[Paul Stamler]

Hi folks:

A couple of months ago, after I'd reported the results of our experiments in
lower-impedance loading of the Shure SM57, a couple of folks asked about the
results on other microphones. Tonight in class we did the experiment; we
tried four microphones as drum overheads, plus two on acoustic guitar. (We
had to clear out of the studio at 10 pm to let the next person in.)

Microphones:
Shure SM57 (again)
Electro-Voice RE15
Electro-Voice PL20
Sennheiser MD421 (Mark I)

Preamp: Universal Audio 2-610, both channels set to 2k load

Loading device: Gizmo (XLR cable with 698 ohm resistor across pins 2 & 3)

Recorder: Radar system, working at 24/96.

With the Gizmo in line, I calculate the load to be 517 ohms.

We used our Studer analog machine's VU for a level meter, and after the
basic level on each mic was set, we matched the two channels to within 0.1dB
(1 pointer-width) using a tone generator feeding into a guitar amp.

Results on drums:

PL20: Some small differences, but very subtle, hard to tell. A bit more
restrained sound on top, perhaps a little thinner on the bottom, with the
lower-impedance load.
RE15: Pretty much the same.
SM57: A lot more difference; with the lower-impedance load, what had been a
wash of white noise turned into the metallic sheen of cymbals, while the
snare sounded much more real. The difference between loadings was clear to
all the students, and to me too.
MD421: Some sort of change in the midrange with the lower-impedance load,
and nobody liked it. Everyone preferred the sound with the 2k load.

Results on drums:

RE15: Again small differences; I heard less pick noise with the
lower-impedance loading, which is a good indication of less ringing. The
differences, though, were easier for everyone to pick out with the guitar
than they were with drums.
SM57: Dramatic difference again; what had been a brittle, harsh, edgy sound
became something one of the students, a confirmed loather of SM57s, said was
"not...half...bad". To me it actually began sounding sort of like my guitar,
which it sure as hell didn't with the 2k load.

This was a quickie test, not hugely rigorous, but I think it supports the
conclusion that SM57s react dramatically well to lower-impedance loading,
while other microphones such as the RE15 and PL20 (supposedly the same as an
RE20) are less sensitive to loading. The MD421, on the other hand, seems to
care a lot about loading, but is happier with a higher impedance. I wish
we'd had time to try it on the acoustic guitar, as in general the guitar
seemed like a more sensitive test than the drums (which surprised me).

Fun night. Thanks to Smitty for the excellent drumming.

Peace,
Paul