John Sayers' Recording Studio Design Forum Archive

The forum formalities;

Objective: Building an accurately sounding Mixing Room
Location: Stockholm, Sweden
Budget: They way things are looking it is going to be over 1000 Euros
Rooms current Dimensions (After sound isolation):
Length 4.6 Meters, Wide 2.17 (corrected Oct 20 2010) Meters and Height 2.89 Meters


Background: This is my first post in this thread but I have posted both on the Design and the Construction forum.
I am building a Mixing Room for commercial purposes (Mixing music for my own label as well as other Clients).

With the assistance of my friends I have built a 145/45 mm wood frame that will eventually house isolation and three layers
of 13 mm drywall glued together with Green Glue (acoustic caulk etc.) in order to isolate sound.

Now I need to fine tune the sound treatment stage of this project-

I have done a preliminary Sketchup design in hopes of creating a reflection free zone around the Mixing position
but I am now leaning toward altering it by slanting the walls leading in to the flush-mounted monitors by 12 degrees and adding slot resonators.

A large ceiling cloud and two large bass traps are also a part of my design.

My plan is to purchase Rockwool isolation (density 50 kg per cubic meter) that usually is used on the layer before the exterior of a house.
It is a relatively stiff isolation and it was the closest I could get to obtain a reasonable cubic meter density range.



After using Bob Golds online modal calculator it seems that my rooms modal problems range from 74.9 with the problematic
real trouble spots range from 110 hz up to 247 hz.



Here are the results of the modal calculator:

Room Dimensions: Length=4.59 m, Width=2.01 m, Height=2.89 m
Room Ratio: 1 : 1.43 : 2.28
R. Walker BBC 1996:
- 1.1w / h < l / h < ((4.5w / h) - 4): Pass
- l < 3h & w < 3h: Pass
- no integer multiple within 5%: Pass
Nearest Known Ratio:
- "18) Dolby's optimum ratios for Film & Music Room" 1 : 1.493 : 2.313
RT60 (IEC/AEC N 12-A standard): 185 ms
- ±50ms from 200Hz to 3.5kHz = 135 to 235ms
- ±100ms above 3.5kHz = 85 to 285ms
- <+300ms at 63hz = 485ms
- 300<RT60<600ms
RT60 (ITU/EBU Control Room Recommended): 159 ms
- ±50ms from 200Hz to 4kHz = 109 to 209ms
- <+300ms at 63hz = 459ms
- 200<RT60<400ms
Absorbtion to achieve ITU RT60: 290 sabins


Question:

How much isolation do I need and how do I approach building my slanted walls, ceiling clouds, bass traps etc.
in order to obtain an absorption level of 290 sabins and attack the nodes that will give me problems in achieving my objective?

(The Sketchup file is a little different then the room in questions which is made out of wood)


Sincerely,

Useg Diaz-Granados

are you planning on building the walls inside out? that could help quite a bit given how narrow the space is. where are the doors in this room?

Thank you for the quick response Glenn!

The best approach to answering your question is by posting some pics.
(note that the room is a work in progress and that the dimensions in the pics are off)

As far as the door is concerned the thought is to buy a new one (42 DB door) or contract somebody to build one for me.

I should also mentioned that we plan to lower the ceiling by 70 centimeters and add 2 layers of drywall that will be Greenglued
together and caulked properly.

I hope that the info I provided is useful.

Sincerely,

Useg Diaz-Granados

any option to make this inside out? putting the drywall layers on the outside of the framing - leaving about a 25mm gap - would let you use the inside insulation to perform most of the treatments and not have to encroach too much on the remaining space. same for the ceiling.

I imagine that those frame things on the walls will be coming off before you start construction, correct? That is no use for isolating your room the way it is now.

I should also mentioned that we plan to lower the ceiling by 70 centimeters and add 2 layers of drywall that will be Greenglued together and caulked properly.

Why do you want to lower the ceiling so much??? 70 cm is nearly 28 inches! I can't see any reason why you would need to lower it that much.

Also, you seem to be saying that you are planning to glue the layers of drywall together with Greenglue: Well, Greenglue is not actually glue, and is not designed to hold things together. You will also need to screw or nail the second layer of drywall, just like for the first layer.

Here are the results of the modal calculator:
Room Dimensions: Length=4.59 m, Width=2.01 m, Height=2.89 m

That's not a very good ratio. If you make the room a little shorter you can get a much better ratio. Change those dimensions to Length 3.85 m, Width=2.01 m, Height=2.83 m and you hit Louden's best ratio perfectly. Much better. The space you save at the back could become a storage closet, a machine room, an HVAC chamber, or even a small vocal or amp booth.



- Stuart -

Thanks’ for your insight and suggestions for the improvement of the room.

Glen, it sounds like an interesting idea but I am afraid I might misunderstand what you mean.

Do you mean placing the drywall on the sound treatment frame (not yet in place) and leaving a 25 mm gap or placing
the drywall on the other side of the frame( facing the adjoining apartment and the other room/drywall that the wood-frame is connected to) and then leaving the gap?

If it is the second option I am afraid I cannot do that since the wood frame already is in place.

Stuart, thank you for informing me about the room ratios. If I understood you right I would have to move
the door up 75 centimeters, which would leave room for a small sound booth, correct?

Sounds like a great idea.

I am afraid that the framing things you are referring to are holding the wood studs into place.

When we connected the wood studs to the wall we were unable to use the roof because the apartment is old
and the roof is reinforced by steel beams. So we used the “frame things” to insure that they can hold the
weight of the free standing ceiling and the cloud we want to install. I am aware of the leakage problems
this presents so we are taking action by caulking them properly
(we will use the studs to sound isolate the room as best as possible).

The roof is currently 2.48 meters high and has to be lowered because of isolation issues (hear the neighbors and they hear me).

I assume this would make the ratio you suggested unusable, please correct me if I am wrong.

I am aware of the Green glue issue ( apologies for any lack of clarity from my part), I have been to their web site (quite a few times).

And finally, I meant lowering the room 70 MM not 70 CM.

Sincerely,

Useg Diaz-Granados

"The roof is currently 2.48 meters high and has to be lowered because of isolation issues (hear the neighbors and they hear me). "

Simply lower the ceiling may not give you the results you think. First, I would add mass to the existing ceiling before I even considered framing anything else.

Brien, can you explain what you mean by adding mass?

I was thinking of adding 70 mm isolation adding 2 layers of drywall and caulking (sound caulk) the roof properly to limit the sound.

Sincerely,

Useg Diaz-Granados

Useg Diaz-Granados wrote:Brien, can you explain what you mean by adding mass?

I was thinking of adding 70 mm isolation (you are meaning insulation, correct?) adding 2 layers of drywall and caulking (sound caulk) the roof properly to limit the sound.

Sincerely,

Useg Diaz-Granados

What I mean is to add mass/sheetrock directly to the existing overhead ceiling, no air, no insulation, install it to the existing sheetrock ceiling.


What ever sound is coming through to your area, you have to slow it down at the source or as near the source as possible. So while you want to add your new ceiling with mass to your new framing, basically you have an existing coupled double sided (upper floor/ceiling) assembly that is your overhead ceiling, so you want to add mass/sheetrock to that ceiling to stop sound as your first line or attack.

Then you develop your air space, frame and install new sheetrock on the new ceiling in your newly framed room.

Thank you for the clarification Brien.

A problem is that the ceiling contains massive steel beams. We are not able drill into it.

Another problem is the air duct. The Air duct gives us only a total of 96 mm to play with including the drywall.
Adding more drywall would mean a reduction of that space.

I have a question Brien. How about using dense 20 mm thick 155 kg per cubic meter isolation on the top layer of
the suspended ceiling and then placing a layer of 4mm MDF board along with 45 mm insulation (yes i meant insulation ) before installing the 2 layers of drywall?

Could that do the trick?

Sincerely,

Useg Diaz-Granados

Stuart: According to this http://forum.studiotips.com/viewtopic.php?t=684
Louden’s ratios do not take the non-Axial modes into account. I other words his room ratios can be inaccurate.
An accurate calculator (or competent) Acoustician should take into account Axial, Tangential and Oblique modes.

I am not claiming that I yet understand all things but common sense dictates that one

a) Uses a calculator that takes this dimension into consideration and
b) Measure the room in order to make proper adjustments.

The calculator I used takes the non-Axial modes into account.

I have a question Stuart; do you have any I empirical evidence that you can present to contradict these statements, if you do I would love to know.

Sincerely,

Useg Diaz-Granados

As long as you have a rectangular and not a square, it may be as good as it gets, especially if you need all the room you can get.

Louden’s ratios do not take the non-Axial modes into account.

That's not correct. Louden's ratios actually do take into account all three types.

You seem to be misunderstanding what Eric wrote there. Let me quote it here, with some parts left out and some emphasis, to make it clear:

"When studying lots of Louden's room ratios, ... one will notice that without the NON-Axial modes ... those ... ratios should be rejected resulting from an UGLY looking distribution."

Eric does NOT say that Louden didn't consider tangentials and obliques! On the contrary, he said (correctly) that if you REMOVE those considerations from Louden's ratios, and ONLY consider axials, then his ratios look pretty bad. They only work well BECAUSE Louden did indeed consider axials, tangentials and obliques.

It says the exact opposite of what you think it says.

In other words, if you take a Louden ratio and IGNORE the non-axial modes, then that Louden ratio will look really bad. But if you take the full context, with all three types of modes, then Louden's ratios make sense.


That was the precise purpose of Eric's post: to point out that you cannot ignore non-axial modes, sine they are very important to overall room response. He was making that point if you only consider axial modes, you could end up with a ratio that looks just fine but will actually turn out to be terrible, since tangentials and obliques play a large part too.

In any event, I ALWAYS consider all three types of modes, and I ONLY use calculators that do the same.

So I don't need empirical evidence to "prove" my point that Louden #1 is way better than what you had originally: I have all the evidence I need from several calculators that show this to be the case. If your calculator is not showing that Louden #1 ( 1 : 1.4 : 1.9 ) is way better than your original ratio ( 1 : 1.43 : 2.28 ), then there is something drastically wrong with your calculator!

Did you look at the Bonello diagram for those two ratios for example? Louden #1 is smooth, while your original is all over the place. In fact, if you check on that very same table that you linked to, done by Eric, you'll see that Louden #1 is number 5 on the list, while the one you had originally is way down at number 18.

Or plot them both on Eric's "Green Island Diagram", and see where they end up...

The calculator I used takes the non-Axial modes into account.

So do all of the ones I use. So either yours is flawed, or you are not reading it right.



- Stuart -

I stand corrected Stuart!

Thank you for your insight. Which calculator do you use by the way?
Do you have a link to a calculator that suggests room adjustments (like the ones you did) based on the length, W and height?
Made a mistake on how wide the room is 2.17 meters not 2.017

Here is the info I got from Bob Gold's mode calculator:

Computed Information:
Room Dimensions: Length=4.59 m, Width=2.17 m, Height=2.89 m
Room Ratio: 1 : 1.33 : 2.12
R. Walker BBC 1996:
- 1.1w / h < l / h < ((4.5w / h) - 4): Fail
- l < 3h & w < 3h: Pass
- no integer multiple within 5%: Pass
Nearest Known Ratio:
- "10) M. M. Louden: 1971: 6th best ratio" 1 : 1.4 : 2.1
RT60 (IEC/AEC N 12-A standard): 185 ms
- ±50ms from 200Hz to 3.5kHz = 135 to 235ms
- ±100ms above 3.5kHz = 85 to 285ms
- <+300ms at 63hz = 485ms
- 300<RT60<600ms
RT60 (ITU/EBU Control Room Recommended): 163 ms
- ±50ms from 200Hz to 4kHz = 113 to 213ms
- <+300ms at 63hz = 463ms
- 200<RT60<400ms
Absorbtion to achieve ITU RT60: 304 sabins
Volume: 28 m^3
Surface Area Total: 56 m^2
Surface Area Floor: 9 m^2
Surface Area Ceiling+Floor: 18 m^2
Surface Area Front Wall: 6 m^2
Surface Area Front and Rear Wall: 12 m^2
Surface Area Left Wall: 13 m^2
Surface Area Left and Right Wall: 26 m^2
Surface Area 4 Walls: 38 m^2
Surface Area 4 Walls + floor: 47 m^2
(sabins - front wall - carpet) / Left+Right+Rear wall: 41 %
(sabins - front wall) / Left+Right+Rear wall: 69 %
Schroeder Fc: 142hz
Frequency Regions:
- No modal boost: 1hz to 37hz
- Room Modes dominate: 37hz to 142hz
- Diffraction and Diffusion dominate: 142hz to 568hz
- Specular reflections and ray accoustics prevail: 568hz to 20000hz
Count (37.4-254hz) : Axials=13, Tangentials=54, Obliques=72
Count (37.4-100hz) : Axials=4, Tangentials=4, Obliques=0
Critical Distance (direct = reverberant field): 3.40m



Freq % Wavelength, 1/2, 1/4 p,q,r Mode Group Weighting
37.4 hz 9.21 : 4.6 : 2.3 (1,0,0 Axial) Start iso, End iso
59.6 hz 37.2% 5.78 : 2.89 : 1.44 (0,0,1 Axial) Start iso, End iso
70.4 hz 15.3% 4.89 : 2.45 : 1.22 (1,0,1 Tangential) Start iso
74.9 hz 6% 4.6 : 2.3 : 1.15 (2,0,0 Axial)
79.4 hz 5.6% 4.34 : 2.17 : 1.08 (0,1,0 Axial)
87.7 hz 9.4% 3.93 : 1.96 : 0.98 (1,1,0 Tangential)
95.7 hz 8.3% 3.6 : 1.8 : 0.9 (2,0,1 Tangential)
99.2 hz 3.5% 3.47 : 1.74 : 0.87 (0,1,1 Tangential)
106.1 hz 6.5% 3.25 : 1.62 : 0.81 (1,1,1 Oblique)
109.1 hz 2.7% 3.16 : 1.58 : 0.79 (2,1,0 Tangential)
112.3 hz 2.8% 3.07 : 1.53 : 0.77 (3,0,0 Axial)
119.2 hz 5.7% 2.89 : 1.44 : 0.72 (0,0,2 Axial)
124.3 hz 4.1% 2.77 : 1.39 : 0.69 (2,1,1 Oblique)
124.9 hz 0.4% 2.76 : 1.38 : 0.69 (1,0,2 Tangential)
127.1 hz 1.7% 2.71 : 1.35 : 0.68 (3,0,1 Tangential) Near
137.5 hz 7.5% 2.5 : 1.25 : 0.63 (3,1,0 Tangential)
140.7 hz 2.2% 2.45 : 1.22 : 0.61 (2,0,2 Tangential)
143.2 hz 1.7% 2.41 : 1.2 : 0.6 (0,1,2 Tangential)
148.0 hz 3.2% 2.33 : 1.16 : 0.58 (1,1,2 Oblique)
149.7 hz 1.1% 2.3 : 1.15 : 0.58 (4,0,0 Axial)
149.9 hz 0.1% 2.3 : 1.15 : 0.57 (3,1,1 Oblique) Near
158.7 hz 5.5% 2.17 : 1.09 : 0.54 (0,2,0 Axial)
161.2 hz 1.5% 2.14 : 1.07 : 0.53 (4,0,1 Tangential)
161.6 hz 0.2% 2.13 : 1.07 : 0.53 (2,1,2 Oblique)
163.1 hz 0.9% 2.11 : 1.06 : 0.53 (1,2,0 Tangential)
163.8 hz 0.4% 2.1 : 1.05 : 0.53 (3,0,2 Tangential)
169.5 hz 3.3% 2.03 : 1.02 : 0.51 (0,2,1 Tangential)
169.5 hz 0% 2.03 : 1.02 : 0.51 (4,1,0 Tangential)
173.6 hz 2.3% 1.98 : 0.99 : 0.5 (1,2,1 Oblique)
175.5 hz 1% 1.96 : 0.98 : 0.49 (2,2,0 Tangential)
178.8 hz 1.8% 1.93 : 0.96 : 0.48 (0,0,3 Axial)
179.6 hz 0.4% 1.92 : 0.96 : 0.48 (4,1,1 Oblique)
182.0 hz 1.3% 1.89 : 0.95 : 0.47 (3,1,2 Oblique)
182.6 hz 0.3% 1.89 : 0.94 : 0.47 (1,0,3 Tangential)
185.3 hz 1.4% 1.86 : 0.93 : 0.46 (2,2,1 Oblique)
187.2 hz 1% 1.84 : 0.92 : 0.46 (5,0,0 Axial)
191.4 hz 2.1% 1.8 : 0.9 : 0.45 (4,0,2 Tangential)
193.8 hz 1.2% 1.78 : 0.89 : 0.44 (2,0,3 Tangential)
194.4 hz 0.3% 1.77 : 0.89 : 0.44 (3,2,0 Tangential)
195.6 hz 0.6% 1.76 : 0.88 : 0.44 (0,1,3 Tangential)
196.4 hz 0.4% 1.75 : 0.88 : 0.44 (5,0,1 Tangential)
198.5 hz 1% 1.74 : 0.87 : 0.43 (0,2,2 Tangential)
199.1 hz 0.3% 1.73 : 0.86 : 0.43 (1,1,3 Oblique)
202.0 hz 1.4% 1.71 : 0.85 : 0.43 (1,2,2 Oblique)
203.3 hz 0.6% 1.69 : 0.85 : 0.42 (5,1,0 Tangential)
203.4 hz 0% 1.69 : 0.85 : 0.42 (3,2,1 Oblique)
207.2 hz 1.8% 1.66 : 0.83 : 0.42 (4,1,2 Oblique)
209.4 hz 1% 1.64 : 0.82 : 0.41 (2,1,3 Oblique)
211.1 hz 0.8% 1.63 : 0.82 : 0.41 (3,0,3 Tangential)
211.9 hz 0.3% 1.63 : 0.81 : 0.41 (5,1,1 Oblique)
212.1 hz 0% 1.62 : 0.81 : 0.41 (2,2,2 Oblique)
218.2 hz 2.7% 1.58 : 0.79 : 0.39 (4,2,0 Tangential)
221.9 hz 1.6% 1.55 : 0.78 : 0.39 (5,0,2 Tangential)
224.6 hz 1.2% 1.53 : 0.77 : 0.38 (6,0,0 Axial)
225.5 hz 0.3% 1.53 : 0.76 : 0.38 (3,1,3 Oblique)
226.2 hz 0.3% 1.52 : 0.76 : 0.38 (4,2,1 Oblique)
228.1 hz 0.8% 1.51 : 0.75 : 0.38 (3,2,2 Oblique)
232.4 hz 1.8% 1.48 : 0.74 : 0.37 (6,0,1 Tangential)
233.2 hz 0.3% 1.48 : 0.74 : 0.37 (4,0,3 Tangential)
235.7 hz 1% 1.46 : 0.73 : 0.37 (5,1,2 Oblique)
238.1 hz 1% 1.45 : 0.72 : 0.36 (0,3,0 Axial)
238.2 hz 0% 1.45 : 0.72 : 0.36 (6,1,0 Tangential)
238.4 hz 0% 1.44 : 0.72 : 0.36 (0,0,4 Axial)
239.1 hz 0.2% 1.44 : 0.72 : 0.36 (0,2,3 Tangential)
241.0 hz 0.7% 1.43 : 0.71 : 0.36 (1,3,0 Tangential)
241.3 hz 0.1% 1.43 : 0.71 : 0.36 (1,0,4 Tangential)
242.0 hz 0.2% 1.42 : 0.71 : 0.36 (1,2,3 Oblique)
245.4 hz 1.3% 1.4 : 0.7 : 0.35 (0,3,1 Tangential)
245.4 hz 0% 1.4 : 0.7 : 0.35 (5,2,0 Tangential)
245.6 hz 0% 1.4 : 0.7 : 0.35 (6,1,1 Oblique)
246.3 hz 0.2% 1.4 : 0.7 : 0.35 (4,1,3 Oblique)
248.3 hz 0.8% 1.39 : 0.69 : 0.35 (1,3,1 Oblique)
248.6 hz 0.1% 1.39 : 0.69 : 0.35 (4,2,2 Oblique)
249.6 hz 0.4% 1.38 : 0.69 : 0.34 (2,3,0 Tangential)
249.8 hz 0% 1.38 : 0.69 : 0.34 (2,0,4 Tangential)
250.5 hz 0.2% 1.37 : 0.69 : 0.34 (2,2,3 Oblique)
251.2 hz 0.2% 1.37 : 0.69 : 0.34 (0,1,4 Tangential)
252.6 hz 0.5% 1.36 : 0.68 : 0.34 (5,2,1 Oblique)
--------------------------------------------------

Thank you for the clarification Brien.

Sincerely,

Useg Diaz-Granados

Thank you for your insight. Which calculator do you use by the way?

Bob Golds is usually the first one I try, to get a rough idea of what works and what doesn't. FOr more detailed stuff, I use Chris Whealy's. I downloaded that from "somewhere", but I really don't recall where. I still have Modecalc somewhere, I think, but I seldom use it. And a few others that I downloaded from various places, but don't have loaded on this computer. But Bob Golds is good enough for most stuff.

Do you have a link to a calculator that suggests room adjustments (like the ones you did) based on the length, W and height?

Nope! Wish I did! I adjust by hand, after looking at the result, to see what works and what doesn't. Plain old "trial and error" approach.

Made a mistake on how wide the room is 2.17 meters not 2.017

Ooops! Hope you don't make mistakes like that when you start cutting wood!


- Stuart -