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Topic: cinema sound design

Monte L Fullmer
Film God

Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004

posted 03-27-2009 10:12 PM

quote: Steve Guttag
it isn't the best conductor to make the termination with though.

What would happen if you crimped on either a forked or ring connector on that solid, then filled it with solder..would this then work for solid and tight termination to the lugnuts on the amplifier?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-28-2009 07:57 AM

That would work but don't crimp too tightly...just enough to hold the crimp on until you solder. Note, any flexing on that joint will work against it...also the more the solid cable is flexed the more the conductors will likely break.

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John Hawkinson
Film God

Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002

posted 03-28-2009 10:41 AM

This thread is so weird.

With respect to the last question, of course it depends on the gauge of wire, but best practice is to long heavy wire runs solidly terminated and then a short flexible patch to the amplifier (and on the speaker end). Any electrical fitting designed for good termination is probably appropriate for such a junction. I wouldn't use wire nuts, but realistically they're probably fine for No. 10, though of course they don't keep the wire from flexing, which makes them a poor choice if nothing is clamping the cable itself. Use a terminal block.

Of course if you're running 8AWG, similar advice applies, though you're not going to be running 8AWG solid [ha ha!]. But even stranded, those gauges are quite stiff.

(We ran some 8AWG and terminated the speaker-side with eurostyle terminal blocks and a few inches of No. 12 to pretty Speakon receptacles. Works great. On the other side, we ran the No. 8 straight into banana plugs to the amps. That was a mistake, huge pain in the neck to deal with strain relief and keeping them in the amps. On the other hand, we haven't gotten around to redoing the amp side. But do it right from the start.)

But again, don't pick a wire gauge out of a hat. Pick it based on the distance of your wire run, the resistance you can tolerate (based on damping factor), and the power levels.

I don't understand Geena's comment. It's not difficult to remedy so you recommend getting one anyhow? [Smile]

Honestly, panel-mount RCA jacks are easy enough to add, and you can wire them into any cinema processor. Seems like something the installer should deal with, anyhow, since the right place for such jacks will vary from install to install.

Steve, I can't believe you didn't mention EG18! [I realize it's slightly tangential to this, but still].

--jhawk

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-28-2009 01:04 PM

I'm nothing, if not tangential...I like trig.

EG18 is not too prolific on designing sound systems though. The Dolby Technical Guidelines is a good place to start.

As to wire nuts...I use them all of the time and generally use tape as a strain-relief...I've NEVER had one fail. If one is joining stranded to solid, solder is just about a must. Also, don't use junk materials or even wire nuts...and yes you can get them to work with #8.

John, RE: Bannana plugs and #8...it is doable but a pain, as you noted. Many 5-way posts will let you put the bananna plug in from the side and tighten down the "screw" onto the plug for a secure connection

Here is a blurry picture of the back of such a rack...the amps are QSC MXa series

Belden has come up with some real nice "speaker" wire. It is jacketed Red/Black with a twist (though they don't broadcast that part) and a real high/fine strand count. They have it all of the way down to 10awg too (1313A). You can get 4 conductor Bi-Amp (you can also use 4 conductor for the MF/HF section of a tri-amp). The 4-conductor goes down to 12AWG. By fine strand I mean 259 34awg makes up a 10awg conductor. Oh and another plus, Belden doesn't wind it onto a tiny core and make a slinky out of the last 50-feet.

For those looking for high-strand count 8awg...think about your friends in the Welding world...that is small stuff or them but welding cable is often very high-strand count.

Steve

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John Hawkinson
Film God

Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002

posted 03-28-2009 03:47 PM

Wait, why are we looking for high-strand-count 8AWG? Surely no one would do the full run that way (it's quite expensive!), and as for the last few feet to the amps/speakers, what's wrong with going up to 10AWG?

Now, if we're talking about lamphouses...

--jhawk

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-28-2009 06:42 PM

Given a choice? You don't want any splices in the speaker cable, like any other cable. I dislike terminal blocks to transition because you create numerous points for a bad connection. I have absolutely run #8 the full distance from amp to speaker...in fact, I think you would find, if the detail was there...#8 going to the bottom amps in that picture (MX-3000a amps). In this case it was THHN stranded, not "speaker wire" I also don't know of a cable manufacturer that makes a high-strand count red/black twisted...perhaps a white/black. There is always the clear jacketed twin-lead stuff but who wants to pull that?

Steve

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John Hawkinson
Film God

Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002

posted 03-28-2009 06:59 PM

Err, well, obviously you don't have a special set of 8AWG speakon connectors, so do you run the 8AWG into screw terminals on your JBL speakers?

I mean, sure, keep the number of splices to a minimum, but I think one on each end of a huge run isn't too big a price to pay...

--jhawk

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Louis Bornwasser
Film God

Posts: 4441
From: prospect ky usa
Registered: Mar 2005

posted 03-28-2009 08:44 PM

Look inside anyone's subwoofer and note how small the wire is (short run). There is no shame in a short run of #12 or #14 on either end of the long, low loss cable. Louis

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Marc Hansen
Film Handler

Posts: 93
From: Seattle, WA, USA
Registered: Dec 2000

posted 03-29-2009 12:23 PM

If you put the amps at the speaker end and send a low level signal to them will you have problems with picking up more noise in the line? The wire would be cheaper but how much would it degrade the sound?
Marc

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 03-29-2009 01:22 PM

It works fine if you used balanced lines. The problem is that it makes it harder to diagnose problems if there is no way to monitor the amplifier output in the booth.

Another approach that I have seen in older systems is to run 70v lines from the amplifiers in the booth to the backstage area. This also saves money on wiring, but requires expensive transformers at each end if you care about sound quality.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 03-29-2009 01:59 PM

quote: Steve Guttag
I dislike terminal blocks to transition because you create numerous points for a bad connection.

Steve, I am curious as to your opinion regarding wiring surround speakers together. Do you use wire nuts for that, a terminal block, etc?

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 03-29-2009 03:28 PM

95% of the time, wire nuts. Wire-to-wire connection. Never had a failure or noise. I ID the lines so trouble shooting is a breeze if a speaker develops a problem (foam rot or some such).

I've done a few systems with terminal blocks but when you add up the connection points and the potential for failure...I just don't like the added connections.

As for stepping down the wire guage at each end...it isn't the end of the world and I will do it when making drops....but ideally, I'll make it splice free (no drops).

The arguement of the wire in the cabinent as a justification is worthless...what about the wire on the voice coil? Is that a justification for running 30awg? In fact, I know some top sound guys that run the speaker wire straight to the drivers (separate runs to each LF driver).

Steve

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Martin Brooks
Jedi Master Film Handler

Posts: 900
From: Forest Hills, NY, USA
Registered: May 2002

posted 03-30-2009 10:23 AM

quote: Scott Norwood
The best sound that I have ever heard in a theatre was in February, 2000 in the Cinerama Dome in LA (now the Arclight), from about 1/3 of the way back from the screen and almost dead center. Someone please tell me how to make every theatre sound like that.

I was there sometime before the 1996 to see the revival of Lawrence of Arabia and I thought the sound was terrible (at least as compared to the Ziegfeld in New York for the same film). There was tremendous slap-back echo from the rear walls making dialogue intelligibility very poor. Perhaps they renovated after that and before the Arclight renovation.

Best sound I ever heard (aside from the Cinerama and Todd-AO days) was Close Encounters and Apocalypse Now, both at the Ziegfeld in New York. They had installed extra subwoofers for the original roadshow of Encounters and Apocalypse had the first split surround. When I saw Apocalypse Redux a few years back at the Astor Plaza (before that closed), the sound (or mix) was not quite as impressive.

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Geena Phillips
Expert Film Handler

Posts: 198
From: Norcross, GA / USA
Registered: Apr 2006

posted 04-01-2009 01:18 PM

quote:
I don't understand Geena's comment. It's not difficult to remedy so you recommend getting one anyhow? [Smile] Honestly, panel-mount RCA jacks are easy enough to add, and you can wire them into any cinema processor. Seems like something the installer should deal with, anyhow, since the right place for such jacks will vary from install to install.

I'm just saying that the OP should try to know up-front if the processor has RCA jacks for non-sync or not, because it is easier to have the installer deal with it at the time of installation. I apologize if I wasn't clear about that.

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