Are these as Awesome as i think they are?

Jul 14, 2014 8:25:10 GMT -6 svart said:

Jul 14, 2014 7:39:54 GMT -6 gouge said:

It is only a tuned absorber if it's a sealed box. I'm not so sure it is from the pics.

You're thinking of a tuned "cavity" AKA the Helmholtz resonator.



Anything that restricts the sound wave is somewhat of a tuned device.  Since waveforms larger than the holes will only be partially allowed through, then fractional soundwave won't be fully subject to the absorption behind the opening, resulting in greatly reduced absorption at that frequency.  I'm not saying it's a big deal, but there will be a hitch in the response of the unit toward the low end.  It doesn't seem like it but the area on the sides of the panel is likely up to 20% of the total area.  With holes, you probably lose 5-10% of that.

Remember your physics theory..  The holes have to be in fractional sizes OR this can be calculated via the area of the panel.

This is how "perforated panels" work with single sized holes spread over the face of the panel.  They work as well as Helmholtz (and sometimes are in addition to Helmholtz resonators).

Products such as this:
www.rpginc.com/product_Expo_Panels.cfm
www.customaudiodesigns.co.uk/acoustison-perforated-steel-acoustic-absorbers.htm

Work pretty well by using the "total area" approach.

You can also vary the hole size to get a broader range of absorption (Apologies all around for the use of the purple site):
www.gearslutz.com/board/attachments/studio-building-acoustics/354772d1374567381-porous-absorber-calculator-v1-59-reliability-perforated-panel-porous-absorbe-picture-9.jpg

www.gearslutz.com/board/studio-building-acoustics/855397-porous-absorber-calculator-v1-59-reliability-perforated-panel-porous-absorbe.html


In fact, I made my own using some software I found online..

yes I agree, I think it's just loose terminology as most absorbers are in reality tuned to suit certain frequencies whether broadband or tuned. but to me tuned means membrane absorber, Helmholtz, slat resonator, perforated absorbers etc. all of those treatment rely on a sealed space, whether it be sealed due to a wall behind or as in the rpg example you linked a sealed box they are all really relying on the sound entering, going through insulation, hitting the rear surface and resonating back out to work as designed.

in the mobile version we are looking at in this thread, the sound goes thorough the holes and keeps on going. all the holes are doing if anything is returning some hi freq but at a level I think it would hardly be noticeable. I doubt it's going to do anything to the bass frequencies either because the surface of the sides is just not big enough to have an effect.

I've been fortunate to be a part of the design team on multi use halls and a couple of lecture theatres. all of those projects involved perforated absorbers. mainly because they work well with reduced depths and they are very good at the frequencies from 500hz and up which are the problem areas for those spaces.

I also built my first studio solely out of perforated panels of depths varying up to 12". in effect each internal wall became a sealed perforated panel. it cost a fortune to get all of that plywood laser cut but it looked the part and was very quick to install. in retrospect it worked amazingly well for such a tiny room. these types of treatments are really better suited for medium to large rooms. (not including bad panels in that statement)