Film-Tech Forum ARCHIVE: Outboard Equalizer

This is topic Outboard Equalizer - Yes or No? in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Manny Knowles (Member # 1171) on 02-12-2003, 08:45 PM:

Okay, I'm starting to see the light: The Dolby CP-45 is really a headache-inducing piece of equipment. I haven't really picked up on the noise-reduction issues with the Cat 222SR/A module but, then, maybe this is because I haven't heard great NR at work.

My real issue is with the inboard EQ system. It is really limited. The seven or eight bands start at 63Hz and stop at 1.6 or 1.8kHz. There are parametric bulk EQ dials for Bass and Treble. Very few of the bands controlled by the dials on the EQ actually correspond to the bands on an RTA. I think 63Hz and 1kHz are the only frequency dials that match up with a standard ISO band.

QUESTION #1

I am wondering if I could do better by setting the inboard EQ to "Flat" (or as flat as is possible by "eyeballing" the dials to the 12 o' clock position) and then send the channel outputs to outboard EQ's (and then to the amps).

Is there some hidden danger(s) I should know about before attempting this? I can think of just one potential problem -- the EQ controls would be exposed and could accidentally (or deliberately) get moved out of alignment.

QUESTION #2

I can clearly see the 500Hz crossover dip on the RTA. Do I want to...

(a) raise that band to bring it "flat" relative to the other bands; or
(b) lower all of the others to the level of the 500Hz dip (because it's preferable to "cut" bands); or
(c) leave the dip because it's normal
(d) none of the above

QUESTION #3

Why did they bother giving me a 63Hz dial? Isn't that in the LFE range? Should I turn that down (or off) or do I want to have some of that low end in the main channels? Is the subwoofer affected by how much LF is present in the main channels AFTER the equalization circuitry?

Posted by Gordon McLeod (Member # 33) on 02-12-2003, 09:40 PM:

#1 if you put in external eq make sure they are narrow band filters 1/3 octave
Rane, MXR and KlackeTechnic make excellent eq units
#2 THe crossover dip could be the driver are 1 out of phase (have you tried reversing the high frequency phase to see if it getts better 2 the time alginment of the high vs the low frequency driver
#3 the stage speakers need to be flat to 63 hz the sub is seperate beast to that. Unless you are using a fancy crossover that allows for bass management

Posted by Manny Knowles (Member # 1171) on 02-12-2003, 10:35 PM:

Thanks, Gord.

I will try reversing the polarity in the HF tomorrow and report my findings here.

Posted by Michael Hunt (Member # 772) on 02-13-2003, 11:50 AM:

If you do use external EQ, make sure that nobody can 'play' with it.
Some manufacturers can supply tamper proof kits for their external equalisers.

I'd add BSS Eq. to the list - been using their FCS 960 units for years, without a problem, unlike a Klark Technic unit we have...

Some out there are bound to contradict, but I'm of the opinion that its better to cut offending frequencies that to boost ones that are lacking...

Posted by Jon Bartow (Member # 241) on 02-13-2003, 12:54 PM:

Manny,
I agree that the CP-45 is quite limited, but it does have it's place. Having set up many of these beasts I can say that I usually can get the auditorium eq to be decent without "over-eqing". The eq controls are broadband, not narrow band like a 31 band eq. And they do interact with one another. Unless your auditorium has bad accoustics you should be able to get a decent response out of it.
Are you using the CP-45's crossovers or are you using external crossovers?
Jonathan

Posted by Manny Knowles (Member # 1171) on 02-13-2003, 05:27 PM:

This raises a point I did not mention. Perhaps you had guessed. This is a bi-amped application. I am using the crossovers in the processor and I have bypassed the crossovers in the speaker cabinets (JBL 4670D). The LF wires go straight to the LF transducers.

By the way, thanks to those who posted or emailed.

I did not get back to EQ'ing today so I can't give feedback just yet. But I will.

Please take a look at my "Testing Amplifiers" thread. This auditorium is in serious trouble.