[Dixielandjazz] Recording Low Tones
willc at nova.edu
Sat Mar 1 17:33:47 PST 2003
Dear Nancy, Steve & Co...
Understanding why acoustical recording was so frequency and sensitivity
limited may be easier if you remember the tin-can and string telephones
of your kidhood. The frequency response was limited and you had to yell
so loud the apparatus was pretty much unnecessary.
In acoustical recording, the morning-glory horn led to a mica diaphragm
to which a cutting needle was attached through mechanical linkage. The
horn and "cutting head" assembly was attached to a lathe-like mechanism
driven by a weight-powered motor with a flyball governor to turn the
turntable under the morning glory at a precise speed (78 rpm by the 30s)
and to move the horn and cutting head assembly across the disc to
produce the spiral groove.
When sound struck the mica diaphragm, the cutting needle wiggled and the
needle moved up and down (vertical recording) or side to side (lateral
recording) to cut the groove containing the sound wave wiggles
(modulation) in the wax (later shellac)
It may be evident that there are a few problems with this arrangement.
The horn taper and necessarily small diaphragm size and the mechanical
linkage all conspire to limit frequency response, as did the speed of
the turntable. The limit on maximum sound level was set by the stiffness
(limited mechanical compliance) of the diaphragm and the maximum
excursion of the needle before it cut into an adjacent groove. The
softest recordable sounds were also constrained by all the elements of
mechanical resistance - the diaphragm, the linkage, the resistance of
the wax being cut and also by noise (called "rumble" transmitted up into
the platter from the motor and flywheel arrangement.
It should be pretty obvious that "loud" was necessary and that the "mix"
- the balance of loudness of the various instruments and a vocalist -
depended both on how far each instrument was from the morning glory and
the gonadality of each player.
Many years ago I was with a Hollywood turntable/tone arm/phonograph/tape
recorder manufacturer and was very much involved in the recording
industry. I was for a time an officer of the LA chapter of the Audio
Engineering Society. And even now, as I sit at my computer, I can look
across the room at the Ampex 351 recorder I used to record albums.
Having now given you far more information than you probably wanted, I
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