TLA
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Post by TLA on Dec 31, 2021 15:39:46 GMT
My music room is 15x21 feet. I'm removing all of the drywall. The stud walls have 16" centers. I'll add Rock board 30 or 40. I will install a membrane surface to the entire stud wall perimeter. New stud walls will be build in front of existing walls with rock board and acoustic fabric for broadband absorption.
Looking for suggestions for the type of material and installation method for the membrane walls. Looking for most efficient bass absorption possible?
Quick and easy choice is 1/4" drywall screwed onto resilient channel at 24" centers. Maybe not the best material for maximum absorption.
ADD: The wall depth will be about 8". Would I achieve more low frequency flatenning with 6-8" of rock board as opposed to 3-4" of rock board in front of the membrane wall?
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Post by rock on Dec 31, 2021 20:46:18 GMT
I don't know how much 1/4" drywall on RC will absorb LF. My guess is that it may at least also reflect a fair amount of mid bass and higher up back into the room if it even absorbs much low bass at all. It could work the way you expect but panel absorbers are tricky to tune and you might need to experiment and make test measurements, take is apart and do it again a few times until you get it right.
However 8" thick mineral wool (Roxul etc.) will make a great broadband absorber if you leave it exposed to the room. Of course you will want to cover it for cosmetic reasons and for this you could use any acoustically transparent material just like the absorber panels we talk about all the time on this forum.
Now, if in your case you don't want to absorb mid or highs, covering the mineral wool with foil, thin plastic sheeting or kraft paper will enhance the LF absorption while reflecting some mids and highs back into the room...exactly like the bass traps we talk about all the time here.
Bass traps are most effective in corners (you already know this because you've read all the stickies by now, right?) because LF tends to accumulate there. So if LF control is a priority for, you can frame across the corners and install mineral wool there too before you cover with plastic and decorative cloth.
What I do know is that that last I heard, Ethan recommends porous absorbers over resonant panels even though he has build them in the past as you can see from his "Build a Better Bass Trap" article.
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Post by rock on Jan 1, 2022 15:23:10 GMT
Hi TLA, I re-read your post and I'm a little confused as to exactly what your plan is. A diagram would really help. Are you building a double wall for sound isolation from other rooms in the building? That's a great idea but if that's what you are doing, but you need to know that sound isolation (AKA"soundproofing") requires different techniques and materials than acoustic treatment. In short, for acoustic isolation, you need 3 layers, 1. Mass (usually two 5/8 drywall sheets thick), 2. Air space (filled with insulation) and 3. another Mass layer (two more 5/8 drywall sheets) if separate stud walls are used, at least one needs to vibration isolated from the floor and ceiling with compressed mineral wool. There's more details and I left out a lot but doing this will do nothing for room acoustics. After your isolated room is finished, only then can you start treating it acoustically. You can get away without building a double stud wall and just use a single stud wall with 2 sheets DW on one side and 1 or 2 sheets DW on resilient channel on the other side with insulation in the stud cavity. The latter is probably pretty good but I didn't mention "flanking" which is sound and or vibrations transmitted around the wall through adjacent walls, floors and ceilings etc. which can can negate some of your efforts. But I still wonder if isolation is even in your plan so in any case, a graphic of your plan would help. If you would like to see graphics of the above, I got this info from Rod Gervais' book www.amazon.com/Home-Recording-Studio-Build-Like/dp/143545717X
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TLA
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Post by TLA on Jan 1, 2022 22:19:42 GMT
Thanks Rock for detailed response. My plan is to make the room as close to anechoic as possible. It will be used for stereo listening and for speaker measurements together with outdoor free field measurements for speaker design purposes. Eliminating sound transmission isn't necessary but some reduction is needed. Its a basement room and need some reduction to rest of the home. In the diagram the 3.7' opening opens to furnace room - This wall and door can be open absorbers. the 10.3' opening will have track doors made with absorbers. the 2.5' opening connects to a hallway The entire room will have a high quality fit and finish with fabric and trim I'm now leaning toward 5.25" stud wall with 24" centers with 4" of rockboard 40. The openings have doors with 3" rockboard. no membrane anywhere, thanks! There is some ducts but cant do much about it except to box them and add about 1" thick rock board. The openings and furnace room will help with room modes.
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Post by rock on Jan 2, 2022 15:42:44 GMT
Thanks for the details. I free handed some more detail to your walls. It's not to scale but it should give you my basic ideas and I have made some assumptions from your illustration. To begin with, your anechoic goal can best be achieved by complete coverage with absorption. The floor is the exception and can be left reflective but you can use rugs or carpet. I added studs and insulation open to the room in your drawing. Hopefully the ceiling is open and you can also fill it with "fluffy" fiberglass (over 8" thick FG is considered just about as good as mineral wool/rockboard). You can cover the ceiling with fabric too. I also added more insulation in the corners for more bass trapping. You can also add more insulation in the ceiling/wall corners but if the ceiling is deep enough, filling the ceiling might be enough. For isolation, here's some things to consider: You'll see I used your yellow wall and drew a line to indicate a double layer of drywall to help reduce transmission. I also show a cut in two places to stop flanking. There are of course more serious flanking paths into the ceiling/floor above that will be difficult if not impossible to correct so you'll need to live with some room to room transmission. Being aware will allow you to do the best you can. For the ceiling/floor adding mass can help. If the floor above is open it's easier to add mass from above but it usually is not, so adding MASS (not bass, this was a typo) from below involves cutting drywall lengths to fit between the studs above (all in Rod's book). Ducting is another transmission path. Insulating around the ducts can help keep outside sound from entering the duct. If the duct is metal vibrations will travel the length. One way to stop this is to replace a section of metal with a section of insulated flexible duct; this will break the transmission path. Those are the general ideas, I hope you can make use of some. TLA room plan sketch.pdf (450.66 KB) Attachments:TLA room plan sketch.pdf (450.65 KB)
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TLA
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Post by TLA on Jan 2, 2022 17:31:40 GMT
You got me thinking. I can add more flanking, to ceiling etc. The wall that has the 21 foot dimension is outside foundation wall. I will be adding subfloor, likely drycore unless there's a better choice. Floor will be carpet. The ceiling depth is 12 inches and can fill completely.
I didn't really want corner traps but now trying to figure out if I can make it work.
Thanks!
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Post by rock on Jan 2, 2022 19:34:11 GMT
You wrote: "I can add more flanking, to ceiling etc."
I think maybe you meant "insulation" i.e. fiberglass etc. not flanking... You want LESS or ZERO flanking. Flanking is the conduction of sound vibrations in building materials that "goes around" a well built massive wall which minimizes or negates it by allowing the vibrations to enter the intended isolated room or area via another path. Flanking = Bad.
For the foundation wall, you'll have less to little sound transmission to the upstairs through the concrete BUT, you want a good seal of any space (compressed mineral wool, dry wall, caulk) along the joint between the foundation wall and the floor/wall above.
Sure, If you have a moisture problem seems like dricore is a choice (sorry, I don't have any experience/advice with that problem) but I doubt that it will influence the acoustics one way or the other. There is a thought that a reflective floor in an otherwise anechoic room gives the occupants a kind of spatial orientation by hearing footsteps etc. The other idea is that with total bandwidth ceiling absorption (excellent choice!) and partial bandwidth (hi mid and hi freqs only) as with carpet, that there is an imbalance in frequency spectrum of absorption and ringing etc. (I read about this from F. Alton Everest). If you do want to put something soft on the floor, a rug that is easily put down and moved is a good choice.
Regarding Corner Basstraps: Constuction wise, it should be as easy as framing across the corner and filling with insulation. Whether you want to or can give up the floor space is the only real problem I can figure.
Good Luck! Keep us posted!
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TLA
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Post by TLA on Jan 3, 2022 2:15:31 GMT
I meant to say anti-flanking, by removing solid connection from walls to ceiling.
The subfloor is going in the entire basement to keep space warmer. I was hoping subfloor would create some losses because it is floating but you're probably right and doesn't add any absorption. The floor treatment could be wall to wall carpet or vinyl plank like rest of the basement and then throw down a large rug..
The corner traps will take up space that could be used for some very deep 1920's chairs that we have. I wonder if membrane traps flat in the corners and properly tuned would produce good results.
Overall some great help. more thinking required. first steps are drywall removal, duct relocation. then framing, installing more receptacles etc, etc.
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Post by rock on Jan 3, 2022 14:49:49 GMT
Oh, anti-flanking, OK. But you'll still have the direct SPL on the ceiling/floor above. It really depends on how much attenuation you want. One thing I mentioned that you can do is to increase the mass of the bottom of the subfloor above you with drywall. If in doubt of structural status of your building, it's a good idea to hire an engineer to give an OK to adding mass, 2 layers is pretty heavy! (Details in Rod's book)
About the bass traps: With 100% absorption on the walls and ceiling, it could possibly be enough to get away without bass traps. Acoustic testing can give you the answer but not until you're farther along but you of course will be able to add them later. The deeper/thicker the wall Rockboard, the lower the frequency of absorption. Thin foil, plastic, paper etc. does also enhance LF absorption at the expense of some mid & hi freq reflection. Strategic placement/use of plastic etc, so sound source is not reflected back the the listening position is how bass traps are generally located. You might be able to do the same by locating plastic etc. as such. You could do this by trial and error/testing before you install your final decorative fabric.
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TLA
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Post by TLA on Jan 12, 2022 3:10:43 GMT
I'll keep you posted, with measurements, Thanks!
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TLA
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Post by TLA on May 11, 2022 0:10:36 GMT
I've started to remove the drywall.. One wall is the outside wall with a 2x4 stud wall with plastic, insulation and concrete foundation wall. I will leave the wall untouched.
The Concrete wall will be lossless so I'm thinking That I need some type of membrane over the wall so sound strikes "membrane" first and not the concrete. So from inside the room the layers would consist of acoustic fabric, rockboard, air gap, "membrane", air gap, vapour barrier, pink insulation, black tar paper, then concrete..
Do you suggest using a membrane? What is a good acoustic membrane material? for the purpose of creating a flatter bass response then the concrete wall would produce.. The rockboard addition will be max 3 inches..
Thanks, Joel
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TLA
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Post by TLA on May 11, 2022 1:41:35 GMT
I guess what I'm looking at is Diamphragmatic
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Post by rock on May 12, 2022 12:45:48 GMT
...for the purpose of creating a flatter bass response then the concrete wall would produce.. What you should want to do is to absorb the sound and eliminate (as much as possible) the reflections. Resonant absorbers can be built and Ethan has a page describing them if you want to go that route but if you read the details, porous absorbers are recommended for DIYers. So, if you use porous absorbers, thicker = Better lower LF performance so go as thick as possible. Below ~8" use rigid rockwool or FG above ~8" use fluffy FG. Sorry, I don't have a recommendation for membrane. Maybe someone else here can help.
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Post by Hexspa on May 13, 2022 0:57:25 GMT
I can't recommend a membrane either but thin plywood should work. You'll probably want to attach insulation to damp it though; or at least have some in the cavity behind it. Honestly, I don't know - I stick to absorption in the room for now.
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TLA
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Post by TLA on May 15, 2022 15:02:44 GMT
Thanks for the help. I thought pictures might generate more idea.. I'll build second 2x6 wall (filled with rock board) in front of the 4 walls with a small gap between them. The wall with the pink insulation is the only wall I'm considering for a membrane. Since I removed the drywall from 16 inch centers I'm wondering if the drywall had more acoustic performance than pink insulation in front of concrete.. One aspect of this room is the ceiling.. In my piano room thread I show pictures of Quadratic Diffusers.. I love the appearance and feeling of more height. the-audio-expert.freeforums.net/thread/780/piano-roomI would prefer the aesthetic of wood diffusers but for Stereo listening and speaker designing room, I imagine Insulation covered with acoustic fabric might ne best.. The depth between floor joists is 12". I could install 3" rockboard at the top. This leaves 9 inch depth diffusers with F low of under 500hz.. 12 Inches of rockboard will go lower so not sure which way to plan this.. Attachments:
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