absorption and grazing sound

[bert stoltenborg]

Maybe some of you find this interesting.

A client wants to absorp SBIR.
He was advised by some companies and has gotten several samples of absorbing material.
Some of these materials have a fairly hard finish and I wondered if these won't reflect sond, especially grazing sound from a speaker hitting the absorption at the mirrorpoint

So I did a little test:
I aimed a tweeter (Monacor D25N) in a small cabinet at the sample and placed the microphone at the receiving point as is explained here: viewtopic.php?f=8&t=3831

The samples (about 300 x 300 mm) are from:
Ecophon (http://www.ecophon.com/nl/products/Modu ... nds/Focus/), it is mineral wool with a finish
Rockfon (http://www.rockfon.nl/u/website_eu_prod ... 0Eilanden/) it is mineral wool with a finish
Akotherm (http://www.akoestiekwinkel.nl/producten/l/akotherm/) made from recycled plasic bottles, no finish
And I added
normal glasswool for gaps
And I put some speaker cloth over this wool to emulate a traditional baffle.

Angle of incident is about 30 degrees.

[bert stoltenborg]

This is how the direct sound from the tweeter is altered by the reflection.

[Yannick]

Amazing. That rockfon is actually far worse than a perfectly reflective poly...

The recycled bottles aint so bad.

[andrebrito]

Hi Bert,

Excuse my ignorance but how do you make sure the measurements from the omni mic don't come from other reflective
surfaces inside the room that are close to the device under test ?

Do you use a window get rid of unwanted reflections ?

[bert stoltenborg]

Yes, Andre, it is explained in the viewtopic.php?f=8&t=3831 PDF.

[bert stoltenborg]

Amazing. That rockfon is actually far worse than a perfectly reflective poly...

The recycled bottles aint so bad.

The Rockfon has a decorative finish that is real hard, as does the Ecophon, Yannick.