Absorption at 50Hz and broadband diffusion at the same time.

jacko · 11th April 2008

I need my back wall to be absorptive at 50Hz (cause the distance from the front is 3.44m), but at the same time I'd like to diffuse the midrange with some kind of RPG type diffuser.

Just for absorption I can build a perforated Helmholtz panel which would be 8" (20cm) deep. The problem is that it will reflect mid frequencies straight back to my listening position.

On the other hand mounting a Shroeder diffuser will sort out midrange problems but the 50Hz will stay untreated.

I need advice.
Perhaps I could build a Schroeder diffuser which would be perforated to serve also as a Helmholtz resonator?

Or maybe Shroeder at the level of ears +- 0.5m and above that Helmholtz panel up to the ceiling?

bpape · 16th April 2008

Diffusors should not have absorbtion exposed or it ruins the diffusion. The only thing I can think of is to build a large poly with relatively thin facing that would give you some absorbtion in the bottom end yet still scatter the mids and highs.

Bryan

Jax · 17th April 2008

Wouldn't installing bass traps in the corners of the back wall absorb some of that 50Hz?

If so, I'd just add diffusion (skyline or well-cavity) to the back wall and bass traps in the corners. If the subs are still too strong, maybe surrounding the diffusors with wall-spaced panel bass traps would help. But I'm no acoustics expert and I'd be glad to check out any follow up comments to my guesses.

11th April 2008	#1
jacko Lives for gear Joined: May 2004 Location: Wroc?aw, Poland Posts: 727 Thread Starter	Absorption at 50Hz and broadband diffusion at the same time. I need my back wall to be absorptive at 50Hz (cause the distance from the front is 3.44m), but at the same time I'd like to diffuse the midrange with some kind of RPG type diffuser. Just for absorption I can build a perforated Helmholtz panel which would be 8" (20cm) deep. The problem is that it will reflect mid frequencies straight back to my listening position. On the other hand mounting a Shroeder diffuser will sort out midrange problems but the 50Hz will stay untreated. I need advice. Perhaps I could build a Schroeder diffuser which would be perforated to serve also as a Helmholtz resonator? Or maybe Shroeder at the level of ears +- 0.5m and above that Helmholtz panel up to the ceiling? __________________ http://www.milaszewski.com/

16th April 2008	#2
bpape Lives for gear Joined: Jul 2005 Location: St. Louis(Wildwood), MO Posts: 764	Diffusors should not have absorbtion exposed or it ruins the diffusion. The only thing I can think of is to build a large poly with relatively thin facing that would give you some absorbtion in the bottom end yet still scatter the mids and highs. Bryan __________________ I am serious, and don't call me Shirley Bryan Pape Lead Acoustical Designer GIK Acoustics

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17th April 2008	#3
Jax Lives for gear Joined: Jul 2002 Location: San Francisco Posts: 4,779	Wouldn't installing bass traps in the corners of the back wall absorb some of that 50Hz? If so, I'd just add diffusion (skyline or well-cavity) to the back wall and bass traps in the corners. If the subs are still too strong, maybe surrounding the diffusors with wall-spaced panel bass traps would help. But I'm no acoustics expert and I'd be glad to check out any follow up comments to my guesses.