# Physics Help sound level intensity

#### smith22

A person standing a certain distance from an airplane with three equally noisy jet engines is feeling a sound level intensity bordering on pain, 120dB. What sound level would this person experience if the captain shut down one engine?

this is what I did:
B-120=10log.33
and ended up with 125 dB as the intensity

What am I doing wrong since I am reducing the factor by 3 and its still not working?

Related Introductory Physics Homework Help News on Phys.org

#### Doc Al

Mentor
I see two problems:

(1) The sound level should be lower with only two engines running: log.33 is negative.

(2) You have the wrong ratio of intensities: What's the ratio of intensities for 3 engines versus 2 engines?

#### geosonel

smith22 said:
A person standing a certain distance from an airplane with three equally noisy jet engines is feeling a sound level intensity bordering on pain, 120dB. What sound level would this person experience if the captain shut down one engine?

this is what I did:
B-120=10log.33
and ended up with 125 dB as the intensity

What am I doing wrong since I am reducing the factor by 3 and its still not working?
let I0 be ref sound intensity level
sound level (db) w/3 engines = 120 db = 10 log10( 3(I/I0) )
= 10 log10(3) + 10 log10( I/I0 )
= 10 log10(2*(3/2)) + 10 log10( I/I0 )
= 10 log10(3/2) + 10 log10(2) + 10 log10( I/I0 )
= 10 log10(3/2) + 10 log10( 2(I/I0) )
= 10 log10(3/2) + (sound level (db) w/2 engines)

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving