Wednesday, February 9, 2011

Why is there uncorrectable room boom in the first place?

I have a fairly typical sized living room for USA, it's about 14 by 15.5 feet with an 8 to 9.5 foot vaulted ceiling.  The passageways through entry and kitchen are wide so they also may make the room slightly larger acoustically.  My primitive calculations suggest I should get half wave resonances in the range of 30-40Hz, however they actually appear around 38-55hz.  It so happens that my Kurzweil synthesizer is right in the back corner of the room where you get a hugely resonant response (body shaking) in the 38-55hz range.

Now one interesting thing about half-wave resonances is this: In a closed room, they have their maximum amplitude away from the center of the room and towards the walls.  Full wave resonances have a third maximum amplitude in the center.  My full-wave resonances should be at double the frequencies of the half-wave resonances, so about 76-110Hz.  (I have dealt with that part of the boom by underlapping the crossover and by applying room correction, as described in earlier posts.)

So it seems, probably, that typical rooms have half-wave room boom in the range of 30-60Hz.  That's a pretty important band for bass fundamentals.  Half-wave boom is the kind that seems to accumulate around the walls of the room.

Now most serious audiophiles listen to music from a listening position more in the center of the room rather than the periphery.  If you do that, and you have half-wave boom in the range of 30-60Hz, you could probably benefit from the Boom Control I described in the previous post, to handle recordings with a lot of 30-60Hz energy.

Here's an interesting page on standing waves and resonances...I need to learn more here...perhaps my analysis isn't entirely correct yet.

Thinking about the above, it appears that the room modes (1/2 wavelength, 2/2, 3/2, etc) indicate the room is operating like a open tube because the maximum volume (antinodes) for those are on the sides.  The quarter wavelength series works like closed tubes, and typically have node on one side and antinode on the other.

Here's the Wikipedia entry on Room Nodes, which notably includes the comment that the attempt to equalize the sound in one position may actually make it worse in others.

Here's another interesting discussion showing another room effect, the 1/4 wavelength from the rear wall effect.  Also nice ETF measurements of actual room nodes:

No comments:

Post a Comment