Magic room treatments?
In the Feb 98 Home Theatre magazine in the fine article on Room Treatments.
They compare different room treatment products made by 3 different
manufacturers. Absorbers, diffusers, bass traps, ...
I noticed something really strange.
All 3 products basically have a "suckout" in the 85Hz region. It is a dip
of about 2 or 3dB. Now why do all three vastly different products do
basically the same thing at 85Hz? The untreated room didn't.
Michael Green's products; Notice the +4.2dB peak at 29Hz?
This is truely amazing. A passive product that actually boosts bass!
I love it. You only get a +3dB gain when you double amplifier power,
how do you explain a +4.2dB gain at 29Hz from a passive device? It seems
like this defies the laws of physics or something.
Now if this frequency hump happened at a higher Hz then I could believe
that sound was being reflected directly at the listening position.
That explaination would suit me just fine, HT mag put a diffuser in the
wrong spot or something. But at 29Hz? Bass is basically omni directional
at this frequency so it is not likely that it was being focused in any
direction. Bass at 29Hz has a wavelength of about 39 feet. Now is it
possible that placing tuned wood things around the room changed the
standing wave nature of the room? I don't think so, the Floorstanding
PZC's are just not big enough.
So what happened?
I trust that HT mag's measurements are accurate. These guys do good work.
So what happened?
Is the passive "floorstanding PZC" a resonating device that emits sound?
I hope not, and if it does I sure wouldn't want it in my living room!!
I'd deduct points for that kind of behavior!!! (:
Erik Olson wrote:
> In the Feb 98 Home Theatre magazine in the fine article on Room Treatments.
> Michael Green's products; Notice the +4.2dB peak at 29Hz?
> This is truely amazing. A passive product that actually boosts bass!
> I love it. You only get a +3dB gain when you double amplifier power,
> how do you explain a +4.2dB gain at 29Hz from a passive device? It seems
> like this defies the laws of physics or something.
I re-read the article and the +4.2dB gain at 29Hz is a delta with the
un-treated room. That means the 29Hz boost was real and NOT the effect
of all the other frequencies being damped down even more.
The size of the room treatments were relatively small too. My guess, less
than twenty square feet of frontal surface area. This shouldn't be enough
to have such an effect on the standing wave nature of the room.
I just finished the sections on standing waves in Alton Everest's "Master
Handbook of Acoustics". Excellent, I recommend it. I've read stuff
by Toole and things in other books but this is by far the most comprehensive
collection on room modes that I have ever seen.
I still don't understand HT magazines results on Michael Green's products.
A significant bass boost by a passive device? I don't get it.
I guess I have to look at Helmoltz resonators again. Maybe Mr. Green's
PZC bass product is actually a tunable resonator.
Kind of an anti bass trap!!
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