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That's possible that you are introducing a null to compensate for the resonating wall.
 

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Discussion Starter #22
Bryan,

When i place the mic closer to the front speakers aprox 4.2 foot, the 120 hz problem is gone.
What is your conclusion to this?

Thanks,
Mike
 

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It could be either a modal problem or a boundary interaction from reflections on the side walls. Try going back to where you were and measuring a foot off to one side and see what happens.
 

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Discussion Starter #24 (Edited)
Bryan,

I have made the frontwall completly dead like you suggested.
There is much more imaging and i can hear things that i could not hear before because of frontwall reflections. It seems treathing the upper wall, from where the sloping begins made a hugh improvement regarding reflections.

But, i find the room sounds too dead right now, its not pleasant listening to music, ht is fine..

As for the 120hz problem, i have not measured but moving my head one or two foot to the right or to the left does not seem to help. Moving head two foot to the front, and bingo everything is there...but that is on middle of room and not doable with movie watching.
Its not only 120hz related, overall performance is much better two foot the front.

What do you think, has it something to do with the one layer sloped back wall? Is it possible the low frequencies go trough this one layer drywall and are stuck in the 2meter cavity bhind?

Also the entire ceiling is one layer drywall with lots of cavity behind, i am thinking this is acting like a helmholz resonator...

I am willing to do anything to make this room sounds great!

THANKS A LOT!
 

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Well, 2 channel and HT are different design goals. If moving forward fixes the problem and nothing else has, then moving is the answer. This is why one gets the seat right first, then picks a screen size.

Bryan
 

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Discussion Starter #26 (Edited)
Hmm, well i am not moving much further.
Goal was 60% music, 40 % ht

I made some progress ( rew wise )but also moved backwards.

Still a lot of questions stay unanwserd.

MORE CONFUSED THAN BEFORE!
 

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Personal opinion: a well-controlled room may sound a bit dead, but dead (acoustically) beats poorly controlled any day. And great imaging is the best goal you can reach for with 2-channel. Give yourself a chance to start discovering more detail in the music and I'll bet you never want to go back to a more live sound. Just a guess.
 

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I would agree 100%. It is very different certainly than what you're used to. If you live with it a while and then were to undo it, you'd be surprised how quickly you'd go back.

You can use a thin facing like some 5-10 mil plastic high on the front wall to minimize the high frequency absorption from that portion but you still want the middle of the wall full range.

Bryan
 

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Discussion Starter #29
You guys are probably right, i am alreay finding it a bit less dead.
New question: what about ceiling, its about 2.3 m high and i am planning on installing a star ceiling, do i have to absorp it also? Or leave it?
 

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I wouldn't do the whole thing in absorption. Maybe just the reflection zone and leave the rest live.
 

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Discussion Starter #31
While i was further studying room treadment, i found this:


Highly Directional Speakers (horns, rear-absorbed electrostatics, ribbon panels)
With more direct than reflected sound placement is usually easier. Electrostatics and
ribbons with wider horizontal dispersion require greater care in placement.
Spaciousness: fair to good
Localization: fair to excellent

Actualy i am using horn speakers, so it could be possible that afterall there simply is not enough reflected sound (ambiance, spacines) anymore...( complete frontwall, first and second sidewall reflection points are already treated.)
 

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Discussion Starter #32 (Edited)
Well, i have my sound back!!! And i dont have t move to the front.

By turning the isolation ( i have a diffusor) in the first reflection zones so the aluminium is facing frontwards, i have my sound back, front stage is hugh, refind, voices are super, image is good, ambiance is greath and even bass and midbass are a lot better and refind.

One problem, i can hear the aluminium vibrate from time to times.

this is defenitly de way i have to go but need a solution for the vibrating aluminium.
if anyone as a solution i am curieus to know!
 

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remove the aluminum and cover with thin plastic - something like maybe 5 mil or so. That will still give you some highs back but be easier to stretch tighter.

Bryan
 

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Discussion Starter #34
Bryan thanks again for the recommandation, will try it tommorow.
I also did a quick test and covered the isolation with mdf, it gave not the same result as with the isolation covered with aluminium, i think the latter diffuses more...gives also some mid absorption aswell.

Sometimes you can not follow the standards, trial and error...
 

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Discussion Starter #35 (Edited)
Frontwall is almost done, i removed the resonating ply on the upper sloped ceilig and covered with fabric.
This made a huge difference!!!

In the second step i removed the resonating ply on the backwall aswell, behind the ply is 8" of isolation covered with plastic.

Soundwise this is even worse than before on the graph i can see that the huge dip on 120Hz has moved to 90Hz.

Should i cover the backwall less absorbing and cover with MDF or something?
Behind the lower backwall is some cavity, should i cover this also with MDF or use it later for maybe a pannel absorber?

Your help is much appreciated!
 

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By removing the ply, you've essentially uncovered the 'horn' in the rear of the room. I think the absorption in the rear is still a good thing. I would try some MDF on the REAR (hidden) side of the rear wall. Cover the front(exposed) side of the insulation with some 5-10 mil plastic and then fabric.
 
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