Drive In Movie Sound - Quick and legal ? ????

[Pete Alcock]

I came across this unit which is interesting. I'm not sure if it would be classed in the same way as those devices that allowed you to "beam" the output of a a portable CD player to your old fashioned car radio? Neat that the FCC in the US allow very low power transmitters without a license. I doubt that it would do stereo though (pilot tone and encoding the "S" signal), so the in-car reproduction would be a little lame.

 

Rolls Low Power FM Transmitter.

 

If you could get permission from Ofcom to use something like this, it might partially solve the problem. Just thinkin'

Edited June 15, 2020 by Pete Alcock

[bruce]

Hi Pete,

That’s a 4mW transmitter.

 

OFcom do permit the use of unlicensed “micro transmitters” as you describe for in-car use (etc), but power is restricted to 50 nanowatt erp. So a range of a couple of metres max.

[Jivemaster]

I have most certainly had breakover from a in-car Tx unit while in a traffic jam so I suppose you could use one Tx for say three or four cars but it would always be iffy technically and getting it passed by Ofcom (etc) could be hard and not quick.

[dbuckley]

I do both movies and look after a radio station.

 

If you are going to do drive in movies, and transmit in the FM band, please consider getting a decent transmitter, and since you are in the UK, the BW Broadcast range is the obvious (but admittedly, fairly expensive) candidate, because, firstly, they are competent transmitters, and with the correct per-emphasis to match the UK broadcast standards, but secondly, they also incorporate a "processor", in broadcast speak, which in audio terms is a multi-band compressor, which will not only keep the FM modulation within legal limits, preventing splatter, but will reduce the dynamic range, so the movie will literally sound better on a car system.

 

If the movie audio is coming out of a "proper" movie processor, and it would be better if it is, you'll have the 5.1 outputs, so you'll want to mix those down to stereo, so mix L/R hard left and right, pan the centre to centre, about 6dB louder than L/R inputs, and then mix the L/R surrounds in mostly L/R about 6dB down on the main L/R inputs, and see how that sounds. If you mix in the LFE output at all, mix it in at quite a low level, it'll pump the compressor, and most car systems won't reproduce what comes out of it very well. Most folks advise just forgetting about it.

Edited June 21, 2020 by dbuckley