QRD Diffusors (how they work)

Posted: Fri Mar 21, 2003 10:21 am

I dare not contest Mr.Himes math on that one!

Isn't the REAL issue how much does the COUCH absorb? And what effect does it have on direct reflections back to the mix position? And last, but not to be overlooked, were the cows who donated the leather african or european? Laiden or unlaiden? Wink

That studio rendering (its ALL computer generated! Way cool.) is my favorite. The colors are incredible. I especially like the finished fabric over the ceiling and front end hiding the treatmetns.

Oh yeah, and the Gretch. NICE. Although, I think I see a Behringer compressor in the rack....... Cool

Freedom! :p:

Jeff

Posted: Fri Mar 21, 2003 12:10 pm

If I might, a couple of thoughts on a truly excellent discussion...

As has been mentioned earlier, there are a number of room design theories currently in fashion. And there are a number of tools available to implement one of these theories. In the end, most of these tools fall into one of three categories: Absorption, Diffusion, or Reflection.

It seems to me shortsighted to dismiss a tool, or even a room design just because you haven't tried it or don't understand it. All of these tools and all of these design theories can be, and have been used to build a room where serious work can be done.

I hope to be designing a new room for myself later this year (my last??) and I am really wrestling between LEDE(tm) and the Non-Environment approaches. My biggest concern with LEDE(tm) or RFZ(tm) is that they do not accurately reflect the spaces where the music will ultimately be heard. (OK, in the case of my stuff they very likely are the exact space, but you get the idea!) Having said that, I've found it quite easy to get repeatable, easily translated results from LEDE(tm) and even pseudo-LEDEL rooms. Go figure!

If I were designing a room, the very first question I'd ask is how will it be used? Next I'd try to determine if there is a leaning towards one or more of the general room design theories. Hopefully, the answers to these two questions won't conflict<G>!

Once you've covered this part, actually designing the room acoustically is well defined process. Really, it isn't black magic or rocket science so much as it is careful attention to detail and the ability to see the room as a "system".

Specific thoughts...

Diffusion is NOT about controlling flutter echo or even early reflections, it's really about simulating a reverberent field in a statistically non-reverberent space. Or, in english, a diffusor has the ability to psychoacosutically move the back wall back a bit by randomly scattering the reflections that would have occurred from a flat surface. It is a trick, but one that works quite well, and when done properly really sounds pretty nice.

Keep in mind that if you are going to use diffusion on the back wall you need to leave sufficient space between the back of your head and the back wall for the diffuse field to develop. I don't remember the formula at the moment, but in every case where I've done the calculation it comes out to 11-12 feet, which is a lot of space. There are probably other designs that can use less space, but I've not tried them.

I really like the poly's as diffusors in larger rooms, but I've never had the money to build a control room large enough to take advantage of them<G>... yet! QRD and PRD designs provide a very square-foot effective means of adding diffusion in smaller spaces.

I had the great fortune to meet Dr. D'Antonio at a Syn-Aud-Con class many years ago, and at the time he was anything but bashful about the details of how his diffusors worked. I know he has published a number of papers as well, so the information is out there, I'm not sure it is really fair to say they keep it shrouded... although the mysticism approach does seem to be frighteningly effective in this marketspace<G>!!!

Lastly (really), my hat is off to the AcidAcoustics, when design time rolls around I will be checking you out!!!

Bill

Posted: Fri Mar 21, 2003 1:10 pm

Jeff,

Quote:

Isn't the REAL issue how much does the COUCH absorb?

What I was alluding to was that the carpet is providing, shall we say plenty of sabins in the high end, making it a very precise situation with the rest of the treatments. Easy to overkill the high-end sabins...In Manzella's case, I'm sure he's got it all worked out. He probably needsthe high-end absorption to balance out all that reflective wood. Beautiful studio though...I just want people to think about the all too common situation of excessive high-end absorption due to wall-to-wall carpet treatments. I'd be very surprised if that leather couch was a random choice, because it makes sense as a balance to the carpet, frequency-wise.

Quote:

What do you guys have to say about the use of diffusion behind the speakers on the front wall like this?

Those are RPG Abffusors, Quadradics with absorption and Guilford fabric coverings. Since nearfields tend to splash around up front, I'd say that's a pretty clever way to provide a balance to all that absorbtion in the front, while keeping a with the basic absorptive theme. Nearfields are still gonna have bass cancellations, though. Remind me to tell you about the Terminator X sessions sometime, and the epiphony I had regarding near-fields and bass tones. That's epiphany, not Epiphone. But I have had a couple of those, too.

--Wes

Posted: Fri Mar 21, 2003 1:41 pm

Wes,
I follow with the absorbtion coE stuff. Lots of people overlook things, like you said. Don't forget the people too....! It is amazing to hear the difference in our church WITH or WITHOUT people when the band is jamming.
AND...

Are you refering to THE Terminator X? As in the 'angry at whitey' TerminatorX? The one who I jammed to while in college (I am whitey....so it was confusing for friends...)

ChuckD. Flava-Flav. Terminator X.
Bass! How low can you go?
Death Row. What a brother knows.
Once again it is the _____alable
Prime Animal
(chuck)D Public Enemy Number one.......

THAT Terminator X?

I listened to tons of different music. Angry rap was often countered with grunge and classic rock.

I'm taking off for the weekend tonight, but I'll be eagerly waiting to see your reply!

(I'm working with a friend from college - caucasian, blonde, chubby chemical engineer- who wants to do nothing more than be a rap star. Have I posted "happy daddy's day" lately? Hmmm. I'll have to. Way Funny.)

JZ

Posted: Fri Mar 21, 2003 1:52 pm

Hi Bill,

Welcome to the discussion.

Quote:

My biggest concern with LEDE(tm) or RFZ(tm) is that they do not accurately reflect the spaces where the music will ultimately be heard.

I really see the two as quite different, since the RFZ method, by removing early reflections from the zone with geometry, instead of absorption by necessity, allows for the live/ dead issue to be addressed on a case by case basis. These rooms can sound very much like a normal environment, which is a huge selling point IMHO.

Quote:

I've found it quite easy to get repeatable, easily translated results from LEDE

Sounds like you're doing something right!

Quote:

Diffusion is NOT about controlling flutter echo or even early reflections, it's really about simulating a reverberent field in a statistically non-reverberent space

Well, the second half of your sentence sounds right, but diffusors are one of the many methods employed to remove flutter echos, and they certainly will remove them. I mean, what is FlutterFree* but a mini QRD diffussor? I think maybe you're saying that they do much more than that, and I would agree.

Quote:

it comes out to 11-12 feet

Lots of factors involved there, but please don't tell me it can't be done, cause then I'll have to go out and try it!

Quote:

I'm not sure it is really fair to say they keep it shrouded

I was just having a little fun. I've worked with Dr. D'Antonio on studio projects for years, and you're absolutely right, he's the one of most forthcoming, helpful, and let me add intelligent individuals in this business. I think he's not too distraught over the fact that number theory ties most normal people's minds in knots, however. Keeps him from having to resort to psuedo-science to keep ahead. So it was in jest. But if I really wanted to poke fun at him I'd start putting little trademark* symbols* after all my nouns*.
Wink

--Wes

Posted: Fri Mar 21, 2003 4:54 pm

Wes...Dude....Terminator X?! Spill it man!

Peace,

James

Posted: Fri Mar 21, 2003 10:50 pm

Jeff, James,

Quote:

THAT Terminator X?

Yeah, as far as I know there's only one Terminator X. I didn't even know who he was the first time he booked the studio -- I'd just gotten a call from a guy named Mr. Rogers who said his son was moving down from NYC to NC and needed a place to record some demos. He showed up with this antiquated computer that looked like it had really been around the block a few times - it might even have been an Atari - and a young rapper from Durham.

The thing about Terminator was that he coaxed all these wildly inventive sounds out of that old piece of crap computer - stuff you just wouldn't think of to do. But the one aspect that was fairly straight ahead was the kick drum. Yeah, you guessed it, the old TR-808. Wouldn't really be vintage rap music without it, now would it? A lot of studios have to worry about blowing their speakers on a hip hop session, but that wasn't the case with X. We always kept the speakers at a reasonable volume, except occasionally I'd crank up the Ureis to check out the bass. Cause you know, you need quite a bit of that 808 stuff in the mix.

Where the story gets interesting is the first time I switched between the soffit mounted Ureis and a pair of 8", bi-amped Haflers that were behind the console on stands, about 2 ft. in front of the wall. You know how the 808 has a definite note to the sound, right? Well what kinda freaked me out was that when I switched to the Haflers, the 808 actually changed pitch. Yeah, you heard me right. Depending on which pair of speakers I monitored on, the sucker was changing pitch by a lot (m6th?), and the pitch was lower on the Haflers. Holy Moly and Great Caesar’s Ghost! I started to breath a little heavy because I didn't want to screw up this very first mix, and frankly I wasn't even that sure how to mix a rap record since that's not really my forte. Hell I'd just figured out who the guy was a few minutes earlier from the lyrics the kid was spittin out.

So I grabbed a pair of headphones and put ‘em on, just to see what note they gave me on the 808. And what do you know, they jived with the Ureis. So I just said screw the Haflers, I'm gonna mix on the Ureis. I can't abide by a pair of speakers that isn't even sure what note is being played. And that's pretty much the last time I ever trusted a pair of near fields.

To this day, I don't have an exact explanation for the change in pitch, because whenever X was in the studio I was too busy to nerd out on it. But it did cause me to start a series of experiments with speakers and boundaries, which eventually culminated in my TapeOp article on bass waves. After testing my studio with sine waves (moving the Haflers around even slightly caused gross differences in bass response) I went to as many studios as I could over a period of months - Nashville, California, you name it. After testing countless rooms, many very expensive, I came to the conclusion that near fields are just prone to faulty bass response. I also learned that no amount of bass trapping will completely eliminate standing waves, not by a long shot. And that you DO NOT want deep bass traps that extend out into the room unless they are overhead. Panel traps or Helholtz resonators that are against the wall are the way to go, from what I've learned.

If you're interested in reading more about bass wave cancellation, check out the TapeOp article. Ethan recently posted it with the FAQ.

:p: --Wes
By the way, X is a very mild mannered guy. Not at all like I would have expected.

Posted: Sat Mar 22, 2003 9:42 am

Hey Wes,

After I saw you posting here I did some digging and saw that you used the Uries. Are you still using them? Can you still get parts for them? My first studio experience used Uries. I thought they sounded pretty freakin' good. I was reaaaally green then though. I've thought about finding a pair for when I build my room but parts availability and such has me a little cautious.

Peace,

James

Posted: Sat Mar 22, 2003 9:57 am

James,

Quote:

Uries. Are you still using them? Can you still get parts for them?

Yes, and I love them. They are 809's, which are the right size for my rather small control room (approx. 2500 cu.ft.). I've only had to find parts for them one in 15 years, but I'm sure they're out there, even though Urei is out of business. JBL may have them. You know, sometimes the best way to get parts is not from the company anyway. When I was in Wales once, I ran across a guy who had every imaginable part for Hofner basses from any year they were ever made. And with the web, guys like that are easy to find.

Keep in mind that Ureis will usually sound terrible unless they are soffit mounted in a rigid wall, at the proper listening angle, and with sufficient isolation from the surrounding structure.

--Wes

Posted: Mon Mar 24, 2003 3:14 pm

Quote:

Originally posted by Wes Lachot:
Hi Bill,

Welcome to the discussion.

Thanks!

Quote:

I really see the two as quite different, since the RFZ method, by removing early reflections from the zone with geometry, instead of absorption by necessity, allows for the live/ dead issue to be addressed on a case by case basis. These rooms can sound very much like a normal environment, which is a huge selling point IMHO.

Interesting point... I have never had the opportunity to attempt an RFZ design, not sure I'd want to tackle it<G>... but when you put it that way. I lumped them together because they are both treatments that recognize the impact of reflections, and try to manage them!

Quote:

Diffusion is NOT about controlling flutter echo or even early reflections, it's really about simulating a reverberent field in a statistically non-reverberent space

Well, the second half of your sentence sounds right, but diffusors are one of the many methods employed to remove flutter echos, and they certainly will remove them. I mean, what is FlutterFree* but a mini QRD diffussor? I think maybe you're saying that they do much more than that, and I would agree.

Yeah... poorly phrased on my part!

Quote:

it comes out to 11-12 feet

Lots of factors involved there, but please don't tell me it can't be done, cause then I'll have to go out and try it!

Oh, I'd guess nearly anything can be done! One of the first rooms I worked in was probably less than 10 feet deep, housed a Tascam Model 15 too, which probably dates me a bit, anyway, the designed skewed the back wall pretty severely, and it worked. The owner did really good work there!

Quote:

I'm not sure it is really fair to say they keep it shrouded

I was just having a little fun. I've worked with Dr. D'Antonio on studio projects for years, and you're absolutely right, he's the one of most forthcoming, helpful, and let me add intelligent individuals in this business. <snip>

I over-reacted. I've heard him slammed more often than he deserves... and I think it's too bad.

On another topic... I too use Urei 809s as my main monitors. Right now they are due for reconing, one of the cones completely collapsed... I've never actually heard that sound before, and I'll tell you, it was blind luck that the troubleshooting got to the speaker as quickly as it did!!! Very scary sound...

Anyway, I've tried a couple of replacement HF drivers, and even toyed around with the cross-over, but they just got them pretty close to right. I love them for good old rock and roll. I do wish they weren't quite so fatiguing though.

Bill

Posted: Mon Mar 24, 2003 3:45 pm

Wes,

> To this day, I don't have an exact explanation for the change in pitch <

Maybe a resonance in the speaker cabinet, which was excited by the impulse part of the drum sound?

--Ethan

Posted: Mon Mar 24, 2003 5:38 pm

Ethan

Hmm, I hadn't thought of that...

--Wes

Posted: Fri Mar 28, 2003 2:04 pm

Wes,
My room will be approximately 2500 cu. feet also, and I have been trying to decide whether to soffit mount the monitors or not. Your comments certainly make me think more about soffit mounting.
My question is, for a room this size and a relatively small budget, what models of monitors do you suggest I check out for soffit mounting? I see and read alot about near fields these days, but I'm not aware of what's recommendable for soffit mounting.

Thank you,
Scott

Posted: Sat Mar 29, 2003 5:44 am

Scott,

There are not that many companies that make monitors designed for soffit mounting, and some of the popular ones are very pricey. They generally fall into two camps: concentric and nonconcentric. The concentric type would be Urei or Tannoy. The Ureis are no longer made, but they can be found used, at bargain prices. People either love 'em or they hate 'em. I personally like mine (809s)

Tannoys are similar, more modern sounding, and I think a good deal for the money. Here's the link:
http://www.tannoyna.com/professional/index.html

In the nonconcentric camp, there are (among others) Boxers and Dynaudio. Here are the links:
http://www.boxerspeakers.com/t2/t2main.html

http://www.dynaudioacoustics.com/Default.asp?Id=289

None of these are perfect, in my estimation. The nonconcentric types tend to have wide dispersion and a modern, "hifi" sound, accompanied by image smearing due to so many drivers and crossovers. The Tannoys have a much more focused, "point source" sound to the imaging, but I wish the crossover point was higher. Alas, there is no perfect monitor. But at least soffit mount monitors can give you bass you can believe in. Bear in mind that room modes come into play more with soffit style speakers.

Hope this helps-

--Wes

Posted: Sat Mar 29, 2003 10:25 am

Lots of Questeds in soffits, as well, especially the bigger ones.

My main recommendation with soffiting monitors is, do it right. If you've never done it before, do it with the guidance of some acoustician who has. You can't push the holes in the walls around until they sound right, and if they're placed weird, everything else is bandaids.

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