Noise cancelling acoustical improvement to a communications device

A cellular telephone for reducing background noise comprising a housing having a receiver portion and a speaker portion; the receiver portion having a voice port and a noise port; a microphone isolator located within the receiver portion; at least one noise canceling microphone having a front end and a back end enclosed by the microphone isolator; an windscreen placed in front of the microphone and internally behind the voice port; and an acoustical port to permit a pressure gradient noise porting placed at the back end of the microphone and internally behind the noise port.

FIELD OF THE INVENTION 
This invention relates to a noise canceling wireless, e.g., cellular 
telephones and, more particularly, to a pressure gradient microphone 
located within a microphone isolator of a cellular phone for canceling or 
reducing background acoustic noise so that speech intelligibility is 
enhanced. 
DESCRIPTION OF THE PRIOR ART 
As is to be appreciated, in numerous situations, the presence of background 
acoustic noise is undesirable in voice transmissions. As an example, 
consider the situation in which a cellular phone user is attempting to 
conduct a telephone conversation in a noisy environment. In this 
situation, loud acoustic background noise is received by a microphone in 
the cellular phone and converted to an electrical signal which is supplied 
to the telephone(s) of the person(s) having the conversation with the user 
and is converted thereat to an acoustic signal. This results in distorted 
sidetones. As a result, the person to whom the user is communicating 
constantly hears the loud background noise because of these sidetones. 
Further, when the person is speaking, such speech is combined with the 
background noise and, as such, may be difficult for the other person(s) to 
understand. As a result, the user often has to raise his/her voice and 
literally shout into the microphone of the cellular phone to be heard. 
Furthermore, the signal representing the background noise is also supplied 
from the microphone in the cellular phone to the sidetones in a cellular 
phone or telephone handset or the like. Thus, the sidetones are distorted 
due to the background noise, which distorts the acoustic signal, and then 
impairs speech intelligibility. 
The conventional cellular phones, such as the Qualcomm QCP-800 cellular 
phone, do not reduce background noise to improve performance of cellular 
phones or the like utilized in a noisy environment or the like. Rather, 
the standard microphones utilized in such conventional phones are 
omnidirectional microphones. These standard microphones accept background 
and audio signals and conveys an electrical signal, which is degraded by 
ambient noise. Furthermore, an omnidirectional microphone accepts signals 
in all directions, including ambient noise propagating in more than one 
direction which is transmitted as an input signal to the microphone 
together with the audio speech. 
Thus, the utilization of the omnidirectional microphone in the standard 
cellular phone does not prevent speech from being distorted in a noisy 
environment or when utilizing digital means to convey sound signal when 
using cellular phones. Support that the speech is distort when using 
omnidirectional microphones in cellular phones is shown in the comparative 
testing performed by Andrea Electronics Corporation of a conventional 
cellular phone and a phone of the present invention. 
For instance, a standard Qualcomm QCP-800 cellular phone uses a "Personal 
Communications System" (PCS) that digitally compresses speech into a 
narrower bandwidth by calibrating the speech through a CODEC algorithm. 
However, unwanted background noise is also processed with the speech 
through the CODEC algorithm, which in turns degrades the speech compressed 
algorithm. As shown by the Articulation Indexes, to be fully discussed 
below, only 5 correct words out of 100 are recognized by the tested 
Qualcomm QCP-800 cellular phone. 
Furthermore, the Qualcomm QCP-800 cellular phone is used in connection with 
computer software that samples speech at a narrower bit rate in a narrower 
bandwidth. It is desirable to cancel noise before it is transmitted to the 
software sampling to prevent an inaccurate software voice sampling. The 
current voice sampling, which includes ambient noise, of a Qualcomm 
QCP-800 cellular phone interferes with the speech transmission leading to 
a decrease in the speech enhancement or speech intelligibility 
performance. 
Conventional omnidirectional microphones cannot simply be replaced with 
noise canceling microphones having pressure sensitive surfaces with a low 
gain to enhance noise canceling without typically having to replace the 
cellular phone with a new cellular phone. Simple replacement of the type 
of microphone does not solve the problem. Rather, as will be discussed in 
the present invention, the mechanical/acoustical arrangement of the 
microphone within the necessary input ports must take place so that noise 
cancellation occurs. This is because the mechanical/acoustical arrangement 
of the noise canceling microphone allows for sound equalization of the 
noise received from the noise port to achieve performance in the 
articulation indexes described herein, as such, would be relatively 
expensive. 
Thus, the prior art has failed to provide a relatively low-cost means for 
reducing background noise to an acceptable level for use with wireless 
telephones cellular phones or the like by mechanically/acoustically 
diffraction means, and a cost-effective means for enabling existing 
wireless telephones that use digital network to reduce background noise to 
an acceptable level. 
OBJECTS AND SUMMARY OF THE INVENTION 
An object of the present invention is to provide an acoustical improvement 
to cellular phones which overcomes the problems associated with the prior 
art. 
Specifically, it is an object of the present invention to provide a noise 
canceling cellular phone which reduces background noise by 
mechanical/acoustical means thereby increasing the speech intelligibility 
for the speaker and listener. 
More specifically, it is object of the present invention to provide noise 
canceling cellular phones as aforementioned which is relatively 
inexpensive. 
It is still an object of the present invention to provide a relatively 
low-cost noise canceling acoustical improvement to existing cellular 
phones to enhance speech performance which is operable with standard 
battery operated power. 
Another object of the present invention is to provide a relatively low-cost 
acoustical improvement to the manufacture of cellular phones or to be 
readily adaptable to existing cellular phones to provide a functioning 
noise canceling microphone that equalizes the noise received from the 
noise port with the noise received from the voice port to convey only the 
audio signal to the receiver portion or sidetones. 
An aspect of this invention is to provide a cellular phone having a noise 
canceling microphone placed within a microphone isolator, which contains a 
noise port and voice port, an acoustical baffle placed internally behind 
the voice port, and a acoustical opening to permit pressure gradient noise 
porting so that the ambient noise is mechanically canceled from the noise 
received with the speech received. The cellular phone for reducing 
background noise comprising: a housing having a receiver portion and a 
speaker portion; the receiver portion having a voice port and a noise 
port; a microphone isolator located within the receiver portion; at least 
one noise canceling microphone having a front end and a back end enclosed 
by the microphone isolator; a windscreen placed in front of the microphone 
and internally behind the voice port; and an acoustical port to permit a 
pressure gradient noise porting placed at the back end of the microphone 
and internally behind the noise port. The preferred noise canceling 
microphone is a pressure gradient microphone, but any unidirectional 
microphone having a low gain will enhance the noise cancellation 
performance. 
Other objects, features and advantages according to the present invention 
will become apparent from the following detailed description of the 
illustrated embodiments when read in conjunction with the accompanying 
drawings in which corresponding components are identified by the same 
reference numerals.

DETAILED DESCRIPTION 
FIG. 1 illustrates a wireless telephone or cellular phone 8 utilizing a 
noise canceling acoustical improvement in accordance with an embodiment of 
the present invention. As shown therein, the wireless telephone unit or 
cellular phone 8 having a speaker portion and receiver portion generally 
includes a microphone isolator 9, a noise port 10, a voice port 13, dense 
foam 11, acoustical opening 15 that is sized and tuned for a desired 
frequency response, a windscreen 14, and a noise canceling microphone 12. 
The cellular phone 8 can be coupled to a telephone unit (not shown) by way 
of RF waves or can be battery operated. The wireless telephone or cellular 
phone 8 of the present invention mechanically diffracts the noise received 
from the noise port 10 with the noise received from the voice port 13 so 
that the noise is canceled from the speech inputted into the voice port 13 
from the user. 
In FIG. 1, the microphone isolator 9 is illustrated within the receiver 
portion of the housing of the cellular phone 8. The isolator 9 can be 
comprised of rubber, dense foam-like material, or another suitable damping 
material. This isolator 9 is internally beneath the acoustical port holes 
or in close proximity to the voice port 13 of the cellular phone 8. The 
noise canceling microphone 12 of the present invention is preferably a 
pressure gradient microphone available from Panasonic or Primo. 
Alternatively, a unidirectional microphone that has a FET with a low gain 
having low sensitivity to be more effective for active noise cancellation. 
These low sensitive microphone with low gain that accept near field 
responses can be utilized in the present invention. 
The pressure sensitive microphone 12 has a front end and a back end having 
pressure sensitive surfaces with holes or openings on each surface. These 
holes permit sound to enter from the back of this microphone as well as 
the front of this microphone. The pressure gradient microphone responds to 
a difference in pressure. Therefore, to have effective noise cancellation 
with a pressure gradient microphone the sound pressure of the background 
noise must arrive simultaneously or at approximately the same time with 
the sound pressure from the background noise and audio signal received 
from the voice port. 
When the pressure sensitive microphone is place in the cellular phone 8 as 
shown in FIGS. 1 and 2, the microphone isolator and ports must be so 
arranged so that the noise entering from the back of the microphone from 
the noise port and the noise and speech entering from the voice port 
equalize or cancel out the noise portion of the signal. 
As stated, the preferred pressure gradient microphone 12 responds to the 
difference in pressure at two closely spaced ports, the voice port 13 and 
the noise port 10. When used in an environment where the pressure gradient 
of the background noise is isotropic, the electrical signal produced by 
the pressure-gradient microphone due to such background noise is 
effectively zero. Since the two opposite sides of a pressure-gradient 
microphone respond to acoustic pressure, as previously mentioned, the 
microphone isolator 9 is created or modified so as to enable these two 
sides of the microphone to respond simultaneously with the acoustic 
pressure. 
Therefore, the noise that enters from the noise port reaches the pressure 
gradient microphone and reaches the noise that enters with the speech from 
the voice port and by acoustical/mechanical means cancels the background 
noise and increases speech intelligibility. 
To achieve the optimal performance of the noise canceling microphone 12 
located in the cellular phone 8, the microphone isolator 9 is milled at 
the perimeter to a width to achieve the desired noise cancellation curves 
shown in FIGS. 3 and 5 and the articulation indexes of sound to noise 
ratio as shown in the data in Tables 1 and 3. The preferred width of the 
perimeter of the microphone isolator 9 is 1/10th or 0.1 of an inch. The 
width of the isolator must allow for pressure gradient noise porting or 
noise flow through from the noise port 10 to reach the pressure gradient 
microphone surface to cancel out with the noise flow received together 
with speech from the voice port, which provides for the desired frequency 
responses shown in FIGS. 3 and 5. The acoustical modification 15 permits 
pressure gradient noise porting so that the noise is 
mechanically/acoustically canceled for the audio signal input to the 
microphone shown in FIGS. 1 and 2. 
In addition, the sides of the microphone isolator are sized to a dimension, 
preferably at a 45 degree angle, to fit properly within the receiver 
portion of the cellular phone 8 so that optimum microphone coupling is 
achieved as shown in FIGS. 3 and 5 and the articulation index of sound to 
noise ratio as set forth in Tables 1 and 3. 
A windscreen 14 is comprised of dense foam-like material, preferably 100 
ppi plosive windscreen, inserted internally behind the voice port 13 of 
the cellular phone 8 in FIG. 2. The purpose of the windscreen 13 is to 
enhance or attenuate the wind noise, spitiness, or other ambient noises 
that exist when utilizing the cellular phone in a noisy atmosphere or 
outdoors. The windscreen 14 acts as a structural baffle that may be 
comprised of a structural member adapted to provide an acoustical 
separation between the microphone and voice port. Alternatively, an 
acoustical baffling arrangement could be utilized in place of a structural 
member. Thus, acoustic distortions are minimized. 
The two lead wires (not shown) of the noise canceling microphone 12 were 
connected to the circuitry contained on the circuit board assembly (not 
shown) that consist of amplifiers to amplify the electrical signal before 
being transmitted to speech that reaches the listener's ears. Such 
circuits enable calibration processing to be performed on the noise 
canceling microphone, which is preferably a pressure gradient microphone. 
However, any unidirectional microphone that has a low FET gain and low 
sensitivity can be utilized in the present invention. Further, such 
circuits may be included on a printed circuit (pc) board which may be 
installed within the cellular phone. The circuit board may contain 
additional circuit elements for processing the signals received from the 
noise canceling microphone and for amplifying signals for supply to the 
speaker as described in U.S. patent application Ser. No. 08/339,126 filed 
Nov. 14, 1994 (PCT No. US95/14756 filed Nov. 14, 1995) and U.S. patent 
application No. 08/485,047 filed Jun. 7, 1995, both applications which are 
incorporated herein. 
The wires must be oriented and preferably placed so as not to cover or 
adversely affect the flow of sound conveyed through the voice port 13 and 
noise port 10 of conventional cellular phones. The lead wires must not 
interrupt the flow of noise that is received from the ports, which is 
eventually canceled from the audio signal. The procedure to install at 
least one noise canceling microphone 12 in a cellular phone requires that 
the soldering be preferably a non-flux soldering. Non-flux soldering 
prevents future resin contamination of the noise canceling microphone. 
Conventional flux based soldering material would interfere with the proper 
functioning of a noise canceling microphone rendering it inoperative. 
Although the above embodiment has been described as having only one 
microphone 12, which mechanically cancels out the noise from the 
arrangement of the pressure sensitive surfaces of the noise canceling 
microphone with regards to the input ports, the invention is not so 
limited and any number of microphones may be utilized. For example, the 
digital means of canceling noise by utilizing two or more microphones can 
also be used provided there is adequate space. The present invention can 
be utilized with at least two noise canceling microphones in a cellular 
phone that is in a clamp shell design (similar to the operation of a 
lap-top computer), or with a NOKIA 9000-GSM phone. The NOKIA phone can be 
opened for viewing the LCD terminal inside, or to log onto the Internet 
terminal, to log onto the terminal, for accessing E-mails, and for other 
multimedia access. When the NOKIA phone is closed, the phone is used for 
talking, like the Qualcomm QCP-800. Because of the additional external 
layers, an acoustical baffle or windscreen cannot be utilized to insure 
noise is canceled by sound equalization. In that embodiment, two noise 
canceling microphones or electret microphones can be used to digital 
cancel noise by the acoustical arrangement of the microphones. The 
utilization of two or more noise canceling microphones is fully described 
in U.S. patent application Ser. Nos. 08/339,126 (PCT No. US95/14756) and 
08/485,047, which have a common assignee with the present application, and 
which is hereby incorporated by reference; however, such subject matter is 
not believed necessary to the understanding of the present invention. 
In that alternative embodiment using a NOKIA 9000-GSM, acoustic signals 
composed of speech or the like and background noise are supplied to a 
first microphone located on the top layer of the shell design or the 
portion that flips up vertically, and converted therein into a 
corresponding electrical signal which is thereafter supplied to the plus 
terminal of the op-amp. The background noise is supplied to the second 
microphone located in the bottom layer or stationary portion of the 
cellular phone and converted therein into a corresponding electrical 
signal which is thereafter supplied to the minus terminal of the op-amp. 
The op-amp is adapted to subtract the noise signal from the second 
microphone from the speech and noise signal from the first microphone and 
to supply therefrom an electrical signal representing substantially the 
speech to the cellular phone 8 whereupon the speech signal is transmitted 
therefrom through RF waves to the receiving party. The top cover 7 is 
attached to the cellular phone 8 by use of adhesives or the like or 
alternatively may be sonically welded together. 
In this same alternative embodiment, a receiver portion or the flip portion 
(not shown) may be configured which includes one or more microphones 
operating as a first microphone (not shown) and one or more microphones 
operating as a second microphone (not shown). In this configuration, when 
using multiple microphones for the first and/or second microphones, 
respective variable current limiting resistors are preferably provided for 
all but one microphone for the first microphone and for all microphones 
for the second microphone. 
Thus, the outputs from the first and second microphones, respectively, 
would comprise a weighted sum of several such microphone output voltages. 
The current limiting resistors are preferably set to respective values so 
as to minimize some functional of the difference of the first and second 
microphones, respectively. The criterion for selecting the values of the 
current limiting resistor or equivalently the weighing function of each 
microphone could be selected according to any well known gradient search 
algorithm, so as to minimize the functional. 
As is to be appreciated, by using the above-described devices and materials 
for acoustically improving the receiver portion of the conventional 
cellular phones, the cost for constructing such receiver portion is 
relatively low. Further, the power consumption of the receiver portion is 
kept relatively low. As a result, the receiver portion may be powered by 
the standard power available in a battery chargeable cellular phone and, 
as such, does not require additional power or transformers or the like. 
Furthermore, although the receiver portion (not shown) has been described 
for assembly with existing cellular phones, such receiver portion, or a 
slight variation thereof, may be installed in new cellular phones to be 
manufactured, like Qualcomm Original QCP-800. 
Upon activating the cellular phone 8, e.g., by transmitting the password of 
the user and entering and sending a telephone number, a signal from the 
noise canceling microphone 12 is supplied through circuitry, preferably a 
resistor and a capacitor coupled to an operational amp and then outputted 
as a resulting signal. 
The high frequency signals, such as those over 3.7 kHz, are then removed 
from the amplified output signal as well as any dc signals that may be 
present and the resulting signal is supplied to a speaker so as to be 
converted thereat into an acoustic signal. 
By so arranging a noise canceling microphones, a sound (in particular a 
background noise) originating from two different sources enable the sound 
to be mechanically as well as acoustically canceled before transferred to 
the sidetones to the ear of a receiving party. The physical design of the 
microphone as seen in FIGS. 1 and 2 is the determining factor in the S/N 
increase. Examination of these drawings shows that the location of the 
microphone pressure sensitive surface provides the optimum separation of 
the signal going to the voice microphone and noise ports in the near 
field. This separation is a primary component in the determination of the 
signal in the S/N ratio. 
FIGS. 3 and 4 are active noise cancellation curves of with and without the 
noise canceling acoustical embodiment of the present invention. 
FIG. 3, top line, representing near field response and the bottom line, 
representing far field response conducted at the facilities of Andrea 
Electronics Corporation. This curve in FIG. 3 with the noise canceling 
arrangement as shown in FIGS. 1 and 2 shows the noise canceling 
performance at close speaking range. For instance, at 100 Hz, background 
noise of almost 30 dB was canceled with the embodiment of the present 
invention. However, at far speaking range the pressure gradient microphone 
of the present invention had no real effect in canceling noise. For 
instance, at 10 kHz, there was only about a 1 dB change with using a noise 
canceling microphone. 
However, in FIG. 4, with is representative of the prior art, the top line 
representing the near field responses. This curve in FIG. 4 clearly shows 
almost no differential in utilizing an omnidirectional microphone for 
noise cancellation in the far and near field response, which has no effect 
on speech intelligibility. 
In FIGS. 5 and 6, frequency responses curves are represented for the noise 
canceling microphone and for the standard (prior art) omnidirectional 
microphone. In FIG. 5, the horizontal axis represents the frequency 
response of a pressure gradient microphone utilized in a Qualcomm QCP-800 
cellular phone over a decibel range represented by the vertical axis 
conducted at the facilities of Andrea Electronic Corporation. This curve 
in FIG. 5 when compared to FIG. 6 represents no change in the frequency 
response of a noise canceling microphone as compared to a non-noise 
canceling microphone. That is, no sacrifice in frequency response is 
reported with using a noise canceling microphone having pressure sensitive 
surfaces. FIG. 6 is representative of the frequency response of a standard 
microphone utilized in the prior art. The only change appears to be less 
than a 1 dB at 1 kHz, which trivial change in overall frequency 
performance. 
Using interpretation of speech intelligibility AI and ANSI S3.5-1969, a 
redesigned Andrea Audio for QCP-800 System of the present invention and a 
standard (prior art) microphone utilized in a conventional Qualcomm Audio 
System (QCP-800) were tested and the results were as follows: 
TABLE 1 
______________________________________ 
ARTICULATION INDEX: 
INVENTIVE BOOM MICROPHONE 
1/3 Octave Band 
S/N (Db) Weight Factor 
Articulation (1) 
Center Freq. (Hz) 
[NPR-FPR] (BW Corrected) 
Weight (W) 
______________________________________ 
200 22 0.00046 0.01012 
250 23 0.0012 0.0276 
315 17 0.0012 0.0204 
400 14 0.0016 0.0224 
500 12 0.0016 0.0192 
630 10 0.0023 0.023 
800 09 0.0023 0.0207 
1000 08 0.0028 0.0224 
1250 07 0.0035 0.0245 
1600 05 0.0043 0.0215 
2000 04 0.0044 0.0176 
2500 03 0.0039 0.0117 
3150 0.5 0.0039 0.00195 
0.24307 
______________________________________ 
TABLE 2 
______________________________________ 
ARTICULATION INDEX: 
STANDARD (PRIOR ART) MICROPHONE 
(Original Qualcomm Audio System) 
1/3 Octave Band 
S/N (Db) Weight Factor 
Articulation (1) 
Center Freq. (Hz) 
[NPR-FPR] (BW Corrected) 
Weight (W) 
______________________________________ 
200 0 0.00046 0 
250 2 0.0012 0.0024 
315 2 0.0012 0.0024 
400 1 0.0016 0.0016 
500 1 0.0016 0.0016 
630 3 0.0023 0.0069 
800 5 0.0023 0.0115 
1000 1 0.0028 0.0028 
1250 1 0.0035 0.0035 
1600 2 0.0043 0.0086 
2000 0 0.0044 0 
2500 0 0.0039 0 
3150 0 0.0039 0 
0.0413 
______________________________________ 
The following table performs a matching articulation indexes between the 
present invention and the prior art QuaLcomm cellular phone to determine 
the overall percentage of syllables, words, or sentences understood 
correctly by utilizing the acoustical improvement of the present invention 
in a Qualcomm QCP-800 cellular phone: 
##STR1## 
Interpretation of speech intelligibility using AI and ANSI S3.5-1969 shows 
an accuracy level of approximately 70% using a 0.24307 articulation index 
for the present invention versus an accuracy level of approximately only 
15% using a 0.0413 articulation index for the standard omnidirectional 
microphone in a conventional Qualcomm original QCP-800 cellular phone. A 
comparison of this data reflects a reduction in error ratio by the present 
invention (i.e., AI (15%) standard microphone, noise canceling AI (70%) by 
present invention). Furthermore, additional AI is expected when constants 
are corrected to be active down to 50 cycles and below. Literal evaluation 
of the AI calculation states that for every 100 words spoken, the present 
invention will produce 75 correct words or 25 errors, and prior art 
standard microphones will produce 5 correct words or commit 95 errors. All 
data and calculations were collected and performed at Andrea Electronics 
Corporation. Both microphone systems were tested at Andrea Electronics 
Corporation under the same conditions. 
FIGS. 7A, 7B and 7C illustrate the certain positioning of the microphones 
with regard to an artificial mouth 40 or the loudness rating guard-ring 
and AEN positions. The tests run at Andrea Electronics Corporation and 
test results tabulated in Tables 1-3 and in FIGS. 3-6 were conducted at 
the AEN positions so that TOLAR responses met the conventional standards. 
The TOLAR responses achieved during the physical testing of the Qualcomm 
QCP-800 cellular phone met the physical spacing requirements shown in 
FIGS. 7A-7C. FIG. 7B illustrates the rotation of the handset about the XX 
axis. FIG. 7C illustrates the rotation of the handset about the YY axis. 
In FIG. 7A, where the center line of the X axis intersects with the center 
line of the Y axis is the centerline of the earpiece or the ear reference 
point 41. The axis of the artificial mouth is designated by 43, while the 
plane of the ear cap and ear is 42. 
Furthermore, although preferred embodiments of the present invention and 
modifications thereof have been described in detail herein, it is to be 
understood that this invention is not limited to those precise embodiments 
and modifications, and that other modifications and variations may be 
affected by one skilled in the art without departing from the spirit and 
scope of the invention as defined by the appended claims.