Steve's Web Junkyard

Some folks on the Antique Radio Forum were reminiscing about the old ads in magazines for "the big ear". 

The subject of the Popular Electronics shotgun mic project came up.

There's a nice build from the Green Bay Professional Packet Radio group. They host a scan of the original article. James Thompson also hosts a scan of the Popular Electronics article.

I had one of the kids in the Parker Model Rocket Club build up a couple of shotgun mics based on the article. We used model rocket cardboard body tubes instead of the aluminum tubes used in the original Popular Electronics version. I'll post a photo when I get a chance.

By the way, the description in the Popular Electronics article of how the mic works is totally bogus. It's just a phased-array antenna, with the tubing being delay lines. 

Sound from the front travels toward the mic. Some of it is picked up by the longest tube, but it travels at the same speed in the tube as in free air, so it stays in phase as the sound travels to the mic element at the back. The same thing happens with the other shorter tubes. 

Sound from the side gets picked up by all the tubes more or less simultaneously, but it has to travel differing distances to the mic element due to the different lengths of the tubing. Summing these phase-delayed copies of the sound wave results in partial cancellation of the sound from the side.