I have a few questions about the CM-310 handheld Differoid microphone:
1. How many more decibels of gain before feedback would I get from the CM-310A microphone compared to a standard cardioid vocal mic?
2. What is the CM-310A's off-axis rejection in decibels?
3. Would a CM-310A be a good choice for a soft singer because you can turn up the mic more than others before feedback?
Reply: The CM-310A has at least 6 dB more gain-before-feedback than a standard vocal mic when both mics are used with lips touching the metal grillescreen. That's nearly twice as loud. Some users have reported that the CM-310A has as much as 12 dB more gain than standard vocal mics.
The off-axis rejection of the CM-310A is 33 dB at 160 degrees off axis at 1 kHz, and 35 dB at 160 degrees off axis at 100 Hz if you include proximity effect at 100 Hz.
Although the CM-310A has been used mostly with very loud bands to get the vocal above the musical backup, the CM-310A would be good for softer singers for the reason you mentioned. The mic needs to be used with lips touching the grille, otherwise the voice gets cancelled because the CM-310A cancels sound at a distance. The CM-310A has more gain-before-feedback without the external foam windscreen, but it has less breath pop with the foam windscreen, so it's a good idea to experiment.
Some bands that have used the CM-310A are Jeff Matthews, Nirvana and Soundgarden.