|
Post by guitarman713 on Mar 11, 2017 18:45:11 GMT
Hello Ethan,
I've got a "recessed" entry doorway into my single room home recording studio with dimensions of 12.25' L x 10.54' W x 9.3' H (actually the walls are 8'tall and begin to slant in towards a center rectangular portion of the ceiling that is a flat 10' high, I've determined the average height to be about 9.3').
The entry way is 2.16' deep, 3.25' wide, and 9' tall. So should I consider this as adding about 70 square ft of surface area and 63 cubic ft of volume to my overall room dimensions when doing room mode calculations and sabin/reverberation time calculations, or does it even matter?
I'm wondering if this entryway gives me any sort of acoustic advantage, like naturally trapping bass or reducing flutter? This entry way will be directly to my right when I'm sitting at the listening position, and its directly opposing a 4x6ft window on my left wall.
I'm also wondering if I should treat it with a bass trap in the wall-ceiling corner above the door, or put a diffusor in there? Or perhaps a 4" home made OC 703 panel? Or maybe its best to just leave it alone because it isn't a problem.
The other thing I'm wondering about is your statement that it is not possible to have too many bass traps, so apply as many as you can. Is this true if you are hoping for sufficient bass trapping by only using 4-6 inch thik OC 703 panels in corners, on walls, and on ceiling? Or is it only true for specially made membrane type bass traps like your mini and mondo traps? Will sticking to only the OC 703 provide too much absorption at higher frequencies and too little absorption at lower frequencies and result in a dead sounding room? I'm basically unsure if I need to limit the number of OC 703 panels I use or should I just go to town and build as many as I can?
I have read the majority of your articles and forums and have learned a lot, thank you very much for sharing your knowledge with the rest of us!
Marco
|
|
|
Post by Hexspa on Mar 11, 2017 21:08:39 GMT
My understanding is that the likelihood of going over budget or losing one's patience comes far before you have too much broadband absorption.
Deadness isn't desireable in small rooms but it's an inevitable byproduct of improving low end response. Plus, whatever reflections you have are probably prone to flutter echo or other unwanted resonances. Therefore, once your low end is treated to the degree desirable then you can add diffusion to add liveness back in or improve what's there.
I'm having trouble visualizing the shape of your room. My understanding is that anomalies, like your door, are better at your rear and do help break up modal response. Being that it's at the side it will change how your side wall acts as a modal barrier. It adds volume, which is good, but potentially at the cost of symmetry. It could also cause additional resonances. Plus, since it's a door, there's not a ton you can do to treat it.
Anyway, if half of this is false I look forward to being corrected.
-m
|
|
|
Post by rock on Mar 11, 2017 22:02:22 GMT
From what I gather, there is no door but a door size opening into the room from a small hallway. If this is the case, as Hex stated, this is probably better at the rear and being on the side can mess with the symmetry. To balance the door opening, which in theory acts like a non reflective absorber, treat the opposing wall with the same area size and shape wide band absorber. Inside the small doorway, minimize reflections back into the room with absorbers. I don't think you have to go crazy with deadening the doorway area but a few well placed panels should knock down any flutter echoes and one on the back of the door (if it is at the end of the doorway) will absorb sound which may otherwise be reflected back into the room. You want wide band so build the panels like RFZ's without paper/plastic that you would for corner bass traps.
Bass trap would be fine above the doorway but you should do that all the way around the room if you can as well.
As usual, you need all the bass traps you can fit. If you measure as you go, you should see improvement.
As far as calculations, if you are so inclined, calculate both ways and then compare with measurements.
Cheers, Rock
|
|
|
Post by guitarman713 on Mar 11, 2017 23:34:11 GMT
Thanks guys. I guess the main thing I'm trying to figure out is if I should be following guidelines for reverberation time to be between .2 and .4 seconds for this size of a room (1200 cubic ft) and whether or not using the sabine equation and calculating absorption for each frequency band is necessary or even accurate (which I've already done). My spreadsheet for calculating absorption and RT60 times is showing me I could easily add "too many" traps and 703 panels (I could easily add enough for the calculated RT60 times to go below .2 seconds, especially below 2kHz, if I placed 703 panels on all of the surfaces I'd like to.
Wondering if I should limit my 703 panels to hit just the main early reflection points (sides, front, ceiling), or just put them everywhere I think they'd help out to get maximum absorption and then just hope for the best experimenting with diffusion.
I've also heard mixed things about diffusion working in small rooms. I'm going to add diffusion, just not sure to what extent and how that could effect reverberation times. Also trying to find out if particular diffusor types are better for smaller rooms, or if variety is best.
|
|
|
Post by guitarman713 on Mar 12, 2017 0:09:47 GMT
I guess if I wanted more surface area coverage with out adding "too much" absorption I could go with 2 inch thick 703 panels instead of 4 inch thick, or use the FRK version for some of the panels.
The question of "too much" absorption still remains...
|
|
|
Post by rock on Mar 12, 2017 15:18:09 GMT
The biggest problems with small rooms are, and what we treat first are LF peaks, nulls and modal ringing plus early reflections and flutter echo. Lower RT60's will be a byproduct of those treatments, not the goal. Measure LF peaks/nulls with the 2D freq response and modal ringing with the 3D waterfall graph. If anything, you can use your RT60 measurements to fine tune your ratio or balance of RFZ absorbers (wide band) to bass traps (made with paper/plastic fronts to improve LF thereby reflecting some mid/high) to achieve a flat RT60 in which case you could adjust the ratio by adding more absorbers of one kind or the other.
As far a 2" VS 4", thicker is better everywhere. With 2" you'll remove mid/highs while doing little to nothing for LF modes, etc which you have too much of anyway.
In another thread I read, Ethan recently said all (small?) rooms sound bad, we want to make them less bad. So I take that to mean no, you cannot have too much absorption.
Cheers, Rock
|
|
|
Post by Hexspa on Mar 12, 2017 19:12:48 GMT
free your mind of having fear of using too much absorption unless your room is really big and of a golden proportion -Yeats
|
|
|
Post by guitarman713 on Mar 12, 2017 19:52:45 GMT
Looking at Ethan's "rigid fiberglass density tests" again. This is the only data I can find on comparing 703 and 705 (plain and FRK) at frequencies below 125Hz. All of the other published absorption coefficient data stops at the 125 band. Am I correct to conclude from his test that the 705 FRK is superior for frequencies below 200 Hz? His results appear to show a slight advantage with 12 3-inch 705FRK in comparison to 6 6-inch 705FRK. I am curious to know if 12 panels of 6" thick 705 FRK would have been even better than both of his tests. Regardless, it appears that for low frequencies, his tests demonstrate that 705FRK at least 3-inches thick is the way to go. Does anyone know of any other data that may support that conclusion?
I'm considering going with 6 6-inch 703 plain for my RFZ panels, and 6 4-inch 705FRK panels spread around the room to help support LF control (to supplement my manufactured membrane style corner bass traps).
It seems that everyone agrees that spacing the panels away from the wall leaving airspace equal to panel thickness significantly improves absorption compared to mounting directly against the wall?
|
|
|
Post by rock on Mar 13, 2017 2:09:38 GMT
Ethan's test with 3" and 6" panels was to show the same volume distributed was better than doubled up. You are also correct to conclude that even better LF results could be obtained with 12 6" panels.
With so few panels, you too may get better results with 12 3" instead of 6 6" but even better with 12 6". Yes, spacing equal to thickness is good.
6 4" FRK's is on the sparse side too. What is the area coverage of your other membrane traps and where are they located?
Cheers, Rock
|
|
|
Post by Hexspa on Mar 13, 2017 4:34:33 GMT
It seems that everyone agrees that spacing the panels away from the wall leaving airspace equal to panel thickness significantly improves absorption compared to mounting directly against the wall? We agree cause it's true
|
|
|
Post by guitarman713 on Mar 13, 2017 12:55:39 GMT
What is the area coverage of your other membrane traps and where are they located? Haven't bought them yet, but I'm pretty sure I'm going with GIK's Tri-traps, soffit traps, and Monster traps. for the bass traps. They appear to be a better bang for your buck than Realtraps Mini and Mondo traps. Was thinking of getting some of each because they each have different absorption peaks. Planning on stacking each wall-wall corner from floor to ceiling. Right now I'm considering 4 Tri-traps, one at the bass of each wall-wall corner. Then was thinking of topping off 2 corners with the Soffit traps, and the other 2 corners with monster traps. You're right, I'll need more than 6 4-inch 703 panels for my RFZ. I'm thinking 12 now. From what I've said here so far, here are the RT60 times I'm getting on my spread sheet (from 125Hz to 4kHz bands): RT60 0.19 0.21 0.25 0.31 0.33 0.31 So based on the advice I'm receiving here (since my room is not large and of golden proportion), I should basically just ignore those RT60 times and continue on to make some 705FRK panels to spread around the wall-ceiling corners. Hey,I just thought of a slogan adaptation: "KEEP CALM AND TRAP ON!" So in order to achieve the boost in bass absorption with the FRK, you want the FRK paper side facing the room, right? Or does that just effect the absorption at the higher frequencies? Is it correct that using the 705FRK will boost bass absorption no matter which side the paper is on, but if you want to limit higher frequency absorption you should put the paper facing the room?
|
|
|
Post by rock on Mar 13, 2017 22:19:37 GMT
Right, don't worry too much about RT60.
AFAIK, FRK goes on toward the room for better LF performance.
Cheers, Rock
|
|
|
Post by Ethan Winer on Mar 16, 2017 16:16:48 GMT
You're already getting great advice, so I'll address only this: The entry way is 2.16' deep, 3.25' wide, and 9' tall. So should I consider this as adding about 70 square ft of surface area and 63 cubic ft of volume to my overall room dimensions when doing room mode calculations and sabin/reverberation time calculations, or does it even matter? Mode calculations are mostly meaningless for a room that's already built. If the modes look bad you'll be upset and unable to do anything about it. If the modes are good I suppose you can feel smug and pat yourself on the back for your good luck.
|
|