Air Gap Discussion

[bert stoltenborg]

Interesting random pic bert! On another forum deedeeyah posted spectra of presumably large gigs. Pronounced HF roll off. I have looked at Erics Baffles and Ethans fibre tests. The reason I started this ball rolling here is that I am not at all convinced that isolated panels do benefit from airgaps. More precisely, I think there is a gradual failure as area is decreased. Ethan sent me some Lab tests years ago. Like bobgolds.com, the 1:1 gap greatly helped LF. But again, the ANSI sampling is 10 sq contiguous yards afaik? I will look thro Erics Baffles again. Andre did you sot simething specific in that? Ta all

I removed the pic, I load it up here.

[bert stoltenborg]

You can use it this way:

If you have a source powerlevel of, say, 100 dB(A) you can correct for a specific spectrum by subtracting that spectrum.
So for a popspectrum:
63 Hz - 100 dB(A) minus 27 dB = 73 dB
125 Hz - 100 dB(A) minus 14 dB = 86 dB, etc
When you energetically sum these data you'll get the 100 dB(A) again.
This way you can easely calculate f.e. the sound transmission loss of particions for sound with a specific spectrum.

[Soundman2020]

Thanks, Bert. That's very useful, actually! A simple aid to judging real sound levels, based only on an SPL reading and knowing the music genre/venue.

It sort of indirectly implies that restaurants sound rather "tinny" and "nasal"... no surprises there!

[DanDan]

Now if there is significant mass to the absorbent material and membrane absorption occurring...

And 'springiness' I reckon. A 705 / Minitrap panel is quite heavy and quite resonant. This is quite audible and holds up when they are free hanging or even outdoors. I sometimes wonder if the less springy materials such as Rockwool or Cotton perform as well as the classic and tested. I wonder how heavy and springy were Eric's Polyester panels.

Corner_RT424-vs-Gap-600-1.jpg (24.75 KiB) Viewed 26532 times

Corner_RT424-vs-Gap-600-1.jpg (24.75 KiB) Viewed 26532 times

I reckon this pretty massive corner bonus is caused by placing a damped somewhat resonant panel into a LF 'Horn'.
Conversely let's say, a loudspeaker needs to be fully sealed to the Horn.
I strongly suspect that straddling the corner from floor to ceiling, with no gap to any boundary would perform even better than a single, or several gapped 'leaky' panels.

But my question here is of a different scenario. i.e. A single MiniTrap in the middle of a wall. Will it perform better attached to the wall or with an air gap? If better with the airgap, what is the optimum air gap? Then what happens if you include a second trap, butted together, then with a lateral gap between them. And so on? I wonder if Glen has tested this in the GIK test room?

[Soundman2020]

And so on? I wonder if Glen has tested this in the GIK test room?

Good question: I think I need to invite him to join up here...

- Stuart -

[Avare]

What has been bothering is "ideal." with porous absorbers the norm is to aim for 4 times the impedance of air. Even there is a range of absorption. None of it is ideal because there is no ideal.

[sgleason]

Then what happens if you include a second trap, butted together, then with a lateral gap between them.

Edge effect?

[DanDan]

Indeed sgleason. Two of the edges of the two traps are removed by butting together. So a loss there. But a gain due to the doubled surface area. I just wonder if there is any testing out there to know accurately if it is better to gap them, and if so how much before they begin to operate similar to isolated singular panels.
DD