Scott says:
Building high transmission loss room partitions to diminish noise propagation into other rooms is a different elephant from the job of installing absorptive elements on the inside surface of room boundaries for the purpose of diminishing sound reverberations,
Excuse me Scott? I may not be an expert on acoustics, but don't get condensending . I've been posting in this forum for quite a long time and do not appreciate your ivory tower approach. Building high TL partitions vs treating them are hardly Einstein depth concepts. Thats not to say I don't appreciate your friendlier insights.
Scott says
PS: having a solid panel on one side of a gobo can be useful in that you then have an absorptive surface counterpoised with a reflective one - but that doesn't make it better than one with both sides absorptive -
It does if your trying to keep one instrument from bleeding into another mic
Scott, you apparently misinterpreted my misunderstanding I wasn't asking about the performance of a gobo with one side absorptive vs 2 side absorptive, although now I understand a non backed gobo would inherently be a 2 sided absorptive unit. I didn't before this point. AND, a gobo with two sides absorptive can still have a boundary between them. I was trying to understand how an UNBACKED absorber in free space would absorb ANYTHING.
I was simply confused regarding the working principle of resistance absorption. I was under the impression, via all the illustrations I've seen over the years, in books as well as on the net, that resistance absorbers...SOMEHOW NEEDED a boundary (and this is where the confusion started) to make this 1/4 wave concept work. Not ONCE, did any literature on the subject mention the fact that a panel of say 703, anywhere, anyplace, all by itself, with no back, ABSORB. Perhaps, via extrapolation on my part, via statements to the effect that a resistance absorber had virtually NO effect on the TL of a partition, I concluded that sound transmitting though the material was NOT absorbed, unless it reflected from a boundary behind it. SOMEHOW. THAT is why I asked for a physics lesson. Another concept I must not have fully understood is "vector pressure"...ie..I was under the impression that a freestanding absorber would have "equal" pressuree surrounding the entire surface..ie..if free hung in space...all 6 faces. So much for "layman" interpretation of partial physics lessons.
And now that I think about it. What the heck would "1/4 wavelength" have anything to do with an UNBACKED absorber, as the "explanations" usually define the 1/4 wavelength thingy in relationship to a BOUNDARY...ie.. ZERO VELOCITY-MAXIMUM PRESSURE at the boundary, MAXIMUM PRESSURE-ZERO VELOCITY @1/4wavelength from said boundary...no? sheeezus, what am I missing here. Where is the "frequency/pressure/velocity relationships for an UNBACKED absorber in freespace?
I know it may seem very stupid to you guys. However, this is the problem with quasi physics illustrations for laymen who simply want to improve their home studios, but don't want to waste money and time on things that don't work. They really don't explain the underlying principles in relationship to the one that is being illustrated.
One more thing to clear up.
Scott says:
Placing the material against a boundary doubles the effective thickness of the material. Hung in free space it will still absorb, but to down to about twice the lowest of material against a boundary.
Another member says:
And, as we've been discussing, the absorption would be somewhat "halved" by the use of the solid backing.
aaaaaah....now I'm really confused. These two statements SEEM to contridict themself. The first suggest a boundary would "double the effective thickness(whatever that means), and the second suggests it would "halve" the effective thickness. Which confuses me even more. In the first instance, when a lab tests these materials, and gives a frequency band/thickness table of absorption coefficients, are these coefficients based on this material in FREE SPACE, or with a boundary??? Scott suggests that placing them against a boundary will "double the effective thickness"..in relationship to what? Absorption coefficients of the same patch of material hanging in free space with a given coefficient of material HALF the thickness of the one placed on a boundary??? Or absorption coefficients of the same patch of material with a given coefficient for material TWICE the thickness of the material placed against a boundary
Furthermore, I'm still trying to get a handle on 1 SABINE. I understand the concept of an open window 12"x12"=1 SABINE of absorption. What I don't understand, is how thick a piece of material such as 703 would have to be(given an EXPOSED face of 12"x12" and flush to a boundary with the rest of the material enclosed by a box)to perform the same as an open window of the same size. i.e. .....An absorption coefficient of 1 does NOT equal 1 Sabine of absorption...OR DOES IT?
Thanks again guys. Well, time to go eat crow.
Hmmmm, Ethan, have I missed something all these years?
You didn't offer didly squat other than pretending your illustrious reputations somehow implied 