CEA-426-B-1998 Loudspeakers Optimum Amplifier Power《扬声器 最佳功放功率》.pdf

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1、 ANSI/CEA Standard Loudspeakers, Optimum Amplifier Power ANSI/CEA-426-B R-2011 July 1998 NOTICE Consumer Electronics Association (CEA) Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purch

2、asers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards, Bulletins and other technical publications shall not in any respect preclude any memb

3、er or nonmember of CEA from manufacturing or selling products not conforming to such Standards, Bulletins or other technical publications, nor shall the existence of such Standards, Bulletins and other technical publications preclude their voluntary use by those other than CEA members, whether the s

4、tandard is to be used either domestically or internationally. Standards, Bulletins and other technical publications are adopted by CEA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, CEA does not assume any liability to any patent owner, nor does it

5、 assume any obligation whatever to parties adopting the Standard, Bulletin or other technical publication. This document does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this document to establi

6、sh appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. This document is copyrighted by the Consumer Electronics Association (CEA) and may not be reproduced, in whole or part, without written permission. Federal copyright law prohibits

7、unauthorized reproduction of this document by any means. Organizations may obtain permission to reproduce a limited number of copies by entering into a license agreement. Requests to reproduce text, data, charts, figures or other material should be made to CEA. (Formulated under the cognizance of th

8、e CEA R3 Audio Systems Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2012 Technology manufacturers stated ratings must clearly specify any such enclosure. No external crossover network shall be used except as specified by the manufacturer. Systems provided with enclosures and/or crossove

9、r networks are to be tested with crossover networks and enclosures intact, unless otherwise specified by the manufacturer. 4 Normative references 4.1 EIA-299-A Loudspeakers, Dynamic - Magnetic Structures and Impedance 4.2 IEC-60268-5 Sound System Equipment. Part 5: Loudspeakers 4.3 Keele, D.B Low Fr

10、equency Loudspeaker Assessment by Nearfield Sound-Pressure Measurement, Journal of the Audio Engineering Society, vol. 22, no. 3, p. 154 (1974) 5 Definitions Full range is defined as substantially including bass, midrange, and treble frequencies occurring in music and speech. 6 Test methods 6.1 Appa

11、ratus 6.1.1 Compact disc player with “Track Repeat“ function (if using the CEA compact disc with recorded test signals) 6.1.2 Power amplifier minimally rated at the test power CEA-426-B 36.1.3 CEA compact disc with recorded test signals, or other means for generating test signals as defined in Annex

12、 A (normative) 6.1.4 True RMS voltmeter with input impedance at least ten times the loudspeaker rated impedance, and with an ac bandwidth of at least 40 Hz to 10 kHz 6.1.5 Sine wave generator covering 40 Hz to 10 kHz 6.1.6 1/3-octave real time audio analyzer using class 2 or class 3 filters, capable

13、 of displaying “total SPL“ 6.1.7 Measuring microphone, omnidirectional, with flat frequency response 0.5 dB from 40 Hz to 10 kHz and dynamic range upper limit of 140 dB SPL minimum. 6.1.8 Switched 20 dB attenuator, described in Annex B (normative) 6.2 Test conditions and operator notes 6.2.1 Each te

14、st may be conducted with a fresh sample of the product, or the tests may all be performed on one sample. 6.2.2 The loudspeaker shall be tested as the manufacturer specifies it to be used. If no such specification is provided, individual transducers shall be tested on a baffle of reasonable proportio

15、ns whose area is no less than ten times the nominal area of the transducer. The accelerated life test at continuous power may also be conducted with the transducers in free air. Complete systems shall be tested intact. The test shall be conducted at an ambient temperature of 25 C 5 C and relative hu

16、midity of 30% to 80% in a room or enclosure that maintains these conditions and does not change fundamental resonance frequency more than 5%. 6.2.3 If a crossover or filter network is specified by the manufacturer, it shall be installed according to the manufacturers instructions. If no such network

17、 is specified, the amplifier and voltmeter shall be connected directly to the loudspeaker terminals. 6.2.4 Verify that the speakers rated impedance complies with EIA-299-A. Calculate the test voltage to be applied to the speaker, using this rated impedance. Test voltage is equal to the square root o

18、f the product of the optimum amplifier power and the rated impedance. 6.2.5 CAUTION WEAR EAR PROTECTION! High sound levels of annoying signals are produced which can cause hearing damage with prolonged exposure. The operator is advised to wear appropriate protection such as ear plugs, preferably bal

19、anced attenuation devices which will still permit the operator to listen critically for distortion or other signs of distress in the device under test. CEA-426-B 46.2.6 Test sequence Power compression is the least stressful test and should be run first, followed by the distortion test, with the acce

20、lerated life test performed last. 6.3 Section A power compression This procedure tests the degree to which acoustic output of the speaker is compressed at the optimum amplifier power. 6.3.1 Procedure Refer to Annex A.1 and A.3, and to the equipment block diagram in Annex B (normative). 6.3.1 Place t

21、he microphone in a close-mic position (refer to Keele paper cited in section 4.3), on axis with its geometric center, and connect the microphone output to the input of the 1/3-octave real time analyzer. Using the switched attenuator, apply the variable rate swept sine wave test signal to the speaker

22、 at an amplitude 20 dB below the optimum amplifier power, and record the reference spectrum of the speaker output. 6.3.2 Reduce the drive level by 6 dB. Using the switched attenuator, simultaneously raise the amplitude of the test signal by 20 dB and attenuate the output of the microphone amplifier

23、by 20 dB; this applies considerably less than full power to the loudspeaker. The spectrum produced should track the original curve, but should be about 6 dB lower in amplitude, indicating little or no compression taking place. At this time, the operator should listen for distortion; there should be

24、minimal distortion at this reduced power level. If severe distortion occurs, the operator should stop the test, noting the frequency at which the distortion was worst, and should proceed immediately to the distortion test procedure described in section 6.4. If only minimal distortion is heard, the o

25、perator should slowly restore the drive level to the maximum value, or until power compression is observed, whichever occurs first. To avoid overheating high frequency drive units, the bursts of test sweeps should be kept brief only three or four cycles before a pause when near full power. 6.3.3 Rep

26、eat the test sweep for one full minute, and then record the output spectrum. If no compression takes place, the displayed amplitude of the measured spectrum will be identical to that of the previously recorded signal at all frequencies. The speaker shall have passed the test if each 1/3 octave band

27、of the displayed spectrum of the full power signal is reduced in amplitude by no more than 6 dB compared to the reference level established in section 6.3.1 from 40 Hz to 10 kHz or through the bandwidth specified by the manufacturer. 6.4 Section B Distortion 6.4.1 This procedure measures harmonic di

28、stortion at the optimum amplifier power using sine wave test signals at 1/3-octave spaced IEC center frequencies. When a limited frequency range is specified, the speaker need not be tested outside the specified range. The test signals are contained on the CEA compact disc. As with the power compres

29、sion test, the test CEA-426-B 5signal can be started at reduced level and slowly increased to the maximum. The operator should be particularly careful at frequencies found to be suspect in the power compression test. In general, speakers are likely to have high distortion at the lowest frequency spe

30、cified and near crossover frequencies in multi-way systems. Continuous sine waves at full power can burn out tweeters in a matter of seconds. Measurements in the tweeters operating range must be made very quickly. Usually, two seconds is all the time needed for the analyzer to settle. If the operato

31、r needs to see it again, allow a cool down period of ten seconds or more. 6.4.2 Procedure Place the microphone in a “close-mic“ position (refer to Keele paper cited in section 4.3), and connect its output to the input of the 1/3-octave real time analyzer. Apply the sequence of sine wave test signals

32、 to the speaker at the optimum amplifier power. Within its specified bandwidth, the speaker shall generate harmonics whose RMS sum amplitude is less than that of the fundamental. Using a spectrum analyzer with a “total SPL“ display, the harmonic content of the signal will be less than that of the fu

33、ndamental if the “total SPL“ is greater than the amplitude of the fundamental by no more than 3 dB. For speakers with multiple drive units, repeat the procedure with the microphone centered on each drive unit. The speaker shall be considered to have passed this criterion if the “total SPL“ displays

34、no more than 3 dB greater amplitude than the amplitude of the fundamental for each frequency tested within its specified bandwidth. For speakers with multiple drive units, each iteration of the test must pass. 6.5 Section C Accelerated life test at continuous power This procedure simulates the worki

35、ng life of the speaker by testing its ability to withstand a test signal at half the optimum amplifier power for an extended duration without suffering an irreversible and unacceptable change in performance parameters or integrity. The speaker is unlikely to fail quickly in this test because it has

36、already been subjected to full-power over the entire frequency range by the previous tests. The criterion for passing this test is that the speaker not acquire a permanent shift in parameters such as free air resonance frequency. Therefore, we will only know that the speaker failed when it has perma

37、nent damage. The risk can be reduced somewhat by monitoring the speaker during the test with a spectrum analyzer or by ear and disconnecting the test signal when a change is noted. Permanent shift may or may not have occurred at this point. If it has not, it cannot be assumed that it will either pas

38、s or fail the eight hour test. If the speaker does pass this test, then its rating has been verified. 6.5.1 Break-in Select the calibration sine wave tone on the compact disc, and adjust the amplifier output level to read 3 dB lower than the voltage calculated in paragraph 6.2.4, (i.e. the calculate

39、d voltage multiplied by 0.707). Set the compact disc player to repeat the band containing the weighted noise test signal continuously. Apply the break-in signal to the loudspeaker for an uninterrupted period of one hour. At the end of the break-in period, let the magnet structure cool to below 35 de

40、grees C, determine and record the speakers fundamental resonance frequency. CEA-426-B 66.5.2 Test Select the calibration sine wave tone on the compact disc, and adjust the amplifier output level to read the voltage calculated in paragraph 6.2.4. Set the compact disc player to repeat the band contain

41、ing the weighted noise test signal continuously. Apply the signal to the loudspeaker for an uninterrupted period of eight hours. 6.5.3 After a minimum recovery period of one hour, and after the magnet structure surface temperature has cooled below 35 C, apply a sine wave signal of half the test volt

42、age to the loudspeaker and sweep through the rated bandwidth specified by the manufacturer, or from 40 Hz to 10 kHz if no rated bandwidth is supplied. The loudspeaker shall have passed the accelerated life test if there is no test induced noise or structural damage that render the loudspeaker unsuit

43、able for its intended application, and the fundamental resonance frequency has not dropped more than 10% below the recorded reference frequency. 7 Marking, labeling, packaging A loudspeaker or loudspeaker system may be labeled by the manufacturer with a CEA optimum amplifier power rating at or below

44、 the maximum input power in watts at which the loudspeaker or loudspeaker system passes CEA criteria for all three tests, power compression, distortion, and accelerated life. The rating must clearly specify any special test conditions such as special enclosures, ambient conditions, crossover network

45、s, etc CEA-426-B 7Annex A (normative) This section describes the contents of the test compact disc containing the calibration and test signals for all the tests defined in this standard. It is recommended that this compact disc be used for these tests to avoid the possibility of error in generating

46、the test signals. For those who wish to generate their own signals, a complete description of each signal is presented in this annex following the description of the compact disc. A.1 Test CD description Contents of CEA Loudspeaker Power Rating Compact Disc 0 min Track 1. 1.0 kHz Reference sine wave

47、. Ramps up. 1 min Track 2. Life test noise at RMS amplitude 3 dB lower than Refrence. 31 min Track 3. Variable rate sweep, 0.5 second cycle time. 41 min Track 4 to 29. Pure tones at reference amplitude on ISO 1/3 octave preferred center frequencies, 20 Hz to 5 kHz. 15 seconds followed by 5 seconds s

48、ilence for each frequency. 25 tones, 8:20. 49 min End. A.2 Amplitude calibration Band # 1 of the test CD contains a 1000 Hz sine wave to be used to calibrate the amplitude of the signals. The test tones for the distortion test and the swept sine for the power compression test signal are recorded at

49、the same level as the calibration tone, and the noise signal is recorded at a level such that its rms level is 3 dB lower than the calibration tone. Therefore, the signal level need be set only once to achieve the proper levels for all tests, and power calculations may be based on this setting. A.3 Variable rate sweep test signal A.3.1 The test signal specified for the power compression test is a variable-rate swept sine wave of constant amplitude. The power spectrum of this signal is determined by a variable sweep rate, and is the same as the weighted noise s