Bass trap in a cabinet

[travelboy]

My room needs more treatment for absorbing very low frequencies. I have a cabinet covering one wall. I thought about putting bass traps inside the cabinet (in the corners of the room). Basically the same way you would treat the room with bass traps if the cabinet wasn't there. The only difference is that there are wooden doors in front of the absorbers. The doors sit 3mm (1/8 inch) in front of the cabinet's walls, so air can flow in and out despite the doors.

Big question: how does this perform acoustically?

My reasoning is that most of the sound waves will probably reflect from the doors, but this should mainly be the case for mid and high frequencies. Mid and high frequencies are not a problem (they don't reflect towards the listening position). Low frequencies should go right through (or around) the doors, into the cabinet, and get absorbed by the bass traps. Am I right?

[tINY]

Basically, you are right.

How much the small slit around the edge will effect sound transmission is hard to say - if you drill a 1/4 inch hole every 2 inches or so....





-tINY

[johndykstra]

Originally Posted by travelboy

My room needs more treatment for absorbing very low frequencies. I have a cabinet covering one wall. I thought about putting bass traps inside the cabinet (in the corners of the room). Basically the same way you would treat the room with bass traps if the cabinet wasn't there. The only difference is that there are wooden doors in front of the absorbers. The doors sit 3mm (1/8 inch) in front of the cabinet's walls, so air can flow in and out despite the doors.

Big question: how does this perform acoustically?

My reasoning is that most of the sound waves will probably reflect from the doors, but this should mainly be the case for mid and high frequencies. Mid and high frequencies are not a problem (they don't reflect towards the listening position). Low frequencies should go right through (or around) the doors, into the cabinet, and get absorbed by the bass traps. Am I right?

The inside of your cabinet will have a natural resonance. The traps with in will be particularly good at absorbing that particular frequency, and slightly limited (depending on the thickness of the doors) than it would be at other frequencies were the doors to be removed.

[travelboy]

If I stand in such a cabinet and listen, the sound is somewhat damp (lacking high frequencies), but the low frequencies are there. This would support the assumption of my original post.

A thought experiment: let's say I place a mic inside the cabinet, send the signal to a low pass filter and compare the signal level to a different position outside the cabinet… I will probably measure that the level is a bit lower. Thus, the effectiveness of the bass traps will also be lower. Now… can I calculate how much less effective they are? i.e. does a signal drop of 3 dB translate into halved effectiveness?

[Magickman]

Just stuff the cabinets and see what happens.

I can pretty much guarantee you there will be a positive change in the room. How much? How much better with the doors open/closed?? Who knows. Impossible to calculate. Just do it and see what happens!


Then report back here with your findings!!

-MM