Room accustic problem, possible reflection? - AVS Forum
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post #1 of 15 Old 09-25-2013, 04:10 AM - Thread Starter
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Hey everyone, my first post.

I have an annoying problem in my little theater setup.

 

The setup it self consists of three LCR speakers (Jamo d500 THX) in the front, and two surround speakers ( System Audio Saxo 1)

on each side of the listening position. Coupled with a Velodyne spl 800 Ultra subwoofer.

 

The speakers are driven by a Harman Kardon AVR 355 receiver and a Creek Audio amplifier.

Source for material is a Cambridge Audio Azur 751BD.

 

Now to the problem, i noticed a couple of days ago that the sound from the center channel seemed to emanate not only from the 

center channel but also between the actual center and right channel.

 

I decided to investigate and therefor turned of all speakers except the center to see if there was an in balance between the speakers

them self's but that was not the case. 

Even though all speakers except center channel is turned of the sound seems to come from the right...

 

How can this be, I have tried everything.

I have added absorbents to the wall, checked early reflection points using a mirror.

The only thing that helped somewhat, solved maybe 75% of the problem was to move the center of axis to the left.

 

Does any one have any ideas, thoughts on the matter?

 

 

   My room with furniture, absorbents etc. (rear speakers removed, not to clutter image)

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post #2 of 15 Old 09-25-2013, 10:47 AM
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Is the right speaker really tight to the right corner? You have four reflection points. The bedroom wall, the right wall, the ceiling, and the floor... right???
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post #3 of 15 Old 09-25-2013, 11:30 AM
 
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What was your source material to determine that the center channel? What does a sound pressure meter show when using pink/white noise? How are the surround speakers balanced with respect to the listening position?

As fbrang pointed out the amount of reflection on the right side is significantly shorter (more focused likely) than on the left.
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post #4 of 15 Old 09-25-2013, 12:31 PM
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Quote:
Originally Posted by lillgunde View Post

I have added absorbents to the wall, checked early reflection points using a mirror.
The only thing that helped somewhat, solved maybe 75% of the problem was to move the center of axis to the left.

Does any one have any ideas, thoughts on the matter?
These two things are the only way to fix this (well, for less than $10,000 or so). Absorption on the right wall will need to be extensive and thick, but as you noted the better solution is through layout.
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post #5 of 15 Old 09-25-2013, 12:47 PM
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When you say that you noticed a couple of days ago do you mean exactly that or wasn't it happening before?

Those speakers are placed horizontally, could it be a faulty mid? the one to the left in the center speaker in this case?

__________

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post #6 of 15 Old 09-25-2013, 11:30 PM - Thread Starter
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Thanks everyone for jumping in.

 

The right speaker is indeed in the corner, only place i could but it.

The gain that the corner placement adds (+5db) is adjusted with the level settings.

 

I only noticed the center channel issue a few days ago because the LCR speakers are only two weeks old.

You could actually call it a panning problem, the center is panned to the right and this is even though

the front left/right speakers and the rear speakers are disconnected.

 

The issue is at its worse when there is a dialog playing.

I am not using any audyssey or ezset eq (harman kardon equivalent) since I am running a analog setup.

 

Cambridge bluray player has 7.1 analog outputs (wolfson upsampling dac 192/24bit)

 

 

Better with real picture than paint...

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post #7 of 15 Old 09-25-2013, 11:35 PM - Thread Starter
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Picture of the absorbents. Ecophon Master A with 1 inch (2.5 cm) distance to wall.

 

 

Table and the things on it was of course removed to see if this would help.

It did not....

 

LCR speakers have been rotated around to see if the center was faulty. 

But they all sounded the same.

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post #8 of 15 Old 09-26-2013, 06:02 AM
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The image shift is due to early reflections off the right wall. You might have some success in stabilizing the stereo image by adjusting the toe-in or aim of the left and right loudspeakers, but the center will require reconfiguring your absorption panels. If you could record the ETC of the center and move the panels around (maybe space them farther off the wall?) you need to find the arrangement that reduces the specular reflections from the right wall to be 20dB below the level of the direct sound. You may find that enough sound is reflecting off the floor and ceiling near the right wall that the absorption will need to be extended vertically floor to ceiling.

Even after that, the asymmetry of walls is really difficult to correct completely.
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post #9 of 15 Old 09-26-2013, 09:46 AM - Thread Starter
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Thank you hopefulfred, great stuff.

I have been moving around bits and pieces of studio grade absobents, and also some auralex panels throughout

the room. I have yet to find the troubled area.

 

Early reflection point (first) for center speaker is on the right hand corner of the left most absorbent.

Even when treating with every single panel I had the problem remained.

 

I am going to try the floor next...  bring out the big guns, blankets and sheets :)

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post #10 of 15 Old 09-27-2013, 10:30 PM
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Wondering, have you tried the left and right speakers flipped vertically? A little toe-in on the right speaker perhaps as well? Not a particularly easy space. Tried a phantom center?
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post #11 of 15 Old 09-28-2013, 03:06 AM - Thread Starter
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Left and right speakers are not the issue, both of them sound amazing.

It is the center speaker, alone without the other speakers that is the actual problem.

 

The sound from the center speaker is perceived to come not only from in front of the listening position 

but also from the right of the listening position. 

 

No luck as of yet in solving the problem, tried some absorption on the floor and again with the first reflection 

point. 

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post #12 of 15 Old 09-28-2013, 04:16 AM
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Just a thought. have you asked other people if they also hear this or is it just your? I have better hearing in my left ear than right.. You also said this started a few days ago.. any thing happen since then that could have effected hearing.. concert, trip to the range, weekend on reserve training etc etc
I realize the sound field would change because of the way our head and ears are shaped but have you tried turning around on your knees in the seat to see if you still hear the majority of the sound from the wall side..
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post #13 of 15 Old 09-28-2013, 02:29 PM
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Try a phantom center? could run the left speaker 1 dBA hot compared to the right. Works better in some spaces. Your TV is small and the speakers are close together, this could work.
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post #14 of 15 Old 09-30-2013, 10:23 AM
 
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I'd still like to know what the SPL readings are at the normal listening area?
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post #15 of 15 Old 10-01-2013, 12:35 AM - Thread Starter
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The way I have measured my setup is to set the speakers to have the same spl output at

the actual listening level, not some imaginary level that I will never listen at.

 

A normal listening level for me would be when the receiver is at the -25 position.

This volume yields a 53 db level for the SUB, LEFT, CENTER , RIGHT channels and I then run the left/right surround

speakers 3 db lower (50 db).

 

Find the -3 db difference for the surround channels to be a nice balance.

Which is also something Dolby ran with at one point.

 

"Surround 3 dB Attenuation
This flag is used when projects are mixed in a facility that normally presents feature films and is 
properly calibrated to film standards for sound reproduction levels. It is usually left off for projects that 
are mixed in facilities that are calibrated video style. Video-style facilities use the same sound pressure 
level (SPL) for each speaker. Film facilities set the surround speaker levels 3 dB lower than the front 
channel speaker levels
. All levels are set individually. The setting of this parameter tells the Dolby 
Digital encoder how to set the gain for the surround channels before encoding.

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