How many rockwool panels?

[JakeKalka]

Im going to start building panels for my control room. I did an online analysis from ATS Acoustics, but im unsure if it's correct. My room is about 130sq.ft. Length is 13ft, Width is 10ft, Height is 8ft. I have wood flooring and the walls are drywall. ATS said my target reverb time is .20 - .40 at 1000Hz. The graph that tells you how many panels you need says, that for a room of 144sq.ft. you need 18 panels to result at .21 reverb time at 1000Hz.
18 panels just seems like way to much to me. So im asking you guys if you could help me out with this. Am I reading the graph wrong? Or do I really 18 panels?

[takman]

Never heard of this method, or ATS....

Not a good way to approach this IMO. We are not concerned with reverb time, as this is a small room. and a true reverberant sound field doesnt exist in a small room. We are however concerned with specular reflections.

Treat the room surgically, and keep the energy. with 18 panels it is going to be a very dead room. Some people like that, not me though!

You only need as many panels necessary to create an RFZ. And as much bass trapping as possible. and if you want to take it a step further, diffusion on the back wall.

Test the room and then treat. Not the other way around.

[boggy]

For recommendation about RT60 in control room, this papers may be appropriate:

1. "Multichannel surround sound systems and operations", AES Technical Council, Document AESTD1001.1.01-10, New York.
2. “Methods for the subjective assessment of small impairments in audio systems including multichannel sound systems”, ITU-R Recommendation BS.1116 (rev. 1), ITU, Geneva, 1997.
3. W. Hoeg, L. Christensen, R. Walker, “Subjective assessment of audio quality– the means and methods within the EBU”, EBU Technical Review Winter 1997, pp. 40-43.
4. "Listening conditions for the assessment of sound programme material: monophonic and two–channel stereophonic", EBU Tech. 3276 – 2nd edition May 1998, European Broadcasting Union, Geneva, Switzerland

Target value for RT60 from 0.3-0.4s is too high for control room with volume 1040ft3 (38m3) , like this . In recommendations listed above you can find that rooms with (usable) volumes from about 200-400m3 (7000-14000ft3) needs to have RT60 in this limits, and you don't have this volume for sure.

You can find a nice compilation of reverberation time recommendations and calculation methods here, at Acoustic Design Group site.

Known methods for control room design (LEDE, RFZ, N-E) cannot be implemented directly in small rooms (when volume is smaller than about 100m3 or 3500ft3), because non-negligible problems in bass response (reflections of walls that can cancel direct wave at listening position at some frequencies).

So, worst thing in small rooms is bass response, and fact that is virtually impossible to treat room modes right, because all are shifted deeper in audible range, and they are more pronounced (walls is closer, attenuation because distance is much smaller). Instead of this, we need a big quantities of absorbing material, and some methods to bring reflections back in room in front of all this absorption, and to get higher RT60, but not too high, of course.

Simplest method for bringing back reflections... I described in one post in this thread:
Can bamboo wall treatment help dead room?
And more complicated and more expensive method is discussed in his own thread:
MyRoom Acoustic Design


Hope this helps

Boggy

[Jens Eklund]

http://www.gearslutz.com/board/6507362-post2.html

[takman]

Originally Posted by boggy

Known methods for control room design (LEDE, RFZ, N-E) cannot be implemented directly in small rooms (when volume is smaller than about 100m3 or 3500ft3), because non-negligible problems in bass response (reflections of walls that can cancel direct wave at listening position at some frequencies).

i have a room i am building a studio in now. It has a volume of 43 cubic meters. 3.6m width, 4m length, 3m height.

Are you saying that i cannot implement a good ( albeit not textbook perfect) LEDE/ RFZ design?

im confused here.....

even control rooms that have volumes over 100 cubic meters will still have some low frequency problems. They would have to be really large....longer than the low frequency wavelengths...say 56 feet at 20hz.


The smaller the room gets, the more problematic controlling the low frequencies become. But that just means you need to add more bass trapping, and thick panels with a large gap for first reflection points. Even large control rooms utilize bass traps.

not arguing just trying to understand.

thanks

[boggy]

Originally Posted by takman

i have a room i am building a studio in now. It has a volume of 43 cubic meters. 3.6m width, 4m length, 3m height.

beautiful small room with excellent ceiling height!

Originally Posted by takman

Are you saying that i cannot implement a good ( albeit not textbook perfect) LEDE/ RFZ design?

Yes, neither LEDE nor RFZ are invented with small(est) rooms in mind, because in (too) small rooms you possibly cannot have enough space for treatment to properly implement neither of designs, or you just need a bigger room.

Originally Posted by takman

im confused here....

Me too, for years.
When we were doing a room tunings and reparations of acoustics that performance poorly, we always found in a small (but literal) "LEDE" rooms implementations, a some pretty strong cancellation points at listening place at low frequencies, from back wall (if it is literally stiff!), whatever position for speakers and listening position we choose. For example, in LEDE design, "stiff" back wall must have, at least, serious resonant membrane absorber if you like to your LEDE works in a small room at low frequencies. Audible flutter echo from (back) side walls and ceiling/floor is a second problem, not related only to small rooms... etc. All of this problems CAN be solved with standard, or not that standard methods, but back wall in LEDE should not be literally stiff (or literally "Live") if we like that LEDE really works in a small room.

Even LEDE inventors say* that both "Live" and "Dead" ends in LEDE may be (acoustically) "transparent" for audio waves below this frequency:

f= 3*c/a

c - speed of sound
a - smallest room dimension

this means that "stiff" walls may (must) be absorptive below this frequency, but... we need a more space (behind) for absorbers... translated, that means a bigger room...
BTW, authors also says that all important for "LEDE effect" is above this frequency.
And yes, this means Invisible Alpha! (again)

Originally Posted by takman

even control rooms that have volumes over 100 cubic meters will still have some low frequency problems.

Correct and true.

Originally Posted by takman

They would have to be really large....longer than the low frequency wavelengths...say 56 feet at 20hz.

Not necessarily that large, sometimes people forget that sound level drop when we increase distance... even if we have cancellation points.. or room modes... they wouldn't be pronounced that much, like in small rooms, because air, even if it is still a transport medium for sound waves, is also an absorber. Also, back walls shouldn't be literally stiff...

Originally Posted by takman

The smaller the room gets, the more problematic controlling the low frequencies become. But that just means you need to add more bass trapping, and thick panels with a large gap for first reflection points. Even large control rooms utilize bass traps.

Yes, i agree.

Originally Posted by takman

not arguing just trying to understand.

Me too.

Originally Posted by takman

thanks

Thank you for exchange of thoughts...

Cheers

Boggy

* - "The LEDE (TM) Concept for the Control of Acoustic and Psychoacoustic Parameters in Recording Control Rooms" , D. Davis, C. Davis, 63rd AES Convention, 1979

[takman]

boggy,

have you seen lupos room?

-25db RFZ/ISD, in a room well under 100 cubic meters in volume.


LEDE room with Haas trigger

[boggy]

Originally Posted by takman

boggy,

have you seen lupos room?

-25db RFZ/ISD, in a room well under 100 cubic meters in volume.


LEDE room with Haas trigger

I look this thread very carefully but I can't find any information about measured room modes or, at least, frequency response at the best position.
ETC analysis doesn't tell you much about bass response in room.

You can see our results that we get in even smaller room (3.56x3.67x2.55m), but with burst decay sonograms.
Bass response is always a first priority, and if you don't have room modes dampened, you cannot hear full effect of diffuse sound field, for example, because it is masked by "wild" bass behavior.


Cheers,

Boggy

EDIT: And design isn't RFZ, but MyRoom