sony Z7 headphones, an audio combo I would describe as accurate and detailed with a bit of warmth but never bright. I believe the brightness I heard is a result of an accurate representation of your very good system reproducing music in a substandard room.
     I describe your room as substandard because your room looks and sounds like it consists of 6 hard and highly sound reflective surfaces (ceiling, floor and 4 walls) with the only acoustic room treatment being a medium sized and thin rug on the floor, which apparently has no positive acoustic effect.
     Both of your speakers have been launching sound waves into this highly reflective and acoustically unfriendly environment/room from about 50 Hz on up, or about 27 Hz on up if you utilize the optional Merlin BAM electronic component-Bass Augmentation Module. The longer and omnidirectional bass sound waves under about 250 Hz behave much differently than the much shorter and unidirectional midrange and treble sound waves behave in your room.
     However, a common behavior of all sound waves is that they will continue moving at the speed of sound outward until they meet a hard and reflective room surfaced boundary such as a ceiling, floor or wall. At this point, the sound waves are redirected, bounce or are reflected off the hard surfaced boundary and continue on in this new direction until they encounter the next hard surfaced room boundary and are redirected once again. In a highly reflective room with many hard surfaced room boundaries, this process continues until the sound waves either encounter an acoustic room treatment or run out of energy. Here’s a pair of diagrams visualizing this process - just scroll down to the direct vs reflected sound diagrams on this linked page:

https://www.magicoaudio.com/news/magico-news-for-fall-2019

     As you can see, Magico estimates that about 80% of the sound you hear at your designated listening seat is reflected sound. Based on the brightness I heard on your video, you may be receiving even a higher percentage of reflected sound at your seat.
     If I was an audio doctor, I’d be admitting your room to the ICU right about now and calling your room’s next of kin. The bad news is your room is acoustically seriously ill. The good news is that your room’s not dead yet and there is a reasonably priced cure called acoustic room treatments. I suggest you visit the GIK Acoustics website linked below and request a free acoustic analysis of your room.

https://www.gikacoustics.com/acoustic-advice/?gclid=CjwKCAjw2a32BRBXEiwAUcugiOIH9bLbsRdKbH7SIwJe9I9n3ltBBVZk96n6Qk1nsiH2ZK3Q58nsiRoCUTAQAvD_BwE

     I’m in no way associated with GIK, just a very satisfied recent customer. I find it hard to imagine how you could possibly be perceiving the high quality, wide and deep, three dimensional stereo sound stage illusion, with solid and stable images of the musicians properly arranged and portrayed realistically within it, that I know your Merlin speakers are capable of creating when precisely positioned in relation to your listening seat.
     I believe you’re going to be amazed at the significant and dramatic improvements that an assortment of properly positioned, high quality acoustic room treatments actually make to your room and overall system sound quality performance.
     Sorry about sidetracking this thread a bit but I’m certain you’ll consider this reasonably priced investment a complete bargain once you experience the exceptionally positive results it provides.

Best wishes,
Tim

Considering the Via Wave Srt7 ribbon tweeter also a drop in replacement in my cabinet in combo with the Purifi. Crossover should be straightforward and simplistic.  Tom 

I agree, ck out the small but potebnnt 6.5 Seas magnesium mid woofer here in my system. 
lots of bass here in Miles Davis Kind of Blue. 
I still have a  sub that will add ina  new upcomming YT vid.
 Adding for classical muisc,
,But here in this jazz, the 6.5;'s offer a  full rich bass. for my sized room/sub not necessary/nor needed. 


  https://www.youtube.com/watch?v=-viI0SYQHko&t=1s

Asked and answered:

https://www.stereophile.com/reference/1104red/index.html

The Purif measurements here made for very interesting reading:

https://hificompass.com/en/reviews/purifi-audio-ptt65w04-01a-midwoofer

In particular, nice to see that IM distortion measurements for drivers is still being used to good effect, since I posted an article about this here, but also the possibility for a 3-way speaker to improve clarity by removing IM distortion, and by extension, a properly integrated subwoofer.

But I hope everyone immediately stops doing 6.5" midwoofers with Mundorf AMT tweeters, tats my very own shtick. :)

I will be comparing it to Scanspeak 8545 in Merlin VSM.

drop them in where 

Myself and 2 other Audiogon members have received our Purifi PTT6.5 WO4 drivers this week. Longtime coming with all the Covid delay. They look amazing ..fit and finish and unique features can hardly wait to drop them in.    and they will for both Seas and Scanspeak drivers.  Purifi sent along a template gasket that perfectly matches the drivers bolt pattern of the 2 brands I mentioned. All three of us have speakers from different manufacturers so the outcomes will be interesting to hear and hear about. Stay safe..Tom

Small drivers doing bass or big drivers doing high frequency doesn’t sound like a great plan. There are better ones out there.........

I’ve never said otherwise. My entire point of this thread was about room gain, and how it affects a speaker’s response.

Audiophiles focusing too much on -3 dB points may not fully understand what is affecting their sound quality.

Small drivers doing bass or big drivers doing high frequency doesn't sound like a great plan.    There are better ones out there.........

No there is not.

No there isn't. 

Doing it manually allows one to decide by ear which actions are the most beneficial. Often only minor intervention is necessary.

is what toole say. So in other words this all comes back to custom tuning by ear which is what ive been advocating all along. 

So much misinterpretation. I’ll quote the good Floyd Toole where he explicitly discusses his feelings on the importance of using EQ:

So, if one has a known neutral loudspeaker what does "room EQ" bring to the party? Above about 500 Hz, very little that is reliable - mostly general spectral trends; not detailed irregularities, for reasons mentioned in my last post. At low frequencies equalization is almost certainly beneficial and easily measured steady-state data are all that is necessary.

The full posting is below:

https://www.audiosciencereview.com/forum/index.php?threads/an-enticing-marketing-story-theory-withou...

So, there we have it. Toole explicitly says that EQ is "almost certainly beneficial" for bass frequencies. Stop arguing that he said something else.

I’m done.

@asvjerry

Yep, though all those measurements were quasi-anechoic, while mine are in-room. :)  Plus, those are meant to be near-field monitors. The measurements are overall not atypical for a two way. Shame that built in correction for boundary reinforcement isn't easy/typical in passive and home speakers.

'Ell, even I'd buy a pair....*L*

Happy Saturday to all...*S*

Hey, Eric...this appeared in the 'cunning trick' forum...

https://audioxpress.com/files/attachment/2689

...and I thought you'd enjoy it.  The speakers shown over a major mix board may be just a 'trade trick' (sic), but it definitely fits within your proposition. ;)

Cheerfulls, J

Thanks for the audioxpress article, very interesting about phase and zero phase in recording and playback. It seems like the effects of phase linearity and accuracy are subtle, also.  

You are welcome. One thing I like about Toole a great deal is we hear the same things. Others may find phase and phase linearity big deals, and for them it might be but after lots of listening to Thiel and Vandersteen it is not that big a deal for me. I was thinking of playing with rePhase and Roon to attempt this digitally, but after reading that I'm going to forget about it.

Thanks again for your honest and useful advice.

My pleasure. Glad I helped, I envy your ability to get so much gear installed.  Much more than I can do in an apartment.

Hello Erik,
     Thanks for the audioxpress article, very interesting about phase and zero phase in recording and playback. It seems like the effects of phase linearity and accuracy are subtle, also.  
     Yes, I liked dealing with Mike Major of GIK on my free room analysis and I'm very impressed with the effectiveness and quality of their room treatments thus far.  I'm very optimistic about the detailed room treatment plan I created with the very capable assistance of Mike.  
     Phase one was the installation of the stacked GIK Tri Traps in all 4 corners and some GIK 244 bass trap panels along the front and rear walls.  Phase two will be having a local Indianapolis hi-end shop, The Audio Solution, install the remaining 12 combination of a balance of absorption and diffusion midrange/treble frequency wall panels throughout my room, with the strategy being mainly diffusion at the front and rear of my room and mainly absorption in-between.
      I'll probably start a thread of the perceived results in a few weeks.  My intent will be to just be honest and describe my impressions as I hear them.
   Thanks again for your honest and useful advice.

Tim

Unexpectedly, however, I did notice an improvement in my system’s midrange clarity and the level of detail within the soundstage illusion, too.

@noble100

I literally just read a posting that explains this. Look at the comments from Dr. Kippel:

https://audioxpress.com/article/zero-phase-in-studio-monitors

I quote him below:

For the same reason amplitude modulation (a bass signal f1< 100 Hz modulates a high frequency signal f2> 300 Hz) generates much more differences than phase modulation, aka Doppler).

Of course, it is possible you just had higher order room modes too. :)

I’m currently hesitant to add EQ to my system since my system currently just requires adjusting the cutoff frequency and the volume on my 4-sub DBA bass system’s sub amp/control unit, I don’t believe it’s necessary for bass improvement in my system/room and I believe simplicity is a benefit.

Honestly you’ve done plenty, besides, doing EQ correctly requires a great deal of measurement and fine judgement. I’m not religious about adding EQ when none is required either. In my own space I have a lot of GIK and have lived happily with no EQ until recently adding Roon. The EQ changes I’ve made anyway have been pretty subtle. Now play some Holtz or the sound track to Battlestar Galactica. :)

erik_squires: "I am against religious advocacy of any particular methodology. EQs, room treatment and multiple subs are all useful choices. "

 Hello Erik,
    I'm getting closer to 100% agreement with you on the effectiveness of all 3 methodologies contributing to the quality of bass in one's system and room: EQ, bass room treatments and multiple subs.  As I've stated and based on personal experience, I was already convinced that multiple subs is an excellent solution in my system even without the EQ and room treatments methods utilized at all.
     In a fortunate and timely occurrence relevant to this topic, I just received and installed some GIK room treatments.  My complete order consisted of 10 cartons of room treatments intended to improve my room for all frequencies in the audible spectrum but I decided to initially just install the bass room treatments to better isolate and access their effectiveness on the bass performance in my room.  These installed bass room treatments consist of stacked triangular bass traps (GIK named them TRI Traps) in all 4 corners and some 5.25" thick rectangular bass trap panels(GIK named them 244 panels) along the front and rear walls of my room.  
     As you may recall, I was a bit concerned that adding bass room treatments might negatively effect the already extremely good bass performance I had already attained without the use of any bass room treatments or EQ at all. But I was convinced by the consistent advice from Duke Lejeune, you and GIK Acoustics that bass room treatments, mainly bass traps, would do no harm and only prove to further improve the bass performance perception in my room.  It was hard for me to imagine how the bass performance in my room and system could get even better in any bass quality but I decided to give the bass traps a try, anyways.
     So, I positioned the stacked pairs of GIK bass traps in all 4 corners and played some familiar acoustic music with good bass (CD versions of the Some Devil album by Dave Mathews and theBrushtail Fairytales by Jack Johnson).  I think it's important to state that these are only my initial impressions after installing the bass traps yesterday and listening for a relatively short period of time, my impressions may change after more extensive listening time. The results were somewhat surprising to me.
    Your advise was correct, I can discern no negative effects from the addition of the corner bass traps.  The bass remained just as smooth, fast detailed, powerful, dynamic and natural with the bass traps deployed as went not utilized.  But I didn't discern any improvements in any bass quality, with the possible exceptions of bass detail and depth, either.
     Unexpectedly, however, I did notice an improvement in my system's midrange clarity and the level of detail within the soundstage illusion, too.  This was a pleasant surprise that I enjoy but currently find difficult to explain.  I do expect further improvements in my system's midrange and treble performance quality once I install the numerous GIK absorption and diffusion panels I ordered and have received but the midrange improvements of adding bass traps was completely unexpected.
     So, I currently believe that multiple subs and bass room treatments are both valid methods of improving an individual's overall system bass performance.  That's 2 of the 3 methods, that you suggested as good methods of improving bass performance, that I can confirm as effective based on my personal experiences and I strongly suspect EQ is also an effective method.  
     I'm currently hesitant to add EQ to my system since my system currently just requires adjusting the cutoff frequency and the volume on my 4-sub DBA  bass system's sub amp/control unit, I don't believe it's necessary for bass improvement in my system/room and I believe simplicity is a benefit.
      One of my main intentions of this post is to let you know that I agree with you that EQ, room treatments and multiple subs are all effective methods of improving bass performance.  
     My other main intention is to let you know that I'm not sure or overly concerned with whether or not you are including me as a religious advocate of the multiple sub DBA method, since I've found this method to be the most effective method based on my experience and the only one of the 3 methods you mentioned that represents a very good solution all by itself.  
     In matters of supreme beings and supreme home audio bass performance, I naturally but also philosophically, consciously and deliberately attempt to remain agnostic. I prefer to base my decisions on matters of personal choice on more scientific, pragmatic, personally experienced and logical factors when possible.  
    However, I believe a belief in a supreme being requires a bit of a leap of faith but a belief in the effectiveness of  room treatments, multiple subs and likely even EQs only requires an audition. 

Thanks for your wise advice,
                   Tim

I had a brief email exchange with him about my Walsh DIY's a couple of years ago.
He generously applauded my attempt, and wished me good luck.

It's been suggested to me that I ought to use an L/R 2nd order passive with my 2-way versions....

I think I might do just that....Just Because. *S*

...but I'll include a bi-amp option anyway...being the 'active guy I is...;)

RIP, Sir...and thanks for all of us.

;), Eric..

BTW....I wasn’t aware that Linkwitz had passed away. :( There was a time in my life I lived within a mile of him, and wasn’t aware of it....

Yeah, it was a real shock to me too. The man’s work has been with me since I worked in theater sound in the 1980s. THX used LR filters in the active crossovers they shipped, and I was just getting into filters at the time. Of course, this marriage carried over to the THX satellite/subwoofer standards much later.

I never got to meet him. I read he had retired, and then bam, he was gone.

Best,

Erik

*L*  You got the gist of that NEC disclaimer, Eric.
Between the lines is:
"If you guess wrong, it's your butt in the pliers, bunkie." ;)

Anytime I 'play' with AC, I 'go down' a wire gauge (10 for 12, that sort of thing)...do the same with speakers. *G*  Can't hurt...

And that's what I surmised from your rally with @pirad.... one can apply whatever means one cares to, but will have to deal with that choice in an apropos way.  And accept the consequences of that/those choice(s).

Basically, Simple.  It's the devil in the details as usual....

In the near future, I'm looking forward to having a more 'reasonable, normal' space to set up 'fresh, clean slate'. *S*  It's been more than a little while since I've had that opportunity...

BTW....I wasn't aware that Linkwitz had passed away. :(  There was a time in my life I lived within a mile of him, and wasn't aware of it....

Ignorance is bliss...until it isn't. 

Better ;),
J

Thanks @asvjerry

To be clear I am not AGAINST the use of multiple subs to solve a problem.

I am against religious advocacy of any particular methodology. EQs, room treatment and multiple subs are all useful choices.

I am reminded of a textbook I read on the National Electric Code, which I will attempt to paraphrase below:

The NEC only tells the electrician what is possible, legal and safe but it is up to the electrician to determine what the right solution is for a given situation.

Best,

E

Personally, I'd like to thank pirad and erik for their exchanges; it's one of the primary reasons I return here...^5's guys.

If you two hadn't disagreed, we'd all be the poorer and less informed of the nuances of the subject.  Which, like most audiophilia, is complex in itself....and is then plopped into our various and varied spaces....

....followed by head scratching and 'wt...' observations....;)

For the record, bass traps in my 'space' would be a physical improbability, as would most any other enhancements.  A long story that you can be spared.   Suffice to say, 'room averaging' from multiple locations to multiple memories.  This gets 'averaged' down to 3 'main' selections; an 'average entire', suitable for 'local Muzac", 'sweet spot', and 'center/all'....
...and then there's the different sets of speakers involved....
Yes, I keep notes....;p  My memory only has so many slots...*L*

Thanks again for your patience with each other...

Regards, J

Ps: I like foundation cracking bass, when it’s in the music, I also like to hear the purr of the tremolo. Both are important to me.

thanks

Hello Erik-squires,
Would you kindly describe your sub system and room treatment that gets you down to 16Hz? And the room size? 

Thanks,
Me

I'm not sure if this is applicable, but something I have noticed.

When my next door neighbors (several throughout the years) would play their small systems, it was quite audible in my space.  However, I've played my system, which obviously has much greater bass extension and capacity, and yet didn't hear it next door.

So obviously something in those small speaker systems was hitting a resonant frequency which was exciting the wall,  while my more spread out bass didn't.  Perhaps these systems (seemed like powered speakers) uses the resonant frequency to make bass, and higher end systems with smaller woofers don't.  

erik_squires:"What you are missing from my argument is bass traps. I never said EQ alone solves all issues, but rather that EQ and room acoustics are complementary."


Hello Erik,
     You're correct, I should have included bass traps in my post comment and understand you recommend using EQ in conjunction with bass traps for attaining good in-room bass response from a single sub at a designated listening position.
     Although I'm currently getting excellent in-room bass response throughout my entire room using a 4-sub DBA system with zero EQ and bass traps, I recently ordered about $3,500 worth of GIK room treatments, including stacked bass traps for all 4 corners and some 51/4" thick panel bass traps for the front and rear walls. 
      I originally was dead set against bass traps because it seemed silly to deploy a high quality and fairly expensive 4-sub DBA system in my room and then buy a bunch of large, expensive and ugly bass traps to sop up the extra bass frequency energy in the same room. I felt the bass quality was already near state of the art in my room, had difficulty imaging how it could be further improved and didn't want to jinx the bass quality I'd finally attained after years of searching for a bass system that sounded so powerful, dynamic, detailed, accurate, natural and integrated so seamlessly with my large Magnepan main speakers.
     But GIK, Duke Lejeune, you and others convinced me that bass traps will only further smooth out and improve the bass quality that already exists in the room. So, I decided to trust the consistent advice of the efficacy of bass traps ang give them a go.  I'll give an update after they're installed and I listen to the results awhile. 
     I'm always looking to improve the quality of my system so, who knows, I just may give EQ a go next. I'm kind of conflicted since bass quality is my most important priority but the simplicity of functionality is a close second priority 
.

Tim

Why is base spelled like bass, the fish? I thought we were discussing some rather smallish fish.

Someday I suspect, when Jesus has definitely got us for a sunbeam,
our works may be adequately assessed.

The one area where EQ is unquestionably needed is in the bass, below about 400-500 Hz - room modes and adjacent boundary effects. It is necessary to attenuate resonant peaks, avoiding filling narrow acoustical interference dips. With multiple subwoofers it is possible to attenuate room modes and for the EQ to benefit more than a single listener. It is not difficult, but not everybody does it. Other mistakes result from trying to "fix" non-minimum-phase ripples in steady-state room curves. EQ at mid and high frequencies should be broadband "tone control" kinds of spectral balance adjustments, but too many systems think they know better.

Well, finally we have enough nuance here to pull apart all the different discussions you’ve been conflating, @pirad. Honestly Pirad, being so well read I have to wonder what your motives are. Did you deliberately misread the Toole article you shared?

This paragraph is pretty much what I’ve been recommending, with the caveat that again, he’s not considering the use of bass traps fully. Bass traps will make those narrow sharp dips less deep, and therefore correctable. He’s talking about the exclusive use of EQ, alone. I have never suggested that as a panacea. I’ve always said that the room acoustics enable the EQ to work. And in fact, his statement here is one you’ve argued against:

The one area where EQ is unquestionably needed is in the bass, below about 400-500 Hz - room modes and adjacent boundary effects.

Yes, this is exactly my point. He’s also recommending a light hand, again, agreed to. Didn’t you try to tell us all EQ was all bad? It’s pretty interesting how you can pull out so many great articles and conveniently omit what doesn’t suit your promotion of swarms. In fact, he never says "if you use multiple subs you don’t need EQ."

Now again, in detail:

With multiple subwoofers it is possible to attenuate room modes and for the EQ to benefit more than a single listener.

Correct. He doesn’t say "you can’t do this with an EQ and bass traps" which is what you keep reading into his words. In fact that’s the whole problem. You keep reading entire phrases into his articles in a very self-serving manner. In fact, like bass traps, he’s saying that multiple subs make the EQ work better. This shoots your entire agenda of not using EQ at all completely out of the water. Wow, @pirad, you’ve basically destroyed your own arguments with Toole. Again.

My original statements, are and continue to be, one sub with bass traps and proper EQ is amazing. I know because I’ve measured and heard it. Further, good room acoustics make small speakers sound larger. They do this by controlling the resonant modes which make the bass sound flabby and boomy. So, again, the vector for the frugal audiophile who wants to limit his hardware purchases to me is clear:

Room acoustics --> Subwoofer --> DSP for EQ and integration


What you may be missing also is that DSP isn’t just about EQ. DSP also plays an important role in setting the proper crossover settings and delay, which JL Audio also points to. And, like Toole, I’ve seen and heard horrible, absolutely horrible sounding ARC. It’s gotten much better, and JL is one of the better brands. It is also FAR TOO EXPENSIVE. Really, besides the woofers, the main selling point of JL is how good they sound and how easy they are to install and have sound good.

So, given that the average audiophile is not a speaker builder, if they don’t have room for a swarm, a single sub, well placed, properly integrated to the room and speakers is really a great solution. Two is better.

The only area of contention really is how good automated systems are, and that as other acousticians have found, you can even fix unfixable dips with the right room acoustics.

And what if you don't want a sub? Again, room acoustics are where you start.

I have Active Linn Tukans, and they sound excellent, no need of any subwoofer. After more than 40 years I founded that the room is the most important aspect.

For those interested in "room EQ", including bass, this is an interesting discussion that Floyd Toole joined and argued for multiple subs. It's fairly long, so for those with limited time I quote below relevant excerpts from dr. Toole's contribution. 
https://audiosciencereview.com/forum/index.php?threads/an-enticing-marketing-story-theory-without-measurement.7127/

..." Below this [transition] frequency judicious equalization can be used to address individual prominent room resonances, but it is only functional at the point of measurement - the prime listening location. All other seats will be different. This is the reason why multiple subwoofers are advantageous, along with the greatly increased efficiency.

The one area where EQ is unquestionably needed is in the bass, below about 400-500 Hz - room modes and adjacent boundary effects. It is necessary to attenuate resonant peaks, avoiding filling narrow acoustical interference dips. With multiple subwoofers it is possible to attenuate room modes and for the EQ to benefit more than a single listener. It is not difficult, but not everybody does it. Other mistakes result from trying to "fix" non-minimum-phase ripples in steady-state room curves. EQ at mid and high frequencies should be broadband "tone control" kinds of spectral balance adjustments, but too many systems think they know better.

With bass performance accounting for about 30% of our overall factor weighting in sound quality assessments there is work for EQ at low frequencies - at least for the prime listening location. The fundamental problem is that all bass sounds are propagated through a three-dimensional acoustically resonant chamber - the room. There is no dominant "direct" sound in the normal sense because at all resonance frequencies the energy builds at a rate determined by the Q, and correspondingly decays. This behavior is different at every location in the room, meaning that multiple listeners do not share the same bass experience. To address the needs of multiple listeners multiple subs are powerful assets in attenuating room resonances and thereby reducing seat-to-seat variations. With signal processing in the signal paths to each of the multiple subs room modes can be made to almost disappear, certainly pushed well below thresholds of detection (e.g. Harman's Sound Field Management). Section 8.3 describes elaborate research on this topic, one finding of which was that active multiple sub solutions were better than necessary at attenuating room resonances - a nice result. Because humans tend to ignore ringing - now there was a surprise - even relatively crude frequency response smoothing at bass frequencies can be greatly beneficial.

Any woofer or subwoofer I have ever encountered does not change its power response "vigorously" - they are minimum-phase systems that are quite well behaved. However, room modes/standing waves do change dramatically with location of the ears or mic. That is the problem to be addressed. Mode cancelling/attenuation using multiple subs greatly simplifies the situation, but only when the budget allows. Good news is that with multiple subs the total system efficiency rises, so they can be smaller subs.

My present system uses four subs in a sound-field-managed configuration. There are no "booms". Bass is exceptionally "tight", and there is no audible evidence of being in a small room in what is heard at low frequencies - no measurable or audible resonances.

In my room with four small SFM processed subs fhere are no audible modes in the sub range - the room is "gone", leaving only deep tight bass  No bass traps required. Not everyone realizes that multiple subs are highly efficient - more small subs are vastly preferable to a single monster sub.

...There are passive multi-sub solutions for rectangular rooms:

Welti, T.S. (2012). “Optimal Configurations for Subwoofers in Rooms Considering Seat-to-Seat variation and Low-Frequency Efficiency”, Audio Eng. Soc. 133rd Convention, Preprint 8748.

The core of the problem is resonances in small rooms. Bands don't play in small rooms. A real drum energizes a certain set of small-room modes, giving it a room-modified sound. The same thing happens with a single woofer in the same location. Different small rooms would yield quite different real and reproduced drum sounds. 

The notion of multiple subs and EQ is to neutralize the contribution of the room to what we hear, so that we have a better chance of hearing what the mic picked up and the recording engineer heard.

Seemingly endless promotion of "room EQ" algorithms - a for-profit exercise - is partially responsible, aided by human nature which is inclined to believe a good story. It is an ingredient in "faith based" audio - if you believe it, you just might hear it. Even though some EQ exercises "sound similar" does not mean that any are as good as they could be - perhaps the important similarity is at low frequencies."...

@noble100

I agree with Erik that a single sub properly positioned, with PEQ and DSP correction can provide good bass response at a single designated listening position but will likely result in poor bass performance at numerous other positions in the room.

What you are missing from my argument is bass traps. I never said EQ alone solves all issues, but rather that EQ and room acoustics are complementary.

In theory, you could fix all room modes with proper bass traps, but few of us are able to afford something akin to the Magico listening room.

The magic sauce is the use of both. The traps stop the ringing, the EQ corrects what’s left and you can get something damn good that works for multiple listening locations.

Of course, a true pro will measure several different listening locations and attempt to use an average to decide what to adjust.

Still, Toole’s argument of "how do we know what is right" holds true. Even after this, the use of a discriminating ear is very valuable.

Also, to reiterate, I have nothing against the swarm besides cost, complexity and space. :) I mean, as far as I can tell from reading it should sound great. It’s the cultishness of the idea it is the ONLY possible way to have good bass. It isn’t.  If you have the money and space for 4 subs, by all means, have at it, but don't compare it to a poorly integrated single sub as proof it is the only way to go.

Best,

E

     I'm a big fan of the 3-4 sub distributed bass array (DBA) concept. Although I've only personally used the 4-sub Audio Kinesis Debra DBA system in my system/room, it functions so incredibly well that it's not hard for me to imagine that a 3-sub DBA could function nearly as well.
     I agree with Erik that a single sub properly positioned, with PEQ and DSP correction can provide good bass response at a single designated listening position but will likely result in poor bass performance at numerous other positions in the room.  
     There are a few other downsides with this approach. One is that PEQ/DSP is very good at attenuating bass peaks identified at specific bass frequencies at the listening seat, since it simply decreases output power demand on the amp(s)at these peak frequencies. However, PEQ/DSP is limited in its ability to correct all bass dips and nulls identified at various specific bass frequencies at the listening seat, since these require increasing and not decreasing power at these bass dips and nulls. This takes a lot of power especially at deep bass frequencies to correct and the amp(s) need to be powerful enough to supply power for both the normal deep bass notes and the very sudden and high power demands for bass dynamics at varying deep bass frequencies and amplitudes. So, it's really not a limitation of the PEQ/DSP circuitry itself, but a limitation of the amp(s) that must meet this circuitry's power demands.  
    Further, powerful high quality class AB sub amps, possessing more moderate damping factors, reproduce more accurate and natural deep bass frequency note's decay times than high quality class D amps, possessing extremely high damping factors, are capable of. The use of class D amps to power subs often tends to result in the truncation of deep bass frequency note's decay times which sounds inaccurate and unnatural.
    In my experience, I've also found that 2 subs perform and sound about twice as good as a single sub at a designated listening seat. I believe this is due to two factors:

 1. 2 subs reproduce deep bass that is more powerful, dynamic and seems more effortless than a single sub because the bass output of both subs is cumulative and each individual sub is operating nowhere near its limits.
AND
 2. The use of 2 subs, each optimally positioned sequentially and independently in relation to the designated listening position, begins to provide the benefits of having multiple subs launching bass soundwaves into the room and these benefits increase in degree as more subs continue to be added to the room (with diminishing improvements resulting beyond about 4 subs); these additional benefits are bass that is perceived as being smoother, faster, more accurate, more detailed and better integrated with the main speakers.  
    Continuing on the bass upgrade path,I've found that the use of 4 subs independently positioned in a distributed bass array sound and perform about twice as good as 2 subs, maximizing both categories of bass quality improvements listed above.
    My claim is not that the 4-sub DBA concept is absolutely the best bass system in , it's just definitely the best I've heard and used to date. I believe a linear bass array(LBA?), with multiple subs lined up horizontally along the front wall at precise separation distances between them, could outperform a 4-sub DBA. But the LBA concept has serious downsides like the need for no rear wall for soundwave reflections to reflect off of and its dreaded and awful WAF.

Tim

You write in your comments to Toole:
"It’s 2020, who on earth uses steady state measurements?? "

Toole does not give a definition of "steady state" in this paper, the readers learn it in EE101. Lacking that , some believe it is better to negate a simple concept like that because it sounds stale in 2020. The rest is just a consequence.

Apparently we read different papers from two different universes, each with its own laws of physics. In your universe the definitions of physical states (eg. "steady state") follow circular logic.

@pirad

I’m not feeling very charitable. Did you not understand how Toole used the term? That may explain where your reading went awry. Right up at the top of the paper.

As a parting note: "room EQ" makes poor systems sound better in the listening spot by acting as an ersatz speaker correction technique.

Man, you really can’t read context can you? Like, at all. Toole writes a paper about how hard it is to judge a room response and you claim it proves vaccines cause autism, but later, you claim Toole never said anything.

Toole never really studied distributed bass, he left it to Welti. Geddes had the last word though.

So, you are bringing up Toole as your authority to prove Toole said you can’t fix bass problems .... but he didn’t really study distributed systems, so he couldn’t know, and therefore your use of the paper was to.... blow smoke.

Here, I answered fully this issue in another thread.


I used to work in motion picture equipment industry, including design, installation and set up of some of the best sounding motion picture audio gear in the world. I also make my own loudspeakers and do my own room EQ.

My views are pretty much the same as those posted by JL Audio, though as I posted elsewhere, I disagree with them in some nuanced ways:

https://forum.audiogon.com/discussions/me-vs-jl-audio-an-open-discussion?highlight=me%2Bvs%2Bjl%2Bau...

The problem you’re having rooze, and the mistake you’re making, is the same one I made and everyone makes and that’s following the conventional wisdom, because the conventional wisdom is WRONG! The conventional wisdom is based on the idea that because sound is waves and bass is waves then bass must be the same as midrange and treble. When its not.

That’s not the conventional wisdom, and not what I’ve seen anyone propose. The general solution, as written by and accepted by professional acousticians and installers, for getting deep bass in a room with moderate spend is bass traps + EQ.


http://ethanwiner.com/basstrap_myths.htm


My views and recommendations are also largely in line with what GIK Acoustics would recommend, so please, contact them directly and ask.

https://www.gikacoustics.com/

If you have lots of room, time and money, get more subs, and a custom room. Otherwise, I stand by my advice of using a DSP based solution along with appropriate room treatment and question your judgement and qualifications.

Best,

Erik

Apparently we read different papers from two different universes, each with its own laws of physics. In your universe the definitions of physical states (eg. "steady state") follow circular logic. Let’s leave it there. As a parting note: "room EQ" makes poor systems sound better above Schroeder frequency, in the listening spot, by acting as an ersatz speaker correction technique. It does not improve systems designed properly from the start. That’s how it works in my universe anyway. Toole never really studied distributed bass, he left it to Welti. Geddes had the last word though. He also allowed bass EQ in some circumstances and so do I after him.
www.gedlee.com

And I want to let go of this subject with another point:

The multiple sound problems Toole is addressing in this paper is going to be exactly the same with a swarm.

Best,


Erik

What is your definition of "steady state measurements"?

I’m using Dr. Toole’s, which is clear from his contrast with time-gated measurements.

Please note, this paper is from 2015, what changed since then in the area we are discussing?

My past experience in motion picture auditoriums goes back decades. I’m just utterly surprised RTAs are still used in a theater at all.

He discounts the claims made by the proponents of so called "room EQ". And the inadequacy of "room" bass traps is self evident.

You are missing the entire context of his paper. His paper is about how to set EQ, whether to use reference or house curves and if so why and how we could validate them. Essentially he’s asking how we get to neutral. He doesn’t say we can’t fix room modes.

It does not address small room bass modes, which are a catastrophic attack on anything like neutral. Again, others have covered this directly and precisely. He’s not talking about that at all.

His point if I may be allowed to paraphrase the good doctor:

"We don’t have a very good way of understanding how the ear brain mechanism perceives complex sound, so the idea of using either steady state or gated measurements to set the color is laughable."  The last part I think modern systems have started to get a little better at, at least for the bass and room gain, but as I said, it's basically personal taste converted to DSP code.

And again, I agree with everything he said. He’s brilliant and correct, and attempting to claim he discounts the use of bass traps, or EQ to fix problems is not in this paper. In fact, he’s asking HOW to use EQ.

What is your definition of "steady state measurements"?
Please note, this paper is from 2015, what changed since then in the area we are discussing? Dirac and others were there. Toole is not talking specifically about bass. He discounts the claims made by the proponents of  so called "room EQ". And the inadequacy of "room" bass traps is self evident. How can you fit an elephant into a shoe box?