Please elaborate if you could on constructing a false ceiling. I am looking to slope my ceiling towards the front of my room ala Johns diagram showing hanging absorbers above. I have an existing ceiling height of 8' 6" and was also wondering the best angles (i.e. 1 or 2) and with the limited height what would you recomend as to the best way to insulate since I may not have room for hanging absorbers.
thanks
false ceiling construction?
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knightfly
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knightfly
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- Joined: Sun Mar 16, 2003 11:11 am
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Sorry for the delay - I've finally gotten some time to give this some more thought, and I agree that you wouldn't have much room for hangers with that low a ceiling.
IF your walls aren't splayed, you won't be able to achieve a Reflection Free Zone (RFZ)per se - but you can get SOME of the reflections off your back with a two-angled false ceiling.
Keep in mind that I've not done this myself yet, only studied at every opportunity for the last 15 years so I don't goof up my own (soon to be started) separate free-standing, high-ceilinged, 1700 square foot facility.
You don't mention the other two dimensions of your room so I can't guess whether you have the room to splay the side walls also - as far as the false ceiling, I'd frame it with 2x lumber on 24" centers, just like any other ceiling construction except for angles. You'll need to consult span charts for dimensions of framing - Douglas fir, #2 and better, with no rooms above, 2x4 on 24" centers can span just over 9 feet. Same, except 2x6, spans up to 15 feet. Same, except 2x8, will span 19 feet.
Then, if the room is large enough so that you have at least 11-12 feet behind your head when seated at the mix position, I'd put light paneling on the joists, with heavy rockwool suspended (on wire, for example) so as NOT to touch the panels - line the REAL ceiling/walls behind this construction with 3-4 inch OC 705 FRK and forget the hangers (too little room) - with a long enough room, you would want some sort of diffusion at the rear such as QRD's, built poly's, and/or slot resonators. With a shorter room (less than 11-12 feet behind your head) you'll need to ABSORB the rear wall so as not to get phasing problems at the mix position.
If your room is smaller and you can't get the 11-12 foot distance from your head to rear wall, I'd replace the paneling on the (false) joists with 2" 703 and cover it with cloth, maybe with a thin plastic film first to keep the shedding under control. If you use the plastic, I'd go with heavier cloth to absorb highs (remember, this is for the SHORTER room)
The actual ANGLES for a RFZ can be done with any CAD program that allows you to do primitive Ray Tracing - ( by "primitive", I mean MANUAL)
I've been using Generic Cadd 6.1 for years, but it's a DOS-based app (runs fine on Win98) - I just picked up a copy of Turbo Cad 8 at Staples for $39.95, a friend has been using it and likes it - I've got to get more disk space on my laptop before I install it, but it looks VERY comprehensive (includes some 3-d capability) and is only about $3000 cheaper than the industry standard Autocad - it's compatible with the DXF file format too. I don't know yet whether it can save as a raster format, such as JPG or BMP -
Using the speaker as a source, draw lines to any proposed boundary wall, measure the angle of incidence and copy that to the angle of reflection (where it goes after it hits the wall) and continue that reflection path until the path length is at least 22 feet long - then, randomly pick ANOTHER direction from the speaker source, and do it again, until you're convinced that NO reflection path from either speaker to either ear is shorter than 22 feet. (This isn't a magic distance, it's just enough so that reflections can't get back to your ear in less than about 24 milliseconds)
If any reflection path encounters a proposed bass trap or other broadband HEAVY absorption, don't worry about path length.
I hope that helped some - again, sorry it took so long... Steve
IF your walls aren't splayed, you won't be able to achieve a Reflection Free Zone (RFZ)per se - but you can get SOME of the reflections off your back with a two-angled false ceiling.
Keep in mind that I've not done this myself yet, only studied at every opportunity for the last 15 years so I don't goof up my own (soon to be started) separate free-standing, high-ceilinged, 1700 square foot facility.
You don't mention the other two dimensions of your room so I can't guess whether you have the room to splay the side walls also - as far as the false ceiling, I'd frame it with 2x lumber on 24" centers, just like any other ceiling construction except for angles. You'll need to consult span charts for dimensions of framing - Douglas fir, #2 and better, with no rooms above, 2x4 on 24" centers can span just over 9 feet. Same, except 2x6, spans up to 15 feet. Same, except 2x8, will span 19 feet.
Then, if the room is large enough so that you have at least 11-12 feet behind your head when seated at the mix position, I'd put light paneling on the joists, with heavy rockwool suspended (on wire, for example) so as NOT to touch the panels - line the REAL ceiling/walls behind this construction with 3-4 inch OC 705 FRK and forget the hangers (too little room) - with a long enough room, you would want some sort of diffusion at the rear such as QRD's, built poly's, and/or slot resonators. With a shorter room (less than 11-12 feet behind your head) you'll need to ABSORB the rear wall so as not to get phasing problems at the mix position.
If your room is smaller and you can't get the 11-12 foot distance from your head to rear wall, I'd replace the paneling on the (false) joists with 2" 703 and cover it with cloth, maybe with a thin plastic film first to keep the shedding under control. If you use the plastic, I'd go with heavier cloth to absorb highs (remember, this is for the SHORTER room)
The actual ANGLES for a RFZ can be done with any CAD program that allows you to do primitive Ray Tracing - ( by "primitive", I mean MANUAL)
I've been using Generic Cadd 6.1 for years, but it's a DOS-based app (runs fine on Win98) - I just picked up a copy of Turbo Cad 8 at Staples for $39.95, a friend has been using it and likes it - I've got to get more disk space on my laptop before I install it, but it looks VERY comprehensive (includes some 3-d capability) and is only about $3000 cheaper than the industry standard Autocad - it's compatible with the DXF file format too. I don't know yet whether it can save as a raster format, such as JPG or BMP -
Using the speaker as a source, draw lines to any proposed boundary wall, measure the angle of incidence and copy that to the angle of reflection (where it goes after it hits the wall) and continue that reflection path until the path length is at least 22 feet long - then, randomly pick ANOTHER direction from the speaker source, and do it again, until you're convinced that NO reflection path from either speaker to either ear is shorter than 22 feet. (This isn't a magic distance, it's just enough so that reflections can't get back to your ear in less than about 24 milliseconds)
If any reflection path encounters a proposed bass trap or other broadband HEAVY absorption, don't worry about path length.
I hope that helped some - again, sorry it took so long... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
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knightfly
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Sen, I just dropped by to check on things briefly, on my way to bed after 12 hour graveyard shift but will get you more info in a day or so (one more 12-hour graveyard shift to go)
Basically, what I was intending here was to use the false ceiling as a panel trap. That would require different thickness of panel depending on the size of the room and modal considerations. I have a formula for figuring this out, but not with me at the moment. The thicker the panel, the lower the frequency, but also the more sound pressure required to excite the panel - I'd say somewhere between 1/4" and 1/2" ply, but again I'd have to check my sources for resonant frequency and tie that into any parallel dimensions of the room. If no parallel dimensions, then a broader band treatment might be better. I'll give it some more thought and get back to you... Steve
Basically, what I was intending here was to use the false ceiling as a panel trap. That would require different thickness of panel depending on the size of the room and modal considerations. I have a formula for figuring this out, but not with me at the moment. The thicker the panel, the lower the frequency, but also the more sound pressure required to excite the panel - I'd say somewhere between 1/4" and 1/2" ply, but again I'd have to check my sources for resonant frequency and tie that into any parallel dimensions of the room. If no parallel dimensions, then a broader band treatment might be better. I'll give it some more thought and get back to you... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
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knightfly
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- Joined: Sun Mar 16, 2003 11:11 am
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OK, Sen, here 'tiz -
The formula for Fo of a panel absorber is:
Fo= 170/sqrt(m)(d), where Fo is the resonant frequency in Hz, m= surface density in lbs/sq ft of the panel, and d= depth of the airspace in inches.
One example - the surface density of 1/4" plywood is listed as .74 lb/sq ft - from the chart in Everest's book (too lazy to calculate this when there's already a chart) 1/4" ply with an air space of 5.5" would have an Fo of about 87 hZ, where the same plywood with an air space behind of 20" would resonate at about 45 hZ.
The beauty of using ceiling splays as panel absorbers is that you have wideband absorption due to the varying depth behind the panel. According to Everest's chart, putting 1/2" (instead of 1/4") plywood on a false ceiling having a depth ranging from 6" to 20" would result in absorption all the way from 60 hZ down to about 30 hZ. Using 1/4" ply in the same case would go from roughly 85 hZ down to 45 hZ. If the range of depth were greater, you'd have even wider band absorption. The higher frequencies that weren't absorbed would be reflected to the rear, where either wideband absorbers or diffusors (depending on the depth of the room) could take care of the rest.
Again, Sen, this isn't a "one size fits all" scenario so the rest of the proposed room would need to be taken into account. Also, the overall amount of absorption would depend on whether you wanted a tighter sounding room for mixing without the room making your mix seem more reverberant than it is, or a more natural, larger room for tracking strings, etc -
Hope that helped... Steve
The formula for Fo of a panel absorber is:
Fo= 170/sqrt(m)(d), where Fo is the resonant frequency in Hz, m= surface density in lbs/sq ft of the panel, and d= depth of the airspace in inches.
One example - the surface density of 1/4" plywood is listed as .74 lb/sq ft - from the chart in Everest's book (too lazy to calculate this when there's already a chart) 1/4" ply with an air space of 5.5" would have an Fo of about 87 hZ, where the same plywood with an air space behind of 20" would resonate at about 45 hZ.
The beauty of using ceiling splays as panel absorbers is that you have wideband absorption due to the varying depth behind the panel. According to Everest's chart, putting 1/2" (instead of 1/4") plywood on a false ceiling having a depth ranging from 6" to 20" would result in absorption all the way from 60 hZ down to about 30 hZ. Using 1/4" ply in the same case would go from roughly 85 hZ down to 45 hZ. If the range of depth were greater, you'd have even wider band absorption. The higher frequencies that weren't absorbed would be reflected to the rear, where either wideband absorbers or diffusors (depending on the depth of the room) could take care of the rest.
Again, Sen, this isn't a "one size fits all" scenario so the rest of the proposed room would need to be taken into account. Also, the overall amount of absorption would depend on whether you wanted a tighter sounding room for mixing without the room making your mix seem more reverberant than it is, or a more natural, larger room for tracking strings, etc -
Hope that helped... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
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Sen
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- Location: Melbourne, Australia
good that the site is back on, 
thanks to mighty John!
thanks heaps Steve,
That formula is really useful..BTW, is it from Everest's MAster Handbook of Acoustics or some other title, Coz I just bought the fourth edition of the master handbook the other day, but haven't come across this formula yet...great book though...I prefer the back part with all the drawings and pics
thanks to mighty John!thanks heaps Steve,
That formula is really useful..BTW, is it from Everest's MAster Handbook of Acoustics or some other title, Coz I just bought the fourth edition of the master handbook the other day, but haven't come across this formula yet...great book though...I prefer the back part with all the drawings and pics
Kind regards
Sen
Sen
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knightfly
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Yeah, fourth edition page 206 - it's listed in the index under panel absorbers - (doesn't say formula, just panel-type absorbers)
Just don't quote too much Everest to John, 'specially regarding rectangular rooms :=) keep in mind Everest is in his 90's, living in Santa Barbara Calif. according to the flyleaf - some of his ideas have been improved on in recent years, but the Master Handbook is still a really valuable resource. As much of a "black art" as acoustics tends to be, it seems to me that there's room for more than one person to be "right"... Steve
Just don't quote too much Everest to John, 'specially regarding rectangular rooms :=) keep in mind Everest is in his 90's, living in Santa Barbara Calif. according to the flyleaf - some of his ideas have been improved on in recent years, but the Master Handbook is still a really valuable resource. As much of a "black art" as acoustics tends to be, it seems to me that there's room for more than one person to be "right"... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...