Few sound questions

[HarveyD]

Hey guys, just have a few questions on sound

1) How would changing the pitch, affect a sound wave? (like when sketching it)
If a sound being produced in an audio frequency oscillator (or any other device) has the same pitch as a singer, then the waves produced would be exactly the same right?

2) Why does the intensity of a sound decrease markedly with distance from a source?
Is it because the sound wave loses energy as it travels through (and reacts with the air particles)? Or do I need to explain it a little clearer?

3) When two sound waves are cancelled, where does the energy go?
Just dissipates into air?
Is it the same reason for what happens to the energy when reflected waves cancel at the nodes?

4) How do sounding boards increase the intensity of sound?
Just through resonance? i.e. resonance increases the oscillations and the energy within the system etc
Or does it involve restricting the destructive interference?

Thanks! Any help is appreciated.

[xZero]

1) T=1/f, if we increase frequency the period is gonna decrease so the waves would be closer to each other.

2) Its coz the energy is distributed over a larger area as the distance increases so the intensity decreases as well

3) the energy transforms into heat energy

[HarveyD]

so we basically take pitch and frequency as the same thing?

[Aurelian]

so we basically take pitch and frequency as the same thing?

Frequency refers to an actual physical characteristic of a wave which exists independent of human perception. Pitch, on the other hand, is a subjective quality relating to how we *hear* sounds (even if pitch is principally determined by a wave's frequency) and hence does not exist independent of human perception.

[HarveyD]

ah k, thansk

how would I draw standing waves? (like on the second question attached)

[Thelimz]

4. When a baffle is placed around a speaker, the waves produced from the back of the speaker can no longer interfere with the waves produced from the front. For example. During a compression at the front there is a rarefaction at the back. This back wave then diffracts and destructively interferes with the wave from the front because it is out of phase. This situation can be reversed with a rarefaction from the front and compression at back, also resulting in destructive interference. Thus, as there is no longer any destructive interference (in an ideal baffle) then intensity of sound increases.

Note. Addition of ports can make use of the back waves which are out of phase. Here they reflect from the back wall of the box and then, if the dimensions of the box are correct, can constructively interfere with the waves from the front (in phase), increasing intensity of sound. The port is a hole at the front of the box.

[tchung]

4) The sounding board located in an instrument such as a guitar increases the sound intensity through resonance. When the guitar string vibrates, the forced frequency causes the sounding board to resonate also as it has the same natural frequency. However, as a sounding board has a larger surface area than a guitar string, it is able to vibrate more air molecules and creating a bigger air pressure variation. As a result this creates a louder noise.

1) The wave produced by an audio frequency oscillator would not be the same as 1 produced by a  singer. The wave produced by the device would be a pure sound wave with a distinct frequency ( a sinusoidal wave) however the sound wave produced by the singer would not be a pure one, it will be a superposition of sound waves with a different timbre despite possibly having the same frequency characteristics.