Hi Guys,
I just registered. I've been looking over the web over the last couple of days for shotgun mic information, and stumbled on this forum. I remember the old Popular Electronics shotgun mic, and wanted to build one. Here are 2 links that I found -
http://www.oldbird.org/mike_home.htm
http://members.shaw.ca/roma/twenty-eight.html
I blew the numbers into a spreadsheet and discovered that the 1" increments leave wide gaps in the high end frequency (3381Hz to 6762Hz), so I redesigned it to use and 11.5% increments in frequency instead, and get a little more range to boot. I'm going to use 4 foot, ~0.30" OD shipping tubes and solvent weld them together to keep it light. Here are the lengths for an 11.5% gun (in inches) -
47.96, 43.01, 38.58, 34.60, 31.03, 27.83, 24.96, 22.38, 20.08, 18.00, 16.15, 14.48, 12.99, 11.65, 10.45, 9.37, 8.40, 7.54, 6.76, 6.06, 5.44, 4.88, 4.37, 3.92, 3.52, 3.15, 2.83, 2.54, 2.28, 2.04, 1.83, 1.64, 1.47, 1.32, 1.18, 1.06, 0.95
and the corresponding frequencies (in Hz) -
141, 157, 175, 195, 218, 243, 271, 302, 337, 376, 419, 467, 521, 580, 647, 722, 805, 897, 1000, 1115, 1244, 1387, 1546, 1724, 1922, 2143, 2390, 2665, 2971, 3313, 3694, 4119, 4592, 5120, 5709, 6366, 7098
Good Luck all!