I purchased a so-called "matched set" of Studio Concepts C4's.

http://www.studioprojects.com/c4.html reveals some negative comments:
http://www.harmony-central.com/Recor...ects/C4-1.html
(defects, excessive noise floor, rolloff)
that suggest that the upper end may not be as flat as advertised:
http://www.studioprojectsusa.com/pdf/c4.pdf

Q/C issues aside, there are notably good reports about this mic, with none
of the complaints of dark coloration and reported 8dB treble falloff for the
Rode NT-5. However, one user did report a limitation not Q/C related. He
said, "The noise floor is unacceptable for ambient micing..."

If one of these days I have a loc that's quiet enough to hear a pin drop, I
might want to record the venue ambience. It appears that there is a very
special requirement for ambience mikes: a noise floor lower than that
required for all other applications. Are there mikes that are specially
qualified for recording ambience? Would they be large diaphram condensers?
Can the ambient field be reasonably sampled by a microphone with poor
off-axis characteristics?

In perusing the MXL catalog, an interesting fact was observed. Their very
cheapest line of large diaphram mikes,
http://www.mxlmics.com/condenser_mic...ser_index.html, which have 6 mil
diaphrams and not-so-smooth frequency response, have high advertised s/n
ratios: 80 dB for the 990. It is unclear to me what relationship diaphram
thickness would have with frequency output, or why this mike should have
such a high s/n.

Comments?