GB/T 51091-2015Technical code for listening test room engineering (English PDF)

2 Terms

2.0.1 listening test room - room used for listening tests on electroacoustic products, equipment and systems.

2.0.2 acoustical design - measures taken during the architectural design process to secure, from the acoustic point of view, that the building meets the requirements.

2.0.3 reverberation time - time needed for the average sound energy density to decay from its original value to one millionth of it (60 dB) after the sound has reached a steady state and the source has been stopped.

2.0.4 background noise - noise from all other sources than the sound source under test; also called the noise floor.

2.0.5 sound coloration - phenomenon in which the original timbre is altered under the influence of the indoor frequency response and other factors.

2.0.6 NR noise rating curve - family of curves by which permissible noise values are rated by octave band sound pressure level, the rating value of each curve being the octave band sound pressure level figure at 1000 Hz, also called the NR value. In rating, the NR value of the curve reached by the highest limit among the octave bands governs.

2.0.7 sound absorption material - material that absorbs incident sound.

2.0.8 sound absorption coefficient - ratio, at a given frequency and under given conditions, of the sum of the sound power absorbed by the boundary surface or medium and the sound power transmitted through the boundary (a wall or a partition, for instance) to the incident sound power. The measurement conditions and the frequency are to be stated.

2.0.9 sound diffuser - component that increases the diffusion of the sound field through the nature, shape, dimensions or special construction of the material.

2.0.10 sound absorber - component made mainly for sound absorption, using the space inside the room.

2.0.11 sound insulation door - door whose sound insulation capacity is raised by a special construction and manufacturing process.

2.0.12 sound insulation window - window whose sound insulation capacity is raised by a special construction and manufacturing process.

2.0.13 nominal area - area formed to a particular length-to-width ratio for the process requirements of a listening test room; it usually differs from the floor area in figure by 5 %.

2.0.14 sound lock - building construction in which two sound insulation doors are provided at the entrance of a room in order to increase the sound insulation performance, with a sound absorbing space left between the two doors.

2.0.15 air-borne sound - sound propagated around with air as the medium.

2.0.16 structure-borne sound - noise propagated from mechanical vibration through the building structure.

2.0.17 single-number quantity - single sound insulation parameter settled by the method laid down in the current national standard GB/T 50121-2005 Standard for rating of sound insulation in buildings, taking as a whole the sound insulation performance of the test specimen in the one-third octave bands from 100 Hz to 3150 Hz (or in the one-one octave bands within the range 125 Hz to 2000 Hz); its unit is the decibel (dB).

2.0.18 weighted sound reduction index - single-number quantity that characterises the air-borne sound insulation performance of a building component.

2.0.19 weighted standardized level difference - single-number quantity of the air-borne sound insulation performance between two rooms, obtained with the reverberation time of the receiving room as the correction parameter.

2.0.20 weighted normalized impact sound pressure level - single-number quantity of the impact sound insulation performance of a floor or floor construction, obtained with the sound absorption of the receiving room as the correction parameter.

2.0.21 weighted standardized impact sound pressure level - single-number quantity of the impact sound insulation performance of a floor or floor construction, obtained with the reverberation time of the receiving room as the correction parameter.

2.0.22 spectrum adaptation term - correction value that has to be added to the air-borne sound insulation single-number quantity because the sound insulation spectrum differs and because the noise spectrum of the source space differs. When the noise of the source space has a pink noise frequency characteristic, the correction obtained by calculation is called the pink noise spectrum adaptation term; when it has a traffic noise frequency characteristic, the correction obtained is called the traffic noise spectrum adaptation term.

2.0.23 impact sound pressure level - average one-third octave band sound pressure level (SPL) in the receiving room, expressed in dB, when the floor under test is excited with a standard tapping machine.

3 Site selection and plan design

3.1.1 The environmental noise of the main building housing the listening test room should comply with the provisions for sound function zones of category 2 and above in the current national standard GB 3096 Environmental quality standard for noise.

3.1.2 Air conditioning machine rooms, fan rooms, cooling towers and refrigerating machine rooms should be placed in a building separate from the one that houses the listening test room; when they are inside the same building, they should be far from the listening test room.

3.1.3 The plan arrangement of the building shall be laid out reasonably according to the spatial dimensions, shape, environmental requirements and running conditions of the listening test room, the control room and the ancillary rooms.

3.1.4 The listening test room shall keep clear of sources of strong electromagnetic field radiation; where that cannot be avoided, effective electromagnetic shielding measures shall be taken.

3.2.1 The listening test room shall be located in the area of the site where noise and vibration interference is smaller.

3.2.2 The control room and the ancillary rooms should adjoin the listening test room.

3.2.3 The control room should adjoin the rear wall of the listening test room.

3.2.4 The entrance door should be positioned on a side wall of the listening test room and towards the rear wall.

3.2.5 The arrangement of the loudspeakers shall comply with the relevant provisions of the current national standard GB/T 12060.13 Sound system equipment - Part 13: Listening tests on loudspeakers.

3.2.6 The arrangement of the listeners' positions shall satisfy the following requirements: (1) for two-channel stereo reproduction, the minimum listening distance should be 1.0 to 0.8 times the spacing between the loudspeakers; (2) each listener shall be at least 0.6 m from the side wall and at least 1.5 m from the rear wall; (3) the seats of the front row and of the rear row shall be staggered, and the gap between the two rows of seats shall be such that the listeners are comfortable.

4 Acoustical design

4.1.1 The room acoustic quality of the listening test room shall meet the requirements of subjective sound quality assessment of electroacoustic products, equipment and systems.

4.1.2 The acoustical design shall cover the room dimensions, the reverberation time and the sound absorption and diffusion treatment.

4.1.3 The transmission frequency response within the listening area of the listening test room should be flat, there shall be no perceptible sound coloration, and acoustic defects such as echo, flutter echo, sound focusing and resonance shall not appear.

4.2.1 The floor area of the listening test room shall be settled according to the category and nature of the sample or system under assessment and the number of listeners.

4.2.2 Listening test rooms may be divided into three types, small, medium and large, and the nominal room area, room height and room proportions corresponding to each type should comply with Table 4.2.2. The table gives, for the small type, a nominal area of 25 m2 to 80 m2 and a room height of 2.7 m to 3.0 m; for the medium type, 80 m2 to 200 m2 and 3.1 m to 4.9 m; for the large type, 200 m2 to 500 m2 and 5.0 m to 8.0 m. The height (H) to width (W) to length (L) proportions for the small type are 1:1.6:2.5, 1:1.5:2.39 and 1:1.96:2.59. The proportion column of the medium and large types is a single merged cell holding three values, 1:2.5:3.2, 1:2.27:3.14 to be chosen when H is 4.1 m or more, and 1:1.96:2.59 to be chosen when H is 4.6 m or more.

4.3.1 At a frequency of 500 Hz the reverberation time of small and medium listening test rooms shall lie between 0.3 s and 0.5 s (Figure 4.3.1-1), and that of large listening test rooms shall lie between 0.4 s and 0.6 s (Figure 4.3.1-2). The two figures plot the permitted band of reverberation time T against room volume V, Figure 4.3.1-1 over a volume range of some 70 m3 to 1000 m3 and Figure 4.3.1-2 from 1000 m3 upwards; the bands are read from the graphs and their end values are not tabulated in the text.

4.3.2 The frequency characteristic of the reverberation time, as a ratio relative to 500 Hz, should comply with Table 4.3.2. For small and medium listening test rooms the ratio is 1.0 to 1.1 at 63 Hz, 1.0 at 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz and 4000 Hz, and no value is given at 8000 Hz. For large listening test rooms it is 1.0 to 1.2 at 63 Hz, 1.0 to 1.1 at 125 Hz, 1.0 at 250 Hz, 500 Hz, 1000 Hz and 2000 Hz, 0.8 to 1.0 at 4000 Hz and 0.8 at 8000 Hz.

4.3.3 The reverberation time may be calculated by formula (4.3.3), in which T is the reverberation time inside the listening test room in seconds, V is the room volume in cubic metres, S is the room surface area in square metres, alpha with a bar over it is the average sound absorption coefficient and m is the attenuation coefficient of the sound wave in air in reciprocal metres; the figures for 4m shall comply with the provisions of Appendix A. The equation itself is printed as a fraction with the numerator 0.163V and is not reproduced here.

4.3.4 The reverberation time should be calculated separately for the centre frequencies from 63 Hz to 8000 Hz.

4.4.1 The sound absorption inside the listening test room shall cover the sound absorption of the various sound absorption materials and constructions of the ceiling, walls and floor, of the ventilation openings, of the sound insulation doors and windows, and of the seats and the listeners.

4.4.2 Dissipative sound absorption materials should be chosen for the sound absorption material, and the following requirements shall be met: (1) materials with different frequency characteristics of the sound absorption coefficient shall be combined so that the average sound absorption coefficient over the whole frequency band is balanced; (2) the sound absorption material shall have a test report on its sound absorption coefficient, and the testing of the sound absorption coefficient should comply with the relevant provisions of the current national standard GB/T 20247 Acoustics - Measurement of sound absorption in a reverberation room; (3) the fire performance and the environmental performance of all sound absorption materials and constructions shall comply with the provisions of the national standards in force, and their colour tone and appearance shall make the listeners feel comfortable; (4) the backs of the seats should not be higher than shoulder height.

4.4.3 The sound absorption material should be distributed and shall comply with the following provisions: (1) the sound absorption coefficient of each pair of boundary surfaces should not exceed that of the others by more than 1.4 to 1; (2) the sound absorption of the wall surface faced by the listeners shall be increased; (3) sound absorption treatment shall be given at the indoor wall corners; (4) carpet with sound absorbing performance shall be laid on the room floor.

4.4.4 The provision of diffusers should comply with the following provisions: (1) scalene triangular or curved diffusers may be provided on the two side walls, and wave-shaped diffusers may be provided on the ceiling; (2) the dimensions of the diffusers shall be greater than one seventh of the diffused wavelength, and the boundary surface faced by the listeners should be made a sound absorbing surface; (3) small listening test rooms need not have diffusers, but the shape of the room should be made a non-parallel irregular shape.

5 Noise control design

5.1.1 Before the architectural design of the listening test room, comprehensive measures shall be taken, according to the process requirements and in relation to the position, direction and strength of the noise and vibration sources, in respect of the protective separation distance, the plan arrangement, sound insulation, vibration isolation and noise reduction.

5.1.2 The noise control design shall control the various noise sources inside and outside the building that cause interference to the listening test room.

5.1.3 The listening test room should use the rest hall, the entrance hall and the corridors as a means of isolating outside noise or of preventing outside interference, and at the same time the rest hall, entrance hall and corridors should be given sound absorption and noise reduction treatment.

5.1.4 A sound lock should be provided at the entrance of the listening test room.

5.2.1 The noise level inside the listening test room shall not exceed the NR values of the noise rating curves laid down in Table 5.2.1, which sets the permissible noise criterion at NR-15 when the ventilation and air conditioning equipment is switched off and at NR-20 when it is switched on.

5.2.2 The octave band sound pressure levels of each NR value shall comply with Table 5.2.2. For NR-15 the one-one octave band sound pressure levels in dB are 65 at 31.5 Hz, 47 at 63 Hz, 35 at 125 Hz, 25 at 250 Hz, 19 at 500 Hz, 15 at 1000 Hz, 11 at 2000 Hz, 9 at 4000 Hz and 8 at 8000 Hz. For NR-20 they are 69, 51, 39, 30, 24, 20, 16, 14 and 13 at the same nine frequencies.

5.3.1 The air-borne sound insulation performance of the enclosure structure of the listening test room and the impact sound insulation performance of the floor above it should comply with Tables 5.3.1-1 and 5.3.1-2. Table 5.3.1-1 requires a weighted sound reduction index Rw of 60 dB or more for partition walls and floors and of 55 dB or more for the sound insulation observation window; for sound insulation doors it requires the weighted sound reduction index plus the pink noise spectrum adaptation term (Rw + C) to be 35 dB or more for a simple sound insulation door, 40 dB or more for a sound insulation door with a sound lock and 45 dB or more for a sound insulation door without a sound lock; for the external wall it requires the weighted sound reduction index plus the traffic noise spectrum adaptation term (Rw + Ctr) to be 45 dB or more. Table 5.3.1-2 requires, for the floor above the listening test room, a weighted normalized impact sound pressure level Ln,w of less than 40 dB by laboratory measurement and a weighted standardized impact sound pressure level Lnt,w of 40 dB or less by field measurement.

5.3.2 The sound insulation design of the enclosure structure shall comply with the following provisions: (1) the sound insulation design should be calculated separately for each one-one octave band within the centre frequency range 125 Hz to 4000 Hz, and the low frequency sound insulation performance below 125 Hz should be estimated; (2) the calculation of the sound insulation of the wall body shall meet the requirements of Appendix B of this code.

5.4.1 The design of the sound insulation door shall satisfy the following requirements: (1) the air-borne sound insulation performance of the sound insulation door shall comply with Table 5.3.1-1 of this code; (2) the door leaf of the sound insulation door shall be of multilayer composite construction filled in the middle with porous sound absorption material; the joint between the door leaf and the door frame shall have sealing measures, and so shall the joint between the door frame and the wall opening.

Status of this code

Announcement No. 780 of the Ministry of Housing and Urban-Rural Development, dated 8 March 2015 and reproduced in the front matter, approves the Technical code for listening test room engineering as a national standard numbered GB/T 51091-2015, to take effect on 1 November 2015. The prefix GB/T makes it a recommended standard.

The foreword states that the code was drawn up under the 2011 work plan of the Ministry (Jianbiao [2011] No. 17) by the Electronic Engineering Standard and Quota Station of the China Electronics Standardization Institute of the Ministry of Industry and Information Technology together with Beijing Aotewei Technology Co., Ltd. and other bodies, and that it is divided into 8 chapters and 2 appendices covering general provisions, terms, site selection and plan design, acoustical design, noise control design, design requirements of the public disciplines, construction and quality acceptance, and acoustic measurement and acceptance. The Ministry of Housing and Urban-Rural Development is responsible for its administration and the Ministry of Industry and Information Technology for its day-to-day management, while Beijing Aotewei Technology Co., Ltd. is responsible for interpreting its technical content.

The front matter of this copy carries no supersession line of the kind that names a replaced code, so no superseded code is recorded.

What the pages of this copy cover

The pages available for this copy are the front matter and printed pages 2 to 11 of the body. The table of contents above is taken from the first contents page and therefore runs as far as Chapter 7; the entries for Chapter 8 and for the appendices fall on the second contents page, which is not among the pages available. The foreword names Chapter 8 as acoustic measurement and acceptance and states that the code has two appendices, which clause 4.3.3 and clause 5.3.2 identify as Appendix A, on the values of 4m, and Appendix B, on the calculation of the sound insulation of the wall body.

Chapter 1, general provisions, falls on printed page 1, which is not among the pages available, so no text of it is reproduced above.

Note on an inconsistency in the original

In Table 5.3.1-2 the two rows of the impact sound insulation requirement are not written with the same inequality sign: the laboratory measurement row prints the weighted normalized impact sound pressure level Ln,w as less than 40, with a strict inequality, while the field measurement row prints the weighted standardized impact sound pressure level Lnt,w as 40 or less, with a non-strict one. Both are reproduced above as they are printed.