Need advise on DIY Deep Bass trap (1 Viewer)

[Eric Ha]

I recently finished remodeling my family room and am having trouble with bass FR. I have a deep null at 40hz and am not able to move the sub. I'm using a parametric eq but really want to build a couple bass traps to flatten out the FR.

Can anyone tell me what can be built in the way of a wall mount trap that significantly absorbs frequencies that low? Most that I see don't give much info below 65hz. I like the examples from Ethan Winer but didn't know if they would be effective at 40hz.

Thanks in advance, Eric.

 

[Wayne A. Pflughaupt]

Eric,

Why in the world would you want absorption for a frequency where you have a null?

 

[Eric Ha]

I have read that nulls are caused by opposing sound waves cancelling each other out at the listening position. I have also read that bass traps flatten out peaks AND nulls in a room by absorbing the reflected sound. Is this not correct?

Anyway, how can I fix a 25db drop at 40hz without moving my sub or listening position. I'm wanting to avoid boosting the null that much with my parametric.

 

[Ethan Winer]

Wayne,

> Why in the world would you want absorption for a frequency where you have a null? <

Eric nailed it. Nulls are caused by reflections, so adding absorption reduces the severity of the nulls.

Eric: Building a bass trap tuned to 40 Hz is not trivial because it has to be very large and deep. You'll find detailed plans for wood panel bass traps on my personal web site:

www.ethanwiner.com/articles.html

Scroll about 1/3 of the way down the page and find "Build a Better Bass Trap." Note that the deep-bass trap there is tuned to around 90 Hz. To move its center frequency down to 40 Hz you'll want to increase the plywood thickness to 3/8 inch and also increase the cavity depth to about 8 inches. I think you'll also want to make the rigid fiberglass at least twice as thick to two inches, or maybe even four inches thick. I've never built a trap tuned that low so I can't say for sure.

--Ethan

 

[Eric Ha]

Thank you very much Ethan. I needed to have some sort of baseline to start with. Thanks for the response!