U.S. patent number 3,692,959 [Application Number 05/084,823] was granted by the patent office on 1972-09-19 for digital hearing aid gain analyzer.
This patent grant is currently assigned to Electone, Inc.. Invention is credited to Paul F. Lamp.
United States Patent |
3,692,959 |
Lamp |
September 19, 1972 |
DIGITAL HEARING AID GAIN ANALYZER
Abstract
A digital display hearing aid gain analyzer is provided for
measuring the gain of hearing aids over a predetermined frequency
range. A sine wave oscillator generates a predetermined sine wave
frequency in an anechoic chamber. The hearing aid to be tested is
then connected in the chamber to a microphone pickup housed in a 2
cubic centimeter coupler and picks up and amplifies the sine wave
signal in the chamber which is then converted from a linear sine
wave signal to a logarithmic signal to a digital type signal
indicative of the gain of the hearing aid which is then displayed
on Nixie tubes.
Inventors: |
Lamp; Paul F. (Casselberry,
FL) |
Assignee: |
Electone, Inc. (Orange County,
FL)
|
Family
ID: |
22187433 |
Appl.
No.: |
05/084,823 |
Filed: |
October 28, 1970 |
Current U.S.
Class: |
381/60 |
Current CPC
Class: |
H04R
25/30 (20130101) |
Current International
Class: |
H04R
29/00 (20060101); H04r 029/00 () |
Field of
Search: |
;179/175.1A,175.1R,17R,1N,1MN ;181/.5AP |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Claffy; Kathleen H.
Assistant Examiner: Olms; Douglas W.
Claims
I claim:
1. A gain analyzer apparatus for measuring the gain of audio
amplifying devices comprising in combination:
a. chamber means;
b. signal generating means for generating predetermined audio
frequencies;
c. transducer means coupled to said signal generating means and
located in said chamber means for producing said audio frequencies
in said chamber means;
d. microphone means located in said chamber means and having means
for acoustically coupling the output of an audio amplifying device
thereto, whereby said audio amplifying device is adapted to
amplifying said audio frequencies in said chamber means and apply
said amplified audio frequencies to said microphone means;
e. analog to digital conversion means coupled to said microphone
means for generating digital signals from the output from said
microphone means, said digital signals being indicative of the gain
of the amplifying device being analyzed; and
f. counting means coupled to said analog to digital conversion
means for counting digital signals received from said analog to
digital conversion means.
2. The apparatus according to claim 1 in which said chamber means
is an anechoic chamber.
3. The apparatus according to claim 1 in which said counting means
includes Nixie display tubes for displaying the counted digital
signals as the gain of said amplifying device at a predetermined
input frequency.
4. The apparatus according to claim 3 in which said transducer
means is a speaker.
5. The apparatus according to claim 4 in which said microphone
means includes a microphone in a 2 cubic centimeter coupler for
coupling the amplifying device to said microphone.
6. The apparatus according to claim 5, in which said microphone is
located in a coupler having a simulated human ear cavity.
7. The apparatus according to claim 6 in which said signal
generating means is a sine wave oscillator.
8. The apparatus according to claim 7 in which said amplifying
devices are hearing aids having microphones amplifiers and
receivers with said receivers coupled to said microphone means for
transmitting sound picked up and amplified by said hearing
rectifying
9. The apparatus according to claim 1 in which said analog to
digital conversion means includes a rectifying means for rectifying
said signals from said microphone means and a logarithmic amplifier
for converting linear signals from said rectifying means to
logarithmic signals whereby the output of said analog to digital
conversion means will be in decibels.
Description
BACKGROUND OF THE INVENTION
The present invention relates to gain analyzers and especially to
gain analyzers for analyzing the gain of hearing aids displaying
the gain in digital form.
In the past it has been common to provide various types of gain
analyzers for different types of amplifiers. This has been
especially true in audio amplifiers in which the gain is measured
as the ratio of the output voltage to the input voltage. These
circuits generally relate to the input and output voltages, and are
measured by isolating the circuit from the remaining circuit and
providing means for measuring the input and output voltages and
comparing these voltages. However, these types of gain analyzers
have not been satisfactory for hearing aid testing in that they
require that the hearing aid be dismantled and a predetermined
voltage applied to the amplifier section and measured at the
output, which voltage must be measured across various ranges of
frequencies. The hearing aid microphone and receiver of the hearing
aid must be tested separately.
Accordingly, it is one object of the present invention to provide a
gain analyzer for hearing aids in which the hearing aid can be
easily attached without disassemble and the gain rapidly measured
and displayed in digital form across a range of stepped frequencies
to determine how well the hearing aid is operating and whether it
requires repair or replacement.
SUMMARY OF THE INVENTION
The present invention relates to a gain analyzer for hearing aids,
or the like, having a digital display. A sine wave generator or
oscillator is provided which can generate a sine wave over a wide
range of frequencies in predetermined steps which waves are
converted to sound by a transducer located in an anechoic chamber.
The hearing aid to be tested is placed in a chamber with its
receiver end connected to a microphone pickup in a 2 cubic
centimeter coupler which coupler simulates the cavity of a human
ear and isolates the microphone from the chamber. With the hearing
aid turned on the microphone will pick up signals generated by a
sine wave oscillator. Analog-to-digital conversion circuitry
converts the signals from the hearing aid to digital signals
indicative of the gain of the hearing aid. The digital signals are
counted and displayed on Nixie tubes in digital form.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of this invention will be
apparent from a study of the written description and the drawings,
in which
FIG. 1 is a perspective of a gain analyzer illustrating the inputs
and digital displays; and
FIG. 2 is a block diagram of one embodiment of the electrical
components of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, a gain analyzer is illustrated in a casing
11 and having a control panel 12 with an on-off switch 13 and a
light 14 to indicate when the apparatus is in an operative
position. Push-switches 15 allow the selection of any one of a
plurality of frequencies, in this case starting with 250 through
4,000, having steps of 500, 1,000, 1,500, 2,000 and 3,000. The
control panel also has a digital display output 16 which displays
the gain of an amplifier in decibels in digital form for easy
reading and has a reset switch 17 and a count switch 18. A liftable
top 20 allows a hearing aid to be inserted inside an anechoic
chamber for testing.
Referring now to FIG. 2 each of the switches 15 controls the sine
wave oscillator 21 to generate a predetermined sine wave frequency
which is applied to a calibration 22. The calibration board
consists of a series of parallel connected adjustable resistors or
rheostats each in series with a switch so that each one can be
switched and adjusted to assure the correct output level for that
frequency. THe signal is next applied to a speaker amplifier 23
where the signal is amplified which amplifier is coupled to a
speaker 24 through a coupling capacitor 25. Speaker transducer 24
is located in an anechoic chamber 26 and reproduces the sine wave
at a predetermined frequency and gain in the chamber 26. The
chamber 16 may have a hearing aid 27 placed therein with its
receiving tube 28 connected to a microphone or similar transducer
30. Thus with the hearing aid turned to an on position, the sine
wave oscillator operated at a predetermined frequency, the hearing
aid will pick up the sound generated in the chamber 26, amplify it,
and produce the amplified sound in the sound tube 28 which is
picked up by the microphone 30 housed inside a commercially
available 2 cubic centimeter coupler which simulates the human ear
and also isolates the microphone 30 from the chamber 26. Microphone
30 impinges the signal upon a microphone amplifier 31 which
amplifies the signal and couples it through a capacitor 32 ro a
precision AC rectifier 33. The AC rectifier 33 converts the
alternating current signal to direct current which direct current
may be intermittent in nature. The AC rectifier 33 applies the
signal to a DC logarithmic amplifier 34, which amplifier provides
an amplified output which is a logarithmic function for conversion
of linear-to-log, hence decibels, of the input, which signal is
then applied to an offset amplifier 35 and then to a wide band
voltage controlled oscillator 36. The voltage controlled oscillator
is one in which the oscillator frequency varies in proportion to
the controlled voltage being applied to the oscillator. These
signals are then applied to a Schmitt trigger 37 which gives fixed
output levels for predetermined input levels. The output of the
Schmitt trigger is applied to the first decade counter 38 which
provides one pulse output for each pulse applied to the input
decade counter. The output of the decade counter is applied to
inverter 40 into a second decade counter 41. Inverter 40 inverts
the signal from a decade counter for the decoder driver 42 which
drives a units Nixie tube 43 for displaying the units portion of
the output in decibels. Second decade counter 41 receives only one
input pulse for every 10 input pulses to decade counter 38 and
therefore counts in tens. The output from the decade counter 41 is
applied to a second inverter 44 for inverting the signal and
applying to the decoder driver 45 for providing the output for the
display Nixie tubes 46 which is a tens unit. A reset switch 27
discharges the decade counter for resetting the display tubes for
the next frequency test. A counting switch 48 is connected to a
one-shot or monostable multivibrator 50 which is activated by the
count switch 48 and will actuate the monostable multivibrator 50
for gating counting signals to the decade counter 41. The
monostable or one-shot multivibrator 50 has only one condition of
steady state equilibrium in which the circuit can remain for an
indefinite period of time and there is one condition of momentary
equilibrium in which the circuit remains on for one millisecond
period of time. Each time the triggering pulse from the count
switch 48 is applied the circuit first switches to the momentary
equilibrium condition and then after a finite period of time
reverses to the original condition and remains in that condition
until another pulse is applied. Thus, by pushing the count switch
48 a gate is opened for 1 millisecond by the monostable to allow
counting of pulses from the voltage controlled oscillator to the
decade counter. Although the voltage controlled oscillator runs at
a 5 digit frequency, the 1 millisecond gate allows only the first
two digits to be counted, hence increasing the count accuracy
1,000:1.
Thus it should be clear at this point that a digital hearing aid
gain analyzer has been provided which will accept a head worn type
hearing aid and measure its gain displaying it in decibels by
virtue of Nixie display tubes. The power supply for the electronic
circuits is not illustrated since it is of course assumed that
power supply will be required which may include simple half wave
and full wave bridge rectifiers to provide the desired voltages.
The analog circuitry may comprise the sine wave oscillator 15, a
voltage control oscillator 36, a microphone amplifier 31, a
precision rectifier 33 and direct current logarithmic amplifier 34
and an offset amplifier 35. Sine oscillator 15 is a Wien bridge
type which produces a pure sine wave to drive a speaker 24 with
pure tone. This tone in turn is sensed by the hearing aid 27 to be
measured; the gain of the hearing aid is in turn sensed through a
microphone 30 and amplified by the microphone amplifier 31. This
amplified signal is rectified by the precision rectifier circuit
33. The output of this rectifier 33, which is a varying minus DC
voltage, drives a DC logarithmic amplifier 34 converting a linear
voltage into a logarithmic one, hence converting it to decibels. DC
log amplifier 34 drives the offset amplifier 35 which in turn
supplies the voltage controlled oscillator with a voltage
comparable to the gain of the hearing aid 27. The voltage
controlled oscillator 36 is a wide-band complimentary type
flip-flop driven by a current source. Its frequency will vary
depending upon the gain of the hearing aid. It is this frequency
that is fed to the digital counter which in turn displays it as
decibel gain. The digital displaying counter circuitry enhances a
units and tens counter of the binary type. Units to be counted are
produced by a voltage control oscillator 37, shaped through a
Schmitt trigger 37 and fed into the unit counter 38. The counting
time is determined by one-shot multi-vibrator 30 which may be set
to a 1 millisecond time period. Since this is a manual type
counter, the reset switch 48 must be operated before the count
switch will allow the counter to count. The individual circuits
used in the present invention are of conventional design and other
circuits of the same general type can be utilized as desired.
Accordingly this invention is not to be construed as limited to the
particular forms disclosed herein since these are to be regarded as
illustrative rather than restrictive.
* * * * *