# physics

At a recent rock concert, a dB meter registered 112 dB when placed 1.70 m in front of a loudspeaker on the stage.
(a) What was the power output of the speaker, assuming a hemispherical radiation of the sound and neglecting absorption in the air?

(b) How far away would the intensity level be a somewhat reasonable 85 dB?
I used the equation I = P/(4pi r^2); Rearranging the equation I did: 112/4pi 1.7^2 = 4067.482 W, but this was incorrect. I also converted 112 dB to 11.2 bels, but also wrong. Any suggestions?

(a) Convert 112 dB to the equivalent power per unit area. Then multiply that by the hemisphere area 2 pi R^2, with R = 1.70 m.
(b) Ypur answer weas incorrect because they asked for a distance and you gave them a power number.

Dropping from 112 dB to 85 dB is a 27 dB reduction in power per area. That corresponds to a 10^(27/10) = 501 reduction factor in power per area. Using the inverse square law, that can be achieved with a sqrt(501) = 22.4 increase in distance. That would put the listener 1.70 x 22.4 = 38 meters away

1. 👍 0
2. 👎 0
3. 👁 142

## Similar Questions

1. ### Physics

At a recent rock concert, a dB meter registered 118 dB when placed 1.60 m in front of a loudspeaker on the stage. (a) What was the power output of the speaker, assuming a hemispherical radiation of the sound and neglecting

asked by BILL on April 1, 2011
2. ### English

In which sentence is the underlined verb in the passive voice? a. The rock group is giving the concert just one more time. b. By then the rock group was already giving the concert. c.The rock group will have given the concert by

asked by Samii on November 30, 2015
3. ### math

Set up 2 equations that can be used and solve. Phil reported that the receipt from a recent concert totaled \$916 furthermore he announced that 560 people attended the concert. Students were charged \$1.25 each for admission to the

asked by keyla on November 15, 2012
4. ### Algebra

In a recent year, 16.3% of all registered doctors were female. If there were 47,600 female registered doctors that year, what was the total number of registered doctors? Round your answer to the nearest whole number.

asked by Charlie on March 30, 2014
5. ### Pre-Algebra

The treasurer of the student body at a college reported that the receipts from a recent contact totaled \$916; Furthermore, he announced that 560 people had attended the concert. Students were charged \$1.25 each for admission to

asked by Tyler on February 1, 2014
6. ### Pre-Algebra

In a recent year, 31.8%of all registered doctors were female. If there were 54,700 female registered doctors that year, what was the total number of registered doctors?

asked by Harmony on May 15, 2017
7. ### math

In a recent year, 23.3 % of all registered doctors were female. If there were 46,800 female registered doctors that year, what was the total number of registered doctors?

asked by jaykwon on February 15, 2018
8. ### English

posted by rfvv Thursday, April 5, 2018 at 6:01am 1. The concert is over. 2. The concert is finished. 3. The concert ended. 4. The concert finished. [Are they the same in meaning? Can we use all the sentences? Which ones are

asked by rfvv on April 16, 2018
9. ### Physics

A rock is thrown straight up from a cliff which is 38 meter above ground. After 2 seconds the rock is at 21.3 meter above ground. What was the velocity at first when the rock was thrown. Ignore resistent of the air.

asked by Axel on September 17, 2017
10. ### Math

A recent poll of concert attendees that would pay 200.00 for a "Rain,A Tribute to the Beatles" concert ticket has a margin of error of +3.5%.How many attendees were polled?

asked by John on December 14, 2009

More Similar Questions