Motorcycle stereo audio system with VOX intercom

United States Patent [19]
Stafford et al.
[54] MOTORCYCLE STEREO AUDIO SYSTEM
WITH VOX INTERCOM
[75] Inventors: Larry E. Stafford, Mesa; John J.
Lazzeroni, 732 E. Stella Rd., Tucson,
both of Ariz. 85730
[73] Assignees: John J. Lazzeroni; Melinda K.
Lazzeroni, both of Tucson, Ariz.
[11]
[45]
Patent Number:
Date of Patent:
4,754,486
Jun. 28, 1988
tions between the motorcycle driver and passenger
providing for stereo listening in each of both right and
left helmet earphones wherein intercom communica~
tions may be had through microphones always acti
vated located proximate the mouth of both driver and
passenger where when initiating speaking over the mi
[51]
Int. 01.4 ............................................. .. H04B 1/00
[52]
US. Cl. .................................... .. 381/86; 455/238;
381/56; 381/110; 381/94
crophone, the stereo output of one side of the earphones
is reduced by approximately one/half while the stereo
output of the other side earphones is terminated com
pletely and the intercom conversation is heard in full
over that single side of earphones. Upon the termination
of the intercom conversation, the invention circuitry
returns both sides of earphones to the pre-existing level
of stereo output. The above is accomplished by dividing
[58]
Field Of Search ..................... .. 381/25, 56, 72, 74,
all sounds which come in over the microphone into a
[56]
381/94, 110, 86; 455/238
References Cited
low and high frequency range separated by an audio
speaking range wherein the outputs of the low and high
[21] Appl. No.2 37,557
[22] Filed:
Apr.13, 1987
U.S. PATENT DOCUMENTS
4,380,824
4/1983
4,677,389
6/1987 OpdeBeek et a1. ............... .. 455/238
Inove .................................. .. 381/86
FOREIGN PATENT DOCUMENTS
0058733
4/1985
Japan ................................... .. 381/86
Primary Examiner-Forester W. Isen
Attorney, Agent, or Firm-J. Michael McClanahan
[57]
frequency range ?lters are constantly sampled and com
pared with the energy output of the audio speaking
range of frequencies. When the energy in the speaking
range of frequencies exceeds the energy in the low and
high frequency range, such is indicative that a party is
speaking into the microphone and the circuit automati
cally terminates the output of one earphone, reduces the
other by half, and injects the intercom on the earphone
whose stereo had been terminated.
ABSTRACT
An improvement to motorcycle intercom communica
ATTENUATOR
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19 Claims, 2 Drawing Sheets
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that when utilizing the intercom system, the voice may
MOTORCYCLE STEREO AUDIO SYSTEM WITH
not exceed the previously set sensitivity for a relatively
VOX INTERCOM
loud noise level and thus not be heard.
In addition, many of these VOX systems (voice acti
BACKGROUND OF THE INVENTION
5 vated systems) are such that they turn off immediately
at the end of the last word of the person speaking so that
1. Field of the Invention.
if there is a pause between the words of the speaker, the
The ?eld of the invention is motorcycle stereo and
system will have already shut down. Then, when the
intercom systems between the motorcycle rider and
system comes back on for the next word spoken, the
passenger.
2. Description of the Related Art.
Currently available are audio stereo systems for mo
torcycle riders and passengers as motorcycle accesso
?rst word will appear chopped or missing altogether by
the time it takes the system to get back activated.
Further, the problems with the VOX systems cur
ries which provide means by which the motorcycle
rently available as motorcycle accessories are exacer
bated with the new style of sport type motorcycles
rider and passenger may enjoy stereo music from a
carried tape cassette player or radio receiver. These 15 presently coming upon the market in that they have
systems comprise primarily two channel ampli?er sys
tems that input into the jack receptacle of tape cassette
players and radio receivers, amplifying the sound in
each channel and then directing it to sets of earphones
smaller farings and less wind protection for the driver
and passenger than the touring type motorcycles, and
consequently more outside and extraneous noise are
present.
or headsets worn by the motorcycle driver and passen 20 Thus it is obvious that there is need for a stereo audio
ger. In many cases, earphones are ?tted interiorly to the
system with VOX intercom which overcomes the prob
protective helmet worn by the rider and passenger and
lems above discussed, i.e., that will automatically com
so oriented that the left channel of the stereo will appear
pensate for increased wind and other noise so that both
in each of the left helmet earphones of the rider and
the rider and passenger are not constantly having to
passenger, and the right stereo channel appearing in the
right helmet earphones of the motorcycle rider and
25
passenger. In these cases, electrical cords connect to the
earphone of each the rider and the passenger and plug
adjust the sensitivity control to compensate for varying
wind and other noises, and for a VOX system that stays
on for a period of time even after the last person has
spoken until it is reasonably clear that there will be no
into convenient connectors or jacks of the sound system
more
conversation, and then, after muting the stereo
30
to receive the stereo audio entertainment.
system, brings the system back to full volume.
The problems come when attempts are made to inter
connect the stereo system with an intercom microphone
Additionally, it is obvious that there is a need for a
motorcycle stereo audio system with VOX intercom
system which permits intercommunication between the
which
permits the monitoring of the stereo audio sys
rider and passenger while traveling on the motorcycle.
In most cases, the microphone is similarly attached to 35 tem while the VOX intercom system is being used.
These and other objects and needs are set out in the
each helmet worn by the motorcycle rider and passen
enclosed speci?cation of Applicant's invention.
ger such that it at all times is immediately forward of,
but in close proximity to the party’s mouth. For such
SUMMARY OF THE INVENTION
systems, inherent problems reside in the fact that wind
The embodiment of the invention described consists
noise and other outside noises are picked up in addition 40
of
a motorcycle stereo audio system with VOX inter
to the spoken word by the microphone and sent into the
com wherein the electronic circuit automatically com
interconnected stereo and intercom system. One solu
pensates for increased wind and other noises by com
tion has been to activate the microphones of the inter
parison of newly arrived noises which impinge on the
com system by means of separate on/off switches so
that they may be turned on when one of the parties 45 microphone with sounds which existed to that point.
The system is installed on a motorcycle, the bike is then
wishes to speak, and then turned off at the conclusion of
taken out and ridden at the speed which creates the
the conversation. Of course, systems of these type re
move the previously listened to stereo or radio pro
maximum noise, generally the legal speed limit, and the
sensitivity potentiometer set at that point where the
grams from the earphones, so what would have been
said on these programs have been lost. This may be vary 50 noise is not passed into the intercom system. This sensi
tivity setting will be different for different motorcycles,
important, especially if one were listening to the news
or waiting for an announcement.
Other solutions have been to have the microphone
system on all the time, yet, adjust the sensitivity of the
system so that noise and other sounds below a certain 55
level are not ampli?ed throughout the system, and,
when speaking above that noise level, the speaking
voice will be ampli?ed and placed upon the earphones
of both parties. However, systems of this type always
need continuous adjustment depending upon the noise
level. Unfortunately also, the noise level appears to rise
as a direct function of the speed of the motorcycle, thus
continually requiring adjustment of the sensitivity level
different type farings on motorcycles, different helmets,
microphones, speakers in helmets, however, once it has
been set then it will not need again be utilized.
More speci?cally, the subject invention segregates all
sounds in the audio range coming into the microphone
into three frequency ranges. Many frequencies which
appears as noise in a system and which are due to wind
or vibrations are relatively low frequency noise, in
many cases less than 20 cycles per second. Additionally,
many other noises, such as sirens, may have a frequency
principally above 6 kilocycles per second. Accordingly,
the speaking audio range, nominally 500 hz to 4 khz, is
segregated within the intercom system and is the fre
to eliminate the noise. That, of course, introduces addi
tional problems, such as if the motorcycle has been 65 quency range through which the intercom system is
operated. Audio sounds having a frequency below 200
traveling at a high rate of speed when last using the
hz, and above 6 khz, are also segregated and then used
intercom system and the motorcycle then slows down,
the manually adjusted sensitivity control is set so high
as a means for comparison of the energy contained in
3
4,754,486
these low and high bands to the energy in the audio
speaking band. Thus, at all times, means are provided
whereby no absolute level of noise or speaking into the
microphone will interject itself into the VOX intercom
system, but always a comparison is made between sur
rounding ambient noise in the low and high bands to
noise or other speaking in the audio range. Therefore
only when the relative level of speaking is above the
noise detected in the low and high bands of frequencies
does the speaking interject itself into the VOX intercom
4.
?lter is then led directly into the amplifying system for
the left earphone in order that it may be there heard.
No signal is directed to the left channel ampli?er
from the band pass ?lter until the energy of the audio
signals passing through the band pass ?lter exceed the
energy of the signals passing through the low and high
?lter systems.
By selective use of capacitor draining resistors at
tached to the two charged capacitors, the output of the
comparator during time of the the presence of audio
system and on to the earphones worn by the motorcycle
signals in the band pass ?ltering system is prolonged an
rider and passenger.
Accordingly, once sensitivity has been set for the
system on the motorcycle at the level of highest noise,
no more setting is necessary and the VOX intercom
system and the microphones remain on at all times and
will operate to impart the spoken words into the ear
phones of the rider and passenger only when the micro
additional 3 to 4 seconds after the last word is spoken to
phone is spoken into regardless of the level of the out
side noise. However, when an extremely loud noise is
perceived which does have energy in the audio speak
ing range, such as a nearby siren, the system permits the
sound of the siren to actuate the VOX intercom system
so that the rider and passenger, for safety’s sake, are
permitted to hear the sounds so that they may react to
it as needed. After the sound has passed away, the sys
ascertain that the speaker is through talking or to give
an opportunity to the other party to talk before the left
and the right stereo channels are brought back to full
volume in both left and right earphones.
Accordingly, it is an object of the present invention
to provide a motorcycle stereo audio system with VOX
intercom wherein the noise interference level at all
speeds and under all conditions is always compensated
for before the VOX system becomes operative.
It is another object of the subject invention to provide
means for continuing the VOX intercom system on an
additional period of time to provide time opportunities
between spoken messages.
Accordingly, the system, as operating, channels the
It is still a further object of the subject invention to
provide a motorcycle stereo audio system with VOX
intercom wherein the sensitivity control to account for
left and right output of a stereo cassette player, or radio
noise may be set once depending on the motorcycle and
receiver into each of the left and right helmet earphones
other surrounding noise generators and then not be
re-set for different noise levels of the motorcycle.
Other objects of the invention will in part be obvious
and will in part appear hereinafter. The invention ac
tem returns to its prior state.
, ’ of both rider and passenger respectively, only inter
rupted by the presence of speaking or possible emer
gency sounds in the audio frequency range. When that
' happens, the previously existing music or sound in the
right stereo channel is dropped out completely in both
the right helmet earphones while the left channel stereo
music or radio receiver sound is muted by approxi
, mately one/half in both the left helmet earphones. The
_ j intercom system then works fully in the right helmet
earphone of both the rider and passenger simulta
neously. By this means, the radio receiver, still playing
cordingly comprises the apparatus possessing the con
struction, combination of elements, and. arrangement of
parts which are exemplified in the following detailed
disclosure and the scope of the Application of which
will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
1‘ ‘at one/half sound in the left ear, may still be monitored
For further understanding of the features and objects
of the subject invention, reference should be had to the
for something that the party’s were listening for and
' following detailed description taken in connection with
when it is heard, merely by terminating the intercom
munication, in 3 to 4 seconds, the radio receiver or
stereo player is brought back up to its full restored
volume in both the left and the right ears.
The above is accomplished by means of three ?lters,
a low pass ?lter which cuts off at approximately 200 hz,
a band pass ?lter which captures audio signals in the
range of 500 hz to 4 khz, and a high pass ?lter which
passes all audio sounds above 6 khz. The outputs of both
the low pass and high pass ?lters are combined, half
wave recti?ed, and then summed by charging a capaci
tor, the voltage upon which is then directed to the
negative input of a high input impedance comparator..
The audio signals in the band pass range of 500 hz to 4
khz are similarly half wave recti?ed and averaged by
charging a second capacitor, the output of which is
the accompanying drawings wherein:
FIG. 1 is a functional block schematic diagram of the
subject invention;
FIG. 2 is a complete schematic of the subject inven
tion; and
FIG. 3 is a combined perspective view and block
schematic drawing of the subject invention with motor
cycle rider and passenger.
In the various views, like index numbers refer to like
elements.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENT
Referring now to FIG. 1, a functional block sche
matic diagram of the subject invention is detailed.
Firstly, and beginning at the upper left hand portion of
directed to the positive input of the same high input 60 the FIGURE, microphone 20 is shown having its out
impedance comparator. The comparator is character
put directed to volume control potentiometer R100, the
ized as having a positive voltage output only when the
center tap of which is directed to preamp 1 which pro
voltage of the positive input exceeds the voltage of the
vides up to 40 db of gain for the audio signal from the
negative input. Upon an output from the comparator,
microphone. Thereafter, the output of preamp 1 is di
the left stereo channel from the radio receiver or take
rected to band pass ?lter 2 which passes the audio sig
cassette player is terminated through use of an active
nals in the frequency range of 500 hz to 4 khz, rejecting
attenuator and the right stereo channel is attenuated by
frequencies outside this audio range. The output of
half. The audio speaking voice output of the band pass
preamp 1 is also directed to low pass ?lter 4 which is so
5
4,754,486
designed to pass audio signals having frequencies of 200
hz or less. In addition, band pass ?lter 2, which includes
both a high pass ?lter and a low pass ?lter in its con
struction, ?rst passes all frequencies above 500 hz to a
6
outputs a signal only when the input from recti?er 5, the
audio speaking range signal, is greater than the input
from the recti?er/mixer 6, the combined audio noise
frequencies signal. Such is accomplished by placing the
second ?lter which rejects all frequencies above 4 khz. 5 output of recti?er 5 to the positive input of comparator
However, the output of the ?lter passing 500 hz and
7, the output of recti?er/mixer 6 to the negative input of
above is directed to high pass ?lter 3 which permits
comparator 7, and then searching for positive output
passage of audio frequencies above 6 khz.
from comparator 7. Thereafter, the output of compara
Thereafter, the outputs of band pass ?lter 2, high pass
tor 7 is directed to three attenuators, 8, 10, and 11.
?lter 3, and low pass ?lter 4 are directed to a pair of 10
recti?ers, speci?cally, the output of band pass ?lter 2
directed to recti?er 5 and both the outputs of high pass
?lter 3 and low pass ?lter 4 to recti?er/mixer 6. The
purpose of recti?er Sis to convert the audio signal from
the band pass ?lter 2, by means of a half wave recti?er,
Attenuators 8 and 10 receive the left and the right
channels respectively of a stereo-audio input, such as
from a radio receiver or stereo tape cassette much like
the portable carry-around tape players. Since the inven
tive device is to provide music or other entertainment to
the motorcycle driver and passenger, such as ' stereo
to a dc voltage which will charge capacitor C11, the
collected voltage of which will be later compared. Rec
ti?er/mixer 6 converts the audio signals from both the
music, the left and right stereo channels are passed
high pass ?lter 3 and low pass ?lter 4 to a dc voltage by
means of a half wave recti?er, this dc voltage being
and passenger, the stereo entertainment is only inter
rupted by either the driver or passenger using the inter
through attenuators 8 and 10 and on and into the respec
tive left and right helmet earphones of both the driver
used to charge capacitor C16, the output of which will
com system, i.e., speaking into the microphone immedi
ately in front of the party’s mouth. The microphone is
output of recti?er 5 as represented on charged capacitor
on constantly, however, energy in noise passed by the
C11.
low and hi pass filters is characteristically greater than
The purpose of recti?er 5 and recti?er/mixer 6 is to 25 the noise passed by the audio speaking range band pass
search for energy in the different audio ranges which
?lter 2, and thus the output of comparator 7 is zero,
will be indicative of certain things. As previously men
since it only outputs a positive signal when its positive
tioned, the speaking range which has been selected to be
input from recti?er 5 is greater than its negative input
ampli?ed and eventually placed on one (nominally, the
from recti?er/mixer 6. Comparator 7 output, when
right) of the earphones of each of the driver and passen 30 present, act upon attentuators 8 and 10 such that when
also directed to the same comparator as receives the
ger is the audio range of 500 hz to 4 khz. Noise, as
previously mentioned, covers all frequencies, however,
one disturbing source of noise to the motorcycle rider
and his passenger is wind noise due to the passing of the
there is an output from comparator 7, which means that
the driver or passenger is speaking into the microphone,
attenuator 8, which feeds the left earphone, reduces the
left stereo channel signal amplitude by approximately
motorcycle through air and the characteristic noise is
one/half and thus the sound in the left earphone by
dependent upon the type of motorcycle, its construc
one/half. At the same time, the output from comparator
tion, and most importantly, the shape and size of its
7 totally inhibits the right stereo channel signal which
cowling. The trend is to make the wind protective
theretofore was passing through attenuator 10 so that
cowling on sports type motorcycles of smaller size than
the output of attenuator 10 goes to zero.
the wind protective cowling on the touring type motor 40 At the same time, the output of band pass ?lter 2,
cycle. Consequently, the wind noise on sports type
which is the audio speaking portion, is injected into a
motorcycles is greater in amplitude than the wind noise
third attenuator 11, and allowed to pass through attenu
on touring type motorcycles. Further, the great major
ator 11 by virtue of the presence of the output of com
ity of the wind noise is in the low frequency range
parator 7 which has also been directed to attenuator 11.
generally below 200 cycles per second. In addition, 45 The output of attenuator 8, which is the left stereo
high frequency noise, many times noises such as emer
gency vehicle sirens, also manifest themselves to the
rider and are picked up by the microphone and con
veyed to the hearing of the motorcycle rider and pas
senger.
Accordingly, the sounds which are picked up by the
microphone and ampli?ed by the preamp may be con
channel, is directed to power ampli?er 9 which in turn
outputs its signal to loudspeaker or earphone 13 which
is nominally the left earphone. The output of attenuator
10, the right stereo channel, is directed to power ampli
?er 12 whose output is directed to loudspeaker or ear
phone 14, the right side helmet earphones of the rider
and passenger. When audio speaking frequencies are
present because of an output from band pass ?lter 2,
ing range of 500 hz to 4 khz and the noise range below
attenuator 11 is activated while attenuator 10 is deacti
and above the speaking range. Obviously, however, 55 vated, and the output of attenuator 11 is directed to
noise in the speaking range will be carried through the
power ampli?er 12 and then on to the right hand
veniently divided into different audio ranges, the speak
system as if it were being spoken by the motorcycle
rider or passenger into their respective microphones.
However, as a practical matter, due to the proximity of
the microphone to the mouth of the rider or passenger,
in most all cases, except for perhaps emergency vehicles
passing very near, the voice of the driver and/or pas
speaker or earphone 14.
Consequently, when the intercom between the driver
and the passenger is being utilized, the stereo sound in
the left helmet earphones of both the driver and passen
ger is reduced by approximately one/half, while the
right channel stereo signal is completely inhibited in the
senger will be greater than all frequency noise. Accord
right earphone; however, the intercom comes on unat
ingly, the output of recti?er 5, after storage upon its
tenuated in the right earphone. By such method, the
attendant capacitor C11, is directed into comparator 7 65 driver and passenger may communicate between each
where it is compared with the output of recti?er/mixer
other. However, if the radio or stereo input is being
6, also represented by the voltage on a charging capaci
monitored for some announcement or the like, it will be
tor. The output then of comparator 7 is such that it
heard, and, if an emergency vehicle or the like passes in
7
4,754,486
8
signals greater than 500 hz is directed to the positive
the proximity, such that energy is placed into the speak
ing range of frequencies, the siren or other overly loud
signal will be heard in the right earphone. If the sound
input of operational ampli?er 26, and to the positive
input of operational ampli?er 30. Operational ampli?er
is outside the speaking range, i.e., it has more energy in
26 is the low pass ?lter portion of band pass ?lter 2
the low and high frequency range than the speaking
shown in FIG. 1 and it passes only audio signals below
4 khz. Operational ampli?er 30 is the high pass ?lter 3
range of frequencies, comparator 7's output will be
shown in FIG. 1 and it will be discussed later.
inhibited and stereo music will return to the earphones.
As previously mentioned, the output of operational
This, in itself, if happening while the intercom is being
ampli?er 24 is coupled into the positive input of opera
used, is a warning to the parties that an emergency
10 tional ampli?er 26 by means of capacitor C6. In addi
vehicle or other loud noise if present.
tion, the input is do biased by means of resistor R12
Functional blocks numbers 1 through 7 comprise the
connecting it with the voltage source one/half B+
intercom system, blocks 8 and 9 the left attenuator and
previously discussed. Op amp 26, being a low pass RC
ampli?er system, blocks 10 and 12 the right attenuator
active ?lter, uses resistors R15 and R14 to set the pass
and ampli?er system, and block 11 the intercom attenu
ator.
band gain to unity. A portion of op amp 26 output is
Referring now to FIG. 2, a complete schematic of the
subject invention is detailed. Beginning again at the
used with capacitor C8 in conjunction with resistors
R13 and R16 and capacitor C7 for feedback. This forms
the frequency determining network to select a Q of 10
and a 12 db per octive slope for the frequency roll off.
same point used in the description of FIG. 1, on the left
hand side, middle portion of FIG. 2 is shown micro
phone 20. Microphone 20, of which there may be more
In addition, the output of op amp 26 is loaded by resis
tor R17. The output of operational ampli?er 26 is the
than one as shown, connects with volume control po
output of band pass ?lter 2 as shown in FIG. 1 and
tentiometer R100 and parallel resistor R1 to selectively
reduce the audio signal from the microphone in accor
comprises audio signals in the range of 500 hz to 4 khz.
Proceeding downward from the band pass ?lter 2,
dance with the volume sought on the output on the
earphones later discussed. The audio signal from the 25 high pass ?lter 3, as shown in FIG. 1, is detailed com
prising operational ampli?ers 30 and 32, the positive
microphone 20 then passes dc isolation capacitor C1 to
input to ampli?er 30 receiving the output of the high
input to the base of preamp transistor Q4. The base of
pass ?lter portion of band pass ?lter 2, namely, the
transistor Q4 is do biased through means of resistor
output of operational ampli?er 24. Op amp 24 is loaded
divider network R2 and R3. The collector of transistor
; .Q4 is attached to B+ ?rst connecting series resistors R4 30 by resistor R11. A portion of the output of operational
ampli?er 30 is also fed back to its positive input by
. and R5. Between resistor R4 and R5 is do de~coupling
means of R26 which, in conjunction with capacitors
: ‘ capacitor C2 which grounds any electrical spikes which
C12 and C13, form the frequency control of this ?lter.
. might appear on B+. The emitter of transistor Q4 is do
A gain of one is selected for this circuit and a Q of 10 is
a biased by resistor R6 with ac grounding capacitor C3
' paralleling resistor R6. The output of transistor Q4 is 35 used for a 12 db per octive slope of the frequency roll
off. Lastly, the output of op amp 30 is then directed to
taken from the collector where it is directed to the
the positive input of ampli?er 32 after passing through
, . positive input of operational ampli?er 24 after being dc
~~ isolated by series capacitors C4 and C5. The output of
coupling capacitor C14. The positive input to op amp 32
is also do biased by means of resistor R27 tied to one/
Q4 is also directed to operational ampli?er 34 which
~ will be discussed later. Operational ampli?er 24 is the 40 half B +. The op amp gain is selected by the ratio of R28
and R29, R29 being the feedback and R28 being refer
?rst active element of band pass ?lter 2 as shown in
ence to ac ground. Both operational ampli?ers 30 and
~» ‘FIG. 1 whereas operational ampli?er 34 is a portion of
32 comprise the high pass ?lter 3 as shown in FIG. 1
low pass ?lter 4 shown in FIG. 1.
and pass audio signals above a frequency of 6 khz.
Operational ampli?er 24 is wired as shown in the
Turning now to the low pass ?lter 4 as shown in FIG.
FIGURE to operate as an active high pass ?lter, passing 45
1, and as had been previously mentioned, the output of
all audio signals having a frequency greater than 500 hz.
preamp 1 shown in FIG. 1, namely transistor Q4, is
Operational ampli?er 24 is connected as a high pass RC
directed to the positive input of operational ampli?er 34
active filter, with resistor R7 and R8 controlling the
through a coupling capacitor C17. Operational ampli
pass band gain using a portion of the output feedback to
the negative input. This is determined by the ratio of R8 50 ?er 34, being a low pass RC active ?lter, uses resistors
R35 and R34 to set the gain to one. A portion of opera
to R7. Resistor R7 is connected to the voltage source
tional ampli?er 34 output is used with capacitor C19 in
§B+. As shown at the bottom of FIG. 2, the voltage
conjunction with resistors R36 and R37 and capacitor
§B+ is obtained from voltage B+ + through a resistor
C18 for feedback. This forms the frequency determin
divider network comprising resistor R66 in series with
resistors R67 and R68, with one/half B+ being taken at 55 ing network to select a Q of 10 and a 12 db per octive
slope for the frequency roll off. Thereafter, the output
the connection between the two equal resistors, R67
of op amp 34 is directed to the positive input of op amp
and R68. Noise on the one/half B+ line is grounded by
36, ?rst being coupled through capacitor C20 and the
means of bypass capacitor C38 also connected at mid
point between R67 and R68.
positive input also being dc biased by means of resistor
'
R38 connected to one/half B+. The gain of the op amp
36 is set by the ratio of resistor R40 to R39, R40 being
the feedback and R39 being reference to ac ground by
being tied to §B+. The output of op amp 36 then is the
output of low pass filter 4 as shown in FIG. 1 and passes
A portion of the output of op amp 24 is also fed back
to its positive input by means of R10 which, in conjunc
tion with capacitors C4 and C5, form the frequency
control of this filter. A gain of one is selected for this
circuit and a Q of 10 is used for a 12 db per octive slope
of the frequency roll off. In addition, the positive input
to operational ampli?er 24 is positively biased by means
of resistor R9 connected between it and one/half B+.
The output of operational ampli?er 24, which are audio
65
only audio signals below the frequency of 200 hz.
The outputs of high pass ?lter 3 and low pass ?lter 4
as shown in FIG. 1 are combined in recti?er/mixer 6
comprising in FIG. 4, ?rstly the dc isolation capacitors
9
4,754,486
10
C15 attached to the output of op amp 32 and capacitor
C21 connected to the output of op amp 36. Resistors
input from a stereo radio receiver or stereo cassette
R30 and R41 provide a discharge path for C15 and C21
to ground. The audio output of both op amp 32 and 36
player and is illustrated in the upper right hand portion
of the circuitry shown in FIG. 2. Firstly, the signal is
are each half wave recti?ed by means of diodes D2 and
inputted to terminal 17 where it is resistance divided by
means of resistor divider network comprising resistors
R42 and R43, these resistors also loading the output of
the signal source, with the center point then continuing
?rst discussed. To attenuator 8 is directed the left stereo
D3 respectively, and then the outputs (after the diodes)
are combined and will be directed to the negative input
of comparator 38 which will be later discussed. How
ever, prior to the entry into the negative input of com
parator 38, charging resistor R31 is in line with the
combined outputs of diodes D2 and D3. The output
then goes to capacitor C16 which ?lters out any abrupt
into coupling capacitor C22. Thereafter, the resistor
signal reduction circuit, which permits the reduction of
the left stereo output during times of intercom usage is
detailed showing series resistors R45 and R46, the com
bined resistors then being shunted by resistor R44. At
the junction of resistors R45 and R46 is connected the
change in the voltage coming from the high and low
pass ?lters. The rate at which the system will respond to
changes in the noise range is controlled by the RC time
collector of transistor Q1, which grounds that point
constant of R31 and C16. The rate at which the system
will recover from loud noise is controlled by the RC
time constant of R32 and C16. This is the output of the
during intercom usage and will be discussed later. From
the junction of resistors R44 and R46, the signal is again
coupled by means of capacitor C23 into the input of
high pass and low pass ?lters which will be compared to
the output of the band pass ?lter by high input impe
20
dance comparator 38.
The ?rst and second inputs to the integrated circuit
shown in FIG. 1, the output of operational ampli?er 26
is loaded by means of resistor R17 and then directed to
dc isolated by capacitor C9. In addition, the output of
op amp 26 is also directed to attenuator 11 as shown in
FIG. 1 (this will be discussed shortly). The gain of op
prises the active element of the power ampli?er block 9
shown in FIG. 1.
Returning now to the output of band pass ?lter 2 as
the positive input of operational ampli?er 28 after being
power ampli?er 42. Power ampli?er 42 in FIG. 1 com
25
comprising power ampli?er 42 are bypassed by capaci
tor C24. The output is high frequency bypassed through
capacitor C27 to ground. Amp 42 gain is set by the ratio
of R49 and R50 and then fed back to the second input
through capacitor C25. In addition, power ampli?er 42
is connected to B+ +, being ac bypassed by capacitor
amp 28 is determined by feedback resistors R20 and
R19. Resistor R19 is connected to voltage source §B+. 30 C26 to ground. The output of power ampli?er 42 then
is coupled to terminal 18 by capacitor C28, and on to
Resistor R20, which is a potentiometer, is the sensitivity
adjust pot for the system. Such sensitivity adjust is ma
nipulated so that the override of the intercom does not
function until a person speaking into the microphone,
together with noise in the band pass ?lter, exceeds the
road noise in the low and high frequency range. Once
the value of resistor R20 is adjusted in an actual trial on
the road at, say 55 miles per hour, it will need not be
readjusted again.
the left earphone of both the helmet earphones of the
rider and the passenger on the motorcycle.
The other stereo input, namely the right side stereo
input from the FM radio or stereo tape player is di
rected into attenuator 10 as shown on FIG. 1 and which
is shown in complete detail in the upper right hand
comer of FIG. 2. Like the left hand stereo attenuator 8,
the input from the stereo radio receiver is connected to
Continuing, the output of op amp 28 then is do iso 40 terminal 19 and is voltage divided through resistors R51
and R52, which also loads the signal source. This is
' ,lated by means of capacitor C10 and continued on to
, half wave recti?er diode DI, the line ?rst being tied to
coupled through capacitor C29 and then series resistor
R53. Attached following resistor R53 is the collector
output of transistor Q2, the base of which receives the
capacitor C11, similarly as did the outputs of diodes D2 45 output of comparator 7 previously discussed to ground
the right input during times of intercom activity and
and D3 from the high pass filter and the low pass ?lter,
which will discussed shortly. Continuing on, the right
to form a dc voltage dependent on the energy level in
side stereo input then is referenced to ground by means
the audio range of 200 hz to 4 khz, and then inputted to
of grounding resistor R57 and then continues on into
comparator 38. The recovery or on time after the last
communication is controlled by discharge resistor R22 50 series resistor R56 and capacitor C30. Thereafter, ca
pacitor C30 feeds into the ?rst input of power ampli?er
to ground in the RC ratio of R22 to C11.
44, power ampli?er 44 being the active element of the
Thus, appearing at the positive input of high input
power ampli?er block 12 shown in FIG. 1. Attached
impedance comparator 38 is the positive dc voltage
also to the input of power ampli?er 44 is the output of
from charged capacitor C11 (recti?er 5 of FIG. 1). The
band pass ?lter 2, the connection ?rst being interrupted
combined positive voltage outputs of op amp 32 and 36,
by attenuator 11 (transistor Q3) as shown in FIG. 1.
after recti?cation through diodes D2 and D3 and charg
This will also be discussed shortly.
ing capacitor C16 (high pass and low pass ?lters 3 and
Both the inputs of power ampli?er 44 are bypassed by
4 FIG. 1), places a positive voltage upon the negative
capacitor C32 and then like power ampli?er 42, the
input of comparator 38 for voltage comparison with the
output gain set by the ratio of R62 and R63 and then
output of op amp 28 as represented by the voltage on
coupled back to the input through capacitor C33. The
capacitor C11.
ground through resistor R21. After half wave recti?er
diode D1, the resultant positive signal then charges
Comparator 38 operates such as to have a positive
output then is directed to terminal 21 and on to the left
output only during those times when its positive dc
voltage input (from band pass ?lter) exceeds the posi
tive dc voltage to its negative input (from high pass and
low pass ?lters).
earphone of the helmet earphones of both the driver
and the passenger after passage through capacitor C36.
65 Here again, the B+ + input to power ampli?er 44 is
bypassed to ground through capacitor C34 to eliminate
Before discussing how the output of comparator 38 is
high frequency electrical spikes or oscillations. The
used, the attenuators 8 and 10 as shown in FIG. 1 will be
ampli?er is also grounded.
11
4,754,486
Now an explanation of how the output of comparator
38 affects operation of the invention. As indicated ear
lier, comparator 38 emits a signal which reduces the
stereo output on both left earphones by approximately
one/half when a party speaks into the microphone to
12
diminished by a factor such that its output is reduced by
approximately one/half the sound previously heard in
the right earphones.
With the above explanation, the operation of the
invention has been described. The only part remaining
is the power supply which supplies the operational
voltages to the circuit. That power supply is shown in
the lower portion of FIG. 2 and firstly is derived by
utilize the intercom system or when a sound greater
than the usual noise level enters the always activated
microphone. At the same time, the output of compara
tor 38 completely cuts off the stereo sounds from the
attachment of terminals 25 and 27 to the positive and
radio or tape cassette player in both right side ear 10 negative terminals respectively of the battery of the
phones where, through a separate yet to be discussed
motorcycle. The positive side is then led to fuse F1 and
electronic network shown in FIG. 2, the speaking voice
then through choke L1. To assure that no negative
or sound greater than noise level received by the micro
spikes are residing on the positive power line, diode D4,
phone is heard by both right earphones being used as an
in line with the current, then passes only the positive
intercom system. As previously discussed, comparator
directed current. The output of diode D4 is directed to
38 has a positive output only when there is suf?cient
energy exiting from the band pass ?lter operational
the input of voltage regulator VR1, an integrated cir
cuit whose output is a regulated 9.8 volts which has
ampli?er 26.
been termed B+ +. The regulated output has two by
pass capacitors attached to it namely, capacitors C41
and C42. From the 9.8 volt B+ + output, resistor R64
At that time, the output level of comparator 38 is
placed upon the base of transistor Q2 situated near the
upper right hand corner of FIG. 2. The output of com
parator 38 is ?rst resistor divided to ground by means of
resistors R54 and R55 with their joinder point con
feeds back to input 1 of VRl and on to parallel ground
combination of R65 and C40. An output of 8.8 volts,
hereinbefore referred to as 3+, is obtained from the 9.8
volt B++ by means of resistor R66. Capacitor C43
nected to the base of transistor Q2 where the emitter of
transistor Q2 is grounded. Upon the appearance of a
25
positive voltage greater than the voltage drop across
the base emitter unction (nominally 0.7 volts), transistor
Q2 will be turned on and thus grounding the collector
connected to the right side output of the stereo radio or
: stereo multiplex player, thus terminating any input into
power ampli?er 44 by reducing it to zero at that point.
The input from the microphone 20 as shown in FIG.
of D4.
The voltage which has been referred to previously as
one/half B+ is obtained through a voltage divider
network shown connecting to the power supply B+
comprising a resistance divider network of R67 and
1 2, is directed to the input of power ampli?er 44 by
directing the output of the band pass ?lter operational
ampli?er 26 through series capacitor C37 and resistor
R61 and then on to both series resistor R60 and capaci
bypasses electrical spikes which might appear on B+.
The negative side from the battery in the motorcycle is
directed to a second choke, L2 and then grounded.
Capacitor C39 then connects the ground of the output
R68, both being equal voltage with the opposite end of
35 resistor R67 connected to the 8.8 volts and resistor R68
grounded. Also, at the central point between resistors
‘ tor C31 and also to the collector of transistor Q3. The
R67 and R68 where the one/half 8+ is obtained is
emitter of Q3 is connected to B+ and the base is con~
connected a bypass capacitor C38. This also establishes
nected to the output of comparator 38 through a resistor
this point as an ac ground point.
divider network comprising resistors R59 and R58, the 40 The following is a parts list of the different elements
. other end of resistor R58 connected to B+. Q3, when
comprising the invention.
"turned on, provides an ac ground to B+ for the output
of operational ampli?er 26 through capacitor C37 and
resistor R16. At most instances, and when there is no
output from comparator 38, transistor Q3 is constantly
was
45
on since the voltage to its base is determined through
the current path from B+ to ground through resistors
R58, R59, R54, and R55. However, when there is an
output from comparator 38, voltage upon the base of Q3
rises and thus turns the transistor off and permitting the 50
audio signal from operational ampli?er 26 to proceed
through resistor R60 and capacitor C31 to the input of
power ampli?er 44 and thus to terminal 21 and on to
both right earphones.
In addition, the output of comparator 38 is also di 55
rected to the base of Q1 which is operably attached to
the input of power ampli?er 42 which powers both left
earphones. When there is a positive output from com
parator 38, transistor Q1 is turned on since its base is
attached to the central point between voltage divider
resistors R48 and R47. At that time, the collector is
grounded through the emitter of transistor Q1 and thus
grounds the junction of resistors R45 and R46 so that
the sole path of the left audio channel from the radio or
tape cassette player is through resistor R44 and is at a 65
level reduced approximately one/half as to when resis
tors R45 and R46 were in parallel with resistor R44 and
not grounded. Thus the input to power ampli?er 42 is
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R1 1
R12
R13
R14
R15
R16
R17
220
1 M
330K
68K
10K
270
27K
33K
10K
10K
lK
220K
10K
27K
33K
10K
1K
R18
330K
R19
R20
R21
R22
R23
R24
R25
R26
R27
R28
R29
R30
lK
10K Pot
47K
82K
22K
33K
10K
10K
330K
1K
10K
47K
'
R36
R37
R38
R39
R40
R41
R42
R43
R44
R45
R46
R47
R48
R49
R50
R51
R52
10K
10K
330K
1K
10K
47K
68
82
22K
4.7K
15K
2.2K
lOK
220
15
47
220
R53
4.7K
R54
R55
R56
R57
R58
R59
R60
R61
R62
R63
R64
R65
10K
2.2K
15K
470K
2.2K
10K
4.7K
4.7K
220
15
220
1.5K
4,754,486
13
R31
R32
R33
R34
R35
33K
470K
220K
39K
R66
R67
R68
R100
47
1K
1K
5K
Capacitors C11 and C16 which are charged up by the
outputs of the band pass ?lter and high and low pass
?lters respectively, are energy storage devices charged
by current from the respective ?lters. As such, the volt
33K
w
Cl
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
1
10
10
.03
.03
4.7
.004
.004
.1
1
10
.0015
.0015
.1
.1
10
10
.1
.1
.1
1
1
.1
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
C24
C25
C26
C27
C28
C29
C30
C31
C32
C33
C34
C35
C36
C37
C38
C39
CA0
C41
C42
C43
ages on the capacitors, which are a function of stored
.01
100
.47
.47
220
1
.1
.1
.01
100
.47
.47
220
1
47
.1
10
.1
470
47
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
uf
electrical energy, are the voltages which are compared
by comparator 38.
10
As mentioned previously, the device is installed and
adjusted by taking a short tour on the motorcycle at a
speed up to the speed of maximum noise interference,
which will nominally be in the area of the speed limit
whereupon the sensitivity adjust, namely feedback re
15 sistor R20 to ampli?er 28, so that the normal usually
noise in the band pass circuit does not exceed in energy
value the noise in the low pass and high pass ?lters.
Once that has been set, it need not be set again. The
20
volume control potentiometer R100 on the microphone
input will have to be adjusted simultaneously in order
that the words spoken into the microphone will exceed
the noise level as adjusted by the sensitivity adjust R20.
Referring now to FIG. 3, a perspective view of a
partial motorcycle driver and passenger, together with
block schematic diagram of the invention is shown. For
ease of drawing, the motorcycle is not shown, however,
the relative positions of the motorcycle driver 82 to the
passenger 84 is shown as they would be sitting on their
respective seats on the motorcycle with the passenger
30 behind the driver; Block 88 shows the container in
which the electronic circuits of the invention are
25
w
D1
D2
D3
D4
14
the negative input to comparator 38 does not present as
formable a challenge to the intercom override.
-continued
1N9l4
1N9l4
1N914
1N9l4
Signal
Signal
Signal
Signal
Power
D5
1N4002
-- Q1
2N4401
NPN Signal
Q2
Q3
Q4
2N4401
2N4403
2N4401
NPN Signal
PNP Signal
NPN Signal
U1
U2
LM324
LM324
Quad op amp
Quad op amp
U3
U4
LM383
LN383
Power amp
Power amp
U5
LM317
Adj regulator
Fl
L1
L2
MISCELLANEOUS
2 Amp
Slow Blow
RFC
Inductor
RFC
Inductor
housed, additionally showing as inputs the left and right
stereo channel from the associated stereo radio receiver
or audio cassette player 86, each channel connecting
35 with the appropriate terminals 17 or 19 as described in
FIG. 2. Shown exiting from block 88 are the wire sets
89 and 87 running to the left earphones 13 and micro
phones 20 of the driver and passenger respectively. As
had been earlier described, the microphone is attached
to the helmet worn by each of the parties and is situated
proximate each respective party’s mouth. The ear
phones are mounted inside the‘helmets, however, for
illustrative purposes, are shown as solid line elements in
Features which have been built into the subject in
FIG. 3. The right earphones (not shown) are on the
vention is the relatively short time in which the VOX 45 opposite side of each helmet and are connected by wir
intercom may be utilized. For example, no resistive
ing in wire sets 99 and 87, crossing over from the left
impediment is placed between the output of the band
pass ?lter, operational ampli?er 26, and the positive
input to comparator 38. Accordingly, capacitor C11
charges rather rapidly to build the necessary voltage to
turn on comparator 38 and quiet the previously existing
stereo sounds and inject the intercom speaking. Simi
larly, the intercom system is‘kept alive for three to four
earphones.
While it is realized that the subject invention has been
presented as an accessory for a motorcycle rider and
passenger, it is apparent that the system may also be
used in other types of noisy environments, such as, for
example, a machine shop area. In this case, the output
could be attached to headsets worn by the employees
seconds after the last word is spoken and no more en
or, a loudspeaker on the wall. Here, only the right chan
ergy is passed by the band pass ?lter to capacitor C11, 55 nel of the system would be utilized since usually an
where resistor R22 controls the discharge rate of capac
nouncement type wall mounted loudspeakers are not
itor C11, the capacitor whose voltage is inputted to the
stereo equipped. In any event, having strategically
positive input of comparator 38. In contrast, the output
placed open microphones around the machine shop
of the combined low pass ?lter and high pass filter is
would permit nearby properties to utilize same and
charged through resistor R31 in series with capacitor
C16, the charging capacitor which supplies the voltage
to the negative input of comparator 38. This allows
60 would broadcast what was said over the din of the
environment.
While a preferred embodiment of the device has been
capacitor C16 to build up more slowly than capacitor
shown and described, it will be understood that there is
C11 so that capacitor C11 will always predominate
no intent to limit the invention by such disclosure, but
when there is energy in the band pass frequency region. 65 rather it is intended to cover all modi?cations and alter
Additionally, the discharging resistor R32 for capacitor
nate constructions falling within the spirit and the scope
C16 is of a greater value than the intercom capacitor
of the invention as de?ned in the appended claims.
C11 discharging resistor, R22. That way, the voltage on
We claim:
15
4,754,486
1. Improvements in a motorcycle stereo audio system
for a motorcycle rider and passenger, the improvements
comprising:
an intercom system adapted to receive a speaking
voice and extraneous audio frequency noise and
output a control signal when the speaking voice
exceeds the extraneous audio frequency noise;
a left attenuator and ampli?er system adapted to re
ceive as an input the left stereo channel of an asso
ciated stereo audio signal and to output the left
stereo channel, said left attenuator and ampli?er
16
said ?rst storage device exceeds the energy stored in
said second storage device.
6. The improvements in a motorcycle stereo audio
system as de?ned in claim 5 further including a plurality
of left hand speakers, said left speakers operably con
nected to said left attenuator and ampli?er system, and
a plurality of right hand speakers, said right hand speak
ers operably attached to said right attenuator and ampli-
?er system whereby the associated stereo audio signal
left stereo channel and right stereo channel output their
audio sounds on the left hand speakers and right hand
system also receiving said intercom system control
speakers respectively.
signal output;
7. The improvements in a motorcycle stereo audio
system as de?ned in claim 6 wherein said intercom
attenuator is operably connected to said intercom sys
a right attenuator and ampli?er system adapted to
receive as an input the right stereo channel of an
associated stereo audio signal and to output the
right stereo channel, said right attenuator and am
pli?er system also receiving said intercom system
control signal output;
an intercom attenuator operably connected to said
right attenuator and ampli?er system, said inter
com attenuator receiving said speaking voice and
control signal output from said intercom system
whereby when the speaking voice exceeds the
extraneous audio frequency noise, said intercom
system control signal output attenuates said left
stereo channel of the associated stereo audio sys
tem band pass ?lter.
8. The improvements in a motorcycle stereo audio
system as de?ned in claim 7 wherein said right attenua
tor and ampli?er system includes means to terminate the
associated stereo audio signal right stereo channel and
said left attenuator and ampli?er system includes means
to attenuate the associated stereo audio signal left stereo
channel, said means to terminate the right stereo chan
nel de?ning means to ground the associated stereo
audio signal right stereo channel and said means to
attenuate the left stereo channel de?ning means to
ground a portion of the associated stereo audio signal
left stereo channel.
tem, terminates the right stereo channel of the
9. The improvements in a motorcycle stereo audio
associated stereo audio system, and inputs said 30 system as de?ned in claim 8 wherein said means to
speaking voice from said intercom attenuator into
terminate the associated stereo audio signal right stereo
the right attenuator and ampli?er system to output
channel de?nes a ?rst transistor, said transistor receiv
said speaking voice.
ing the output control signal of said comparator, and
2. The improvements in a motorcycle stereo audio
said means to ground a portion of the associated stereo
system as de?ned in claim 1 wherein said intercom
audio signal left stereo channel de?nes a second transis
system further includes a plurality of microphones to
tor, said second transistor also receiving said compara
convert the speaking voice and extraneous audio fre
tor output control signal whereby when said compara
quency sounds to electrical signals, a preampli?er oper
tor outputs its control signal, said first transistor
ably attached to said microphones, and a plurality of
grounds said right stereo channel and said second tran
?lters operably connected to said preampli?er, said 40 sistor grounds a portion of the left stereo channel and
?lters adapted to segregate the speaking voice signals
thereby attenuates it.
from the extraneous audio frequency noise signals.
10. The improvements in a motorcycle stereo audio
3. The improvements in a motorcycle stereo audio
system as de?ned in claim 9 wherein said intercom
system as de?ned in claim 2 wherein said plurality of
attenuator includes means to permit input of said speak
?lters includes a band pass ?lter adapted to segregate 45 ing voice into said right attenuator and ampli?er sys
the speaking voice signals, and a high pass ?lter and low
tem, said means to permit de?ning a third transistor,
pass ?lter to segregate the extraneous audio frequency
said third transistor operably connected to said compar
noise signals.
ator control signal output and said right attenuator and
4. The improvements in a motorcycle stereo audio
ampli?er system whereby when said comparator out
system as de?ned in claim 3 wherein said intercom
puts its control signal, said third transistor permits the
system further includes a recti?er and ?rst energy stor
input of said speaking voice into said right attenuator
age device operably connected to said band pass ?lter to
and ampli?er system for the duration of said control
rectify and store the energy content of the speaking
signal.
voice electrical signals, and a recti?er/mixer and sec
11. The improvements in a motorcycle stereo audio
ond energy storage device operably connected to said
system as de?ned in claim 10 wherein said intercom
high pass ?lter and said low pass ?lter, said recti?er/
system further includes means to delay restoration of
mixer receiving the extraneous audio frequency noise
the associated stereo audio signal left stereo channel and
signals, summing them, rectifying them, and storing the
restoration of the associated stereo audio signal right
energy content of the extraneous audio frequency noise
stereo channel for a set period of time following the
signals.
termination of said speaking voice, said means de?ning
5. The improvements in a motorcycle stereo audio
a discharge resistor operably attached to said ?rst en
system as de?ned in claim 4 wherein said intercom
ergy storage device whereby there will be a delay after
system still further includes a comparator, said compar
the termination of said speaking voice before the associ
ator operably connected to said recti?er and ?rst en
ated stereo audio signals are fully restored in order that
ergy storage device and said recti?er/mixer and second 65 there may be further speaking voices if desired.
energy storing device to compare the energy stored on
12. The improvements in a motorcycle stereo audio
each respective storage device, said comparator operat
ing to output a control signal when the energy stored in
system as de?ned in claim 11 wherein said intercom
system further including means to resist the restoration
4,754,486
.
17
18
of the associated stereo audio signals following termina
tion of said speaking voice, said means including a resis
tor operably connected to said second energy storage
device, said resistor in line with said second energy
storage device whereby signals to charge said second
500 hz and a second RC active operational ampli?er
?lter adapted to cut off signals having a frequency
greater than 4 khz; said high pass ?lter is an active
operational ampli?er ?lter; and said low pass ?lter is an
energy storage device to overcome said ?rst energy
17. The improvements in a motorcycle stereo audio
system as de?ned in claim 16 wherein said recti?er/
active operational ampli?er ?lter.
storage device at said comparator are resisted by said
resistor.
13. The improvements in a motorcycle stereo audio
system as de?ned in claim 12 wherein said recti?er
mixer includes a ?rst ?xed gain ampli?er and ?rst diode,
said ?rst ?xed gain ampli?er connected to said high pass
?lter and outputting electrical signals having frequen
cies greater than 6 khz to said ?rst diode, said ?rst diode
then outputting a high frequency half wave recti?ed
signal, and a second ?xed gain ampli?er and second
diode, said second ampli?er operably attached to said
includes means to sensitize the operation of said com
parator, said means to sensitize including a variable gain
feedback ampli?er operably connected between said
band pass ?lter and said ?rst energy storage device, said
means to sensitize de?ning a variable resistor operably
attached to said ampli?er feedback whereby said vari
able resistor varies the gain of said ampli?er to reduce
low pass ?lter and outputting electrical signals having
frequencies less than 200 hz to said second diode, said
second diode then outputting a low frequency half
wave recti?ed signal, both said high frequency half
or increase the band pass ?lter output to said ?rst en
wave recti?ed signal and said low frequency half wave
ergy storage device and thereby sensitize the operation
of said comparator.
'
20 recti?ed signal summed and directed to said second
energy storage device, and said second energy storage
device comprises a capacitor.
18. The improvements in a motorcycle stereo audio
14. The improvements in a motorcycle stereo audio
system as de?ned in claim 13 wherein said left hand
speakers and right hand speakers respectively comprise
left earphones and right earphones respectively.
system as de?ned in claim 17 wherein said left attenua
15. The improvements in a motorcycle stereo audio 25 tor and ampli?er system comprises means to increase
the resistance to the passage of said left stereo channel,
system as de?ned in claim 14 wherein said band pass
said means of resistance including paralleled resistors,
?lter is comprised of resistors and capacitors to pass
one parallel leg of which may be grounded in order that
signals having frequencies in the range of 500 hz to 4
the left stereo channel must go through said other paral
khz, said low pass ?lter is comprised of resistors and
capacitors to pass signals having a frequency less than 30 lel resistor and thus have its resistance to flow increased
whereby when one of said parallel resistors is grounded,
200 hz, and said high pass ?lter is comprised of resistors
the signal to the ampli?er is reduced thereby reducing
and capacitors to pass signals having a frequency
the output in said left speaker.
greater than 6 khz.
19. The improvements in a motorcycle stereo audio
16. The improvements in a motorcycle stereo audio
system as defined in claim 15 wherein said band pass 35 system as de?ned in claim 18 wherein said second en
ergy storage device comprises a capacitor.
?lter is a high pass active operational ampli?er ?lter
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adapted to pass signals having a frequency greater than
50
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