How bass traps work

[fredk]

Out of curiosity, how exactly does a bass trap even out the bass response?

Since its a broadband trap, why dosn't it it remove bass evenly across the spectrum and leave you with lower levels of the same uneven room response?

 

[bpape]

Hi Fred.

Most peaks and nulls are caused by how 2 waves from 2 different surfaces/directions interact. If you have 2 waves of the same frequency hitting from opposite directions, they cancel - causing a null. If you get 2 that interact in phase with each other, you get a peak in response. These also explain why you get these things only at certain places in the room that are multiples or fractions of wavelengths.

By absorbing the sound off of one of the 2 surfaces, you end up with the constructive or destructive interference being greatly reduced - thereby leaving you with a smoother response.

Bryan

 

[fredk]

Hmm. OK, I guess I knew about the combining waves, but didn't think it through.

I understand that some first reflections from side walls are desirable and helpfull in the mids and highs, but since bass is perceived as omni directional I want to get rid of as much of the reflection as possible? In effect I want to listen to the bass directly generated by the sub.

Hmm... so for the bass notes that go boom (and there are some notes that REALLY stand out) I am hearing direct sound plus added reflections. For notes that don't redonate and sound ok, I am hearing (mostly?) only the sound directly generated by the sub. Is that right?

 

[bpape]

Not exactly. You're just not in a place where the wavelengths of those non-resonating notes are combining. They will somewhere else in the room. This is why seating location and sub/speaker location are so critical. You sit where you are in the fewest problems.

This is also why placing seating FIRST and letting it drive everything else (speaker position, screen size, etc.) is critical. If you place your seat to get a viewing angle, that's backward. If you place your seat to get proper spacing from speakers, that's backward. Get the seating right first, then the speaker and sub location to minimize as many issues as possible. Treatment can then help address specific issues that remain as well as dealing with decay times in general.

Bryan