Since sound absorbers like I need are not sold, I came up with the idea of building them myself.
I need damping in a relatively narrow band on bass frequencies, at about 40, 60 and 80 Hz, it makes sense to build dampers with a membrane.
I found one page what seems to give easy absorber calculations: http://mh-audio.nl/Acoustics/PResonator.html
I also found an example where the damper made based on the previous calculation seems to work https://www.musiker-board.de/threads...echnet.741282/
You can see see results on example link on the post before last on pictures with header "Zur besseren Übersicht vorher - nachher", I used Google translate to read this page.
However, there are small doubts for me.
How the calculation sheet doesn't take into account membrane stiffness at all, only mass and panel depth?
How can such a small absorber have such a large effect on 30 Hz as seen the sample page images?
Did I miss something here?
Have someone other bass sound absorbers built ideas what can be DIY?
I need damping in a relatively narrow band on bass frequencies, at about 40, 60 and 80 Hz, it makes sense to build dampers with a membrane.
I found one page what seems to give easy absorber calculations: http://mh-audio.nl/Acoustics/PResonator.html
I also found an example where the damper made based on the previous calculation seems to work https://www.musiker-board.de/threads...echnet.741282/
You can see see results on example link on the post before last on pictures with header "Zur besseren Übersicht vorher - nachher", I used Google translate to read this page.
However, there are small doubts for me.
How the calculation sheet doesn't take into account membrane stiffness at all, only mass and panel depth?
How can such a small absorber have such a large effect on 30 Hz as seen the sample page images?
Did I miss something here?
Have someone other bass sound absorbers built ideas what can be DIY?
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My plan is Low Q Helmholtz resonators as shown in "The Master Handbook of Acoustics"
Page 225-229 describes the Taming of 47hz modal ringing with measurements and drawing of a cylindrical HR made from a concrete forming tube.
Typically HR's are implemented after extensive low frequency treatments have been installed. Goal is to reduce the last bit of ringing that remains.
I have been very curious about Diaphragmatic absorbers. After much consideration decided on extensive built in broadband absorbers and in the room HR's. I'll see how it goes as to how well I will tame the low fr modal ringing..
Page 225-229 describes the Taming of 47hz modal ringing with measurements and drawing of a cylindrical HR made from a concrete forming tube.
Typically HR's are implemented after extensive low frequency treatments have been installed. Goal is to reduce the last bit of ringing that remains.
I have been very curious about Diaphragmatic absorbers. After much consideration decided on extensive built in broadband absorbers and in the room HR's. I'll see how it goes as to how well I will tame the low fr modal ringing..
I have tried a Helmholtz resonator and measured it's effect on the room. One panel (2ftx6ft) was it was not enough and I was unwilling to build more to see how many I would actually need.
I have not tried the "limp panel mass" but I also had the same sizing dilemma. The calculators can determine the freq response of the absorber, but how do I determine how big the panel needs to be? I'm currently paused trying to link the radiated power in the room to the required absorbed power to fix it.
I have not tried the "limp panel mass" but I also had the same sizing dilemma. The calculators can determine the freq response of the absorber, but how do I determine how big the panel needs to be? I'm currently paused trying to link the radiated power in the room to the required absorbed power to fix it.
This is actually interesting book. I probably also find answer for my question "How the calculation sheet doesn't take into account membrane stiffness at all, only mass and panel depth?" There is used surface density of the panel/membrane and membrane is specific material with known stiffness. In this book is given formula for plywood and formula is not very accurate.
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Reading up on Resonant panel absorbers! I see what you are referring to:
Figure 9-21 for plywood calculated and actual measurements for plywood, fig 9-22
Panel material weighed, Calculated, built and measured for target frequencies appears to be the way forward for these to have a high percentage of effectiveness. It would be fun with the right room and budget.
I resort back to fig 9-8 showing absorption for 3 pound density of 4 thicknesses, showing 4" absorbs much lower than 1,2 or 3 inch.
4" min is mentioned often on Audio expert forum. I'm still a little unsure if 8 pound density is better choice than 3/4 pound -
I watch this guy sometimes.. I like this one. It's inline with the stance I've had for many years!
Figure 9-21 for plywood calculated and actual measurements for plywood, fig 9-22
Panel material weighed, Calculated, built and measured for target frequencies appears to be the way forward for these to have a high percentage of effectiveness. It would be fun with the right room and budget.
I resort back to fig 9-8 showing absorption for 3 pound density of 4 thicknesses, showing 4" absorbs much lower than 1,2 or 3 inch.
4" min is mentioned often on Audio expert forum. I'm still a little unsure if 8 pound density is better choice than 3/4 pound -
I watch this guy sometimes.. I like this one. It's inline with the stance I've had for many years!
Good question. I don't have the answer. I would have measured the room while experimenting with the various absorbers and panel materials.
But now you got me thinking. How do we properly measure them. I need to know!
This paper doesn't have that information but it was a good read anyway.. Mentions heavier gases than air will lower the resonant frequency.
https://dogbreath.de/misc/PlaneAbsorberResonance.pdf
Acoustic fields uses carbon in theirs.. is that similar to giving more mass to the air in the chamber?
But now you got me thinking. How do we properly measure them. I need to know!
This paper doesn't have that information but it was a good read anyway.. Mentions heavier gases than air will lower the resonant frequency.
https://dogbreath.de/misc/PlaneAbsorberResonance.pdf
Acoustic fields uses carbon in theirs.. is that similar to giving more mass to the air in the chamber?
In interesting document https://fitzpatrick.se/wp-content/uploads/2019/03/TPDA-White-Paper.pdf
I find that "Measurements of mobility with the Laser Doppler Velocimeter (LDV) show the tuning
of the absorber".
I find that "Measurements of mobility with the Laser Doppler Velocimeter (LDV) show the tuning
of the absorber".