high vs low air flow resistivity *confused*

[avare]

Originally Posted by HiFiPizza

I'm confused about the ideal air flow resistivity of porous absorbers. Should it be HIGH or LOW for a) first reflection absorption and b) bass traps? Three different people tell me three different things. So I ask here, I think you guys will know it right.

It involves the thickness. The thicker the absorber, the less GFR. Think of it like alcohol. If you want a total of 1 ounce of alcohol, you can drink 2.5 ounces of 80 proof vodka or 20 ounces of beer.

Your question of the two types of absorbers comes down to, you guessed it, how thick they are. For first reflection points, the minimum depth I recommend is 8" (200mm).

Andre

[Jens Eklund]

+1

[HiFiPizza]

So, I got some 10cm glaswool with a lenghtwise GFR of ?5 kPa/s.m². Can I use this for first reflection or will it leave me nothing? BTW it's not for a pro studio, "just" an audiophile 2 channel listening room.

[avare]

Originally Posted by HiFiPizza

So, I got some 10cm glaswool with a lenghtwise GFR of ?5 kPa/s.m². Can I use this for first reflection or will it leave me nothing? BTW it's not for a pro studio, "just" an audiophile 2 channel listening room.

If the question mark is 1, then yes.

Unquestionably,
Andre

[HiFiPizza]

Damn, sorry, it's not supposed to be there! The GFR (lengthwise) is 5! Not 15! Is it still good enough for an listening room or won't I be happy?

[avare]

Originally Posted by HiFiPizza

Damn, sorry, it's not supposed to be there! The GFR (lengthwise) is 5! Not 15! Is it still good enough for an listening room or won't I be happy?

You could be happy from many things. It is not a question of "good" but appropriate at 10 cm thickness. I recommend doubling it to 20 cm thickness for first reflection points.

Andre

[Alkamist]

Originally Posted by avare

It involves the thickness. The thicker the absorber, the less GFR. Think of it like alcohol. If you want a total of 1 ounce of alcohol, you can drink 2.5 ounces of 80 proof vodka or 20 ounces of beer.

Your question of the two types of absorbers comes down to, you guessed it, how thick they are. For first reflection points, the minimum depth I recommend is 8" (200mm).

Andre

Andre,

I have been messing around with some numbers with a porous absorber calculator and I seem to be getting really good results with 8" of a ~8000 Pa*s/(m^3) absorber with an 8" airgap. I would really like to do something like this for all of my panels in my studio but I can't seem to find a good material that I can easily buy in bulk with this GFR. Can you perhaps give me any pointers in what material to buy and where to find it?

Thank you very much!

[avare]

Originally Posted by Alkamist

Andre,

I have been messing around with some numbers with a porous absorber calculator and I seem to be getting really good results with 8" of a ~8000 Pa*s/(m^3) absorber with an 8" airgap. I would really like to do something like this for all of my panels in my studio but I can't seem to find a good material that I can easily buy in bulk with this GFR. Can you perhaps give me any pointers in what material to buy and where to find it?

Thank you very much!

Six city blocks east of my home and 1 km north. Seriously, where are you? As you may have noticed absorption is not that sensitive to GFR. Safe n Sound is around 10,000 rayls. At that total thickness 16" "pink fluffy" (GFR ~4k rayls) would be just as good, and probably cheaper.

Andre

[Jens Eklund]

Originally Posted by avare

I recommend doubling it to 20 cm thickness for first reflection points.

+1

[jim1961]

I am using 12" (300mm) R19 (pink fluffy - 5000 ralys) at first reflection points with good results. If you have that much real estate, I would use it.

[avare]

Originally Posted by jim1961

I am using 12" (300mm) R19 (pink fluffy - 5000 ralys) at first reflection points with good results. If you have that much real estate, I would use it.

+1.

Andre

[Alkamist]

Originally Posted by avare

Six city blocks east of my home and 1 km north. Seriously, where are you? As you may have noticed absorption is not that sensitive to GFR. Safe n Sound is around 10,000 rayls. At that total thickness 16" "pink fluffy" (GFR ~4k rayls) would be just as good, and probably cheaper.

Andre

Sorry, I forgot to mention I live in the Orlando FL area. And wow if I can get away with using regular pink fluffy I will definitely do that. I'm thinking 16" with a 16" airgap if I can. My sub-bass would be really tight then haha. If I find that is not realistic for my situation I guess I'll just have to go with Safe n Sound.

Originally Posted by jim1961

I am using 12" (300mm) R19 (pink fluffy - 5000 ralys) at first reflection points with good results. If you have that much real estate, I would use it.

Nice! How big of an air gap are you using? Do you mind elaborating on your mounting method?

[jim1961]

Originally Posted by Alkamist

Nice! How big of an air gap are you using? Do you mind elaborating on your mounting method?

No air gap. When its this thick, no air gap is necessary. What I did was build a 60" wide x 72" high (in 3 sections) cage out of 1x2 and covered it in cloth.



I plotted 12" no gap (blue) and 16" with a 16" gap (green). Just depends how much absorption you need in the low bass to which way to choose.

[Alkamist]

Originally Posted by jim1961

No air gap. When its this thick, no air gap is necessary. What I did was build a 60" wide x 72" high (in 3 sections) cage out of 1x2 and covered it in cloth.

Attachment 312362

I plotted 12" no gap (blue) and 16" with a 16" gap (green). Just depends how much absorption you need in the low bass to which way to choose.

Thanks =D

Yeah I figured 16" with a 16" airgap would be a lot better in the sub-bass region. I'm just a little concerned that 32" coming out of both side walls would feel a bit encroaching. There is also the possibility of the frame on the sides causing too much reflections. I'll just have to do some brainstorming I guess. Maybe I'll go with 12" material with a 12" airgap or something.

[jim1961]

It looks like 20" with no gap does nearly as well as 16" plus a 16" gap. Saves 12"

[Alkamist]

Originally Posted by jim1961

Attachment 312384

It looks like 20" with no gap does nearly as well as 16" plus a 16" gap. Saves 12"

Ooohh thanks for the tip!

I guess I just need to figure out whether or not I want to spend the money for the extra 4" of fiberglass. I'm planning on going absolutely bonkers if I can find enough R-19 at a low price. I could potentially treat my first AND second reflection points with one monster panel on each side =D

[avare]

Originally Posted by Alkamist

Ooohh thanks for the tip!

I guess I just need to figure out whether or not I want to spend the money for the extra 4" of fiberglass. I'm planning on going absolutely bonkers if I can find enough R-19 at a low price. I could potentially treat my first AND second reflection points with one monster panel on each side =D

Filling it is best. If you want to feel like you are saving lots of money, compare doing the trap with 703! "Regular pink fluffy" is dirt cheap compared to 703 etc. Do not screw yourself with false savings.

Andre

[Alkamist]

Originally Posted by avare

filoinj git is best. If you want to feel like you are saving lots of money, compare doing the trap with 703! "Regular pink fluffy" is dirt cheap compared to 703 etc. Do not screw yourself with false savings.

Andre

Yeah I think I might just go with filling the whole space. It seems to be pretty efficient, and it performs quite well as the angle of incidence gets larger. Either option though is worlds cheaper than 703