Do you think you need a subwoofer?

Hi Tim getting back to the best bass I have heard in my system . I have been using DSP controlled stereo bass for three years with great results . After hearing a dynamic system with 4 subs I was inspired to try it myself .My system is centered on a DSPeaker anitimode 2.0 the DSPeaker only has I analog input I paired it up with a DIY 4 input 2 output Bent audio TAP x passive autoformer volume control . the DSP is inserted in a in and out loop . For amps I am using a pair of modified VTL 100 mono blocks using 2 KT-120 tubes ea. puts out about 75 watts . My speakers are Ohm Walsh 2.2000 in custom cabinets that are placed on top of the REL Q201e subs . The power amps have caps in the signal lines to cut the L/F off @  50 hrz . the subs take over from there . I use a analog as well as a digital front end . And for movie night i have a Outlaw Pre Pro that is another source and of course more amps and speakers . My system is far from simple .The only simple thing is it can be turned on with one button that was so that my technically bankrupt wife could use it . I had to design this system around the limited space I have . After adding 2 more subs at the back of the room the bass response has evened out much more then with the stereo subs . Works like active room treatments. All I can say on good recording I give myself goose bumps and that's with both digital and analog . And Raul you may piss off some people but you make us think and that's not bad its good science .RC              

Dear friends: I started this thread almo9st 20 years ago but things are that as many other audiophiles I followed learning not only in this subs issue but in the audio world genral subjects.

Well, in the last 2 years I made it several chnages/up-dates/up-grade to my room/system and mainly to my speakers crossover parts.

So and thank's to a thread dialogue in Agon where I 'm participating last nigth I decided to try different changes in my subwoofers PHASE that's a subject that not only in this thread but in no other thread or audio forum never read in deep the critical importance of Phase in the subs to stay sure that's room/speakers integration is " optimal ".

Started listening to Original Motion Pictures  CDs source with MUSIC as Day After Tomorrow, Gladiator, Thin Red ine and the like. Almost all goes deep in the bass through synthesisers. During my late nigth session I left the PHASE at the best position my ears told me and I gone to sleep with some doubt about.

So, early this morning I come back to my system to continue testing PHASE in the subs and this time with acoustic instruments in several LPs I own and used mainly the Telarc 1812 recording that comes with several kind of bass at diferent frequency bass ranges and my last nigth doubt came out: the choosed Phase was wrong and when finally my analog Phase tests session I achieved a quality level I was not prepared to attain, it was something unexpected and the best it happens to me in many ytears with my audio system.

That's why I urge all of you that already own subs in your systems to " play " seriously with the Phase control in your subs and if you already do it then try it again to confirm is ok for you.

Patience is only what we need but the rewards are huge on this Phase critical subject.

I never imagined its crucial importance.

My findings where confirmed in an Agon thread by a true Agoner expert in that and other audio subjects as is : @deep_333  ..

R.

Wow...this thread has lived for 20 years. And in the wrong category.

Raul, I assume you’re referring to the electrical phase of the signal delivered to your subwoofers with reference to the electrical phase of the signal delivered to your main speakers. This is known to make a difference. But usually one can only alter the phase relationships by 180 degrees, by reversing leads or inserting a phase switch. Are you able to test differences in phase that are >180 or <180 degrees but more than zero degrees? If so, how?

@rauliruegas It is phase and time. The Australians call it " launch time"  The sub has to be in phase with the main speakers and the signal from the main speakers and subwoofer have to reach your ears at exactly the same time. Changing only the phase angle of the subwoofer is going to change the amplitude response of the system is unpredictable ways. The system may sound better or worse depending on taste and even the music you are playing. It can drive you crazy. One minute you think you have it sounding great, the next minute not so much.

@lewm  Many subs have continuously variable phase angle over 180 degrees, but without the ability to match arrival times the phase angle control is a real double edged sword. Once matched in time and phase everything sounds great. You REALLY need to try subwoofers with your SLs. Get an inexpensive MiniDSP  crossover to start. This will give you a good idea what the advantages are, then you can get a more elaborate unit down the road. Benchmark Media Systems uses a MiniDSP SHD studio and two of their own DACs.

I just finished the first pair of model 4 subwoofer. I'll be putting a picture on my system page. 

Dear @mijostyn  : " One minute you think you have it sounding great, the next minute not so much. "

More or less is what happened when started to test it that nigth but from yesterday till today the romm/system reproduced sound is just nothing less than sublime.

Last time I seen your virtual systwem the subs were directly seated in the floor, for me not the best any sub position. The new cilindrical boxes looks fine and similar to a transmision line subs that I listened several years ago. Have good luck with.

R.

Dear @secretguy  : " And in the wrong category. "

Could be but when started this thread I decided in that way. Not many analog lovers were using subs in their systems like today times. In those old times and through this thread several gentlemans ( including me ) learned a lot about this subs crucial/vital audio subject.

R.

@rauliruegas I never said that! From the second I first fired them up I knew Sub model 3 was deficient, but I did learn a lot from building them. Sometimes you have to know what does not work to know what might work. Sub model 4 was inspired by Magico's Q subs, except I took it several steps further. 

The most efficient location for subwoofers is in a corner followed by up against a wall, 6 to 9 dB more efficient. The problem with these locations is you can not integrate the subs properly with strictly analog equipment. It requires digital bass management.  You are putting the subs where they sound best. I am putting the subs where they work best then making them sound even better.

My subs are not transmission lines. They are a balanced force, acoustic suspension (sealed) design with resonance free (and I mean totally resonance free) enclosures. The walls are 1 7/16" thick. The 10 sides are only 4" wide and they are arranged in a cylinder, an inherently very stiff structure. They are much smaller and lighter than the Magicos making them more practical in all situations. They weigh just over 100 LB each. There will be four of them eventually forming an 8 driver linear array. They are 2 dB down at 20 Hz without any processing. @skoss heard them yesterday. You might ask what he experienced. The picture is up on my system page. 

The sound is not where I want it yet. The system is now dead flat from 20 Hz to 12 kHz. I can boost the subs by adjusting their volume relative to the stats, but this makes the bass too warm. The sound is also on the bright side, again because to is corrected to flat. There will be a EQ program in the DEQX and it is supposed to be in the next upgrade. That will allow me to program the amplitude curve to my taste, bass increasing 3 dB/oct below 100 Hz and a shallow drop from 1000 Hz so that 20 kHz is down 6 -12 dB. 

@rauliruegas I think I had the wrong member. It is @sksos ​​​or @sksos1 who heard them yesterday. 

@mijostyn  : Sorry but your post has no meaning for me or I made a poor explanation in my other post.

R.

Dear friends : In this subs issues we have to follow the Physics rules. Here a room mode calculator:

Room Mode Calculator_0.xls (live.com)

and here why at one seat position 2 subwoofers are good enough to listen MUSIC, we don't need 4 but we can use those 3-4 additional in HT but not need it for MUSIC only:

Microsoft Word - whitepaper10.doc (harman.com)

R.

" Two subwoofers, at opposing wall midpoints, performs very nearly as well as four at the midpoints and gives a much better LF factor. "

That’s the Harman conclusion. Now, if we are using our room/system mainly to listen MUSIC where is the bass range we need be reproduced by subwoofers?

Mainly from around 50hz-60hz and down at least to 16hz but 80%-90% of our daily reproduced MUSIC bass range belongs from 60hz/70hz to 30hz and for me this is the main ( other than put at minimum the Doppler effect/IMD ) desired dedicated drivers to bass reproduction and here the phase subs control is way critical. Yes some kind of instruments MUSIC reproduction needs that the subs can works fine from 25hz to 16hz, fine means with absolute aplomb. My Velodyne has usuable 10hz frequency but not so important.

In my latest phase experienced tests I been totally sure about because the overall reproduced sound over all the system frequency range was and is improved in its quality levels as ever before the phase subs change and was only this parameter the one I touched in the subs : same volume, same crossover point, same everything including the subs positions, nothing then but the phase.

Other critical and way important issue when we are integrating subwoofers in our MUSIC system is to have a " rigth " blend " between the sub’s crossover point and the main woofers crossover point.

It has to works exactly as speakers designers do it with his speakers where they choose the rigth crossover frequency of the different filters ( HP, LP, BP ) using normally between first and third order for those filters according each frequency range driver to BLEND . No one use 6 or eigth order filters because the issue is to BLEND and not separates the frequency ranges. Then, this BLEND along the Phase are crucial.

R.

Well, Velodyne makes the blend at crossover frequency with a second order filter shape and latter on pass through fourt order and finished at 48db per octave in my HGS and the Velodyne HP is a first order filter (6db. ).

The name of the game is that blend at 12db per octave along the 6db per octave that in my case is not made by the Velodyne but at the input of my Levinson monoblocks..

R.

Dear friends: from my last sub changes I confirm that that doppler developed characterisc in woofer main speakers must be should be at absolute minimum.

The issue is that the bass range is all about MUSIC room/system quality level reproduction and the bass rage must be perfectly blended inside the bass range. This is high mid-bass, mid-bass, low mid-bass, low bass and deep bass.

That blend must permit that we be aware of eacg bass frequency range with out a bass frequency range " leader " or " leaders " and all those is the true challenge we have with the subwoofer room/system integration.

That bass frequency ranges blend will gives me the best MUSIC rythm ever and the perception of dimensional MUSIC presentation where each track performs in its each territory that’s our room seat position.

With out all those we can’t really have true MUSIC enjoyment and only " something " that we like it..

Not an easy task that bass range frecuencies blend because it’s as complex as a speaker design where the designer needs not only to choose the rigth drivers but the rigth crossover frequency for each driver and the crossover filter shape that permits a seamless blend that’s what makes the differences between a good speaker and a very good or excelent speakers.

Here mijostyn  looks as he knows about and maybe could share his point of views.

R.

@rauliruegas is right in many ways with a few caveats. 

In a normal point source system two subwoofers is fine and more does not add much. Line source systems require a driver every 4-5 feet along a wall to form a line source subwoofer to match the main speakers.

I would not bother with subwoofer drivers smaller than 12". 10" drivers are fine if you use two of them per enclosure. Most big point source systems require two 15" subwoofers. The smaller the driver the greater the distortion levels at a given volume.

Blending the subwoofers into the main speakers using second through 4th order slopes is appropriate for all subwoofers except a small number of truly excellent units. Subwoofer enclosures are extremely hard to make. Most of them are musical instruments and have a particular sound. If you use a steep slope with these subwoofers the cross is very noticeable. Turn the volume up and place your hand on the sub enclosure. If you feel any vibration you have a musical instrument. Subwoofers that have no sound of their own (do not vibrate at all) can be run higher up using very steep slopes 8-10th order (digital only) as there is little sonic difference between the subs and the main speakers at the crossover point. Here the important factor is keeping the sub out of the midrange where you will hear it. Subs are integrated correctly when you can't tell they are there. Using a low pass filter only on subwoofers is a sad proposition. Easily 1/2 the benefit of using a sub is cleaning up the midrange of the main speakers. You have to use a high pass filter on the main speakers to do this. It is not done because of the added expense of electronics and cables. 

I believe all subwoofer systems should run down to 18 Hz. Music does not go that low but venue clues do. Large venues breath at very low frequencies. With some live recordings you can feel the venue. Subwoofers should be felt more than heard. This is the difference between a live and reproduced performance. Proper subwoofers give you the feeling and excitement of a live performance. 

In my mind there is no difference in the requirements of a theater vs music system. A great music system will sound just fine in theater mode and is quite capable of rattling your teeth.

These are some important concepts to keep in mind when buying subs. Balanced force design. Some of the vibration you feel is the enclosure shaking in opposing response to cone movement. Placing a driver at opposite ends of the enclosure cancels out these forces lowering the musical instrument factor. Smaller enclosures are better because they are easier to control lowering the musical instrument factor, but they will require more power and possibly EQ. A box is the worst shape for a subwoofer. The best shape would be a sphere, but this is impossible to make. The next best shape is a cylinder. Cylinders have inherently stiff walls and are less prone to resonance than flat walls. Cylinders are relatively easy to make and I am surprised that nobody is making cylindrical subwoofers. Open baffle subwoofers are IMHO a silly concept and a florid waste of power. Why some people think they are great is more an indication of how poor many enclosed subwoofers are. There are many excellent subwoofer drivers out there. Dayton makes a Reference sub driver for any situation and I do not see how you can do any better. DIY by all means. Think big pipe with a driver in each end. You can get aluminum pipe in almost any dimension, cap the ends, drivers, binding posts and cleverness. 

Subwoofer drivers take a beating and even the best ones fail on occasion. It is not a bad idea to keep a spare driver handy. The drivers evolve and it is unlikely you will be able to get the same driver after 10 years. Without a spare you will have to replace all of them. 

I'm happy with my Genelec 8351Bs that reproduce accurately down to 32 Hz with no subwoofer. Most of what I listen to, i.e. recordings of acoustical instruments and ancient 78 RPM records, isn't recorded below that, anyway, so I don't care. It would be nice to have one, but the amount of expense and trouble I'd have to go to to get something appropriate would be far disproportionate to the amount of enjoyment I'd get out of hearing the handful of recordings I listen to with crazy-low notes. I have better things to worry about.

Dear @mke246: Well, your powered 3-way monitors are really good ( I had the opportunity to listen it. ) specially at near field position.

The weakness ( if any ) is when you have a greater room and don't listen at near field position where the bass range at higher SPL just distorts, nothing is perfect and in my case even that normally I listen at near field position my room is to big and I listened to evry kind of MUSIC with low bass content. I don't know how you considere Organ instrument as an acoustic o0ne or not but not only the organ scores but what mijos posted about the venue breaths.

I don't know the kind of room you have and your seat position but maybe you are acandidate to integrate a pair of subs using only low-pass filter, using the subs as a low bass reinforcement crossover30hz-40hz 8th order filter shape. Just thinking " loud "..

R.

Good points, I may think about getting a pair of Genelec 7360s in the distant future. Not something I really need but might be fun to have. I mostly work on ancient acoustical and early electrical recordings from the 1910s through 1933 or so, and the bass response on those cuts off around 100 Hz on the acousticals and maybe 50 Hz on the really well-recorded electricals. Even 100-year-old records are often surprisingly high-fidelity if restored properly. I have a few Fats Waller organ records which are very well-recorded for the 1920s with big luscious room tone, but they don’t test the monitors’ capabilities in the least. I do listen to modern music on streaming on rare occasion and remember just how great my equipment is! I’m almost always in my office in the near field restoring old records. If I have a listening party I can use a different GLM setup and tilt the monitors a bit to move the sweet spot back. Subs would be overkill for my needs, but I guess I’ll keep them in the back of my mind. It may be a while--there’s always a more pressing need like getting more custom stylii made or a rare record. Down the road, I could see squeezing them into the budget.

@mke246 Cool Loudspeaker. I assume you have them up on stands? I saw Ain't Misbehavin 3 times. 

Think of it this way, you are getting two subwoofers to improve the performance of your Genelecs. Your woofers cross to the midrange at 320 hz. Middle C is 256 Hz. Your woofers are handling a very important chunk of the midrange. The Doppler effect inducing frequencies start at about 100 Hz and the effect increases as the frequency goes down, the worse being under 40 Hz. Genelec did a smart thing by rolling off the woofers at 32 Hz to save power and avoid the worst of the problem, but it is still there. Subwoofers used with a two way crossover will lower distortion in your Genelecs. I can't believe the processor that comes with them does not have digital bass management considering they also sell subwoofers. I am all in on  active speakers. The excellent latency and group delay performance of your speakers is due to digital processing. The easiest way to integrate subwoofers into a system is digital bass management and you are already there. When you do play modern recordings the bass will put a big smile on your face. 

I have a bunch of 78s. I can hear through to the instruments and voices and extrapolate to what the real sound must have been like, but the sound is awful. They are fun to play. Many of them have severely tortured spindle holes from changer use, talking about wow. I use an Ortofon specifically for 78's. It has a humongous stylus.  I also have a collection of popular music on 10" discs, the 45's of the day. 

One of the tragedies of my life was my Grandmother's ancient Victrola with the flowered horn. I thought I had dibs on it, but it got sold out from under me. I've never seen another that was in such good shape. 

Dear @mke246  : Good. The other parameter that we have to know with your Genelec's is at what frequency crossover those 8" woofers to the mid-range....

R.

Now that I read the mijos  post I can see that the frequency is at 350hz ( I can't find it ). So, if it's at 350hz then the HP is desired to has down there but in the other side you are really listening at near field, even that the IMD is there and you can clean up. Maybe Genelec can help you to choose Genelec subs at your specific needs.

R.

Dear @mke246  : I think that you are living a great first hand experiences listening to those very old recordings as that of Fats Waller. Congratulations.

R.

Most collectors playing 78s are not going to hear the full potential of the records because their equipment is the equivalent of playing an LP on a Crosley. Bad stylus fit, bad EQ, suboptimal processing capabilities, or simply not playing an archival-quality copy. 78s will never sound like an LP-era recording, but you can make them sound like the best reissue CDs out there or better with the right equpment.

My 8351Bs are on stands on my large standing desk--sort of by necessity. They measure well in GLM software, and my room is treated with GIK panels. I mostly remaster on Sennheiser 800S headphones because I have a young child who’s usually sleeping when I have my ’free time’. I admit I haven’t put much thought into the concept of crossover frequency. The tuba and string bass on old jazz records sounds nice and tight, but I listen mostly to 78s probably limits my scope of reference when I listen to anything more modern. I’ll be researching subs and will probably pick up a pair when the time is right.

Genelec recommends 7370A subwoofers (around $4k each) for the 8351B but also has said in the past that 7360As (around $2.5k each) are fine if your room is on the smaller side and you listen at lower-to-moderate SPLs, which would fit my situation. Most people who implement subs with 8351Bs seem to leave the crossover frequency in the neighborhood of the default 85Hz. Still a bit on the fence--most of my music is pretty light on the sub-bass and that's a hefty investment for something I'll only get big benefits from on infrequent occasion. The 8351Bs are pretty strong at reproducing the bass on 98% of what I listen to.

@mke246 Again it is not just the added bass performance you are looking for. It is improving the performance of your 8351Bs. 85 Hz is OK, but I would go higher at 100 Hz. Just removing turntable and record rumble from the 8351Bs will make a significant improvement.

@rauliruegas I got that crossover frequency directly from Genelec's literature. 

I use Channel D's Pure Vinyl Program for RIAA correction. It also has every EQ curve known to man. My phono stage is digitized, the signal is converted to a USB channel, sent to the computer that applies the chosen EQ curve and sends it back to the Lynx Hilo on a different USB channel. I can also record it to the hard drive in the process and do a lot of fun things like apply a pop and click filter that is very effective. 

I love Fats Waller songs but I prefer to listen to Art Tatum play. 

@mke246 : This thread exist and I started mainly to learn and understand that the main function to integrate 2 self powered subs to an audio room/system that’s used to listen MUSIC is to cleand up the whole mid/HF frequency ranges putting the main speakers IMD at minimum using a hiugh pass crossover filter and as an additional " side benefit " those subs permits no9t only to go deeper in the bass range but with a dedicated amp/drivers to that bass range be listened spot on.

Now I think that due to your personal needs in reality you don’t needs to add sub’s due too that your Genelec speakers are great self powered tri-amp excellent design where you not only can have 113 db SPL but can go down to 32hz and even usuable 28hz an according with specific model measurements your speakers at continuous 86dbs is THD is so low that maybe you can’t be aware of its levels and the low bass at that SPL is just accurated and only at over 95db SPL the speakers goes inside trouble.

Additional to all 5hose you normally listen at true near field position and different that mijostyn I don’t need to insist in subs for you. I listened your speakers and for any one it’s an " eye/ear opener ", excellent monitors truly accurated that’s main characteristic for an studio monitor.

R.

After doing some research the past couple nights I'm strongly considering adding a pair of Genelec 7360s to complement my 8351Bs. I know Genelec recommends the 7370s, but I think the 109 dB SPL of the 7360s is more than enough for my needs (even 80 is pushing it for me and 90 is usually borderline painful--not sure how some of you do it!), and my room is on the smaller side. The 7370s wouldn't really even fit without some creative rearranging.

I'm not sure I fully understand the measurement side of things and whether it would be an upgrade in more than just the sub-bass with these particular monitors. I do have a couple bigger nulls in my GLM at 72 and 108Hz that the subs probably will help address.

Listened to some stuff with deeper bass the past couple days to refresh my memory, and I'd call my current setup nice and tight and reasonably full range but a little light on the deep tones you can really feel--no surprise there. Even looking at those Fats Waller organ records recorded in a church studio in Camden, NJ by Victor Records in1927, they have crisp, well-defined bass as low as 31Hz! Incredible! I think my monitors technically are capturing it, but I could see how a sub would be a more effective solution to reproduce this type of record, or any record, accurately. Would like to understand the numbers a bit better.

Dear @mke246  : Good. That " well defined bass as low as 31hz " yes is incredible coming for 1927.

Good luck with your 7360's.

R.

Dear friends: Along the other 2 Harman links I posted in this page this one could be interesting for almost all of us:

Harman How to Listen

R.

@mijostyn  : Balanced force in sub's is not something new, Thiel and ML did it along other manufacturer before.

" I am surprised that nobody is making cylindrical subwoofers. " , not today but in the past HSU was a proffesional proponent of that design and they manufactured subs's that gone as lower as usuable 4hz frequency.

In reality, it's almost nothing new about sub's but differences in its quality design implementation and digital crossover technology that in the past never been used.

R.

@rauliruegas I did not say it was new and I recommend ML subs all the time. KEF does it with the Blade.  Magico does it with their Q subs. 

I am not familiar with HSU, but good for them. You are also right that digital bass management with crossovers, room control and EQ have improved the situation greatly.

I have two Model 4 subwoofers up and running. They measure great with a slowly downward sloping curve from 100 Hz down. They are 3 dB down at 20 Hz. This is without correction, with the crossover deactivated. They do not shake or vibrate at all running a 20 Hz test tone and white noise at 90 dB which is as loud as I can go before things start falling off shelves. 

good.

Got the Genelec 7360As integrated into my system just now. With GLM adjustments they're pretty good for my needs, especially mono stuff where the minor deficiencies in one channel offset the other. I'm sure I could improve it a bit if I adjusted placement a bit, but great for now. Bass presence is massively improved across the board, even with stuff with 'average' bass, e.g. bowed string bass. Glad I stumbled into this thread and thought it over! These things are incredible.

@mke246 Great bass always brings a huge smile to my face, it is the part that makes you want to get up and dance.

Dear friends: I think this link belongs to this thread:

Microsoft Word - whitepaper10.doc

and this tinformation too:

" 

The ONLY correct way to add a sub to system is to define everything ABOVE the sub’s [frequency] range as an entity; clearly define the impulse, phase, and lastly frequency response of this entity; and then make a new "2-way" system where the sub is one way and everything above it is the ’other’ way. The parts must be combined correctly so that there are no cancellations and no smearing of time-related musical events.

This CANNOT be easily measured in the frequency domain, because you could have (as an example) an 80 Hz signal coming from both the mains and the sub, and if the sub is 12.5 msec late the two sources will "seem" to be in phase but the sub really will be 360 degrees, or one full wavelength late. It is the impulse smearing that this affects, but people don’t measure that because there is no simple "hand held" phase or impulse meter as there is an SPL meter.

The REASON this meter does not and essentially cannot exist is that in order to measure impulse response or phase response you need a starting REFERENCE point, (in time) and in a speaker system, since the signal has to travel through circuitry, amplifiers, passive crossovers inside the speaker box and then hit the driver; therefore the first reference point MUST be acoustic.

There ARE computer based impulse response systems such as the TEF, ( very quick technical blurb HERE; full story HERE ) but they are involved, require real instrumentation, are expensive, have a seriously steep learning curve, and they are absolutely not the kind of thing most ’consumers’ -- or audiophles, can be bothered with or have patience for.

So the overall view of adding a sub is this: In essence you are designing and assembling a new speaker system which is "2-way": the sub is one way and everything "else" above it in frequency is the 2nd way.

Simply connecting a sub to existing mains speaker (or amp) terminals ( or self powered subs. ) is the WORST POSSIBLE WAY to do this. EVERYTHING scientific and acoustic about this method is wrong, from the additive delay issues to the back EMF of the mains affecting the LF signal. However there are plenty of people who simply do not understand correctly integrated bass, and they will be reasonably happy simply sticking another box on to their system without regard to timing, phase and frequency issues, and they will think it sounds "ok" or "good" and for those people it doesn’t really matter.

Indeed the only thing that does matter is an individual’s happiness with their system, whether I or anyone else thinks it’s right or wrong.

But I want you to know and understand the truth, so to get purely technical...."

along this:

" 

TYPES OF "MAIN" SPEAKERS

In addition to all the above, there is the complex issue of the "main" speaker you are coupling to. There are essentially 6 types of speakers that exist:

1) sealed
2) port in the front
3) port in the bottom
4) port in the back
5) a dipole, which is a flat panel such as an electrostatic (Sound Lab, Magnepan, Quad, Beveridge, Martin Logan, etc.)
6) an true omnidirectional system such as the MBL or the BEOLAB 5.

Each of these speaker types couples somewhat differently to the room, and certainly to a sub in that room, and therein lie the problems in acceptable integration.

A port is ALWAYS nothing more than a cheap way to attempt to get free bass out of an enclosure and /or driver that's too small. It's a holdover from the 1930's when because of driver inefficiencies (especially when compared to today's units) you had to do everything possible to increase the useable output over the desired range of low frequencies.

At one level, all the guyz want 9 foot speakers in the living room (read "man-cave"). All spouses, of whatever gender, want tiny 3" speaker cubes that disappear, but expect 9-foot results from them. Since they haven't repealed ohms law or any other laws of physics while we were sleeping, the only way to get correct sound is to move a correct amount of air.

Lets examine ported speakers. We'll start with the worst case, the port in the front. At mid bass frequencies, say 50-80 Hz, the LF driver moves IN the cabinet, the air in the cabinet is elastic, and the port air moves out of the cabinet. Because of the frequency at which the cone is moving, by the time the cone moves out (forward) again, the port air is now moving out, so in front of the cabinet the two air pressure sources sum together and you get a fake bass "bump" or "boost".

As you go lower and lower in frequency, at some low frequency the air pressure from the LF driver and the air pressure from the port are exactly opposite each other, so they cancel, and there is no more audio at that frequency: it disappears.

When the manufacturer of a speaker cabinet defines the frequency response (i.e., 37 Hz - 20kHz +/- 3dB) this is what is defined by the entire arrangement of the port and the air in the cabinet and the driver. At some low frequency the port air is exactly out of phase with the driver air pressure and since they cancel, there is NO output from the cabinet into the room. Therefore with a ported cabinet, the entire sloppy concept is this juggling game between the response of the drivers under air pressure, the passive crossover inside the box, the port size and placement.

You must understand that ANY driver goes down to 0 Hz, or DC. If you put a battery across a speaker, the cone moves out and stays there. If you were to have a DC coupled power amp feeding a speaker - ANY speaker, from a 1" dome tweeter to an 18" rock n roll stage bass driver - and you put 4 Hz into it, it would simply move back and forth at 4 Hz. Of course in order to actually "hear" the audio it would have to be in the generally accepted passband of 20-20,000 Hz and the cone diameter would have to be enough to actually move some air in the room. So it is the overall combination of the driver size, the excursion, the box size, (therefore the air back pressure) and many other factors that determines the overall response of that "speaker" AS AN ENTITY.

That means IF you were to simply put those same frequencies through the mains and the sub (that means with no crossover, and this is the mistake that nearly everyone makes) you would now have 3 sources of LF energy and differing phase: the 'main' LF driver, the port, and the sub, all fighting with each other in the time domain. A further corollary is that since the air inside the [mains] cabinet is elastic, the phase relationship of the port air to the driver air is also a sliding one; that means it's "out of phase" — and smearing — over a wider range of frequencies than you might think.

If the port is on the back, again, a cheap attempt to use the back wave bouncing off a wall to give 'additional' bass, you have the ADDITIONAL issue of the transit time it takes for the back port pressure (already delayed because of the elasticity) to leave the cabinet, travel back, hit a wall, and bounce back around the front of the cabinet again; therefore this LF wave MIGHT be "in phase" with the front driver BUT BE 360 OR EVEN 720 DEGREES LATE; therefore it sounds like the bass frequencies are ok in the frequency domain but the IMPULSE RESPONSE is now muddied.

Also, in the case of back ported or (type 5) dipole speakers, since the path length from the back of the speaker to the wall and bouncing back around to the front of the speaker is a fixed physical entity, at some frequencies you are adding and at some frequencies you are canceling: you have simply made a physical/mechanical frequency comb filter that you can't do anything about. Sound Lab's answer to this (for use with their flat panel electrostatic speakers, which are dipoles) is they sell you a "Sallie", which is an absorber to absorb the entire back wave output of the electrostatic panel. Since now there is no comb filtering; all you are therefore hearing is the front signal.

PORTED SUBS

A ported sub for home use is even more wrong than ported mains. Now you would be attempting to acoustically add together in the room at least SIX low frequency sources with differing phase and frequency slope conditions: the LF drivers in your two mains, their ports, the sub driver, and its port. In addition, since it's a bandpass it cannot go down low enough for serious Home Theater effects. (that typically means a real 20Hz or close to it.)

In some cases such as a bandpass sub used in a club or on a modest-sized stage in your local pub, you are most concerned with efficiency and not with getting frequency response "flat" down to 20 Hz; therefore a correctly set up bandpass box that might roll off at 35 to 45 Hz is quite sufficient and also very efficient for the defined purpose. And again, as a point of reference, "flat" response in the frequency domain is FAR AND AWAY the LEAST important phenomena: impulse response in the time domain is the most important, but it cannot be measured with a handheld meter therefore almost everyone simply ignores it. If you're interested in learning about the newest (and evolving) pro sound system / stage methods of "steering" bass, Dave Rat has some very cool videos here:

part 1  www.youtube.com/watch?v=VwLH7zP6Lwo

part 2  www.youtube.com/watch?v=B-3pURYOwfw

part 3  www.youtube.com/watch?v=aSZK9Altvm8

There's a nice article here:
www.prosoundweb.com/channels/study_hall/tech-topic-friends-in-low-places

But back to our Home / HI-FI / 2-channel / Audiophile / Surround Sound systems: There is ONLY ONE truly correct way to "add a sub" to a system in an controlled listening room situation: you must correctly cross over the 2 sealed cabinets; and their timing must be correct. ANY other method will lessen the focus and clarity and imaging you have tried so hard to preserve.

I have many clients and customers with extremely exotic high-end 2-channel systems that are all chasing the holy grail of 3D holographic sound imaging, and until they follow my distinct guidelines they are never completely satisfied with the results.  "

Regards and enjoy the MUSIC NOT DISTORTIONS,

R.

Raul that was a very informative posting. The fellow you quoted, in simple language broke down a crucial concept to be more easily grasped at its basic fundamental level. I hear the voice of experience in the point he is making.

I have downloaded that PDF and will be reading it in the near future.

@theophile  :  Bass range is where MUSIC " belongs ". As better the room/system bass management as better the overal quality level MUSIC reproduction and only self powered dedicated subwoofers reproduce the "  rigth " Transient Response  that's where MUSIC starts.

R.