1. What would you expect to happen to the sound of a violin if you made the bridge much heavier? (This is done by clipping a ``mute" to the bridge of the violin.) Recall two features- how well would a heavier bridge do in transmitting the vibrations, and what would happen to the primary bridge resonance of one did this?
The bridge has a natural resonance on the body of the instrument (with the restoring force given by the wood of the top). The more massive bridge would be moved less by the strings, making the transmission of vibration to the wood of the body less. The lower resonant frequency would also make the higher frequecies transmitted to the body less.
2. What would happen to the playing of a violin if one put soap instead of rosin on the bow?
It is the special character of the rosin which gives the violin bow its special friction behaviour-- where the force of friction is much higher if the string is moving at almost the same speed as the bow, than if it is moving faster. Without that the bow would not provide teh negative resistance necessary to make amplify the vibration of the string, and the string would not vibrate. Soap is an ideal material which operates in just the opposite way to rosin. The bow would damp out any vibrations, rather than amplifying them.
3. At times in an auditorium, the speaker "howls" or whistles due to "feedback"? What do you think is happening?
This is another case of negative resistance, in this case supplied by the amplifier. In a cartoon like that in describing the clarinet, let us say a pulse of sound is emitted by the speaker. This sound will travel to the microphone. It will take a time equal to the distance between the speaker and the microphone to travel that distance. The amplifier will now amplify that sound. and send it back through the speaker. As long as that amplification is greater than than the loss due to the inverse square falloff of the sound from the speaker to the microphone, this signal will get progressivly louder on each circuit until finally the amplifier saturates and cannot amplify the signal any further.. The exact mode which will be amplified most will depend on the efficiency of the speaker at the various frequencies, and the amplification of the amplifier at various frequencies. It will be a harmonic of the inverse of the time of propagation from the speaker to the microphone.
4. What effect on the playing of a flute would the fact that it is made of gold or platinum rather than say plastic have?
Hmm, this is a repeat of the problem on assignment 5.
5. Why is it more difficult to understand a woman or a child than a man? (Recall importance of the formants in making the vowel sounds, and examine how well the formants are mapped out by the harmonics of the various voices).
The vowel sounds are determined by our brains by noticing which bands of frequencies are loudest due to the resonances of the vocal tract. For a speaker, usually a man with a very low voice, the voice will have many harmonics in each span of frequencies. (Eg, if the voice is at 100Hz, there will be a harmonic each 100 Hz in teh spactrum. On the other hand if the voice is at 400 Hz, more typical of a woman, the harmonics only occur at 400, 800, 1200, 1600,...Hz. Ie there are harmonics only at a quarter of the frequencies that the mans voice has. This means that there are far fewer frequencies for the the brain to use to determine where the resonances of the voice occur. This makes it harder for the brain to figure out exactly where those resonances are and thus makes it harder to figure out which vowel the person it trying to say.
Why does amplifying a quiet speaker not make his/her voice very much clearer? See the note to the first part of this question).
A quiet speaker will usually produce notes with very few harmonics-- ie is almost
completely the fundamental. However to figure out which vowel the person is trying to
produce, the ear needs many harmonics to see which frequencies are accentuated by
the resonances of the vocal tract. Without lots of harmonics, the brain has a
hard time figuring out which vowel it is. Amplifying the voice does not really
help, since the problem is more that there are simply not enough harmonics to determine
what the vowel is, than that the voice is too quiet. One of the secrets of making the
voice distinct and well understood it make sure that the voice operates so as to produce
a wide spectrum of harmonics. Having a low voice, and having the vocal cords
completely close on each puff going through them both help to make the voice clearer.
Amplification does help a bit, since it makes the very soft harmonics louder,
but of course it also makes the fundamental louder as well, tending to mask the
harmonics. Ie, amplification is not a panacea to the problems of a quiet speaking voice.