when considering 1,2, or more subs, one must think about what they want their desired results to be. meaning that some people may need more subs (large seating area perhaps), but 2 is not better 100% of the time. if you take quality into account (quality vs price actually), then 2 is better what at what point? id say one really good sub (x dollars cost) is 90% better than two that are half as good (x total dollars cost).

you can have 1000 subs but if their low-end frequency response is 40Hz, they arent ever going to go below 40Hz. i know that is one specific example, but a valid one, as frequency response is an easily comparable number amongst subs... whereas instead of that 1000 subs, you could have 1 that goes really low.

id rather have one really awesome performing subwoofer and a small sweet spot, than some pretty good subs that blanket the room. when i am watching a movie, i dont tend to mill around, i sit in the same spot every time and watch the whole thing through (some pauses for bathroom/food, etc. of course). its silly to sacrifice quality in the attempt to get more sound, especially seeing as that more sound probably isnt going to be useable anyway.

naturally, if money was no object then you could get a bunch of awesome subs, but it usually is.

i think a lot of people get multiple subwoofers to say that they have multiple subwoofers, not really to get better sound. its their money though, so waste away.

i do not disagree that 2 subs of y quality are almost always better than 1 sub of y quality, but most people dont double their budget for subwoofers when they realize they need 2... also, sometimes 2 subs causes more noticeable nodes than 1 sub did...

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This post has been brought to you by curegeorg, thanks for reading.

curegeorg's comment:

is an odd contrast to soundhound's comment (when describing mutual coupling and the resulting effects):

Anybody care to elaborate on a point so we are all in agreement at least on our physics?

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gonk -- 950 Review | LFM-1 Review | Pre/Pro Comparison Chart | Saloon Links

The effects of mutual coupling and efficiency increases when using multiple subs can be looked and varified up in textbooks on sound reproduction, especially those that deal with professional installations that are more likely to use multiple subs. The "Handbook of Sound System Design" by John Eargle (of JBL Professional) is a good place to start.

The exact same principles apply to home installations as they do to professional ones - the same laws of physics apply.

Maybe they don't apply to some people though.

[This message has been edited by soundhound (edited August 24, 2004).]

I suppose that if the subwoofers in curegeorg’s example had wonderful output down to 40Hz, and absolutely no output at 39Hz and below, there would be no bass extension benefit. However, most subs with normal roll-off and a rated low end of 40Hz are still going to have some workable output even half an octave lower at 28Hz. The setups mentioned by soundhound seek to take advantage of those frequencies still present below an individual sub’s rated low frequency. This doesn’t mean you’ll get a interactive rating of 28Hz, but 34Hz or so wouldn’t be unrealistic in this example.

In the articles I mentioned previously, two subs provided better bass extension than four subs or more, even if four subs would provide better overall room averaging. The article(s) also point out that a two or four sub setup has advantages over a theoretical 1000 sub setup and is better than each of the five or seven loudspeakers in a multi-speaker setup all reproducing bass into the subwoofer regions. The latter is true because the best placement of subs for best bass in a room are not usually where the other speakers reside. See the articles for details.


[This message has been edited by bestbang4thebuck (edited August 24, 2004).]

A newbie looking at this thread will be out of luck if he or she wants to opt for one double quality sub instead of two lesser subs at given budget. You’ve stated what to do but not how to.

There are HT enthusiasts with limited space and would rather do away with less number of speakers if the result is certain. In this case, due to uncertainty, those people seeking better low-end performance may have to compromise on space and go with multiple subs.

Perhaps if this question could be answered: The 3db down point for the sub is where it is 3 db down from the reference level. Now if the second sub is added under ideal conditions then there should be a +3 db increase across the frequency range. This raises the reference level by 3 db. Now, why would the F3 point be different than before? Everything should be the same, just 3 db louder.

This is in an ideal model with perfect interaction. Real world setups will get much too complex for us right now.

[This message has been edited by JT Clark (edited August 24, 2004).]

To address 2 points:

If a stereo bass sub config is used with a MC format, mixing the mono .1 signal equally into both subs will collapse the stereo effect.

As was pointed out, this is in rare cases of source material, but still part of the equation, and likely moreso as MC audio evolves.

Summing the .1 channel with redirected bass can result in 'no problems' unless, like my setup, you have 1 sub that's designed for LFE and another sub that's designed for redirected bass.

If a sub is capable of very high output at very low frequencies (which it has to be to be capable of playing RB+LFE+10 anywhere near ref levels), it generally isn't as good a sub for redirected bass.

Conversely, if a sub is designed for redirected bass, it can't play the summed signal well, if at all.

If you seperate the 2 signals, like I have, each sub has less output requirement, allowing for money saved in each sub's case. Also, as I've said, generally, the redirected bass sub has a higher F3 and is designed to roll off at 12 dB/octave while the LFE sub has a lower F3 with a steeper roll off to protect it from damage.

So, it isn't a matter of having no problem summing RB and LFE into 1 or more subs (obviously it 'works', or none of us would have our sats set to 'small') as much as it affords less flexibility in sub selection and reintegration of redirected bass.

For JT’s question, not the answer one would hope for:

The beginning of the answer is that the ideal model for a +3dB across-the-board rise is an anechoic environment where two subwoofers would be co-located, but none of us lives in such a situation. Separate the subs by more than about 10% of the wavelength of a frequency in question and place these subs in real room and you’ve got the complex situation you mention where sophisticated computer modeling can’t exactly predict real world results and experimentation and measurement become the means of pursuing the best results, even for true experts. Suffice to say that the lower frequencies, say 30Hz and down, from dual subwoofers in many real world environments, will tend to reinforce each other more so than the frequencies going upward toward 80Hz, which tend to experience more of a smoothing/leveling effect when coming from multiple sources.

The middle of the answer lies in that zone you mention: too complex for us now, at least in these posts. I got my start in the mid 70’s with a book called Sound System Engineering. The current edition is 665 pages and has almost no ‘easy answers’ that would satisfy what is sought in this post. While some of what’s pictured in this book may seem outdated, the principles hold true regardless of the era from which a particular piece of equipment originated. If you have an aptitude for this kind of material, look in books or online.

The near-end of the answer, if you don’t want to spend a lot of time learning the middle, doesn’t have to be difficult if you’re willing to have a some trust in those that have studied, carefully modeled, tested, measured and evaluated aspects of at least part of the question at hand. Their answer: used properly, two of a given subwoofer is better than one (for several reasons beyond a simple +3dB gain).

This doesn’t answer questions with budget factored in, such as: which is better, two $300 subs or one $600 sub? Two $600 subs or one $1200 sub? The only way you’re going to know which will be better for you in your environment is to audition both solutions, taking the time to carefully set levels and try for the optimum placement of one sub or a pair. If that’s too difficult for one reason or another, you’re back to weighing research and opinions and taking your best guess.

Opinion time: I tried it both ways. I now have two subs, not for bragging rights but because the dual sub setup sounded and measured better once setup to my satisfaction. At the end of the day, those that have differing opinions don’t have to live with my choices, but I do.

Poll time: among those that have tried one and tried a pair, how many have stayed with two subs and who has gone back to just one? If you went back to one, was the decision primarily financial, or because you found little or no better results with two? Or for some other reason?

OK, I’m going to try and stop writing about this now. I’ve said my peace. I hope some find it helpful.

I understand about what y'all are saying about the benefits of 2 subs (or more). (That's why I'm considering it! )

But I have pinged some experts at a couple of sub companies, one of the HT mags, and other users like us, and most agree that the benefits are potentially there, just that more often than not, a 2nd sub makes things worse, i.e., comb filtering, making the peaks and valleys worse, etc. And I've even passed on that I have access to an RTA and the desire to try and make this work, but doesn't change their conclusions.

Obviously this is a hobby, and I don't mind messing around a little bit to learn something new, but ... Shoot.

One of the suggestions I got from a sub maker was... Ignore that one plot I posted earlier, but do a whole bunch more measurements around the room and for repeatability, and average them together, and *then* see how bad things are with my current setup. I did the measurements last weekend, and I'm about 25% of the way through the analysis, and although I still have dips showing up at 51 Hz and 134 Hz, the others are effectively gone.

Maybe it comes down to theory vs real setups, or how much flexibility I have to move things around in my current setup to improve things, etc. Kind of like a problem with many equations, and many variables within those equations. There's no direct solution but trial and error.

OK, so I'm not going to stop writing just yet

Yes, attempting to have the the benefits of dual subs can be 'more work, more fuss, more frustration' trying to get it right, if both subs are meant to support each other in the same role. (Segregating the duties of two subs, as bossobass has, is an approach with different potential benefits. More on that later, I hope, in a friendly exchange of ideas.)

Yes, analysis should be throughout the listening portion of a room, not just a single location, whether using something like RTA or a self-setting parametric EQ.

You won't really know what can be accomplished until you try. Certainly finding out if one sub can provide what you're looking for makes sense, as does finding out what the problems are in a room and seeking to minimize them.

KCB, your approach seems just the right path to be on: measure, learn, adjust, repeat until satisfied ... or exhausted! No one is going to find 'perfection,' just a degree of satisfaction. IMHO, your last paragraph is a great summary.


[This message has been edited by bestbang4thebuck (edited August 25, 2004).]