1、MIL-M-238 13A(SHIPS) 21 December 1964 SUPERSEDING MIL -M- 238 1 3(SHIPS) 12 December 1963 (See 6.4) MILITARY SPECIFICATION MICROPHONES, INTERCOMMUNICATION AND ANNOUNCING SYSTEMS, NAVAL SHIPBOARD v . _- 1. SCOPE 1.1 Scope.- This specification covers microphones designed for use in intercommunication
2、and announcing systems aboard Naval ships. The microphones are noise canceling types suitable for use in noisy areas. 1.2 Classification.- Microphones shall be of the following types, as specified (see 6.2): Type Ml24/SIC - Hand held, equipped with 18 inch length of MCOS-5 cable and six pin connecto
3、r (replace- M125/SIC - Hand held, equipped with 120 inch coil cord and six pin connector (replacement for types M132/SIC - Hand held, equipped with 120 inch coil cord and six pin connector.(replacement for type M13l/WIC - Hand held, equipped with 120 inch coil cord and ten pin connector (replacement
4、 for type ment for type IC/MPM-3). IC/MPM-6 and M-l14/U). IC/MPM-4). M - 106/U). 2. APPLICABLE DOCUMENTS 2.1 The following documents, of the issue in effect on date of invitation for bids or request for proposal, form a part of the specification to the extent specified herein. SPEC1 FICATIONS FEDERA
5、L QQ-N-281 QQ-B-750 - Nickel-Copper-Alloy (Monel and R-Monel) Bars, Plates, Rods, Sheets, Strips, - Bronze, Phosphor, Bar, Plate, Rod, Sheet, Strip, Flat Wire and Structural Wire, Forgings, and Structural and Special Shaped Sections. and Special Shaped Sections. MILITARY MIL-1-631 MIL-S-901 MIL-C;91
6、5 MIL-1-983 MIL-Cl10544 - Connector, Plug and Receptacle, Electrical, Audio, Waterproof, Ten Contact, MIL-E- 17555 - Electronic and Electrical Equipment and Associated Repair Parts, Preparation MIL-E-21981 - Electronics Type Designations, Identification Plates and Markings, Requirements - Insulation
7、, Electrical, Synthetic-Resin Composition - Shock Tests, H.I. (High-Impact); Shipboard Machin Prigid. ry, Equipment and Systems, Requirements For. - Cable, Cord and Wire Electrical (Shipboard Use). - Interior Communication Equipment, Naval Shipboard, Basic Design Requirements For. Polarized. for Del
8、ivery of. For. STANDARDS MILITARY MIL-STD-105 - Sampling Procedures and Tables for Inspection by Attributes. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-M- 238 13A(SHIPS) DRAWINGS BUREAU OF SHIPS 9000-S6502-74117 - Microphone, Plug and Recept
9、acle. (Copies of specifications, standards, drawings, and publications required by suppliers in connection with specific procurement functions should be obtained from the procuring activity or as directed by the contracting officer .) 2.2 Other publications.- The following documents form a part of t
10、his specification to the extent specified herein. Unless otherwise indicated, the issue in effect on date of invitation for bids or request for proposal shall apply. OFFICIAL CLASSIFICATION COMMITTEE Uniform Freight Classification Rules. (Application for copies should be addressed to Official Classi
11、fication Committee, 1 Park Avenue at 33rd Street, New York 16, New York.) AMERICAN STANDARDS ASSOCIATION (ASA) Z24.8-1949 - Laboratory Standard Pressure Microphones, Specification For. S1.6-1960 - Acoustical Measurements, Preferred Frequencies For. (Application for copies should be addressed to the
12、American Standards Association, 10 East 40th Street, (Technical society and technical association specifications and standards are generally available for New York 16, New York.) reference from libraries. They are also distributed among technical groups and using Federal agencies.) 3. REQUIREMENTS 3
13、.1 Preproduction sample.- Prior to beginning production two samples shall be tested as specified in 4.2 (see 6.3 and 6.3.1). 3.2 Description.- Microphones shall be hand held types. Each microphone shall consist of either a dynamic or magnetic element and a press-to-talk switch housed in a plastic ca
14、se with a microphone cable and connector attached as specified herein. Unless otherwise specified (see 6.2), a microphone holder assembly as specified in 3.11 shall be furnished with each microphone. 3.3 General Features.- In addition to the requirements specified herein, the microphones shall be in
15、 accordance with the following paragraphs of MIL-1-983. Whenever a requirement of MIL-1-983 conflicts with a requirement of this specification, the requirement of this specification shall govern: Fungus - inert materials Toxic materials wood Metals Protection against corrosion Rounded corners and ed
16、ges Drilled and tapped holes Extended storage Gunblast (see 3.12.13) Shock, vibration and inclination (see 3.12.15 and 3.12.16) Soldering Workmanship and general examination 3.4 Form factor.- The general configuration of the microphone case shall be such that it fits well in the hand. The microphone
17、 case shall fit and lock into the microphone holder assembly specified in 3.11. 3.5 Plastic material.- The plastic material used in making the microphone case shall be of such quality that it will withstand all of the tests specified herein without evidence of physical damage. Plastic material shall
18、 be black, 2 * .*=- -3 _ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-M-238L3A 58 777770b 0352572 7 MIL-M-23813A(SHIPS) 3.6 Replaceable parts.- The microphone design shall allow easy replacement of the press-to-talk switch and the microphone c
19、able. 3.7 Cables and connector plugs.- Microphones shall be equipped with cables and connectors as specified in 3.7.1 through 3.7.3. The cable shall be secured by a clamp in the microphone case to prevent strain on the microphone electrical terminals. 3.7.1 Microphone type M124/SIC.- The type M124/S
20、IC microphone shall be equipped with an 18-inch length of type MCOS-5 cable in accordance with MIL-C-915 and a microphone connector plug of the type shown on Drawing 9000-S6502-74117. 3.7.2 Microphone types M125/SIC and M132/SIC.- Type M125/SIC and M132/SIC microphones shall be equipped with a 120-i
21、nch length (extended) of retractable cordage conforming to the general requirements of MIL-C-915 for MCOS-5 cable, except that it shall be coiled. (Koiled Kords, Inc., type 4230, or equivalent is considered acceptable.) Type M125/SIC and M132/SIC microphohes shall also be provided with a micro- phon
22、e connector plug of the type shown on Drawing 9000-56502-74117. cable of the type specified in 3.7.2 and a type U-77/U microphone connector plug in accordance with MIL-C- 10544. 3.7.3 Microphone type M131/WIC.- The type M131/WIC microphone shall be equipped with a microphone 3.8 Press-to-talk switch
23、.- The press-to-talk switch shall be a positive action double pole single throw switch and shall be capable of closing the control circuit when actuated. It shall be mounted in such a manner that the pushbutton is at the top of the microphone. The electrical circuit of microphone types M124/SIC and
24、M125/SIC shall be in accordance with figure 2. The electrical circuit of microphone type M131/WIC shall be as shown on figure 3. phone, cord, and plug with all garts named for rapid and easy identification, shall be supplied with each micro- phone. 3.9 Electrical circuit.- The electrical circuit of
25、microphone type M132/SIC shall conform to figure 1. 3.10 Wiring diagram.- A printed card, tag, or label showing a schematic wiring diagram of the micro- 3.11 Microphone holder assembly, type MT-3400/SIC .- Each microphone holder assembly shall be assembled in accordance with figure 4 from the follow
26、ing individual parts: (a) Microphone clamp.- One microphone clamp as shown on figure 5 made of annealed cold rolled Monel with satin finish in accordance with QQ-N-281. (b) Spring.- One spring as shown on figure 6 made of phosphor bronze material in accordance with QQ-B-750 and nickel plated or of c
27、opper-nickel-alloy material in accordance with QQ-N-281. (c) C a loudspeaker driver unit is mounted behind the head and coupled to the lips by a 3/4 inch diameter tube. This head shall be mounted on a clothed dummy resembling the upper part of the human torso in its acoustic properties ,) large to c
28、ontain the artificial head (and dummy), and such that the sound pressure 2 feet in front of the artificial head is not changed in any octave band by more than 0.5 db, upon complete removal of the head (and dummy) from the region. The sound pressure and first order pressure gradient shall be constant
29、 to within 1 b. with respect to direction and position over a 5 cubic foot region containing the artificial head, measured in the absence of the head, in each octave band. shall bethermal noise. Sufficient equalization shall be provided so that the spectrum level will not vary more than 2 db. in any
30、 octave band used for the test. and Kaer Model 2112 One-Third and Full Octave Band Analyzer shall be used in performing the noise cancel- ing test. The octave bands shall be centered at 250, 500, 1000, 2000 and 4000 cycles which are the preferred frequencies listed in ASA publication S 1.6-1960. 4.6
31、.4.1.2 Diffuse sound field.- A diffuse random noise field shall be provided in a region sufficiently 4.6.4.1.3 Signal source.- The signal, both for the artificial head voice and diffuse random noise field 4.6.4.1.4 Filters.- AGeneral Radio Company, type 1558-Ai? Octave-Band Noise Analyzer or a Bruel
32、 4.6.4.1.5 Calibration.- Both the aktificial head voice and the diffuse random noise field shall be calibrated in each band with a probe microphone. For calibration of the artificial head voice the probe microphone shall be positioned with its axis at a right angle to the axis of the voice. The tip
33、of the probe microphone shali be placed 1/4 inch from a plane across the front of the lips which is perpendicular to the voice axis. The microphone to be tested shall not be mounted in the normal test position during the calibra- tion of the noise field and the voice. For calibration of the diffuse
34、random noise field the probe microphone shali remain in the position used for calibration of the voice and the artificial head and dummy shall be removed. 4.6.4.1.6 Measurement of random noise discrimination.- The true r.m.s. value of the sound pressure and microphone output voltage shall be measure
35、d in each case. After calibrating the sound sources as described in 4.6.4.1.5, the noise canceling microphone shall be mounted in the normal position of use on the artificial head. The point of the microphone closest to the center of the mouth shall be 1/4 inch from the plane of the lips“ or as clos
36、e thereto as is consistent with the term “normal position of use.“ The microphone audio circuit shall be terminated with a 150 ohm non-inductive resistor. The increase in microphone sensitivity to the artificial voice signal, over its sensitivity to the diffuse random noise (each sensitivity defined
37、 as the ratio in decibels, reference 1 volt/microbar, of the output voltage to the sound pressure measured in 4.6.4.1.5) shall be measured in each octave band. 4.6.4.1.7 Calculation of articulation index.- The value of the Articulation Index (A.I.) shall be calculated by inserting the measured value
38、s of C; and the appropriate values of W; and Q; from table V into the formula: 5 A.I. =C; i=l Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-MIL-M-238 13A(SHIPS) where Ci is the random noise discrimination (expressed in decibels) in the ith octave b
39、and (i = 1, 2, 3, 4, and 5); Wi is the articulation index weighting factor for each band; and &i are the constants for each band listed in table V. The angular brackets indicate that if the quantity within them is less than zero or greater than 30, it is to be taken as zero or 30, respectively. Tabl
40、e V - Calculation of articulation index. Band No. Center frequency I (cycles per second) 250 500 1000 2000 4000 Limits (cycles per second) 180-355 355-710 7 10- 1400 1400-2800 2800-5600 .O72 I .136 224 .318 1 .227 10.1 8.8 4.7 - 1.4 4.6.4.2 For production samples.- Production samples shall be tested
41、 as specified in 4.6.4.2.2 and the test results, expressed as specified in 4.6.4.2.3, compared with those obtained for the preproduction sample subjected to the same test to determine compliance with 3.12.4.2. 4.6.4.2.1 Preproduction sample as a standard.- One of the preproduction samples which has
42、been tested at a Government laboratory and meets the requirements of 3.12.1, 3.12.2, 3.12.3 and 3.12.4.1 shall be used as a standard microphone to which production samples shall be compared. The preproduction sample used for a standard shall not have been subjected to any of the environmental tests
43、required by 3.12.11 through 3.12.16. 4.6.4.2.2 Test procedure.- The sound source for this test shall be the artificial voice specified in 4.6.1.2. The artificial voice output shall be adjusted to produce a sound pressure level of 50 microbars at a point on- axis and 1/2 inch in front of the voice fo
44、r test frequencies of 400 and 1000 C.P.S. The microphone output volt- age shall be measured across a 150 ohm resistive load for each of the following test conditions. , 4.6.4.2.2.1 Close talking on-axis.- The microphone shall be mounted in the normal test position as 4.6.4.2.2.2 Distant talking off-
45、axis.- The microphone shall be positioned in front of and facing the arti- ficial voice with its principal axis parallel to that of the voice. The position of the microphone shall be such that the center of its face is at a point 3 inches from the center of the front opening of the voice on a line d
46、rawn at a 45 degree angle to the principal axis of the artificial voice. 1 specified in 4.6.1.4. 4.6.4.2.3 Ratio of on-axis to off-axis voltage output.- The ratio of output voltage measured with the microphone on-axis as specified in 4.6.4.2.2.1 to the output voltage measured with the microphone off
47、-axis as specified in 4.6.4.2.2.2 shall be expressed in decibels for each of the two test frequencies. 4.6.5 induced voltage.- 4.6.5.1 Electromagnetically induced voltage.- The microphone to be tested shall be complete with micro- phone cable and connector plug. A 150 ohm noninductive resistor shall
48、 be connected to the microphone audio circuit at the connector end of the cable. The press-to-talk switch shall be closed and a 0.5 ampere r.m.s. 60 C.P.S. sinusoidal current made to flow through the control circuit leads. The induced voltage shall be measured across the 150 ohm resistor. Results sh
49、all comply with 3.12.5. 4.6.6 Microphone endurance test.- A warble frequency signal of 800 to 1250 C.P.S. at a voltage of 25 millivolts (r.m.s.) shall be applied across the microphone voice coil for an uninterrupted period of 8 hours with the microphone in an ambient room temperature of 72 i5“ F. Results shall comply with 3.12.6. 4.6.7 Switch endurance test.- The microphone control circuits shall be connected to a 115 volt 60 C.P.S. supply through suitable resistance and inductance to cause a current of 0.5 amperes a
