To give some context, I am designing a cosplay armor costume that somewhat muffles everything that is spoken while wearing it. I have a simple low power audio amp that I was intending to use to amplify my voice and place a small (3") speaker on the outside of the armor, theoretically enabling me to be easily heard outside the outfit without needing to really raise my voice. However, because of the restricted possible range between the mic and the speaker, by the time the volume of audio from the speaker is at acceptable levels, it is evidently picked up again by the mic inside the costume, and produces an annoying squeal from the speaker that rapidly increases in loudness until the amp's volume is turned down, at which point the level of audio from the speaker is undesirably low. The amp is a physically separate device from both the speaker and the (suitably biased) microphone, so I could potentially add some custom electronics to either location. I cannot change any of the properties of the amplifier itself, which takes a line-in, and can directly drive a speaker.
Yes, I know there are commercial stormtrooper amps that likely do most of what I am wanting to accomplish here, but I'd like to see if I can work a solution out myself, and hopefully not have to splurge more than a hundred dollars on what amounts to nothing more than a voice amplifier.
And to that end, I was thinking of possibly using an inductor that coupled with the impedance of either the mic or speaker, depending on inductor placement, would have an L/Z time constant such that the cutoff frequency would be approximately 1.5khz, which is far enough above normal spoken communication that I am hoping it should not interfere with normal voice communication, and still below the frequencies of the squeals produced, which according to the decibel meter that I used to check, peak at well over 2khz.
But I am not sure if that will actually work, nor am I sure whether it would be better to place it on the input or output even if it did.