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Topic: Echo because of EQ....

Kurt Werbrouck
Film Handler

Posts: 7
From: 9000 gent Belgium
Registered: Aug 2004

posted 01-12-2013 04:11 AM

Hello,

Since we are installing the DCP100/300, we have noticed that we have ,in some screens with lengt above 26meters, echo in the middle of the auditorium (2/3 lenght and 1/2 witdh). When moving some meters to the left / right, the echo is gone.
Could that be coming from the eq. of the Hf freq sections??

Does someone have a parameters for the dcp100/300 for a JBL4675 and jbl5674/QSC sc443.

Thanks for the help.....

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 01-12-2013 09:03 AM

It is my understanding that you can't EQ echo.
I have tried and it doesn't work.

Maybe you can EQ in such a way as to lessen the effect of an echo but EQ won't make it go away. Echo is a physical phenomenon.

Reposition and/or re-aim your speakers.
Keep the sound from bouncing off the walls and make sure the horns converge on the right spot.

Remove or dampen any objects that could serve as surfaces for sound to echo.
Insulation on the walls behind the screen. Proper sound treatment on walls and surfaces in the auditorium.

Finally, double check speaker phasing and channel assignment.
Is "left" really on the left and is "right" really on the right? Are your speakers working in phase and all at the right levels?

The reason I say all this is because I work at a multi-purpose venue that has difficult sound qualities. I spent a LOT of time getting rid of echos and fixing up the sound in that room.

Some rooms can be made to sound really, really good. Other rooms, because of their design, can sound better but will never be perfect.

Unfortunately, I'm in the second category. My theater's main purpose was a concert hall. Movies were brought in as an afterthought. It will always be difficult to remove every last echo.

But, the things I listed above were what I had to do in order to tame that room.

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Harold Hallikainen
Jedi Master Film Handler

Posts: 906
From: Denver, CO, USA
Registered: Aug 2009

posted 01-12-2013 04:51 PM

Could it be an improperly set surround delay? By the way, I was recently reading about surround delay and why it's there. From what I read, matrix decoders would leak a little screen channel audio into the surround channels. Since you're closer to the surround speakers, the sound arrives from there first. You ears/brain determine the source of the sound partially on arrival time. Since this screen channel sound is arriving from the surround speakers earlier than from the screen, you think it's coming from the surround speakers, even though the screen speakers are louder. Adding a surround delay masks this leakage by making sound always arrive sooner from the screen channels.

Now that we discrete tracks for each speaker, with no crosstalk, is the surround delay necessary? Of course, if you play any content that does not use discrete channels, it would still be necessary. So, it may still be best to include the typical surround delay. Just thinking, though...

Thanks!

Harold

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 01-12-2013 05:38 PM

Delay in digital is for different reasons and substantially less than used for a matrix decoder.

As a test...stand where you are hearing the echo (without anything playing)...clap your hands once (relatively hard) and listen...if you hear more than just the one clap...you will have found a big part of your problem...insufficient room deadening...particularly on the rear wall (but also the sides). The more box like your room (parallel walls) and the less deadening your have...the worse it will be (progressively so with larger rooms).

At a MINIMUM, you should have 2" of fiberglass or similar material on the entire rear wall and all surfaces behind the screen. On the side walls you should have not less than 1" fiberglass to below ear level. These are rules of thumb and a proper acoustic analysis can determine the best amount/location. Another area that is often forgot is the ceiling...make sure there is 6" of insulation above those tiles. Though it won't help with echo per-say it will improve dialogue and reverberation 250Hz and below.

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Marco Giustini
Film God

Posts: 2713
From: Reading, UK
Registered: Nov 2007

posted 01-13-2013 04:56 AM

In a proper room run pink noise from both Left channel and Left surround channel. Then change the delay in real time while listening to PN - CP750 allows you to do so.
You'll find that the apparent source of sound moves back and forth with the delay. A proper surround delay is then important for digital as well.

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Kurt Werbrouck
Film Handler

Posts: 7
From: 9000 gent Belgium
Registered: Aug 2004

posted 01-17-2013 02:27 PM

Hello,

Thanks for the replies. The delays from surrounds are ok. Can bad Xover freq , jbl 4675 set to 630Hz? I am now using 800Hz on the Lf and 550Hz for the Hf. first impression is that it seems to be better, less echo...

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