Suppressor reduces noise propagated through ducts. It provides high attenuation in given duct length. Entire device forms acoustic trap which utilizes reflective elements on ends to direct sound energy into sound-dissipating element in center. Device achieves large suppression by utilizing interactive effects of different suppression devices

Zorumski, W. E.

English

NASA Technical Reports Server

Jacivary 1975	 B74-10261 
NASA TECH BRIEF 
Langley Research Center 
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. 
Noise Suppressor 
A noise suppressor developed at Langley Research 
Center is a device which reduces noise propagated 
through ducts. It provides high attenuation in a given 
duct length, significantly higher than do prior devices, 
and also possesses broadband noise suppression 
ability. This device could.be used for the suppression 
of noise from modern turbofan aircraft engines, in 
noise attenuation in airflow ducts, and in mufflers for 
internal combustion engines. 
The noise suppressor consists of multiple bands of 
acoustically absorbent liners on the , inside wall of the 
duct. These bands are placed in;adjacent positions 
along the duct axis and are made from single or 
multiple layers of porous sheet material separated by 
a spacing medium such as honeycomb. The first band 
is a sound-reflecting element which reflects sound 
back toward the source and also reflects sound which 
is directed toward the source from another point in 
the duct. The second element is a band which dis-
sipates sound energy. The physical properties 'of the 
second band are adjusted to minimize the trans-
mission of sound from the first and third element 
bands. The third element is a band where sound 
which has passed through the first two bands is 
reflected back to the second band to be dissipated. 
The entire device forms an acoustic trap which 
utilizes the reflective elements on the ends to direct 
the sound energy into the sound-dissipating element 
in the center. The noise suppressor may also be made 
of groups of reflective and dissipative elements placed 
in the duct as splitters, rather than as bands around 
the duct perimeter, to provide sound suppression. The 
device achieves large suppression by utilizing the 
interactive effects of these different suppression 
devices.
Notes: 
1. A set of acoustic equations in matrix form has 
been derived for the sound field in and radiated 
from multisection ducts and may be obtained 
from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.75 
(or microfiche $2.25) 
Reference: NASA TR R-419 (N74-23274), 
Acoustic Theory of Axisymmetric Multi-
sectioned Ducts 
2. Technical questions may be directed to: 
Technology Utilization Officer	
-) 
Langley Research Center 
Mail Stop 139-A 
Hampton, Virginia 23665 
Reference: B74-10261 
Patent status: 
This invention has been patented by NASA (U.S. 
Patent No. 3,830,335). Inquiries concerning nonex-
clusive or exclusive license for its commercial develop-
ment should be addressed to: 
Patent Counsel 
Langley Research Center 
Mail Stop 313 
Hampton, Virginia 23665 
Source: William E. Zorumski

Langley Research Center

(LAR-11141) 
Category: 03 (Physical Sciences) 
This document was prepared under the sponsorship of the National
	
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Noise suppressor

A tuned noise suppressor is described consisting of annular acoustically porous elements for incorporation into the inlet and exhaust ducts of turbofan engines. The apparatus uses sound wave absorption, reflection, and incompatibility for achieving high noise reduction in the short distance. In addition, it has a duct of uniform inner diameter which does not block the duct flow

Noise suppressor

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