OK - in another thread we were talking about diffusers, as you know I like to do. :) Fireblade asked if I could offer some suggestions, he wanted to build some diffusers to try out in his absorptive treated room. I figured this would be an ideal opportunity to use this for a build log.
The concept and design of diffusers is quite easy, IMO. The goal is twofold. #1 and most obvious is to diffuse the reflected sound - which offers better frequency response at the listening position. #2 is *time delay* to help with the muddied, smearing of the direct speaker sound. This time delay is was helps your brain filter out the reflected sound from the direct sound. And that's really want we want, we want to hear our direct sound, without deadening the reflected sound, and we get the advantage of more even frequency response at our listening position!
The problem with absorbers only, is that it's terribly unnatural. Our ears/brain evolved to listen to the timing of sound as it passes both your ears. That (approximately) six inch space between your left ear and right ear is all the brain needs to locate the direction and distance of the source of a sound. So absorption only allows you to hear the direct sound better, but it sounds odd to us because the instruments that make up our music, aren't played in a vacuum. There should also be spacial queues involved in the delayed reflections that help our brains paint a picture of that instrument, it's harmonic content, and the room it is playing in. That's where diffusers come in.
So we need a few things for a successful diffuser. The key points are depth, width and number of the individual wells, and the width of the overall device. Depth helps with the time delay and low frequency diffusion. The width ties in with the depth to define how low the diffusers can diffuse. And the width and number of the individual wells define how high in the high-frequency we can go. Our goal is to go as broadband as possible within our space, budget, and builder skills. If you're buying diffusers, then they also have to figure in shipping costs and limitations (think of the Decware diffusers). There is A LOT of math involved in figuring this all out. It's not *random* like some pages would have you think. There are limitations as to how deep a well can go before you *need* to widen the well. There are (physical) limits to how small the width of the wells can before before air viscosity becomes a problem. And of course, if you make them too complex (like my design for my personal ones), you have to have the skills, tools, and shop to be able to build them accurately!
Thankfully there is a great software tool out there written to do 99% of the math for us - we just need to define what we can fit in our room, and build with our skillset and budget. That tool is QRDude created by my (online) friend who goes by the screen name Collo. You can find this software here:
http://www.subwoofer-builder.com/qrdude.htmWith this software, we can build devices that are effective from around 275hz, up to just over 12khz. But they'd be HUGE and complex. (like my personal design that I have been able to successfully build LOL)
So, my questions for Fireblade:
How deep can I go on these? I'd personally say a minimum of 6", but we could go up to 13" deep. Again, that's DEEP. The deeper we go, the wider these are also going to be.
Next question, width and height. Height doesn't affect the sound really, only the wall coverage. So taller the better - but you can also stack two smaller diffusers to make one super tall diffuesr if that suits you. Width is the important factor. Typically I shoot for 2' wide. If you need more coverage, you simply build more diffusers.
Lastly, complexity! I would love if we could all build 3' wide, 3' tall, 12" deep broadband diffusers with 29 1" wide wells!! But it's a PITA to get that much wood cut accurately, *And* assemble it accurately. I've not been able to do it for myself - but I'm also a whimsical slacker. I get really into the build, run into some issues I didn't count on, get frustrated and put it aside for a while...or years.
The diffuser I designed for Palomino was 6" deep, ~ 1.5" wide wells, and has 13 individual wells - so I believe it's just under 24" wide - it's range is really only 697-4777. If you're up for it Fireblade, we could push that a little further. Say 8" depth, 1" wells, and QRD 19! This would have an effective range of 646hz-6880hz!
To be continued -