Need advice on acoustic treatement

[Anis]

Hi everyone
I'm planning to treat my listening room (without insulation) for a HIFI/HC use.
I have no experience in Acoustic Treatement and I based most of what I'm planing to do on what I've read.

Therefore, I need your heeeelp and opinion about my results :

First of all, here is my room (all dimensions are in meter) :



A picture of it : (sorry about the quality !! )



Dimensions Are de 4,55 m x 3,95 m x 2.76 m (L x l x H).

-Non treated room's characteristics :

Without any treatement, reverberation is naturally too long, the room suffers from flutter echo, modal resonances and for sure, many other things I don't even know.

Without any gear to measure Rt60, modal resonances and more, I made only simulations :

-Rt60 :
With a french excel sheet (Tr-optimat from isolation et traitement acoustique, sonorisation et acoustique), I made a +/- 15% approximation :



-Modal resonances :




-Schroeder frequency :

f = 3c/Lmin = 375 Hz

-Sizing the treatement :

-Tr60 :
I will use DIY panel absorber with 705-FRK.

In order to reduce Rt60, I need :

-22,5 m² of 705-FRK 2" on wall.
-3 corner-traps 1m x 2,50m
-1 couch 3 seats
-3 m² thick carpet

Rt60 will be approximately like this :



Wich is better !

-Modal resonances :

After reading "Acoustic Treatment and Design for Recording Studios and Listening Rooms" by Ethan Winer, I thought about spacing the absorber panels from the wall as much as possible and orientating them in order to keep a broadband absorption as low as possible. But would it be enough for let say 42 Hz ?

-Diffusion :

The non tread walls with absorption will be treated by qrd diffusion made of plywood DIY panels. I size them with QRDude.

It has to work above the Schroeder frequency wich is in my case 375 Hz. But then, panels would be so deep that I won't respect the minimal seating distance from them. I chose then 575 Hz, wich is fine for my room.

Placing the acoustic elements, speakers and listening positions :




For more absorption in the bass, i thought about that :



So ? What do you think ? Where am I doing mistakes ?

And before beginning any construction, I have some questions :


1-Can I replace proper measurements by simulations ?
2-Does someone has absorption coefficients for 705 FRK spaced from wall ?
3-Should I go for 1d ou 2d diffusors ? Wich is best : one N19 or 4 N7 in a Barker series ?


Thanks in advance

[Glenn Kuras]

After reading "Acoustic Treatment and Design for Recording Studios and Listening Rooms" by Ethan Winer, I thought about spacing the absorber panels from the wall as much as possible and orientating them in order to keep a broadband absorption as low as possible. But would it be enough for let say 42 Hz ?

If you make the broad band bass trap really thick and place it in the corners it will effect 42hz, but for frequencies that low I would go with tuned.

[John White]

Anis,

I hesitate to think that your decay times should be a primary concern especially considering home theater use. (You did mean HT, right?)

Low frequency treatment will almost certainly affect your times in the upper ranges to some extent no matter how you cut it. Regardless, the use of 705 FRK or similar will certainly influence the higher ranges as well according to http://www.bobgolds.com/AbsorptionCoefficients.htm
Even with the FSK, it is still very lossy in a broad spectrum.

T60 may not be as appropriate in a such a small room as perhaps T30/T20 as you can measure with REW Basic acoustic measurement primer v2.1

I like the use of diffusion with absorption. It may take a fair bit of planning to coordinate an effective strategy to maximize their effectiveness. For instance, placing absorption in front of diffusion seems counter productive.

[Anis]

Thank you for you quick answering !

If you make the broad band bass trap really thick and place it in the corners it will effect 42hz, but for frequencies that low I would go with tuned

I will then place as much absorbers in corners as I can and then tune some if it's not enough. Maybe i'll help with some equalizing as well...

I hesitate to think that your decay times should be a primary concern especially considering home theater use. (You did mean HT, right?)

What should I look for then ? (Yes, Home Theater )

Even with the FSK, it is still very lossy in a broad spectrum.

Yes, you're perfectly right. I'm afraid of muting the room in high frequencies ! I chose the FRK to reduce absorption in high frequencies compared with plain 705 for example. What do you advise me then to avoid this ?

T60 may not be as appropriate in a such a small room as perhaps T30/T20 as you can measure with REW http://www.gearslutz.com/board/studi...er-v2-1-a.html

I'll posts results asap !

For instance, placing absorption in front of diffusion seems counter productive.

Shoud I put only absorbers on side walls ? or something else ?

[John White]

Originally Posted by Anis

What should I look for then?

Sorry, that wasn't to say that it wasn't important. Evidently two channel and multichannel listening requirements have different target goals for decay times. As I understand it, HT users often don't require or demand as even decay times across the spectrum. I can only guess it has something to do with the ambiance created by the surround speakers.

There is such a thing as an absorption calculator that estimates the amount of broadband one needs for a given space. I believe John Brandt has one on his web page. I don't know how it translates to HT use.

Yes, you're perfectly right. I'm afraid of muting the room in high frequencies ! I chose the FRK to reduce absorption in high frequencies compared with plain 705 for example.[

The FRK will definitely help towards that end. Without it the room would almost certainly be lopsided. Your proposed use of a carpet, however, may compromise your efforts. Again, I'm not sure if it is truly detrimental in a multi channel listening setup.

Should I put only absorbers on side walls ?

The general guideline is to use high frequency absorption on reflection points in relation to the listener where as your 705 FRK would work well to tame low frequencies especially when placed straddling corners.

There are more great tips in the "Stickies" threads at the top of the pages.
Good luck with a fun project. My only hard recommendation is to initially build such that you can arrange your implements of destruction as your understanding grows.

[Glenn Kuras]

Yes, you're perfectly right. I'm afraid of muting the room in high frequencies ! I chose the FRK to reduce absorption in high frequencies compared with plain 705 for example. What do you advise me then to avoid this ?

If that is the case then I would look at a soffit design for the broad band bass control as it will reach 40hz well and not over deaden the highs as you are not covering as much wall surface area.