Do you guys do this?

I purchased room analyzing equipment and downloaded REW so I so physically see how our subwoofers were interacting with the room's acoustics. Without room analyzing capability, one is just guessing.

As to the article, that's an interesting concept but in our world, we're dealing with rooms attached to kitchens, dining rooms and entryways and measurements are interconnected. But I like the ideas offered in the article.

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Edited by BeeMan458 - 2/26/13 at 1:36am

Nope.

Since bass is omnidirectional even if you take the approach in the article shouldn't you also be conserned with where the side of the sub is placed??? They say about 5 ft out in an 18ft long room, but how far away from the side wall should it be?

I don't do this anyway. I either use the sub crawl method or already know where the subs are going because of aesthetics.

And very correct. Our natural tendency is to place our speakers where they look the best, and that usually results in symmetrical placement. In the directional frequencies, above 100Hz, that's OK, as we're mainly hearing the direct radiation from the speaker. In the non-directional frequencies what we hear is as much sourced from boundary reflections as it is direct from the speaker, and symmetrical placement tends to concentrate those reflections in a few frequencies, rather than spreading them out across the passband.

Agreed. I have 3 subs placed asymmetrically around my asymmetrical room.

Craig

I generally agree with the concept of random placement. The only exception may be if you're lacking SPL, a corner placement for all your subs may be a good idea.

In a similar note, i think it's better in many setups to use non identical subs. There are no subs that have a flat frequency response and if you have identical subs, you'll be reinforcing the same highs and lows. Better to get subs that have different high and low spots.

If you need more SPL, you need better subs. Corner loading excites all the room modes maximally. It usually causes boomy, muddy bass, But you do get more SPL.
It would be totally random that the differing frequency responses would be synergistic with each other AND with the specific room modes of a specific room. However, you're still left with different output capabilities, different FR's, different LF extensions, different transient responses and different gain structures. Integrating those differences into a cohesive "system" is FAR harder than integrating identical subs with identical output, FR's, extensions, transient responses and gain structures. It's not that it can't be done, but it requires more effort and skill on the part of the integrator. Myself, I'll take identical subs, all day, every day.

Craig

It wouldn't be random. Every brand and make of sub has an inherent frequency response due to the way it's constructed. Some frequencies have a gain above unity, some below. Otherwise, why would anyone purchase one sub over another? They would all sound exactly the same.

We have two subs and with our room's acoustics being what they are, a third sub would be a benefit as opposed to a detriment. Just saying.

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Edited by BeeMan458 - 2/26/13 at 8:23am

This article was either written by a single guy or a divorced guy. The most important part of where you place your subwoofer is WAF:

WOW! Looks like this thread got HI-jacked.....^^^ if you are using the RCA LFE input to the sub its just a low level signal that is being sent to the sub. As long as the info is there the sub's amp will do the rest and your subs will output the same thing.

If reading about someone with 3 subs causes you to have that reaction, you should head over to the DIY section.

Really, like we need another thread de-railer, especially one who quotes the existing pre-eminent thread de-railer.

deleted...
Edited by RickMa - 2/26/13 at 10:59am

It would be "random" that the FR of a given sub, or a combined pair of them, would have the exact inverse FR to offset the transfer function of a specific room. Let's say your room's transfer function has a significant peak at 40 Hz and a null at 63 Hz. Are you going to buy one sub with a significant dip at 40 Hz to offset it the peak and another sub with a peak at 63 Hz to offset the null? Of course not. You buy subs based on their output, extension, alignment, size, aesthetics, etc. Then you place them in the room and deal with the in-room acoustics after the fact. Trying to buy 2 different subs to try to offset the room acoustics will be an exercise in futility.

But have fun tryin'...

Craig

Key take home points of the article, asymmetrical placement and two subs are better than one. The setup of non-dentical subs is the same as identical subs. Even identical subs have different frequency response since they are in two different locations in the room. IMO the use of identical subs is over-blown. Gedde's uses asymmetrical placement and non-identical subs.

You are welcome and entitled to your opinion. However, IMO, the use and integration of non-identical subs is vastly over-simplified. Many purport that it is easy and virtually always beneficial to use non-identical subs together. That may be possible in a volume limited, extension limited system, where the inferior subs are used to simply augment and flatten the frequency response of the singular "good" sub. If that is the only goal of the multi-subwoofer system, it can work very well. Geddes and others have shown this to be true.

However, many of us who have multi-sub systems want those same goals... PLUS the added benefit of higher output and deeper extension. For us, only multiple, identical, high output, deep extension subs, optimally placed and integrated, will get the job done.

It's all about your priorities and goals. If you just want a modest system for music, with great frequency response to 30 - 40 Hz, multiple dissimilar subs using the Geddes approach will work fine. OTOH, if you want high output to ULF's, forget Geddes and go with multiple identical high-performance subs. Integrate them properly and sit back and enjoy the pressurization, chest-pounding, pants-flapping bass.

Craig
Edited by craig john - 2/26/13 at 7:04pm

Of course I'm not suggesting finding a sub that perfectly offsets any FR weakness of another sub. All I'm saying is if you buy identical subs, the two subs are almost guaranteed to have the same weak spots, while if the subs are different, the chances of overlapping weak spots is diminished.

I'm not talking about correcting room acoustics. Which you'll have regardless of which subs you select. I'm strictly talking about primary sounds eminating directly from the drivers.

+1. Why forge a chain and then intentionally add weak links?

I don't think anyone is suggesting it's a good idea to match two subs with vastly different capabilities. I think there are situations where having two comparable non-identical subs can sound better than having matching subs. Like pairing a VTF-15h with a XV15 may, in some setups, sound better than 2 VTF-15h's. Not in every situation, but in some situations. I have 9 subwoofers right now in 6 setups and I've learned that there are no hard and fast rules with subwoofer setups. Every sub in every room in every spot sounds different.

What's going to happen when the week link goes into spasms while the better sub is chugging merrily along?

So what? The room will dominate the final response anyway. You place the subs in-room where the combined response is the flattest possible at the listening position/area. Whether the "weak spots" of identical subs or the "weak spots" of different subs will be beneficial to this process will be totally random and will depend entirely on the SPECIFIC room they're used in.


You gotta get past the "primary sounds emanating directly from the drivers." That condition only exists in an anechoic space. It can't possibly exist in a room. In a room, the response becomes a "steady state" response and the ROOM dominates the response. Here is a group of graphs that explain it:

This is the baseline outdoor groundplane response of my subwoofers. It is quite flat from 19 Hz to over 200 Hz.



This is the response of one of my subs in the left 1/5 sidewall position. The room has a HUGE impact on the response:



This is the response of a second sub placed on the front wall 1/3 of the way from the right front corner. Here the room has a HUGE, but completely different impact on the response:



Here is the third sub, located in the rear at 1/5 of the left side wall. Note that all 3 subs have DIFFERENT transfer functions to the listening position, and the response is dominated BY THE ROOM:



None of the subs individual responses looks ANYTHING like the baseline response. This is because the wavelengths at bass frequencies are so long that the reflections off the room boundaries combine with the direct wave and cause constructive and destructive interference. This is what causes the different frequency responses at different locations throughout the room.

Here is the response of all 3 subs combined and EQ'd with Audyssey XT 32. An 80 Hz crossover has been set and the speakers are turned off:



Bottom line, this phenomenon occurs no matter which subs you use, whether they are identical or different. How they interact with the room will be determined by the room and their placement within the room. Advocating different subs to try to have an impact on this is completely missing the big picture. Using dissimilar subs have all the problems I noted before, different outputs, extensions, gain structures, etc. Those differences make integration MUCH harder.

As Bill said: "Why forge a chain and then intentionally add weak links?"

Craig
Edited by craig john - 2/27/13 at 7:18am

Craig John,

You're arugments only reinforce my position that having identical subs is not critical. If the room dominates, why is it so important that the subs are identical?

Because it's not just about frequency response. Using dissimilar subs, with dissimilar outputs, dissimilar LF and upper bass roll-offs, different gain structures, etc. makes it MUCH harder to integrate them.

If they have dissimilar outputs, the sub with less output will hold back the sub with more output. You won't be able to realize all the output of the higher output sub without causing the lower output sub to distort or compress. If both subs have the SAME output, and they're gain-matched, they'll both drive the same output into the room, they'll both hit their limits at the same time and they'll both be able to be used to their full potential.

If one sub has lower extension than the other sub, and you calibrate the combined response, you'll turn down both subs... effectively turning down the lower extension of the deeper sub. The deep stuff is where the fun is, and likely the reason you bought the better sub. Why turn it down if you don't have to. Use identical subs with the same LF extension and neither will be turned down.

If dissimilar subs have different gain structures, it is much harder to gain-match them. You could always use level-matching, but that is likely to exacerbate the problems of the lesser sub holding back the better sub. If the subs are identical, it's easy to gain match them.

If you use 2 subs with different transient responses, you may be able to get them in phase with each other at some frequencies, but at others they'll be out of phase. Using identical subs with the same transient responses will eliminate this problem.

Look, many people use dissimilar subs and get results they like. I'm just saying that I would never advocate that as a starting position, especially not to try to offset the weaknesses of one sub with the other. That is highly unlikely to work out in any given, specific room becuase the room dominates the response. Identical subs makes a lot more sense and most people would be better off using identical subs for all the reasons I just explained.

Which is exactly what I'll be doing.

The WAF is a strong force indeed and money don't grow on trees so a man's gotta do, what a man's gotta do and if that means pounding a square peg into a round hole using a bigger hammer, then that's what a man's gotta do.

In my case, currently I'm looking at a third subwoofer solution for the purpose of smoothing out a pair of nulls at a measured 37Hz and 74Hz. Living in my world, not somebody else's world, all the reasonable tricks have been effected so I'm looking to a third subwoofer as a room smoothing solution. The intent is to smooth a final null problem and extend the range of the existing pair into the lower, <22Hz octaves and the subwoofer under consideration is a SVS, PC12-Plus.

The point, the current sub under consideration has vastly different capabilities over the existing pair of 12" drivers but due to the nature of the PC12-Plus, it "WILL" integrate well with both the existing pair of subs into the room's acoustics and "WON'T" overpower the two subs it's going be asked to join. The reason why? Bbecause it's not expected for the PC12-Plus to have it's full potential called upon.

(The purpose of the above, in quotation CAPS is to state, I don't care what others have to say on my above.)

Rules to my above:

Must pass WAF.

THX reference levels are not a consideration as the wife can only handle -20 to -15 on the MVC so there's no point in pushing THX reference listening levels. Boo-hoo, on my part.

There will be no room treatments.

Placement of subs must meet "NORMAL" expectations of contemporary living room decor.

Cost is not a factor but size consideration and the ability to fit and blend in the decor is a paramount consideration. In our venue, different is better and a column over a box, is an aesthetic improvement.

Current consideration is being given to a separate, five channel, amplifier.

Based on my above, I think and would recommend mixing and matching "vastly different capabilities" so as to get what one wants, not what others want.

(And no I don't like it but a man's gotta do, what a man's gotta do, even if it means.......)


A big thumbs up to your above. Too many hard rules makes for a very inflexible environment as it's about the end, not the means.

You think having identical subs is more importat than I do. That's fine. We all have different opinions.

Just curious, if using a down firing sub with two ports, what is considered the 'center' of the sound origination? (I realize that these differences of inches are only theoretically since no furnished room is perfect.)

I'm not sure what you mean by center, but both the driver and ports are pushing and pulling air. In opposite directions with a slight delay.

If you're asking where the driver would be placed with a same sized sealed sub to give the same sound, I would guess a little closer to the ports, but not much. And it would vary with frequency since the tubes have a resonant frequency where they omit a disproportionate amount of sound..