A few months ago, I wrote an article explaining how noise-canceling headphones work, and, in it, I referenced the Grateful Dead’s Wall of Sound, their huge sound system. I mentioned it because, since all the speakers were behind the musicians, it required noise-canceling microphones to prevent feedback.
A reader was kind enough to send me a document he got from the Grateful Dead organization back in 1974, explaining how the Wall of Sound was set up, and how everything functioned. I’d like to share this document, because it is very interesting, offering a detailed explanation of the Wall of Sound.
First, here’s a schematic of the Wall of Sound, showing which instrument each column of speakers was for. (Download a larger version of the image.)
The document begins discussing “THE GRATEFUL DEAD’S SOUND SYSTEM, HOLLYWOOD BOWL – JULY 1974.” It says:
“Recently there have been major changes in the Dead’s sound system, bringing it a step closer to the ancient ideal of the perfect sound system. This is a technical report; from the standpoint of the ideas on sound reproduction incorporated into its design, and with a description of its sub-systems.”
If you’re a recording engineer or audio geek, you’ll find this all very enlightening. If you’re just a fan, you may still find it interesting, since it determined how important the Dead – and, notably, Owsley Stanley – considered their sound, but also led to the Dead’s hiatus from late 1974 to mid-1976. The Wall of Sound was so unwieldy that it required a huge, expensive crew, and lots of trucks. The Dead was spending a fortune on this sound system, requiring more concerts in bigger venues, but still not leaving much profit. So they eventually called a halt to it.
You can see the Wall of Sound in the Grateful Dead Movie (Amazon.com, Amazon UK), which was recorded during the band’s pre-hiatus run at Winterland in October, 1974. You see the trucks that are carrying the equipment, and you see some pre-concert footage showing the road crew setting it up. It was a monster, and, according to those who heard it, offered near-perfect sound, even several hundred feet away.
So, download a PDF of this document and read for yourself what the Wall of Sound was all about.
Ok, so unfortunately your reference to the Grateful Dead”s differential vocal mic implementation has nothimg to do at all with active noise cancelling headphones. The Dead’s system uses two identically matched precision mics just slightly offset from each other and wired out of phase. Thus the only zone of pickup is the same as the distance between the two capsules. Thus, the mics could not “hear” the monitors, no feedback.
Active noise cancelling was first proposed by Harry F Olson in the early 50s. Modern implementations (headphones most popularly) use dsp powered algorithms to filter out background noise. There is also a large body of active noise cancelling used in industrila applications such as exhaust systems and HVAC.
Ok, so unfortunately your reference to the Grateful Dead”s differential vocal mic implementation has nothimg to do at all with active noise cancelling headphones. The Dead’s system uses two identically matched precision mics just slightly offset from each other and wired out of phase. Thus the only zone of pickup is the same as the distance between the two capsules. Thus, the mics could not “hear” the monitors, no feedback.
Active noise cancelling was first proposed by Harry F Olson in the early 50s. Modern implementations (headphones most popularly) use dsp powered algorithms to filter out background noise. There is also a large body of active noise cancelling used in industrila applications such as exhaust systems and HVAC.
Jesse, the noise cancelling, or feedback cancelling system has everything to do with the way the headphones work. Take a microphone that picks up everything except what you want to keep and mix it 180 degrees out of phase with the good sound and there you have it.