MIL-STD-740-1(SH) SUPERSEDING MIL-STD-740B(SHIPS)(IN PART) 13 January 1965 (See 6.6) MILITARY STANDARD AIRBORNE SOUND MEASUREMENTS AND ACCEPTANCE CRITERIA OF SHIPBOARD EQUIPMENT AMSG N4O08 AREA HFAC DISTRIBUTION STATEMENT A Approved for public release; distribution unlimitedMIL-STD-740-1(SH) 30 December 1986 DEPARTMENT OF DEFENSE NAVAL SEA SYSTEMS COMMAND Washington, DC 20362-5101 Airborne Sound Measurements and Acceptance Criteria of Shipboard Equipment 1. This Military Standard is approved for use by Naval Sea Systems Command Department of the Navy, and is available for use by all Departments and Agencies of the Department of Defense. 2, Beneficial comments (recommendations, additions, deletions) and any perti~ nent data which may be of use in improving this document should be addressed to: Commander, Naval Sea Systems Command, SEA 5523, Department of the Navy, Washington, DC 20362-5101 by using the self-addressed Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter. itMIL-STD-740-1(SH) 30 December 1986 CONTENTS Paragraph 1. SCOPE, PURPOSE, APPLICATION, IMPLEMENTATION, AND APPROACH .. 1 Scope 2 Purpose 3 Application ... 4 Implementation 5 Approach .. 5 5 5 1 Measurement 2 Acceptance criteria . 3) Acceptability of equipment . . REFERENCED DOCUMENTS .-- 1 Government documents lel Specifications and standards 22 Other publications .. 3 Order of precedence « : DEFINITIONS « Symbols . Terminology -+++++ Sound Frequency « Level .. Sound pressure Sound pressure level .. Sound level Arweighted sound level . Tol Equivalent A-weighted sound leve: 7 Peak A-weighted sound pressure level . C-weighted sound level . 0 Band s+. 1 Band level « 2 Band-edge frequencies « 3 Band-center frequency (f¢) (geometric) ..++- 4 Bandwidth « 5 Octave band 6 Octave band sound pre 7 Transient sounds « 8 Steady state sounds ... 9 Equipment « 0 0. 0. 0. 0. 0. 0. 1 1 Equipment grades . 1 Grade 2 Grade 3 Grade ods Grade 5 Grade 6 Grade 220 Mounting 226211 Resiliently mounted equipment iit BUBUUUE RE EERE EE ES UUUUUUEWULUNNENParagraph 3-2-21-2 3424022 MIL-STD-740-1(SH) 30 December 1986 CONTENTS - Continued Solidly mounted equipment . Contracting activity « GENERAL REQUIREMENTS Equipment sampling « Equipment evaluation plan . ‘Testing Reporting standards Reference quantity identification Measurement bands « Plotting format . DETAILED REQUIREMENTS . Airborne sound acceptance criteria »... Measurements «.. Microphone mounting and orientation « Required measurements seeee A-weighted sound pressure level measurements « C-weighted sound pressure level measurements Octave band sound pressure level measurements .. Peak A-weighted sound pressure levels « Windscreen performance Measurement procedures A> and C-weighted sound pressure level measurement procedures « Octave band sound pressure level measurement procedure ++ Peak A-weighted sound pressure level measure- ment procedure « Measurement locations Small equipment Medium size equipment Large equipment - External influences Mounting of equipment Mount ing methods Foundations « Mounting fixture Calibration of instrumentation Laboratory calibration Microphone calibration wee Electrical calibration for airborne sound measuring system .. Frequency response Linearity calibration .... Field calibration «s+... Equipment operation conditions during measurements Normal conditions . ivParagraph Figure Table IL NOTES « MIL-STD-740-1(SH) 30 December 1986 CONTENTS ~ Continued Special operating conditions Selection of units « Reports Warning plate Drawing and manual information . Intended use . Technical proposals Implementation guidance « Data requirements . Subject term (key word) listing Supersession data .... Grade equivalency . Changes from previous issue « FIGURES Sound measurement locations for small equip- ment, in addition to location of operator's head Sound measurement locations for medium size equipment, in addition to location of operator's head Sound measurement locations for large equipment « Sound measurement locations for valves Standard test fixture .... TABLES Acceptable octave band sound pressure levels in dB re 20 uPa « Equivalent A-weighted sound levels in dB v/v 17 18 19 20 a1MIL-STD-740-1(SH) 30 December 1986 1. SCOPE, PURPOSE, APPLICATION, IMPLEMENTATION, AND APPROACH 1.1 Scope. This standard prescribes instrumentation and procedures required for the measurement and analysis of, and maximum acceptable sound level criteria for, airborne sound generated by shipboard equipment. 1.2 Purpose. Airborne sound measurements are conducted to demonstrate that equipment levels are within the limits specified herein. 1.3 Application. This standard supplements specifications and similar documents applicable to all shipboard equipment. 1.4 Implementation. Implementation guidance is provided in section 6. 1.5 Approach. 1.5.1 Measurement. Two basic types of measurement are required by this standard: Weighted sound pressure (average for all measurements and peak for selected measurement) levels; and octave band sound pressure levels. 1.5.2 Acceptance criteria, Airborne sound acceptance criteria are speci- fied in 5.1. 1.5.3 Acceptability of equipment. Equipment 1s acceptable when none of the airborne levels measured at the designated locations exceed the applicable acceptance criteria. 2. REFERENCED DOCUMENTS 2.1 Government documents. 2.1.1 Specifications and standards. Unless otherwise specified, the fol- lowing specifications and standards of the issue listed in that issue of the Department of Defense Index of Specifications and Standards (DoDISS) specified in the solicitation form a part of this standard to the extent specified herein. SPECIFICATIONS MILITARY MIL-P-15024 - Plates, Tags and Bands for Identification of Equipment. Mounts, Resilient; General Specifications and Tests for (Shipboard Application.) Mounts Resilient: Types 6E2000, 62900, 6E900BB, 7450, 7E450BB, 6E150, and 6E100. MIL-H-19379 ~ Mounts, Resilient, Mare Island Types 11M15, 11M25, and 10M50. MIL-M-19863 - Mounts, Resilient: Type 5B5SO00H. - Mounts, Resilient, Type 5M10,000H. MIL-M-17185 1 MIL-M-17508MIL-STD-740-1( SH) 30 December 1986 STANDARD MILITARY MIL-STD-1621 - Acoustical and Vibrational Standard Reference Quantities. (Gopies of specifications and standards required by contractors in connection with specific acquisition functions should be obtained from the contracting activity or as directed by the contracting officer.) 2+2 Other publications. The following documents form a part of this standard to the extent specified herein. Uniess otherwise specified, the issues of the documents which are DoD adopted shall be those listed in the issue of the DoDISS specified in the solicitation. The issues of documents which have not been adopted shall be those in effect on the date of the cited DoDISS. AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI) S14 = Sound Level Meters, Specification for. $1.6 - Preferred Frequencies and Band Numbers for Acoustical Measurenents. $1.10 = Calibration of Microphone, Method for the. S1.11 = Octave, Half-Octave, and Third-Octave Band Filter Sets. (Application for copies should be addressed to Publication Sales, Dept. STD, American Institite of Physics, 335 East 45th Street, New York, NY 10017.) (Nongovernment standards are generally available for reference from 1ibra- ties. They are also distributed among nongovernment standards bodies and using Federal agencies.) 2.3 Order of precedence. In the event of a conflict between the text of this standard and the references cited herein, the text of this standard shall take precedence. 3. DEFINITIONS 3-1 Symbols. Symbols used herein are as follows: f£. = Band-center frequency (geometric) (see 3-2.13) £] = Lower band-edge frequency (see 3.2-12) £2 = Upper band-edge frequency (see 3.2+12) La = A-weighted sound (pressure) level (see 5.2.2+1) Lg = C-weighted sound (pressure) level (see 5.2242) mts] soem lpeesearadievell DIM = Distributed isolation material (see 3.2.21) 3-2 Terminology. 3.241 Sound, Sound is: (a) An oscillation in pressure, stress, particle displacement, particle velocity, etc., in a medium with internal forces (e.g, elastic, viscous) or the superposition of such propagated oscillations. (b) AnMIL-STD-740-1(SH) 30 December 1986 auditory sensation evoked by the oscillation described above. In the case of possible confusion the term “sound wave” or “elastic wave” may be used for con~ cept (a), and the term "sound sensation” for concept (b). The medium in which the sound exists is often indicated by an appropriate adjective, e.g-, airborne, waterborne, structureborne. 3.2.2 Frequency. ‘The frequency of a function periodic in time is the reciprocal of the period. The unit of frequency is the hertz (Hz). Ome Hz is equal to one cycle per second. 3.2.3. Level. The level of a vibratory quantity is the logarithm of the ratio of that quantity to a reference quantity of the same kind. The base of the logarithm, the reference quantity, and the kind of level shall be indicated. 3.2.4 Sound pressure. Sound pressure is the root mean square (rms) value of the vibratory pressure. 3.2.5 Sound pressure level. Sound pressure level, in decibels (4B), is 20 times the logarithm to the base ten of the ratio of the measured sound pres- sure to the reference sound pressure. ‘The reference sound pressure for atr- borne sound is 20 micropascals (yPa) = 20 micronewtons per square meter (j\N/m?) = 0.0002 microbar. Lp = 20 logio (p uPa/20 uPa). 3.2.6 Sound level. Sound level is the quantity in dB measured by a sound level meter satisfying the requirements of ANSI $1.4. Sound level is the fre~ quency weighted sound pressure level obtained with the standardized dynamic characteristics “fast” or “slow” and weighting A, B, or C. The unit of any of the sound levels is the dB. The weighting employed shall be indicated, other wise the A-weighting is understood. 3.2.7 Acwerghted sound level. A-weighted sound level is the quantity measured using a sound level meter with weighting set on A and is a measure of human response to sound. 3+2-7.1 Equivalent A-weighted sound level. Equivalent A-weighted sound level 1s the level equivalent to the octave-band levels for the equipment being measured. It is not the weighted sum of the individual octave-band levels but an equivalent level based on experience with spectral shapes of actual shipboard equipment and shipboard spaces. 3.2.8 Peak A-weighted sound pressure level. Peak A-weighted sound pres~ sure level is the A-weighted sound pressure level measured in accordance with 5.2433; d.e., the peak A-weighted sound pressure level measured using a system with total rise time of 200 microseconds or les 3.2-9 G-weighted sound level. C-weighted sound level is the quantity measured using a sound level meter with the weighting set on C. 3.2+10 Band. A band is a continuous spread of frequencies. 3.2+11 Band level. Band level is the level of the sound contained within a particular band.MIL-STD-740-1 (SH) 30 December 1986 3.2.12 Band-edge frequencies. The upper (f2) and lower (£1) band - edge frequencies are those frequencies, above and below the frequency of maximum response of a filter, at which the response to a sinusoidal signal is 3 4B below the maximum response. 3.2.13 Band-center frequency (fc) (geometric). The mid-band frequency is the geometric mean between the band edge frequencies of a band. The geo- netric sean is, the square root of the product of the band edge frequencies, fom (fy x £72, 3.2.14 Bandwidth. The bandwidth of a filter is the difference between f, and £2. This difference may be expressed in Hz, as a percentage of the mid-band frequency, or as the interval between the band-edge frequencies, in terms of octaves or parts thereof, such as one-third, one-fifteenth, etc. 3.2.15 Octave band. An octave band is a band of frequencies in which the ratio of the upper band-edge frequency to the lower band-edge frequency is equal + The octave bands designated in this standard are those whose band-center frequencies are the preferred frequencies as specified in ANSI $1.6. The width of an octave band in Hz is approximately 71 percent of its mid-band frequency. 3.2.16 Octave band sound pressure level. The level obtained using the procedure and instruments as specified in 5.2.2.3. 3.2.17 Transient sounds. For this standard, transient sounds are defined as those sounds’ which occur during turn-on and turn-off of the equipment and infrequent sounds that are less than 15 seconds in duration. If sounds occur at intervals of 1/2 second or less, the sound is considered steady state sound. 3.2.18 Steady state sounds. For this standard, steady state sounds are any sounds which are not defined as transient sounds in 3.2.17. 3.2.19 Equipment. The term “equipment”, when used in this standard, refers to any equipment as a system, subsystem, or part thereof which is being measured to determine compliance with the airborne sound acceptance criteria. Equipment is required to meet airborne sound acceptance criteria which have been established based on the spaces in which it 1s to be placed. 3.2.20 Equipment grades. Equipment grades are as specified in 3.2-20.1 through 3.2.20.6. 3.2.20.1 Grade A3. Grade A3 equipment is that which is to be installed in spaces where direct speech communication must be understood with minimal error and without repetition over a distance of 2 meters (6-1/2 feet) or less. 3.2.20.2 Grade Al2. Grade Al2 equipment is that which is to be installed in spaces where direct speech communication must be understood with minimal error and without repetition over a distance greater than 2 meters (6-1/2 feet).MIL-STD-740-1(SH) 30 December 1986 3+2.20.3 Grade B. Grade B equipment is that which will be placed in spaces where comfort of personnel in their quarters is the principal consideration. 3+2+20.4 Grade C. Grade C equipment is that which will be placed in the sonar room, sickbay, library, or other spaces requiring low sound levels and which are not covered in other categories. 342.2065 Grade D. Grade D equipment is that which will be placed in spaces where avoidance of hearing loss is the prime consideration and intelligible speech communication is not normally required. 3.2.20.6 Grade E, Grade E equipment is that which will be placed in high sound level areas where voice communication is accomplished with high vocal effort and where amplified speech and telephones are normally available. 3.2.21 Mounting. 3+2.2141 Resiliently mounted equipment. Resiliently mounted equipment is equipment which is isolated from a support structure by Navy approved resilient mounts. Navy approved resilient mounts are mounts in accordance with MIL-M-17185, MIL-M-17508, MIL-M-19379, MIL-M-19863, or MIL-N-21649. For the purposes of this standard, DIM mounted equipment is considered to be solidly mounted equipment. 3+2+21+2 Solidly mounted equipment, Solidly mounted equipment is equipment which is attached directly to the supporting structure. For the purposes of this standard, DIM mounted equipment is considered to be solidly mounted equipment. 3.2+22 Contracting activity. Contracting activity, when used in this standard, is the Government or its authorized representative. 4+ GENERAL REQUIREMENTS 4s Equipment sampling. If sampling is called for by the acquisition specifications or the contract or order (see 6.3), selection of equipment for test shall be on the basis of conformance to the drawing requirements for that equipment, and shall not consider advance measurements, observations, or opinions about the acoustical performance of the particular equipment sample. 4.2 Equipment evaluation plan. When specified in the contract or order, an equipment airborne sound measurement plan shall be prepared (see 6.4). 4.3 Testing. The Government shall have the option to witness all tests conducted to meet contractual requirements. When specified in the contract or order, notification of tests letters shall be prepared in accordance with the data ordering document (see 6.4). 4.4 Reporting standards. 4s4s1 Reference quantity identification. ‘The applicable reference quantity shall be indicated on every table, figure, and graph, and at least once in the text. The reference quantity may be introduced by “re” which indicates that the level is “with reference to”. For example, the 125 Hz octave band level re 20 uPa is 85 4B.MIL-STD-740-1(SH) 30 December 1986 4.4.2 Measurement bands. The bandwidths of the measurement basis shall be reported together with the measured levels. Normal procedure for reporting measured levels shall include the bandwidth and the band center frequency with the level. For example: the one-third octave 100 Hz band level was 85 dB re 20 uPa, the 10 Hz bandwidth 100 Hz band level was 85 dB re 20 uPa, or the 6 percent bandwidth 100 Hz band level was 85 dB re 20 uPa. 4.4.3 Plotting format. Plotting formats shall be in accordance with MIL-STD-1621. That is, all plots of data in which a level in dB on a linear scale is plotted against frequency on a logarithmic scale shall be made on graphs in which a factor of ten in frequency is equal in length to 25 dB (preferred) or 50 dB. Where the bandwidth of analysis is one-third octave or larger, one factor of ten in frequency shall be 50 mm (preferred) or 2 inches in length. The ordinate and abscissa of all graphs shall be labeled so that levels and frequencies can be readily understood without need to refer else~ where in the report. 5. DETATLED REQUIREMENTS 5.1 Airborne sound acceptance criteria. The octave band sound pressure levels of the equipment, measured at the locations of 5.3 shall not exceed the limits given in table I for the equipment grade specified (see 6.3). Where no equipment grade has been specified, grade Al2 requirements shall apply. Finally, no equipment shall have a peak A-weighted sound pressure level in excess of 140 4B. Equipment which fails to meet the acceptance criteria shall not be installed an the ship until the following have been accomplished: (a) When specified in the contract or order, a sound test failure notification and recommendations report shall be prepared for each deficient equipment item measured (see 6.4). (b) The Government or the contracting activity has accepted the deficient equipment or directed the specific course of action. The final decision, with respect to acceptance, will be made by the Government. TABLE I. Acceptable octave band sound pressure levels in dB re 20 uPa. Equipment Octave band center frequency in Hz grade 31.5} 63 | 125 | 250 | 500 | 1000 | 2000 | 4000 | 8000 a3 75 72 | 69 | 66 | 63 60 57 54 SL Al2 66 63 | 60 | 57 | 54 51 48 45 42 B 75 72 | 69 | 66 | 63 60 | 57 54 51 c 72 69 | 66 | 63] 60 57 54 51 48 D 1 ag | 35 | 82 | 79 76 | 73 70 67 E 82 79 | 76 | 73 | 70] 67 64 61 58MIL-STD-740-1(SH) 30 December 1986 5+2 Measurements. The measurements required by this standard are made using a microphone connected to a sound level meter. No obstruction, including the instrument operator, shall be between the equipment being measured and the microphone. 5.2e1 Microphone mounting and orientation. It 1s desirable but not required that the microphone for these measurements be mounted on a rigid frame or stand, and that it be connected to the sound level meter by a cable at least + 2 meters (6-1/2 feet) in length. If the microphone has the random incidence calibration specified in ANSI $1.4, the microphone shall be clamped so that the principal sound arrives at the diaphragm at near grazing incidence. The instruc~ tions for the sound level meter which is being used shall be reviewed to assure that the microphone is properly oriented if other than random incidence calibra~ tion has been performed. If it is necessary to have the microphone attached directly to the sound level meter which 1s held in the hand of an observer, the microphone orientation shall still be the same as that appropriate to the micro phone on a cable. 5.2.2 Required measurements. Unless otherwise specified (see 6.3), the following measurements shall be made: 52-241 Acweighted sound pressure level measurements. A-weighted sound pressure level (Lq) measurements shall be obtained for all equipment in accor- dance with 5.2.3.1 and shall be made at the locations specified in 5.3. These measurements will be used to determine the locations at which the octave band and peak A-weighted sound pressure measurements will be made. 5+2.2-2 Coweighted sound pressure level measurements. C-weighted sound pressure level (Ic) measurements shall be obtained for all equipment in accor- dance with 5.2.3.1 and shall be made at the locations specified in 5.3. These measurements will be used to determine the location at which the octave band sound pressure measurements will be made. 5+2+2+3 Octave band sound pressure level measurements. Octave band sound pressure level measurements shall be made for all equipment in accordance with 5+243.2 at the location of the highest La level and the location of the highest Lg level as measured for 5.2.2.1 and 5.2.2.2. Octave band measurements shall also be made, where applicable, at the location of the operator's head. In addition, octave band measurements shall be made at all other locations where the level exceeds the equivalent A-weighted level of table II. Equivalent A-weighted sound level is not a criterion but rather a screening tool used to identify where additional octave band sound pressure level measurements must be taken. TABLE II- Equivalent A-weighted sound levels in dB. Grade Sound level a3 63 Alz 54 B 63 c 60 D 79 E 70MIL-STD-740-1(SH) 30 December 1986 5+2.2e4 Beak A-weighted sound pressure levels. Peak A-weighted sound pressure levels shali be monitored for equipment generating transient sounds using the procedure specified in 5.2.3.3 at the location selected from 5.2.2.1 and where applicable at the location of the operator's head. 5.2.2.5 Windscreen performance. When a windscreen is used in accordance with 5.3, and when specified in the contract or order, data shall be prepared (see 6.4) which demonstrates that the windscreen does not change the frequency response characteristics of the microphone by more than 1 dB in any octave bands specified for measurement (see 5.2.3.2). A correction factor which accounts for the change in frequency response may be applied to the measured levels. 5.2.3 Measurement procedures. Unless otherwise specified (see 6-3), measurement procedures shall be as specified herein. 5.2.3-1 Ac and C-weighted sound pressure level measurement procedures. Using a sound level meter meeting the requirements of ANSI Si.4, type 2 instru- ment; set it either on A-weighting or C-weighting as appropriate and slow meter response, and then record the maximum of the meter indication at each location as La and Ig. 5.2.3.2 Octave band sound pressure level measurement procedure. Unless otherwise specified (see 6.3), unweighted octave band sound pressure level measurements shall be made for at least the bands with band-centers from 31.5 to 8000 Hz, using an instrument set for slow meter response and with filters at least as good as those specified in ANSI S1.11 for class II filters. The input to the octave band instrument will normally be the output of the sound level meter which was used for the La and Lg measurements. If any other input is used, the quality and frequency range of the microphone and associated circuitry shall be that required for a type 2 sound level meter in ANSI S1-4. These measurements will be compared to the acceptance criteria. 5.2.3.3 Peak A-weighted sound pressure level measurement procedure. The peak A-weaghted sound pressure level measurements shall be made using either a peak reading sound level meter or a combination of instruments with equivalent characteristics, such as a sound level meter and an impact meter, or a sound level meter and a calibrated oscilloscope. The measurenents shall be made with a sound level meter, or equivalent, meeting the requirements of ANSI S1.4 for a type 2 meter with addition of a measuring circuit that will make a peak sound pressure level measurement where the total rise time of the instrumentation does not exceed 200 microseconds. The rise time of the peak detector shall be such that a single pulse of 200 microseconds duration produces a meter indication within a 2 dB of the indication produced by a pulse having a duration of 10 microseconds and equal peak amplitude. The amplitude of the 10 microsecond reference pulse shall be such as to produce a meter deflection 1 dB below full- scale. 5.3 Measurement locations. Unless otherwise specified (see 6.3), both A-weighted sound pressure level and C-weighted sound pressure level shall be measured at each of the locations described herein. The number of locations depends upon the size and type of the equipment, as indicated on figures 1 through 4. These figures depict typical equipment configurations; the con- figuration details are provided for visual reference only. Sound levels areMIL-STD-740~1(SH) 30 December 1986 also to be measured at the typical position of an operators head if the equipment has an operator position associated with it. Microphones shall be placed at loca~ tions approximately 1 meter (3-1/4 feet) from the rectangular envelope which just encloses the equipment, except for the typical position of the operator's head (see 6.3). Also, 1£ the equipment has air openings at any of the designated locations, the microphones may be relocated from the designated location to mini- mize air flow over the microphone. For such cases, the separation between the measurement location and the designated location shall be minimized and shall be not greater than 1/3 meter (1 foot). In addition, a windscreen shall be used on “the affected microphone (see 5.2.2.5) to further minimize airflow effects. All distance measurements shall be within plus or minus 10 percent. 5.3.1 Small equipment. For equipment whose maximum dimension is less than 2 meters (6-1/2 feet), the sound levels (La and Lg) shall be measured at a minimum of 5 locations as shown on figure 1, in accordance with the following procedure, except for valves where only three locations are required at two opposite sides and at the valve operating mechanism (see figure 4). The micro- phone shall be placed 1 meter (3-1/4 feet) from the rectangular envelope of the equipment as follows: (a) on each of the four sides on the vertical centerlines at a distance 1 meter above the base of the mounted equipment, or if the one meter location is above the top of the equipment, measure at the height of the horizontal centerline of the equipment, and (b) above the equipment, over the center of the horizontal plane of the envelope. 5.3.2 Medium size equipment. For equipment whose maximum dimensions are betweea 2 and 4 meters (6-1/2 and 13 feet) the sound levels (La and Lg) shall be measured at locations shown on figure 2, in accordance with the following pro- cedure. The microphone shall be placed 1 meter (3-1/4 feet) from the equipment envelope as follows: (a) on each of the four sides on the vertical centerlines at a distance 1 meter above the base of the mounted equipment, and at successive intervals of not more than 1 meter distance along each side of the equipment envelope and (b), above the equipment, over the center of the horizontal plane of the envelope and at successive intervals not greater than 1 meter apart in the horizontal plane. For equipment comprised of any sides whose dimension is less than 2 meters, the measurement positions shall be in accordance with 5.3.1. 5-3-3 Large equipment. For equipment whose maximum dimensions are greater than 4 meters (13 feet) sound levels (Lg and Lc) shall be measured at locations shown on figure 3, in accordance with the following procedure: The microphone shall be placed 1 meter (3-1/4 feet) from the equipment envelope as follows: (a) on each of the four sides on the vertical centerlines at a distance | meter above the base of the mounted equipment, and at successive intervals of not more than 2 meters (6-1/2 feet) distance along each side of the equipment envelope, and (b) above the equipment, over the center of the horizontal plane of the envelope and at successive intervals of not more than 2 meters in the horizontal plane. For any side whose dimension is less than 4 meters (13 feet), the measurement position shall be in accordance with 5.3.1 or 5.3.2. 5.4 External influences. Measured levels of equipment sound shall not be adjusted to compensate for the effects of ambient magnetic, electrical, and acoustical fields. Ambient effects shall be at least 10 dB below the levels specified for the equipment. No reflecting surface shall be nearer than 1 meter (G-1/4 feet) to the microphone for any measurement, except measurements whereMIL-STD-740-1(SH) 30 December 1986 the operator's normal head position is closer than 1 meter to the equipment. Corrective measures shall be taken to reduce the effects of external sources on the equipment's measured sound level. In cases where pipes are connected to the equipment, within 1 meter of the equipment, a flexible connection shall be inserted in each pipe run between the equipment and any external piping. Acoustical filters, damped piping, or similar devices shall be employed to reduce fluidborne pressure pulsation effects from external sources. The equip- ment shall be located away from other machinery items. If this is not possible, machinery which is not necessary for the test shall be shut down. 5-5 Mounting of equipment. Unless otherwise specified (see 6.3), mounting methods shall be as specified herein. 5.5.1 Mounting methods. Equipment shall be oriented in its normal ship- board installation position. Equipment shall be resiliently mounted as described below regardless of how the equipment is to be mounted in service. Resilient mounts and subbases or bedplates shall normally be the same ones used for ship~ board installation. The subbase used for the equipment evaluation shall not exceed the weight of the shipboard subbase (see 6.3). For the purposes of this standard, the terms subbase and bedplate refer to support structure which is required for shipboard installations and which is necessary for purposes such as to hold one or more components within alignment or to provide a means for attachment to the ship. Resilient mounts used in such a case shall be loaded in accordance with the load range specified in the mount specification. The frequencies of the natural modes of vibration of the mounted equipment in the vertical direction shall not exceed 11 Hz or one-fourth of the lowest forcing frequency, whichever is lower. Resilient mounts conforming to MIL-N-17508, MIL-N-19379, MIL-M-19863, or MIL-M-21649 shall be used where possible. If these mounts cannot be used, commercial mounts for which data can be provided to show they meet the frequency requirements and which are otherwise suitable are acceptable if approved by the contracting activity. When the above mounting methods cannot be met, equipment mounting shall be as approved by the contracting activity. When used in Navy shipboard application, resilient mounts shall be in accordance with MIL-M-17185. The complete assembly shall be supported on a rigid and massive floor, preferably of reinforced conerete or case metal to prevent interaction between the equipment and floor. 5.5-1+1 Foundations. Any foundation pedestals, cradles, etc., required to accommodate resilient mounts shall assure that the installed mounts provide the vibration isolation of the assembly from the foundation for which the resilient mount is designed. Foundations shall have a natural frequency of not less than 25 Hz and shall not have fixed base natural frequencies within plus or minus 0.4 (square root of 2, minus 1) times the fundamental rotational or other primary forcing frequency of the machinery or equipment. In addition, they shall not have natural frequencies within 0.4 times other machinery or equipment exciting frequencies between 0 and 500 Hz. Exciting frequencies shall include but not be limited to rotational, two times rotational, electrical frequencies and harmonics thereof, pump vane frequencies, pressure pulsations, ball bearing frequencies, etc. For the purposes of this standard, the term foundation refers to support structure which is used below the resilient mounts and which may or may not resemble the shipboard structure. 10MIL-STD-740-1(SH) 30 December 1986 545-2 Mounting fixture. Some equipment may be measured while solidly mounted on a resiliently mounted test fixture. This equipment will nornglly consist of units which have a relatively light framework or structure (for example, controllers, control cubicles, nonrotating or nonreciprocating equip~ ment) and which is to be solidly mounted on shipboard. For the purposes of this standard, the term mounting fixture refers to structure which is used solely for the purpose of resiliently mounting equipment for noise testing, 1s not used for shipboard installations, and 1s used above the resilient mounts. The contracting activity will specify whether a mounting fixture is required (see 6.3). Those items requiring attachment to a mounting fixture shall be attached at the normal points of attachment of the equipment. The fixture shall be stiff between points of attachment and shall not have a natural frequency within plus or minus 0.4 times the fundamental rotational frequency or other primary forcing frequency of the machinery or equipment. In addition, they shall not have natural frequencies within 0.4 times other machinery or equipment exciting frequencies between 0 and 500 Hz. If the equipment being measured contains internal sound isolation mounts, the mass of the fixture shall be great enough to permit these internal mounts to function properly. The mass of the fixture shall not exceed 30 percent of the total mass of the equipment. For equipment whose mass exceeds 900 kilograms (kg) (2,000 pounds), the mounting fixture of figure 5 is recommended. It is preferred that equipment items be bolted directly to the fixture, however, the optional mounting pads and clamps shown on figure 5 may be used to attach the items. If in specific cases, the mounting fixture of figure 5 cannot be used, the alterna~ tive mounting fixture shall be approved by the contracting activity. The combined assembly of equipment item and mounting fixture shall be resiliently mounted and oriented so that the item is in its normal shipboard installation position. 5.6 Calibration of instrumentation. Instrumentation used shall have been calibrated and have been found to meet the requirements specified herein. 5.6.1 Laboratory calibration. A laboratory calibration shall be made of all sound measuring instrument components within 12 months prior to each use, or after exposure to mechanical shock or other unusual disturbing conditions, of upon request by the Government inspector. Calibration instrumentation, including the sound level calibrator used for field calibration (see 5.6.3), shall have a calibration within 6 months prior to each use traceable to the National Bureau of Standards. The laboratory calibration of components shall be accurate within the instrument manufacturer's specification or plus or minus 1 dB, whichever is more stringent. 5+6-141 Microphone calibration. Calibration of microphones shall be per- formed by one of the methods specified in ANSI $1.10. When secondary microphones are used, they shall be kept under controlled conditions in the equipment manu- facturer's laboratory and used only for calibrating the microphones used for equipment measurements. 5.6.2 Electrical calibration for airborne sound measuring system. A cali- bration of each complete airborne sound measuring system including microphone or simulated microphone, preamplifier, amplifiers, meter, analyzer, level recorder or plotter, magnetic tape recorder, as applicable and'so forth, shall be made by introducing known voltage and frequencies in series with the transducers. Cables and connectors shall have the same electrical characteristics (impedance, fre- quency response, capacitance, etc.) as those used during equipment measurement. ttMIL~STD-740-1(SH) 30 December 1986 Whenever any component of the measuring system is changed, a laboratory calibra- tion shall be performed for the new component, and an electrical calibration shall be made with the new component in the system. System calibration shall be made accurate within plus or minus 1 dB. 5.6.2.1 Frequency response. Known voltages at know frequencies shall be introduced into the system such as to simulate the microphone output, and the level shall be recorded. The frequencies selected shall be: (a) For analyzer with fixed filter sets, the band-center frequency of each filter in the specified frequency range. (b) For analyzers with tunable filter sets used to scan continuously a band of frequencies; at the lower limit, upper limit, and at least two intermediate frequencies (including 500 Hz if within the scanning range) in each frequency range scanned. 5.6.2.2 Linearity calibration, At a low frequency, at 500 Hz, and at a high frequency, calibration shall be made at the following voltages: (a) Equal to the microphone output that represents the lowest acceptance level for the applicable equipment specifications. (b) Equal to the microphone output that represents the highest acceptance level for the applicable equipment specifications. 5.6.3 Field calibration. Total system calibrations using a sound level calibrator or equivalent shall be performed for each instrument configuration used in making the required measurements. These calibrations shall consist, as a minimum, of a single frequency at a known sound pressure level being intro- duced into the microphone from a sound source and adjustment of the system so that the system readout, i.e., the meter or recorder, is indicating the proper sound pressure level. A-weighting will make the proper sound level different from the calibrator sound level. Also, when calibrating the peak measuring circuit, the indicated sound level shall be 3 4B higher than the rms level coming from the sound source. Field calibration of the total system shall be performed for each instrument configuration prior to its use in making a particular type of measurement, i.e., calibrate prior to La and Lc measurements, prior to octave band measurements, and prior to peak A-weighted sound pressure level measurements. Also, each instrument configuration shall be field cali- brated prior to its use each day. Also, whenever any component of the measuring system is changed, a field calibration shall be made with the new component in the system. If the usual instrument settings and small adjustments do not produce the proper sound level indication during calibration, this normally indicates a problem which must be corrected prior to use of the instrument system. Field calibration shall be accurate within plus or minus 2 dB. 5-7 Equipment operation conditions during measurements. Equipment operat- ing conditions shall be as specified herein and in the contract or order (see 6.3). 5-71 Normal conditions. Equipment shall be operated under normal ener- gized operating conditions including sufficient warmup time to reach normal operating temperature. Multiple speed equipment shall be measured at each operating speed. Variable speed equipment shall be operated at maxinum, 1/2, and minimum speed (5 percent of maximum if equipment can be operated down to 12MIL-STD-740-1 (SH) 30 December 1986 zero speed). Where equipment has pumps or fans as components, these components shall be operating during measurements. Where equipment operates as a result of a signal, a representative signal shall be used to energize the equipment during measurements. Background measurements shall be made with the equipment not operating for each microphone and location under the normal environmental condi- tions that will be present when the equipment noise measurements are obtained. 5.7.2 Special operating conditions. If operating conditions other than those specified in 5.7.1 are required (see 6.3), such as during change of operating mode, including starting and stopping of the equipment, these special requirements shall be specified in the equipment specifications. 5.8 Selection of units. Unless otherwise specified (see 6.3), measurements to determine compliance with airborne acceptance criteria shall be made on every unit with the following exception: for nonrotating, nonreciprocating, if the first three units of a design are below the criteria by 10 dB or more at all frequencies, following units shall be selected for test in accordance with the sampling procedures for the applicable selective testing as specified in the equipment specifications. 5.9 Reports. When specified in the contract or order, a test report for each equipment measured shall be prepared (see 6.4). 5.10 Warning plate. The equipment which meets the criteria of this standard shall be prominently identified by affixing a warning plate bearing the legend, “quiet Design’ Equipment ~ Handle with Extreme Care.” The plate shall be either type A or B of MIL~P-15024. Unless otherwise specified (see 6.3), the require- ment applies only to rotating and reciprocating equipment. 5.11 Drawing and manual information. In addition to the information required on drawings by the applicable equipment specification, the assembly drawings shall contain specific notes as to assembly procedures and tolerances to be maintained during overhaul so that machines may be restored to designed level of quietness. Maintenance information pertinent to quietness, including assembly techniques and procedures, shall be included 1n technical manuals required by the acquisition documents. The title block of assembly drawings of all electrical power equipment shall include the words, “Special Quiet Design (controller or transformer, etc.) MIL-STD-740-1.” ‘Existing drawings are not required to be revised unless the drawings are required to be changed for other reasons. 6. NOTES 6.1 Intended use. This standard is intended for use for equipment acquisition testing. 6-1.1 This standard also prescribes certain warning plate requirements and drawing and manual information requirements for shipboard equipment (see 5.10 and 5.11). 6.2 Technical proposals. When this standard is invoked in acquisitions which require technical proposals for evaluation, the following data should be included in these proposals: 13,(a) (b) (ce) (a) MIL-STD-740-1(SH) 30 December 1986 A list of recommended specification changes which will improve the quietness of equipment and assure meeting the acceptance criteria, An estimate of the amount of improvement in quiet ness and the change, if any, in other characteristics should accompany each proposed change to the equipment specification. Outline of the facilities proposed for installation to comply with the requirements of the equipment specifications. A lst of features to be incorporated in the equipment design for reduction of airborne sound levels. A list of actions that will be taken to assure achievement of specified sound levels. 6-3 Implementation guidance, When this standard is invoked, the following should be specified: (a) (bo) (ec) (da) (e) (f) (8) Acceptance criteria. The airborne sound acceptance criteria of table I are provided for guidance and use only when other criteria are not specified. Either invoke the criteria of table I or specify a separate criteria. When a large number of sources of small size are to be located within 2 meters (6-1/2 feet) of one another, lower criteria will apply and should be based on the following correction factors. These correction factors are cumulative. Correction to be subtracted from Number of sources the v: shown in ti 1 2 to 8 3 4B 9 to 14 5 aB 15 to 22 7 4B 23 and up 9 4B Compactness of sources. When the sources are within 2 meters of one another, 1.e., electronic equipment in racks, subtract 3 4B. Acceptance criteria will be based on the design of the machinery and consideration of intended service, overall ship operational requirements, and prior experience with simlar acceptable machinery. Sampling procedures for equipment to be specified when sampling is desired (see 4.1). If an equipment plan is required (see 4.2). Whether the Government is to be notified of testing, and if so, which organization is to be notified and how long the advance notice time is to be (see 4.3). ‘The grade assigned to the equipment (see 5.1). Whether the Government is to be notified of failure, and if s0, which organization is to be notified (see 5.1(a)). Measurement locations to be specified if measurement locations are not to be in accordance with 5.2.2 and 5.3. 4MIL-STD-740-1(SH) 30 December 1986 (h) Measurement procedures and instrumentation to be specified if they are not to be in accordance with 5.2.3. . (4) The frequency range for octave band measurements to be speci- fied if other than 31.5 through 8000 Hz bands are desired (see 5-2+342). (J) Whether there is an operator position for the equipment and, if 80, give the specific location of the operators head (see 5.3). (&) Mounting methods to be specified 1f the mounting is not to be in accordance with 5.5. (1) The weight of the shipboard bedplate (see 5.5+1). (m) Whether a mounting fixture is required (see 5.5.2). (a) Special equipment operating conditions during airborne sound measurenents (see 5.7 and 5.7.2) to be specified if operating conditions other than the normal full load conditions are desired. (0) Whether an alternate selection of units plan is to be used and, if so, what the plan is to be (see 5.8). (p) If a test report is required (see 5.9). (q) Whether a warning plate is required for equipment which is nonrotating or nonreciprocating (see 5.10). (r) Technical proposal, if required (see 6.2). 6.4 Data requirements. When this standard is used in an acquisition which incorporates a DD Form 1423, Contract Data Requirements List (CDRL), the data requirements identified below shall be developed as specified by an approved Data Item Description (DD Form 1664) and delivered in accordance with the approved DRL incorporated into the contract. When the provisions of DoD FAR Supplement, Part 27, Sub-Part 27.410-6 (DD Form 1423) are invoked and the DD Form 1423 is not used, the data specified below shall be delivered by the contractor in accordance with the contract or purchase order requirements. Deliverable data required by this standard is cited in the following paragraphs. Paragraph no. Data requirement title Applicable DID no. Option 4.2 Equipment airborne sound DI-HFAC-80270 — measurement plan 43 Notification of tests DI-T-23731 Sel Sound test failure notifi-~ DI-HFAC-80271 cation and recommendations report, 542.265, Equipment airborne sound DI-HFAC-80272 5.9 measurements test report (Data item descriptions related to this standard, and identified in section 6 will be approved and listed as such in DoD 5010-12-L., AMSDL. Copies of data item descriptions required by the contractors in connection with specific acquisition functions should be obtained from the Naval Publications and Forms Center or as directed by the contracting officer.) 15MIL-STD-740-1 (SH) 30 December 1986 6.5 Subject term (key word) listing. A ~ weighted sound pressure level C ~ weighted sound pressure level Octave band pressure level Weighted sound pressure level Airborne sound measurements Airborne sound, equipment 6-6 Supersession data. This standard covers airborne sound measurements and acceptance criteria of shipboard equipment formerly covered by MIL-STD-740B( SHIPS) - 6-7 Grade equivalency. There is no direct comparison between these criteria and those of MIL-STD-740B as these are expressed in terms of sound pressure level (re 20 uPa), while in 740B sound power level (re 107!2 watts) was used. Since the time of MIL-STD-740B, noise grade A was divided into A3 and Aj7 and the criteria for noise grade D was lowered by approximately 6 dB. The changes were made to reflect OPNAVINST 9640.1 regarding permissible ship compartment levels. In addition, spectra shape was changed to more closely follow typical shipboard spectra causing the acceptance levels of low frequencies to be more stringent in the new version compared to 740B. Very approximate relationships are given below based on the following assumptions: (a) omni- directional source, (b) equipment size approximately 1 meter cube, and (c) room constant = 186M? to infinity. Category A3, 2 dB greater than 740B for category A Category Aj2, 3 dB less than 740B, category A Category B, 2 dB less than 740B, category B Category C, 3 4B noisier than 740B, category C Category D, 4 dB quieter than 740B, category D 6.8 Changes from previous issue. Asterisks are not used in this revision to identify changes with respect to the previous issue due to the extensiveness of the changes. Preparing activity: Navy - SH (Project HFAC-NO03) 16MIL-STD-740-1(SH) 30 December 1986 MEASUREMENT LOCATIONS FOR SMALL EQUIPMENT : Siceorone POSITIONS su 131824 in addition to location of operator's head.MIL-STD-740-1(SH) 39 December 1986 MEASUREMENT LOCATIONS FOR MEDIUM SIZE EQUIPMENT MICROPHONE POSITIONS SH 131825 FIGURE 2. Sound measurement locations for medium size equipment in addition to location of operator's head.!PMENT JREMENT LOCATIONS FOR LARGE EQUI MEASU! eo TAAL Ay Cy Z (\Y\* ars 7 \MIL~STD-740-1(SH) 30 December 1986 MEASUREMENT LOCATIONS FOR VALVES RESILIENT MOUNTS MICROPHONE POSITIONS SH 131827 FIGURE 4. Sound measurement locations for valves. 20MIL-STD-740-1(sH) 30 December 1986 30 GRIND. FLAT AFTER BENDING CUT ENDS To suIT 6/8 — 11 UNC, 49 HOLES. HOLES To surT equip MOUNTING BOLTS BIB PLATES x 6 28 PLATE 9 « 9 = et = i we + a i at we } aNotes: ‘ Tae a2] T 5 San ink Aan TABLE — 1 REQ‘D All dimensions are in SH 131828 FIGURE 5. Standard test 2 MTG PAD — 4REQ’D notes MATERIAL STEEL TOLERANCES. +1/16 EXCEPT WHERE NOTED ‘TEMPORARILY PLUG TAPPED HOLES CENTERED OVER CAVITIES FILL CAVITIES WITH “SACRETE BLACKTOP” OR EQUIVALENT AND PACK SOLIDLY MOUNTS ARE HALF OF 7E 480 88. ‘STANDARD NAVY MOUNTS WITH FLANGES AND ‘SLEEVE REMOVED ANY MOUNT WITH RUBBER RESILIENT ELEMENTS MAY BE USED, PROVIDED. IT MEETS THE NATURAL FREQUENCY CRITERIA 5 ‘TAPPED HOLES, MTG PADS AND CLAMPS OPTIONAL. ‘SURFACE PLATE MAY BE DRILLED AND TAPPED FOR BOLT PATTERN OF SPECIFIC ITEM TO BE TESTED inches fixture.INSTRUCTIONS: In 2 contimung effort to make our standardization documents better, the DoD provides ths form for use in ‘submitting comments and suggestions for improvements All users of mubitary standardization documents are invited to provide muggestions. This form may be detached, folded along the lnes indicated, taped along the loose edge (DO NOT STAPLE), and mailed. In block 5, be as specific as possible about particular problem areas auch as wording which required interpretation, was too rigid, restrictive, loose, ambiguous, or was incompatible, and give proposed wording changes which would alleviate the problems Enter in block 6 any remarks not related to a specific paragraph of the document If block 7 1s filled out, an ‘acknowledgement will be mailed to you within 30 days to let you know that your comments were received and are being conadered NOTE Ths form may not be used to request copies of documents, nor to request waivers, deviations, or clanfication of ‘specification requirements on current contracts Comments submitted on thus form do not constitute or imply authenzation to wave any portion of the referenced document(s) or to amend contractual requirements, ‘(Fold along thie Tne) (Fold alone thi tine) DEPARTMENT OF THE NAVY COMMANDER NO POSTAGE NAVAL SEA SYSTEMS COMMAND (SEA 5523) NECESSARY DEPARTMENT OF THE NAVY marcel WASHINGTON, DC 20362-5101 UNITED STATES: Fiuactvronenvareusesee | BUSINESS REPLY MAIL FIRST CLASS PERMIT NO 12602 WASHINGTON 0 © POSTAGE WILL BE PAID BY THE DEPARTMENT OF THE NAVY ‘COMMANDER NAVAL SEA SYSTEMS COMMAND (SEA 5523) DEPARTMENT OF THE NAVY WASHINGTON, DC 20362-51017 BOCUMENT NUMBER [2 OOGUMENT TITLE ATRBORNE SOUND MEASUREMENTS AND ACCEPTANCE CRITERIA OF SHIPBOARD EQUIPMENT MIL-STD-740-1(SH) faa NAME OF SUBMITTING ORGANIZATION [y ROORESS (Borevt, City, Stam, ZIP Code) [Oy sawuractunen 1 ormen cneess [5 PROBLEM AREAS 12 Persgranh Number and Wording fia WAME OF SUBMITTER (lant, Phat, Mi) — Optional [= WATLING ROORERS (Sireet City, State, ZIP Code] ~ Optional OD 90%, 1426 PREVIOUS 01 WORK TELEPHONE NUMBER (Incinas Aree Coss) ~ Options! 1S DATE OF SUBMISSION (VYMNDD)