Replying to Little help?

This is not my area of expertise. It's on my assignment, due tomorrow. Hopefully a bunch of you know things about speakers.

""3. At times in an auditorium, the speakers "howl" or whistle due to "feedback" especially if the microphone is in front of the speaker(s)? What do you think is happening? what would be the important features which would determine the frequency at which the speakers howled?""


Also, I'll just throw this in here even though I doubt I'll get an answer, it's the other one I don't know:

""6. The French Horn is an instrument which is played in the same way as a trumpet is. However, the bore on the French Horn is conical, rather than cylindrical. French horn players also tune the modes by sticking their hands into the horns of the French horn. What do you expect this will do to the tuning of the lowest few modes?""

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