Posted by Duke [ 63.87.108.130 ] on April 18, 2007 at 12:04:25:
In Reply to: Re: Room modes and speaker placement posted by Wayne Parham on April 18, 2007 at 09:35:42:
Yes, I want to play with Cara myself first. I probably wouldn't bundle it with the Swarm, but we'll see.
My use of the word "random" was probably too, ah, random. The idea is to stagger the peak-and-dip patterns of the individual subwoofer modules as much as is practical, and that does imply thoughtful placement.
Let me give an example (this isn't to explain something you already know Wayne - it's more for the benefit of someone else who might find this thread). Consider the case of a single subwoofer, located let's say between the main speakers and up against the wall. There will be one path length from the sub to the listener, and another from the sub to the wall behind the listener, then reflecting back to the listening position. At the frequency where the difference between these two path lengths is to one-half wavelength the reflected energy arrives 180 degrees out-of-phase with the direct energy, and a cancellation notch occurs. At the frequency where the path length difference is equal to one wavelength the reflected energy arrives in-phase, so a reinforcement peak occurs. There will be similar peaks and dips associated with other path lengths and other room boundaries. The problem is not that we have too many of these peaks and dips in the bass region - the problem is that we have too few! If they were bunched up closer together (as they are at mid and high frequencies), the ear/brain system would average them out. But in the bass region, the peaks and dips are far enough apart to audibly stand out (has to do with the ear's one-third-octave "critical band" averaging characteristic - I can explain if anyone wants me to).
If we position a second subwoofer asymmetrically in relation to the first, the two peak-and-dip patterns will never perfectly overlap and so the net result will be a smoothing of the in-room frequency response. I chose to use four sub modules for my Swarm system because I wanted to go the next step up - Welti shows for instance that the greater the number of low frequency sources, the smoother the in-room bass. I'll readily concede that arguments can be made for several different placement strategies, but once the Swarm is in the person's home (and their check has cleared my account!), they can experiment.
In practice, my beta testers and I have found that four subs are much easier to place than just one. None of us has had to move them around searching for the right placement (which would probably be a nightmare) - the subs have always worked well where they were plunked down. Well, some thought went into the plunking - perhaps one could say they were "thoughtfully scattered". So far in practice it looks like my theory holds up, but that doesn't mean there isn't room for improvement.
Again, thanks for turning me on to CARA!
Duke
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