best thickness for acoustic absorber??

[praashekh]

what would be the considered one of the best thicknesses for an acoustic panel made of rockwool that could absorb .. the whole frequency spectrum?? i mean absorb VERy VERY low frequencies like 20-40hz range too??

[Nordenstam]

Depends on density of material.

Have a play with this: Porous Absorber Calculator V1.55

Normal fluffy is about 5000 rayls/m with denser fibreboard around 15000-25000.

(download open office if needed, it's a free!)

As you'll see, friction absorbers are not particularly effective at such low frequencies unless extremely deep.

[avare]

Originally Posted by Lupo

As you'll see, friction absorbers are not particularly effective at such low frequencies unless extremely deep.

+1

Andre

[SeniorityFedup]

Friction absorbers?

[avare]

Originally Posted by SeniorityFedup

Friction absorbers?

Difficulty with translating languages. "Friction absorbers" meaning absorbers that work by applying friction to the moving air particles of the sound wave. AKA porous absorbers.

Andre

[praashekh]

the shop guy in my city has some raw glasswool stuff... but doesnt seem very dense.. he also had some rockwool (thinking of using that) .. but he doesnt have anything inthe very dense category.. so i'll have to take maybe 3 2inch rockwool boards and stack them together... this way i'd have 5-6inch thickness.. would 5- 6 inches thick be good enough for all frequencies??

[andrebrito]

You need to work with a membrane and a massive air cavity to achieve absorption at those frequencies... wavelength is just too large on those freqs for porous absorption

[Glenn Kuras]

I know filling the corner will go down to 40hz pretty well, but below that is going to be pretty darn hard. IMO it is all garbage below 40 to 50hz so I would not worry about it.

[praashekh]

Originally Posted by Glenn Kuras

I know filling the corner will go down to 40hz pretty well, but below that is going to be pretty darn hard. IMO it is all garbage below 40 to 50hz so I would not worry about it.

so it wouldbe better to go with superchunks?? instead of just broadband absorbers on the corners?? i dont have One corner fully coz the doors in that way.. its about 8 inches from the corner.. should i put a trap there anyway?/ and make a similar looking one of the other side?? im worried it wont be very symmetrical..:-(.. if i have one small in one corner and one big one in the other corner.. ..

[praashekh]

Originally Posted by andrebrito

You need to work with a membrane and a massive air cavity to achieve absorption at those frequencies... wavelength is just too large on those freqs for porous absorption

wht do you mean by massive air cavity?? and membrane?? what kind of membrane do u suggest?/ and how big should the cavity behind the trap(this is what u mean right) be?? around maybe 3 - 4 inches off the wall??

[Glenn Kuras]

Originally Posted by praashekh

so it wouldbe better to go with superchunks?? instead of just broadband absorbers on the corners?? i dont have One corner fully coz the doors in that way.. its about 8 inches from the corner.. should i put a trap there anyway?/ and make a similar looking one of the other side?? im worried it wont be very symmetrical..:-(.. if i have one small in one corner and one big one in the other corner.. ..

It the corner is in the back of the room (behind where you sit) then symmetry is not that big of a deal. If in the front then yes you want to keep them the same.

[praashekh]

Originally Posted by Glenn Kuras

It the corner is in the back of the room (behind where you sit) then symmetry is not that big of a deal. If in the front then yes you want to keep them the same.

ya its the back of the room... but is 8-9inches from one sideof the wall enough?/ i could have it symmetrical then.. use the absorbers at very slight angles.. maybe 12 - 15 degree angle.. so there wouldnt be a 90 degree wall left.. the front is undone.. but is symmetrical.. though i dont know what to do with it..
Garage conversion to studio.. need help planning..

This is the link to the other post i put up.. to help with the positioning of furniture..:-P...

[Glenn Kuras]

I would not worry about that corner so much. You can always straddle upper corners or floor corner.

[Arksun]

If only doing some initial bass trapping, which areas are most effective. Treating 2-edge corners at direct reflection points, or treating tri-corners of the room with the same amount of material.

Always wondered about that....

[praashekh]

Originally Posted by Glenn Kuras

I would not worry about that corner so much. You can always straddle upper corners or floor corner.

oh alright.. thanks .. anyway.. what thickness do you think that all my other broadband absorbers should be? in order to get to the lowest frequencies?? i know below 40hz is almost no 'music'... but thats where the masses start to 'feel' the music..lol.. thats why need to take care of it a bit...

[Glenn Kuras]

Originally Posted by praashekh

oh alright.. thanks .. anyway.. what thickness do you think that all my other broadband absorbers should be? in order to get to the lowest frequencies?? i know below 40hz is almost no 'music'... but thats where the masses start to 'feel' the music..lol.. thats why need to take care of it a bit...

I would make them no less then 6" and a lot of them.thumbsup

[praashekh]

Originally Posted by Glenn Kuras

I would make them no less then 6" and a lot of them.thumbsup

great.. 6" it is then..:-)... having them at key reflection points would be enough for now i hope.... someday later maybe i'll try and change the shape of the room by making large 6inch panels..(from floor to ceiling).. hope that would work too...:-)..

[Glenn Kuras]

Just keep in mind that if you are trying to hit 40hz and below it will take a lot of panels.

[praashekh]

Originally Posted by Glenn Kuras

Just keep in mind that if you are trying to hit 40hz and below it will take a lot of panels.

lots of panels???/ i didnt get it?? i mean.. just making them thicker would make the frequency lower right?? i didnt know about having more would be better... can you plz explain this?? its very new and interesting..

[SaSi_SiDi]

30 ~ 50Hz range is typically the range of the room modes (resonances). These are standing waves between opposite walls.

These resonances generate really high peaks and nulls with a range of 30 ~ 50 dB between peaks and valleys.

You need lot's of absorbtion to get rid of them and practically, what you need is to eliminate the "oposing walls".

So, one way to achieve this is by covering as much wall surface as possible with absorbers. You could also interweave QRD panels, especially in the back walls, to avoid overdeadening the room.

[praashekh]

Originally Posted by SaSi_SiDi

You need lot's of absorbtion to get rid of them and practically, what you need is to eliminate the "oposing walls".

.

i was thinking of making these thick panels right from the floor to ceiling.. therefore it would be like having a new wall there.. and would make these false walls in such a way that none would be parallel.. maybe make the room in an septagon shape or something.. this would work right?? but dont quite have the money for it now.. so will just do these small 2x4 panels for now at just ear level..

[Glenn Kuras]

Originally Posted by praashekh

lots of panels???/ i didnt get it?? i mean.. just making them thicker would make the frequency lower right?? i didnt know about having more would be better... can you plz explain this?? its very new and interesting..

Your right that making a panel thicker will absorb more low end, but only a given amount at a given frequency. The lower you need it to work the less the panel will absorb, so you need to increase the surface area to yield enough sabins (absorption).
The short answer is more is better.

[praashekh]

Originally Posted by Glenn Kuras

The short answer is more is better.

Got the point..:-).. thanks... will try and make as many panels as possible... for now... later i'll just maybe make complete thick walls of rockwool..