Film-Tech Forum ARCHIVE: Why did my speaker develop a crackle...twice?

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Posted by Paul Looker (Member # 5420) on 09-18-2009, 10:07 PM:

Alright. This is actually the second time I've had this problem. The high frequency has begun to develop a serious crackle. Here's what I'm working with:

-JBL Ultra Stereo Processor
-QSC 1400 Series Amplifier
-EV TL606DW Low Frequency Loudspeaker system with
-An XEQ-504 Crossover Equalizer to
-DH1 high frequency driver on a HP9040 Horn

Again, this is the second time this has happened. The first was about a year ago. The DH1 driver seemed to go bad and started crackling. Replaced it. We were good for a few months. Slowly over the last couple the crackle has been coming back. Before I make any more costly replacements I'd really like to figure out why its happening.

My theory: After the second time it started doing this and talking to our EV dealer about possible reasons I went to the processor and the amplifier to see what I could discover there. It turns out that at some point, before I even started here probably, someone cranked both of the gain switches on the amp all the way up to +6 to cover for the fact that the amp was going bad. When I first started setting the dial to about 5 on the processor was enough to get decent sound. It wasn't the best house in the place but it was far from the worst I've encountered.

Slowly but surely staff checks and opinion combined with customer suggestions drove that dial up to 6 and 6.5. Then we started with the screen vision ads and the way they are designed to play so much louder than everything else just kind of killed that driver.

So basically, in so many, many words, does this sound like the problem is the amplifier or am I just an idiot?

I've had someone tell me they think the problem is coming across the crossover equalizer from the low frequency cabinet. It sounds kind of far fetched to me but is it a possibility?

If its not the amplifier, what else could it be and how do I go about figuring that out?

Posted by Monte L Fullmer (Member # 2797) on 09-19-2009, 02:15 AM:

Bet you crossover system is letting LF into the HF section and those LF's is what's busting up the diaphrams on the HD drivers.

Are you playing DTS, per chance - esp with the DTS 6AD units? Sometimes, these units leave the factory with the default settings in "wideband" instead of "bi-amp". And if it gets left in "wideband", that unit send all freqs in both the LF and HF section of the amplifier and that really busts up the diaphrams in the HF drivers.

Check this area out.

(doesn't Pittsburgh, PA end in an "h"? ... )

Good luck-Monte

Posted by Jonathan Althaus (Member # 5042) on 09-19-2009, 04:06 AM:

Wow, this is odd. We had some slight sound issues today in an auditorium with DTS-6AD, Ultra-Stereo processor and QSC amps.

Posted by Louis Bornwasser (Member # 3063) on 09-19-2009, 07:08 AM:

I find the 6ad to be a bad box

on topic--

1. Get the amp serviced.

2. as a JBL dealer, I have customers who are 95% JBL; yet a slight majority of the replacement diaphragm kits I sell are for EV. . . hmmmmm.

3. ANYTHING that lets l.f. into the h.f. will "blow" the driver. As Monte said above, a defective crossover is one. Another is anything that causes square wave distortion or dc voltage thumps.

4. Third octave eq settings that are extreme (more than a few db) can force some non-FET amplifiers into DC mode. This will eventually result in hf horn failure over time.

Good luck. Louis

Posted by Paul Looker (Member # 5420) on 09-19-2009, 10:01 PM:

A little more information:

-Not using DTS of any kind.
-I think the amp is on the not so good side because running the same settings with the same processor on the same loudspeakers in other houses, processor set to 6.5 is giving me what it would set to 4 in other houses.
-It's kind of hard to tell without crawling up there and unhooking the horn but there may be a slight crackle in the low frequency as well.

Posted by Marco Giustini (Member # 4544) on 09-20-2009, 06:55 AM:

"Same processor" means same exactly, phisycally?
There are levels inside a processor, it would be perfectly normal that you have different sound levels in two different auditorium with same equipment and same knob setting. However, this should NOT happen. If happens, you must have someone checking your B-Chain. Someone better than the previous one [Smile]

If you feel that your amps are going bad, you may have them serviced before B-Chaining.

Posted by Mark Gulbrandsen (Member # 72) on 09-20-2009, 09:16 AM:

Paul, You really do need to have a qualified tech come in and calibrate all your systems.

EV stuff does literally fall apart mounted in place... I hope you don't have any foam surround woofers!! Best thing to do is junk em...

I agree with Louis on the 6AD. Horrible A chain facilities.

Mark

Posted by Gordon McLeod (Member # 33) on 09-20-2009, 09:23 AM:

We have several 6AD and not had many issues

Posted by Mark Gulbrandsen (Member # 72) on 09-20-2009, 12:45 PM:

Gord, they have been as reliable as the other DTS units... they just have a lousy A chain facilities in them. The NR is a joke. The JSD-80 is a much better route. I listened to a DSP-60 recently and even it is far superior.

Posted by Steve Guttag (Member # 268) on 09-20-2009, 08:27 PM:

Of the few DTS-6ADs we have had to deal with...ALL have had problems. From bad cards to bad connectors/cables. I would say they are far LESS reliable than other DTS products.

As for EV speakers and foam...all speakers with foam compliances (aka surrounds) will rot...regardless of who made them. EV only used foam on the "W" series of drivers for cinema (DL15W, DL18W). They, like just about everyone else, don't use foam anymore...though a recone will indeed keep it original. Of course, with EV due to how they pleated their cloth compliances, also had them tear on their own.

Historically, EV has been one of the most truthful in their specifications though. Their spec sheets show how bad they are!

Now, there are some people that really like the EV sound...I'm not one of them but that is the thing with sound...we all seem to have our own preferences. I definitely don't like the sound of the DH1a compression driver...very painful to me.

As to the problem at hand...one really needs to isolate just where the noise is coming from...it definitely does not have to be the speaker itself.

Steve