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Post by MarkusKid on May 30, 2019 18:11:52 GMT
Hi everyone. Well, I'm currently building some DYI bass and other traps and had two quick questions I'm hoping I can get some answers to.
First question, what can I use in place of the factory FRK material? I bought un-faced 702 0r 703 of varying thickness. I got a hole bunch of it for $15 a panel from a building supply house that went out of business and needed it gone. I understand it needs to be glued on and with the FRK facing the room. Second question, When it comes to points of first refection, should I use the thinner or thicker panels? And the FRK (or equivalent) should be faced towards the wall, with an air gap. Is this correct?
Thank you, I appreciate an help.
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Post by MarkusKid on May 30, 2019 18:13:53 GMT
Sorry, I meant $5 a panel not $15. Not that it matters, lol.
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Post by ultrasonic on May 30, 2019 18:30:59 GMT
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Post by Hexspa on May 30, 2019 21:24:41 GMT
Welcome, Markus. Congrats on your deal. Firstly, use spray glue and only as little as you need - which isn't much - to adhere the FRK. The membrane itself can be any number of materials from paper-thin metal, grocery bag material or even a combination thereof. The exact properties of each are unknown so use common sense.
The standard way to mount FRK is facing the room. Ultrasonic, as you'll see if you read his thread, has inquired into the possible benefits of rear-facing FRK but the fact is that it's experimental - possibly good, better, or worse - and it's not what I advise de rigueur.
Rigid panels, such as yours, may be up to 8" thickness before you're better off using fluffy insulation. While I have never used panels that thick, I can confirm that the difference between 2" and 4" is substantial as far as RFZ panels go. Being that RFZ is all about mid-to-high frequencies, I don't know where in thickness any point of diminishing returns occurs or whether it does in that application.
One thing is for sure and that is that you want maximum surface coverage and also 4" is pretty much the minimum thickness you use for bass. In other words, if you can cover your key areas with 4" but not quite cover them with 8" then opt for the thinner panel with more covered area. However, if you can maximally cover your key surfaces with 8" then - by all means - do so. Your definition of 'key area' will generally mean RFZ and angled corner panels but can also include targeted modal treatment on parallel walls though that is more advanced, in my opinion.
Above all: keep it simple and don't worry about the minutiae until you master the basics.
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Post by MarkusKid on May 31, 2019 15:26:03 GMT
Thanks, Hexspa and ultrasonic.
I'm a little confused now. Why? because, well this is Ethan's site and he's the expert and I'm under the assumptions all his claims are backed be data. Ethan posted on another forum (are links allowed?) that at non-reflection point to face the paper/FRK towards room and for reflective areas to face the the paper/FRK towards the wall if there is an air gap. And he specifically said, if you are going to mount them flush to the wall, then using FRK on the back defeats the purpose. What am I missing? It's not like Ethan to make recommendation without first having done his research and experiments. Very confused now!
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Post by Hexspa on Jun 1, 2019 10:25:05 GMT
From what I've gathered from his site, I don't use FRK for my RFZ panels. Ethan has said that he's tested rear FRK but I haven't seen any conclusive comparative data. You're free to listen to whoever you choose but FRK usually faces the room and dosn't go on RFZ panels.
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Post by MarkusKid on Jun 2, 2019 2:02:30 GMT
It's not about choosing who to believe, I don't know you or Ethan. I do know in another thread on this very site (right above this one in fact) Ethan stated days ago that he did in fact test paper on back facing the wall on RFZ panel and the results were improvement over no paper. I'm just trying to understand why you don't seem to agree with him, you don't seem to have any data, Ethan claims he ran tests, but also can't provide data. Do you feel Ethan is mistaken or mis-remembering his testing?
Thanks for the help!
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Post by ultrasonic on Jun 2, 2019 7:40:32 GMT
When it comes to points of first refection, should I use the thinner or thicker panels? My (novice) understanding is that acoustically thicker is better, since it extends the frequency range over which they are effective. 2" with a 2" gap seems to be generally taken as sufficient for the primary role of RFZ panels though. The advantages of thinner panels are being cheaper and taking up less space.
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Post by Hexspa on Jun 2, 2019 12:59:37 GMT
It's not about choosing who to believe, I don't know you or Ethan. I do know in another thread on this very site (right above this one in fact) Ethan stated days ago that he did in fact test paper on back facing the wall on RFZ panel and the results were improvement over no paper. I'm just trying to understand why you don't seem to agree with him, you don't seem to have any data, Ethan claims he ran tests, but also can't provide data. Do you feel Ethan is mistaken or mis-remembering his testing? Thanks for the help! Fair enough. Here's my understanding: Ethan knows a lot - and with great accuracy. What he doesn't know is your exact room - no one does - especially until you take a measurements. Therefore, some of his advice will not apply to every situation. I know this because his general advice to 'treat the rear wall completely' did not produce the best results in my room - at least with the amount of broadband absorption currently at my disposal.
I want to add one thing here: there's likely a gap between the results of one's hypothesized first layout and the final optimized arrangement. In other words, it's all well and good to start with rules-of-thumb and your best educated guess but, ultimately, the acoustic measurement will bear out the truth. In that sense, unless you're either willing to make iterative improvements or find someone to help you - paid or otherwise - any general information will only take you so far.
Ever since I realized this, I only talk about what I've personally tested. If I mention something with which I have no first hand experience, I qualify it as such - like diffusion. Strangely, I've rarely heard of rear-facing FRK for RFZ until this week and now you and ultrasonic both are questing for knowledge. I don't have experience with testing this, nor have I seen reliable data nor is it standard industry practice to measure a panel this way.
Furthermore, and I can be wrong, it seems like most of the people who want to know esoteric information such as this tend to be those with no experience treating a room properly whatsoever. I can forgive this, of course, since I was exactly in this spot not long ago. However, for all of these reasons, I have a standard concept which I liberally apply to all who are beginning their acoustics journey.
I base it on what is my best understanding through experimentation and measurement. This way, if something goes wrong, I can diagnose it. Also, it has the added benefit of me not speaking out of my butt.
It's one thing to take information on authority - totally valid - but it's quite another to know what works for you and develop your own concept - and to stick to it - when sharing information with others. I've been considering testing this reverse-FRK but I've got other things higher up on my priority list right now. Perhaps one day I will - it's definitely an area with demand but little supply.
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Post by Hexspa on Jun 2, 2019 13:01:14 GMT
When it comes to points of first refection, should I use the thinner or thicker panels? My (novice) understanding is that acoustically thicker is better, since it extends the frequency range over which they are effective. 2" with a 2" gap seems to be generally taken as sufficient for the primary role of RFZ panels though. The advantages of thinner panels are being cheaper and taking up less space. 2" vs 4" for RFZ panels, for me at least, was like night and day. The extra thickness gives you more clarity lower in the spectrum - definitely within the range of a stereo image. In other words, 2" will focus the hi hats well enough but 4" will get you stereo delays around 200Hz for synth chords and vocals. FWIW, Ethan has never shied away from recommending even 6" for RFZ and I would love to make all my panels 1' fluffy with a 1' gap before long.
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