autocinema audio transmitter options

[Miguel Moreno]

Hello all on film tech family, hope you and your family are ok.
These have been very difficult days for the film industry, especially for us who are independent. I think that in my city we will start to open in the middle of June but with many restrictions, so I want to be prepared to start with a proposal for my bosses, to initially open as a drive-in theater. I just need to find the audio transmitter but i don´t know exactly wich equipment is correct. I´ve never been on a drive-in theater . Do you guys have any recomendation? Thanks a lot Mike Moreno

[Lindsay Morris]

Mike,
One that I am familiar with is the FMuser 15W Stereo transmitter made in China. Very easy to setup and use but depending upon what FM frequency band requirements are in your location tread carefully.

Here in Australia one can legally without a license have an output of up to 3W using a frequency that is NOT in use in your location. No idea what other countries require.

The FMuser can be tuned to any channel very easily and the output can be adjusted to give you just enough to cover the drive in field.

There are packages on the FMuser website which include transmitter, feeder cable and omni directional aerial.

The audio input is L & R Stereo at Line Level.

[Miguel Moreno]

It look perfect Lindsay.


how is the connection from the audio processor to the transmitter?

[Marin Zorica]

You should downmix LCR to mono or to stereo depending if you have mono or stereo transmitter. Some audio processors like Dolby and others have LCR outputs which you can feed directly, some can do mix like L&C to L and R&C to R channel internaly like JSD 60 or, you can just use small audio mixer, feed L C R channels to it and mix it on mixer, than feed mixer outputs to transmitter inputs.

[David Buckley]

Playing a movie direct into a FM transmitter won't sound great in a car: between the audio source and the transmitter there really needs to be a compressor, ideally a multi-band compressor, usually called a processor. Not only does this "fit" the audio much better into the FM bandwidth, it keeps the FM bandwidth "legal", both in the technical and regulatory senses, so it doesn't over modulate, and thus exceed the bounds of a legitimate FM signal, which not only keeps your signal within the bandwidth of where is should be on the FM dial, but also means it doesn't sound horrible on your customers receivers.

Problem is, processors are expensive, and the big brand name processors are really expensive, so even a low cost processor will exceed the cost of a small-ish transmitter, so these days it's cheaper to buy a processor that has a transmitter built in for free, that just happens to be marketed as a transmitter. But compared to the coin that Dolby and QSC charge, it's not outrageous, it's professional gear for the professional marketplace.

[Lindsay Morris]

Mike,

You do need L & R Stereo and as Marin has said various processors allow you to remix the digital sound into L & R signal that is suitable to feed an FM transmitter and the one I had dealings with was the the JSD 60 ( I think) on which you can select exactly what you want coming out of the L & R output connections. One needs to be careful that if you mix any of the Sub Woofer in that you keep the levels lower than what you would hear in a cinema as the average car sound system is not overly tolerant of plenty of sub signal.
In between the Processor output and the FM transmitter input it is best if you send it via a Limiting Amp so it prevents the transmitter being over driven as David has pointed out so that the dynamic range is reduced and what comes out in the car radios is quite good sound.
Not sure what is available outside Australia but there were 2 or 3 makers of Limiting amps based here which were quite good to setup and proved quite reliable and most broadcast transmitters I have worked with ALL had Limiting amps in the audio chain before it went into the transmitter inputs.
You might find something on flea bay that is suitable... a limiter is an early version of the more common compressors which usually have a heap of extras added in which all adds to the cost but a good basic compressor CAN be made to act as a Limiting Amp.

[Marcel Birgelen]

For what it's worth... we're working on a pop-up drive in project too and we're going to use an Orban Optimod 5500i as the compressor. Now those devices cost about as much as your average cinema processor and are targeted at the broadcast industry. But for a temporary audio processor with multi-band compression functionality, ask a local audio rental company. Remember, those guys are all grounded for indefinite times and are probably more than willing to help you out.

[Mark Gulbrandsen]

I always installed BW Broadcast Transmitters because their sound quality is fantastic and they are extremely reliable. At first I sold the TX-1 which was discontinued a few years later, then the TX-5 which could be adjusted down to 1 watt output. But now it appears the smallest one they make is the TX-30 which can be varied between 5 and 30 watts output. Granted you could use that one too with an appropriate RFattenuator to keep the power out to about a watt... I can not recommend the Ramsey transmitter. NOt only is it not FCC approved, but it also only sounds ok and does not include all the bells and whistles a good transmitters comes with. BW includes a limiter/compressor that you would not know is even in the chain! Also, the TX-30 is only slightly more expensive than the last TX-5 that I sold a few years ago.

https://www.bwbroadcast.com/

[Gordon McLeod]

For FM transmitters i used the decade line that were made in Montreal with a Smart MOD2b DI that provided separate outputs to a mono am mono speakers a LT/RT to the FM stereo transmitter

[Dave Macaulay]

We have used the Odyssey DI6-3 drive-in mixdown unit in several skytops. It's a passive downmixer that gives a stereo centre-weighted output - L and R are down a few dB and LS/RS a bit lower. Plus a mono signal to use for the snack bar area. No EQ , gain control, anything else. It's a basic resistor mixer.
Most have had no processor - just a D-A converter feeding the DI6-3, and a basic stereo mixer for gain and tone control (plus mic and nonsync inputs) feeding the transmitter. All have used a Decade transmitter but maybe that's just because we are in Canada. No complaints so far, and it avoids having to make up something custom.
In the film era we would usually modify a CP50 to only output the track's L/R stereo signals - just doing Dolby decoding, EQ, and gain control.

[Steve Guttag]

The JSD60 can be put into Drive-In mode where it will "out-of-the-box" do the mix downs so you can have stereo to the FM, mono to the ramps fixed volume mono to the snack bars...etc. Though not widely know, the JSD60 is VERY configurable as to what channels track with the volume versus fixed...it isn't as easy as merely putting things into drive in mode but with the appropriate access, it can be set up to accommodate most any Drive-In needs. As I recall, it is discussed in the manual but not too much hand holding.

[Miguel Moreno]

Thank you very much to all.
I will get to work on it and I hope I can tell you when the project start.

Best regards.

Mike Moreno

[Sean McKinnon]

For the price of a normal cinema processor a Q-Sys core 110 and DCIO (-H if you want HDMI audio too) will allow you to create any mix down you want, apply compression, apply limiting, and output a stereo feed to a part 15 transmitter. Plus you get a mic input, monitor output, and some relay outputs as well as all the extra I/O on the 110 itself that can be used for snackbar feeds, speaker on pole feeds etc... Plus you can create custom mixes and processing chains for each type of output.

[David Buckley]

Can I just second getting a BW transmitter; not only is it a rather useful transmitter, and can be adjusted in power output down to zero to match the needs of your area, but it has the right kind of compression, a multiband compressor, more usually called, in radio terms a processor, which will give superior results to standard compression, and it is designed specifically for the job. Just feed it uncompressed L/R from your mixdown from however you achieve it, and increase the drive so that on normal programme material the multiband is just tickling, and see what it sounds like, it should sound quite good. Don't go too hard or you'll sound like a terrible top forty station and induce listener fatigue.

[Mark Gulbrandsen]

The drive ins that I installed them at always had people show up with big sound systems in cars and vans. The broadcast sound from the BW's was really impressive to say the least.