Film-Tech Forum ARCHIVE: THX crossover SG-01

This is topic THX crossover SG-01 in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Magnus Eriksson (Member # 6085) on 02-26-2018, 01:38 PM:

How can I connect to this unit?
This week me and my colleagues are replacing some sound equipment at a (soon former) THX auditorium. New sound processor, crossover and power amps. All 35mm gear to the scrap yard. The front speakers remain though, 3-way Electro Voice something from 1998 (I haven´t crawled in behind the baffle wall for a closer look yet).
But I would like to have a look inside the SG-01, just to get a rough starting point for the new crossovers. But how? I see the RS-232 connector, but then?
/M.E.

Posted by Dave Macaulay (Member # 813) on 02-26-2018, 02:15 PM:

These were set up by the installer for the speaker used, I don't have a setup program. Probably look at the speaker specs for the recommended crossover frequencies?

Posted by Marcel Birgelen (Member # 6801) on 02-26-2018, 05:13 PM:

It's THX, so this box is sealed and not user-configurable. You can try to flash the JBL firmware onto it, maybe it works if you're lucky, but the settings will be gone.

I would lookup the make of the speakers and go from there to find their optimum crossovers. You want to see how stuff looks back there anyway I guess? [Smile]

Alternatively, if you have the equipment, you could also simply try to plot them.

Posted by Magnus Eriksson (Member # 6085) on 02-27-2018, 04:11 AM:

OK, tried to make a shortcut. They are never successful
After a dusty visit far back stage we found: Electro-Voice TL606DMT + HPK-Variplex-B. The documentation says 330Hz for top/bottom crossover (HF/MF passive).
But: we are not able to find anything regarding HF/MF crossover parameters. And this is an active 3-way system. Does anyone here know?
Edit: HF/MF passive of course

Posted by Sam D. Chavez (Member # 1841) on 02-27-2018, 09:47 AM:

I would ask Ryan Mendoza at THX. I've lost track of them over the years but they and Ryan are still there I've been told.

Posted by Marcel Birgelen (Member # 6801) on 02-28-2018, 01:11 AM:

So, in your case, the passive crossovers in the 3 (or 5?) MF/HF units where bypassed and you do have specific HF outputs connected on your SG-01?

Posted by Jay Wyatt (Member # 8768) on 02-28-2018, 01:24 AM:

If you have a copy of SMAART you could run a transfer function (TF mode) between the input and output of the THX box. The magnitude response would reveal the DSP thats going on under the hood. Capture a trace for each output (Lo,mid,hi) and overlay them on top each other.

Posted by Magnus Eriksson (Member # 6085) on 02-28-2018, 02:12 AM:

quote: Marcel Birgelen
So, in your case, the passive crossovers in the 3 (or 5?) MF/HF units where bypassed and you do have specific HF outputs connected on your SG-01?

Yes, exactly. And the Le/Re (former SDDS) speakers will remain but not connected.
We will hook up a RTA on the outputs today and have a look.
/M.E.

Posted by Marcel Birgelen (Member # 6801) on 03-01-2018, 08:31 AM:

I think I've quick-scanned the same manuals available on-line as you have and they indeed don't mention any specific cross-over frequencies for the MF/HF speakers. I suppose because they were initially not designed to be operated this way but with passive cross-overs only.

If you've got access to an RTA and the box is still working, it should give you some answers.

I suppose you're going to replace the SG-01 with some more up-to-date crossover solution?

Posted by Mark Gulbrandsen (Member # 72) on 03-01-2018, 11:34 AM:

If you want to replace that X-over I'd go with something like a QSC x-over as it will likely have your speakers correct files in it's library already.

Mark

Posted by Gunter Oehme (Member # 499) on 03-01-2018, 12:05 PM:

There was a 3 way active version of the speaker named Variplex (w/o 'B').
The data sheet for the 3 way active Variplex specifies 330 Hz LR 24 dB for LF/MF and 1560 HZ LR 24 dB for MF/HF xover.

I've also got the EV recommended eq settings for the EV DSP controller EX34 which are
for MF section: 740 Hz, Q=1.3, -3 dB and 1360 Hz, Q=1.6, +5 dB
for HF section: 3000 Hz, Q=1.5, -7 dB and 5400 Hz, Q=2.2, -2 dB.
These settings may be helpful as a starting point.

Please note that there was a different speaker version Variplex II which was introduced around 2003. The Variplex II requires different xover frequencies and eq settings.