PhysicsWaves

# EU6D 2015-02-04 Noise and Beats

Created 3 years ago

Duration 0:24:50
74
Mr. Weisenfeld talks about Noise and Beats from Hecht Chapter 11.
Slide Content
Tags: Physics Waves
1. ### Slide 1 - EU 6.D: Interference and superposition lead to standing waves and beats.

• Mr. Weisenfeld
2. ### Slide 2

• Hecht, Section 11.9, pg 395

4. ### Slide 4 - Let’s compare “white noise” and “pink noise”

• On the next two slides you have 2 minute samples of
• White noise
• Pink noise
• Adjust the volume how you like and then take a listen.
• What I want you to think about is which noise seems to have a lot of low frequency content versus high frequency content.
• Also think about which noise you feel like you could listen to for an extended period of time, many people do this for relaxation.
5. ### Slide 5 - White Noise

• Adjust volume as needed, I turned it down.
6. ### Slide 6 - Pink Noise (As Opposed to White Noise)

• Pink and White Noise have different frequency spectra.
• The amount and frequency of the sounds that make up these “noises” are different.
• Adjust volume as needed, I turned it down.

8. ### Slide 8 - Visualizing White Noise

• (a) is gauge pressure, since sound is a compression wave, we are plotting the pressure at a point as the wave passes by in time.
• (b) Breaking down that signal into the frequencies it would take to produce it.
• It is an equal mix of sounds at all audible frequencies.
9. ### Slide 9 - Pink Noise, on the other hand.

• Here is how they differ in spectrum, i.e. the intensity or amount of each sound frequency.
10. ### Slide 10 - Galileo on sound

• Hecht, Section 11.9, pg 395
11. ### Slide 11 - A Siren

• By “tapping on air”, i.e. interrupting a flow of air in a regular way, a siren is created.
• I don’t think police car sirens are like this anymore, but old-fashioned air-raid sirens are exactly like this, only at a bigger scale.
• Click to hear a smaller siren.
• Hecht, Section 11.9, pg 396
12. ### Slide 13 - Can you hear the beats? (Pulsations of sound?)

• Volume is turned low, turn up until you are comfortable.

14. ### Slide 18 - Hands on with Beats.

• In the next slide you get to change the frequencies of two waves.
• A couple of things to try
• One really big, one really small
• Close together, but small
• Close together, but big
• Can you see the beats?
• When do you not see the beats? Why?
15. ### Slide 20

• Hecht, Section 11.9, pg 397, Example 11.11
16. ### Slide 21

• Hecht, Section 11.9, pg 397, Example 11.11
17. ### Slide 22 - A final word, everything makes sound, not everything makes music.

• Hecht, Section 11.9, page 397