1. Three functions of a pre-amplifier: a) to boost weak signals, such as those from a phonograph, to "line level," i.e. to maximum voltages of a few volts; (b) to route signals between inputs and outputs, for example, to send the audio from a compact disk player to a cassette player for recording, and (c) to provide signal conditioning, through the use of bass and treble controls and filters.

2. Longitudinal waves - the wave disturbance is parallel to the propagation direction, e.g. sound waves. Transverse waves - the wave disturbance is perpendicular to the propagation direction, e.g. light waves and other forms of electromagnetic radiation.

3. A microphone is a transducer that turns sound pressure fluctuations into variations in voltage. When connected to an oscilloscope, voltage is displayed on the vertical axis, and time on the horizontal axis.

4. The reverberation time is defined to be the time for an impulsive sound to decay to one one-millionth of its initial intensity. It depends primary on (a) the volume of the listening space, in cubic meters, and (b) the total area of sound-absorbing surfaces in the space, in square meters.

5. The frequency is: f = 344 m/s divided by 0.086 m (8.6 cm = 0.086 m), or 4000 Hz. The new wavelength is 268 m/s divided by 4000 Hz, or 0.067 m (6.7 cm).

6. Standing waves are geometric patterns of vibrations, corresponding to large amplitude motion. Waves are traveling back and forth between the extremes of the object, but overlapping in such a way that they appear to be standing still. Such patterns occur at special frequencies corresponding to resonance in the vibrating system. There are many examples of standing waves in audio systems: the audio signal itself tends to be the result of instruments that are creating standing waves. Speaker cabinets have resonant frequencies, especially, for example when used in a bass-reflex port configuration. Standing waves on the cones of speakers affect the frequency response. Room resonances can affect listening quality and correspond to standing pressure waves.

7. A tube closed at both ends has resonant frequencies that are integer (1, 2, 3,...) multiples of v/2L. Here, the fundamental frequency is (344 m/s) divided by (2 * 0.6m), or 287 Hz. The next two harmonics are at 2*287 Hz = 574 Hz, and 3*287 = 861 Hz.

8. The tube closed at both ends has antinodes at both ends. The fundamental has one node, in the middle of the tube. The first harmonic has two nodes, each at a distance of one-quarter of the tube length from either end of the tube. The third harmonic has 3 nodes, one in the middle and the other two at a distance of one-sixth of the length from either end.

9. The vocal chords vibrate at the pitch frequency of the voice, creating a harmonic spectrum corresponding roughly to a triangularly shaped waveform. The vocal tract consists of the pharynx, soft palate, mouth, teeth, etc., and has resonances, called vocal formants, that have adjustable frequencies as the tract itself is adjusted. These adjustments cause the output spectrum of emitted sound to vary, enabling the speaker to create different vowel sounds.

10. Dispersion refers to the spreading of sound waves in space as they are emitted by a loudspeaker. It is due to diffraction, which depends of the ratio of the sound wavelength to the loudspeaker diameter. A general rule is that sound will be dispersed signficantly if the wavelength is comparable to or larger than the speaker diameter.

11. Using the expression for the resonances of a box, as utilized in lab, the second lowest frequency will correspond to zero nodes along the 10 meter and 3 meter dimensions, and one node along the 6 meter dimension. So this frequency is (344 m/s) divided by 2*(0.6 m) = 287 Hz.

12. The decibel increase is (10 dB) * log (4/0.2) = 13 dB.

13. From 0 dB to 120 dB corresponds to 12 powers of ten in the intensity, so the sound intensity changes by 10^12, or 1,000,000,000,000 times, over the entire range of human hearing!

14. The main resonance of a speaker depends upon the compliance of the suspension system and the mass of the cone.

15. For each 10 dB increase, loudness doubles. Ninety dB corresponds to 9 doublings, or 2^9 = 512 times louder.