Chapter 16: Sound 16-1 Characteristics of Sound 16-3 Intensity of Sound: Decibels 16-4 Sources of Sound: Vibrating Strings and Air Columns

Syllabus Class Meetings: Section 001:MWF 9:30-10:45, SIMS 209 and Section 002 MWF 11:00-12:15, SIMS 209 Office Hours: Tuesday 11:00am-12:00pm, and Wednesday 1:00pm-3:00pm or by appointment. Cell phones, tablets, and computers are not allowed in class. Presence in the labs is required, a missed lab is a 0, unless you are able to make it up or have a solid excuse such as being in the hospital.

Homework problems are due on the dates indicated on the class calendar. Your work is due on time, with the exception of reasonable documented excuses. Late work will be docked 50% of face value and 100% after solutions have been posted. Grading Homework 15% Three in Class exams 10% each Final Exam 30 % Lab 25% The letter grade will be assigned as follows: 100% - 93% = A; 92.9% - 89% = A- ; 88.9% - 86% = B+; 85.9% - 80% = B; 79.9% - 76% = B- 75.9%-73% = C+ ; 72.9% - 67% = C ; 66.9% - 64% = C-; 63.9%- 60% = D; 59.9%- 0% = F

Sound vZINSEY

16-1 Characteristics of Sound: Problem 3 3.(I) (a) Calculate the wavelengths in air at 20°C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. (b) What is the wavelength of a 15-MHz ultrasonic wave?

Problem 8 8.(II) A person, with his ear to the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 0.75 s apart. How far away did the impact occur? See Table 16–1.

Loudness: related to intensity of the sound wave (energy transported by the wave per unit time across unit area) Pitch: related to frequency Audible range: about 20 Hz to 20,000 Hz; upper limit decreases with age Ultrasound: above 20,000 Hz Infrasound : below 20 Hz Sound is a longitudinal wave represented by the equation 16-1 Characteristics of Sound

Copyright © 2009 Pearson Education, Inc Intensity of Sound: Decibels Example 16-3: Sound intensity on the street. At a busy street corner, the sound level is 75 dB. What is the intensity of sound there?

Copyright © 2009 Pearson Education, Inc Intensity of Sound: Decibels Example 16-4: Loudspeaker response. A high-quality loudspeaker is advertised to reproduce, at full volume, frequencies from 30 Hz to 18,000 Hz with uniform sound level ± 3 dB. That is, over this frequency range, the sound level output does not vary by more than 3 dB for a given input level. By what factor does the intensity change for the maximum change of 3 dB in output sound level?

Copyright © 2009 Pearson Education, Inc Intensity of Sound: Decibels Conceptual Example 16-5: Trumpet players. A trumpeter plays at a sound level of 75 dB. Three equally loud trumpet players join in. What is the new sound level?

Problem (I) What are the lowest and highest frequencies that an ear can detect when the sound level is 40 dB? (See Fig. 16–6.)

The intensity of a wave is the energy transported per unit time across a unit area. The human ear can detect sounds with an intensity as low as W/m 2 and as high as 1 W/m 2. Perceived loudness, however, is not proportional to the intensity Intensity of Sound: Decibels

The loudness of a sound is much more closely related to the logarithm of the intensity. Sound level is measured in decibels (dB) and is defined as: I 0 is taken to be the threshold of hearing: 16-3 Intensity of Sound: Decibels The unit of the sound level β is decibel (dB)

An increase in sound level of 3 dB, which is a doubling in intensity, is a very small change in loudness. In open areas, the intensity of sound diminishes with distance: However, in enclosed spaces this is complicated by reflections, and if sound travels through air, the higher frequencies get preferentially absorbed Intensity of Sound: Decibels

The intensity can be written in terms of the maximum pressure variation. With some algebraic manipulation, we find: