[Michael_Joly]

Had a chance to investigate ten different MXL 603 capsules from various production runs today. There were two parameters I was interested in documenting and comparing - capsule capacitance and diaphragm resonance.

The first parameter - capsule capacitance, affects sensitivity and output level of the capsule. The second - diaphragm resonance, affects high frequency response tuning.

I found capsule capacitance varied over a 50% range at the extremes with most capsules being within 25% of each other's capacitance measurement. In one particular case I found a capsule that was 100% lower in capacitance value than nominal and its output level was down at least 6db. By working with the number of diaphragm-to-backplate spacers and adjusting retaining ring torque I was able to tune all ten capsules very close to an ideal nominal value. It appears stock capsules could have a couple of dB level variation between them but can be corrected to less than 0.5dB with tuning.

As for diaphragm resonance - I was actually surprised to find the stock diaphragms where quite close to each other - within 12% of a nominal resonant frequency. This is good because the diaphragms are permanently attached to their mounting rings and cannot be re-tensioned. It appears whatever mechanized assembly process is used for diaphragm tensioning is fairly accurate and yields consistent results in this parameter.

In summary, I was impressed that the MXL 603 capsules do seem to fall within acceptable amplitude sensitivity and resonant frequency tuning ranges. And in the case of amplitude sensitivity can be brought to within 0.5dB of each other by tuning diaphragm-to-backplate spacing and retainer torque.