Tutorial Week 2

Q1 In a recording room an acoustic wave was measured to have a frequency of 1KHz. What would its wavelength in cm be?

The wavelength is 0.333cm. I worked this out by doing the following calculation :

v = fλ

λ = v  = 333   = 0.333cm

       f     1000

Q2 If a violinist is tuning to concert pitch in the usual manner to a tuning fork what is the likely wavelength of the sound from the violinist if she is playing an A note along with sound from the pitch fork?

Q3 If an acoustic wave is traveling along a work bench has a wavelength of 3.33m what will its frequency be? Why do you suppose that is it easier for this type of wave to be travel through solid materials?

The frequency of the wave is 100Hz. I worked it out by doing the following:

v = fλ

f = v = 333  = 100Hz

      λ    3.33

Q4 Sketch a sine wave accurately of amplitude 10, frequency 20Hz. Your sketch should show two complete cycles of wave. What is the duration of one cycle? What is the relationship between the frequency and the duration of one cycle?

Here is shown two cycles of a sine wave with amplitude 10 and frequency 20Hz. The duration of one cycle is 1/20th of a second as the frequency tells us that 20 cycles will happen in 1 second therefore to find the period of one cycle you use the formula T = 1/f so T = 1/20.

Q5 Research the topic “Standing Waves”. Write a detailed note explaining the term and give an example of this that occurs in real life. (Where possible draw diagrams and describe what represent)

Standing(stationary) waves disturb but do not actually pass through the medium, it remains at a constant position. Stationary waves happen both in the air with sound waves and also in the ocean. If two waves collide because they are travelling towards each other the they cant go anywhere and become stationary.

Q6 What is meant by terms constructive and destructive interference?

Constructive interference is when two waves are happening at the same time but trough meets trough and peak meets peak. The two waves never touch but simply coexist.

Destructive interference is when the same two waves are not moving together and therefore trough meets peak and peak meets trough. The waves touch once a cycle and the resultant wave created by the two is a line.

Q7 What aspect of an acoustic wave determines its loudness?

The amplitude of an acoustic wave determines the loudness.

Q8 Why are decibels used in the measurement of relative loudness of acoustics waves?

Q9 How long does it take a short 1KHz pulse of sound to travel 20m verses a 10Hz pulse?

The time would be the same as the frequency of the sound does not effect the time taken to travel the same distance as speed remains constant at 333m/s.

Q10 Does sound travel under water? If so what effect does the water have?

Yes sound travels under water however it has a slower speed than in air so will take longer.

 

Digital Signal Processing Lecture

The Fundamental is the accumulation of all vibrations that merge together to create what is also known as the Basic tone. Other Vibrations however create a series of harmonic tones. The harmonic is a multiple of the fundamental tone(frequency) i.e. 2 x Fundamental, 3 x Fundamental.

The Amplitude of a sound wave is basically the height of half a wave, i.e. measured from the origin to the peak or trough. The higher/lower(or bigger/smaller) this is determines the level of the sound. For example, a wave with a high amplitude will strike the ear drum harder and therefore the sound is louder.
These measurements are hard to make and therefore sound is actually more often expressed in terms of Sound Level, measured in decibels.

All living creatures have and upper and a lower threshold of hearing which is the quietest or loudest a sound can be but also the frequency a sound can be to hear it. A humans threshold is different from other creature and therefore can hear different things.


Sound intensity = 10log10(Isound/IStandard) DB

The Inverse Square Law implies that the further you are from the source the quiter the sound is. Therefore a sound wave loses intensity over distance.
An echo however is the percieved copying of a sound due to reflection of the sound waves off of objects i.e. a tunnel. Time difference= (d1 + d2)/v
r(t) = s(t-d0/v)+alpha s(t-time dif)

Room reverb is similar to an echo with the exeption that it involves multiple reflections of the sound wave and the can all reflect back to the same point.