Multiple Subwoofer Placement

Ron Party

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Apr 30, 2010
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#1
Earl Geddes's position on multiple subwoofer placement is, essentially, that three subs are needed and you don't need to put the subs at specified locations. I know Frantz is a strong advocate for Dr. Geddes's approach. There seem to be some basic rules that apparently have proven to produce the best results:

  • Put one sub in a corner close to the mains speakers. Location for the second sub is flexible with the one condition that it should not be in a corner. Side wall or back wall, near the midpoint is preferred. The third sub goes wherever one can put it that is not too close to the other two. And, finally, I believe Geddes recommends getting one sub off of the floor.

On the other hand, the research that Todd Welti and Allan Devantier performed seemingly suggests a (slightly?) different approach:

  • Placing 2 to 4 subwoofers in the room’s corners, wall midpoints, or at 25% and 75% along the wall dimension.

I may be simplifying or (more likely the case) misunderstanding the two approaches, but I'm just wondering if these approaches are or are not consistent with one another. Of course some of this is room and sub dependent, but I thought this would be a good jumping off point for a new thread, particularly since we have people like Mark Seaton, a preeminent subwoofer guru, and Ethan Winer, a preeminent room acoustician, on board.

Which of these approaches (or others) have people tried and what have people learned produced the best results.
 

Ron Party

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Apr 30, 2010
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#3
For those reading this thread, the paper Amir referenced contains the research of Todd Welti and Allan Devantier to which I made reference.
 

audioguy

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Apr 21, 2010
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#4
We placed mine by experimentation. But we started with one near the left front speaker but next to the wall, placed the second one near the right rear corner and then kept measuring (with a product like REW) and moving each sub until we got the smoothest combined response. Practicality (as in having a sub at a spot where getting to the seats was inconvenient) did play a role in eliminating some of the potential spots as did door locations and center channel locations.

The (semi) final resting place is that the front left sub is about 25% down the wall and the rear sub is very near, but not in, the corner. The second two subs are symmetrical to the first two. The other night I tried to use some of the locations as specified in that paper and the response got worse. The four corners was really bad and moving the rear sub as per instructed also made it worse. I think the Harmon papers is a good starting point but, at least in my case, it was not the best spot.
 

FrantzM

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Apr 20, 2010
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#5
Amirm

I would use "better known" in place of best. Geddes paper is not as well written but if one cares to go through the graphs, one can get a sense that Earl Geddes's in into something here, the main differences between the Harman protocol and Geddes is that Geddes counts on random positioning of the (at least) 2 remaining subwoofers with the main as previously noted in the corner behind the speakers e third to be placed in a corner being the speakers... I did try his method and was achieving the best bass both subjectively and objectively in my now defunct system. I don't have the data anymore, but I was about -7dB at 9 Hz and essentially flat between 15 and 100 Hz .. , using 3 subs, with full range speakers I used the un-audiophile Behringer to corect phase and response of the subs (it was ONLY in the 3 subs path, it is definetly not good up there unmodified) ... I definitely will go that route again
 
Jul 1, 2010
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#6
We have seven or eight subs in the studio at work, varying in quality from Martin Logan and REL down to entry-level Definitive Technology. Every one of them seems to sound better off the floor and away from the walls.

But bear in mind that is a purely subjective call from someone who is most definitely not a bass head.

P
 

RUR

WBF Founding Member
Apr 21, 2010
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#7
And, finally, I believe Geddes recommends getting one sub off of the floor.
What, exactly, is the wisdom behind this, BTW? Decoupling the sub from the vertical mode? If so, why not all the subs?

I keep meaning to conduct the experiment with REW measurements, but volunteers to help lift the 120# sub are in short supply and my LF is pretty flat, already.
 

FrantzM

Member Sponsor & WBF Founding Member
Apr 20, 2010
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#8
p

It is a little more complicated than that.. Do have a look at the Geddes paper I posted .. One sub in the corner has the advantage of bossting its output especially its lower frequncies. For example, a sub whose anechoic reaches , says, 15 Hz at minus 15 dB ... could have its output reinforced by the corner placement .. Now comes the interesting contribution from the other subs ... their output "fill" (for the lack of a better word) the through in FR and , interestingly attenuate the peaks, however counterintutive, at first this might seem.

I must tell you that I was very worried abut the temporal differences , after all the distance to the listeningposition are different and even ore than for the full range .. Fact is it takes our brain about 40~50 ms to register a 50 Hz tone so that few millisecond difference that such solution entails is not much of a problem ... However the audiophile that I am would not feel satisfied. The Behringer DCX-2496 helped aligned temporarily the subs in front of the mains for the one in the back I frankly didn't bother .. A more sophisticated solution such as TacT, DEQX or Behold would have don the same maybe not as cost-effectively .. This unit is not IMO suitable for the upper frequencies but for the lows it is almost overkill and cost less than $300 ... A good investment for the brave. This unit is not meant for the faint of heart ..


For more enjoyment or those who cares have a look at these discussions..

AVS 3-Sub Discussion
or the measurements from a person who performed the experiment.
MEHLAU

I must add that it is very difficult to evaluate a subwoofer subjectively, most of the subjective impression associated with subs come from set-up. I am of course assuming a technically correct and competent subwoofer with good measurements ... And NO !! I am not implying that all subs are created equal.. Some are better than others both subjectively AND objectively... I also will add that the best bass in most cases require the use of multiple subs even if your mains are capable of extended LF ... Not a question of quantity (SPL in the bass) but of smoothness of FR, thus subjective quality as well.. I believe there is at least another person on this board who uses this method and also Geddes speakers .. His input would be interesting Right? R ;) ?
 
Apr 3, 2010
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Seattle, WA
#9
What, exactly, is the wisdom behind this, BTW? Decoupling the sub from the vertical mode?
I think the reason is the same as varying the position in the X, Y axis. Same modal situations exist vertically as the sound doesn't care if it is going in that direction or the the other two. The reason it is not usually recommended is that it is considered impractical for most people to change the height of the sub. And as you mention, by removing it from the floor, you will lose the subsonic feel that may be useful for movies and such.

I think the Harman paper touches on this if my memory is right.
 

FrantzM

Member Sponsor & WBF Founding Member
Apr 20, 2010
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#10
Hi

While this discussion is about the Geddes Subwoofer method. The agreement between many seems to be that the best results are obtained using multiple subwoofers, at least 3 in most.. This paper is from by Todd Welti and Alan Devantier both I suppose colleagues of our own Tonemeister at Harmon

Low-Frequency Optimization Using Multiple Subwoofers*

Sor those impatient skip to page 15 of the pdf for some figures .. :)
 

Gedlee

WBF Technical Expert
Jul 21, 2010
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Novi, MI
#11
Amirm

I would use "better known" in place of best. ... the main differences between the Harman protocol and Geddes is that Geddes counts on random positioning ...
Hi all

It is important to note that Welti only tried symetrical placements, so naturally this is what he recommended. I have tested both and I agree with Welti's results, but the random configuration just works out better. So its not a matter of our disagreeing, he never tested random so he can't agree oir disagree.

I never wrote a paper on the subject, only some brief "notes" on what I have concluded.

I gave an AES presentation about a month ago on this topic and I will post the powerpoint slides at some point.
 

Ron Party

WBF Founding Member
Apr 30, 2010
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#12
Dr. Geddes, thank you very much for joining our small but growing forum! And a special thanks to Randy for getting Dr. Geddes to join!

I am strongly looking forward to your powerpoint slide presentation.
 

Steve Williams

Site Founder, Site Owner, Administrator
#13
Hi all

It is important to note that Welti only tried symetrical placements, so naturally this is what he recommended. I have tested both and I agree with Welti's results, but the random configuration just works out better. So its not a matter of our disagreeing, he never tested random so he can't agree oir disagree.

I never wrote a paper on the subject, only some brief "notes" on what I have concluded.

I gave an AES presentation about a month ago on this topic and I will post the powerpoint slides at some point.
welcome to the forum

we all look forward to your input
 

RBFC

WBF Founding Member & Super Moderator
Apr 20, 2010
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#14
Agreed. Thank you for your participation! Only when we can get information that has a solid background can we make better informed decisions.

Lee
 
#15
Dear friends: Here and in the other subwofer threads I read almost everything to learn about subwoofer ( mainly placement. ) but I wonder why ( you that use it ) to use subwoofers in a music dedicated stereo system, even if we own full range speakers. Which answers do you have?.

regards and enjoy the music,
Raul.
 
#16
Dear friends: Here and in the other subwofer threads I read almost everything to learn about subwoofer ( mainly placement. ) but I wonder why ( you that use it ) to use subwoofers in a music dedicated stereo system, even if we own full range speakers. Which answers do you have?.

regards and enjoy the music,
Raul.
Well this is my answer, this is what I found ( and share. ) through my experiences trying and achieving the seamless integration of two separate and self powered subwoofers in a true stereo fashion to my full range passive loudspeakers:

Why it is important the use of subs on our home stereo audio systems ?

Well, for we can hear what is on the recording ( analog / digital / any ) we need a series of links ( audio items ) to build the whole chain for the music/sound reproduction.

All the links on the system chain are important and all of them have their particular distortions that put the " colors " to our " audio pictures ".

In this audio chain, in the analog case , the most imperfect links are at the front end: phono cartridges and the speakers. Here is where we have a lot of distortions ( of any kind ) because these audio music " transducers " are truly an imperfect ones against electronics ( for example ). So, for me, these are the " tweak " links on the audio chain.

In this forum all of us already learn how to improve the cartridge link for a better music/sound reproduction ( less distortions ), but not many of us take care about the speakers distortions, other than the room interaction, that really " color " the final sound that we hear.

Why we take care about: VTF, VTA/SRA, Overhang, resonance tonearm/cartridge, SUT or not SUT, unipivot, air bearing, cables, tubes or not tubes, SS, DAC's, CD transports, and the like when all what we do can be corrupted at the end of the audio chain with full of speakers/room distortions.

Where the subs can help us ? :

Intermodulation Distortions: Almost any three ways speaker ( all two ways/one way ) has it's crossover frecuency ( low driver ) between 150Hz and 450Hz. I can assume that any of ours speakers system goes down flat ( at least ) between 60Hz to 20Hz.

What does that means ?, well that a single driver has to reproduce frecuencies/harmonics from 20Hz/60Hz to 150Hz/450Hz. With that kind of frecuency range here exist a great intermodulation distortions that put it's " color " on the sound reproduction.

You have to imagine that that single woofer/driver has to reproduce, at the same " time ", a 30Hz frecuency along a 350Hz frecuency: here is where exist that IM that gives heavy distortions in what we hear ( there is no perfect driver: moving coil, electrostatic, ribbon, etc.. The speaker designers has to choose the best " trade offs ", but the distortions are there. ): less clarity, less resolution, less precision, less natural balance, less pitch, les, less, less......., and this is what we are really hearing: LESS MUSIC.

If you read any manufacturer specifications on their speakers they never " write " the value of the IM or harmonic distortions, they tell us the frecuency range and how is flat on that range but never " talk " about distortions. I think that you know that when we have a speaker frecuency specifications, say: 28Hz to 22kHz +,- 3db, that is a very nice spec, that speaker low driver don't stop at 28hZ it's goes a few hertz below that frecuency with heavy harmonic distortion that increase the IM distortion of the sound reproduction of that driver and these additional distortions have a severe degradation in the reproduction of the MUSIC.

What happen when that low driver is free from those frecuencies ? ( main speakers: monitors or full range, it does not matters. My main speakers are flat to 22Hz and only 5db +.- at 18Hz and I have benefits with the seamless subwoofers integration to my system ), below 80Hz ( this is the crossover frecuency that I find the best point to start to blend a subwoofer. ):

SUDDENLY the " lights are on ", your music/audio " life " its born: the mid bass is clean, the midrange is clean, the highs are clean: high resolution every where ( the distortions are almost gone ), and now you can really hear for the first time the MUSIC through your home stereo audio system: what a pleasure!!!!!.

This is truly a discovery for all of us that cares about MUSIC. We really discovery what kind ( quality/quantity ) of audio system we really have ( now we can do any evaluation of any audio item, not before. ) and where to work for a future improvements.

Now that we already settle in the subwoofers ( self powered ) with our main speakers ( yes, it is a hard work to do. We need at least: very good ears, love for music, experience with live music, patience, time and good muscles. We have to work with: location of subwoofers and the main speakers too, phase, crossover frecuency, volume/gain. We need two subwoofers not one and this issue is critical. TIP: avoid the common asumption that the crossover point should be at the low frecuency flat response of the main speakers, example: the speakers are flat at 40Hz, then you choose 40Hz for the frecuency crossover between the subs and the speakers, this is a great mistake: remember that we use subwoofers not only for a better and extended low bass but for a better midrange/midbass too. So, the frecuency crossover will be over that 40Hz: not at 40Hz or below 40Hz. ), we have others advantages:

- better quality low bass ( you can have at least one more octave ) and mid bass ( quantity? : you choose it: volume/gain ) ). Now we can heard the " foundation " of the MUSIC ( and its harmonics ) and this single issue is stunning for the pleasure to hear any kind of music. Now, we are nearest to the " real MUSIC ", nothing less.

The first time you can hear the subwoofers right blended on your stereo home audio system: YOU NEVER COULD LIVE WITH OUT THEM AGAIN, ANY ONE CAN.

- An improvement in the soundstage reproduction in all parameters: deep, front/side location, wide of the stage, etc...

- the main speakers amplifiers works best ( less distortion, more headroom, less chance of clipping, less amplifier stress, etc...) with out to handle the frecuencies range that now are handle by the dedicated subwoofers amplifiers. This is important for an SS amplifier but for the tubes ones is a must.

- Now the low bass frecuencies are handle for a dedicated driver that was build with specifics characteristics for to work in that frecuency range and this low bass driver is matched with an amplifier ( self powered subwoofers ) that was build with specifications that mates excatly what the low bass drivers needs about: frecuency response, output impedance, damping, power, etc..... You can't ask for more!!!

- Not only the IM distortion goes down but the harmonic distortion of the low driver of your main speakers goes down too.

- Usually the location of the speakers in our room ( with out subs ) is a " compromise " ( trade off ) between the best performance at the bass against the best performance at the mid/high frecuencies ( only in a few cases the location is with out any " trade offs ". ), when we integrated the seamless subs in our audio system we can have the best of both " worlds " and you will be in " heaven ", now we can put the main speakers in the best room location and the low bass drivers ( separate subs ) in its best location too!!!


Some people use subs with their full range speakers (FRS ) as a bass reinforcement, this IMHO is a misunderstood that can do more harm that any good to improve the system quality performance:

maybe is not very clear about the seamless integration in a true stereo fashion of powered subwoofers with " full range " speakers like Dynaudio Evidence/Temptations, Dali Megaline, Wilson Maxx3/Alexandria, etc, etc,...

We can think that with a FRS the integration of two powered subwoofers can't do any help to improve the quality sound reproduction. I can tell you that even with FRS the integration of subs can help a lot, let me to give my opinion about::

- That elusive full octave in the low bass is a headache for any one, especially for the loudspeaker manufacturers: they have to choose very carefully the right trade-offs about.
In the other side, we the FRS customers have to choose the right amplification device for really " take-out " and " live " that marvelous low bass reproduction through those passive FRS: a very hard task, it does not matters the speaker design and the amplifier design.

- There is no single external / stand alone amplifier that can work or do a better job than a low bass dedicated amplifier like the one that comes with a powered subwoofer:
think that this dedicated bass amplifier was designed/tailored to match every single woofer parameter: impedance, frecuency response range, damping, power, distortion, etc, etc,...

- It is not only this dedicated amplifier what makes this subwoofer approach/technology ideal to handle the low bass octaves.
The driver/woofer is designed/tailored too for that specific low frecuency range.
There is no passive FRS, at any price with any amplifier, that could beat a self powered subwoofers in that frecuency range. When you have and hear the subs on your system you never can live again with out those subwoofers.

Here we have to remember other important issue: the best subwoofers are SERVO CONTROLLED, this characteristic give to the subwoofer a heavy advantage over a passive FRS about the low distortion that a well designed subwoofer had against a higher distortions on any passive FRS. The Velodyne unique design permit that woofer driver control through that the signal is " measured/tested " 10,000 each second to control the woofers " behavior ", this permit that Velodyne sub's has an impressive ( lower than ) 0.5% on THD where other sub's like the JL Audio ( new " toy " in the block ) has 6%!. This sole spec made a difference in quality performance for the better in the Velodyne's that btw many people thinks are " mid-fi " and this kind of thinking is IMHO a misunderstood or low knowledge on the whole subject. Btw, the Velodyne's are sealed design that in my experience performs with better quality than " ported " sub designs.

If is true that sub's place is very important issue IMHO in a two speaker system ( for music listening. ) the choice of subwoofers is critical and important too. With HT almost any sub's can works but in a two speaker system IMHO we have to look for the best quality performance in that foundation music frequency range and its main contribution to the overall system sound so we have to take care on our each one sub's choice.

In any case, true advantages on seamless integration of two powered subs in true stereo fashion:

- lowest speaker system Harmonic Distortion and IMD.
- better low bass quality.
- deep/and lower bass frequency response.
- right low bass system/room quantity.
- better system mid bass, mid range, hf, soundstage, etc quality performance.
- higher system SPL/headroom with lower overall distortions.
- better amplifier main speakers performance.
- better main/satellite speakers quality performance too.
- better speaker system room integration.
- better, better, better, etc, etc.

this is what I learn about: a full and better home audio system quality performance !!!!!!!

Regards and enjoy the music,
Raul.
 
Last edited:

Gedlee

WBF Technical Expert
Jul 21, 2010
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Novi, MI
#17
You need for the LF sources to be spread arround the room, but the mains needs to be precisely located for imaging of the HF. This will not yieled the best LF situation. You need to add a couple of subs at alternate locations about the room to extend and smooth the highly modal LKF region in a samll room. You can keep the mains "full range", this won;t hurt, but adding a couple of subs located away from the mains will dramatically smooth out the LF response.
 

audioguy

WBF Founding Member
Apr 21, 2010
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#18
Sub Placement, EQ and Distance Differences

Both the Harmon Papers and Geddes strategies recommend various sub placements for positioning multiple subs to achieve the most linear frequency response. In either of those two approaches (particularly Geddes), it will be likely that one or more of the subs will NOT be the same distance from the main LP as another sub. In fact, you could end up, in a four sub room, with all four subs different distances from the main LP.

While I understand the approach of EQing all subs as one, the Audyssey SubEQ (as an example) provides the ability to deal with subs where two of them are different distances from the main LP. It pings the two sets of subs, determines distance differences (as well as gain) and adjusts accordingly. Products like the QSC DSP 30 also provide that capability. In my case, when (using the DSP 30) I delayed the rear subs to match the distance of my front subs, the un-EQ'd FR got slightly worse. Either of these products only work when you have two subs or sets of subs with different distances to the main LP. Having 3 or 4 or more subs at different distances eliminates the use of any of these devices (from, at least, a practical perspective).

So my question is: How important is it to compensate for distance differences when dealing with multiple subs that are placed in such a way that they are different distances from the main LP. And I ask this not from some theoretical position but rather sonically ---- can you hear it?.
 

Gedlee

WBF Technical Expert
Jul 21, 2010
364
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Novi, MI
#19
So my question is: How important is it to compensate for distance differences when dealing with multiple subs that are placed in such a way that they are different distances from the main LP. And I ask this not from some theoretical position but rather sonically ---- can you hear it?.
No one has the answer from the "subjective - can you hear it" approach since to my knowledge no one has done any valiud studies in this reagrd. So theory is all we have. Theoretically it doesn't make the slighteset difference what the distances are since in the end all that matters is how everything sums together. Our hearing does not have the ability to distinguish 'time of arrival" differences at these short distances and LFs.
 
#20
I'll add my two cents, based upon half a century of building, arranging and installing subs in my numerous iterations of sound systems in search of the ultimate high fidelity:

Subs should not be placed in a spaced-out configuration. Such a configuration causes the individual subs to act as separate sound sources. Separate sound sources interfere with one another, causing comb filter effects. Also, there is a decent article written on this.. Google "power alley effect" and you can read it for yourself.

Corner placement is necessary for weak subs that are incapable of producing flat output to the desired lowest frequency. Musically, that should extend to at least 16Hz with full power output in anechoic measurement.

A better configuration is grouping all the subs together across the soundstage, leaving no gaps between the woofer modules. This will behave like a single, larger, unified sound source, and the radiation pattern will be much more uniform.

Another benefit, which is audible, is that the transient response of the system will be that much better. Even at lower bass frequencies, unless the sound is an organ pedal, the unity of the fundamentals and harmonics arriving at more similar times will result in better impact, more of an edge, instead of a 'whump' when a bass drum is hit.

There is a common misconception that subwoofer placement is non-critical because 'bass is non-directional'. This is not entirely accurate. The body can feel from which direction the impact is coming from. Bass is a tactile experience, and when the low frequency aligns with the harmonic energy that forms a transient, the result is much more of a sense of immediacy and impact.

Back in the old days, when I had my electro dynamic woofers, driven by tube amplifiers with a few tens of watts, bass was scarce and corner placement was a necessary compromise. Today, with advanced woofer designs and plenty of raw power, the corner compromise is no longer needed. Now we can afford proper sound-staging and time alignment of all drivers. Try it. And put on a Frederick Fennell recording with marching band music (I prefer the Holst Music for the Royal Fireworks CD from Telarc, track 3 for easily-heard results) that has some terrific bass drum whacks.

Using a room as a corner horn is just no good. Plasterboard makes a very poor horn, as it is prone to numerous resonances and spurious harmonics generation and will color the sound.
 

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