Um you cant do noise measurements like that.. They must be done in a vacuum or in an anechoic chamber.. But not in a "quiet room" and where is your baseline measurement that shows the noise of your preamp? how are you subtracting your self noise of your signal chain?
Chris
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Actually the noise measured in a vacuum will be the electrical noise only. There are excellent white papers from B&K and Knowles on condenser mike noise sources freely available on the web. Since a condenser capsule is a reciprocal device you can actually measure the vacuum-state noise by replacing the capsule with an equivalent capacitance. I think Eric did try to calibrate the mike sensitivities out (IIRC he has access to a B&K calibration chamber) and since the low end is usually dominated by the bias resistor/capsule capacitance noise anyway (non-RF mikes) you can get a reasonable measure of the noise with a little care in isolation from 500Hz and up sources. I also don’t think he was trying to create standards quality reference measurements, just a rough comparison for people with no access to the different mikes or equipment.
In the end it’s a matter of physics, the noise performance of a small 10pF electret is just limited with respect to a 1” externally polarized capsule. The diaphragm stiffness and mechanical loss of the air load will for the most part determine the noise floor at the high end. At least the noise that no amount of circuit sophistry will reduce. It’s silly to argue on noise alone against the Rode. There are excellent nature recordings around made with them, but I can imagine that they are difficult to manage in the field.
BTW I personally think some of the problems people have in comparing mikes for noise is that the sensitivity is measured at a reference frequency and the actual response has dips and peaks right in the same region where the self noise dominates. I could easily see several dB’s of real difference as well as personal perceptual differences.
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To do real noise measurements you need a real chamber there is no way around that. There is a huge difference between a capacitor and a diaphragm of a mic. Electronically speaking they are the same but there are many other factors besides just replacing the diaphragm for a cap and calling it a day.. The huge problem here is that unless you have a calibrated cap for each mic and you can "unscrew" the diaphragm from the preamp, Not always the case then how can you do a real noise measurement in a nonanabolic environment?
Chris
