This is an audio circuit that generates interference when someone speaks loudly - it provides a way to "train" your colleagues to speak in a softer tone.
I was just reading Brian Fuller’s article on the Best Engineering Practical Jokes. From there I bounced over to the original submission of the winning entry, which was How to shut the sales guy up by Bob Stevens.
This really was a great practical joke that made me laugh out loud. Then I started reading the comments. These were all interesting, but one especially caught my eye. This is where a reader with the screen name Antedeluvian said:
I am reminded of a circuit by Bob Pease, if I remember correctly, to make a member of staff at National talk in a softer tone. It was an audio noise generator and as the voice grew louder so did the audio disturbance forcing the speaker to raise his voice above the noise in a positive feedback loop. Must've been awfully noisy while "training" the offending party!
Of course Bob Pease
– who was a well-known expert in analog electronics – recently passed away in a tragic accident. He was one of a kind who will be sorely missed. He also had a great sense of humor. One of his quotes was “My favorite programming language is ... solder.”
I also recall seeing a picture of him on the top of a flat-roofed building throwing a digital computer over the edge. The computer had just left his hands and was on its way to oblivion. I think the accompanying caption was something like “There’s one digital computer that will never lie to me again.”
(I just tried to find a copy of this picture on the web, but I failed. If you know of one, please post a comment telling the rest of us where it is).
As an aside, I once met Bob Pease at a debate on the pros and cons of Fuzzy Logic. Bob was not a fan of Fuzzy Logic as I recall, but that has absolutely no bearing on what we’re talking about here (grin).
Returning to Antedeluvian’s
comment, another reader replied:
That circuit is called the "Hassler" (www.national.com/rap/Story/widlar.html)
So I of course bounced over to this article on Bob Widlar
, which was written by Bob Pease. In the middle of the article I found the following:
One of the celebrated things Widlar did was to put a "hassler" in his office. When a person came in to his office and spoke loudly, this circuit would detect the audio, convert the audio to a very high audio frequency, and play back this converted sound. The louder you talked, the lower the pitch would come down into the audio spectrum, and the louder it would play. So if you really hollered, it would make sort of a ringing in your ears. Of course, if you noticed this "ringing" in your ears, and stopped for a while to listen, the "hassler" circuit would shut up. He gradually got people to stop yelling at him. I mean, Bob really was almost always a soft-spoken person. He didn't have to yell or shout to get his message across. When he did speak, and softly at that, people would soon realize that it was a good idea to listen to him.
This sounds like a great idea. My first thought was that I would love to see the original circuit and build one (does anyone know where that circuit can be found?). My second thought is that with all of the new digital signal processing techniques that are around these days, maybe we could do something similar – but more sophisticated – using a low-cost FPGA evaluation board (does anyone have any ideas?).
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