Helmholtz with rounded corners on outside edges of slats?

[EricHarrington]

Has anyone ever see the affect rounding the outside corners of the slats in a Helmholtz absorber? It seems to me that since the absorption material is based on sound velocity, the rounded corners on the Outside only would in effect amplify the air velocity coming out the back of the slats towards the absorption material increasing it's absorption, at least in the bass frequencies. Is this true? In fact ideally it should be parabolic in curve I think.

[gullfo]

this might be one of those things to do some experimentation with - straight, beveled, rounded - inside and out. define a HH with a set of slats. possibly using a replaceable face plate. then create several different variations: beveled - 45, 30, 15 degrees on outside, then inside, then rounded - simple, parabolic on outside then inside. the straight setup should become your baseline and then test each version to see which one provides improvement and which has a negative effect. obviously this would be a narrowly targeted testing - say 70hz. but the experiment could be broadened later using different targets to see if the improving shapes work across other frequencies as well.

[DanDan]

Intriguing. I guess there could be a sort of horn loading in reverse effect. The slightly broader area on the outside may present and easier impedance to the incoming wave. The slight narrowing may have a small transformer type of effect, tending towards the higher impedance of the enclosed space and fibre.

[EricHarrington]

I was thinking since the velocity is the key to absorption with most glass board etc.. that the horn effect would increase the velocity of the air on the backside and hence absorption. Of course it also reduces the area so it may be a trace off. The idea came when I was thinking of a way to make a shallow absorber that would still function against a wall.