|
|
 
|
|
Author
|
Topic: Static in Low Frequencies in Surrounds
|
Rich Ferrando
Film Handler
Posts: 64
From: Royal Oak, MI
Registered: Nov 2003
|
posted 11-07-2004 09:31 PM
I noticed this week that in one of our houses, the right surround speakers are clipping badly when they experience very low frequencies. The surrounds aren't actually "surround" speakers, but rather are EV Sentry 100A studio monitors.
My best guess is that these speakers just can't handle the low frequencies, but it doesn't sound like the left surrounds are experiencing the same level of difficulty (I can hear the static, but I'm not sure if it's coming from the lefts or if its being reflected from the rights - it's a very small auditorium.)
For a bit of history in this house - the surrounds were mono, driven by one channel on a QSC 1400 amp, until April when we installed digital sound (Dolby soundhead, DA-20, Ultra Stereo JS-200 processor.) Now, the left surrounds are still connected to the old QSC 1400 that drove both sides, and the rights are on a new QSC amp (it's from the ISA series - don't have the model number with me.) The amp driving the right surrounds does not have anything connected to channel 2.
I don't think that it's an issue of volume level, because the left and right surrounds, at least from my ear, sound approximately the same (I can't really test this scientifically, since I neither have an RTA nor know how to use one.)
Any ideas?
| IP: Logged
|
|
Jack Ondracek
Film God
Posts: 2348
From: Port Orchard, WA, USA
Registered: Oct 2002
|
posted 11-07-2004 10:29 PM
Hi, Rich.
This is the kind of situation that 5 people might attack from 5 different directions... each of which is probably as good as the other.
Initially, a RTA probably won't do you much good. You're hearing distortion, so you'd probably be better off with a scope... at least to start with.
You didn't mention if you had a monitor in your sound rack. Many of them let you compare the output of your processor channels to what the amplifiers are sending the speakers. If you have one, you'd be able to listen for distortion at those two points. If nothing there, then the speakers would be suspect... it's a matter of elimination.
If you have no monitor and no scope, you can poke around the different signal paths with a small amp & a pair of headphones... just don't go into areas that are beyond your ability to get out of.
If you can get the volume levels back to where they were originally, try turning the amplifier level down on the right surround channel. If the distortion goes away, you can at least eliminate your processor as being the source of the problem. Unfortunately, you still have two other components to eliminate... the amp or the speakers... and for that, you need something from the list above... or a tech that has the gear to find the problem right away.
Good luck!
| IP: Logged
|
|
Randy Stankey
Film God
Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99
|
posted 11-07-2004 10:56 PM
I believe it was in a Sherlock Holmes novel where it was said, "When you have eliminated the impossible, whatever remains, however improbable, must be the truth."
Therefore, I ask, "What have you done to eliminate as many possible sources of trouble as you can?"
Try running a test showing and turning amplifiers off one by one until the interference is gone. Once you have found that, follow the path of the signal back to its source to see if you can find a cause. If you have a multi-channel booth monitor it would be a big help. An Inductive Amplifier (AKA: A "Banjo") is also a good thing to have in cases like this.
If you suspect a blown speaker, you could swap the wires on the putput of the amps from side to side to see if the problem moves. If it moves, the problem is in the amps/wires/processor(s)/projector. If it does not move, the problem is likely in the speaker.
Do be careful! If it IS a blown speaker, whatever problem that caused it to blow in the first place COULD still be lurking. If you do the wrong thing you might end up with TWO blown speakers! ![[Eek!]](eek.gif)
| IP: Logged
|
|
Ferdinando Innocenti
Film Handler
Posts: 79
From: Genova / Italy
Registered: Jun 2004
|
posted 11-08-2004 12:23 AM
First, be sure about the problem. As Randy said, turn the surround amplifiers off one by one, and try to understand where the problem is.
Then, as you have an amplifier channel free, you can swap from one channel to the other and from an amplifier to the other.
If the static is always in the same surround, it’s a speaker/processor fault.
Then, you can swap the surround outputs of the Panastereo too (I hope, in Italy there are only Dolby processors!), and if the noise is in the same speakers, you’ll be sure it’s a speaker problem.
Ciao
Nando
[ 11-08-2004, 09:33 AM: Message edited by: Ferdinando Innocenti ]
| IP: Logged
|
|
|
|
|
|
|
|
|
|
All times are Central (GMT -6:00)
|
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
Printer-friendly view of this topic