Subjects covered in four reports are described including: (1) mathematical techniques for combining decibel levels of octaves or constant bandwidth: (2) techniques for determining equation for power spectral density function; (3) computer program to analyze acoustical test data; and (4) computer simulation of horn responses utilizing hyperbolic horn theory

Hayes, C. D.

Lamers, M. D.

Shipley, J. W.

Slusser, R. A.

English

NASA Technical Reports Server

July 1972	 B72-10341 
NASA TECH BRIEF 
NASA Pasadena Office
	
-9 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Acoustic Spectral Analysis and Testing Techniques 
Four reports have been published (see references) 
that outline some recent developments in acoustic spec-
tral analysis. The subjects covered are described below. 
The Octave and One-Third Octave Acoustic Noise 
Spectrum Analysis discusses mathematical techniques 
for combining decibel levels of octaves or constant 
bandwidths with an overall spectrum level; determining 
the octave levels in a second octave system when the 
levels in the first octave are known; and determining the 
one-third octave levels when the octave levels and the 
decibels-per-octave slope are known. 
In Power Spectral Density Analysis, generalized 
techniques are developed for determining the equation 
for a power spectral density function. Moreover, an 
equation is developed that determines the root mean 
square of a power spectral density function. 
The report on A Digital Technique For Determining 
113 - Octave Sound-Pressure Levels With a More Uniform 
Confidence Level describes a- computer program that 
analyzes acoustical test data. The program uses a fast 
Fourier subroutine to calculate the discrete Fourier co-
efficients that transform the time-domain data to fre-
quency-domain data. Multiple Fourier transforms are 
used to convert the narrow-band frequency data to 1/3-
octave data. 
In the Acoustic Spectrum Shaping Utilizing Finite 
Hyperbolic Horn Theory, sound spectra of high-intensity 
sound are shaped for single horns and multiple-horn arrays. 
This technique utilizes computer simulation of horn 
responses by use of the hyperbolic horn theory. 
References: 
C. D. Hayes and M. D. Lamers, Technical Report 
32-1052, Octave and One-Third Octave Acoustic Noise 
Spectrum Analysis.
C. D. Hayes, Technical Report 32-928, Revision 1, 
Power Spectral Density Analysis. 
J. W. Shipley and R. A. Slusser, Technical Memoran-
dum 33-422, A Digital Technique for Determining 
1/3-Octave Sound-Pressure Levels With a More Uni-
form Confidence Level. 
C. D. Hayes, Technical Report 32 . 1141, Acoustic 
Spectrum Shaping Utilizing Finite Hyperbolic Horn 
Theory. 
Note: 
Requests for this documentation and other informa
-
tion may be addressed to: 
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91102 
Reference: B72-10341 
Patent status: 
No patent action is contemplated by NASA. 
Source: C. D. Hayes, M. D. Lamers,

J. W. Shipley, and

R. A. Slusser of

Jet Propulsion Laboratory of

California Institute of Technology

under contract to

NASA Pasadena Office

(NPO-1 1554) 
Category 03 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
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Acoustic spectral analysis and testing techniques

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