Bass Trap Formula?

[jmz93]

I should know this but don't ... How do I figure out how big a bass trap has to be, to help control a given center frequency?

About halfway back in my room, I get a huge bump around 50-55 HZ. 

thanks.

[Jimna]

In this thread I show you how I made mine.  Dunno if that helps?

http://taperssection.com/index.php?topic=129212.msg1705609#msg1705609

[live2496]

I should know this but don't ... How do I figure out how big a bass trap has to be, to help control a given center frequency?

About halfway back in my room, I get a huge bump around 50-55 HZ. 

thanks.

There is a handy program here. http://www.mh-audio.nl/user/acoustic%20calculator.asp
You can use that to calculate helmholtz resonator dimensions (see my reference to this below). It also has a bunch of helpful functions for diffuser design and calculating room modes.

Rock wool panels or Owens Corning 703/705 (like in Jimna's thread) make effective panels for broadband absorbtion. It probably will be adequate to dampen most of the problems. If you build a corner bass trap that will also address a broadband range of frequencies, but to lower frequencies than panels.

But if there is a lingering problem frequency at the listening position you can build a Helmholtz Resonator to address a specific frequency.

I would try to address any problems with broadband absorbtion first. Then re-measure and if you have a specific mode that is a problem then build a helmholtz resonator to address that.

There is probably lots of info to be found on the net regarding this, but here is one article:
http://www.audioholics.com/education/acoustics-principles/helmholtz-resonant-absorber

[Jimna]

Rock wool panels or Owens Corning 703/705 (like in Jimna's thread) make effective panels for broadband absorbtion. It probably will be adequate to dampen most of the problems. If you build a corner bass trap that will also address a broadband range of frequencies, but to lower frequencies than panels.

The helmholtz resonator is cool, but owens corning 705 4-6 inches thick will also absorb lows too.  Ethan Winer has proven that.  I thought about building a helmholtz resonator in my livingroom (where I have my HT) since I could hide it as part of the wall or ceiling, it's quite a commitment and even harder to sell a wife on.

I have the blue prints to HR here somewhere.

[live2496]

Yeah, I found threads where Ethan says if you use enough panels you will effectively dampen the room modes. He says he hasn't messed with HR's enough to advise people about them. I suppose there is a reason why he sells panels and diffusors.

I would try panels first and foremost and then remeasure the rooms response.