> "The Astatic D-104 was designed as a *communications* microphone with a carefully shaped frequency response for speech and not for extreme high or low frequency response."
Although the presence rise was a design attribute of the mic, limited low-end response was not. The D-104 was produced in the early 1930s as a communications microphone intended for reasonably good, balanced audio response in the AM mode -- not SSB. SSB as used in radio communications is a post D-104 phenomenon. Use of the D-104 pre-dates common SSB use in the amateur service by 20 years. According to Astatic, their 2-stage buffer amp was designed as an active impedance transformer as low-Z solid-state devices were being ushered-in during the 60s Astatic never intended for the preamp to be used as a "power mic" device. It was the Citizen's Band operators who made the added gain function popular. That said, Astatic could have designed a much better buffer for the D-104. > "The graph of the audio response published by Astatic, using the built in amplifier, shows 0 dB at 1 kHz. Below 1 kHz the output drops off smoothly to -5 dB at about 200 Hz, then more steeply down to -10 dB at 100 Hz where the published curve ends." The typical D-104 with 2-stage preamp is substantially more response limited than that shown in Astatic's graph. The response plot shown in their instruction sheet is hardly a scientific measurement and the response can vary considerably across cartridges. > "That roll-off is important since excessive low frequency response robs a signal of intelligibility and "punch" since the bulk of the energy, but virtually none of the modulation in the spoken voice is down in those ranges." True of weak signal communications. Not true when the SNR is high - and the reason for the disclaimer at the end of my post. If your theory is correct, I doubt Elecraft would have included ESSB as a design feature into the K3, The lowest fundamental of the deepest male voice can be measured as low as 70 Hz -- and is typically 75-85 Hz. It's not that spoken voice does not produce frequencies that low, it's that historically, SSB transmissions have been deliberately bandwidth-limited. > "That rising characteristic to a peak in the roughly middle point of the speech audio spectrum is what made it so effective in communications and made it so popular." The D-104 became popular for a variety of reasons including cost, aesthetics, availability in the golden age of AM, reasonably good and balanced frequency response, etc. Paul, W9AC _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
