US2159533A - Recording system - Google Patents

Description

May 23, 1939. c. RAYMENT 2,15 33 RECORDING SYSTEM FiledJan. 27, 1936 2 Sheets-Sheet l 191. mm AMPLXIFIER INVENTOR,

LYNDON C. RAYMENT.

May 23, 1939. c. RAYMENT RECORDING SYSTEM Filed Jan. 27, 1936 2 Sheets-Sheet 2 INVENTOR,

LYNDON c. RA YMENTI ATTORNEYS.

Patented May 23, 1939 UNITED STATES PATENT OFFICE 3 Claims.

My invention relates to a recording system, and more particularly to a means and method of recording body movements.

My system is particularly adapted for the reproduction of amplified heart sounds and may thus be termed, in one embodiment of its use, an electrical stethoscope. It is, however, adapted for recording and reproducing amplified signals corresponding to the movements or vibrations in other bodies, either animate or inanimate. As a typical illustration of my system, I shall describe it as set up for the recording and reproduction, in amplified form, of heart sounds.

Broadly, my invention comprises a microphone adapted to respond to body movements, an amplifier, a translating and recording device, and, in many instances, a sound reproducer so located as to allow the operator of the microphone to listen, at the same time that graphs are being made on the recorder.

Inasmuch as bodily vibrations are usually of relatively low power, and extremely large amplification factors are needed in order that either satisfactory sound reproduction be obtained or a proper graph recorded, there is always a tendency for the output of the system to react through the medium of the air in a room, for example, with the microphone and thus cause howling, as is well known in the telephone art. Furthermore, the recorders needed for this type of work are necessarily delicate and capable of responding to fine variations in energy, and would easily be ruined by the application of overloads such as might occur, for example, if a microphone were dropped, if loud sounds reached the microphone, or if any similar extraneous vibration energized the system during or between the actual recording of the movements desired.

It is, therefore, the main object of my invention to provide a system for recording or reproducing bodily movements wherein the system is energized or rendered responsive only when the microphone is applied in proper position to receive energy from the movements to be recorded, and in addition, to provide means for preventing sounds or other extraneous vibrations from reaching the microphone during the actual recording period.

My invention possesses numerous other objects and features of advantage, some of which, together with the foregoing, will be set forth in the following description of specific apparatus embodying and utilizing my novel method. It is, therefore, to be understood that my method is applicable to other apparatus, and that I do not (Cl. 18l24) limit myself, in any way. to the apparatus of the present application, as I may adopt various other apparatus embodiments, utilizing the method, within the scope of the appended claims.

Other objects of my invention may be more 5 fully understood by reference to the drawings, in which:

Figure l is a diagrammatic view of a complete recording and reproducing system, as adapted for the recording of heart sounds.

Figure 2 is a longitudinal sectional view of one preferred form of microphone.

Figure 3 is a view partly in section and partly in elevation of a preferred recording device.

Figure 4 is a view partly in section and partly in elevation, showing the moving coil suspension used in the microphones shown in Figure 2.

Figure 5 is a graph, reproducing an actual record as taken by the recording system shown in Figure 1.

Referring directly to Figure 1, a patient I whose heart sounds it is desired to record, has placed thereon a microphone assembly 2 in the proper position to receive movements within the body corresponding to the so-called heart sounds".

The output of the microphone 2 is led through an amplifier 3, and the output of the amplifier is then passed to a recording assembly 4, there. preferably being a sound reproducer or loud speaker 5 in parallel with the recorder so'that the operator of the system may listen to the results obtained by the application of the microphone to the patient.

It will thus be seen that it is probable, and indeed quite preferable, that both the recording system 4 and the loud speaker 5 be within the same room as the microphone 2 and the patient. There will never be danger of reaction between the loud speaker 5 and the microphone 2 at any time when the responsive element of microphone is shielded from sound vibrations within the room.

It is also obvious that any heavy sound vibrations within the room would, if the responsive element of microphone 2 be exposed to them, cause large output currents within the amplifier, with a consequent tendency of overloading the recording device. I have, therefore, provided a special type of microphone, two particular embodiments being shown, one in Figure 2 and one in Figure 4. The embodiment shown in Figure 2 will be discussed first.

As I prefer to utilize a velocity-responsive microphone, my vibration-translating device is built as an electrodynamic microphone having a case 6, a central pole piece I and a top plate 8, all cooperating to form a magnetic path broken by an annular air gap 9. The air gap is energized by magnetization of the case, top plate and central pole piece by current passed through field coil I0, through leads H from a source 12, as shown in Figure 1.

An annular moving coil l3, mounted on a frame I4, is positioned in the air gap and is maintained therein by a plurality of arms l5, forming a spider, as shown in Figure 5. Leads I 6 to the moving coil are conveniently brought out along two of the spider arms.

The moving coil is provided with a pyramidal connection H which terminates normally without touching a diaphragm I8, preferably nonresilient but supported from the casing by an annular resilient ring I 9. Outside the diaphragm and resilient ring is positioned a guard 20, preferably of soft rubber.

The recorder shown in Figure 3 is conventional and forms no part of the instant invention. It is in effect an electrodynamic reproducer similar to the microphone, all parts being numbered as the microphone except that the central connection I! is provided with a bearing 2i engaging the end of a recording arm 22 pivoted on a support 23, the end of the bearing arm carrying a recording point 24 touching a chart 25 near the periphery thereof, the chart in turn being mounted on a turntable 26 driven by a motor 21 through proper gears 28.

With the microphone described, the action of the recording system is as follows: The amplifier and fields of the microphone and recorder are energized but no recording will take place due to the fact that the connection ll does not touch diaphragm IS. The recorder system as a whole is therefore not responsive in any manher, even to large noises in the operating room, nor can there be any air reaction because vibrations of diaphragm i8 will not be transmitted to the moving coil.

The operator then positions the microphone on the chest of the patient, as shown in Figure 1, the guard 20 first coming in contact with the body all around the microphone. Thereafter a gentle pressure upon the microphone case pushes the flesh in contact with the diaphragm I8, and further pressure pushes the diaphragm in contact with the central connection l7. Immediately this latter contact takes place, the entire system becomes responsive to any movements transmitted from the body to the diaphragm, as the moving coil i3 will be moved in synchronism with the movements of the diaphragm l8. Current will be generated; this current will be amplified and passed on to the loud speaker 5 through which the heart sounds may be heard.

When the operator deems it proper, he sets in motion the turntable 26 with its chart, and the motion of the recording arm 22 will cause a graph 29 to be recorded on the chart The operator may talk, or other extraneous noises may take place in the operating room, but no part of this sound will reach the micro-phone because of the guard 25]. In addition, during the recording period, the sounds from the loud speaker 5 will not cause reaction, for the same reason.

Immediately the microphone is lifted from the patient, the resiliency of the annular ring ll causes the diaphragm l8 to break connection with the moving coil, and the whole system ceases to respond as there will be no input, even though the diaphragm I8 is energized.

Small variations in pressure on the microphone assembly 2 are unimportant because the moving coil type of microphone is velocity-sensitive and, therefore, within a relatively large range, it makes no difference whether the moving coll I3 is operating in exactly the same position in the air gap. It is not necessary, however, for the operator to definitely hold the microphone in place at all times, for when the patient is lying down, as shown in Figure 1, the micro phone itself may be made of such weight as to provide the proper pressure to maintain the device responsive.

I have found with a system of the sort described, wherein the initial input device is shielded from extraneous vibrations during recording and rendered ineffective between recordings, that I am able to obtain graphs with utmost accuracy; and, more important, these graphs are reproducible either on the same machine after a lapse of time, or on machines built to the same specifications and having the same constants, thus allowing direct comparison of graphs without the necessity of obscure interpolation factors due to a large number of variables.

I claim:

1. In combination with an amplifier and an output circuit including a sound reproducer, an input device comprising a casing containing an exposed contact diaphragm movable in response to movements of an object when applied thereto, and an internal microphone normally disconnected from said diaphragm, a sound-excluding barrier around the periphery of said diaphragm so arranged as to exclude sound from said diaphragm when said surface is applied to said object, said microphone being so positioned with relation to said diaphragm that the pressure of application of said surface to said object will move said diaphragm to connect said microphone thereto.

2. An input device comprising a casing containing an exposed contact member movable in response to movements of an object when applied thereto, and an internal microphone having an actuating member extending toward said contact member and terminating to leave a gap therebetween, a sound excluding barrier around the periphery of said contact member so ar-'.

ranged as to exclude said sound from said contact member when said contact member is applied to said object, whereby pressure applied to said casing forcing said barrier against said object will cause said contact member to move, closing the gap and connecting said contact member to said actuating member.

3. An input device comprising a casing containing a diaphragm movable in response to movements of an object when said diaphragm is applied thereto, a microphone within said casing, said microphone being normally disconnected from said diaphragm, the discontinuity being of such an amount that when pressure is applied to said casing, forcing said diaphragm against said object, that said diaphragm will be connected to said microphone.

LYNDON C. RAYMENT.

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