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Building Acoustic Panels at Low Cost

alex-z

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If you mount the panels a bit further from the wall it will enhance the low frequency absorption. Porous absorbers work best at points of high velocity and low pressure, walls create a boundary layer of low velocity and high pressure. This is why in some studio applications you will see free-standing panels placed at specific distances, to sit wherever the sound wave velocity is highest for the problem frequency.

The reason RT60 isn't relevant for "small" rooms is that the sound waves at lower frequencies don't have space to fully propagate. The sound field is a cluster of discrete reflections (room modes) rather than a diffuse sound field. You can compare the RT60 of 2 concert halls, but not 2 typical rooms.

You can still look at the decay times to check if the panels are working, they are just not a comparative tool. For example, if you know a room mode exists at 150Hz, you place the panels to reduce it, and if the decay time goes down the panels are placed fine. But you cannot compare a 400ms decay time in 1 room and think it will sound the same in another room with 400ms decay time.
 
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If you mount the panels a bit further from the wall it will enhance the low frequency absorption. Porous absorbers work best at points of high velocity and low pressure, walls create a boundary layer of low velocity and high pressure. This is why in some studio applications you will see free-standing panels placed at specific distances, to sit wherever the sound wave velocity is highest for the problem frequency.

The reason RT60 isn't relevant for "small" rooms is that the sound waves at lower frequencies don't have space to fully propagate. The sound field is a cluster of discrete reflections (room modes) rather than a diffuse sound field. You can compare the RT60 of 2 concert halls, but not 2 typical rooms.

You can still look at the decay times to check if the panels are working, they are just not a comparative tool. For example, if you know a room mode exists at 150Hz, you place the panels to reduce it, and if the decay time goes down the panels are placed fine. But you cannot compare a 400ms decay time in 1 room and think it will sound the same in another room with 400ms decay time.

Will the low frequency absorbtion with a greater gap still work if the back panel I'm using is solid? I was under the impression that this effect would not work with a solid back panel, only if the acoustic material is accessible on both sides.
 

alex-z

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1/8" backing board won't be blocking much low frequency energy, so an air gap should still provide some gains. I can't speak to the specific amount, as my panels are fabric backed.
 
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