Film-Tech Forum ARCHIVE: Portable Audio Set Up : Suggestions?

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Posted by Joshua Lott (Member # 240) on 08-06-2004, 08:29 PM:

I am trying to put together the ideal set up for a portable 35mm projection booth.

Currently I am looking at the sound system. I would like to use EV speakers (personal preference), but if there is something better out there I would consider that.

The problem that I am running into is putting together a system that is flexible enough to switch venues.

I am looking at going into

School gyms(this has been previously discussed about how difficult that will be.)
Auditoriums set up for plays
Convention Centers
Outdoor venues

What type of calibration equipment should I look to include when purchasing?
I will be using at LEAST a Dolby SR processor (not sure which yet.) But would prefer to have Dolby Digital. Will digital create additional problems? How can they be solved?

This portable set up will be in each location for at least 3 days. Sometimes more.

The smaller the package, the better. As this will be transported by air to 90% of the locations.

I am trying to keep the best quality possible. I would like to recreate the atmosphere and quality of a well maintained theatre.

Suggestions?

Posted by Luciano Brigite (Member # 1104) on 08-06-2004, 10:08 PM:

Will you use the system for anything else or just for film sound?
If it's only for film, a good processor with a set of power amps
neatly assembled inside a equipment case will do the work, remember that being in somewhat open spaces you'll need more power wich will calls for bigger amplifiers, making it heavy for transport. if the places you'll set it up aren't bigger than a average theatre, the same kind of amps will work, however , recreating the athmosphere of a theatre in an open place is harder to achieve.EQ'ing may become an issue then it'd be better a processor with a 1/3 eq per channel. you'll need an RTA and a pink noise card for setting it up .
Digital will add only one more equipment in the case and more cabling, I think digital processors (DTS,SR-D) are more sensitive to transport and may fail sooner than the analog due to their component soldering ( my oppinion tho..).
For speakers maybe another choice would be the ones designed for live shows (maybe it's the ones you're planning to use?) instead of theatre designed ones.
I have a set-up somewhat like the one you want, composed by a CP50 with upgraded cards + OBE and 3 power amps of 300W/channel + a spare amp. assembled in a metal/wood case. I use when I want to see a movie in my garage or then once in a theatre when someone messed it's sound rack and damaged the power amps and the processor's outputs, I put it to run there while repairing their system. my speakers are cheapo,unbranded ones,but does the work very well for me.

Posted by Dean Kollet (Member # 1789) on 08-07-2004, 02:09 AM:

I'd maybe go for JBL....they take some abuse....and as far as the case....couldn't you just use the cases that bands use when they tour?

Posted by David Buckley (Member # 2600) on 08-07-2004, 02:17 AM:

This is a budget question as much as anything. And how much bass you want (which is another way of saying how flat the bottom end of the system needs to be).

Conventional approach would be amps and speakers.

If you are shifting kit by air weight is important, so get amplifiers that have switch mode power supplies, sometimes called class D. A really good example is pulse amplifiers, which are widely used to drive array speaker systems. There is a 4 x 300w model, which might be ideal for what you require, and fit into 2u of rackspace. This means your processor and amps will fit into a gator case.

An alternative arrangement might be to use self-powered speakers, and thus not have separate power amps at all. Just distribute mains and line level audio.

I'm assuming you can get by with full range single amped speakers here. If this isnt the case then come back. In my opinion, as long as you are not clipping, then 300w is handle-able without biamping. If you go much above that, the economic and common sense case for biamping (or even 3x or 4x) starts to become stronger.

So I should state for the record that if are playing earthquate you will be disatisfied with the low end power of this sort of system. if you need earthquake, come back, and I'll add some more suggestions :-)

For room equalisation, you might choose something like the Sabine ADF4000 Power-Q Adaptive Audio Signal Processor. I've not tried this model, but it claims to auto-eq a room in 15 seconds, which is well faster than I've ever eq'd a space :-)

Just for clarity here; room eq is useful so that what the audience hears is not significantly impacted by the vagaries of venues that have nasty resonances, or tuned spaces that suck out specific frequencies. You still need to get the a-chain eq flat in the processor off the pink noise film loop, to account for the vagaries of the a-chain itself.

Another important question, given your desire for "cinema" sound, is dynamic range, especially in the context of the types of venues you will be playing in. Providing you have big enough amps, its easy to have enough headroom in a theatre to provide the "whisper to roar" dynamic range of modern film. In a gym, or any somewhere with not-quite-quiet enough air conditioning, low level dialogue may get lost below the venue's noise floor, and high level programme may end up clipping the amps, so you may (in fact, probably) need to reduce the programme's dynamic range. I dont know, but I would hope the dolby or smart processors could do this, as this is the most elegant place to compress. I dont think doing it ahead of the processor is a good idea 'cos you are compressing an encoded signal, and doing it after the processor is going to need a multichannel compressor; stereo is common but more than that is not, and thus would need some sidechain wiring bludge.

Caveat: I'm new to cinema, but old hand at sound reinforcement, and of the opinion that any half decent modern PA will be of at least as good a quality and capability as a typical cinema. Not necessarily better than the best cinema systems maybe...

Posted by Mark Gulbrandsen (Member # 72) on 08-07-2004, 09:10 AM:

I agree with Dean but not for his reason of them taking abuse. They almost always sound better than the equivelent E-V speaker does. I'd use one of the mid size cinema series, carpet the outside opf the cabinet and put metal corners on the cabinets. They's hold up to being moved around for quite a long time that way.

Mark

Posted by Robert L. Fischer (Member # 2424) on 08-09-2004, 04:53 AM:

I definitely recommend JBLs. I've never heard anything that sounds better from my experiences.

Posted by George May (Member # 1060) on 08-09-2004, 07:47 AM:

I do mobile 35 mm shows too, both inside and out of doors and take all my stuff round in a small car (VW Polo, plus a trailer). Audiences are up to 500'ish out of doors. I use 3 x JBL TR125s for the L,C,R speakers at the front on standard speaker stands. They are physically rugged, I can carry them on my own and have good punch. I like them a lot. I use Matrix UKP-1000 (500 watts per channel)amplifiers and a Dolby CP55. I prefer having the amps next to me in the 'booth', compared to active speakers, as I can then keep an eye on and continually adjust the balance and volume as the show progresses. As I tend to do one night shows, I don't have time to EQ each venue. For three days it would be worth it.

HTH and good luck.

George