Chris Rossi wrote:
"Arny Krueger" wrote in message
...
Phil Allison wrote:
"Arny Krueger"

An interesting related article can be found at
http://www.eetasia.com/ARTICLES/2002...MSD_POW_AN.PDF

Most interesting is:

"Figure 3 shows the effect of preamp input resistance (and
capacitance) on frequency response of a Shure SM57 with 100 feet of
common cable. The upper
curves, 10 kS and 3 kS, are typical of transformer-less mic preamps
while the lower curve, 1.5 kS, is typical of a transformer input
mic preamp. Note
the ultra-sonic peaks in response caused by insufficient damping".

This chart gives some insight into the output impedance of a SM57.
To summarize, there is negligible change in response at 3 KHz with
load impedances varying from 1,500 ohms to 10,000 ohms. IOW, the
source impedance of a SM57 in the normal audio range (20 KHz) is
quite small. Other sources
give it as being 150 ohms or 310 ohms. It may be even less -
perhaps 75 ohms or less. The same charts show an approximate 5 dB
range of response at
20 KHz but less than 1 dB variation at 10 KHz. None of this is all
that audibly significant.

** Fig 3 in the Jensen article shows an overall variation of less
than 2dB at 20kHz for the three load impedances at the end of 100
feet of cable driven by an SM57. At 15 kHz, or the highest
frequency an SM57 actually reproduces, the variation is less than 1
dB while at 10 kHz that variation is less than 0.5 dB.

The HF response variation between different samples of the SM57 is
a lot greater than that !!

This article seems to throw quite a bit of cold water on the many
claims of dramatic sonic differences due to real-world variations in
the loading of SM57s by various preamps and cables.

I was under the impression that the interesting loads for the SM-57
were reactive rather than resistive. I think Mark McQ added some
reactive load (a low pass filter on the input for RF rejection) to his
RNP in part for this reason.

Check figure 4 in the reference:
http://www.eetasia.com/ARTICLES/2002...MSD_POW_AN.PDF
for information about the effects of reactive loads on the SM-57.

Basically, with a load on the order of a relatively large 25,000pF there a
mere 2 dB increase at 15 KHz. A large 2,500 pF load gives just a 1.2 dB
increase at 20 KHz. Both peaks are fairly narrow and lightly damped, so
their effects in the main part of the audible range (10 KHz) are less than
1.5 dB (25,000 pF) or less than 0.3 dB (2,500 pF).

Since the RNP and the GRE have been mentioned, perhaps people who have them
can see what's inside the box in this area. Compared to the mic's response
variations in the same frequency ranges, this is all chump change.