Film-Tech Forum ARCHIVE: Sub EQ

This is topic Sub EQ in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Antonio Marcheselli (Member # 373) on 07-26-2002, 06:37 AM:

Let's say that you have a sub like this on RTA

Equalizing a sub means cut off the main resonance of the room.
Would you cut just the 60hz peak

Or cut up to reach 40Hz

What is the correct procedure?
Thanks

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Antonio Marcheselli
Florence, Italy

Posted by Gordon McLeod (Member # 33) on 07-26-2002, 08:04 AM:

It is always best to attempt to attinuate the offending frequency rather than boosting the others

Posted by Antonio Marcheselli (Member # 373) on 07-26-2002, 08:41 AM:

Gordon,

It isn't what I meant! Both my example are cutting on 60Hz. I wonder if It is better to cut up to have 60Hz = 50Hz or to have 60Hz = 40Hz.

This is my Home SW, but one of our theater has +/- the same response (4645C) but with less resonance on 60. Will be better to cut just the 60Hz or the entire 50-70 Hz band?

Bye

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Antonio Marcheselli
Florence, Italy

Posted by Steve Guttag (Member # 268) on 07-26-2002, 01:23 PM:

I would have to know just what that subwoofer could do but on the surface, I'd try to EQ to 40Hz based on your printouts...BTW which analyzer did you use? Spectra Plus?

Steve

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"Old projectionists never die, they just changeover!"

Posted by Antonio Marcheselli (Member # 373) on 07-26-2002, 01:52 PM:

Steve,

Was SpectraLAB, is it different from spectraplus?

Uhm... You're right. Who equalize should know what the speaker can do before equalize.

Let's suppose that that graph are about a 4645C sub (without B6). Since 4645C has a flat response up to 35 Hz, means that is not flat up to 35Hz is a room resonance, right?

Bye

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Antonio Marcheselli
Florence, Italy

Posted by Justin McLeod (Member # 1329) on 07-26-2002, 03:58 PM:

How would someone go about getting some training in the EQ dept. Is their a do it your self guide somewhere where a person like myself with no skills can learn how to do it? I do know that RTA's are a bit expensive and i know that affordable RTA's have been discussed on this site but which RTA would you reccomend for a beginner to start out with, including the mics.

Posted by Oliver Pasch (Member # 1335) on 07-29-2002, 10:35 AM:

Hi Antonio,

i would always recommend to do as less equalizing on the sub as you can. Answering your question, please don't even try to cut the 60 Hz down to the 40 Hz level, although i believe that you won't be able to have a - 18 dB cut with a regular cinema-processor. What you see on your RTA will mostly be a resonance peak caused by the room-acoustics and not the first audible wave coming from the cabinet. You should firstly go and listen to it, probably using the DOLBY Jiffy-Testfilm, and maybe after that you don't want to equalize anything at all. We use a lot of JBL 4645 down here and from my experience they sound best without any EQing at all.

By the way: where and HOW do you put your microphone in the auditorium and what kind of floor is there? Wood?

Kind regards
from sunny Germany

Oliver

Posted by Antonio Marcheselli (Member # 373) on 07-29-2002, 02:01 PM:

Oliver,

That graph is not about a 4645B, it is my canton AS25 (HT sub) but our 4x4645B in one of our theater has approx. the same response.

Our tech cut gently at 60hz, -4dB. But since that speaker are flat up to 35, I wonder if we can try to cut up to the same level of 40Hz...

The floor of the theater is in linoleum.

Bye
Antonio

Posted by David Baum (Member # 568) on 08-03-2002, 05:07 AM:

the 4645C sound best not equalized ? ok, they have pretty natural flat response down to 25hz or (from 100hz) but still, they need some EQ. the SF3 module with the QSC DCA amps is one good solution to high pass at 20 or 25 and boost at 25-30hz. But EQ to try to make sound 1 or 2 4645C like 6 or 8 is wrong if that's the target: first, enough subs, stacked, enough power (800-1500Watts, real watts that is), high pass at 20 or 25hz depending on the power used, then EQ to flatten things out.
I use 2 4645C in my HC with a Berhinger parametric EQ and the power amp high pass at 18hz, 18db per octave (it's a small amp for now, 2x250 at 4ohms, AB, cooled). Next will be a QSC DCA 2422 or 3422 with SF3.
Well that does not answer the question

but this chart looks pretty awful, in terms frequency response!

Posted by Gordon McLeod (Member # 33) on 08-03-2002, 10:13 AM:

Oliver said"What you see on your RTA will mostly be a resonance peak caused by the room-acoustics and not the first audible wave coming from the cabinet."
In large rooms the standard for equalization is the room included not the near field (first wave) response. There is only one brand of sound system that uses near field eq techniques and the rest of the industry doesn't support that philosphy

Posted by Steve Guttag (Member # 268) on 08-03-2002, 10:17 AM:

To add to Gordon's response...with a subwoofer, virtually all subtracks are long in duration and will "build up" in the room. This gives further support to evaluating a room resonance. It is also the reason I recommend only using the "continious pink noise" spec when judging subwoofer power handling.

Steve

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"Old projectionists never die, they just changeover!"