Mutiple mono subs: stacked vs. separate

Aeon Vide wrote:
> Let's have it clear: the main advantage of having multiple
> woofers/subwoofers would be to have directional information for
> low-frequency sounds, a rather questionable benefit

I disagree, I'd rank the benefits of multiple subs in different locations as:

spreading out the room modes and lowering the overall peaks.
in small rooms, equal bass SPL levels for all audience members, 1/r^2
the suck out is less severe (less null mode phenomena in my measurements)
stereo subs; for material that has out of phase bass information (rare but it exists)
difficultly in localizing directionality of sound.

> On the other hand, placement of multiple subwoofers/woofers ARE a pretty 
> awkward thing, you will end up creating multiple "holes" and "bumps" of 
> bass accross your listening area.  Have you never read about the importance 
> of sub placement?  Even when using only one sub you can have terrible 
> cancellation effects caused by wall reflection! And it gets even worse 
> when you have multiple sources.

Actually that is the whole point of multiple subs in different locations.

Terrible? Now that is a harsh word, room modes can be your friend if you are smart enough to know how to use them!

Aeon Vide, I think you are failing to understand this very simple concept:

I'm assuming the mutliple subs discussed here are mono.
You stack subs in a corner, and you get constructive interference, I mean you get a big mode (lots of dB) from room effects.
You have two subs that are not next to each other. You get de-constructive interference. This spreads out the room modes, I mean you get more of them, but their gain is lower in dB.

So it is a trade off, one big mode or several smaller ones. Which one is better? Well, its not that simple. For maximum SPL the stacked subs are king, especially if you equalize. Even though I have stacked subs and I do equalize my bass I believe that the benefits of separated dual subs outweigh the benefits of stacked subs. For the majority who don't equalize their bass, having mutliple subs in different positions is a way to tune (equalize in effect) their rooms bass response. So even if I have a slight leaning against stacked subs, it would be foolish to claim either setup as superior without further arguement and data analysis.

> This is why the one sub/multiple satellite sets are so successful: you have   
> a smoother bass field in the room, setup is much easier, and the satellites 
...

Smoother? This is if you consider one big hump smoother than a couple smaller ones. And the reason "one sub/multiple satellite sets are so successful" is because of two things; economics, one sub is cheaper than two, and consumer convience, "where the heck do I put that second big box?"

> In the case of good home theaters, the sound must be acceptable over a wide
> range of listening positions.

That exactly is a benefit of multiple NON-stacked subs.

> I know that this is difficult to understand if you don't know some acoustic   
> basics and how out-of-phase signals can cancel themselves out at the 
> listener position, but believe me, this is what happen at low frequencies 
> with multiple sound sources.

You are partially correct and that is the point of multiple sub sound sources. But this next factiod is sure to sure to stir your gravy. De-constructive interference is the cause of room modes, so even with your superior stacked subwoofers setup, there is out of phase signal canceling going on, that is why the suck out inbetween the lobes is greater with stacked subs!

You have just enough understanding of "acoustic basics" to be dangerous. I would recommend the next two steps; buying some more acoustics books / reading them. The Radio Shack SPL meter is a great bargin, but you really need to get some more sophisticated test equipment like a spectum analyzer, or an RTA, and a fuction generator.

5/13/99

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