Question

Megadeth decides they need to really jazz up their next show by driving a truck with them and their equipment directly toward the audience at 88 mi h−1 . They want to make sure the audience hears the music as normal. The D string on a 6-string guitar is normally tuned to 146.83 Hz. You can assume a speed of sound of 345 m s−1 . (a) What frequency does Dave Mustane need to tune his D string to so that the audience hears the music at the right pitch. (Assume they are driving toward the audience for every song.) (b) How much does the tension in the D string need to differ from the normal tension that it would have? Is it less or more than normal? (c) The band decides that driving toward the audience is too dangerous, and instead will put the audience on flatbed trucks and have the trucks drive by the band (again at 88 mi h−1 ). What frequency and tension should Mustane’s D string be tuned to? (Assume the audience is driving toward them for every song.) (d) The band gives up on their truck dreams and decides on a normal show. The night of the show, however, the are 40 mi h−1 winds blowing from behind the audience toward the band. What frequency does the audience hear from Mustane’s guitar?

Answer 1

Doppler Effect for Music

doppler effect example = if someone presses down on a horn & the same horn sounds different when the car is coming towards you, then close then going away

(a) The frequency that Dave Mustane needs to tune his D string to so that the audience hears the music at the right pitch is **147.5 Hz**¹.

(b) The tension in the D string needs to differ from the normal tension that it would have by **0.2%**. It is less than normal¹.

(c) If the audience is driving toward them for every song, then Mustane's D string should be tuned to **147.5 Hz** and the tension should be **0.2% less than normal**¹.

(d) If there are 40 mi/h winds blowing from behind the audience toward the band, then the frequency that the audience hears from Mustane's guitar is **146.83 Hz**¹.

Doppler Effect Formula

frequency of the sound wave that an observer hears

EQUALS

frequency of the sound wave at the source

MULTIPLIED BY

speed of sound

DIVIDED BY THE SUM OF

(speed of sound

PLUS/MINUS

speed of the source relative to the observer)

example

f' = 146.83 * (345 + 17.9)/(345 - 17.9) = 151.57 Hz