Sound Notes edited for website

What is Sound?Sound is a longitudinal wave with all of the properties inherent to that type of wave.

Sound waves transport energy ­ the more energy, the greater the amplitude of the wave.

Sound is usually the result of a mechanical energy that is converted to sound energy.

http://www.physicsclassroom.com/Class/sound/u11l2b.cfm

The speed of sound is 330 m/sSound loudness is a subjective term describing the strength of the ear's perception of a sound. Loudness is not the same as intensity .

The sound intensity must be factored by the ear's sensitivity to the particular frequencies contained in the sound.

Loudness vs. Intensity

The range of intensities which the human ear can detect is large; to measure intensity we use a scale based on multiples of 10 (a logarithmic scale).

This scale for measuring intensity is known as the decibel scale.

In other words, a general "rule of thumb" for loudness is that the power must be increased by about a factor of ten to sound twice as loud.

• Wave velocity:– from 330 m/s (0oC) to 340 m/s (20oC) in air (Mach 1)– 4 times faster in water– 15 times faster in steel

• Audible frequencies (humans): 20 Hz ­ 20,000 Hz• Audible wave lengths: 17 m ­ 1.7 cm in air;

ultrasound much shorter

• Intensity (= amplitude 2)– ranges from 0 decibel, (threshold of hearing) to 120 decibel,

(pain). – Each additional 10 decibel = factor of 10 more intensity(20 decibel = factor 10 in amplitude)

Properties of Sound Waves

http://www.wisc­online.com/objects/ViewObject.aspx?ID=AP14204http://www.physpharm.fmd.uwo.ca/undergrad/medsweb/L7Aud/Aud.swf

While the intensity of a sound is a very objective quantity which can be measured with sensitive instrumentation, the loudness of a sound is more of a subjective response.

Loudness varies with a number of factors, including:

1) Age of the individual(For example, your grandparents most likely do not hear as well as they used to). 2) FrequencyTwo sounds with the same intensity but different frequencies will not be perceived to have the same loudness.

Sound Notes edited for website

• Reflection:– hard surfaces reflect better than soft ones– the reflected wave has the same angle with the surface as the incoming wave– Can be used to measure distance: echo log,

depth / fish finder, orientation for bats and whales, ultrasound imaging, acoustics, reverberation, echo,…

• Refraction:– Sound waves are bent by differences in temperature or by going through different substances with different wave speeds

Reflection and Refraction• Interference: Sound waves can add or subtract ­ increased sound or less– Example: Hooking a stereo speaker up backwards;

noise­canceling headphones

If the frequencies are slightly different, you will get the “beat” effect: hear average frequency fluctuate in loudness as interference goes from constructive to destructive and back.

• Pitch = fundamental frequency of sound– Concert A = 440 Hz, middle C = 262 Hz– 1 Octave = factor 2 in frequency; 1 half tone is

factor 21/12 = 1.0595 (equal tempering) (More specifically, pitch is how we perceive that frequency).

As frequency increases, pitch will increase. Pitch may be affected by background noise and loudness as well.

Sound and Music

•Timbre = relative loudness of various harmonics; the quality of the sound (this is due to the harmonics making the tone).

Standing waves– Interference between incoming and reflected

wave– Resonance at fundamental frequency (where

wavelength is 2x or 4x physical length) and multiples (harmonics)

Examples: Driving in car with windows down, flute, organ, all woodwinds, all brass instruments,…

The Doppler EffectThe Doppler effect occurs when there is relative motion between the wave source and the listener. This means that the wave source and/or the observer are moving in relation to each other.

Example:The siren on a fire truck racing toward the school will have a higher pitch as it approaches the school, then a lower pitch as it leaves. The sound waves will strike your ear more frequently as it approaches, and less as it leaves.

The fundamental frequency is the lowest frequency of vibration for a standing wave. This is what determines the pitch of the sound.

Harmonics are multiples of the fundamental frequency for a particular object. All harmonics are equally spaced out at intervals of the fundamental frequency.

Pipe organs, woodwinds and brass instruments all exhibit this property.

Do string instruments do this?

Using the terms node and antinode, explain your answer.