#1647161 - 03/17/04 11:52 PM
Empty Room from Scratch
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jbr
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Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Hi Ethan,
After reading your excellent articles, I've recently emptied my small studio/control room to the living room while I revamp the studio acoustically. It's 12x13x7'6". A window is in the 12'wall and a door in the rear corner. I'll situate the mixing area on the 12' wall with the window. The flooring is wood laminate.
What I planned on doing was to build your wood panel absorbers/traps(all 3 spaced according to your articles)on all walls and a combination 1" rigid rockwool on top of 1" Tectum acoustic tile ceiling cloud.
Does this plan sound reasonable? I was just about to go ahead and start building when I happened across your new forum. Because after reading the many posts here I'm a bit confused on the direction to venture. Many terms are being used interchangeably such as panels, absorbers & rigid fibreglass panels as well as placing things across corners or not.
Any suggestions appreciated.
Jim
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#1647162 - 03/18/04 01:45 PM
Re: Empty Room from Scratch
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Ethan Winer
MP Hall of Fame Member
Registered: 06/12/00
Posts: 5470
Loc: New Milford, CT, USA
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Jim,
In a room that size I think you'll do better to just use rigid fiberglass panels, the thicker the better. See my other post in the thread "Room Layout" where I explain this in more depth.
--Ethan
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#1647163 - 03/18/04 10:21 PM
Re: Empty Room from Scratch
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jbr
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Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Thanks for the reply Ethan. And for saving me some time & work...although I really like to build things.
The rigid material I'm going to use is from Roxul. It's a rockwool product. It comes in 3 densities: RXL40 4lb, RXL60 6lb & RXL80 8lb. And from 1"-6" thicknesses. All 3 can be faced with reinforced foil, though it doesn't say pre or post sale. The RXL40 is about $.40/sqft CDN.
Co-efficient specs for 1" thickness:
RXL40 125Hz-0.07 250Hz-0.32 500Hz-0.77
RXL60 125Hz-0.08 250Hz-0.33 500Hz-0.78
RXL80 125Hz-0.11 250Hz-0.31 500Hz-0.82
Co-efficient specs for 2" thickness:
RXL40 125Hz-0.26 250Hz-0.68 500Hz-1.12
RXL60 125Hz-0.32 250Hz-0.81 500Hz-1.06
RXL80 125Hz-0.43 250Hz-0.78 500Hz-0.90
Co-efficient specs for 3" thickness:
RXL40 125Hz-0.63 250Hz-0.95 500Hz-1.14
RXL60 125Hz-0.78 250Hz-0.89 500Hz-1.04
RXL80 125Hz-0.75 250Hz-0.82 500Hz-0.89
Co-efficient specs for 4" thickness:
RXL40 125Hz-1.03 250Hz-1.07 500Hz-1.12
I noticed the specs don't automatically multiply evenly up from 1"-4". Example: RXL40 1" to RXL40 2" gives more than 3 times absorption at 125Hz. I guess putting 2-1" together equals 1-2". And it would be easier to screw to the wall as 1-2" rather than 2-1" pieces. And I believe the co-efficients decrease at higher frequencies for RXL80 8lb because those frequecies reflect easier off the higher density material. Correct?
Q1. What density would you recommend? I'm leaning towards 4" thickness unless otherwise recommended.
Q2. Would the rigid fiberglass panels across the corners improve the absorption with a pegboard panel on the front?
Q3. For the rear wall would you agree to fix 1" rockwool panels over the entire wall then attach wood trim vertically across the rockwool panels for some reflection? Or another idea?
Q4. Would it be advantageous to complete the horizontal wall/ceiling soffit around the entire room the same as the corners or is that overkill?
I'll use the mirror technique to place other rockwool panels on the side walls.
Thanks for your time, Jim
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#1647164 - 03/19/04 02:32 AM
Re: Empty Room from Scratch
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Andre Vare
Senior Member
Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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When I first read this thread I was going to give a quick reply, but then as I started to do calculations I realized that this could become a fantastic room for its size. I will write in another post the design ideas and various links in order to keep the theory and the practice separate.
saving me some time & work...although I really like to build things
The rigid material I'm going to use is from Roxul. It's a rockwool product. It comes in 3 densities: RXL40 4lb, RXL60 6lb & RXL80 8lb.
Fibrex Industrial Board
Q1. What density would you recommend? I'm leaning towards 4" thickness unless otherwise recommended
Q2. Would the rigid fiberglass panels across the corners improve the absorption with a pegboard panel on the front?
Q3. For the rear wall would you agree to fix 1" rockwool panels over the entire wall then attach wood trim vertically across the rockwool panels for some reflection? Or another idea?
Ethan is the expert on small room response, so take anything that he writes that disagrees with me as being correct.
Q4. Would it be advantageous to complete the horizontal wall/ceiling soffit around the entire room the same as the corners or is that overkill?
What is the construction of the current walls? There may be significant low frequency absorption already present.
Good Luck!
Andre
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#1647165 - 03/19/04 03:59 AM
Re: Empty Room from Scratch
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Andre Vare
Senior Member
Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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As I studied this room I realized that with a bit of design it could be a very impressive room acoustically.There are numerous standards evolving for listening rooms. Although the title implies surround sound only, the contents are mostly applicable for stereo also in AESTD1001:
AES TD 1001
With the exception of criteria directly related to room size, both floor area and volume, almost all of the criteria can be met in this room!
The single biggest problem, is the low end, which is common to ALL rooms. This details a summary of several hundred control room acoustics:
Genelec Monitor Survey
and this details the design and testing of a large monitoring room:
Genelec Room Study
The following is a summary of some of the characteristics, both physical and calculated for the subject (this thread's) room.
Height (ft) Width (ft) Length (ft) Wall/Ceiling Length
7.5 12 13.5 81
1 1.6 1.8
Floor Area Surface Volume
Imp 162 706.5 1215
Metric 14.9 65.1 34.0
RT(sub)60 (s) 0.174
Mode Width (Hz) 12.6
Schroeder (Hz) 143
Sabines req'd 341
Mean Absorption 0.483
RT(sub)60 is the calculated reverb time per the referenced standards.
Mode width is the calculated mode bandwidth.
Schroeder is one calculated frequency below which diffuse conditions can not exist. This is not applicable in such a small room with
heavy damping but it is interesting to know.
Sabine is the number of imperial Sabines required using the Sabine reverberation formula.
Mean absorption is the average absorption coefficient using the above figure.
The two biggest challenges are low end absorption and initial reflection levels/times. The following table shows the first ten modes, their relative strengths, and the difference between adjacent modes.
Freq (Hz) Strength Diff (Hz)
41.9 1
47.1 1 5.2
63.0 0.5 15.9
75.3 1 12.3
83.7 1 8.4
86.2 0.5 2.5
88.8 0.5 2.7
94.2 1 5.3
96.0 0.5 1.9
98.2 0.25 2.2
The big problem is the wide gaps between 47.1 and 75.3 Hz. The spacing is greater than the mode width (12.6 Hz), ignoring that the only mode in between is tangential!
The reflection time can be compensated for by careful arrangement of reflective/diffusive surfaces. That is why I suggested the back wall have angled slats to reflect sound away from the listening area.
Putting 2' wide absorbent on all corners still leaves 180 Sabines of absorption to add/ play with.
I hope this is of value to some people.
Edit:
After I posted this, I ralized that I had overlooked one issue, the significance of placemnet of absorbent material. The following is an academic repro on the effects of changng the postition of absorbent material when testing for its absorption. Quite an eye opener!
Moving Baffles
Andre
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#1647166 - 03/19/04 02:20 PM
Re: Empty Room from Scratch
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Ethan Winer
MP Hall of Fame Member
Registered: 06/12/00
Posts: 5470
Loc: New Milford, CT, USA
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Jim,
Andre nailed it. I have nothing to add.
Hey Andre, stick around, okay? 
--Ethan
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#1647167 - 03/19/04 03:00 PM
Re: Empty Room from Scratch
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caseyLA
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Registered: 03/05/04
Posts: 35
Loc: Los Angeles, CA
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Interesting stuff. Could you guys speak more on the idea of angled slats on the back wall?
The reflection time can be compensated for by careful arrangement of reflective/diffusive surfaces. That is why I suggested the back wall have angled slats to reflect sound away from the listening area.
thanks
-casey
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#1647168 - 03/19/04 10:28 PM
Re: Empty Room from Scratch
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jbr
Senior Member
Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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This is just fantastic! And I'm so happy to have started this thread before starting up my table saw. And it is true that I like building things...at the moment I'm renovating our kitchen and drawing plans for a garage addition.
Andre, thanks for the detailed response, specs for my room and additonal links. 
Ethan, thanks for checking this thread.
I'll peruse and digest the additonal info from Andre's links this weekend. In the meantime Andre wanted to know the construction details of the room:
The room is at the rear of a backsplit on the top floor. The window wall(obviously) and one side wall are exterior. The other two are 2x4 wood stud c/w 1/2" drywall without insulation. Ceiling is 1/2" drywall and attic above filled with loose insulation. I recently closed off the closet(steel stud)and opened it in the adjacent room to give the studio symmetry...plus another closet in the bedroom doesn't hurt. The door(hollow core) is in the side wall at the rear(more on this later). As mentioned earlier, the floor is wood laminate(pergo style). Soundproofing is not required.
The doorway at this time swings into the rear wall of the room from side wall with only a doorknob width available behind. Though, it wouldn't be much effort to change the door to swing out into the hall and shrink the opening from 30"-28". I think I'll do that, now that I think about it.
Put it this way, I can & will accomodate for the acoustical advantages.
Andre, good point about the listening position being close to the rear wall for reflections.
What I need to know are the construction details for building a rear wall as you suggested
...especially the angled slat details.
Q1. Since the corners & soffits are taking care of some/most low frequencies, is it really necessary to create a 4" rear wall? Would 2" or 3" suffice?
Q2. When applying fabric over the MF panels, does it matter if the fabric comes into contact with the MF? Does it need to be spaced out from it?
Q3. Is there any benefit to increasing the corner panels to 5" or 6" MF?
Q4. What is Ray tracing and Sabines.
Thanks so much for your time and knowledge,
Jim
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#1647169 - 03/19/04 11:45 PM
Re: Empty Room from Scratch
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Andre Vare
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Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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You are combining two ideas improperly. The idea of using slats is so that the low end will be absorbed while reflecting the highs. AESTD1001 details in table 2 early sound conditions for the listening position. Specifically reflections from 0-15ms as being at least 10dB below the level of the initial sound for frequencies from 1-8Khz. With smaller rooms, including Jim's a large amount of low frequency absorption is required to control standing waves and pressure zone build up. If the the absorption used is wide band, then the room be very (probably too) dead.
Despite 4" of RXL40 being essentially flat down to 125Hz and 0.75 at 100Hz (Ethan:I spoke with the one of the members of the tech department at Roxul and he gave me that value. Apparently they have several tests done at 1/3 octave intervals down to 100Hz. Unfortunately they do not have any testing above 4kHz though), Jim's room modes start at 42 Hz The only only to control that is either with tuned absorbers (calculations and
construction complexity usually beyond the interest of people who read this forum) or
large amounts of lower effective absorption material. Hence the use of the slats in front
of an absorber that absorbs at low frequencies. The slats reflect the highs while lower frequencies are absorbed by material behind, open at the sides of the slats. More on that
in the construction section of this post.
The intended effect is similar to what the slat absorbers in John Sayers'
John Sayers
and Francis Manzella's
Francis Manzella Design
designed studios back walls. The reason for the angled slats is to save on floor space.
This is sort of like the Controlled Image Design (CID) tried by BBC but applied to the rear wall reflections, primarily because of the limitations of the smaller room sizes. The following reports detail the design construction, and analysis of the first CID room. These documents are very technical in content.
BBC RD 1995-03
BBC RD 1995-04
BBC RD 1995-05
At a minimum, if you are considering doing this, read the last report about the results. In a
thumbnail, sound performance is excellent in the defined listening area, and terrible outside of it. This is not surprising considering how all the reflections are directed to the non listening areas of the room.
A previous report, that was researched as part of the preliminary work for CID is:
BBC RD 1994-11
I recommend this document very highly for anyone wanting to understand and apply acoustic treatment beyond "this is what I have, now tell me what to and I'll do it no questions asked." It is sort of like the next step in acoustic treatment after Ethan's documents.
For construction, consider a saw blade, and the shape made by the teeth. Not surprisingly a wave of this pattern in electronics is referred to as a sawtooth wave. Imagine the angled part of the sawtooth as being the slat, and the straight part (square with the other side of blade, or close to square) as being open to the absorbent material behind the slats.
The simplest fist version would be to cut top and bottom pieces with the sawtooth pattern and then attached slats across the angled portions and leave the straight portions open. Open meaning acoustically. You can cover it with fabric etc.
The two variables in this design are the length and angle of the slats. Reflecting frequencies as low as 1kHz (AES TD 1001 table 2) would require surfaces about a foot wide. To avoid potential comb filtering vary the slat width. The angle would depend on the required direction of the reflected wave, hence my reference to ray tracing. A consideration when doing ray tracing
is not to create a concave (composite) surface. A concave surface would focus the reflections at certain point and create phantom sound sources!
At the next level of construction complexity you can cover a portion of the surface behind the ends of the slats. The more that you cover, the more the system will reflect to a lower frequency.
Another option, and this is really getting into construction labour, is cover the slats with polydiffuser (portions of a circle) surfaces. If you consider this type of finish, ray tracing is particularly important to make certain that the diffracted sound isn't directed right back at the listening position!
Will it help in a smaller room? It all depends on the size. More information is needed.
This post may have more information than you are looking for, but I would rather explain something once, and have all the information presented, as opposed presenting summary "do this" and getting wrong assumptions based on my writing.
I hope this helps
Andre
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#1647170 - 03/20/04 11:11 PM
Re: Empty Room from Scratch
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Andre Vare
Senior Member
Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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Andre, thanks for the detailed response, specs for my room and additonal links.
The other two are 2x4 wood stud c/w 1/2" drywall without insulation
I can't say too much about the other walls and ceiling/floor.
Soundproofing is not required
The doorway at this time swings into the rear wall of the room from side wall with only a doorknob width available behind
Assuming that is a 6.5' door, that will reduce the amount of corner absorbers by 13 ft^2. More to play with on the other surfaces.
Put it this way, I can & will accommodate for the acoustical advantages.
Q1. Since the corners & soffits are taking care of some/most low frequencies, is it really necessary to create a 4" rear wall? Would 2" or 3" suffice?
As a side note. if you had more room, this would be a perfect application for Ethan's panel absorbers!
IF you look at analysis of your room, the lowest frequencies are below the flat absorption range of 4" RXL40 in random incidence measurement. In normal incident measurement, the roll of of low end absorption starts about an octave higher! These can be clearly seen looking at figures 1 and 3 in
BBC RD 1992-11
[/quote]Q2. When applying fabric over the MF panels, does it matter if the fabric comes into contact with the MF?
Does it need to be spaced out from it?[/quote]
No, It makes no difference.
Q3. Is there any benefit to increasing the corner panels to 5" or 6" MF?
BBC RD 1994-11
Going into some detail on this point, first of to make clear that we are writing about design, I am referring to having 4" thick RW angled at 45° straddling across wall/wall and wall/ceilings. If you cut the long sides of the RW so that the sides are flush against the surfaces, this would leave a triangular cavity behind the RW. The
length of the base of the cavity (the surface of the RW) would be around 19" and the depth of cavity (square line from the middle of the RW to the corner) of around 9.5". The area of this triangle would be around 90"^2 or 0.625'^2 . According to the spacing idea, you can almost get the same results by leaving the space empty.
ALL modes peak in corners, so that is where absorption per unit area will be most effective.
I know of no formal or detailed studies of this effect. There is no doubt it exists, but how close is almost? The question becomes one of cost. RXL40 costs a little under $3/ft^3. We are talking about 74 feet of corner treatment, so (74x0.625) about 50'^3. This would cost around $150. Without doing all the detailed cost calculations, in terms of the overall material costs, this is not a major % increase. OPINION, if I were building a similar room to yours, in consideration of the capability of reaching world class standards in acoustic performance, I would spend the money and fill the cavity.
Oops, your question was partially filling the cavity by increasing the thickness of RW, not if to fill it. Take everything above into account. At a minimum it will not hurt acoustically.
Q4. What is Ray tracing and Sabines
Sabines are the units that sound absorption are measured in. A Sabine is the amount of absorption that a square open window of unit (explanation follows) size would absorb. There are two types Sabines that I am aware of: metric and imperial. Metric unit size is a meter square, and imperial is a foot square.
What I need to know are the construction details for building a rear wall as you suggested
...especially the angled slat details.
Important! Especially in this case because of the potential to have a world class 1200 ft^3 room. Do not take things written, especially by me, to heart and start construction immediately. First of all, I make typing misstakes,
and some I miss words and clearly not write good. Also despite all my knowledge I will forget to mention things and sometimes will overlook obvious things. Wait at least one week once you are satisfied with your design for people to review the data and posts in order to correct them.
These types of errors are not unique to this type of forum. In another website that Ethan and post on, had a fairly lengthy discussion about the error in an equation presented in a well known acoustics text. After many posts, it turned out that that particular error had been in the last 3 editions of that text, and that the error came
from another well known sound text. The error is obvious to anyone familiar with mathematical dimensional analysis, but the error has spread through many on line acoustics calculators! One of the RD papers that BBS just released on the net has at one error in the text, possibly two detected byy an astute reader. Some the
testing data is incomplete and many people have misinterpreted part of the results. I have a serious question on the same document with regards to two conclusions in the text. I have posted one, and will post the second one soon.
When referencing other information try to be as detailed as possible and give links if possible. Sometimes the information is not complete, so open to misinterpretation , and sometimes contains outright lies to the uninformed, but obvious to anyone familiar with the field. Have a look at the bottom of page 3 of:
Roxul AFB
Does AFB perform acoustically better than fiberglass? I am not trying to be smart, but trying to make a point about what is written and understanding it completely. For others reading this thread, the reason for the flaw was already
presented by Jim in an earlier post!
Good luck!
Andre
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#1647171 - 03/21/04 02:57 PM
Re: Empty Room from Scratch
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jbr
Senior Member
Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Regarding soundproofing. I live in a hamlet outside of London on a fairly large lot with a horse ranch behind...very peaceful.
It's true that I lose one corner for LF absorbtion because of the door. And it is at the back of the room. And changing the door swing doesn't mean reducing the size of the door. I thought because there is only a door trim width(2.25")available behind the door, I would reduce the door size and therefore increase that distance so you don't see the side of the 4"MF when the door is open...aesthetically speaking really.
I agree, $150 for the corners is not a large amount to spend for the results. I was under the impression that the space in the corner was to be left empty, but I will gladly fill them if the outcome is beneficial.
Thanks again,
Jim
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#1647172 - 03/24/04 02:50 AM
Re: Empty Room from Scratch
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Andre Vare
Senior Member
Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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#1647173 - 03/24/04 10:17 PM
Re: Empty Room from Scratch
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jbr
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Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Yes, the room is general like the bedroom plan from the SAE site. The window for my room is in the front wall in front of the desk.
Very interesting idea for the ceiling. I never thought of that. I can do that, though it would be quite a chore, especially working with the loose insulation in the attic.
I'm not certain I want to decrease the space by 8"MF on the rear wall plus angled slats(for reasons later mentioned)...that would work out to about 12" when complete.
Since I record solo most often, all instrumentation is done in the said room. My main instrument is the drums and knowing in advance the logistics of recording drums alone, I bought Roland V-drums which allows for direct recording(ie.no mics...brilliant). That is why applying 8"MF on the rear wall might not be practical space-wise. Also taking up space are a couple of synths(88 & 61). Though I'm thinking about incorporating one of the synths into the desk. When recording bass and electric guitar, friends use guitar gear with direct outs as well. The only instrumentation to mic are acoustic guitar and vox. So I will need to talk about gobos sometime.
What do you think of these ideas?
Idea 1: Use the same principle with the rear wall as the ceiling.
Idea 2: Let's say I could take over some of the space behind the studio...you know, move the rear wall back a bit. At the very most I could go 16". Would that improve the modes results among other things and would it be a big improvement acoustically? The dimensions would then be 12'wide x ?length x 7'6".
Q1. Regarding the ceiling idea; would that design involve filling the joists with 4"MF with an air gap, then covering the entire ceiling with fabric?
Q2. The wedge pattern you suggest for the corner absorbers would be how deep? 1" suffice? And this is cut into the 4"MF, not added to, correct?
My computer will not open the Moving Baffles wordpad document. Could you save it as a text document and email me the file?
I'm not certain as to the stats to observe regarding the Roxul AFB document. If I posted the reasons earlier, I am embarrassingly unaware. I was posting specs for RXL40, not AFB. Please point the way.
The link for BBC RD 1991-7 does not link for me.
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#1647174 - 03/25/04 02:37 AM
Re: Empty Room from Scratch
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Andre Vare
Senior Member
Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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Yes, the room is general like the bedroom plan from the SAE site. The window for my room is in the front wall in front of the desk.
Are you planing on using general principles from AES TD 1001 for the layout of speakers and listening position?
The salient points being (I'm going to try and list this, I hope it comes out okay):
- speakers acoustical centre 1.2m (4') high
- speakers and main listening position forming an equilateral triangle
In addition the speakers being approximately 0.7 of the length of the wall apart. Also, are you considering soffit mounting the speakers?
As I am perceiving it right now, I see the "sweet spot" as being about 0.75 x 1m.
Very interesting idea for the ceiling. I never thought of that. I can do that, though it would be quite a chore, especially working with the loose insulation in the attic.
I'm not certain I want to decrease the space by 8"MF on the rear wall plus angled slats(for reasons later mentioned)...that would work out to about 12" when complete.
Good info to have. In case you were wondering what the significance is to the design, it is that we know NOT to to aim the reflections toward the centre of the room. That might have a choice made when trying to get the 15ms delay of the first reflections.
Idea 1: Use the same principle with the rear wall as the ceiling.
Idea 2: Let's say I could take over some of the space behind the studio...you know, move the rear wall back a bit. At the very most I could go 16". Would that improve the modes results among other things and would it be a big improvement acoustically? The dimensions would then be 12'wide x ?length x 7'6".
Q1. Regarding the ceiling idea; would that design involve filling the joists with 4"MF with an air gap, then covering the entire ceiling with fabric?
Q2. The wedge pattern you suggest for the corner absorbers would be how deep? 1" suffice? And this is cut into the 4"MF, not added to, correct?
I was thinking more about 2" deep with an angle of 30° between the sides, but that is just an off the top the head figure. I'll do some calculations on that.
Again, 100% correct! The pattern would be cut into the facing layer of 4" MF.
My computer will not open the Moving Baffles wordpad document. Could you save it as a text document and email me the file?
I'm not certain as to the stats to observe regarding the Roxul AFB document. If I posted the reasons earlier, I am embarrassingly unaware. I was posting specs for RXL40, not AFB. Please point the way.
The data that you initially posted about RXL material shows this pattern of reduced low end absorption as density is reduced.
Without getting too technical, in practical terms the absorption of porous materials is dependent on the location of the material in terms of where there is air molecule velocity, and the density of the material. Fiberglass and mineral wool in similar conditions have similar absorption properties. You already posted the data on the RXL material in various densities and thicknesses. This effect of density is visible looking at the 1.6 PCF and 3 PCF 3" thick material at
Knauf
The fiberglass in the Roxul is half the density of the lightest on the Knauf page! The effect of the lighter density reduced sound absorption at low frequencies is even greater!
The link for BBC RD 1991-7 does not link for me.
I sent you email the plans for Joe Egan's studio and mentioned there are a couple of design points related to this design. The rear wall is over 10' behind the listening position. The corners, have bass absorbers, same as this design. The middle of the rear wall has diffusers to spread angle of the reflections and reduce the level
of the initial reflections that go back to the listening position.
The difference in the design that we are working on is due to the size difference. The smaller room requires more absorption, as a percent of total area. That is why this design does not have slats in front of the bass absorbers, meaning the MW in the corners. Because there is not enough distance from the listening position
to the rear wall instead of using diffusers, we are using the angled slats to redirect the sound away from the listening position, at least for frequencies above 1kHz.
John Sayers website was up last night. It might be up now. I couldn't get on but I have always had problems getting on there regularly. When you get on there, look at the studios in the studios under construction section. Several excellent ideas and details on how the studios were built. The wall unit are details construction of several absorbers. Enjoy!
You wrote in the angled slat thread that you are starting to get a really good feeling this. After these 2 posts, so am I! We are communicating clearly and working more towards the details as opposed to the general concepts.
Till the next post;
Andre
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#1647175 - 03/25/04 11:03 PM
Re: Empty Room from Scratch
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jbr
Senior Member
Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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It's all in the details for sure.
The window(slider) is 5'6 x 3'. It's pretty much centered in the wall horizontally. The bottom is 3'5" off the floor. The wall as far as I know is 1/2" drywall, 2x4 wood stud c/w insulation, vinyl siding, earth's atmosphere.
I've set up the gear downstairs as it will appear in the studio more or less. I use HR824's 48" apart and the tweeter at 48" above the floor. They are set on custom-made stands made from MDF & filled with sand(quite heavy to move around as you can imagine). And are 12" off the front wall. My position is equilateral and about 5' off the front wall which just happens to work out to the 38% off the front wall mentioned by Ethan in another thread. Soffit mounting doesn't interest me at all.
I'm not sure about the reversed ceiling idea. Not the outcome, but the amount of work and reno logistics involved. The reversed rear wall does appeal to me though as mentioned in the Angled Slats thread.
And now for something completely different...
When I use the mode calculator from Ethan's site I get different results than your previous post. It must calculate differently than the one you're using.
Room Mode Calculator - Copyright (c) 2003 RealTraps.com - All rights reserved.
Length: 13 Width: 12 Height: 7.5
43.46 47.08 75.33
86.92 94.17 150.67
130.38 141.25 226.00
173.85 188.33 301.33
217.31 235.42 376.67
260.77 282.50 452.00
304.23 329.58 527.33
347.69 376.67 602.67
391.15 423.75 678.00
434.62 470.83 753.33
This ratio (HWL): 1 : 1.60 : 1.73
This volume: 1170
Until next time...
Jim
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#1647176 - 03/26/04 07:15 AM
Re: Empty Room from Scratch
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Andre Vare
Senior Member
Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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The window(slider) is 5'6 x 3'. It's pretty much centered in the wall horizontally. The bottom is 3'5" off the floor.
The wall as far as I know is 1/2" drywall, 2x4 wood stud c/w insulation, vinyl siding, earth's atmosphere.
I've set up the gear downstairs as it will appear in the studio more or less. I use HR824's 48" apart and the tweeter at 48" above the floor.
I am somewhat concerned about that spacing of the speakers though. With them being against the 12' wall, it divides it into three equal sections. This may cause the speakers to sit in pressure nulls, thus causing a dip in response at that
frequency. If you decide to build some supporting furniture specific to the room, try moving the speakers in and out a bit and listen to the low midrange response, or also measure the response.
They are set on custom-made stands made from MDF & filled with sand(quite heavy to move around as you can imagine).
the speakers to tighten the bass response. You can see some current photos of it at:
Galaxy Studios
The design of the original control room is visible at the website of Eastlake Audio
Eastlake Audio
Galaxy Studios is one of the best in the world, and Eastlake is one of the best designers and builders of studios. Even with some of the best builders and designers, final tweaking of the room was still needed after listening tests. And yes the E. Desart mentioned on the Galaxy page is the same as did the research on absorber location in testing.
And are 12" off the front wall. My position is equilateral and about 5' off the front wall which just happens to work out to the 38% off the front wall mentioned by Ethan in another thread. Soffit mounting doesn't interest me at all.
I'm not sure about the reversed ceiling idea. Not the outcome, but the amount of work and reno logistics involved.
The reversed rear wall does appeal to me though as mentioned in the Angled Slats thread.
When I use the mode calculator from Ethan's site I get different results than your previous post. It must calculate differently than the one you're using.
surfaces. The relative strength of the modes are 1, 0.5, and 0.25 respectively. If you compare the results from my spreadsheet with the ones from Ethan's program you will see that the axial modes are identical frequency. The axial modes are the ones with two 0s in the mode column (eg. 1,0,0 and 0,2,0) and 1s in the relative strength column.
Because of the different locations of the reflective points and the angles of the waves as they develop, the modes can not be simply added together to get a composite room response. The results vary quite widely. Figs 2 and 8 in Ethan's
FAQ show this quite clearly
FAQ
Why didn't Ethan include this data in his program? My first guess, and Ethan please orrect me if I am wrong, is a decision based on the detail of information to present and how easily it can be used by people relatively untrained in
acoustics. There is also a question of how much precision to use. Both Ethan and I used the 1130 f/s as the speed of sound. Actually at 21°C the speed is closer to 1134 f/s. If a mode is 98 instead 99 Hz will this have a practical impact?
If you want some more detailed information on this have a look at:
BBC RD 1992-08
BBC RD 1992-09
The two reports are inter-related, and heavy at times with the mathematics. Look at the figures for a thumbnail of the important items. I suggest that at least you read the introduction of the first report. It is mostly in understandable english and provides a good summary of the current state of low frequency response in rooms. The appendix of the first report also provides a bit of an explanation of the lowest frequency where diffusion can exist in a room, and the Shroeder calculation. The Schroeder calculation is the one I use in my spreadsheet.
If you look at the measurement results on studios in the second report, you will see how the room size affects the low end response.
A thought ran through my mind as I read your last post. If you have not heard what a room designed to these criteria sounds like, make a trip to Fanshawe. They should have at least one control room designed to these specs.
Andre
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#1647177 - 03/26/04 09:53 PM
Re: Empty Room from Scratch
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jbr
Senior Member
Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Andre, thanks for your continued support and knowledge. Speaking of which, are you an acoustician? Your profile only mentions music as your occupation.
Window Info:
The horizontal slider is a 2 sash design 50% ventilation. The vinyl sash is 1 1/2" thick. The window panes are 3/4" outside dimensions. Don't know the thickness of the glass itself. They are only a few years old. Why is this info necessary? Early reflection and mode info possibly? And probably resonant frequency?
The HR824's cannot be moved closer together because there are 2x21" CRT's on the work surface between them. Eventually I will have 2x19" LCD's, which will decrease that distance very little. Center of woofer to the other is 54". The 48" is from inside edge to inside edge. The HR824's have switches on the back which adjusts LF according to their position in the room. Are you familiar with the HR824 specs?
The bass response is pretty tight when sitting directly in front of them, but they have never been listened to in a proper acoustical environment, nor on different stands. The room from whence they came was all over the place frequency wise. So I'm looking forward to the finished room.
The equilateral triangle I referenced was horizontally(lateral) in plan view. The 48" is from woofer to woofer to each ear. I am unaware of height being a concern with the triangle.
Without utilizing the reversed ceiling idea how many Sabines of absorption still need to be added? Taking in to account the 4"MF in corners and wall/ceiling areas and back wall.
For the ceiling I'm thinking 1"MF fixed to 1x2 strips over the entire ceiling and possibly thicker over the mix position.
Also looking at Tectum ceiling tiles for areas other than over the mix position. Ideas?
Specs for 1"x24"x24" Lay-in Tectum ceiling tile:
125Hz .40
250Hz .43
500Hz .35
1000Hz .48
2000Hz .60
4000Hz .93
Specs for 2"x24"x24" Lay-in Tectum ceiling tile:
125Hz .48
250Hz .46
500Hz .36
1000Hz .55
2000Hz .74
4000Hz .79
Thanks for clarifying the mode calculator results.
Jim
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#1647178 - 03/28/04 03:33 AM
Re: Empty Room from Scratch
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Andre Vare
Senior Member
Registered: 03/13/04
Posts: 125
Loc: Hamilton, ON Canada
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First off cleaning up some loose ends...
As I am perceiving it right now, I see the "sweet spot" as being about 0.75 x 1m.
quote:
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Idea 2: Let's say I could take over some of the space behind the studio...you know, move the rear wall back a bit. At the very most I could go 16". Would that improve the modes results among other things and would it be a big improvement acoustically? The dimensions would then be 12'wide x ?length x 7'6".
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Sounds interesting. I will play with some dimensions in the mode calculator programs
quote:
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My computer will not open the Moving Baffles wordpad document. Could you save it as a text document and email me the file?
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I will see what I can do. I have never tried to do that in Word.
Speaking of which, are you an acoustician? Your profile only mentions music as your occupation.
What is your background?
Window Info:
The horizontal slider is a 2 sash design 50% ventilation. The vinyl sash is 1 1/2" thick. The window panes are 3/4" outside dimensions. Don't know the thickness of the glass itself. They are only a few years old. Why is this info necessary? Early reflection and mode info possibly? And probably resonant frequency?
The HR824's cannot be moved closer together because there are 2x21" CRT's on the work surface between them. Eventually I will have 2x19" LCD's, which will decrease that distance very little. Center of woofer to the other is 54". The 48" is from inside edge to inside edge. The HR824's have switches on the back which adjusts LF according to their position in the room. Are you familiar with the HR824 specs?
The HR 824s are basically variations on the Genelec model 1031s with the not lately used concept of a passive radiator. Passive radiators were popular in the sixties and early seventies.
The bass response is pretty tight when sitting directly in front of them, but they have never been listened to in a proper acoustical environment, nor on different stands. The room from whence they came was all over the place frequency wise. So I'm looking forward to the finished room.
The equilateral triangle I referenced was horizontally(lateral) in plan view. The 48" is from woofer to woofer to each ear. I am unaware of height being a concern with the triangle.
Without utilizing the reversed ceiling idea how many Sabines of absorption still need to be added? Taking in to account the 4"MF in corners and wall/ceiling areas and back wall.
Placing the MF in the corners (ceiling wall is still a corner acoustically) improves the effective low frequency absorption. The room needs about 340 Sabines of absorption (detailed in following post). doing all the corners with 2' wide MF will give about 160 Sabines, assuming absorption coefficient of 1.
For the ceiling I'm thinking 1"MF fixed to 1x2 strips over the entire ceiling and possibly thicker over the mix position.
Also looking at Tectum ceiling tiles for areas other than over the mix position. Ideas?
Specs for 1"x24"x24" Lay-in Tectum ceiling tile:
125Hz .40
250
Hz .43
500Hz .35
1000Hz .48
2000Hz .60
4000Hz .93
Specs for 2"x24"x24" Lay-in Tectum ceiling tile:
125Hz .48
250Hz .46
500Hz .36
1000Hz .55
2000Hz .74
4000Hz .79
Ideas? Yes 4" MW covered with a pretty fabric. This provides flat absorption down to 125 Hz so that additional absorption to flatten the reverb time is not required. That may seem like reducing the height significantly, but don't forget that 7' ceilings are quite common new multistory buildings, and this would make the height 7'2" under the MW. This is an idea, not the only possibility.
Thanks for clarifying the mode calculator results.
Your welcome.
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#1647179 - 03/28/04 10:10 PM
Re: Empty Room from Scratch
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jbr
Senior Member
Registered: 07/23/01
Posts: 201
Loc: London, ON, Canada
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Andre wrote: "As I am getting into the ray analysis I think we can make it 1.2 m wide (2.5' by 4')"
Good to see the sweet spot is increasing.
Andre wrote: "Depending on the vibration of the walls, this may improve the IM distortion of the sound."
What is IM an acronym for?
Information overload with regards to monitor placement? 
Earlier you wrote:"Some detail clarification please. An equilateral triangle would have a height (base to top) of around 3.5' and what you described is about 4'. What are you considering as the location of the listening position? The edge of the console? 1.5' behind the edge? 6" in front of the edge? Something else?
I forgot to mention before that I consider my head locale as the listening position. I've learned monitor placement refers to 2 separate entities: 1.The vertical placement(height)from the floor, and 2.The horizontal placement which forms a equilateral triangle from your head at one point and monitors at the other two. That's why I wrote:"The equilateral triangle I referenced was horizontally(lateral) in plan view. The 48" is from woofer to woofer to each ear. I am unaware of height being a concern with the triangle." So I guess I need some clarification from you: What do you mean when you stated "An equilateral triangle would have a height (base to top) of around 3.5' and what you described is about 4'."?
Boy, that was a mouthful!
Information overload regarding "...how many Sabines of absorption still need to be added? That's probably true.
Andre wrote:"Ideas? Yes 4" MW covered with a pretty fabric. This provides flat absorption down to 125 Hz so that additional absorption to flatten the reverb time is not required. That may seem like reducing the height significantly, but don't forget that 7' ceilings are quite common new multistory buildings, and this would make the height 7'2" under the MW. This is an idea, not the only possibility."
Is the 4"MF mentioned above to be placed over the mix position only? Would it help any if 4"MF was placed above the drywall ceiling?
I've noticed "A" mountings in the Tectum brochure, but they relate to wall panels only.
My background is 3rd generation upholsterer and retail space planning/design. My musical background goes back to grade 7 with my first drum kit. Now I enjoy writing & recording music as a hobby, though I sometimes yearn to play live again.
I received the "Moving Baffles" file. Thanks. All the text shows up, but graphics 2,4,5 do not.
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