1、 ANSI/CEA Standard Standard Method of Measurement for Powered Subwoofers ANSI/CEA-2010-A July 2012 Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-NOTICE Consumer Electronics Associat
2、ion (CEA) Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining wi
3、th 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 member or nonmember of CEA from manufacturing or selling products not conforming to such Standards, Bulletins or other technical
4、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 standard is to be used either domestically or internationally. Standards, Bulletins and other technical publications are adopt
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6、 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 establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. This
7、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 unauthorized reproduction of this document by any means. Organizations may obtain permission to reproduce a limited number of
8、 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 the CEA R3 Audio Systems Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2012 Technology 60 East 42nd Street, Room 25
9、20, New York, New York 10165-2520, USA; Tel: +1 212 661 8528; Fax: +1 212 682 0477; Internet: http:/www.aes.org. Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-ANSI/CEA-2010-A 2 3.2
10、Definitions Powered Subwoofer A subwoofer that includes an integrated power amplifier. Sound Pressure Level The level of the acoustic pressure radiated by the device under test (DUT), typically measured at a sufficiently great distance and mathematically converted to an equivalent value for a 1 m (m
11、eter) free field measurement distance. Subwoofer A speaker designed to reproduce all or a portion of the audio signals below 120 Hz (hertz). 3.3 Symbols and Abbreviations dB decibel DUT Device Under Test HD+N Harmonic Distortion + Noise Hz hertz kHz kilohertz LF Low Frequency LFCS Low Frequency Cali
12、bration Source M Meter Pa pascal RCF Room Correction Factor rms Root Mean Square SPL Sound Pressure Level V volt 3.4 Compliance Notation As used in this document “shall” and “must” denote mandatory provisions of the standard. “Should” denotes a provision that is recommended but not mandatory. “May”
13、denotes a feature whose presence does not preclude compliance, and implementation of which is optional. “Optional” denotes items that may or may not be present in a compliant device. 4 Standard Test Conditions CAUTION WEAR EAR PROTECTION! High sound levels can cause hearing damage with prolonged exp
14、osure. The operator is advised to wear appropriate protection such as ear plugs, preferably balanced attenuation devices which will still permit the operator to listen critically for distortion or other signs of distress in the device under test. During testing the DUT shall be operated as per manuf
15、acturers instructions. Complete systems shall be tested intact. Testing shall be conducted at an ambient temperature of 22 C 5 C and relative humidity of 30% to 80%. The rms line voltage used to power the DUT shall be within 1% of the nominal rms value specified for use by the DUT (i.e. for a DUT th
16、at requires 120 V, the line voltage used shall be between 118.8 V and 121.2 V). Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-ANSI/CEA-2010-A 3 If a crossover or filter network is s
17、pecified by the manufacturer, it shall be installed according to the manufacturers instructions. All test equipment shall be properly calibrated, and its calibration shall be documented. 5 Test Procedures The purpose of the tests described in this standard is to provide data that will help the consu
18、mer understand how loud in volume, and how low in frequency, the DUT is capable of operating with acceptable frequency response, noise and distortion. 5.1 Determining Maximum SPL Output This test may be conducted in a calibrated anechoic chamber, in a suitable ground plane environment or in a large
19、calibrated room. The DUT shall be tested at the following frequencies: (20, 25, 31.5, 40, 50, and 63) Hz. This represents 1/3 octave spacing. With the input of the DUT connected to the preamplifier, or with its input shorted to ground, and without any input signal presented to the DUT, its volume co
20、ntrol shall be set to the maximum position and the sound pressure level from the DUT and the background noise of the environment and test equipment shall be measured. If the smoothed root mean square (rms) slow sound pressure level (SPL) (i.e., the rms SPL determined using a slow integration time an
21、d then 1/12 octave smoothed) exceeds 50 dB (flat/unweighted) at any test frequency (even though no input signal is present) the DUT, test environment and equipment does not comply with CEA-2010, and the reporting method described in Section 6 shall not be used for the DUT. Also, no reporting method
22、that might be confused with the reporting method described in Section 6 shall be used for the DUT. For each test frequency, a 1/3 octave band limited tone burst centered at the test frequency shall be fed to the DUT. SPL at the tone-burst test frequency Fo (fundamental) and over the frequency range
23、bounded by 1.26xFo and 10.0 kHz, where harmonic (and non-harmonic) distortion and noise (HD+N) occurs, shall be monitored. The signal level presented to the DUT shall be increased until the peak SPL of a 1/12 octave smoothed individual component of HD+N exceeds the level specified in Table 1 and ill
24、ustrated in Figure 1. The signal level presented to the DUT shall then be decreased to just below the occurrence of the above set of conditions. The peak SPL of the fundamental 3 Hz shall then be recorded. That is, the peak SPL is the highest SPL within the range bounded by 3 Hz below and 3 Hz above
25、 the fundamental. This SPL shall be referenced to a 1 m ground plane level. If the fundamental SPL cannot be recorded due to low fundamental output signal level or low signal-to-noise ratio using a single burst tone, averaging techniques shall be used to increase the signal-to-noise ratio of the mea
26、surement. Averaging shall be done in the time domain, or vector averaging shall be done in the frequency domain, prior to spectral smoothing. If the fundamental output still cannot be measured then the reported specification for the affected band (only) shall be “not applicable“ or “NA.” Inability t
27、o measure the fundamental output is most likely to occur at the lowest frequencies. If it is not possible to measure the SPL at the 20 Hz test frequency but it is possible to measure it at the 25 Hz test frequency then the value for the 20 Hz test frequency may be reported as the value for the 25 Hz
28、 test frequency minus 18 dB as an alternative to the “NA” or “not applicable” indication. It is acceptable for a subwoofer to report “not applicable” or “NA” for the 20-32 Hz band and a measured SPL value for the 40-63 Hz band. This procedure shall be repeated for each test frequency. The recorded S
29、PL shall be repeatable to within 1 dB. Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-ANSI/CEA-2010-A 4 Some subwoofers never surpass the HD+N threshold but begin to limit and/or com
30、press the output at some frequencies. If this is the case the peak SPL of the fundamental at the test frequency shall be entered. Note: In developing the above test procedure a goal was to take into account the fact that higher frequency noise that is not harmonically related to the fundamental can
31、have a negative impact on perceived loudspeaker performance. It is assumed that the higher in frequency the noise, the more annoying it will be to the listener. It is also assumed that noise that is closer in frequency to the fundamental will be more easily masked within the human hearing system, an
32、d can therefore be somewhat higher in level and still be acceptable. Table 1: Peak SPL Limits Attenuation Lower Frequency Limit (Hz) Upper Frequency Limit (Hz) Notes 0 dB 16 1.59xF0 Bandwidth bounded by 16 Hz and 2/3 octave above fundamental -10 dB 1.59xF0 2.52xF0 Bandwidth bounded by 2/3 octave abo
33、ve fundmental and 1/3 octave above 2nd harmonic -20 dB 2.52xF0 3.78xF0 Bandwidth bounded by 1/3 octave above 2nd harmonic and 1/3 octave above 3rd harmonic -25 dB 3.78xF0 5.61xF0 Bandwidth bounded by 1/3 octave above 3rd harmonic and 1/6 octave above 5th harmonic -35 dB 5.61xF0 8.5xF0 Bandwidth boun
34、ded by 1/6 octave above 5th harmonic and 1/12 octave above 8th harmonic -45 dB 8.5xF0 10,000 Bandwidth bounded by 1/12 octave above 8th harmonic and 10 kHz Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without
35、license from IHS-,-,-ANSI/CEA-2010-A 5 Figure 1: Harmonic Distortion + Noise Threshold vs. Frequency 5.2 Ground Plane Test Procedure Place the DUT on the floor oriented so that its major radiating element faces towards the microphone, which also rests on the floor (see Figure 2). Measurement distanc
36、e shall be at least 3 m (9.8 ft.). Figure 2: Basic ground plane measurement set-up for a subwoofer system whose driver and port are located on the same face of the enclosure (cut-away side view) The following considerations should be taken into account when planning and executing measurement set-up:
37、 a. The DUT and microphone should be placed as far as possible from walls and any other large acoustic reflective surfaces to maximize reflection times and thereby ensure the lowest possible measurement cutoff frequency. The measurements time-domain window length (interval bounded by arrivals of the
38、 direct source and major reflections) determines the lower bound of the m i c r op ho ne DUT 1 m v en t dri v er 3 m Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-ANSI/CEA-2010-A 6
39、measurement passband. Thus maximum reflection time ensures the best possible low-frequency extension. To keep measurement error to less than 1 dB, the nearest reflective object shall be no closer to the DUT or the measurement microphone than 5 times the DUT-to-microphone spacing. Increasing this dis
40、tance to 10 times the DUT-to-microphone distance will allow reflection errors to be less than 0.5 dB. b. Size of acoustic space, particularly the distance between the DUT and measurement microphone from room boundaries, governs the low-frequency limit associated with a ground plane (2 or half-space)
41、 measurement. The frequency at which 0.75 equals the DUT-to-room-boundary or microphone-to-room-boundary distance, where is acoustic wavelength ( = sound of speed divided by frequency), is the low frequency limit for a particular measurement arrangement. Table 2 tabulates the minimum DUT- or microph
42、one-to-room boundary distance for the standard 1/3 octave frequencies below 80 Hz. Application of an appropriately derived room correction factor (RCF), as described in Section 5.3, greatly extends the low-frequency limits obtainable via the ground plane methods. Table 2: Minimum required distance b
43、etween DUT and acoustically reflective boundaries (walls)1 LF limit (Hz) 0.75 min. distance to boundary m (ft.) 16.0 14.7 (48.2) 20.0 11.8 (38.7) 25.0 9.4 (30.8) 31.5 7.5 (24.6) 40.0 5.9 (19.4) 50.0 4.7 (15.4) 63.0 3.7 (12.1) 1Distance between measurement microphone and walls similarly dictates the
44、low-frequency limit of ground plane measurements, unless room-correction factor is derived. c. A DUT with major radiating elements located on multiple faces of the loudspeaker cabinet shall be oriented so that no point on the DUT is closer than the measurement distance to the microphone, and so that
45、 the microphone is as equidistant as possible from all radiating elements. That is, the measurement distance in this case is the shortest distance between the microphone and the DUT. (Note: The measurement distance must be at least 3 m.) Two possible sample test configurations are illustrated in Fig
46、ure 3. Copyright Consumer Electronics Association Provided by IHS under license with CEA Not for ResaleNo reproduction or networking permitted without license from IHS-,-,-ANSI/CEA-2010-A 7 Figure 3: Two examples of ground plane measurement set-ups for subwoofer systems with major radiating elements
47、 on multiple faces of their enclosures (cut-away view from above) d. Calibration: It is important to ensure that all devices in the measurement chain specifically the microphone, microphone pre-amp and any other devices are appropriately calibrated. Further, measurement practitioners shall follow go
48、od engineering practices and take care to record device settings and any other pertinent measurement conditions. Sufficient information about the test setup shall be recorded to enable a third party to repeat the tests. 5.3 Room Correction Factor Because few acoustic spaces are sufficiently large to
49、 permit measurements down to a high-performance DUTs low-frequency cutoff and because room effects are generally important well above that frequency, measurement accuracy and low-frequency extension may be greatly enhanced by applying a known RCF to data acquired indoors. The acoustic space in which measurements are taken will affect the low-frequency response of a
