[Roy W. Rising]

"Mike Rivers" wrote:
bill wrote:
The speaker did kind of roll off the
birds but I could hear trucks and trains for miles, even farther than
with my own ears. A 4" speaker does seem to be kind of optimum around
200-400 Hz.

A local sound company ... Then they got the idea to hook one up
to a mixer mic input (this was before anyone had "mic preamps") ...

The venerable RCA OP-6 was called a Remote Amp. It had mic-level input and
true line-level out able to drive a Telco line. There was a real VU meter
and a real variable attenuator on the front. It dates back 50 years or
more. And ... it used real "fire bottles" in a VERY quiet circuit design.

--
~ Roy
"If you notice the sound, it's wrong!"