Need help with QRD diffusor!

[Flo Fandango]

Hi all,

I plan to build a QRD diffusor for the back of the control room. The room is quite unfriendly, i treated with bass traps, Helholtz resonators, etc, and I built long time ago a diffusor for the back, but it is not scientifically built, I used a kind of foam and I don't think is working too well. The room is not fantastic, it is 17' x 12' x 6' 7". I am getting at this moment a good stereo imaging, the mixes transfers quite well, but I still have to go and listen to different systems. I have Mackie HR824 with a Mackie 12" sub, a pair of KRK V4 and some Auratones. I plan to sell the Mackies and buy Barefoot - as I like the idea of getting rid of the sub, but before I want to improve the acoustics. You can see pictures of the control room at http://www.fandangorecording.com/rec...dio-photos.htm

I found a calculator at http://www.digitalaudiorock.com/cgi-bin/qrd.cgi and there are a couple of scenario I can go for. The width I have is basically 52 inches, the height is 2'.
I have bass traps in the corner, and helmholtz resonators and some acoustic foam. I want to place some fiberglass bass traps instead of the foam, and a QRD.

I ran two scenarios with the calculator:
1. well width 1", well depth 9", wells per period 7, frequency range is 430 to 6780 Hz.
2. well width 0.75", well depth 9", well per period 43, frequency range 718 to 9000 Hz.
I can make 6 or 7 diffusors with the first scenario, or 1 on the second. What scenario would be better? I imagine the diffusion is better on the second scenario, probably the scattering is better, but the first scenario goes to lower frequency.

If it is better to use the first scenario, are there any recommendations regarding the distance between diffusors?Also, does it make a difference if I make it on wood with cavities (and fill it with some fiberglass) or just full wood?

I would welcome any advice and Ideas. I am quite handy, I have tools, I built everything by myself, and I want to do it myself as I take pride in what I do, not just to save money.
Thank you,

Flo Fandango

www.fandangorecording.com

[tINY]

With that low ceiling, I'd be tempted to not worry about diffusion on the extreme highs. On the back wall, absorbtion should work fine (like wall hangings in front of the diffusers).




-tINY

[Flo Fandango]

Thanks for input... but question: as the ceiling is small, shouldn't I look to put back some highs? The walls are wood, the ceiling is a drop one with acoustical panels (Armstrong), I have a carpet (but also all kind of things on top of it to fight a dead sound...
Flo Fandango
www.fandangorecording.com

[tINY]

The room is small enough that fairly dead is probably a good thing. You can't get very far away from a wall anyway.

If anything, I'd remove the drop ceiling and just put a cloud up for the first reflection off the ceiling.



-tINY

[Flo Fandango]

I had to put the drop ceiling. First, I put Roxul between the joists, then a plastic with metal ( a kind of aluminum), then dryvall against the joists and then the drop ceiling. There is only 1/4" between the tracks of the drop ceiling and the drywall ( it was really hard to install it that way, but I did it. I had to isolate the room, it is under the living room. I used very heavy Armstrong tiles. Then I measured the room and did the acoustic treatment. I had dips of 70 db, I don't have now the graph handy. After treatment (panel bass traps, helmholtz, all kind of corner auralex traps, etc I got 28 db difference between min and max at 20 to 300 Hz. I made a diffuser on the back and three on the ceiling, and I fell that they're not up to task. I also plan to put some more bass broadband absorbtion. The room is not dead, it's not bad, I know it is very small, I get a nice imaging, the reflection zone is very effective, but I want to improve. That is also the reason I asked about the two diffusor scenario, as I want a better dispersion. I want also to improve it as I do not plan to rent space for the studio, so I can keep the prices low, plus the convenience of working at home. I don't like the sub, more precise the idea of using 1 sub, as I can not get a stereo signal through it, that's way I will go with Barefoots mm27 (kind of expensive tough, now they are like 7500 dollars). But I prefer them for my set up, then K&H or Focals.
The diffusers are my primary concern, and, while I have a limited space, I am at 9-10' from the back wall, so a 10" depth diffusor is durable. The initial question -as to how many - 7 or 43 - remains, I just guess that the 43 wells one diffuses better, nobody basically casme up with a clear answer. Any help is appreciated.
Flo Fandango

www.fandangorecording.com

[terry j]

Originally Posted by Flo Fandango

The initial question -as to how many - 7 or 43 - remains, I just guess that the 43 wells one diffuses better, nobody basically casme up with a clear answer. Any help is appreciated.
Flo Fandango

Toronto recording studio Fandango recording mixing mastering sound restoration music studio

Hi Fio, I am new to this too, so I appreciate your questions.

I asked very similar questions in my thread, it may be worth your while to look at some of the answers I was given to this question.

(warning, it is wordy in places, there is a bloke in that thread who...well he basically does not shut up...so just a quick heads up about that)

It goes around the place a bit, so unfortunately you may have to browse a bit to find any answers that work for you.

2 ch listening room, aiming for best possible.

[Flo Fandango]

Hey, tery, thankk you for pointing that to me... useful... looks like 4 or 5 panel with 7 prime is better than one with a large width.
Flo Fandango
www.fandangorecording.com

[Flo Fandango]

Additional question: if I make instead of 4-5 diffusors with 7 prime a single one, but repeating the pattern of prime 7? Are there differences? Of course, it will be repeated like I would repeat 4 or 5 panels.

Flo Fandango

[terry j]

Originally Posted by Flo Fandango

Hey, tery, thankk you for pointing that to me... useful... looks like 4 or 5 panel with 7 prime is better than one with a large width.
Flo Fandango
Toronto recording studio Fandango recording mixing mastering sound restoration music studio

Funny ain't it, I got the opposite view from the same thread!

Bear in mind, (I think) that the question was not definitively answered. I would, for example, much prefer a specific quote from the cox book on the question. AFAICT the 'source' that it's best to have a series of repeated QRDs comes from the dutch site, and tbh I'm not sure he is the definitive source.

Originally Posted by Flo Fandango

Additional question: if I make instead of 4-5 diffusors with 7 prime a single one, but repeating the pattern of prime 7? Are there differences? Of course, it will be repeated like I would repeat 4 or 5 panels.

Flo Fandango

Don't quite understand, I thought that was your intention from the first post?

Also, I must repeat that I am not an expert in any way shape or form, and the last thing I want to do is perpetuate 'internet lore'. That was part of the intent of my thread, to sort the wheat from the chaff.

Regarding the repeat, then the 'rules' for avoiding repetition apply, as laid out in the thread.

A couple of questions...6'7" ceiling?? That is not a misprint? Boy, low ceiling!! Anyway, why have you only got a two foot height to play with for the qrd?

Second, as the room is so small, you need to be able to be at a sufficient distance so the wavefront from the diffusors 'blend', the general rule is three times the lowest wavelength, and for imperial I think the formula is 1130/frequency (????). For the design of Flow=430, that equates to roughly 8 feet. (check all my numbers there)

I don't think your room is big enough to support that.

The other design allows a lesser distance as the Flow is higher, but even then you may be struggling? Both have the same depth, so I guess that indicates the 'depth advantage' that a prime seven gives.

If they were the only two options, then as I came to a different conclusion than you did regarding the repeat or larger prime question, I would go with the higher prime. It should give more complex scattering and temporal signiture, and allow you to be closer to it.

But might be best to wait for more expert advice than to take mine!

[Flo Fandango]

Don't quite understand, I thought that was your intention from the first post?

Also, I must repeat that I am not an expert in any way shape or form, and the last thing I want to do is perpetuate 'internet lore'. That was part of the intent of my thread, to sort the wheat from the chaff.

What I wanted to say: is it better to make 4 or 5 panels with prime 7 and put them one by one, or make a single panel and repeat the pattern (same one basically).

I am a bit confused: why is it better a panel based on let's say prime 19?

As far as the 2' tall, I have a couch, and in the top I have right at the ceiling along the whole back wall 3 Helmholts rezonators, and underneath then I placed some corner bass traps Auralex. So, I'm left with only 2". I plan to move a bit the couch and put behind it a 6" bass trap.
As far as the distance goes, there are 10' between the listening position and the back wall. The length of the room is over 17'. I sit at basically 6' from the front wall.

I know, the ceiling is low, but there is nothing I can do. It is strange, but I get a pretty good sound now, I just wanted to make it better.
Flo

[terry j]

Originally Posted by Flo Fandango

What I wanted to say: is it better to make 4 or 5 panels with prime 7 and put them one by one, or make a single panel and repeat the pattern (same one basically).

nope, don't get it, sorry. To me you are asking about exactly the same options? or maybe I just don't understand the question now..thought I did before.

I am a bit confused: why is it better a panel based on let's say prime 19?

Are you asking 'why is a prime 19 qrd better than a prime 7 qrd'?

Re-iterating I am not the expert, I get the idea diffusion is all about complexity, so the more complex the design the better the diffusion result (?)

Hope you get better help from others more knowledgable than I.

[Flo Fandango]

I did a lot of research- read the Everet book, etc. I decided to go for a 37 prime with 1.25 well size. It became clear that the higher the number, the more complex the diffusion. As the room is small, I have to suplement the absorbtion with some more 4" broadband. I also decided to completely redo the recording room. Thanks for suggestions.
Flo Fandango

[avare]

Originally Posted by Flo Fandango

I did a lot of research- read the Everet book, etc. I decided to go for a 37 prime with 1.25 well size.

Congratulations. Repetition of diffusers is bad, period, without some form of compensation (e.g. Barker Code randomization etc.)

Good luck. Wil you have an iopen house for local gearslutzes to hear it when finished?

Good luck,
Andre

[Flo Fandango]

Yep, I'll let you guys know.
Flo Fandango

[Flo Fandango]

So, after a lot of work, I rebuilt the studio... and I am pretty happy with the results. I bought the materials for absorbers and difusers from Home depot and the acoustic fiberglass from internet. It took a few months to build them. I built a QRD based on 37 prime elements, three polycylindrical ones (placed on ceiling on the back of the control room) and a total of 15 bass absorbers (9 in control room and 8 in recording room). On the video you can see how they are placed (there are two 6" that can't be seen as they are placed at 45 degrees between the front wall and floor). There are also the old acoustical elements I had before- Helmholtz resonators (back wall to ceiling- can be seen in the movie), a few membranes (back wall to sides and sides). For the early reflection I made a 4" acoustic panel (5 x 4') suspended on the ceiling, and i had the sides (some Auralex profiles). Also, there are bass corner traps front wall to sides and ceiling - the thick ones). I have a window glass (three glasses different thicknesses between live and control room, but, when mixing, a 4" acoustic absorber is in place in front of it (can be moved on a rail or taken out when I record).
I replaced the carpet in the recording room (there are two recording rooms, one is treated acoustically, the other is not, I am using mobile absorbers / dividers (in this room I get very nice saxes/trumpets)).
I measured the room using a test CD -each semitone over 9 octaves- from 16Hz to 20KHz. I used my matched pair of QTC49 Earthwork for measurements, and, after a couple of adjustments I got a difference of 9.5 dB between max and min. I have to look for the graph I built after each measurement. In fact, it took like a month until I got this, it was a difficult process. The mic were positioned at the listening position and every measurement consisted of three rounds of measurement, moving the mics 4 inches left and four inches right versus the standard position. I am quite happy, think that the control room dimensions are 17' x 12 x 7'!!!
I have upgraded to Barefoots mm27, it was also a long process of deciding what to select for the upgrade... I have built some very heavy custom stands for them... I got used to them... very happy, no regret whatsover buying them, I had my eyes on them and Focals, discarded Adams and K@H when I listened to them, to me the Barefoots and Focals were the only ones that captured my attention ( I listened to way too many, I am doing extensive homework when I invest money)...
I took a video of the studio, here is the link: http://www.youtube.com/watch?v=ZH0VAhfyp9E

Flo Fandango

www.fandangorecording.com

[PaulP]

Originally Posted by Flo Fandango

So, after a lot of work, I rebuilt the studio... and I am pretty happy with the results. ...
I took a video of the studio, here is the link: YouTube - Fandango Recording

Nice work. The QRD diffusor can be seen quickly at 2:18 in the video. Looks great, love the colour.

Those other skyline diffusors (?) are interesting. Are they made out of pipe insulation ?

Paul P

[Flo Fandango]

Nope, I cut the sides from pine, the top is 1/8 plywood, I used some steam before bending, placed some reinforcement inside, fill with Roxul acoustic, paint. Took a bit of effort, but they do help.

Flo Fandango

www.fandangorecording.com

[PaulP]

I was referring to those alien plant looking purple things hanging
from the ceiling . They can be seen clearly at 1:15 in the video.

Paul P

[Flo Fandango]

They are some diffusers made of ... noodles!!! I wanted to see the effect, I wanted a bit of both diffusing and absorbing effect. They're not built by the formulas, I tried to cut them base on Fibonacci numbers... not too scientific, but I get a beautiful sound... I had a couple of guys coming, and they all love the acoustic guitar sound I am getting, very clear, warm, a lot of distinction... as for vocals, I am still using an sp behind the mic vhen recording solo voice, but I get a nice sound for baking vocal, quite spectacular when done with ribbon.
Do not attempt to use them in the control room, they have effect, but the diffuser I built does a much better job (it better be, it took me 3 weeks to do it!).

Flo Fandango

[Flo Fandango]

Just to add, it's about the swimming noodles...

Flo Fandango