Film-Tech Forum ARCHIVE: How to find a bad driver?

This is topic How to find a bad driver? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Eric Robinson (Member # 2966) on 06-02-2009, 03:20 PM:

I received a report that a speaker in a theatre sounds like it is blown. I have listened to the sound, but have not detected anything unusual. So, I'm curious if there is some test I can perform to stress the speaker in different ways to possibly find the distortion which was reported.

The reported problem was a crackling sound during a normal volume dialogue from Spok during the movie Star Trek XI.

Posted by David Stambaugh (Member # 1102) on 06-02-2009, 04:29 PM:

I dunno, Spock's been through a lot including death and living in at least 2 timelines. Maybe he just had a little phlegm that day.

Posted by Monte L Fullmer (Member # 2797) on 06-02-2009, 04:33 PM:

You can climb backstage and hear your center speaker HF horn to see if that diaphram has cracked since it was during voice that the distortion was resulting from.

You could also have alignment issues, tired amps - all sorts of issues that can cause speaker distortions.

Posted by Bruce Hansen (Member # 281) on 06-02-2009, 04:45 PM:

How to find a bad driver? Look for the person who is talking on their cell phone while behind the wheel.

It could also be dirty connections, or switches.

Posted by John Walsh (Member # 168) on 06-02-2009, 05:26 PM:

Generally, you use a tone generator and sweep up and down. Usuall, you will hit the exact frequency and then you will hear a rattle or something not right.

Posted by Louis Bornwasser (Member # 3063) on 06-02-2009, 09:35 PM:

What kind of driver?

Every time I get these kind of calls, I find either a bad amplifier module or, more likely, really bad EQ or levels in the processor leading to clipping.

The last one was a pair of CP-500s (set up by Dolby employees) with the bass fully off and +-15db EQ in the mid range. Clipping was horrible on Star Trek. Louis

Posted by Steve Guttag (Member # 268) on 06-02-2009, 10:09 PM:

Sweep tones are my favorite...Got a Dolby Jiffy test?

Steve

Posted by Joe Redifer (Member # 3) on 06-02-2009, 10:23 PM:

Move over to Mac where you don't have to uninstall bad "drivers".

Posted by Monte L Fullmer (Member # 2797) on 06-03-2009, 01:40 AM:

(a bad driver is when the face of the driver doesn't grip the ball too well when it's hit out of the teebox and it doesn't give it the reverse spin for good lift as needed causing the ball to drop and die way short of the shot....- okey, hit me [Big Grin]

)

Posted by Eric Robinson (Member # 2966) on 06-03-2009, 10:13 AM:

quote: Steve Guttag
Got a Dolby Jiffy test?

No, but I wish I did. Does anyone know how I can acquire this test film?

I do have a tone generator, so I'll give that a try.

Clipping indeed is a great suggestion in the pre amplifier stages. Any suggestions on how I could introduce some test signals in this area which would expose an error in the EQ settings or would it just be better to perform a B chain from scratch and see what happens?

As for the comic relief replies...thanks all...funny stuff [Wink]

Posted by Louis Bornwasser (Member # 3063) on 06-03-2009, 02:40 PM:

Look in any Volvo!

seriously:

Plug into the power amp input with your oscillator and sweep.

As regards EQ; us old-timers can just look at the eq settings and tell if there are "issues." 1. Are most settings "up' or "down?". 2. Are settings "violent" (fully up or down.) 3. are setting up and down right next to each other? 4. Is every setting somewhere other than zero? (Should be 8 or less in an average cinema room.) Louis

Massive correction is best done with the bass-mid-high control, with smaller correction performed with the third octave controls. Louis

Posted by Eric Robinson (Member # 2966) on 06-03-2009, 05:56 PM:

quote: Louis Bornwasser
Plug into the power amp input with your oscillator and sweep.

I was just thinking about employing this method. Thanks for the confirmation.

The EQ looks fairly reasonable mostly centered around 0 for each band which may vary as much as 2 db boost or cut. The curve looks parametric and not jagged. For channels L, C, and R.