The Drive In Movie Theatre & Radio

The drive-in movie theater was invented in 1933. The sound sucked pretty bad then, and it pretty much continued to suck for about 40 more years. (I'm not making this up. I went to drive-ins as a little kid.) But FM radio didn't exist yet either so the expectations were set pretty low.

When the first drive-in opened in Camden NJ, a company by the name of RCA Victor designed the sound system. They called it "Directional Sound". Using 3 main speakers mounted next to the screen, they tried to blast the volume so that even the cars in the back could hear.

There were 2 major problems with this type of sound system. Since light travels slightly faster than sound, the sound arrived at the back rows late, i.e out of sync with the picture. The second problem was that while everyone in the entire drive-in could hear the sound, so could the neighbors, passing cars, and overhead planes. Some complaints stated that farm animals were disturbed miles away. This system was replaced with the individual window-speakers most movie goers are probably familiar with.

It was in the early 70's that radio sound came into practical use at the drive-in. Although the idea had been kicking around since the 1950's, with some systems even calling for a separate box the patron would purchase and reuse, it was made practical by Cinema Radio, a company started by Fred J. Schwartz after experiencing what he felt was poor sound quality at a drive-in.

The big change since 1950 was that the majority of cars now had radios. By 1970 the number was up to an estimated 97%. The timing was perfect. Normally transmitting a radio signal would require a facility license.  But under part 15 they were allowed to operate without any licensing by the FCC. They passed on licensing these Low Power stations as long as they kept it under 50 milliwatts. [Closed cable FM was also exempt for the same reason.] These broadcasts usually could be received via your car radio, or by a transistor radio which you could borrow from the snack bar. Initially these were AM stations but the policy spread to FM licenses as that became adopted as the standard. FM is what remains in use to this day at most drive-ins. Read more here.

The earliest version of Part 15 goes back to 1938. This was meant to govern devices which emitted incidental radio waves as a means of governing that source of interference. That initial set of rules were adopted in November 1938 and remained unchanged until 1957. It was then that the rules needed retooled as the 15 microvolt uV/m exemption had already been leveraged for purposeful, not incidental use. More here. 

RELATED DRIVE IN RADIO FIRSTS:
In 1986 FM stereo sound was introduced via FM broadcast at broadcasting is introduced at Shankweiler's in Orefield, PA. This is also America's oldest, continually running Drive in. In 1999 The Boulevard Drive in was the first drive in theater in the world to install digital sound. They broadcast at 89.7 FM in Kansas City. I am told that their fixation on high quality audio has made it superior to that of many indoor theaters.

There is now even a company trying to buy time before, between and after the movies run on the radio signals at the drive-ins! They distribute content via CD-R mailed weekly. It's an interesting niche service. More here.