# DIY Diffusor, treatment of first reflection



## Baldin (Apr 10, 2008)

I have for some time been working on a usable and efficient treatment of some nasty first reflection in my listening room.

Absorption was a no go, as it made the sound muffled and the stereo image smaller.

I have by now come to find that diffusors are the way to go in many applications, as it tends to keep the life in the music and makes the sound more airy and the soundstage larger.

The final result, are diffusors made of fiber glass (fleece cloth with polyester/epoxy), made so that the forst reflections are now skattered and reflected back towards the back wall, instead of towards the listening position.

The result:
I first listned to music, using the temporary stands to make it easy to put them up and down. From the very first note, thare was no doudt that it was a big improvement.

The sound stage was wider and deeper. The room simply feels larger. Tha sound seems much more detailed, and it’s easier to pick out different instruments or place the singer on the stage. Also the aggressiveness in the upper mid to treble is much less pronounced. The sound seems more carm, and you can play louder before it starts to get tireing.

Well, after the first listening sessions, with a feeling that this is just better, it was interesting to make some measurements.

First take a look at the impulse response for the left side (the result is the same for the right side). Without the diffusors, it’s easy to see the first reflection only 1 mS after the main pulse. It’s actually quite large, and it’s quite obvious that it will smear the sound.

With the diffusor in place, the reflection is simply gone. The beauty of this solution, compared to absorption, is that the energy and sound of the reflection is not gone. It is still there. It’s bounced back at the backwall and the big polydiffusor there, and the sound will arive later to add to the feeling of space.

Was it worth it?

Yes without doubt. Maybe it’s not the most pretty solution, but I can hardly think of something more efficient, and without the downside of absorption.

How big is the improvement?

It’s in the same order as going from a good speaker to a very good speaker. It’s just so obvious that there is an improvement. This is nothing like fiddleing with two types of capacitors, different op-amps in your amp, cables or anything else. This is quite measurable, the sound is just so much better.

So the conclusion: Go do it! You will not regret it


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## Prof. (Oct 20, 2006)

Firstly, welcome to the Shack Baldin..

I'm a little confused..Do you have this diffuser at the first reflection point only, or on the back wall or both?.
Also, is this a commercial product or did you make it yourself?
Some more pics.of the room overall would be good..


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## Baldin (Apr 10, 2008)

Hi Prof.

These special diffusors are only placed at the first reflection point.
Yes I made them myself:sn:

At the backwall between the speakers I have a big poly diffusor, from floor to ceiling. This is NOT what does the trick here, but it helps.

I acyually wanted to post a few links, to my homepage and to my blog, where you'll be able to see it all. ....... so if you could give me the possibility to post links it wuld be great (have not posted 5 times yet:sad:


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## Prof. (Oct 20, 2006)

Baldin said:


> These special diffusors are only placed at the first reflection point.
> Yes I made them myself:sn:


Wow!!..very nicely done..They look very professional..:T
I would be very interested to see some construction pics. if you have any..



> I acyually wanted to post a few links, to my homepage and to my blog, where you'll be able to see it all. ....... so if you could give me the possibility to post links it wuld be great (have not posted 5 times yet:sad:


You can go to the "Post Padding" thread and run up your count there..
To link to your Blog, just click on to the "Insert Link" in the reply box..


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## robbo266317 (Sep 22, 2008)

Looks interesting. How did you come by the dimensions or did you simply try different sizes and depths for the fins?


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## Baldin (Apr 10, 2008)

Hi, Prof.
Ok, here is a link to my blog, where you'll find the description of the building process.

http://www.sensibleaudio.dk/BaldinsBlog/?page_id=21

For more pictures of my listening room, please se my homepage.
Pictures here are not updated with the two new diffusors.

http://www.sensibleaudio.dk/HomeTheater/HT.htm


Hi, robbo266317

The ribs are calculated using the simple mirror-reflection method (incomming angle = out going angle), see attached picture. This is of course only true for higher frequencies, due to the limited hight of the ribs (here around 10 cm), which should be ok for frequencies from 1-2 kHz and up.
Some of the sound will be reflected back towards the front wall, some will be scattered (diffuse) on the tops of the ribs.


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## Prof. (Oct 20, 2006)

VERY nice Baldin..:clap: :T..
Your theatre, website and Blog...all very classy..
As it happens, your room is exactly the same size as mine!

I had a brief read as I'm about to go out..I'll get further into it when I get back..
Thanks for the links..


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