Back Wall question for Ethan!

[Mr.Smith]

Well anyone else can chime in, but I am specifically gearing it towards him because I read something in his acoustics article about the rear wall which states:

"For someone with a very small budget, making the rear wall of a control room totally dead may be the only solution. At least that gets rid of flutter echoes between the front and rear wall, though at the expense of sounding stuffy and unnatural. But it's better than the hollow boxy sound you get from a plain flat reflective surface. Another option is to make the rear wall of a control room partially reflective and partially absorbent. You can do this by making the wall totally dead, and then covering it with thin vertical strips of wood to reflect some of the sound back into the room. If you vary the spacing from strip to strip a little, you'll reduce the coherence of the reflections a little which further improves the sound."

Got it, understood, Great. Now my only problem is that I never hear people on this forum talk about this solution, only diffusion. I have only seen this in some of the bigger studios.

I have most of my bass trapping done and I even tested out different methods to find the best options (went with FRK facing room/DIY superchunkish style). I pretty much deadend the entire ceiling since I have a low ceiling and a hard floor surface. I have a RFZ but now am working on rear wall and flutter echo. Again I dont want the room to be overly dead (especially with the dead ceiling). So my question is:

- Can I use the method you speak of in my situation? or is it too small still?
My room is 10.23 feet long and by the time you minus the 38%, yada yada, I am left with about 6.25 feet behind me. Now I know diffusion starts to work around 6ft so I think its cuttin it a little bit close. What do you think?

thanks.

[tonio]

Basically, the latter portion of that statement IMO sounds like a form of a slat/slot resonator type treatment. Slat/slot resonators do have have diffusion properties as far as I remember.

So how is your ceiling treated?

In my previous room, I had 75% of the ceiling rafters stuffed with that acoustic cotton stuff -Ultracotton, and the front wall was totally covered with 703 or rockwool and numerous other panels/traps. The sabin total was up there and Rt60 was quite low @ 200ms at the high points for a 17x11x9' space. Yeah it was dead, I spent alot of time trying to bring back some ambience in the room, adding, tweeking a poly, slat resonators etc , etc.
to no avail.

At that point I figured its prolly the best it can be, and focused on the the performance, and recording/mixing techniques while keeping in mind the good points and bad points of my "room".

But I digress...

If you provide more complete information, you'll probably get a better informed reply.

T

[Mr.Smith]

Room is about 10.25x11x7.6

I had to do the mix position where front to back is shorter than left to right. Unfortunately it had to be like this.

I have 5 inches on the ceiling with about a 3-4 inch air gap and about 90% covered. pretty much all corners are trapped (about). first reflections are convered, now its the dreaded back wall.

Also since the bed is pretty much taking up a large portion of the back wall, is 6inch panel attached to wall okay, or is a 4inch, with a 2inch gap better? I dont want to come out much more than that or I will feel boxed in.

[tonio]

Based on 10.25' length, you fundamental axial is probably 50 hz or so. 1/4 wavelength is 5'6".

The bed angled out from the rear ceiling /wall junction would probably be a great absorber.

[Ethan Winer]

Originally Posted by Mr.Smith

Can I use the method you speak of in my situation? or is it too small still?

Sure, that will work fine. Add the thickest rigid fiberglass you can manage on the rear wall, then you can experiment with thin wood strips. Maybe cover 20 to 30 percent of the wall. BTW, my intent wasn't a slat resonator, though you might get some of that behavior.

--Ethan

[Mr.Smith]

Originally Posted by Ethan Winer

Sure, that will work fine. Add the thickest rigid fiberglass you can manage on the rear wall, then you can experiment with thin wood strips. Maybe cover 20 to 30 percent of the wall. BTW, my intent wasn't a slat resonator, though you might get some of that behavior.

--Ethan

Great thanks!!

Will that effect the first reflection point and cause reflections back into the mix position?

If so can I not only play with the spacing (for coherence) but also play with the width and the depth of the strips to create more of a diffuse sound? or will that damage the sound?

thanks again

[Ethan Winer]

Originally Posted by Mr.Smith

Will that effect the first reflection point and cause reflections back into the mix position?

Yes, all early reflections can be a problem.

If so can I not only play with the spacing (for coherence) but also play with the width and the depth of the strips to create more of a diffuse sound? or will that damage the sound?

I honestly don't know. So use masking tape first before you glue or nail them in place permanently.

Or you can use a QRD-type pattern such as used by Wes Lachot:

Wes Lachot Design || Studio Design and Acoustic Consulting

(Click the thumbnails in the lower right to see the stripes pattern idea.)

--Ethan

[boggy]

Originally Posted by Mr.Smith

.....

If so can I not only play with the spacing (for coherence) but also play with the width and the depth of the strips to create more of a diffuse sound? or will that damage the sound?

Mr. Smith, instead of "playing with strips" you can use similar principle that is used when BAD panel was designed.
RPG Diffusor Systems - BAD panel

BAD panel is 2D, and you can easily build 1D diffusor/absorber based on similar principle. Strips can be same width, and space between can be zero.

Then you need some pseudo random 1D sequence, and you can use MLS, Maximum length sequence - (Wikipedia) for this, or any other way to generate pseudorandom sequence.

This binary sequence is your plan for mounting wooden strips to surface that you need to be more reflective. For example, you can use "0" for "don't mount strip, leave open" and "1" for "mount strip". This is a better diffusor than simple covering absoptive suface with equidistant strips, or plain wood/MDF/gypsum sheets. At least it has smaller possibility for aliasing than other solutions.

When you use binary diffusor... you can get about 50% covering of surface.

Be careful with orientation of strips... diffusion direction(s) is same as QRD 1D diffusor.

regards

Boggy