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Golden Room dimension?

Discussion in 'Pro Audio Equipment' started by yodermr, Jan 31, 2003.

  1. yodermr

    yodermr Guest

    I am trying to find some good guidelines on room dimensions for a drum recording/ mixing room. The actual structure I have a good feel for but where I'm stuck is what would be the best room dimensions for a basement - 7-8' ceiling.

    I have read about golden dimensions but that doesn't seem to work with the ceiling height and maintaining a minimum room volume.

    Do I just stick with minimum 1500 sqft and non parralell walls?

    Not sure if this is the right area to post this.

    Thanks Much...
    Mark
     
  2. knightfly

    knightfly Active Member

    Mark, low ceilings are always going to be a problem, drums or otherwise. If you try to get a large room volume with a low ceiling, you make it even more difficult to get modal spacing close enough not to give wierd responses due to gaps in mode density.

    I'm assuming, with 7-8 foot ceilings (which is it?) that you meant 1500 CUBIC feet, not square feet? How much room do you have to dedicate to your drum room?

    As to "Golden Ratios", most if not all those sets of numbers were calculated the hard way (before spreadsheets) and I've found that first, ALL of them can be improved on, some slightly and some quite a bit - second, there are other sets of ratios that will give as good a modal distribution.

    I wrote a simple spreadsheet several years ago to use for just such a project, where you have one or two room dimensions you are stuck with and quickly want to ballpark the other dimensions. It's called roomtune, and can be found at ProRec in the files area under roomtune.exe - it is a self-extracting file and contains both Lotus and Excel versions, along with some basic directions in a word6 file. You can download it here -

    http://www.prorec.com/prorec/downloads.nsf/category

    If you don't have Excel or 123, post back with your proposed rough room dimensions and I'll see what I can do for best modal spacing within those parameters.

    Keep in mind that such a small room will have a LOT of bass/low mids to control, and if you have extra space available you should leave enough room for some seriously deep traps/absorbers.

    Once you get some dimensions nailed down, I can help with trap design somewhat - I would hope that you have the carpentry basics down, as I ran into another thread that took 6 pages, about 4 of which were explaining basic carpentry.

    If you actually have 8 feet of headroom AFTER soundproofing the ceiling, one set of dimensions that come out well on modal spacing is 8 x 11.5 x 13 feet, which will have a Cubic Displacement of only 1196 CuFt, but until you get to around 3-4000 CuFt you won't get a room that will naturally support all the frequencies of a drum kit anyway. at least, these dimensions would give a fairly balanced response.

    In addition to the space required for the above room, you'd need space on one wall to go 3-4 feed deeper, part of which could be used for a sound lock (double) door and the rest of which could be used for slat resonator/bass trapping.

    I hope this gives you some ideas - post the rest of your dimensions/thoughts and we'll see what happens... Steve
     
  3. yodermr

    yodermr Guest

    Knightfly
    I recently built a room for myself (that also needs a little help) but this is for a friend who is starting to plan. He has an open basement to work with. I need to verify but if its like mine his ceiling will come to around 7' with all materials. I thought maybe 8' but I need to check.
    I think and again will verify that he has probably 20 X 15 to work with.
    Carpentry skills are not a problem.
    I'll get back to you on specific dimensions.

    Yes cubic ft is what I refered to.

    I downloaded your spreadsheet. Yup looks like the ceiling height constraint is problematic. Will non parrelell walls help here?

    Question on my room... 21 X 11.5 X 7.3. I have a variety of panel bass traps built in. Using Bill Robert's method with the test tone, I have noticed a significant drop from 100 to 140. Just by ear, don't have a db meter. And I'll admit to owning Mackie monitors. I understand bass traps to absorb problem frequencies but what about where they seem to cancel out?

    Thanks for the help
    Mark
     
  4. mchimes

    mchimes Guest

    Hey Guys,

    I'm basically in the same boat w/ a possibly higher ceiling. Building a basement project studio. I've decided to leave my space as one big tracking and mixing space. Otherwise I would be forced to have 2 very small rooms . . . a control room and tracking room. I am opting for one decent sounding room over 2 "so-so" rooms.

    Steve . . . I will check out your program. I was actually thinking about getting RPG's Room Sizer to determine the optimum ratios, but it looks like your program may help. My space is basically 8.5'H (9'8" if I leave unfinished joists) by 23'L by 10'W (flaring out to 15' wide about halfway down the length). I would like to leave the height in the joists to keep all of that room volume up there and the natural diffusion and bass trapping characteristics of the joists (given inserts and traps etc.) But of course it means my ceiling is the floor of the above room thereby causing high sound transmission loss through the ceiling. What do you think?

    I have been digging into Everest's Master Handbook Of Acoustics as a major resource. He seems to lean toward parallel walls to at least be able to predict modal response. He says that splaying the walls (while helping flutter) won't eliminate Standing Waves, only alter their predictability.

    So I need to come down on some ratios myself. And if you have any tips on wall construction. Right now I'm leaning toward 5/8 drywall screwed to a hat furring strip, clipped into one of those new Resilient Clips from New Zealand, which is screwed into the stud. I am looking into the airtight, spray in insulation product called Nu Wool as the insulation. It looks like it would work very well for lowering transmission loss.

    Any thoughts on ratios for me or any other advice?

    Thanks,
    mike
     
  5. mchimes

    mchimes Guest

    Steve,

    Got your very thorough explanation of wall construction in the your Worddoc. Thanks!

    Thanks again for the Spreadsheet. I found one that is slightly less "Roll Your Own" from Dr. Toole at Harman Kardon.

    Here is the link for it . . . it's an Excel Doc. also and very easy to use. Check it out.

    http://www.harman.com/wp/index.jsp?articleId=131

    Thanks,
    Mike
     
  6. knightfly

    knightfly Active Member

    Guys, not that I'm trying to get out of more long answers here, but I'm a little short on time these days so I'm first going to send you to a couple of older posts that may help answer some of your questions - then, after you've read through those if you could re-state your questions I'd be glad to give them a whirl.

    Keep in mind through all this, that you're NOT, repeat NOT, dealing with an experienced, certified (certifiable, maybe :=)Acoustical Engineer, or even close - I've done a couple of rooms, one for myself and one for a friend (long distance) after building one for myself several (about 16) years ago that turned out semi-OK acoustically, but crappy for sound proofing.

    Since that time, I've been studying acoustic theory off and on for the last 15 years or so. You will note, however, that in the second thread I'm linking to, that I asked for and got some feedback from an experienced studio designer and recording engineer from Australia, Mr. John Sayers. From what John commented, I'm apparently interpreting what I've studied fairly well. Bottom line - Caveat Emptor (and, since it's free, what does that tell ya?)

    Anyway, I'll not pretend to know something if I've not read it and at least proven it to myself satisfactorily - so, with that, here are a few pages to check out that may answer or ask more questions - please read them, then re-state whatever questions you have left (or, if I've scared you off, spend your own decade or so doing what I've done, your choice) Here they are, then...

    (Dead Link Removed)

    (Dead Link Removed)

    (Dead Link Removed)

    Mike, on your ceiling STC question, click on the following link, then click on construction (sidebar), then scroll to the BOTTOM of the page. That's what I would do, with maybe only two layers on the RC depending on what the rest of your barrier between the upstairs world is like. By that, I mean that it's pointless to build a 60 db wall and have a poorly fitted, hollow core door leading up un-enclosed steps to the half-sealed door into the kitchen - remember the "weakest link" syndrome...

    Happy reading Mike,Mark; I'll check back in a day or two for any residual questions - and remember, I don't know $*^t... Steve
     
  7. mchimes

    mchimes Guest

    Steve,

    After reading those threads, I may a bit better off than I was thinking. I've already corresponded w/ John Sayers (he drew me up a 2 room studio design for the space . . . but I want to try one room first . . . I can always put a wall in later) and Ethan Winer about bass traps.

    I guess I have the info I just have to make a decision. That is the hard part, bring this down from theory and actually getting my saw out.

    Last night I read a puzzling article from Dr. Toole at Harman that gave me pause. He is on the research end of things and is more geared toward home listening audiophile rooms, but the same principlaes should apply. He basically thinks that all the ratios and "rules" regarding conventional studio/small room acoustics are just about lost on the imperfections and assumptions we make about these spaces.

    So he debunks many of these "rules" (ratios, LEDE, rigid double layered walls) w/ good thinking, but then gives very little in the way of what he thinks a room should be like. It's almost as if he likes bucking the "norm," but has no plan of his own. It's frustrating because I like much of what he says . . . I just don't see a practical design at the end of it and that is what I need right now.

    If you feel inclined, check out this link (click on full white paper) and read about what I'm talking about. Maybe you would have some ideas about what he is getting at:

    http://

    Thanks,
    Mike
     
  8. Ethan Winer

    Ethan Winer Active Member

    Mark,

    > I understand bass traps to absorb problem frequencies but what about where they seem to cancel out? <

    This is a common misconception. Yes, bass traps do absorb bass frequencies, but the net result is an increase in the level of bass reproduced in the room. Without bass traps, low frequency sound waves coming from the loudspeaker bounce off the walls, floor, and ceiling, and collide with each other in the air. This is called acoustic interference and it creates peaks and dips - often very severe - in the response. So by absorbing the waves with bass traps, the reflections that cause the cancellations are reduced. This is exactly why loudspeakers are always tested / measured in an anechoic room - to avoid the inaccuracy and loss of bass due to room reflections.

    --Ethan
     
  9. knightfly

    knightfly Active Member

    Ethan, one of your statements, "Yes, bass traps do absorb bass frequencies, but the net result is an increase in the level of bass reproduced in the room. " - left me somewhat confused -

    By that, do you mean that since a bass trap lowers the PEAK level at anti-nodes, it will also lower the NULL effect, causing more PERCIEVED bass where there would otherwise be a bigger "hole" in the response?

    To me, that's the only way your comment makes any sense - considering that bass traps work by converting sound energy into heat energy, the TOTAL bass energy in the room MUST be less, or no energy would have been converted.

    Mike, thanks for the link - I downloaded the pdf and will read it when I get the chance. Be aware that recording engineers, acousticians and "audio-fools" will kill each other if left in a room without supervision for more than 5 minutes at a time, so there's a good chance that the white paper you linked would have totally confused you (all this without yet reading it, how's that for bias?)

    One thing that helps me sometimes when trying to visualize how acoustics behave - years ago I had a neighbor, about 25 years older than myself, that, when asked what he did, told me he was a "fluid dynamicist"... When I asked what that meant, he said that he designed airplane wings. When I asked what the hell fluid had to do with airplanes, he told me that air was a fluid. The conversation got longer and deeper than that, but I've always remembered that epiphany.

    Gotta go for now - Ethan, I'm seriously awaiting your response - it's always a good day when I learn ANYTHING... Steve (so far, that means EVERY day is a good one)
     
  10. Kurt Foster

    Kurt Foster Distinguished Member

    Previously in this thread "Everest's Master Handbook Of Acoustics" was mentioned. In this book there is information on "Sepmeyer ratios". Look that up. These are formulas for divining "Golden Dimensions". Fats
    ------------------------------------------------------------------------
    Tannoy, Dynaudio, Blue Sky, JBL, Earthworks, Westlake, NS 10's :D , Genelec, Hafler, KRK, and PMC
    Those are good. …………………….. Pick one.
    ------------------------------------------------------------------------
     
  11. Ethan Winer

    Ethan Winer Active Member

    Steve,

    > do you mean that since a bass trap lowers the PEAK level at anti-nodes, it will also lower the NULL effect, causing more PERCIEVED bass <

    No. I'll try to explain it a different way.

    Suppose you have a loudspeaker set up in your back yard, far from the house, and you play some music. If the speaker is relatively flat, then what you hear will be equally flat. The volume of low frequency content is balanced with the mid and high frequencies to sound about as intended by the recording engineer. Outdoors there are no acoustics or reflections, so loudspeakers sound about as flat as their specs indicate.

    If you move the same loudspeaker into a room in your house and play the same music, the bass now has a series of peaks and dips in the response. Both the peaks and the dips are caused by reflections off the walls, floor, and ceiling. At some frequencies, and some locations in the room, the response will rise by as much as 6 dB. This happens where the reflections arrive at your ear perfectly in phase with the direct sound from the speaker, and so add to the direct sound. Though more likely there is 360 or 720 degrees of phase shift, depending on the distance from the wall and thus the delay. If the reflection is almost as loud as the original sound, the increase can approach 6 dB.

    But at other frequencies and locations the response can have dips as large as 20 dB. or even more. The most severe cancellation happens when the reflected waves arrive 180 degrees out of phase with the original sound, and are at a similar level [the walls are very reflective at that frequency]. Again, the actual phase shift is more likely to be 180 + 360 degrees.

    So reflections can cause the volume at some frequencies to be louder than what's coming from the speaker, and it can also cause the volume to be much lower. Adding bass traps absorbs the waves that hit the wall, which is the same as if they went out a window and never came back. So by absorbing the waves before they can be reflected, the increases and cancellations are avoided.

    Here's the key point: Even though a bass trap does indeed absorb bass, it does not impede the sound as it comes from the speaker and goes to your ear. It only absorbs what would have bounced off the wall, and therefore affected the frequency response within the room.

    --Ethan
     
  12. Kurt Foster

    Kurt Foster Distinguished Member

    Ethan,
    That was an excellent reply. I don't think I have ever heard this explained in a more succinct manner. Even I understood that! Thanks for that! ... Fats
    ------------------------------------------------------------------------
    Tannoy, Dynaudio, Blue Sky, JBL, Earthworks, Westlake, NS 10's :D , Genelec, Hafler, KRK, and PMC
    Those are good. …………………….. Pick one.
    ------------------------------------------------------------------------
     
  13. Ethan Winer

    Ethan Winer Active Member

    Fats,

    > That was an excellent reply. <

    Thanks. I'm trying! :D

    --Ethan
     
  14. JSOUND

    JSOUND Guest

    Go here: http://www.mcsquared.com/modecalc.htm

    Plug in your room dimensions and cross reference modes with each other to make sure that no one frequency is duplicated in any 2 modes. Also, it is better if the frequencies are never closer than about 5%.i.e.- 95hz-axial, and 100hz-tangential would be OK. But 95hz axial and 98hz tangential would be too close together(and will build up a bit) so you would have to change one of the room dimensions so the 2 frequencies are farther apart.

    Also, go here: http://www.soundsamazing.ca/listening_room.htm
     
  15. mchimes

    mchimes Guest

    Jay,

    That's the best mode calculator I've seen . . . it even gets the tangential and oblique modes.

    Thanks man!

    Mike
     

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