When the first big outdoor festival/concerts like Woodstock were held, the PA folks encountered a somewhat unexpected problem. With a crowd so large, the normal array of speakers around the stage wouldn’t be enough, no matter how loud they were. To get the best sound to the back of the crowd, speaker towers needed to be constructed a few hundred feet away from the stage.
While this solved the problem of volume to the back of the crowd it created another: Sound traveling through the air moves at 1100 ft/sec (round that to 1000 ft/sec to make it easy). That means the sound coming from the stage takes a while to get to your ears. If you (and the tower) are 250 ft from the stage, the sound from the speakers on the stage takes 250 msec (¼ sec) to reach your ears while you hear the sound from the tower speakers immediately, creating an annoying echo effect. This is due to the path the sound is taking to your ears. The feed to the speakers on the towers from the power amps is electrical. Electricity travels at the speed of light, so the sound coming from the tower speakers gets there instantly – no delay. The sound coming from the speakers on the stage is traveling through the air, so it arrives ¼ of a second later.
The way to counteract this natural delay was to add an artificial audio delay to the signal sent to the tower. The DDL delays the signal going to the towers by the same amount of time that it takes sound to get from the stage to the towers via the air. So, for a person at the tower, the sound from the stage and the tower get there at the same time. The first concert to use delay lines to solve this problem was the 1973 Summer Jam at the Watkins Glen Grand Prix Raceway in upstate New York, and the delays used were Eventide DDL 1745s.
Since common electronics like Random Access Memory (RAM) or integrated Analog to Digital converters hadn’t been invented in 1973, the DDL 1745 used the highest density ICs (integrated circuit chips) available at the time: 1K bit (not byte) shift registers. The 1745 was a big box packed with a slew of these shift registers that provided a grand total of 200 msecs of delay. The 1745s weren’t cheap, with a list price of over $5,000 (1973 dollars; approximately $26,000 today). Back then a fifth of a second of audio delay costs as much as a new car!
Eventide flew a stack of these DDLs up to Watkins Glen and set up the delays in the feed to the PA on the towers situated in the crowd. There were four towers and the delay to each tower had to be carefully adjusted to synchronize the sound coming from the stage. There was some concern about how the 1745s would stand up to the heat, rain and length of the concert, but the experiment was a success and Eventide went on to deploy early delays for sound reinforcement in many venues, including Yankee Stadium in NY. Today using delay to improve live sound is standard practice. Eventide did it first.
Photos courtesy of Tony Agnello