Binaural sound pickup

A binaural sound pickup assembly composed of a hollow cone-like member made of plastic resin and having a flange member on its rear portion on the larger diameter portion of the cone-like member and with a pair of microphones mounted by mounting means at both sides of the cone-like member adjacent the flange member and wherein the hollow cone-like member simulates the acoustic characteristics of a human head but which does not give the physical appearance of a human head.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates in general to sound pickup assembly means and more 
particularly to a novel sound pickup assembly for use in a binaural sound 
recording system. 
2. Description of the Prior Art 
It has been well known to have a binaural recording system for stereophonic 
recording. Such systems are effective for the use of headphones in the 
reproduction and the listener feels as if he is present in the concert 
hall due to the favorable acoustic characteristics. 
It has been known in the prior art to have stethoscope type devices in 
which a pair of microphone units are respectively attached to an arcuate 
resilient pipe at the opposite ends and a pair of projections are attached 
to the microphone units for inserting the ends of the pipe into the 
listener's auditory canals. An output is supplied from the center of the 
resilient pipe. However, since this device is used for sound pickup by 
being directly attached to human ears after a long time during which sound 
pickup occurs the user experiences pain because of the attachment of the 
device to his head. Also, with such device when the human head is moved 
very much the picked up sound can be distorted and appear unnatural. 
For the above reasons a dummy head imitating a human head is normally used 
in binaural recording systems. Such prior art dummy heads are quite 
similar in shape to a human head having a human face and persons sitting 
in the audience as, for example, in a concert who observe such dummy 
pickups are unpleasantly affected by such devices. For example if a number 
of such dummy heads similar to human faces or heads are disposed in a 
concert hall or the like the entire atmosphere of the hall becomes 
unpleasant for human listeners present at the concert and, thus, the 
appreciation of the music is decreased for the persons present at the 
concert. 
It has also been proposed in the prior art to provide a dummy head having 
dummy external ears attached to a cubical shaped box which is not similar 
to a human head or face. However, in dummy pickups of this type, the 
reproduction does not give the sense of direction and distance which is 
desireable in stereophonic binaural sound pickup devices. 
SUMMARY OF THE INVENTION 
A binaural sound pickup assembly according to this invention comprising a 
cone-like member with a projection portion provided at the rear portion of 
the cone-like member and mounting means for holding right and left 
microphones which are located in front of the projection portion. 
An object of the invention is to provide a novel binaural sound pickup 
assembly which has the characteristics of a human head but which does not 
give the appearance to a viewer as a human head. 
It is another object of this invention to provide a binaural sound pickup 
assembly which has the same characteristics as would be obtained if the 
binaural sound recording was made using a dummy head similar to a human 
head and face but wherein the pickup device of the present invention does 
not give the appearance of a human face and head. 
It is a further object of this invention to provide a binaural sound pickup 
assembly such that the microphones can be correctly located opposite to a 
sound source so as to obtain accurate binaural sound recordings. 
It is a further object of the invention to provide a binaural sound pickup 
assembly which is light in weight and can be easily handled so that 
binaural sound recordings can be simply performed even by amateurs. 
It is still a further object of the invention to provide a binaural sound 
pickup assembly in which an acoustic damping member is provided at a 
projection portion of a cone-like member so that unnecessary sound 
relfections may be effectively eliminated. 
It is yet another object of this invention to provide a binaural sound 
pickup assembly in which the mounting position of microphones can be 
freely adjusted so as to coincide with the distance between the ears of a 
user for accurate reproduction. 
Other objects, features and advantages of the invention will be readily 
apparent from the following description of certain preferred embodiments 
thereof taken in conjunction with the accompanying drawings although 
variations and modifications may be effected without departing from the 
spirit and scope of the novel concepts of the disclosure and in which:

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1, 2 and 3 illustrate a first embodiment of the invention and 
comprise a binaural sound pickup assembly 1 which serves as a dummy head 
according to the invention and is comprised of a first truncated cone 
shaped member 2 having a rear large diameter portion and a forward small 
diameter portion. A disc shaped back member 3 forms a flange on the rear 
end surface of the first member 2 at its large diameter. The binaural 
sound pickup assembly 1 may be formed of, for example plastic resin and 
the first member 2 will normally be hollow. The second disc shape member 3 
is mounted to the first member 2 so as to cover the rear opening of the 
large diameter portion of the first member 2. As shown in FIG. 2, 
bilateral microphone mounting means 5 and 6 are provided near the 
flange-like second member 3 on a horizontal line passing through the 
center of the rear large diameter portion of the member 2. 
FIG. 3 is an enlarged sectional view illustrating the microphone mounting 
means 5 which is comprised of a receiving portion 7 provided on the 
cone-like first member 2 and the extending receiving portion 7 has an 
outer curve surface against which a microphone can be received. A plate 
member 8 is formed with an opening through which a screw or bolt 9 extends 
which is threadedly received in an opening formed in the cone-like member 
2. Thus, the right and left microphones 10 and 11 can be attached to the 
conical member 2 by adjusting the screw 9 so as to move the plate 8 to 
clamp the microphones in place. 
Acoustical damping members 13 and 14 which may be made of rubber are 
attached to the flange-like second member 3 adjacent the microphones 10 
and 11. The microphones 10 and 11 are mounted to the mounting means 5 and 
6 so that their vibrating plates face the second member 3. The acoustic 
damping members 13 and 14 may also extend about the entire periphery of 
the second member 3 and be formed in a ring shape if desired. 
As shown in FIG. 2, the binaural sound pickup assembly 1 is supported by a 
base stand 15 and the height of the pickup assembly 1 may be adjusted by 
moving it upwardly and downwardly on the supporting post of the stand 15. 
Under normal operating conditions the small diameter portion of the cone 
is pointed toward a sound source and the correct sound pickup will occur. 
Since generally the right and left microphones are adapted to pick up 
sounds reflected from the flange-like second member 3 or direct sounds 
from the exterior periphery thereof, the second member 3 acts like human 
external ears and, hence, the binaural sound pickup operation can be 
obtained with good characteristics. Also since the second member 3 is 
provided with acoustic damping members, it will resemble the 
characteristic of human external ears more accurately. This has been 
verified by data taken in experiments which will be described later. 
FIGS. 4 and 5 illustrate a modified example of the invention of a binaural 
sound pickup assembly 100. A cone-shaped first member 102 is composed of a 
front portion 102a which is formed in a tapering manner and has its front 
end surface closed. The front portion 102a mates with a larger truncated 
conical shape member 102b which has a front opening smaller in diameter 
than the rear opening of the front portion 102a. Member 102b has a larger 
rear opening which is received in a third tapered truncated conical rear 
portion 102c which has a front opening smaller than the rear opening of 
the intermediate portion 102b such that the portions 102a, 102b and 102c 
can be respectively telescoped together to form a relatively flat unit or 
can be telescoped outwardly to the position shown in FIG. 4 for operation. 
The rear portion of portion 102c is attached to a disc 106 which has a 
larger diameter than the outer diameter of the rear portion 102c. The 
exterior peripheral face portion extends from the peripheral surface of 
the rear portion 102c and forms a collar-shaped second member 103 upon 
whose front surface facing the member 102 is attached acoustic damping 
material 105. A pair of pivoting arm plates 107a and 107b are pivotally 
attached to the center of the member 103 and have ends C-shaped members 
107c and 107d which are slidably mounted adjacent the surface 105. 
Mounting means 114 and 115 are respectively connected to the ends 107c and 
107d for mounting microphones 111 and 112. 
The arm plates 107a and 107b can be pivotally moved to different positions 
so that the positions of the microphones 111 and 112 relative to the 
cone-shaped first member 102 can be freely adjusted from the horizontal 
position in the upper and lower directions as shown in dotted line in FIG. 
5. This allows the distance between the microphones 111 and 112 to be 
adjusted as desired. In the embodiment illustrated in FIGS. 4 and 5 the 
front portions 102a and intermediate portion 102b can be telescoped back 
into the rear portion 102c as shown in dotted line in FIG. 4 to 
substantially reduce the size of the unit when in its stored condition so 
that the unit can be easily transported. 
FIGS. 6 and 7 illustrate a further modification of the invention comprising 
an assembly composed of a front balloon-like inflatable hollow member 208 
formed as an expansible conical-shaped member. The first member 208 is 
attached at its rear surface to a disc 209 which has a diameter larger 
than the outer diameter of the rear portion of member 208 such that its 
outer peipheral face portion projects beyond the peripheral surface of the 
first member 208 to form a flange-like second member 202 which as an 
acoustical dampling member 205 attached to its front surface. The disc 209 
is provided at the center of its rear surface with an air inflating and 
deflating pipe 210 for the first member 208 into which a removable plug 
213 is received to allow inflation and deflation of the member 208. 
Arcuate slots 211a and 211b are formed in the member 209 and a pair of 
pivoted arm plates 212a and 212b are pivotally attached to the center of 
the disc 209 and have tip portions 212c and 212d which extend through the 
slots 211a and b respectively to the front side of the disc member 203. 
Mounting means 204a and 204b for microphones 203a and 203b are, 
respectively, formed on the ends of arms 212a and 212b, respectively. In 
this example, when the assembly 200 is not used the plug 213 is removed 
from the pipe 210 to allow the hollow member 208 to be deflated so that it 
assumes the dotted shape illustrated in FIG. 6 and the unit takes up very 
little space. When the device is to be used, the plug 213 is removed and 
air is supplied into the member 208 to inflate it to the solid line 
position illustrated in FIG. 6 and the plug 213 is inserted into the air 
tube 210. 
In the embodiments described above, if the collar portion of the extending 
disc on the back of the conical shape front portions are made of an 
acoustic damping material such as rubber it is not necessary to attach a 
separate acoustic damping member to the front face thereof. 
Acoustical experiments have been conducted with the invention during which 
the orientation of a sound image when the sound pickup assembly or dummy 
head is used as well as when an actual human head is used. As illustrated 
in FIG. 1, dummy heads of six different types were used in the experiments 
with the lengths H of the first members being either 100, 150 or 200 mm. 
The diameters D of the collar member were either 240 or 260 mm. In 
addition, as a human head two kinds were used, one being a male head M and 
the other a female head W. A drum was used as a sound source and beaten 
four times each second. Seven directions were selected among twelve 
directions at every 30.degree. relative to the sound source. Thus, a sound 
pickup operation occurs from each of the above selected directions by 
right and left microphones mounted on each dummy head and each human head 
so as to record the picked up sound on a magnetic tape of a recording 
apparatus. Further, a recording operation is carried out similarly as 
described above by means of a dummy head (as shown in FIG. 1) wherein the 
length H of its cone-shaped first member and the diameter D of its 
collar-shaped second member are respectively fixed at 100 mm and 240 mm in 
the cases when the microphones are arranged horizontal and also when they 
are shifted above and below repectively by 30 .degree.. 
The magnetic tape recorded as described above is produced with a suitable 
machine to produce a sound signal which is furnished to a listener 
listening with a headphone. In these circumstances, the listener imagines 
himself to be located at the center of a clock and indicates the positions 
of the hour and minute hands as he listens to the movement of the 
reproduced sound signal and these indications by the listener are recorded 
on a data sheet. After the recorded sound signals have all been reproduced 
and listened to, the contents of the data sheet are compared with the 
recording positions so as to obtain data with respect to the following 
three experimental research items. 
A. Rate of correct answers: A rate (%) of correctly decided direction of 
sound source in which an error within .+-. 30.degree. is permitted. 
B. The appearance rate of unnatural sound images: a rate (%) of appearance 
of unnecessary sound images such that the location of sound is unclear a 
sound image enters into a head, a sound is heard from the upper direction 
and the like. 
C. The rate of misjudging at front and rear sides: The rate (%) of making 
symmetrical misjudgments with respect to a line connecting both ears (such 
as in a case of 1 and 5 o'clock or 10 and 8 o'clock with the front being 
assumed as 12 o'clock), wherein an error within .+-.30.degree. is allowed. 
The results shown in graph A, B and C of FIG. 8 were obtained as the 
average values and standard variations of the respective experimental 
items described above. 
It will be understood that the sound pickup by actual use of a human head 
has good results as compared with a dummy head, but the dummy head with 
the length H of its first member being as 200 mm and the diameter D of its 
second member as 240 mm is almost the same in operation as the human head. 
FIG. 9A shows the relationship between directions of sound sources picked 
up by human heads and listener's indicating directions, and FIG. 9B shows 
the relationship between directions of sound source picked up by two kinds 
of dummy heads having the lengths H of the first member and the diameters 
D of the second member being set as 200 and 240 mm and 150 and 240 mm and 
listener's indicating directions. That is, FIG. 9A is the case where human 
heads are used, while FIG. 9B is the case where dummy heads are used. In 
each figure, abscissa indicates actual direction of a sound source and 
ordinate indicated direction indicated by a listener with an original 
point (0.degree.) being set as the front. A 45 -line from the original 
point (0.degree.) is made as a correct answer reference line a and lines 
intersecting the correct answer reference line a at right angles 
respectively at points of 90.degree. and 270 .degree. are made as front 
and rear misjudging reference lines b. 
In these graphs, if the indication number of a listener is expressed by the 
size of a circle, the sound pickup indication conditions at the human head 
and the dummy head exhibit the same tendency. If an indication error of 
.+-. 30.degree. is allowed at each of the correct answer reference line a 
and front and rear misjudging reference lines b, it will be noticed that 
most of the data are included in a correct answer area and front and rear 
misjudging areas. Furthermore, it will be seen that the possibility is 
high for lateral sound sources to be judged as lateral (90.degree. and 
270.degree.) and that there is a possibility which is high for misjudgment 
of sound from the front 0.degree. or from behind 180 .degree.. However, 
the possibility is quite small that a sound from the rear 180.degree. will 
be misinterpreted as being from the front 0.degree.. The above mentioned 
sound pickup assembly in each embodiment was formed as a truncated cone 
shaped but the same result is obtained even with a convex shape such as a 
hemisphere. When the sound pickup assembly is formed to be conical shaped 
as in the above described embodiments, there is an advantage in that the 
orientation can be correctly established. 
As described above, according to this invention with the simple 
construction of a dummy head in combination with a conical shaped first 
member and a collar shaped second member it is possible to obtain the same 
sound pickup effects as the case where a human head is used for binaural 
sound pickup and hence the device is very practical. Furthermore since the 
dummy head is not unnecessarily moved as occurs with a human head the 
sound pickup can be carried out in a stable state for long periods of time 
and the binaural sound pickup of natural sounds is possible. 
While the principles of the invention have been described in connection 
with specific embodiments and particular modifications thereof it is to be 
clearly understood that this description is made only by way of example 
and not as a limitation on the scope of the invention as defined by the 
appended claims.