feedback seems to be the issue, which is understandable since it is a microphone
I wonder if a soundhole cover would kill or reduce the feedback of the Mi-Si Air.. I've been looking for one of these pre-made for UKULELE (and NOT guitar) all over the internet, but have found none. However, I wonder if a test to cover the soundhole with some blue painter's tape would verify if a soundhole cover would help. If so, I have a few plastic lids I could cut down to size if/when I were to get one of the Mi-Si Air pickup/mic units.
FYI: feedback is usually caused by the mic 'hearing' the sound speaker, and over and over again, and the sound waves cause that howling sound, which is in fact an oscillation of the sound going from the mic, out to the speaker, and then back into the mic, and out to the speaker ad infinitum.
A soundhole cover will BREAK the cycle both physically and acoustically by interrupting the actual sound WAVES and stopping them from going back in to the mic at an amplitude (volume) that can be heard and re-amplified.
The other option to mitigate feedback is to use a form of EQ, called a NOTCH filter, and tune it to the offending oscillating frequency and reduce the amplitude of that frequency as far as possible, and usually lowering of -12 to -24 db is enough. Remember that the decibel (db) units are LOGARITHMIC (Base-10)and not LINEAR, which means a change of -1db is actually a 10-fold decrease in amplitude, so it does not take much gain reduction in NUMBERS to cut the volume of the howling feedback.
Also, using a mic, you want to put the speakers of the PA or amplifier in FRONT of you, pointing AWAY from you and INTO the CROWD, and NOT behind you.
If the speaker or amp is BEHIND you, you will get feedback all day long, as well as if you are FACING the speaker (just watch any old Jimi Hendrix video and you will see
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