One or two subs


Here is my set up, SF Cremona Ms, Cremona center and SF Toy monitors, Yamaha CXA5000 powered By MC205. My option for sub are these only, please do not suggest another brand, Rel R328, two Rel T5s or two Rel T7s. 60/40 for movies, thanks.
kalbi23

Showing 2 responses by martykl

James' analysis - tho correct in a vacuum - has it backwards.

Reflections off of the walls of your room will cause destructive cancellation to the long wavelengths of low frequencies - whether you're using a single sub or multiple subs or a full range loudspeaker, for that matter. (You can google 1/4 wave cancellation to calculate the frequency (ies) at which this cancellation occurs.)

So, you always start out with a problem when you have low frequency wavelengths in a confined space. The trick is that - per the calculator I mention above - you can manipulate the details of the response interactions by changing the location of the low frequency driver relative to the walls.

Of course, that's tough with full range speakers. Move the woofer and you move the mid and tweeter. The best position for the woofer is usually not the best position for the other drivers - hence the first advantage of using one or more subwoofers instead of a full range loudspeaker.

The oft-cited benefit of using a second sub is that careful placement of that second sub, relative to the first one, can re-inforce the diminished frequency band created by room interaction with the first sub. That is, place the second sub closer to the wall than the first sub and the bass response trough rises in frequency. Optimal placement of a second sub will almost always result in smoother FR than a single sub, because they can re-inforce the output in each others' null area. A third sub is even better, a fourth better yet, and so on. Take a look at the Audiokinesis web cite for a good explanation.

One complicating factor is the software in the AVR. If you're using room correction software, the AVR will do much of the FR smoothing work for you and the benefits of multiple subs may be reduced. I can't comment on the gear you're using, but my general rule is: without room correction, two subs generally are better than one. With software, generalizations are tough.

Good Luck.
James wrote:

Using multiple subs to try to reduce the impact of room resonances is difficult and not very effective, especially since the output of the subs will be reinforcing or cancelling at different frequencies as a function of how far apart they are and where they are relative to the listening position, as well as dealing with room resonance factors.

Well.....

The point of adding a second sub is precisely the phenomenon James describes as a problem. The delta between the response deviations of multiple subs averages back to the norm (anechoic response) - provided you place them carefully.

As to the larger point James is making, again, overall, I'd say "true" (regarding effort, with one caveat) and "false" (regarding potential for good results):

Attempting this exercise by ear is a major PITA. I'm 100% sure that many folks will quit before they get it right.

Doing it with a real time analyzer is much easier and likelier to produce a good result (with more than negligible time required).

Doing it with a high quality automatic room EQ package is a snap and IME will certainly produce excellent results. OTOH, this approach IME often provides excellent results with one subwoofer, so..point taken.

Bottom line: If you take the time, two unEQ'd subs will almost certainly produce smoother bass than one unEQ'd sub.