Today we’re going to talk about a term I call psycho-acoustic space. It’s a big fancy word for really how powerful quadratic diffusion is. And we’re going to work through all of these terms and hopefully by the end of the video you’ll have a pretty good feel about the power of quadratic diffusion.

I’ve been working with it now for 30 years. I think I’ve built every prime number sequence from 7 to 43. If I remember correctly a 43 is 36 inches deep. It’s a big unit but it goes down to a 100 cycles. Pretty nice to have diffusion down to a 100 cycles in a room. If you never heard it, you’ll be amazed at how great it sounds.

So what’s our goal in small rooms? We have large expectations of our small rooms. And my job when we talk on the phone about your room is to bring you back to reality and tell you what’s really possible in your room so that you don’t have such a huge expectation that after you treat your room you’re very disappointed. So we try to bring the expectation and the reality of size, volume and everything into line so that you get a good idea.

Okay, so we have to deal with small rooms. We want them to sound big. How do we get small rooms to sound big? So let’s look. It’s really a balancing act between absorption and diffusion, okay? Absorption to create the definition because too much energy in a room causes what I call mud and soup. So we want to dry out the mud and we want to get rid of the soup. So we want everything to be clean and clear.

So the bottom line here is if we use our absorption and diffusion technologies correctly, we can actually make the room sound a little bit larger to our ears and to our brain. Not physically changing the dimensions of the room by knocking a wall out but by absolutely altering the acoustics of it so our psycho perception, if you will, is greater than the actual physical distance and we’re going to talk about that at the end.

So diffusion of all the technologies has the largest impact. It’s the most powerful tool. It’s also the most misunderstood. And I think it’s the most misunderstood because it’s not used. People just don’t use it. Absorption is easy, they get that, they understand how that works but diffusion is kind of complicated and there is a lot of science to it. There’s distance requirements, there’s all kinds of issues that you have to match up.

So we only use one kind as you all know. And there’s a lot of names out there for diffusion but the bottom line is quadratic the most time-tested, proven and consistent method. Peter D’ Antonio of RPG systems were really the first company to take Bell Labs stuff and flight diffusion and adapt it to audio and make it commercially viable. The rest of us have really gone to school on Peter’s beginnings and there’s not too many of us out there that really understand quadratic. I see a lot of misuses, in a lot of pictures and photos I see. So without experience of building and using we have a pretty good database of what goes where in most small rooms depending on usage.

There’s also a lot of products out there that really aren’t diffusers. My favorite one is the foam diffuser. It’s got bumps on it or something going on and the company calls it a sound diffuser. Well, don’t be hoodwinked by this marketing nomenclature. Look at the science behind the product and know that there’s no way foam could be a diffuser. It’s a sound absorption technology and it won’t give you the characteristics that a true diffuse sound field has. And there’s 5 of them. We went over it many times in other videos, you can do a search and find the 5 criteria for a true diffuse sound field. A couple of them: no spatial irregularities in the frequency response curve, decay times have to be linear so there’s a couple of them right off the top of your head.

So we know in a room we have these 3 sound fields that we have to manage correctly. So only quadratic well-applied, correctly applied will produce the results you need. Let me give you a good example about my studio in Los Angeles which I’ve got to get back to and spend some time listening. It’s been a couple of months but…

The ceiling height in Sacred Ground is 9 foot. That’s net after I treated with prime 11 on the ceiling. So that took 9 inches. So I had about almost 10 foot to start with. I blindfold people and I bring them in and I put them in the chair. Now, these are not your average people in Los Angeles. These are engineers that work for some of the big record companies and some of the big movie and film houses post-production facilities and stuff like that.

And that’s my purpose, that’s my intent to bring people in that have lots of experience listening to frequency and amplitude, especially with music and voice. And I can tell you unequivocally, I’ve probably done it a dozen times, the lowest guess, what do you think would be for ceiling height after they listen to a couple of songs? With a 9 foot actual distance the lowest guess I’ve ever had for ceiling height is 12 feet. So the physical difference between those two is pretty drastic. 3 feet. But their ears and their brain processing the reflections from the diffusers that I put in the ceilings gives you that psycho-acoustic space, that sense that the room is larger than it really is. So diffusion well-applied can give you that.

So you’re going to have a small room, we understand that but let’s do everything in our power to make it sound like a large room, increase the psycho-acoustic space through diffusion.


This is an unedited transcript from our video series from Acoustic Fields. There will be some errors in grammar and sentence structure that occur during this translation process.

For complete understanding and comprehension, please view the video which is included in this text. For any additional information regarding this topic or others relating to room acoustics, please contact us directly at:

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Dennis Foley

Author Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.

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