# Acoustic Panels, rear side with sheet of masonite, efficiency loss ?



## Soulgolem (Jun 12, 2009)

Hi I've been making acoustic panels 2x4' for a while for my practice room and studio with great success using rockboard 40 material.

I started building them for some friends lately and one asked if I could cover the back end with masonite (thin flexible hardwood material often used in the back of drawers and computer desks).

It's very do-able, I can just buy a sheet and nail it to the back side of the panel, but would it have a dramatic effeciency loss ? Those panels are usually hung to the wall.


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## Jordan Chin (Jan 17, 2010)

It shouldn't affect the sound too much if it is attached to the wall... If they however want to place them on them on feet (aka stand them up rather than permanently attach) then I wouldn't use it, it will almost defeat the purpose.

Also remember to make sure your only treating half of the walls... try to stay opposite of each other if you are not using professional panels. (aka if the floor has carpet don't treat the ceiling. If the north wall has treatment, do not treat the south wall etc)


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## ronmac (Sep 22, 2006)

Personally, I would not attach a rigid backing. 

The absorption effect of using the panels is greatly increased if they are mounted slightly away from the wall. This will insure that the maximum energy is absorbed as the sound waves travel through a layer of dissimilar layers. Each time the sound wave transfers from one material to another it loses energy. The energy absorbed by one material will transfer the energy to the adjacent material, but because they are dissimilar there will be an impedance mismatch, and a resultant loss of energy (or absorption).

So, a wave traveling through rock wool, hitting a wall (or hard material attached to the back of the rock wool) will bounce back with more energy (less absorption) than a wave traveling through rock wool, then through air, then reflected off the hard surface, then through air again and back through the rock wool.


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## Jordan Chin (Jan 17, 2010)

Still I would try using the feet idea. Ron has some really good points, and I would defiantly look at some Auralex acoustic panels, and try to model after them.


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