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Post by Joe Hamilton on Feb 23, 2017 17:57:36 GMT
I just got home with my package of 12 ea. 24" x 48" x 2", un-faced OC 703.
Question: Are there significant gains to be had by leaving my wall panel/frame "open-backed", and spacing them just a few inches off the wall? (I can spare the inches on ceiling and walls - it's only me in here).
I read Ethan's article wherein he states that 703 spaced 16" from a wall almost triples 703's absorption coefficient at 125hz. But what about 4"-6" or so? Any figures on that? I'm trying to determine if it would make enough difference to warrant the extra fiddling.
Thanks
Side note: As far as framing around the edge of the 703 panels - leaving the 2" depth open/exposed may not seem like much - but at 288 sq. in. per panel x 12 panels I gain 24 sq feet of absorptive surface. I think that may be worth the extra effort.
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Post by rock on Feb 23, 2017 19:02:57 GMT
First, always leave the back open unless you're building recording studio gobos and even then, you probably want absorption on the back/reverse side. I don't think any of Ethan's designs use and enclosed back. Of course you can cover the back with fabric and still have an "open" back.
Spacing off the wall an equal distance of the thickness effectively makes your panel "work" like it's twice as thick, that is, it extends it's LF performance down one octave. More than doubling the spacing will further improve to even lower freqs but will leave "holes" were some freqs in between will not "see" as much improvement. In general, the use of 4" thick with 4" space is the most common recommendation for against walls and ceilings for reflection areas but 2" will work but with less LF performance. 4" panels across corners are good for bass traps, they should have either foil, paper or plastic spray glued the the front only.
Leaving the sides open does increase the effectiveness but frameless panels add mounting challenges and cosmetically, may not look as nice. Ethan's panels have holes on the sides and Hexspa uses metal "corner bead" to make his frames so much of the edges are exposed.
Cheers,
Rock
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Post by Joe Hamilton on Feb 23, 2017 20:17:19 GMT
Thanks for the informative reply, Rock - 'appreciate it.
Well, my first batch of panels are intended as mid-high freq absorbers. I am just wondering if bringing 703 2" - 4" - 6" off the wall yields any significant imp[rovement in performance - low frequency or otherwise. And while we're at it, I've been around long enough to know that most benefits involve some sort of trade-off. So... in Ethan's example of mounting 2" 703 16" off the wall yielding an almost three-fold improvement at 125hz, is there a reciprocal lowering of effectiveness at the high end? Because you usually cannot get something for nothing.
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Post by rock on Feb 23, 2017 20:46:07 GMT
Please read ALL of Ethan's web material. You'll find a diagram that explains spacing from the wall. Like I said before:
"Spacing off the wall an equal distance of the thickness effectively makes your panel "work" like it's twice as thick, that is, it extends it's LF performance down one octave. More than doubling the spacing will further improve to even lower freqs but will leave "holes" were some freqs in between will not "see" as much improvement. In general, the use of 4" thick with 4" space is the most common recommendation for against walls and ceilings for reflection areas but 2" will work but with less LF performance."
So yes, 4" to 6" space will perform lower than the 2" space BUT there well be frequencies in between that will be missed. That's the trade off. If you want your mid/high panels to operate lower without the "holes", use 4" thick with a 4" space. You'll get the same "hole" thing with the 4" thick if you space farther than 4".
And there is no trade off as far as your mid to highs are concerned so in the case of spacing, you DO get something for nothing if you don't count the space and the effort it takes.
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Post by Joe Hamilton on Feb 23, 2017 21:44:02 GMT
Ahhh... my kind of deal.So I read, "1 inch 703 absorbs reasonably well down to 500 hz, 2" ... is equally absorbent down to 250 hz." Can I then correctly extrapolate that 4" good to 125 hz, 1" with 1" space from wall good to 250 hz, 2" with 2" space to 125 hz, and 4" with 4" space to 62.5 hz? Maybe I'll just unwrap the whole danged bundle of 12 2" pieces and leave it on the floor - I'll be good down to 0.1220703125 Hz. 
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Post by rock on Feb 23, 2017 23:03:15 GMT
You've got the general idea but I think your numbers are too generous. When you say "reasonably well" what do you mean? I'd go up at least an octave or so. The 1/4 wavelength of 1000 Hz is about 3.4". And keep in mind that there's not a sharp cutoff but a gradual rolloff. Besides thickness, you need coverage too. Your pile on the floor will absorb a lower freq...but how much OF IT?
I still suggest you read and digest ALL Ethan's info, what you need is all there.
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Post by Joe Hamilton on Feb 23, 2017 23:20:21 GMT
Rock - I appreciate your patience and feedback. But, "703 fiberglass one inch thick absorbs reasonably well down to 500 Hz. When two inches thick, the same material is equally absorbent down to 250 Hz" is a direct quote from the first paragraph of the section entitled, "MIDRANGE AND HIGH FREQUENCY ABSORBERS" in Ethan's article "Acoustic Treatment and Design for Recording Studios and Listening Rooms", so I figured they were good. You don't agree?
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Post by Hexspa on Feb 24, 2017 1:48:57 GMT
Hey Joe. I heard you shot... n/m. For reference 100mm ≈ 4"  I don't know where I got this - maybe gs - but there you go; a visualization. I'm simplicity's advocate; 4" panels everywhere with 1-4x air gap. Paper your non-RFZ if you're feeling spicy. That's it. -m |
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Post by Joe Hamilton on Feb 24, 2017 2:20:01 GMT
So you saw me w/ that gun in my hand?? (Ruh-Ro).
Thanks for the graphic, H'. Me like pictures.
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Post by Hexspa on Feb 25, 2017 12:26:49 GMT
I guess you could say gapping a 4" panel 3x gives you double the performance at 50Hz while only sacrificing 10-15% at 400Hz, if that graph is to be trusted.
Given how well panels work at that frequency, that you'll be using multiple and since 400Hz is like twice the typical Schroeder cutoff, it seems like a good deal.
-m
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Post by rock on Feb 26, 2017 16:38:39 GMT
Rock - I appreciate your patience and feedback. But, "703 fiberglass one inch thick absorbs reasonably well down to 500 Hz. When two inches thick, the same material is equally absorbent down to 250 Hz" is a direct quote from the first paragraph of the section entitled, "MIDRANGE AND HIGH FREQUENCY ABSORBERS" in Ethan's article "Acoustic Treatment and Design for Recording Studios and Listening Rooms", so I figured they were good. You don't agree? Touché! But I guess the point is that the desired performance at a given freq is subjective below 1.00 since 1.00 theoretically indicates 100% (you'll notice you will see coefficient measurements >1 which should be impossible but this helps to explain: www.sengpielaudio.com/AbsorptionsgradGroesserEins.pdf ) and in any case, as you can see from Hexspa's graph example, the performance rolls off anyway so it all depends where you want to hang your hat. Maybe the main point should be since small rooms need as much LF absorption as possible, it makes sense to use thicker absorbers AND to cover enough area. When in doubt, acoustically measuring your room can indicate problem freqs and possibly the need for either a change of placement or more likely, just more absorbers. Cheers, Rock |
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Post by Joe Hamilton on Feb 26, 2017 16:57:05 GMT
Makes sense. I think I'm just going to start out with the dozen 2" 703 that I've got, stand it off from walls 2", and cover as much surface area of side walls and (sloped) ceiling area as I can. Then later add good & thick 705 to the front & rear walls.
Construction question. I've come up with a design to hold the 703 panels without blocking ANY of it's surface area, but this is going much further off the reservation than I planned (as usual). I see some folks simply wrapping all edges with metal drywall corner-bead, wrapping w/ fabric then installing. This doesn't seem like it would be rigid enough to last over time w/o sagging. Also, there's not too many 'installation' details as to how one would mount this (seemingly) flimsy structure.
Any experience or advice in regard to these two issues?
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Post by Hexspa on Feb 27, 2017 4:45:40 GMT
Makes sense. I think I'm just going to start out with the dozen 2" 703 that I've got, stand it off from walls 2", and cover as much surface area of side walls and (sloped) ceiling area as I can. Then later add good & thick 705 to the front & rear walls. Construction question. I've come up with a design to hold the 703 panels without blocking ANY of it's surface area, but this is going much further off the reservation than I planned (as usual). I see some folks simply wrapping all edges with metal drywall corner-bead, wrapping w/ fabric then installing. This doesn't seem like it would be rigid enough to last over time w/o sagging. Also, there's not too many 'installation' details as to how one would mount this (seemingly) flimsy structure. Any experience or advice in regard to these two issues? I think Ethan's tests showed that more total panels is better so you shouldn't be completely remiss to deploy 12 2" panels. Why do you want to add thick 705 to your front wall? If you're going to add that it would probably be better used on your rear wall or corners. To be clear, in my design (which itself is modified from elsewhere), I did not "simply" wrap the edges in drywall bead then, in turn, wrap that in fabric. My frames are riveted together and then the two are secured with 14 cable ties. The fabric is inside the frame against the insulation itself. It is a very tight, very stable and yet lightweight and open design. Absolutely not flimsy whatsoever. If there's any downside it's that I actually used zip ties which might look cheap to some people. You could probably use ribbon and make them look amazing though. The other downsides are that the edges are sharp and you *will* cut yourself eventually. Also, if you place them on a floor corner, you, or someone you love, *will* step on them bending the frame. Fortunately this doesn't affect their structural integrity much; it's just cosmetic detriment. I hang them using loop or hook screws attached to a basic thin black chain which itself is connected to another cable tie. The original design used mounting brackets so loop hooks could be screwed into the panel but that is totally unnecessary. You are always free to treat your room as you please but there is a great template available for you should you choose to accept it. -m |
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Post by Hexspa on Feb 27, 2017 5:18:33 GMT
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Post by Nigel Spiers on Feb 27, 2017 6:12:27 GMT
Hi Folks, I have mentioned this alternative previously and am still a little surprised that few if any on this forum seem to have taken advantage of Polyester Acoustic Panels. They are similar in acoustic spec to the "703" and "705" panels but have all the following advantages: 1. No need to cover them - they already come with fabric covering. 2. No need for an ugly frame around the panel - they are semi-rigid and never deform or slump even after 10+ years on ceiling or walls. 3. No fibres (fibers) to effect your breathing. 4. Inflammable. 5. Meet every commercial and domestic building regulation. 6. Inexpensive 7. Brilliant for corner bass traps. 8. Super light weight for ceiling and wall panels. 9. Look sensational right out of the box. 10. 25% more absorption than any framed panel. 11. Easy to cut with a bread knife. 12. No fumes. 13. Never fade even in direct sunlight after 10+ years. 14. Never crumble as all foam products do after just a few years. 15. 100% green - made from recycled products. 16. No fumes or glues used in manufacture. 17. No itching or scratching. Try them - you'll love them. Best Regards Nigel Spiers NZ Acoustics Ltd www.nzacoustics.com |
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