Room Acoustics - Absorption Panels Behind ML's

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Stefan_DR3

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I did exactly that. Put a huge blanket up on my wall. Just tucked it in w the suspended ceiling. This gave me a feel for the direction absorption would take it. Now if someone could give me an idea for diffusion like that I would appreciate it. I have no fake plants to try out.
The old “blanket on wall” trick is a common mistake most diy’ers make - too much, too thin. Sucks only your ultra high frequencies and doesn’t help with image smearing or midrange glare. You need fibreglass panels or thick foam.

For diy diffusion try a bookcase or media tower with unevenly spaced/sized media.
 

kach22i

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My speakers used to be against a staircase with open balusters. I built a homosote/plywood wall with perforated metal diffusion and oak grid/trim will with batt insulation with weep holes to trap sound waves behind the speakers. That was in addition to treating all the obstructions in between the speakers that destroy sound stage with foam and wool blankets.

Look at how they set up the rooms in very high-end stereo shops, that's the way to do it.
 

Andrew Perry

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Good_Martin Logan HAF 2 EQ - with Mathematica.jpg

Here are the frequency responses and the linear interpolations calculated with Wolfram Mathematica (red and green lines): both lines are -1.3 dB/octave.
Sub 250 Hz range with Home Audio Fidelity convolution files (DRC); 1600 Hz - 20 kHz with slight (±3dB) 3-band parametric equalization (ROON eq. function).
All responses taken in the listening spot with UMIK-1 microphone in vertical position (90°).
 

johnyjax

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View attachment 19941
View attachment 19940

Here are my ML with Oudimmo Akupan panels (5 cm thickness, 60x120 cm - 2"x 23.6"x 47.2").

Distance Akupan panels - wall: 5 cm (2").
Distance electrostatic panels - front wall: 1 m (about 39").

The graphic shows the difference between before/after panels positioning (blue = with panels).
The system is equalized with DIRAC LIVE digital room correction, and target curves are different (above 1 kHz) in red/blue measurements.
Green line: interpolating line, showing average 1 dB/octave slope of blue graphic response.
Hi. Sorry this might me off the topic. Just wondering, if I toe in the speaker 30 degree, do the absorption location still the same as the one you have or should the absortion panel also be move 30 degree wider to the left and right from the one you have now? thanks.
 

JonFo

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Hi. Sorry this might me off the topic. Just wondering, if I toe in the speaker 30 degree, do the absorption location still the same as the one you have or should the absortion panel also be move 30 degree wider to the left and right from the one you have now? thanks.
Very on topic, no worries.

Absorption of the rear wave needs to be placed in as direct a line of aim from the panel as possible, so if you toe them in, the absorptive panel would likewise need to slide outwards along the front wall. If the angle is such that it's aiming at a corner, then you need to treat both the front wall and the sidewall.
 

johnyjax

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Very on topic, no worries.

Absorption of the rear wave needs to be placed in as direct a line of aim from the panel as possible, so if you toe them in, the absorptive panel would likewise need to slide outwards along the front wall. If the angle is such that it's aiming at a corner, then you need to treat both the front wall and the sidewall.
Thank you for the info. Basically the absorption panel is in line with which way the rear panel facing. Also, 2" panel with 2" air gap, would be enough?
 

JonFo

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Thank you for the info. Basically the absorption panel is in line with which way the rear panel facing. Also, 2" panel with 2" air gap, would be enough?
Correct, in-line with where the rear of the panel is facing.

A 2" thick absorber might not go low enough. Ideally, a 4" thickness, offset from the wall 2 to 3" is the best, as that will absorb evenly down to the 300Hz, and we want to help reduce the dipole cancelation at those lower frequencies, not just mitigate the high-frequency reflections.
 

johnyjax

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Correct, in-line with where the rear of the panel is facing.

A 2" thick absorber might not go low enough. Ideally, a 4" thickness, offset from the wall 2 to 3" is the best, as that will absorb evenly down to the 300Hz, and we want to help reduce the dipole cancelation at those lower frequencies, not just mitigate the high-frequency reflections.
I see. Thank you.
 

Andrew Perry

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Very on topic, no worries.

Absorption of the rear wave needs to be placed in as direct a line of aim from the panel as possible, so if you toe them in, the absorptive panel would likewise need to slide outwards along the front wall. If the angle is such that it's aiming at a corner, then you need to treat both the front wall and the sidewall.
Absolutely 100% agree. :bowdown:
 
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