Multiple Subwoofer Placement

[Gedlee]

The main theory I have is the type of floor I have. Old house, over 130 years old, walls two feet thick of solid masonry, but wooden floor which is not that 'solid' or non resonant.

A lot of people have concrete floors. So I wonder if my floor has a lot to do with it? If so, then praps stuff like the time for the signal to go thru the air is different than the vibration thru the box, coupled to the floor, transmitted thru the floorboards (that are so old there are no tongues or grooves, ie they would all act 'independently' from each other) then into the seat and then the bum.

I would concur with the strong potential of your idea. I did a lot of work on perception of LFs and vibrations in regards to automotive noise, and we concluded that a human is simply not able to distinguish one from the other. At LF we simply cannot tell what we hear from what we feel. Now if you consider that a vibration from a sub will travel though the floor much faster than the sound will travel through the air, then you have a strong potential for a serious problem. My multi-sub setup, which gets rave reviews, is all concrete - no flanking structural vibrations are possible.

Another factor that I know can be significant is the furniture. A sofa with a resonant structure will "sound" as if the room is resonant, but you will detect nothing acoustically - the sofa vibrates and vibrates you with it. You hear a strong resonance, but your microphone measures nothing. For this reason I am very careful about the furniture that I sit on when I listen. Mine all has solid oak frames.

 

[kareface]

Hi mark. my subs are behind me, and one of the 'tell tale' signs that they are not properly integrated IS that the bass does not seem to come properly from the front. Once you have it sorted, there is no change in the perceived direction/source of the bass.

Totally agree with frantz, any directional cues come from elsewhere in the spectrum, surely most have done this?? Play ONLY the subs. Just a horrible tuneless noise, hardly musical.

BUT, I agree with mark also! The FR may measure and look smooth and flat with distributed subs, but if they are not properly time aligned the bodily sensation is odd. You are 'shaken' out of time with the music.

I have often pondered why maybe my system seems to be prone to it? (ie most deny the effect, so maybe mine is particularly sensitive?)

I have a few theories...as mine is controlled by the deqx (of which time and phase is all important) perhaps the foundation in that regard from the mains makes it more critical to get the timing right??

The main theory I have is the type of floor I have. Old house, over 130 years old, walls two feet thick of solid masonry, but wooden floor which is not that 'solid' or non resonant.

A lot of people have concrete floors. So I wonder if my floor has a lot to do with it? If so, then praps stuff like the time for the signal to go thru the air is different than the vibration thru the box, coupled to the floor, transmitted thru the floorboards (that are so old there are no tongues or grooves, ie they would all act 'independently' from each other) then into the seat and then the bum.

So, I use distributed subs but 'have' to pay particular attention to the timing of the 'thumps' from each relative to the mains.The thumps need to arrive at the same time, else it can be clearly 'THUMP thump'.

In the bass region FR means very little. Decay plays a much greater roll. The lower you go the longer the sound presence has to be to localize. It's a myth that you can't localize LF, it just takes longer for you to do it. The length gets long enough the lower you go that it takes too long for localization to occur in normal media. In your instance, the solid floor is likely having an impact in the sense that your decay is too great. One of the reasons people enjoy rooms that are over dampened is it removes spatial cues and creates overall shorter decays make it harder to perceive directionality, giving a 'natural' impression at the cost of excessive decay on the mid-high region (the over dampened tonality). If you have a chance, post a waterfall from 10-100hz, it'll help identify or eliminate one of the potential problems. Bring the decay down helps a lot. Even if the duration at origin isn't long, the summing effect the brain does changes dramatically depending on the total time prior to the end of the haas.

 

[terryj]

Thanks earle. the position the subs are in now are a lot better than my last 'trial' of dist subs, I was lazy back then (it's just an experiment so don't go to too much bother attitude) and they were quite close to me.

This time, deciding to be more serious, they are as far away from me as I can physically locate them. That also puts them in a stronger position on the floor, ie the wall floor interface rather than 'out in the bouncy area' if you follow.

It is definitely the 'physical thump' that is the problem, it MUST be in relation to the music (well, duhh). Ever since my earlier experiences I have been noting other peoples systems, and whether they have concrete or suspended floors. I also mentioned it to get a bit of a 'survey' type thing, yours are concrete for example.

I also strongly suspect that there is a bit of 'cavity resonance' thing happening too (just made that term up, but I think most would understand what I meant) . So, when I get around to reno-ing the room, I will pull up the boards (no tongue and groove helps all of a sudden!!) and go mad with bracing. and maybe even fill the joists with glass. Not much more I can do, dunno if it will help but it can't hurt! (helps with heating insulation too)

hi kareface (first name?? much better than saying kareface all the time), hope the prd's are coming along. I don't doubt for one second that time (or decay if you wish) is extremely important and overlooked, but I could not live with a non flat bass response. I spose I am so used to it that at times it can be torture listening to others systems...and for the most part they are usually (blissfully?) unaware of their lumpy response.

I have one very large bass trap atm (about 1400 wide, 400 deep and 5.2 m high), but will do some more. Funnily enough, I did NOT really notice that much of a difference when I put it in (also added lots of random batts around my room to help with the ringing etc, all at the same time). THOSE helped like you would not believe! The bass trap? Not so much (but maybe I was instead concentrating on the amazing improvement of the other)

Hey! am currently doing a round of measurements, will post the waterfall.

 

[kareface]

hi kareface (first name?? much better than saying kareface all the time), hope the prd's are coming along. I don't doubt for one second that time (or decay if you wish) is extremely important and overlooked, but I could not live with a non flat bass response. I spose I am so used to it that at times it can be torture listening to others systems...and for the most part they are usually (blissfully?) unaware of their lumpy response.

Flat response only stays flat for a moment. It's good to have the initial production at the right DB level, but keep in mind after that point decay takes over. People get too focused on the FR, and overlook a much bigger picture. Decay is what causes the ringing and masking which impact reproduction, not to mention increases LF locality. Also, a perfectly flat response isn't reflective of human perception. At any given DB level we'll perceive different frequencies and directions to varying degrees. If you have something that's mastered for reproduction at a given level and you play even a few DB above or below that point, perception will shift quite greatly. I see too many people who obsess about perfectly flat FR at the cost of reproduction. A flat line can represent a good acoustic environment with the necessary digital corrections when all the other important factors are taken into account along with it. Otherwise it's just a flat line.

I have one very large bass trap atm (about 1400 wide, 400 deep and 5.2 m high), but will do some more. Funnily enough, I did NOT really notice that much of a difference when I put it in (also added lots of random batts around my room to help with the ringing etc, all at the same time). THOSE helped like you would not believe! The bass trap? Not so much (but maybe I was instead concentrating on the amazing improvement of the other)

Hey! am currently doing a round of measurements, will post the waterfall.

Remember, the wall is the last place you want to place a velocity dampener. However, the range you're trying to dampen is more likely below the effective use of broadband anyways. I've experimented with very low density fiberglass for targeting the sub 120hz region. Once you get that low the fiberglass sympathetically resonates. As a result, it actually helps to allow air to move through the material easier, hence low density. It also works better at the points where the pressure is the highest, so it's more wall friendly. I assume your batts were something like r-30, where the density is much lower than most rigid fiber glass.

Kare is fine for now.

 

[Nicholas Bedworth]

Computational fluid dynamics simulation to the rescue

The "solution" isn't readily achievable by discussion. Instead, one has to model the room, and after several thousand iterations of the simulation software, you'll end up with a family of solutions. And if one is willing to mount subwoofers up on the walls, that opens up even more possible solutions.

Some acoustical design consultants have developed such software, and for perhaps $3-5K, will do the analysis. Compared to the cost of a few subwoofers, the fee is reasonable. In some cases, one SW properly placed might well sound better than a phalanx of power-guzzling monsters, although they may impress your friends more than an attempt to explain what CFD is all about.

 

[Gedlee]

Structural vibrations in a listening room can be a serious problem. I go to some extremes to elliminate them or when they are there make sure that they are damped with some type of compound. A weak floor, like would be in an older home, would be a big problem to put subs on. That goodness that I have not had to deal with this situation. A sub could easily shake the whole house with its physical motion, which is quite seperate from its radiated sound. I would try some type of issolation with serious damping to issolate the sub from the structure. Multiple CLD sheets on the floor might be effective - say four or five layers of 3/4" ply glued with a highdamping layer between each.

 

[terryj]

thanks earle, can try that anytime. will do the 'serious' stuff at reno time.

kare, if you insist!!, here is the waterfall of the mains only, just mucking around a bit and trying to learn (more, always)

so no subs, just the mains.

be a few days till I get back to the subs, maybe you'll have some advice to help me going back in

 

[kareface]

Well, the room is likely undertreated. However, it's hard to say for sure what the problems with the subs would be looking at speaker measurements, lol. You can see the influence of the room in the graph, but the subs could be exciting a different set of nodes reletive to the listening position. I'll wait for the second graph to comment.

 

[cjfrbw]

Well, I decided to "Go Geddes!" I already replaced my "chuffer-wheezer" second subwoofer, an old Klipsch KG model rated to 38Hz, with a James EMB 1500. The James had a profound effect on the whole sonic portrait for the positive, not so much in bass volume as in total articulation of the sound stage. It has added a very "Gotham" like effect to the extreme lows.

There seem to be psycho acoustics of both high and low frequencies that are quite mysterious, both ultrasonics and sub-sonics contribute something to the overall effect of the stereo image which seems to be some kind of sub conscious or pre-conscious hearing.

Anyway, I am getting a third subwoofer to place above the listening level in an asymmetric position. That will make two 15 inchers and one 10 incher rated to 20 Hz, all different brands.

Again, the goal is not just to increase the volume of bass, which I could do with a single subwoofer, but to get an increase in the speed, articulation, uniformity and pressurization.

 

[FrantzM]

Well, I decided to "Go Geddes!" I already replaced my "chuffer-wheezer" second subwoofer, an old Klipsch KG model rated to 38Hz, with a James EMB 1500. The James had a profound effect on the whole sonic portrait for the positive, not so much in bass volume as in total articulation of the sound stage. It has added a very "Gotham" like effect to the extreme lows.

There seem to be psycho acoustics of both high and low frequencies that are quite mysterious, both ultrasonics and sub-sonics contribute something to the overall effect of the stereo image which seems to be some kind of sub conscious or pre-conscious hearing.

Anyway, I am getting a third subwoofer to place above the listening level in an asymmetric position. That will make two 15 inchers and one 10 incher rated to 20 Hz, all different brands.

Again, the goal is not just to increase the volume of bass, which I could do with a single subwoofer, but to get an increase in the speed, articulation, uniformity and pressurization.

Carl

Your observations mirrors mine. You won't be disappointed... This method is the real deal and based on very solid science.

 

[cjfrbw]

Well, an additional mystery: when adding the second extended subwoofer, it seemed with no other changes in my system to reduce apparent noise level of the overall presentation by 6 db or so.

Since I listen mostly to vinyl, this is a welcome effect, but I have been struggling to find some explanation and can find none. Was my "chuffer wheezer" sub or its amplifier noisy? Is there some kind of masking effect caused by the deeper, faster and more refined low frequencies?

It just goes to show that no amount of time in audiophilia resolves all perceived mysteries.

I would love it if the objectivists could give me some clue as to why this would have occurred. It seems to be solely from the removal of one medium level and probably compressed bass module and replacing it with a deeper, faster, more competent module.

After a couple of months of pondering, I am truly clueless as to how bass alone could create this apparent effect. Usually, I at least can come up with some kind of theory but I am at a loss with this one.

 

[Gregadd]

Mixing and maxing of subs is allowed by Geddes. Not required.

 

[cjfrbw]

Three different brands of subwoofer will be tuned differently, which seems to me to aid an abet a random pattern of dispersion overall.

Dr. Geddes approach makes sense to me for some reason.

However, making sense to me does not mean that the approach is 1. sensible 2. correct 3. scientific beyond Dr. Geddes own measurements and expertise 4. the only way to skin the cat etc. etc.

It just makes me feel better doing it and has nothing to do with common sense or reality otherwise.

 

[Robh3606]

Well, an additional mystery: when adding the second extended subwoofer, it seemed with no other changes in my system to reduce apparent noise level of the overall presentation by 6 db or so.

Did you have to drop the subs levels down a bit?? I have 3 runing in HT mode and am adding a fourth. Each time I have reduced the LFE levels and also got to run the subs at lower and lower power levels individually. Overall a good thing. I am going to end up with 2 14's and 2 15's so lots of available displacement when needed.

Rob

 

[FrantzM]

Three different brands of subwoofer will be tuned differently, which seems to me to aid an abet a random pattern of dispersion overall.

Dr. Geddes approach makes sense to me for some reason.

However, making sense to me does not mean that the approach is 1. sensible 2. correct 3. scientific beyond Dr. Geddes own measurements and expertise 4. the only way to skin the cat etc. etc.

It just makes me feel better doing it and has nothing to do with common sense or reality otherwise.

cjfrbw

Sorry, long post
The approach is

1.Sensible.

It should be clear for most audiophiles that the best position for imaging/staging seldom coincides that for best bass reproduction in most if not ALL rooms. Audiophiles have accepted the compromise. We place the speakers were the compromise is most acceptable. We already know it is a compromise but one until subs, for which there were no resolution. That is how the vast majority of Audiophile systems are set. Of course there are special cases of mains with powered subs with some degree of adjustability. I have yet to se one with Parametric EQ but I digress. This is a better compromise as the bass can be adjusted to a certain extent The position in the room dictates the distribution of nodes and if there is a null well there is NO WAY to take care of it by EQ. You can only move the whole speaker in which case you lose the best spot for imaging or/bass. So let’s be clear that a powered mains subs is also a compromise, maybe a better one, it remains one nonetheless.

2. Correct

From the above it is clear that one must place the mains where they play the best… and position the bass modules where they provide the optimum bass. So that is a call for subwoofer. Notice no plural yet. Now studies by the Harman Group specifically by Welti and Devandier have shown that the best bass possible is obtained through the use of multiple subwoofers. Their model was based on symmetrical placement and proven to work … This is the correct approach, the one with the least compromises.

3. Scientific
See above. The Geddes approach is based on the randomization of LF sources which creates a more uniform and random distribution of nodes in the room. The more LF the better. One reason this approach works so well with full range speakers. The math behind is not entirely known to me. Geddes has not written a through paper on the subject but there is solid math behind it. Plus the works of Harman to back it
4. This is likely not the only to skin the cat. Harman works are a case in point. One could also build the perfect room but throwing serious amount of acoustic treatment to solve the problem and indeed Acoustic treatment is ALWAYS needed but …

Now about similar subwoofers. The approach works well with any combination. Using the exact same woofer everywhere would likely make little difference. It is my experience and that of others that the third subs is solicitated very little; in my set-up was barely audible even playing by itself. Yet its effect was unmistakable audibly and on measurements... So that calls for a lesser sub… One can be anal and use the same brand but it seems to me that the subs behind the mains is the one that has to be potent, the second can be a lesser model and the third truly a small sub

Audiophiles will come to use that approach more and more. The myths will fall just like more and more audiophiles are using their PC as music sources and with great results … You are on the right path. Persist, measure, the benefits are everywhere in the spectrum … This is the weird thing... Better bass reproduction translates into better midrange... All music benefit from better bass, yes, even vocals and small scale chamber music...
Another thing that remains mysterious to me is the scale and size of music. With big speakers well the soundstage remains that of a a large speaker ..with small speakers, especially the "mini-monitors" their character of smallness doesn't change despite the better, more integrated and extended bass response .. Very interesting...

 

[cjfrbw]

Did you have to drop the subs levels down a bit?? I have 3 runing in HT mode and am adding a fourth. Each time I have reduced the LFE levels and also got to run the subs at lower and lower power levels individually. Overall a good thing. I am going to end up with 2 14's and 2 15's so lots of available displacement when needed.

Rob

My impression has been that the actual total bass is lower but cleaner. The "chuffer-wheezer" was a very competent "butt kicker" placed behind my listening position and served the purpose very well of exciting my flab-o-meter. The chuffer always sounded better in the system than out, the main sub was a rebuilt Velodyne ULD II with a rating down to 15 HZ.

However, the chuffer now seems to have been compressed and non linear in the very least.
Hsu actuallyl makes subs just like this one on purpose for mid bass fill only that are rated from 50 Hz or so. They give a good kick, but no low bass.
Klipsch speakers always just went down to about 50. I guess Klipsch felt that good impact to 50 was more important than actual low bass performance.

However, the psycho-acoustic impact of true, distributed low bass is pretty impressive.

 

[cjfrbw]

Thanks, Frantz,


I have to admit that in spite of my efforts in other areas of my system, bass performance has been an afterthought. I have updated my bass more out of a sense audiophile duty than conviction and only intermittently. I am a basic, unrefined cerwin-vega basshead. If it is there enough, I like it. It doesn't need to be refined or speedy, just there.

Nontheless, many people who have listened to my system have always commented on how much they liked the bass. I even had one guy accuse me of holding out on my "special secrets", to which I could only give an Alfred E. Neumann type grin, since my bass efforts have been pretty phlegmatic.

I attribute the bass of my system not to any kind of systematic approach, but to dumb luck vaguely guided by borrowed principles.

I think my room is mainly responsible by being a "good bass" room to begin with. Trapezoidial cross section with a couple of legs and chambers to mix things up.

I had "additive bass" at first, then went with an active crossover to separate the bass from the mains, then added the improved main subwoofer corner loaded and relegated the chuffer to the back.

I upgraded the previous main woofer with the Velodyne, which made large improvement overall.

When I got my Yamaha receiver, I used the microphone to digitally equalize the two bass channels, which cleaned things up a bit. I have now replaced the chuffer with the full range, which had a more dramatic effect on the system than anything I have done in a while and fully unexpected. It has also been cost effective, since the subwoofers are much less expensive than the main system.

I also use surround sound, which tends to help smooth out the mid bass a lot.

I suspect as you state that the third woofer will be audible, but not as huge as the previous woofer improvement, more of a frosting on the cake kind of thing.

 

[cjfrbw]

Well, I spent some time tonight installing the third subwoofer above ear level, running tones, adjusting levels and getting the phase switch right.

I sat down to listen for a while and the effect of the third woofer is not subtle at all.

I suspect I have some tweaking and dialing to do and need to run the microphone/digital equalizer again, but, man o man, the bass is notice-ably stiffer, faster, more subtle and more transparent to the main stereo image. I am hearing modulations on familiar material I didn't know were there.

Anyway, this bass stuff is mucho mysterioso, but the Geddes experiment already seems to be a resounding success, at least "subjectively" since I have no measuring instruments.

Time to go to bed.

 

[FrantzM]

Well, I spent some time tonight installing the third subwoofer above ear level, running tones, adjusting levels and getting the phase switch right.

I sat down to listen for a while and the effect of the third woofer is not subtle at all.

I suspect I have some tweaking and dialing to do and need to run the microphone/digital equalizer again, but, man o man, the bass is notice-ably stiffer, faster, more subtle and more transparent to the main stereo image. I am hearing modulations on familiar material I didn't know were there.

Anyway, this bass stuff is mucho mysterioso, but the Geddes experiment already seems to be a resounding success, at least "subjectively" since I have no measuring instruments.

Time to go to bed.

YOU ARE NOT MEASURING !!! ?????

 

[RBFC]

Yeah, too bad you're enjoying it so much without even measuring it......

Congratulations.

Lee