Slanted walls

microstrip · Jul 17, 2012

Some of the great custom made listening rooms we can see in in forums have slanted walls, with the purpose of spreading room modes, controlling bass response and creating some diffusion. Is there an optimal angle or a formula for the best angle for a certain room width and length?

Jeff Hedback · Jul 17, 2012

Hello Microstrip,

Nice topic. I consider a total 8deg variance between sidewalls to be minimal (4 deg per side). This is sufficient to reduce flutter echo's and most midrange room ring. However (and the bummer is), that this does not change the modal distribution much if any at all below ~150Hz. There are times when I'll splay each sidewall as far as 12deg out per side. At this point, and with a more complex ceiling shape, you can change the modal distribution where you have less axial and tangential modes as they are driven into oblique paths.

Just last week, I developed an octagonal shape for a studio client that had truly exceptional consistency in terms of sound pressure from 20Hz to 150Hz. I utilized BEM (boundary element modeling) for those studies.

JackD201 · Jul 17, 2012

My teacher, John Storyk of WSDG said a splay of 2 inches for every 10 feet of length was minimum. How many degrees is that?

rbbert · Jul 17, 2012

JackD201 said:
My teacher, John Storyk of WSDG said a splay of 2 inches for every 10 feet of length was minimum. How many degrees is that?

my calculation suggests 0.75 degrees

microstrip · Jul 17, 2012

JackD201 said:
My teacher, John Storyk of WSDG said a splay of 2 inches for every 10 feet of length was minimum. How many degrees is that?

Jack,
My mental calculus only works for the metric system ...

. But I find it too little - it seems to be around 1 degree.

DonH50 · Jul 17, 2012

IME, the main thing slanted walls does is to move the reflection points. Not that it is not worthwhile, but it does complicate room analysis considerably. The trade in reducing first reflections and to some extent reducing higher-frequency (above the low bass) modes iat the listening position s very worthwhile if you can do it. As has been said, it does not help the fundamental deep bass modes, and does not really provide additional diffusion, just redirects the reflections (which itself can be worthwhile as mentioned).

2" in 10' is 2" in 120"; I get 0.955 degrees as the arctan of (2/120).

The "proper" angle depends upon a number of factors, including speaker position and directionality, listening position, and frequency.

FWIWFM - Don

microstrip · Jul 17, 2012

DonH50 said:
2" in 10' is 2" in 120"; I get 0.955 degrees as the arctan of (2/120).
(...)
The "proper" angle depends upon a number of factors, including speaker position and directionality, listening position, and frequency.

Happy to find that my mental calculus is still working, even in imperial units!

I will reformulate my question - what are the effects of choosing an arbitrary small angle, such as 3 or 4º ? Can it get worst than parallel walls?

Jeff Hedback · Jul 17, 2012

As "kinda" mentioned in my earlier post, you can greatly diminish upper mid and high frequency flutter and room ring with these smaller splays (again, 4 degrees is where I would target minimally).

JackD201 · Jul 17, 2012

Aside from the reduction of flutter, just building the false walls will reduce ringing especially if the walls happen to be concrete or CHB which is common in the rim of fire.

Micro, my front wall looks pretty solid but the wood panels are actually tuned labyrinths with 4 inches of rock wool behind them. Behind my painting is compressed fiber glass also about 4 inches covered with Guilford fabric. It was designed with a painting of that size in mind. Without the painting, which is actually angled for the ceiling cloud to catch 2'd refections from it, that front wall just sucks up too much energy and the imaging becomes distant and unfocused. As always a good balance between absorption and even coverage through diffusion should be carefully considered. Personally, I like diffusion in the middle third of the front wall.

DonH50 · Jul 17, 2012

microstrip said:
Happy to find that my mental calculus is still working, even in imperial units!

I will reformulate my question - what are the effects of choosing an arbitrary small angle, such as 3 or 4º ? Can it get worst than parallel walls?

Parallel or angled you have to look at the reflection points and see what works. An angled wall moves the reflections back further but you still have to consider the source (speaker) and receiver (listener). Ray tracing software, or just using triangle in a drawing program, to help get the angles of incidence and reflection equal, can be helpful.

As Jeff said, the angle also reduces interactions among reflections to reduce flutter echo and the like, and may reduce the amount of room treatment needed for optimal sound.

HTH - Don

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Slanted walls

microstrip

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Jeff Hedback

[Industry Expert]

JackD201

WBF Founding Member

rbbert

Well-Known Member

microstrip

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DonH50

Member Sponsor & WBF Technical Expert

microstrip

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Jeff Hedback

[Industry Expert]

JackD201

WBF Founding Member

DonH50

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