# A sound level problem.

#### keydetpiper

In my high school physics class the other day the teacher botched an example problem involving sound level (decibels).

1. Homework Statement
A single sound source produces 105 dB at a distance of 5.0 m. How far away must the observer be to not hear this sound at all?

2. Homework Equations

3. The Attempt at a Solution
The reference intensity I0 is the lowest intensity a human can hear, 1 x 10-12 W/m2, so when the source is far enough away its intensity will be equal to this. The intensity of a sound falls off as 1/d2, so after substituting the information in the problem the equation above can be rewritten as follows:

In this equation, d0 represents the distance to the sound source that produces the reference intensity and d is the distance to the original source, 5.0 m for this problem.
When this is solved for d0, the result is 177828d, or about 890 km. This can't be right! What happened? Thanks in advance for your help.

Related Introductory Physics Homework Help News on Phys.org

"A sound level problem."

### 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