# My listening room project



## jpo (Mar 8, 2008)

http://img90.imageshack.us/img90/7171/img0919dh.jpg
http://img837.imageshack.us/img837/271/img0918x.jpg
http://img641.imageshack.us/img641/1808/13smoothing.jpg
http://img202.imageshack.us/img202/5859/etcw.jpg
http://img835.imageshack.us/img835/9040/nosmoothing.jpg
http://img163.imageshack.us/img163/9550/wateruu.jpg

Hello,
here is my little project.
Room dimensions 6,96x4,36x2,15m. Flutter has already taken care off with couple of polys:bigsmile:
Superchuncks in the front corners.
I played with speaker and listening positions last night and this is the best I could get out of it.
Speakers are 70cm from front and 109 from side walls. Chair is 260cm from front wall and listening triangle is
equilateral.
There is a big hump in the 170-200hz region that I couldn't get rid off. Moving speakers closer to front wall seemed to help a little but overall bass level became too high.
How to determine where to put traps?
That would need 200mm of rigid rockwool or I could build panel absorbers about 32mm in depht...
The room is getting too dry allready so:
Panel absorbers it is.
front wall behind the speakers?
sidewalls first reflection points?
ceiling?
Any advice how to succeed at the first time?
Thanks
Juho


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## bpape (Sep 14, 2006)

Is nearfield your preferred listening setup? You have a nice long room. I'd use it if possible. Try 2.6m to the rear wall. 

Don't get too hung up on the equilateral thing. Just a starting point and really only for nearfield listening.

If moving the speakers helped, then you likely have a boundary issue. Some thick absorbers behind the speaker can help minimize this. 

Also, with those polys, are they filled and damped? If not, they could be resonating in that frequency range and at least adding to the hump.

Bryan


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## Stele (Jul 3, 2010)

I would also move the listening position back so you aren't in the near field, don't worry about the equilateral triangle, just use the measurements as a guide, and remember that your ears are still the best tools we have with our brain being able to listen through 'problems' (assuming non-impaired hearing).

What's interesting is your room height is 2.15m and the wave length of 160Hz is.....2.15m(approx depending on your height from sea level). Perhaps you have a problem with the Floor-ceiling axial mode, and seeing that the floor is tiled I don't think that carpet would be doing anything for the 160-200H region. I would suggest panel absorbers on the ceiling (as floor isn't practical).

With the absorbers in your corners, you could try placing them temporarily in the floor-front wall/back wall corners (or floor/sidewall corners), this could (would) bring other problems that they are killing at the moment, but it would give you a better idea if it is indeed the floor/ceiling mode (unless of course you've got your panels ready to go).

I just took the liberty to plug your room dimensions into the THX room mode calculator (available to THX certified professionals, although I'm sure there are dozens of rooms mode calculators on the net). It came up with 2 axial modes for 160Hz - height and width and a width mode at approx 200Hz. It also pointed a possible Height and width tangential mode at 177Hz. (for those that have never used these calculators before be aware that they assume room symmetry and that these are the accoustical dimensions (rarely are each true) but they are a good guide and starting place).

With what my eyes tell me from your pics and graphs, and the help of the calculator, perhaps you should be looking at width + height. Length seems to not be a problem and I'd suggest that is because of the corner units you have are a large % of the surface area of the front/back walls.

Of course, if the listening room is only ever for the one person in the sweet spots, you could always just take the easy option and equalize...but where's the fun in that hmmm?

Pete


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## jpo (Mar 8, 2008)

Thank you Bryan and Pete.
The rear of the room reserved for other purposes so moving my listening chair to other half of the room is not possible at the moment. Moving the seat back a little rises the level of the allready ringing ~46Hz. So for now close range it is.
I do have a "big headphones" feel sometimes because of the listening distance.

I did some tests earlier this week. Putting 8" of rockwool panels behind the speakers didn't help. It didn't even cure the 120Hz dip which is SBIR of 70cm speaker to wall distance I quess...

Putting the panels on sidewall reflection points against polys ( so there was 200mm airgap) did the trick for the 160-200Hz hump. I had to put two panels side by side ( = 4' wide) to see an improvement. Panels were also from floor to ceiling.
Then I took polys off the sidewalls and put the panels against the side wall-> hump is back. 4" is not enough.

Next step is then to test with panels on the floor.

Thanks again.

Juho
Oh and those polys are open structure and empty. I don't feel them resonating when listening to music.


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## jpo (Mar 8, 2008)

http://img32.imageshack.us/g/vasteet.jpg/
Hello again.
got some spare time and made new measurements. After reading an article from PSaudio website about listening room setup I took every acoustic ellements out of the room. Then I measured the room. 
Front half of the room was empty exept the carpet. There was a terrible slap echo. I started moving the listening chair back 10cm increments and measured every position from 2,6m to 4m from front wall.
Green graph was the best 25-300Hz ( that is what the article said I should look at ). Overall responce is also quite good if you ignore the 48Hz peak.
Oops, I have to put children in to bed now. I'll be back.


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## bpape (Sep 14, 2006)

If you fill the polys, they'll add a little membrane based absorption in the low end.

Your response looks very good. You're essentially within +/-3 in-room which is excellent. You've also improved your decay times.

Bryan


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## jpo (Mar 8, 2008)

Bryan was fast:T
After locating the "best" position for listening chair I put superchuncks in the front corners. Decay times improved immeadedly but freq.responce got worse. Hump rized at 200Hz and a wide dip was found in around 400Hz.
Then I put 100mm thick rockwool to sidewall frp from floor to ceiling 60cm wide. Measured again. After that similar set of wool to front wall sbir points. Those didn't do much to curves. Wasn't happy.

Cornertraps did something harmfull?

I had 3mm thick mdf-sheets from polys which I put against chuncks. That helped some.

The purple curve is with those sheets. Those cover about 2/3 of the chunks.

So nothing on the ceiling so far.

I think I'll cover entire front faces of chuncks and put rockwool sheets to ceiling sbir points next.
Then add some polys if there is still slap or flutter echo left.

Peak at 48Hz won't go away. It has a long decay time too.

http://img710.imageshack.us/img710/9052/membraneabsorber48hz.jpg

How much surface area is needed to smooth that down. If I make absorber like above and cover 20% of backwall ( center of the wall floor to ceiling ). Is it enough?

Thanks 
Juho


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## bpape (Sep 14, 2006)

I would recommend against covering the entire chunk absorber. Decay time is an important factor to consider. What can happen is that there may have been two problems that were somewhat offsetting each other. When you did the corners, there was no longer anything to offset the other issue. 

Have you tried anything on the rear wall behind the seating? 

Bryan


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## jpo (Mar 8, 2008)

There is 50cm deep storage shelf covering entire backwall. On the shelf behind listening chair are piles of suitcases, backbags etc. and cardboardboxes full of my wifes fabrics.
And both sidewalls on the back half of the room are also same storage shelf with various stuff.
How many of you have a lawn mower in your listening room? I have:bigsmile:
I need to do more testing including ceiling and backwall. And sidewalls.
As you said Bryan, cornertraps may just have unmask vertical mode problems like Pete's calculations showed.
So more testing.
Room does actually sound quite good allready. So I'm not in a hurry.
Thanks.
Juho


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