Coupling device accurately calibrates microphones at high sound pressure intensities. The system which uses a liquid as the coupling medium can operate in an automatic mode by using a standard microphone as a control sensor. Feedback from the standard microphone controls the calibration signal level

Gillen, A.

English

NASA Technical Reports Server

September 1967	 Brief 67-10336 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space p1ogram, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Device Enables Calibration of Microphones at High Sound Pressure Levels 
The problem: 
To devise a means of accurately calibrating micro-
phones at high sound pressure intensities (up to 
190 dB; where dB = 20 times the common logarithm 
of the sound pressure intensity, referred to a pressure 
of 00002 dyne per sq cm). Air is not a suitable 
coupling medium for the calibration because of the 
inherent nonlinearity at these high sound intensities. 
The solution: 
A coupling device employing a liquid instead of air 
as the coupling medium. With this device, micro-
phones can be calibrated at sound pressure intensities 
ranging from 110 dB to 175 dB in the frequency range 
of 16 Hz to 10 kHz. 
How it's done: 
The device incorporates a small liquid-filled cavity 
driven at one end by means of a piston consisting of a 
cylindrical stack of electrically excited piezoelectric 
disks having an effective diameter of 1.5 inches. The 
cavity, in the shape of a rectangular prism at one end 
and a conical frustum at the other, has an overall vol-
ume of approximately 1.2 cubic inches. An ac voltage 
applied across the faces of each disk (all of which are 
connected in parallel) sets the composite piston into 
mechanical vibration over a displacement amplitude 
required to produce the desired sound level. Motion 
of the sealed piston against a diaphragm tends to
compress the liquid in the cavity, thereby producing 
relatively high calibration pressures for small displace-
ments. These pressures vary proportionally to the 
displacement of the piston. Needle valves in the device 
isolate the flow of liquid to and from the cavity and 
also to and from a pressure gage, which is used to 
set the sound level. The needle valves have a built-in 
safety adjustment which protects the microphones 
from excessive pressures. 
Notes: 
1. The system can operate in an automatic mode by 
using a standard microphone as a control sensor. 
Feedback from the standard microphone controls 
the calibration signal level. 
2. Inquiries concerning this innovation may be di-
rected to
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B67-10336 
Patent status: 
No patent action is contemplated by NASA. 
Source: Albert Gillen 
of Gulton Industries, Inc. 
under contract to 
Marshall Space Flight Center 
(M FS- l 1980) 
Category 01 
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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Device enables calibration of microphones at high sound pressure levels

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