Intensity Intensity Level and Intensity Spectrum Level The

Intensity, Intensity Level, and Intensity Spectrum Level The spectrum level is the intensity level of the sound wave within a 1 Hz band.

A Sonar System hydrophone band pass filter #1 band pass filter #2 acoustic pressure band pass filter #3 Output

System Output band level band #1 band #2 band #3 frequency • Fourier Transform of the Time Domain Signal • Frequency Analyzer

Example

Fourier Coefficients n fn (Hz) Pmax (Pa) P 2 rms (Pa) I (W/m 2) L (d. B) 0 0 1 0. 5 3. 3 x 10 -7 117 1 110 5 12. 5 8. 3 x 10 -6 131 2 220 3 3 330 4 5 Pressure (Pa) 4 3 2 1 110 220 330 440 f (Hz)

Band Level ISLave f 1 f 2 frequency The Band Level is the intensity level over a band other than 1 Hz.

Example Intensity Spectrum Level (d. B) 60 50 30 100 282 355 frequency (Hz) • Using the plot of ISL as a function of frequency shown, calculate – the band level of every band – the total band level in a band from 150 Hz to 300 Hz

Types of Spectrums tonals Spectrum Level broadband noise frequency

Example What is the total BL?

Common Bandwidths • Constant Bandwidth Df = constant • Proportional Bandwidth – Octave Bandwidth Spectrum Level (d. B) 60 50 30 • f 2 = 2 1 f 1 – Half Octave Bandwidth • f 2 = 21/2 f 1 • Center Frequency 100 fc=141 200 282 355 frequency (Hz)

Preferred Octave Bands

Why do we care? Source Level (SL) and Noise Level (NL) are both examples of Band Levels (BL) where the frequency band(s) are defined by the frequencies of our Sonar System