I sure wish there was a forum for room acoustics.
The family room in my new house has a half-vaulted ceiling over the family room. The ceiling has a simple slope of about 30 degrees which is much higher at one end. Where that peak ends into a vertical wall, I'm going to cut the drywall off the upper portion of the wall, staple grille cloth to the studs, and instead of the drywall, screw on horizontal slats of varying width with slots between them also varying. Then I'm going to build a huge plywood box in the attic, over the unvaulted ceiling inside the roof trusses, and stuff it with Roxol.
I'm hoping to avoid actually doing much calculation or measurement initially by making it extremely broad-band below the frequency that penetrates the slats. On the other hand, the cost of the Roxol insulation could be considerable. It won't be too hard to adjust the slat sizes and spacing if necessary after initial testing. I think I can do a decent job and have it nearly invisible from within the room. Adding high-frequency absorption and diffusion to the parallel walls is much simpler than adding big bass trips within the room.
The family room in my new house has a half-vaulted ceiling over the family room. The ceiling has a simple slope of about 30 degrees which is much higher at one end. Where that peak ends into a vertical wall, I'm going to cut the drywall off the upper portion of the wall, staple grille cloth to the studs, and instead of the drywall, screw on horizontal slats of varying width with slots between them also varying. Then I'm going to build a huge plywood box in the attic, over the unvaulted ceiling inside the roof trusses, and stuff it with Roxol.
I'm hoping to avoid actually doing much calculation or measurement initially by making it extremely broad-band below the frequency that penetrates the slats. On the other hand, the cost of the Roxol insulation could be considerable. It won't be too hard to adjust the slat sizes and spacing if necessary after initial testing. I think I can do a decent job and have it nearly invisible from within the room. Adding high-frequency absorption and diffusion to the parallel walls is much simpler than adding big bass trips within the room.
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Ideally I should also think about some ways to pitch those slats to provide some diffusion in addition to just being a big low-pass filter at the mouth of the stuffed attic chamber behind.
Do you even know you need the bass traps for room treatment? To me, your approach seems a little random. I don't think adding angled slats near the peak of the ceiling is going to accomplish much, and a broadband absorber across the whole room seems like a big project without a guarantee of expected results.
It would probably be considerably cheaper and more effective in the long run to consult a pro who can use this for you. Software - EASE - Enhanced Acoustic Simulator for Engineers
Maybe start by including actual dimensions of your room, wall construction, etc..? Drywall already absorbs a fair amount of "bass". I might also suggest buying the Master Handbook of Acoustics. https://www.amazon.com/Master-Handbook-Acoustics-Alton-Everest/dp/0071603328
It would probably be considerably cheaper and more effective in the long run to consult a pro who can use this for you. Software - EASE - Enhanced Acoustic Simulator for Engineers
Maybe start by including actual dimensions of your room, wall construction, etc..? Drywall already absorbs a fair amount of "bass". I might also suggest buying the Master Handbook of Acoustics. https://www.amazon.com/Master-Handbook-Acoustics-Alton-Everest/dp/0071603328
This is what I used:
REW - Room EQ Wizard Room Acoustics Software
and
https://www.minidsp.com/products/acoustic-measurement/umik-1
Using the curves plotted, I consulted with the GIK people {free} and got some mild modification of one of their standard room kits. That being said, my room is too small to truly treat the 40Hz boom in my room. (room =9.5x14 feet) I would need approximately 6 2x2x1 foot sized traps tuned for 40Hz.
Consider spending $75 for that microphone, and use the free software to at least estimate what you need to do to this room.
REW - Room EQ Wizard Room Acoustics Software
and
https://www.minidsp.com/products/acoustic-measurement/umik-1
Using the curves plotted, I consulted with the GIK people {free} and got some mild modification of one of their standard room kits. That being said, my room is too small to truly treat the 40Hz boom in my room. (room =9.5x14 feet) I would need approximately 6 2x2x1 foot sized traps tuned for 40Hz.
Consider spending $75 for that microphone, and use the free software to at least estimate what you need to do to this room.
I am definitely going to try REW. Posted asking about it months ago. I will need those spectral decay plots later when I balance the diffraction and absorption and tune the absorption.
The simulation software I've tried doesn't handle sloped ceilings or I would want to start there. Instead I get to predict the first room modes for the parallel walls.
I already have a decent measurement mic from my RTA. I suspect it's the same one with a different name on it, as the plastic case is identical.
Most commercial acoustic treatment products are not reasonably priced, and it's a great opportunity for DIY.
The reverberation time in there is ridiculous now with all hard surfaces. And I've never found a room that didn't need a big bass absorber. Of course an absorber that is narrow-band could be a much more effective and economical trap just at the worst frequencies. But the luxury of such a large broadband absorber is a really attractive place to start. The down side is that it requires a lot more stuffing than a more targeted approach. After looking around at various stuffing materials, it seems that one economical way to fill such a large box in the attic is to purchase used cotton-batt futons for $35 each. There's still a million of them in basements, unused since the 1970's. And Roxol seems effective and reasonably easy to handle. I have to measure the attic stair doorway before I purchase something that can't be installed.
Of course later I will also want to add curves, diffraction, and some high-frequency absorption to the two parallel side walls, carpet, etc. also.
The simulation software I've tried doesn't handle sloped ceilings or I would want to start there. Instead I get to predict the first room modes for the parallel walls.
I already have a decent measurement mic from my RTA. I suspect it's the same one with a different name on it, as the plastic case is identical.
Most commercial acoustic treatment products are not reasonably priced, and it's a great opportunity for DIY.
The reverberation time in there is ridiculous now with all hard surfaces. And I've never found a room that didn't need a big bass absorber. Of course an absorber that is narrow-band could be a much more effective and economical trap just at the worst frequencies. But the luxury of such a large broadband absorber is a really attractive place to start. The down side is that it requires a lot more stuffing than a more targeted approach. After looking around at various stuffing materials, it seems that one economical way to fill such a large box in the attic is to purchase used cotton-batt futons for $35 each. There's still a million of them in basements, unused since the 1970's. And Roxol seems effective and reasonably easy to handle. I have to measure the attic stair doorway before I purchase something that can't be installed.
Of course later I will also want to add curves, diffraction, and some high-frequency absorption to the two parallel side walls, carpet, etc. also.
The most accurate bass I've ever heard is in Jon Whitledge's Magic Bus. If you want good clean bass, copy what Jon did. It is extensively documented here : http://www.whitledgedesigns.com/magicbus_build_acoustical.php
I use multiple subs, and that works very well, but the results aren't quite as good as what Jon has achieved. Multiple subs sound *significantly* better than a single sub.
Dipole subs sound different than both solutions above, and sound good.
These are three solutions which are proven to work. I would discourage you from going down the road you're going, as I've never seen room treatment which successfully solved the bass problem. (Jon is the exception, and his solution is completely different than yours.)
Yes, for sure. Silly of people to waste time chasing the fantasy of surgically precise 6th order boxes* when rooms are the big determinant of bass at home.
You should start by taking Toole's book out of the library.
The term "trap" is used for some kind of gizmo which is carefully tuned or located for specific (and verified) purposes. More generally, the goal is to tame all reflections in your room which in practice means ensuing the bass notes get as much absorption as the rest of the tonal compass. Also, taming reflections that bear an undesirable timing (or loudness) with your speaker sounds.
A good approach is to use Tectum instead of drywall, esp.with bigger depth than 2x4 stud depth and maybe some stuffing. I don't know of a better way to proceed.
A lot of acoustics is non-intuitive so you need to study it a bit.
Ben
*unless they are just doing hobby experiments like some of the keener people on this forum
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Well I'm well on the way doing some things that ALL rooms need, but I changed my plan to use mostly relocatable and reconfigurable panels instead of modifying the house. My original plan would have been cheaper, but much less flexible. I built 30 2'X4'X4" absorbers using the GIK diy frame kits stuffed with ROXUL and covered with two layers of economical cloth meant for tablecloths. I also got 30 various thinner panels from Acoustimac on sale for treating the adjacent hallways and doors. I got several crates of 1'X1' acoustical ceiling tiles that interlock with tongue and groove edges and with beveled surface edges, which look a lot like the classic stuff in studios in the 1950's but now without any asbestos of course. They are not thick enough to have broadband performance unless I mount them over a base foundation layer of cheaper acoustical ceiling tiles meant for suspended ceiling grids. I got 12 2'X4' genuine RPG brand QRD diffusors. I got 4 fractal diffusors cut by hotwire from polystyrene expanded beadboard Styrofoam, and a gallon and an half of white epoxy to coat them with. I got a carpet and some kind of sisal or jute carpet mat under it. I got a better A/D D/A to use with REW. Still a lot of work to set it up before measurement.
Acoustics Blogs
There is an acoustics blog on the Audiocircle webpage:
The Acoustics Circle
And another on the AVS forum:
Acoustical Treatments Master Thread - AVS Forum | Home Theater Discussions And Reviews
There is an acoustics blog on the Audiocircle webpage:
The Acoustics Circle
And another on the AVS forum:
Acoustical Treatments Master Thread - AVS Forum | Home Theater Discussions And Reviews
Good moves. Fun to experiment.
But very hard to have good intuition about absorbents, at least for me. You need to know how each material and each spacing of air-space off the wall affects absorption.
Wise to establish a sold, repeatable, dependable method doing testing (such as a means of exactly repeatedly locating your mic in one or so locations repeatedly). Then to begin to experiment.
Ben
You got that right. The placement of the absorbers is critical . I built them with perfboard as the back panel so there is benefit to spacing them off the wall. The actual ideal placements for velocity absorbers (not pressure absorbers) is never convenient. With my sloped ceiling, hanging panels dangling by one edge mid-way between the parallel side walls absorbs all odd-order modes. Then another panel should be hung 1/4 of the distance between walls. Another 1/6 of the way.
The most effective place for bass traps that I've found is in room corners ...where the energy buildup is....it's like fishing where the fish are 😀
Best trap I've found is big rigid fiberglass steampipe insulation.
Wrap them in fabric for WAF, cap them airtight, and they work.
Here's the best pict of one I could find on phone....
they make great stands too...I've had 300lbs on them no prob...
Best trap I've found is big rigid fiberglass steampipe insulation.
Wrap them in fabric for WAF, cap them airtight, and they work.
Here's the best pict of one I could find on phone....
they make great stands too...I've had 300lbs on them no prob...
Attachments
Reminds me of a related material in the tiny category of things that work at low frequencies: a kind of thick fibreglass white cloth (like an inch thick and a pound per sq foot) that is used for furnace insulation. I've used it for motorcycle mufflers which is a really demanding application.
B.
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