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Reflected sound


tempestious1

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Can any of you recommend a  goodDIY plan for making a good curved sound diffuser?  I just can't see spending $500 plus each on something I know i can make myself for hundreds less. I know they're pegboard and some kind of insulation I think just not too sure how to build it.  

 

 

 

                                                                 

 

 

                                                                                                                                                                                                                                             post-58893-0-71100000-1413218321_thumb.j                                                                             

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Here is a link to the Dope From Hope regarding making cylinders.

 

Long ago I had posted two or three publications.  I've not been able to locate that thread.  I'll give it another try.

 

As you can see, the trick is to bow Masonite. 

 

The nice end caps on your photo look very nice.  I can't think of how to make them in an easy way.

 

WMcD

 

https://community.klipsch.com/dope/Dope_810601_v20n1.pdf

 

Edited by William F. Gil McDermott
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I can't find my old thread.  Over a year or so ? I had posted articles.

 

The following thread has discussion and a link -- now broken -- to the old thread. https://community.klipsch.com/index.php?/topic/135869-small-room-acoustics-and-diffusers/?hl=bonner

 

If I have time over the weekend I will post the articles.

 

WMcD

 

I think this is the thread... 

https://community.klipsch.com/index.php?/topic/135869-small-room-acoustics-and-diffusers/

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One more, it is important.  Dr. Toole reports that a single polycylinder works well.  But arranging them in washboard fashion defeats the effect.  This is important because several of the earlier publication which I posted do show washboard arrangements.  No testing is done in the latter and probably should have been.

 

WMcD

 

Sound Reproduction - Toole - Engineered Acoustical Diffusers.pdf

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  • 10 months later...

Many apologies about the picture quality.

 

Please recall that Dr. Toole reported that setting up a washboard of these cause a great deterioration in effect.  See the post above.

 

I was at Cahn Auditorium last weekend for a performance of South Pacific which was astounding.

 

it is about a 1000 seat house which was put up in 1940.  My impression is that it was refurbished not too long ago.

 

On the side walls there are polycylinders about 18" x 24" each in a checkerboard array.  The array would be 3 units by 9 units, but the long course is interrupted at floor level by exit doors.  And the 9 are interrupted by the 8 blanks of hard wall

 

I tapped a few and my guess is that they are thin Masonite.  You'll see that they are chisel ended (my term) and that is something like Masonite too.  They are covered with coarse cloth but not quite burlap.

 

They also are placed on the back wall of the main floor where there is space.  Doors etc interrupt.  There are some on the face of the balcony, but again the lighting (Leko) positions take much of the space.

 

I hope to go back sometime with a better cell phone or camera. 

post-453-0-70600000-1440984157_thumb.jpg

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https://community.klipsch.com/index.php?/topic/19799-arttos-klipschorn-room/

 

The polycylinders can be made very easily and simply. It just depends on how fancy you want get.

 

You should use tempered Masonite. I use 3/16" for smaller polys = or < 4'x4', and 1/4" for larger polys 4'x8'.

 

If you paint them they should be sealed first with stain-blocking primer otherwise the glues in the Masonite will eventually seep through and discolor the paint.

 

The Dope From Hope paper that Gil referenced (good to see you're still kickin Gil) uses a simple 1"x2" wood frame with the Masonite bent and squeezed into place. You may still have to secure them to the frame. Masonite tends to get softer when exposed to heat (like if it were near a HVAC vent in the winter time). Under these conditions the Masonite will lose some of it's compression from being bent and may fall out of the frame it not secured.

 

The polys don't necessarily need to be closed on the ends. Back filling them with a higher density mineral wool insulation like Roxul Safe & Sound or R80 will increase their effectiveness as bass traps.

 

In my room which undergoing a major renovation at the moment, consequently lots of experimentation, I've simply secured the polys directly to the walls with drywall screws. The small screw holes left can be easily filled and patched with a little bit of drywall compound when they are removed/relocated.

 

People who point out the "inadequacies" of polycylindrical diffusers (some claim they are not even diffusers) often cite research that has not applied them properly. In order to be effective in the time domain (as any true diffuser should) you need to use polys of different radius, size, depth and orientation. Be creative. You can even twist the Masonite, overlap them, at differing angles, etc. They can also make for some dramatic lighting effects.

 

The only downside is that the deep bends that are required to be effective as diffusers also intrude on the room space, like pushing the walls in, which can make the room seem smaller. OTOH, if done right, with proper lighting, the opposite can be achieved. You can make the room not only sound larger, but look larger and higher (ceiling).

 

EDIT: The pic Gil posted above is an example of exactly how polys should NOT be installed. It's not as bad as if they were installed edge to edge, all the same size/radius, but in my qualified opinion those polys should have been much larger considering the size of the space, and certainly more variation in size, radius and orientation.

Edited by artto
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  • 2 weeks later...
People who point out the "inadequacies" of polycylindrical diffusers (some claim they are not even diffusers) often cite research that has not applied them properly

 

On PBS news tonight they had a story on the architect who designed the Walt Disney Hall, with acoustics as the first priority (according to him).  It sure looked like there were some polycylindrical diffusers on the ceiling. 

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