Acoustics Answers

If a sound pressure is measured at 2Nm-2, calculate this in dBSPL.

Two sound waves are travelling through a room filled with Helium gas. Wave A has a wavelength of 1.2m. Wave B has a wavelength of 3.6m. Describe the velocity and frequency of wave A compared to wave B.

A room being used for recording seems to have a very obvious resonance at a particular frequency. On further investigation there does not appear to be any simple relationship between the frequency of the resonance and the physical dimensions between opposite parallel surfaces. Explain why this might be the case (you may need to use a simple diagram to illustrate your answer).

Briefly describe a simple experiment that you could conduct with a minimum of equipment in order to determine the reverberation time of a particular concert hall.

Describe the musical intervals between the first four harmonics of a low C note (128Hz). Express the relationship of these harmonics to each other as simple fractions or ratios.

During a simple experiment in a physics class a student holds a vibrating tuning fork at the open end of various large tubes that are sealed at the bottom. He discovers that one particular tube very strongly reinforces the sound of the tuning fork. If this tube is 26 cm long calculate the most likely frequency of the tuning fork.

An amplifier produces a signal gain such that an input of 1.5 volts rms produces an output of 6.0 volts rms. Express the gain of this amplifier in decibels. (Calculate to the nearest decibel).

An acoustic screen 90cm square stands upright on the floor in a recording booth. The screen is being used to try and reduce the level of sounds reaching a microphone at the opposite end of the booth. Explain in general terms why the screen is very effective at reducing the level of a shaker played behind the screen, but has little effect on the level of a bass guitar amplifier that is placed on the floor behind the screen.

An acoustic screen 90cm square stands upright on the floor in a recording booth. The screen is being used to try and reduce the level of sounds reaching a microphone at the opposite end of the booth. Explain in general terms why the screen is very effective at reducing the level of a shaker played behind the screen, but has little effect on the level of a bass guitar amplifier that is placed on the floor behind the screen.

Calculate the length of an open–ended tube that would produce a fundamental frequency of 491Hz.