Unit 7: Vibrations, Waves & Sound Chapter 20: Sound 20.1 Properties of Sound 20.2 Sound Waves 20.3 Sound, Perception, and Music

DO NOW QUESTION What are four properties of sound waves? (Hint: What are ways to describe waves?) *Answer this question on your notes. ANSWER: Frequency, Amplitude, Wavelength, and Speed

Students will be able to (SWBAT) apply wave properties to sound. Objective Students will be able to (SWBAT) apply wave properties to sound.

The frequency of sound The pitch of a sound is how you hear and interpret its frequency. A low-frequency sound has a low pitch. A high-frequency sound has a high pitch. Each person is saying “Hello”.

The loudness of sound The loudness of a sound is measured in decibels (dB). Remember --- Pitch has to do with the wave’s frequency. Loudness has to do with the wave’s amplitude.

The frequency of sound Almost all the sounds you hear contain many frequencies at the same time. Humans can generally hear frequencies between 20 Hz and 20,000 Hz, similar to voice.

The loudness of sound Most sounds fall between 0 and 100 on the decibel scale, making it a very convenient number to understand and use.

What is the maximum loudness? Flips

The loudness of sound Most sounds fall between 0 and 100 on the decibel scale, making it a very convenient number to understand and use.

Equal Loudness Curve Sounds near 2,000 Hz seem louder than sounds of other frequencies, even at the same decibel level. According to this curve, a 25 dB sound at 1,000 Hz sounds just as loud as an 40 dB sound at 100 Hz.

The speed of sound in normal air is 343 meters per second (660 mi/hr).

The speed of sound Objects that move faster than sound are called supersonic. If you were on the ground watching a supersonic plane fly toward you, there would be silence. The sound would be behind the plane, racing to catch up.

The speed of sound A supersonic jet “squishes” the sound waves so that a cone-shaped shock wave forms where the waves “pile up” ahead of the plane. In front of the shock wave there is total silence. Behind the shock wave, there is a sonic boom.

The Doppler effect When the object is moving, the frequency (or pitch) will not be the same to all listeners. The shift in frequency caused by motion is called the Doppler effect. You hear the Doppler effect when you hear a police or fire siren coming toward you, then going away from you.

If the object is moving toward you, the frequency seems higher. If the object is moving away from you, the frequency seems lower.

Recording sound Most of the music you listen to has been recorded in stereo. The slight differences in how sound reaches your ears lets you know where sound is coming from.

Microphone To record a sound you must store the pattern of vibrations in a way that can be replayed and be true to the original sound. A microphone transforms a sound wave into an electrical signal with the same pattern of vibration.

Digital Conversion An “analog to digital converter” converts the electrical signal to digital values between 0 and 65,536.

CD One second of compact-disc-quality (CD) sound is a list of 44,100 numbers which represents the amplitudes converted sounds.

CD – continued To play the sound back, the string of numbers is read by a laser and converted into electrical signals again by a second circuit which reverses the process of the previous circuit.

Stereo Sound Stereo has 2 recording - one for the right speaker and other from left Stereo seems live because it has slightly different phases for each ear.

Review Question What property of a wave does changing the volume affect? _______________ What would you change in order to increase the pitch of a sound wave? ____________ amplitude frequency

Unit 7: Vibrations, Waves & Sound Chapter 20: Sound 20.1 Properties of Sound 20.2 Sound Waves 20.3 Sound, Perception, and Music

What is a sound wave? Sound waves are pressure waves with alternating high and low pressure regions. When they are pushed by the vibrations, it creates a layer of higher pressure which results in a traveling vibration of pressure.

Pressure and molecules The speed of sound increases because collisions between atoms increase. Therefore, if the pressure goes down, the speed of sound decreases.

The wavelength of sound Wavelength is also important to sound. Musical instruments use the wavelength of a sound to create different frequencies.

Sound wave interactions (Label) Like other waves, sound waves can be reflected by hard surfaces (echo) and refracted as they pass from one material to another. (listening near water) Diffraction causes sound waves to spread out through small openings. (Someone talking around a corner, such as near House 6 office) Carpet and soft materials can absorb sound waves.

Ultrasound is high-frequency sound, often 100,000 Hz or more. We cannot hear ultrasound, but it passes through the human body easily. Medical ultrasound instruments use ultrasound waves to create images of the human body’s interior for diagnostic purposes. Ultrasound The ultrasound image above is a heart.

Standing waves in pipes A panpipe makes music as sound resonates in tubes of different lengths. The natural frequency of a pipe is proportional to its length.

Standing waves in pipes Because frequency and wavelength are inversely related, longer pipes have lower natural frequencies because they resonate at longer wavelengths.

Standing waves in pipes The open end of a pipe is an open boundary to a standing wave and makes an antinode. The pipe resonates to a certain frequency when its length is one-fourth the wavelength of that frequency.

20.1 Investigation: Sound and Hearing Key Question: What is sound and how do we hear it? In this investigation you will… Identify the range of frequencies humans can hear. Describe the how perception influences the sound humans hear. Make and analyze a histogram of class data.

20.2 Investigation: Properties of Sound Waves Key Question: Does sound behave like other waves? In this lab, you will… Listen to beats and explain how the presence of beats is evidence that sound is a wave. Create interference of sound waves and explain how the interference is evidence for the wave nature of sound.

Key 20.3 - When two waves have close but not identical frequencies, you hear beats – an example of the interference of sound waves. The sound alternates between louder and softer because the waves drift back and forth between being sometimes in phase and sometimes out of phase. Look at the picture above. When the waves are in phase, the sound gets louder. When the waves are out of phase the sound gets quieter.

Key 20.3 - HEARING 1. First, the perception of hearing starts at the eardrum, which vibrates. 2. Second, three small bones transfer vibrations to the cochlea. 3. Third, the vibrations make waves inside the cochlea, which vibrates nerves in your ear. Listening to loud sounds for a long time causes the hairs to weaken and break in your ears resulting in permanent hearing damage. People who are deaf or extremely hard of hearing may be able to have a cochlear implant to send information to the brain using the implant instead of the hairs in the ear.

Key 20.3 - MUSIC Harmony is the study of how sounds work together to create desired effects. Rhythm is the regular time pattern in a sound. In the musical scale, notes are each a different frequency.