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naethoven
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16th September 2008
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Angles of Control Room walls

I've been working on a design for my studio, and I've come to this point. The original thread was called "How Much Space Between the Leaves" and has some really good info in it. Feel free to reply there (or here if you wish).

My questions at this point are about the angles of the CR walls.

1) Ideally, does the "real" room need to be a true rectangle with 90% corners, to the exact measurements of the room ratio, and then the faux walls that you see be at different angles to reflect HF to the back of the room, (LF being subject to the "real" room)

OR...

Can the "real" room BE the angled walls of the CR?

2) When I do build a splayed "real" wall, how do I correctly match the ratio I have chosen to use, as I would with a rectangular room?

3) What are the angles for the ceiling, front, and side walls (at each change all the way back) for the CR?

Is there anything else I need to be researching about CR construction?

Thanks guys.
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Without dimensions it's impossible to comment too deeply. Generally, small rooms do better without angles because the angles just make the room even smaller.

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17th September 2008
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Thanks so much Ethan. The interior dimensions of the CR (rectangularly) would be 9.078'H x 12.7'W x 17.25'L. (Louden #1!!) Theoretically, I'd shoot for angling the walls in a way that would keep the room volume the same, just smaller at the front and wider at the rear. I am building from scratch and the only existing walls are the main perimeter.
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Quote:
Originally Posted by naethoven View Post
I've been working on a design for my studio, and I've come to this point. The original thread was called "How Much Space Between the Leaves" and has some really good info in it. Feel free to reply there (or here if you wish).

My questions at this point are about the angles of the CR walls.

1) Ideally, does the "real" room need to be a true rectangle with 90% corners, to the exact measurements of the room ratio, and then the faux walls that you see be at different angles to reflect HF to the back of the room, (LF being subject to the "real" room)

OR...

Can the "real" room BE the angled walls of the CR?

2) When I do build a splayed "real" wall, how do I correctly match the ratio I have chosen to use, as I would with a rectangular room?

3) What are the angles for the ceiling, front, and side walls (at each change all the way back) for the CR?

Is there anything else I need to be researching about CR construction?

Thanks guys.
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Have you looked at John Sayers' forum? That might be a really good resource for you.

Frank
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17th September 2008
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Yeah, just started checkin that out the other day.
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18th September 2008
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Anybody have any info to offer??

Ethan, can you do anything with those dimensions?
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18th September 2008
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The fact is that you don't really *need* to splay the walls in a room that small. If you want to, the plan you have looks fine, though if you're building from scratch I'd involved a professional to design the room for you. That's why I turned you in the direction of John Sayers' web forum. Are you planning on soffit mounting the mains? If that's the case then you *definitely* need to get a professional design guy involved.

From a treatment standpoint all the usual things apply: trapping every available corner and the back wall, plus hitting your reflection points. Was there something specific you wanted to know that we're leaving out?

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18th September 2008
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Ethan, can you do anything with those dimensions?
I'd just leave it with no angles. Slight angles do very little, and large angles eat up a lot of real estate.

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18th September 2008
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In response to Weasel, "Was there something specific that you wanted to know that we're leaving out?"


My main issue is this...My 2 main rooms (CR and Live) tend to be kind of long and skinny. In an effort to avoid that (for aesthetics and I think better acoustics???) I am trying to angle the wall between them equally, so I maintain the same volume, just shifted, smaller at the front, wider at the back. I drew a quick-n-dirty pic to explain. It would make the Live room a little more spacious (for people, not acoustics), and I figure it would probably sound better not being as long and skinny, and being out of parallel. I would shoot for an angle of atleast 1ft for every 10 to 20ft which I think is what Rod Gervais and Everest recommend.

I figured if all the above was true, then the CR side of the wall would be subject to that angle, which might be a good thing according to what I've read about angled CR walls sending reflections to the rear of the room. I am under the impression that this requires less absorbtion on the front end of the room, and therefore retains more HF energy. (Which I think I would prefer.)

The reason I'm so hung up on the angle the control room needs for proper reflections is because that angle in my specific case will also be the angle of the main wall. After I know the angle I can proceed with the rest of the design.

Am I making sense?
Thanks for your help as I wade through the learning process.

Last edited by naethoven; 18th September 2008 at 05:19 PM.. Reason: clarifying my reponse
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After I know the angle I can proceed with the rest of the design.
I am waiting for the complete sketchup file, including the bathroom location and dimensions.

Andre
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18th September 2008
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Andre,
Thanks for chiming in! This is where I'm stuck. I can't figure out how to make the complete sketchup file because the way I see it, everything kind of hinges on the angle(s) of that main wall.

My desire is to make the CR as perfect as I can for my room size and budget, and design everything else around that. When I try to draw a layout, I can't get anywhere because I don't know what the CR front wall angles need to be. If I know those, I measure out 10 1/2" for my inner wall thickness, and measure in from the perimeter of the building 5 3/4" for my outer wall thickness. The space left between is what I have for live/booth space. If I was just going to leave it as a rectangle, or if I knew the exact angles to make the wall, I could send you a sketchup file easily. I'm in the middle of drawing it right now but can't get around this bump.


Going crazy,
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18th September 2008
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Originally Posted by naethoven View Post
Andre,
Thanks for chiming in! This is where I'm stuck. I can't figure out how to make the complete sketchup file because the way I see it, everything kind of hinges on the angle(s) of that main wall.
I THINK you are referring to the front wall that flush with the speakers. Correct?

If so thirty degrees to aim the speakers at the listening position.

Andre
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18th September 2008
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Well, the primary reason for splayed control room walls given your layout constraints is as much about practicality as it is acoustics - it's the only way to create both a reflection-free zone in the control room (essential for monitoring) as well as good sight-lines through to the studio proper (helpful for producer/engineer-musician communication.)

If you can do without a control room window, then yes, the most straightforward way to ensure your CR will perform is to make it rectangular with good proportions and simply treat the first reflection points with absorption (not forgetting speaker/listener placement.)

I should note that in the drawings I previously posted pertaining to your room, the angle of splay for each side is 12 degrees. The thinking is this;

a) because of the relatively short distance to the side boundaries a higher degree of splay may be necessary to effectively create an RFZ.
b) this degree of splay seems to lend itself well to an ergonomic and reflection-free 5.1 setup in terms of surround speaker placement (would mean moving the listener/centre of the circle back slightly.)
c) the 12 degree splay, carried over to the studio side of the wall, should be enough of an angle to provide some acoustical benefit vs. a smaller angle (since the opposite wall of the studio proper would not be splayed.)

The other thing to consider is that although, yes, you are making the CR smaller by adding the angle -half the space you're losing from the CR you're gaining in an already uncomfortably small studio room. Yes, there is about 20 square feet of "dead" space on the other side, but if it's possible to translate this into an exterior window to provide some natural light, then it would be a more than worthwhile trade-off IMO.

Regarding taking splayed walls into consideration in predicting the modal response of the final dimensions - the conventional internet wisdom seems to be to use the average width created by the splayed wall as the width in your calculations (probably fine, provided you're already well within the envelope of a known good proportion.) However I've recently altered my perception of the matter slightly - my current thinking is: the dimensions which are most relevant to the conventional method of predicting rectangular room modal response (e.g. the bobgolds calculator) are the actual remaining rectangular dimensions - i.e. the dimensions of the back of the room. This is based on my (possibly incorrect?) thinking that the splayed walls will diminish the impact of the width axial mode at the front of the room (while making the contribution of oblique and tangential modes more complex and difficult to predict) but the contribution of the width mode at the (rectangular) back of the room remains relevant (if possibly now of less consequence than the length and height axial modes at the listening position.)

Anyway, I agree with the others that if you're serious about this, I'd employ the services of a professional designer - you'll likely learn a lot more that way than by doing it (and possibly messing it up) yourself!

G.
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18th September 2008
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I attached a sketchup pointing out the angles I'm talking about. 30 degrees answers one (or two, symmetrically) of the angles, to form an equilateral triangle with the mixing position, correct? But what about the other angles I'm pointing to?
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18th September 2008
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Graematter,
Thanks for stopping in. Good to hear your input again.

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Originally Posted by Græmatter Audio View Post
Well, the primary reason for splayed control room walls given your layout constraints is as much about practicality as it is acoustics - it's the only way to create both a reflection-free zone in the control room (essential for monitoring) as well as good sight-lines through to the studio proper (helpful for producer/engineer-musician communication.)
That is exactly what I'm trying to accomplish! An RFZ and a line of sight. I should explain more that the portion of the CR wall furthest back in the room that remains straight, would be moved to the left (shrinking the bathroom/closet combo) to make up for the lost volume of angling the front part of the wall inward. ie: Angle the front part of the wall, move the back of it to the left. Or, keep the front part straight and the back part stays where it was originally. My pic may not be revealing of that thinking. Either way, that is the reason I am stuck, because if I angle the front of the wall a lot, the back of the wall (and the center line of the CR, to keep everything symetrical) will have to move a lot to the left. If I angle it a smaller amount, it doesnt' have to move as far. I won't know how big the bathroom can be (not that it matters) until I know what the angles of the CR have to be. Follow me? I just can't design anything else until I know what to do with that wall.
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19th September 2008
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Okay, I'm getting what your query is. Regarding splaying walls (and ceilings) read this thread and this thread. Page 281-283 in MHoA 4th edition discuss it also. I think that is the edition you have.

As an example of a similar layout, but smaller, have a look at this thread. When I first saw it, I thought it was your project!

Having the build out dimensions for the walls is great.

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Originally Posted by Graematter
Anyway, I agree with the others that if you're serious about this, I'd employ the services of a professional designer - you'll likely learn a lot more that way than by doing it (and possibly messing it up) yourself!
He is beyond the dangerous phase he has studied acoustics in the past and has learned a lot in the last few months. He knows much, and more importantly, knows what he doesn't know and where to get that information.

The biggest bit of acoustics knowledge that he has gained is "good studio building is 90% design and 10% construction."

I really should find a synonym for "this thread",
Andre
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19th September 2008
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thank you Andre, those links look to be exactly what I'm looking for. I'll take some time to study them and post again probably tomorrow.

Thanks everybody.
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OK, I can see now that the constraints have changed a bit with a control room of this size - it's larger than my previous drawing and accordingly is less of an compromise in terms of CR volume... however in order to attain these CR dimensions (particularly the length) I fear that you'll be severely cutting down on the space available to your Iso Booth to the point where it will be good for little other than perhaps isolating amps + mic storage... but certainly not an actual performance space. Alternatively you might think about making that your machine room/HVAC location and freeing up space for a more comfortable washroom and soundlock to provide better isolation between the CR and ISO.

The other thing to look out for is that your average studio width is becoming very close to the average height...

G.
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Thank you, thank you, thank you, G. ALL VERY important and good ideas for me to remember. I hadn't been giving much thought to the average dimensions of the studio room, and the thought of swapping the storage area and the booth might be really smart. I had wanted line of sight with the booth in front of me, but if it might be better back there it's worth considering.

'Precciate you checkin' back.

Nathan
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19th September 2008
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However...

If, for example, (about the studio room demensions) I took a cube and splayed all the walls and ceiling drastically, but maintained the same volume, would I still have issues? I guess so... I do know that the problems originate when the wave length = length of travel distance, or its multiples. So I guess travel distance counts for more than volume in this case...

Just thinking out loud. Any thoughts or explanations anyone?
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Quote:
Originally Posted by naethoven View Post
However...

If, for example, (about the studio room demensions) I took a cube and splayed all the walls and ceiling drastically, but maintained the same volume, would I still have issues?
It would be worse. There would be no easy method to calculate how the modes would be. Did you look at MHoA and the pages I referenced?

Looking forward to your updated drawings.

Andre
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24th September 2008
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Howdy there Andre!
Just wondering if you could recommend a book for me (or another source of education). I am looking for a book specifically to teach me details of control room design. I have bought and read Rod Gervais Build it Like the Pros, have begun visiting the John Sayers site (a wealth of info) and I have gone back to my MHofA book and read a few hundred pages, still reading. But I have yet to find deep details of control room design (at least in those books), just basics and overviews of important things. I WANT TO LEARN!!! And I want to build the best studio I can with the space I have.

A few more questions. From the research I have done lately, I have started to think that my quest for a lively RFZ (where reflections are controled via splayed surfaces instead of absorbtion) is fruitless due to the small size of my room and the need of the initial time delay gap.

A possible solultion would be to forgoe this plan, go ahead and splay the walls however I want to in order to create a line of sight (btwn CR and Studio), maximize the room volume cuft, keeping it as far above 1500 cuft as I can, and rely on strategically placed absorbtion for the RFZ. In an attempt to honor good room proportions, I would measure 1st for a rectangle, then splay by pivoting the wall (or ceiling) on it's center point to maintain volume cuft. This way I would end up with relative room proportions, line of sight, maximum volume cuft, and an RFZ. (I will also, of course, design to maintain symmetry.)
My questions are:
1) Are there any angles I should avoid when I am splaying the walls/ceiling? Since the RFZ is mostly dependent on absorbtion and not these angles, the only thing I know of that I should consider when deciding what angles to splay at is the line of sight. Is there an angle that will cause problems? For my situation are there any angles that would "help"?

2) Will my absorbtive material on the splayed side- walls be subject to "grazing" of high frequencies due to the angle of incidence? How do I keep that from happening? (Should I make a sort of stair-step with strips of 703, so the incidence occurs on the front side of the strip?)

3) Would you like to donate $20k to my studio build??????




P.S. I PM'ed this to you 1st, then decided I would post it so everyone would benefit.
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25th September 2008
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I don't know what more to offer for control room design details. What do you feel is missing?

If you are looking for technical specs, AES multichannel guide provides an excellent summary. Geared at multichannel, but most of the specs are evolutions of stereo specs, with the acoustics being almost identical.

Getting about the most technical and still free are the various BBC RD reports and the predecessors covering over fifty years of design. BBC List of RD Reports. There are too many docs there to even try to suggest some without knowing what more information you are seeking.

Quote:
From the research I have done lately, I have started to think that my quest for a lively RFZ (where reflections are controled via splayed surfaces instead of absorbtion) is fruitless due to the small size of my room and the need of the initial time delay gap.
This is correct.

Quote:
1) Are there any angles I should avoid when I am splaying the walls/ceiling? Since the RFZ is mostly dependent on absorbtion and not these angles, the only thing I know of that I should consider when deciding what angles to splay at is the line of sight. Is there an angle that will cause problems? For my situation are there any angles that would "help"?
There are no magic angles. They are all dependent on the specific room and application.

Quote:
2) Will my absorbtive material on the splayed side- walls be subject to "grazing" of high frequencies due to the angle of incidence? How do I keep that from happening? (Should I make a sort of stair-step with strips of 703, so the incidence occurs on the front side of the strip?)
What are you trying to achieve with the material in those locations? If you are working on a RFZ, then grazing angles will not be significant in the room geometry.

Keep reading and keep asking questions. The result will be a better studio for you!
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25th September 2008
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Andre,

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I don't know what more to offer for control room design details. What do you feel is missing?

If you are looking for technical specs, AES multichannel guide provides an excellent summary. Geared at multichannel, but most of the specs are evolutions of stereo specs, with the acoustics being almost identical.

Getting about the most technical and still free are the various BBC RD reports and the predecessors covering over fifty years of design. BBC List of RD Reports. There are too many docs there to even try to suggest some without knowing what more information you are seeking.
Not that anything I KNOW OF in particular is missing, I just want to learn more. For example, I'm considering going back to school for my Master's in Acoustics, so I can do fun things like design recording studios as part of my self employment. I'm just extremely interested in acoustics. My particular application at the moment is focused on control room design, so I'm looking for a book a university might use as a text book in a Master's acoustic class, namely about control room design.


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Originally Posted by avare View Post
There are no magic angles. They are all dependent on the specific room and application.
Am I correct to say: According to the fact of angle of incidence=angle of reflection (atleast with HF), as long as this angle directs the reflection toward the back wall (which in my case will be absorbtive) and are effectively absorbed, my listening position should be reflection free?? Yes?



Quote:
Originally Posted by avare View Post
What are you trying to achieve with the material in those locations? If you are working on a RFZ, then grazing angles will not be significant in the room geometry.
I most definetly am shooting for an RFZ, but I don't really understand what you meant in the second part of the sentence. Could you rephrase please?

With deep gratitude for your time,
N
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25th September 2008
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I'm just extremely interested in acoustics. My particular application at the moment is focused on control room design, so I'm looking for a book a university might use as a text book in a Master's acoustic class, namely about control room design.
Well you have one of them already. MHoA is a funny text, introductory, yet everyone who does studio acoustics has it in their library. After that keeping to studios specifically, Recording Studio Design by Newell. Beyond that you are getting into acoustics and greater than studio acoustics texts. Architectural Acoustics by Long, Acoustics by Beranek, Acoustics by Kuttruff, Diffusers and Absorbers by Cox and D'Antonio, give a solid basis.

The various BBC RD reports I just linked to you yesterday, Cox, Angus and D'Antonio papers on room ratios and treatment, many on the web are also used. Things like McQuay's guide to HVAC design for sound give solid examples of the methodology for HVAC design. Wallace Sabine's Collected Papers on Acoustics (1922) gives an excellent historical perspective on acoustics. Putnam's AES paper on the history of recoding studios (~1980) gives a good historic perspective on studio design up until the 80s. All documents in this paragraph are free on the internet.

Geoff Martin has several papers worthy of note. Toole has several appropriate papers and books. Angus' book on psychoacoustics is useful. Holman's texts on multichannel sound are, well, industry standards.

Design will get into industry recommendations, so the various AES, EBU, ITU, SSF standards and NARAS recommendations will be part of the required knowledge base. Many of these are free on the net.

Salford University has their sound and vibration lab courses and summaries online. One the best acoustics schools around.

Davis, Ballou, Augsburger/Eargle (the JBL Sound System Design Manual) are standards. Eargle on microphones and Everest on Stereo techniques are pretty required reading. Bartlett is pretty much the standard text for mobile recording. If you want bonus points, get Sharp's book on the sound insulation of building elements (Wyle 73-5). Has been obscure, hard to find, and highly referenced for isolation. It is on the web someplace, so at least the price is right.

The NRC has one of the most comprehensive sets of documents on TL testing anywhere, and it is on the web for free. IR-761 is the bible for drywall isolation, as just one example.

Someplace on the web there is a NASA study on absorbent materials below 100 Hz with test results.

For detailed Perforated materials and absorption Schultz's Acoustical Uses for Perforated Metals is just about the last word on the subject. Yes it is on the bet and free.

That is over 2 dozen references to documents to get you started.


Quote:
Am I correct to say: According to the fact of angle of incidence=angle of reflection (atleast with HF), as long as this angle directs the reflection toward the back wall (which in my case will be absorbtive) and are effectively absorbed, my listening position should be reflection free?? Yes?
Very close. Keep any reflections within 15 ms (20 is better) down at least 10 dB. After that they can be bounced around at will, assuming the room size permits good sound for that to begin with.



Quote:
I most definitely am shooting for an RFZ, but I don't really understand what you meant in the second part of the sentence. Could you rephrase please?
At the angles where material is used for controlling early reflections, grazing will not occur.


I am quite impressed by the advice you have been giving out lately. your knowledge of acoustics has grown immensely!

Andre
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26th September 2008
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Thank you so much for all those references. Some of the authors I recognize from MHofA references; I'll have to go back and look at those. I actually have Bartlett's mobile recording book from school as well, also one of my favorites that I haven't looked at in a long time. I have a lot of reading to do. I'll get back to you in 5 years when I'm done...
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Keep any reflections within 15 ms (20 is better) down at least 10 dB.
Ah yes, I remember reading that now. This is the reason small rooms need absorbtion to create an RFZ, right?
How do I know when enough energy from the reflection has been absorbed to "turn it down" 10db? Maybe that's the stuff I learn with a Master's.


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Originally Posted by avare View Post
At the angles where material is used for controlling early reflections, grazing will not occur.
I'm kind of with you, but I'm sorry I still don't really get what you're saying. If I just need to go study something more (to avoid being spoon fed) could you point me toward a specific source? Or maybe you could sketch a pic explaining the grazing answer?

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Originally Posted by avare View Post
I am quite impressed by the advice you have been giving out lately. your knowledge of acoustics has grown immensely!
wow...what an encouraging and wonderful complement. Thankyou.


In the meantime I will try to work on another sketchup of a potential CR with my new knowledge.
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26th September 2008
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Originally Posted by naethoven View Post
Thank you so much for all those references. Some of the authors I recognize from MHofA references; I'll have to go back and look at those. I actually have Bartlett's mobile recording book from school as well, also one of my favorites that I haven't looked at in a long time. I have a lot of reading to do. I'll get back to you in 5 years when I'm done...
I'm glad to provide you with sources for reading material for the weekend.


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Ah yes, I remember reading that now. This is the reason small rooms need absorbtion to create an RFZ, right?
That is one of the reasons absorption is used in small rooms. The other is that small room acoustics sound lousy.

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How do I know when enough energy from the reflection has been absorbed to "turn it down" 10db? Maybe that's the stuff I learn with a Master's.
An absorption co-efficient of 0.9 or greater.


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Or maybe you could sketch a pic explaining the grazing answer?
Grazing is a small angle of incidence, typically meaning less than 5 degrees.. The attached drawing is of a 12' x 17' control room with a 2'x 6' RFZ centered 38% of the length and speakers in a 60 degree location. The shallowest angle of incidence for the first reflection point is 35 degrees.

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In the meantime I will try to work on another sketchup of a potential CR with my new knowledge.
I am looking forward to it. Take your time. The more know, the better your studio will be. And you know, good studio building is 90% design and 10% construction.

Andre
Attached Thumbnails
Angles of Control Room walls-incidence.jpg  

Last edited by avare; 28th September 2008 at 11:13 PM.. Reason: Corrected spelling and added words to makes sentences english.
#28
26th September 2008
Old 26th September 2008
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Great thread gentlemen. Thanks for posting the references Andre!
#29
27th September 2008
Old 27th September 2008
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Originally Posted by Greg Heimbecker View Post
Great thread gentlemen. Thanks for posting the references Andre!
I am glad that you are enjoying it and you are welcome. Welcome to your first post here too!

Andre
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#30
29th September 2008
Old 29th September 2008
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Quote:
Originally Posted by avare View Post
An absorption co-efficient of 0.9 or greater.
Can you give an equation or explanation of this fact that would help me understand the "Why" behind it?

Quote:
Originally Posted by avare View Post

Grazing is a small angle of incidence, typically meaning less than 5 degrees.. The attached drawing is of a 12' x 17' control room with a 2'x 6' RFZ centered 38% of the length and speakers in a 60 degree location. The shallowest angle of incidence for the first reflection point is 35 degrees.
I see. I understand grazing will not matter in my case then.


...back to the 90%...
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