December 17, 2010

Take the free bass trap test

Not convinced bass traps are really worth it? Let me guess - you think they are big and expensive, the interior design committee will never approve and they won't make that much difference anyway! They are toys for rich boys with golden ears.

You need to hear the difference they make. I'm not selling them (perhaps I should be).

The good news is you can try them free. You can rig some up in about 20 minutes, with parts you either already have, or parts you can easily get free.

What do I need?
  • foam of any kind in a large quantity - mattress, couch cushions, spare bags of insulation (hint: couch on the side of the road = free bass trap material). 
  • (optional) louvre door to reflect midrange but let the bass through - you don't want to absorb full range
  • timber
  • rope
Ideally, a basic measurement setup would also be good so that you can measure.

Where do they go?

For this test, corners only. Trap as many corners as you can. In theory a room has 20 corners. 4 of them are vertical where two walls join and run floor to ceiling. Those are the corners you want to start with. Two of them is a good number for the test, do more if you can. You should still notice a difference with just one, but if you do just one make it big, at least for this test. These traps aren't optimal so they make up for that with size.

Curious as to how there are 20 corners in a room? Count the tri-corner ones as well (2 walls + floor/ceiling) and you get an extra 8.

The traps straddle the corner on the diagonal. You don't have to fill it in entirely, simply put them across the diagonal and make them as thick as you can - ideally about one foot thick.

Basic instructions

If you have a louvre door, then simply lean it over the corner on the diagonal with cushions behind it. In that case you won't need anything else. If you don't have the door or a similar membrane, then you could use some long lengths of wood and simply tie the cushions onto the wood - otherwise they won't stay in place. The purpose of the membrane is to reflect midrange and treble so the room doesn't become dead. It has no bass trap function. Other traps use the membrane as an absorber, but this isn't one of those.

How will it sound?

If you use enough trapping, the bass will sound tighter and more controlled. It will sound more like the bass you get outdoors, except with greater output and extension. It is a clear improvement. It may sound like there is also less bass, quite likely due to improved time domain performance. In other words, the bass stops faster.

How will it measure?

You will see a flatter response, where the peaks and dips are damped. The worst room is a concrete bunker. The extreme opposite is an anechoic chamber that works down into bass frequencies. Bass traps take you progressively closer to the anechoic chamber, but in reality you probably can't have too much bass trapping.

The most significant change you will measure is the rate of decay shown in waterfall plots. Unlike EQ, bass traps will speed up the decay rate.

I tried this test myself:
Free bass trap test >

1 comment:

  1. Thanks for the article!

    But, pass on that "hint": (hint: couch on the side of the road = free bass trap material).

    Unless bedbugs are good sound absorbers, of course!


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