Olson, H.F.; Carlisle, R.W. (December 1934). "A Lapel Microphone of the Velocity Type". Proceedings of the IRE. 22 (12): 1354–1361. doi:10.1109/JRPROC.1934.227217. S2CID51630277.
Olson, H.F.; Carlisle, R.W. (December 1934). "A Lapel Microphone of the Velocity Type". Proceedings of the IRE. 22 (12): 1354–1361. doi:10.1109/JRPROC.1934.227217. S2CID51630277.