This standard specifies the measurement method of the electroacoustic frequency response characteristics of the A-ring and B-ring of the sound reproduction system of indoor theaters with a volume of more than 150m3. This standard is applicable to the measurement of the electroacoustic frequency response characteristics of each sound reproduction channel (excluding the sub-bass channel) of the recording control room, appraisal projection room and indoor theater dedicated to movies. GB/T 15397-1994 Measurement method of the electroacoustic frequency response characteristics of the A-ring and B-ring of the sound reproduction system of indoor theaters with a
volume of more than 150m3. This standard is applicable to the measurement of the electroacoustic frequency response characteristics of each sound reproduction channel (excluding the sub-bass channel) of the recording control room, appraisal projection room and indoor theater dedicated to movies. GB/T15397-1994 Standard download decompression password: www.bzxz.net This standard specifies the measurement method of the electroacoustic frequency response characteristics of the A-ring and B-ring of the sound reproduction system of indoor theaters with a volume of more than 150m3. This standard is applicable to the measurement of the electroacoustic frequency response characteristics of each sound reproduction channel (excluding the sub-bass channel) of the recording control room, appraisal projection room and indoor theater dedicated to movies.

National Standard of the People's Republic of China
Measurement methody of A-chain and B-chainelectro-acoustic frequency response of motion-picturecontrol rooms ,review rooms and indoor theatresGB/T 15397—94
This standard adopts the international standard ISO2969-1987 "B-chainelectro-acoustic frequency response characteristics and their measurement of motion-picturecontrol rooms ,review rooms and indoor theatres".
1 Subject content and scope of application
This standard specifies the measurement method of the A-chain and B-chainelectro-acoustic frequency response characteristics of the sound reproduction system of indoor theatres with a volume of more than 150m2.
This standard is applicable to the measurement of the electro-acoustic frequency response characteristics of each sound reproduction channel (excluding subwoofer channel) of motion-picturecontrol rooms, review rooms and indoor theatres. 2 Reference standards
GB3785 Electroacoustic performance and measurement methods of sound level meter G3661 Technical conditions for testing condenser microphones
GB11283 Characteristic parameters of reflective projection screens
3 Measurement conditionsbzxz.net
3.1A Environmental conditions
3.1.1 The sound track position, azimuth angle and gap loss compensation are adjusted correctly and can maintain the adjusted position. 3.1.2 The wow and flutter rate and signal-to-noise ratio meet the requirements. 3.1.3 In the multi-channel sound reproduction system, the phase of the inter-channel electrical signal is correct and the amplitude is balanced. 3.2B Environmental conditions
3.2.1 The position, direction and phase of the high and low frequency speakers of the speaker group are correct; the phases between the multi-way speaker groups are consistent. 3.2.2 The screen frame cover that changes the surface ratio should have no attenuation on the high frequency (good sound transmission performance). 3.2.3 The screen should be free of obstruction and should comply with the requirements of GB11283. The reduction of the commercial frequency (8kHz) should not exceed 5dB. 3.2.4 The signal sound pressure level at multiple measuring points in the audience seating area should be at least 10dB higher than the total noise in the hall within the specified intensity range.
3.2.5 Serious acoustic defects should be avoided in the measured sound field. National Technical Supervision Approved on December 28, 1994, and implemented on August 1, 1995
4 Measuring instruments and test pieces
4.1 Measuring instruments
GB/T 15397-94
4.1.1 Real-time analyzer and matching calibrated test microphones. See G133661 for technical requirements. The integrated frequency response is within the range of 20Hz~20kHz, and the error should not exceed 0.5dB. The analyzer has a relative bandwidth of 1/1 or -1/3 octave analysis function. 4.1.2 Microphone test cable and bracket,
4.1.3 Sound level meter has fast, slow and C iF weight characteristics, technical requirements are in accordance with GB 3785. 4.1.4 Special pink noise generator plug-in component Cat.No.85 or components with the same function. 4.1.5 Audio voltmeter, 20 Hz~~20 kHz±0,5 dB accuracy is better than 2.5 grade. 4.2 Test Film
4.2.1 Optical Sound Track Position Test Film:
4.2.1.1 Dolby Electro-Pink Noise Test Film Cat.No.69 or a test film with similar functions. Subjective Audition Demonstration Film Cal.Nn.351, Cat.No.251 or a film with similar functions, or a copy of the sound track program content that is familiar to you.
Magnetic Sound Track Test Film.
5 Measurement method
5.1.1 The measurement block diagram is shown in Figure 1, which shows two different properties (optical or magnetic) of the sound track playback signal source, the dotted line connects the same-test country similar measurement method
5.1.2 Calibrate the transmission level, use the test piece recorded with pink noise to play the sound (jaw light, power amplifier are not turned on), showing the frequency response characteristics of the A ring under test.
5.1.3 For stereo cinemas, the A loop of each channel should be measured separately: Film
Test film
Photocell
Audio
Optical front
Amp-hour analysis
Millimeter
Audio frequency analyzer
Figure 1 Block diagram of A loop frequency response characteristic test
5.1.4 Record or print the measured A loop frequency response characteristic data. 5. 2 B loop
Digital printer
Electronic recorder calibration
5.2.1 See Figure 2 for the B loop measurement block diagram.
Sleep generator
Subtractor
B loop average current
Power amplifier
GB/T 15397: 94
Function
Audio unit
(Guanqing Hall)
Measurement using microphone
Spectrum analyzer
Sound level meter
Real-time analyzer
Figure 2B Block diagram of ring frequency response characteristics measurement
Record calibration
5-2-2 The signal source used for measuring the frequency response of the sound field should be an electronic wide-band pink noise generator (which should be compatible with the theater signal processor).
5.2.3 Measurement point location in the measured sound field
5.2.3.1 In the mixing studio or recording control room, each The location of the main listener (recording mixer) is a must-measure point. 5.2.3.2 The listening area of ​​the screening room and indoor theater is relatively large. In order to make the obtained measurement results represent the electroacoustic frequency response characteristics of the entire listening area, it is recommended that:
When measuring with 1/octave, no less than 3 measuring points are required, and when measuring with 1/3 octave, no less than 5 measuring points are required. h.
5.2.3.3 When selecting the location of each measuring point, the following conditions should be met:. The distance between all measuring points and the added surface should be no less than 1.5m: h. The height of all measuring points from the ground should be based on the height of the audience's ears after sitting, generally 1. 1~1.2 m, and should be 15 cm above the upper edge of the seat back1
When selecting the measurement point of a symmetrical theater, the measurement point should be at least 1~2 seats away from the film's direction and horizontal center line; d.
For theaters with balcony seats, avoid selecting the measurement base point directly below the balcony flange: In indoor theaters, it is recommended to give priority to selecting point S in Figure 3, and point R in Figure 4 should be added when there is a balcony seat. The selection of other test points should be at least 1.5 m away from S (or R). For low-frequency measurements, the integration capacitor with a time constant should be used as much as possible, and real-time analysis only needs to open a window (that is, the time should be long) 5.2.4 Measurement steps
GB/T 15397—94
Figure 3 Cinema auditorium
Screen to the last row of seats: Width of the rear edge of the seating area
Figure 4 Cinema floor seats
C Center of the front row of the first floor seats to the last row of seats; D Width of the last row of the first floor seats 5.2.4.1 Before measurement, the test instruments and microphones used should be calibrated. Seating area reaches the maximum
Collection area fast ticket
5.2.4.2 Before measurement, a pre-inspection should be carried out against the E ring conditions. For items that do not meet the requirements, they should be corrected and measured. Items that cannot be corrected at the time should be recorded in detail for reference when analyzing the data and drawing test conclusions. 5.2.4.3 Connect all test equipment according to Figure 2 and pre-power on for 10 to 15 minutes before measurement. 5.2.4.4 Turn the power amplifier of the channel to be tested gradually to its normal position, so that the broadband pink noise level emitted by the loudspeaker of this channel reaches 85 dB(C) at the measured point in the hall; in a stereo theater, the center channel should be measured first, and then the left, right and surround channels should be measured in turn. 5.2.4.5 Record or print the measured data.
5.2.5B loop data processing
5.2.5.1 The average value (usually the arithmetic mean) of the sound pressure level measured in each 1/3 octave band in the frequency band of 400Hz to 2kHz is used as the reference sound pressure level.
5. 2. 5.2 Spatial average value If the difference in the sound pressure level of the same segment measured at different observation points does not exceed 1 dB, the arithmetic mean method can be used to calculate the average sound pressure level of each measurement point. If the difference exceeds 4B, the sound pressure level average formula should be used to calculate the sound pressure level average.
Average sound pressure level calculation formula:
GB/T15397-94
L — 10logio
Where: L. —The average value of the sound pressure level measured at several measuring points,dB: number of measurement points,
L—the sound pressure level measured on the segment at the th measurement point, dH. 10 yuan
If there are 5 measurement points, the average value of the sound pressure level measurement values ​​on each frequency band is calculated as follows. L,=10logu[number
[number (10%+10%+10%+10%+10%]] Where: 1——the sound pressure level measured on the segment at measurement point 1, dB; L——the sound pressure level measured on the segment at measurement point 2, dB. And so on.
6 Listening test
This standard specifies the objective evaluation method of the A ring and the B ring (sound system), that is, the measurement method, but for the evaluation of the sound system, listening is also required. Test.
For stereo cinemas, Cat.No.351, Cat.No.251 or similar audition demo films can be used for audition. If you want to emphasize the clarity and intimacy of the dialogue, the sound image shift and realism of the effect sound, the dynamic range and layering of the music, the strong sound level has power without distortion, and the weak sound level has layering without being drowned by noise. For monophonic cinemas, a newer soundtrack with familiar content can be used for screening and playback. GB/T 15397-94
Appendix A
Measurement correction factors
(Supplement)
A1 In order to maintain the consistency of the subjective electroacoustic frequency response, the standard ring characteristic curve needs to be slightly corrected according to the size of the auditorium. That is, the mid- and high-frequency characteristics of large theaters should be slightly attenuated, and the high-frequency response of small theaters should be slightly improved. The correction factors are shown in Table A1. Table A1 Approximate correction factors based on the volume of the auditorium Frequency
—3, 0
A2 Measure the electroacoustic frequency response under the typical working humidity of the auditorium as much as possible. If the humidity is abnormal, it should be corrected according to the following data. When the relative humidity is 20% relative to 1kHz, the high-frequency loss of 10kIIz is about 1dB per 20m. When the relative humidity is 45%, the loss is about 3dB; when the relative humidity is 80%, the loss is about 2dB. A3 After measuring the A ring and the H ring respectively, it is recommended to test the total characteristics of the (A+B) ring. Use a pink noise test piece to play the sound, do not light the mouse lamp, turn on the switches of each power amplifier, and put the stereo processor in the normal operating position. Set the microphone to the S point so that the sound pressure generated by the pink noise is at 85 dB(C).
A4 Pay attention to avoid the situation where the frequency response characteristics are within the tolerance range and the tone is unbalanced. For example, it should be avoided that the total bass response is the maximum positive error (or negative error) and the treble response is the maximum negative error (or positive error). Additional remarks:
This standard was proposed by the Ministry of Radio, Film and Television of the People's Republic of China. This standard is under the jurisdiction of the China Film Science and Technology Research Institute of the Ministry of Radio, Film and Television. This standard was drafted by the China Film Science and Technology Research Institute of the Ministry of Radio, Film and Television.
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