Tuesday, March 1, 2011

Alternative room acoustic ideas

I sent the following reply to friend who sent comment on my blog entry yesterday:

Indeed, the beam does go athwart length.  The peaking is fairly shallow, though, 14 inches or so rise over 8 feet.  I've seen pictures of how trap installers straddle flat traps over the center.  But that may not address the issue you're describing, does it?  How does that work exactly?  I'm also still thinking of suspending something hanging down 10 inches or so as we discussed earlier, to catch the velocity wave.

Your argument is interesting...  Possibly true with correct design.  Funny about the old phony argument that you need big rooms to allow the bass waves to appear.  That's totally false, of course, and Ethan Winer does good job discrediting it at Real Traps site.*  Often control rooms, etc., are fairly small.  Sometimes people with tons of money create small virtual studios with 4 walls all made up of tube traps.

*But I believe big rooms are much easier to deal with for most audio fools.  I have really come to envy my brother in law.  His 3400 sq ft home has a huge living room, could be something like 45x30.  I don't think he appreciates how much other people struggle with modes.  He hears bad bass and automatically dishes out conclusions about amplifier damping factor or the need for one of his tweaks.  He also always suggest people need one of his amps, a 1960's era Sony 3200F, which he always uses with current limiter control set to 25 watts, to get the proper bass control with the acoustic suspension speaker piles he uses (one 10" woofer and one 6" woofer, corner loaded). And he always says all acoustical treatments or room dampening are undesireable, especially tube traps.  So big rooms tend to make it easy, you can be a complete fool and still get reasonable bass.  My last visit in December was a wake-up call.

With sufficiently large room, you can get modes spaced so closely (like 10Hz or so) that they don't make much difference.  In auditoriums, it's usually a non-issue (though you have lots of other issues).  That's why 1/3 octave analyzers are still useful, for auditorium work.  For home use, you need 1/48 or better resolution to see the modes and other reflection effects.

I myself have a couple of unusual arguments.  One is that backwall listening position (which I still use in bedroom) actually helps the bass.  You get all the peaks and no nulls.  Given that situation, EQ works pretty well, and that's exactly what I do (though only with manually set EQ's, the automated version always does too much).  Also, the rest of the room doesn't vibrate that much after the EQ is applied.  Downside is, of course, there is sucked out bass in the middle of the room.  So what?

Given a planar speaker with little bass output, you could put sit on the back (or even corner!) with the speakers as close to you as needed.  Result: greatly augmented bass.

I'm also wondering about subwoofer positioning.  Been looking at Home Theater Shack and one of their newer gurus consistently advises against corner sub placement ("almost never works out best").  I wonder why that's supposed to be so bad. Of course, you easily get more bass output that way.  Two of my systems have corner sub placement (the living room only nearly so because each sub angles out from the corner by length, and they are 4 feet long, and the other corner has no wall because it's entry way) and I'd never thought to question that part.   Not that modes are everything, but they are one of the most important things for bass, and the modes are their regardless of where you place the subs.

Now that I've mentioned the entry way, I actually think now *it* might be causing the cancellation in one channel sub.  The entryway (which connects to hall on other side) acts as a kind of tube.  The point at which the hallway on the other side bends might also be a great spot for bass trapping.

Realtraps has a filtered pinknoise (bass only) you can use to find the low frequency hot spots where bass traps (membrane type) would be most useful.  I plan to try that this month.  But my room has little available space for big bass traps, so this is going to be a struggle.

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