HOW TO TEST PANEL ABSORBER FREQUENCY?

[aluman]

Hello everyone.

I've got 3 panel traps here beeing made to help curing standing waves in my control room (mostly around 135Hz and 175Hz).
These panels are supposed to work in the upper bass region.
I'd like to know the resonant frquency of the panel more precisely.

Does someone on gearslutz know a way of finding this frequency?

I'm not talking about testing the global effectiveness of the traps (this would require expensive testing in an anechoic chamber), I'd just like to know more precisely at what frequency they work.

[Glenn Kuras]

Originally Posted by aluman

Hello everyone.

I've got 3 panel traps here beeing made to help curing standing waves in my control room (mostly around 135Hz and 175Hz).
These panels are supposed to work in the upper bass region.
I'd like to know the resonant frquency of the panel more precisely.

Does someone on gearslutz know a way of finding this frequency?

I'm not talking about testing the global effectiveness of the traps (this would require expensive testing in an anechoic chamber), I'd just like to know more precisely at what frequency they work.

You would need to test it in a lab to know for sure. One of the reasons to buy from a company that has testing.

Glenn

[Ethan Winer]

Originally Posted by aluman

Does someone on gearslutz know a way of finding this frequency?

This is tough without testing, as Glenn said. But you can determine the approximate center frequency based on the trap dimensions. Is this a wood panel trap? Was it built from my plans HERE?

--Ethan

[aluman]

Well thank you for your fast responses.
Glenn, I understand that premaid and tested products should be what I need to finish my room but here in Brussels these items are quite expensive and it's very tempting to do it yourself.
I've seen the products from your companies on the web and it's of course very interesting and cheap in comparaison to what we've got here but with the shipping and the customs and taxes........
Ethan, my boxes are in mdf, ...It's not exactly what you did but the concept is the same: sealed boxes with a vibrating panel and absorption inside.

It's getting late now, tomorrow I will post some pictures and the exact dimensions.

[aluman]

Here are the pictures

the panel.jpg
panel back.jpg
detail.jpg

It's 1165mm x 655mm x 90 mm

The frame is made from 30 mmm MDF and the front panel is 3mm MDF.

[Ethan Winer]

Originally Posted by aluman

The frame is made from 30 mmm MDF and the front panel is 3mm MDF.

Put a microphone very near to the front panel and strike it with the side of your fist while you record. The goal is to hit the front panel with more "thump" and less "click," to excite the natural resonance. Then use a frequency analyzer (or by ear) to determine the most prominent fundamental frequency.

--Ethan

[Glenn Kuras]

Originally Posted by Ethan Winer

Put a microphone very near to the front panel and strike it with the side of your fist while you record. The goal is to hit the front panel with more "thump" and less "click," to excite the natural resonance. Then use a frequency analyzer (or by ear) to determine the most prominent fundamental frequency.

--Ethan

Never done it but it sounds like a rubber mallet with MAYBE a shirt rapped around it might work well.

Glenn

[peeder]

What I did as a quick demonstration was as follows: Take a very directional mic (at least cardioid) and mount the panels to be tested on the wall. Across the room, play pink noise through a full-spectrum monitoring system. Aim the mic at the wall, maybe 10 cm away, and record the response. Now aim it at the the center of the panels to be tested, recording those responses. Compare the spectrum analysis of the different recordings.

Not so accurate but it may help.

[tomdarude]

Or maybe slowly sweep a sinewave up & down and "really lightly" touch the panel and try to feel where the vibration is maxed out....

cheers tom

[aluman]

Ok I've tried these tricks, they seem to vibrate more between 130 and 200 Hz when playing tones and softly touch the panels.
I don't have mallets right now, I'll try that later.
I'll maybe borough a good hypercardio mic to try.

On listening tests with music though it sounds like the correction these panels make is greater than with sine tones.

I find that the operating range of frequencies of the panels is a bit narrower that wath I expected ( between 80 and 250).
Do you think that an other design like the porous absorbers much described on this forum would work better ?
The walls are already covered with 5 cm (10cm on the front wall) glass fiber and rockwool (depending on the places) covered with fabric.
Do you think a trap with 10cm or 15cm thick fiberglass , a wood frame and no backing would be a better choice than the panel traps?
Does this kind of trap work on the top of my already treated walls ?

This room already sounds not bad at all but the room modes (predicted by Modecalc even before the construction began) are driving me mad .


Here is a picture with the 3 panel absorbers:

[Ethan Winer]

Originally Posted by aluman

Here is a picture with the 3 panel absorbers:

I can't see much in the picture, but you need to understand that wood panel traps must be placed flat on a wall. Do not use an air gap or straddle a corner etc. However, they work best when placed near to corners.

--Ethan