John Sayers' Design Forum

John Sayers' Recording Studio Design Forum

A World of Experience
Click Here for Information on John's Services
It is currently Thu Dec 12, 2019 11:38 pm

All times are UTC + 10 hours




Post new topic Reply to topic  [ 11 posts ] 
Author Message
PostPosted: Sat May 13, 2006 10:33 am 
Offline
User avatar

Joined: Wed Apr 19, 2006 9:22 am
Posts: 66
Location: Paris, France
Hello all. I've been enjoying this forum a lot. There is a great wealth of information. Really interesting, thanks to everybody involved.

I'm building a music room on the ground floor of my house near Paris for use as a recording place for acoustic music and rehearsal. It's a one room approach. The box-in-a-box construction is already done : two sheets of plasterboard on 3' x 2 1/2' wood frames with 3' thick insulation in the air gap. The floor sits on Paulstra Beca Anti-Vibration Mounts with insulation between the studs. The ceiling sits on walls, using 6'x1' beams. The existing walls of the house are 50 cm (19.68') thick stone walls. The room dimensions are : lenght 5.58 m, width : 3.86 m on one side and 4.09 m on the other side. Ceiling height : 2.67m.

Using the (free)
Room EQ wizard I found very bad room modes at 82, 87, 142, 130 and 370 Hz.

Using the hunecke.de calculation site I found more or less the same results, especially a nasty first order room mode at 83.1 Hz (see picture below).

My question is : Where would you put the 83Hz resonnant bass traps in a case like this ? The drawing on the hunecke site gives "the square value of sound pressure on the wall of the room. Dark regions correspond to high sound pressure..." In this case, the high sound pressure areas (dark regions) are only in the top and bottom corners of the room.

I was planning to fit a resonnant bass-trap on the rear wall using a 1/3' MDF panel over a 3 1/2' cavity filled with ROCKWOOL "Alpharock" stone wool (equivalent of O/C 705). Is this make sense as it seems that no sound pressure is hitting the middle of the rear wall ?

Any other though about the acoustic treatment for such a room while I'm at it ?

Thanks in advance,

Michel


You do not have the required permissions to view the files attached to this post.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat May 13, 2006 10:52 am 
Offline
User avatar

Joined: Sun Feb 05, 2006 3:09 pm
Posts: 118
Location: Indiana
First, your room is sufficiently far from being a perfect rectangular prism that modal frequency prediction based on a rectaungular room is no longer valid. So, forget about the calculators. Now measurement you can trust. Can you post or send me an impulse? If you can, I'd be happy to take a look at it for you.

If I were you, I would go with porous absorption such as rockwool panels wrapped in fabric. They are more cost effective, much easier to build, and will easily eliminate resonances at the listed frequencies with no guesswork. Also, they are broadband, unlike panel traps, and using broadband treatment is desireable as it will lead to a studio with a more even decay at all frequencies, which is your goal.

You will want to find a more symmetrical location for your listening triangle.

_________________
David M. French


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat May 13, 2006 11:21 am 
Offline
User avatar

Joined: Wed Apr 19, 2006 9:22 am
Posts: 66
Location: Paris, France
David French wrote:
Can you post or send me an impulse? If you can, I'd be happy to take a look at it for you.

Please find the two curves, one of the untreated room, the other with two 3.15' (80mm) 705 panels stacked on each other at every corner of the room.

David French wrote:
If I were you, I would go with porous absorption such as rockwool panels wrapped in fabric. They are more cost effective, much easier to build, and will easily eliminate resonances at the listed frequencies with no guesswork. Also, they are broadband, unlike panel traps, and using broadband treatment is desireable as it will lead to a studio with a more even decay at all frequencies, which is your goal.


I appreciate your point, but after trying the 705 panels (70 kg/m3) I wasn't impressed much by the resulting curve :? Any thought ?

David French wrote:
You will want to find a more symmetrical location for your listening triangle.

You're right. Maybe moving the listening triangle right between the two lateral walls ?

Thanks,

Michel


You do not have the required permissions to view the files attached to this post.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat May 13, 2006 11:46 am 
Offline
User avatar

Joined: Sun Feb 05, 2006 3:09 pm
Posts: 118
Location: Indiana
I meant can you post or email me the MDAT file or (better) the WAV file impulse from the measurements? I need to manipulate the data to see what's really going on, and I'd be happy to do so. Believe it or not, this is what I do for fun. :shock:

A studio properly treated with rigid fiberglass panels will be quite impressive indeed. I should know; I have one. :D Something is going on here, and I'm willing to help you get to the bottom of it.

As for a listening position, definitely try to have your side walls equidistant from you. I would also sit closer to the wall in front of you than the wall in back of you. Pick a logical starting point based on these criteria and measure it, each speaker individually.

_________________
David M. French


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sat May 13, 2006 6:34 pm 
Offline
Senior Member
User avatar

Joined: Sun Mar 16, 2003 11:11 am
Posts: 6978
Location: West Coast, USA
Dave's got you covered here; you didn't mention where the mic was for tests, can we assume it was at the listening position? IF so, and if both speakers were on, you'd get all kinds of wierd results caused by SBIR and other boundary effects, so it's no wonder things didn't change much with and without treatments.

I've found it's much better to achieve plane symmetry from left to right first, then find the "least bumpy" spots for speakers and head, and THEN treat the room.

Otherwise, you tend to miss finding optimum placement of speakers and head because the treatment can (although apparently not in your case) mask the effects of bad placement.

HTH... Steve

_________________
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun May 14, 2006 1:36 am 
Offline
User avatar

Joined: Wed Apr 19, 2006 9:22 am
Posts: 66
Location: Paris, France
David French wrote:
I meant can you post or email me the MDAT file or (better) the WAV file impulse from the measurements? I need to manipulate the data to see what's really going on, and I'd be happy to do so. Believe it or not, this is what I do for fun. :shock:


Hello Dave,

Thanks for the kind help and the (very) fast answers.

I've centered speakers between the lateral walls, and I made a new set of measurements, testing L & R separatly. It actually changed things, but I'm wandering if the curves are actually looking better :

You will find at http://microson.sono.online.fr/Test/ the .mdat file, the two WAV impulse responses, as well as the JPEG of the measured response and the two low freq waterfalls.

I can't really move the speakers closer to the back wall because this is a one room approach and I need to leave some space free for the musicians :o

For the moment, the rear wall the wooden floor and the ceiling are left completly untreated, not too good I suppose. Also, this room is far from symetrical... and I really don't known where I could put the speakers to benefit from some kind of symmetry.

The test have been made using my JBL 4406 (not brand new but in good condition) sitting on shelves, with a 16mm rubber pad between the speakers and the shelves. The microphone is a Behringer test microphone ECM-8000 located at ear position. The Room EQ Wizard software is left with the default settings unchanged. I've used the automatic sweep mode measurement function.

Steve wrote:
IF so, and if both speakers were on, you'd get all kinds of wierd results caused by SBIR and other boundary effects, so it's no wonder things didn't change much with and without treatments.


thanks for the input Steve. I'm wandering what is SBIR ? Is this another name for room modes ? Excuse my ignorance.

Steve wrote:
I've found it's much better to achieve plane symmetry from left to right first, then find the "least bumpy" spots for speakers and head, and THEN treat the room.

Otherwise, you tend to miss finding optimum placement of speakers and head because the treatment can (although apparently not in your case) mask the effects of bad placement.


This is of course the best approach. Unfortunatly most of the construction has been done before I found this forum. So I have to deal with a less than ideal shaped room. The two big windows (covered with wooden slats blinds) are of course great for daylight, but not for acoustics and symmetry.

Next week I'll remove all the treatment and I'll do another set of measurment with the speakers centered between the lateral walls.

Any more though are (very) welcome,

All the best,

Michel


You do not have the required permissions to view the files attached to this post.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun May 14, 2006 3:22 am 
Offline
User avatar

Joined: Sun Feb 05, 2006 3:09 pm
Posts: 118
Location: Indiana
I took a look at your data. I think you had 'C' weighting compensation on. If so, it has caused a rolloff in the bass and has made the measurements largely useless for our purposes.

I love REW as an analysis program, especially for the price, but I don't care for that way it takes measurements. I usually use other software to gater the data and then look at it with REW. When working with people over a distance, I like to send them a test tone, an ordinary sine sweep. They then play this tone though their system and record it, and then, through the wonders of convolution, I turn it into a high quality impulse response file and look at the data in REW. I would like to do this with you if you're interested.

SBIR, or Speaker-Boundary Interference Response is a name for the response (particularly the bass response) that is created when reflections combine with the direct sound. These are not modes, but modes are a special case of SBIR when you have the same thing happening from two directions and a resonance is created. SBIR is really nothing more than comb filtering.

_________________
David M. French


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun May 14, 2006 5:02 am 
Offline
Senior Member
User avatar

Joined: Wed Jun 18, 2003 6:09 pm
Posts: 760
Location: Antwerp/Belgium
:mrgreen: David the auto measurement/analysis tool.
Freeware download

Image

Source: http://www.npl.co.uk/publications/acous ... stereo.gif

_________________
Best regards - Eric Desart
My posts are never meant to sell whatever incl. myself, neither direct, nor indirect.


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun May 14, 2006 5:33 am 
Offline
User avatar

Joined: Sun Feb 05, 2006 3:09 pm
Posts: 118
Location: Indiana
I don't know why, but I just can't help myself!

Geek! :shock:

:D

_________________
David M. French


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Sun May 14, 2006 10:54 am 
Offline
User avatar

Joined: Wed Apr 19, 2006 9:22 am
Posts: 66
Location: Paris, France
David French wrote:
When working with people over a distance, I like to send them a test tone, an ordinary sine sweep. They then play this tone though their system and record it, and then, through the wonders of convolution, I turn it into a high quality impulse response file and look at the data in REW. I would like to do this with you if you're interested.


Hello Dave,

Please send the sine sweep, I'll be happy to give it a try. Sorry about 'C' weighting compensation, this is the standard setting with REW.

All the best,

Michel


Report this post
Top
 Profile  
 
 Post subject:
PostPosted: Wed May 24, 2006 10:04 pm 
Offline
User avatar

Joined: Fri Oct 29, 2004 10:30 pm
Posts: 123
Location: Uk and Portugal
Quote:
David the auto measurement/analysis tool.
Freeware download


ehehhehehehehehe

:D :D :D :D :D


Report this post
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC + 10 hours


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group