1、 CEA Bulletin Home Theater Recommended Practice: Audio Design CEA/CEDIA-CEB22 March 2009 NOTICE Consumer Electronics Association (CEA)/Custom Electronic Design and Installation Association (CEDIA)Standards, Bulletins and other technical publications are designed to serve the public interest through
2、eliminating misunderstandings between manufacturers and purchasers, 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 tech
3、nical publications shall not in any respect preclude any member or nonmember of CEA or CEDIA 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 precl
4、ude their voluntary use by those other than CEA members, whether the bulletin 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 acti
5、on, CEA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard, Bulletin or other technical publication. This CEA/CEDIA Bulletin is considered to have International Standardization implication, but the International Electrotechn
6、ical Commission activity has not progressed to the point where a valid comparison between the CEA Bulletin and the IEC document can be made. This Bulletin does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of th
7、e user of this Bulletin to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (Formulated under the cognizance of the CEA/CEDIA R10 Residential Systems Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION/ CUSTOM ELECTR
8、ONIC DESIGN AND INSTALLATION ASSOCIATION 2009 Technology this will be an interactive decision process, driven by the physical, decorative and budgetary restrictions of the specific job. CEA/CEDIA-CEB22 - 6 - Number of seats Two factors determine how many seats can be accommodated, and their arrangem
9、ent: Viewing angles and sightlines, and Quality and seat-to-seat uniformity of bass. Room size You should first reach agreement with the customer on the size of seats to be installed and the space required to provide access during a performance, including considerations whether extra space is needed
10、. In an existing room, the room defines what seating arrangements are possible. In a new room design, the seating arrangement can help determine the room size and shape. In either case, it is much easier if the room has a rectangular shape. Acoustical treatment Once the room dimensions, loudspeaker
11、locations and seating have been decided, the interior acoustical treatment can be designed. The first requirement of that design is to ensure that dialogue intelligibility is not degraded by excessive reverberation and that tonal errors are not introduced by speaker/boundary interactions. Acoustical
12、 treatments can be designed to meet multiple purposes as required, including: Assisting the front channels in providing a good soundstage Providing localized sounds through the surround channels and Providing immersion or envelopment. Loudspeaker selection You can then select loudspeaker for front,
13、surround and subwoofer applications capable of delivering high sound quality to all members of the audience, at the sound levels required for credible movie and music experiences. Interior design and appearance Matters of interior design are of great importance, and there may be circumstances where
14、appearance prevails over acoustical requirements. Flexibility is important, and it is good to understand what is needed and why so that trade-offs can be made intelligently. The guidelines here in Home Theater Audio Design are sufficiently detailed to insure that all such decisions are informed choi
15、ces. CEA/CEDIA-CEB22 - 7 - Loudspeaker Layout Loudspeaker Layout Objectives Determine the multi-channel configuration to be used Identify the approximate loudspeaker locations Once these two choices have been made, overall room design can progress. (Details of loudspeaker location and mounting will
16、be discussed in “Audio System Component Location and Installation,” pg. 28.) Figure 1 A simple diagram showing the angular ranges within which loudspeakers should be located relative to the prime listening location. The locations of the front loudspeakers follow guidance at . The angular range for s
17、urround loudspeakers is the recommendation in ITU-R BS.775-2 (2006). Loudspeaker Layout Guidelines Loudspeaker layout is defined from the perspective of the prime listening location . In the example in Figure 1, the prime listening location is in the center of the seating area; this is obviously not
18、 a requirement. If there is to be only one pair of surround loudspeakers, as in a 5.1-channel system, they should be placed within the angular range 110 to 120. If there are four surround loudspeakers, as in a 7.1-channel system shown here, the side loudspeakers can be placed symmetrically within th
19、e angular range spanning 60 to about 100, and the rear loudspeakers within the angular range spanning approximately 135 to 150. A 6.1-channel system could obviously have a single center-rear loudspeaker, but it is recommended that the signal be split between two rear loudspeakers. Use additional sur
20、round loudspeakers for large audience areas and in large rooms. Loudspeakers should be spaced by equal angles within the angular range shown in Figure 1. CEA/CEDIA-CEB22 - 8 - Seating Layout Seating Layout Objectives There should be at least one prime listening location Rooms engineered for high qua
21、lity presentation should always have at least one prime listening location where the minimum possible design compromises are made. Replication of the prime listening location Other seats should recreate the prime listening location experience as closely as possible. It should be noted that many of t
22、he performance objectives listed above can be substantially met by proper configuration of the seats with respect to the room and to the installed loudspeakers. Figure 2 This floor plan shows locations of the pairs of nulls for the 2nd order axial (width and length) room modes. The shaded areas indi
23、cate that the designer should locate chairs such that listeners ears are more than 18” away from the nulls. Unshaded areas show acceptable locations for seats. CEA/CEDIA-CEB22 - 9 - Seating Layout Guidelines Seating layout guidelines assume the room is rectangular and that wall constructions are rea
24、sonably uniform. Seat locations should meet requirements for image projection. A central prime listening location In a rectangular room layout with reasonably uniform wall construction, the prime listening location should be at the geometric center of the loudspeaker array, as shown in Figure 1. Oth
25、er excellent seating locations are on the central front-to-back axis. Centerline seating Avoid aisles in the center of the room. Keep the centerline location free for seats between the left and right loudspeakers. The use of multiple subwoofers eliminates the odd-order room modes that otherwise woul
26、d be problematic at these locations. Maintain seat distance from speakers Avoid putting seats too close to any one loudspeaker, as this will result in an unbalanced sound stage, loss of envelopment, and distracting localization to the nearby loudspeaker. Avoid null points Avoid putting listeners hea
27、ds at or near the null points of the low-order (1st, 2nd and 3rd order) axial length and width standing waves (also called room modes). Listeners at these locations will not hear certain bass frequencies. The 1st order modes are particularly bothersome because they cut through the prime listening ar
28、ea. Appendix 1 explains that certain arrangements of two or four subwoofers reduce the problem to the 25% null lines shown in Figure 2. If these subwoofer configurations are used, seats should be arranged to place the heads not less than about 18 inches (50cm) from these null lines. CEA/CEDIA-CEB22
29、- 10 - Low Frequency Room Optimization Obviously it matters greatly if you are working within fixed room dimensions or with room dimensions that you are able to choose. If those dimensions describe a rectangular room, it may be possible to find a seating layout that provides good bass for multiple l
30、isteners. At the very least, these procedures make it possible to identify which seats are likely to be good, and which are likely to be less good. Figure 3 Arrangements of two or four identical subwoofers, driven by the same signal, that simplify the standing-wave patterns in a rectangular room to
31、the one shown in Figure 2. This allows seating locations or room dimensions to be adjusted to avoid problems, or to identify those seats that have less than ideal performance. Note that arrangement (c) is significantly less acoustically efficient than the other options (requiring larger/more subwoof
32、ers and amplifier power for similar sound levels). Arrangements (a) and (b) require double subwoofers at each location to equal the sound levels of (d). Low Frequency Room Optimization Objective Consistent bass across all seats The spectral content and overall level of bass should be consistent acro
33、ss all seats, with no audible resonances. Low Frequency Room Optimization Guidelines Minimize seat-to-seat differences Because of standing waves no two seats are likely to experience the same bass response. Equalization can improve the sound quality, but the seat-to-seat differences remain unless mu
34、ltiple subwoofers are employed in a manner that simplifies the standing-wave patterns in a room. Optimize bass through room management The use of full-range loudspeakers at the front- and surround-channel locations cannot deliver optimum bass to multiple listeners. Neither can a single subwoofer or
35、LFE channel. Optimum bass is possible only when all low frequencies are combined through bass management and then delivered to multiple subwoofers arranged in specific patterns. Figure 3 shows arrangements of subwoofers in a rectangular room. Of these, arrangements (a), (b) and (d) are preferred bec
36、ause they result in higher overall system efficiency, with only slightly CEA/CEDIA-CEB22 - 11 - decreased seat-to-seat uniformity. Double subwoofers at the mid-wall positions in (a) and (b) result in acoustical output comparable to that of arrangement (d). The subwoofers should be identical, mounted
37、 similarly with respect to the room boundaries, connected in the same polarity and set to the same output levels. Alternative Methods for Low Frequency Room Optimization One alternative low frequency room optimization method requires no specific room shape, subwoofer, or listener locations. It does,
38、 however, require specific acoustical measurements and signal processing. Similarly, yet another method is discussed in Appendix 1. It also assumes that the room is rectangular, but requires that the seating area be reasonably centered in the room. For each of several subwoofer arrangements, the alt
39、ernative methods allow users to identify the room dimensions that minimize seat-to-seat variations in bass. These two methods can be used separately or in conjunction with each other. A SUMMARY OF THE PROCESS 1. Select optimal combination of subwoofer layout and room dimensions. If room dimensions a
40、re fixed, select optimal subwoofer layout for that set of dimensions. Refer to Figures 2 and 3, and Appendix 1. 2. Use at least two subwoofers at different locations. In rectangular rooms, the arrangements of Figure 3 are preferred. 3. Damping of low-frequency room resonances is always desirable Thi
41、s may be achieved by using certain forms of wall construction, but only if it does not interfere with requirements for sound isolation. Techniques that result in high sound transmission loss also tend to result in massive and stiff inner wall surfaces. In those cases, it will be necessary to use spe
42、cially-constructed low-frequency absorbers. In general these will be of the diaphragmatic, membrane or panel type, and they should be located in high-pressure regions of the standing wavescorners are ideal locations. 4. Choose designs which allow further optimization during calibration Designs which
43、 allow control of individual subwoofer level and delay are particularly helpful in optimizing non-rectangular or otherwise non-trivial room designs. Judicious variation of levels and delays between multiple subwoofers can reduce audibility of resonances. 5. Include a high-resolution parametric equal
44、izer in the design, dedicated to the subwoofer The equalizer should be able to place the filters center frequency with a resolution of 2 Hz or better, and have at least 6 independently adjustable filters. Separate equalization channels for each subwoofer can be useful as well. Final equalization sho
45、uld be made at the prime listening location with all subwoofers operating simultaneously. Additional analysis using modal calculators is possible, for example the method available at http:/ The objective is to place the subwoofers so that they do not couple excessively into any mode which causes var
46、iation in sound levels in the seating area, and/or place the CEA/CEDIA-CEB22 - 12 - seats so that they do not sit in the dips of any modes. The accuracy of this approach may be affected by factors such as non-ideal wall construction, low-frequency absorption from upholstered furniture, etc., which i
47、s not accounted for in simple modal calculators. If the room is substantially non-rectangular, it is much more difficult to optimize. Steps 2-5 above are still recommended. Refer to Appendix 1 for a more detailed discussion of low-frequency optimization of the room. CEA/CEDIA-CEB22 - 13 - Sound Isol
48、ation Sound isolation is required for two purposes: 1) To prevent external noise from compromising the carefully engineered low background levels in the theater space; and 2) To prevent high sound levels inside the theater from being audible outside the space. Sound isolation is achieved, in part, b
49、y partition construction for three levels of room sensitivity: typical, sensitive, and non-critical. The recommended partition construction depends on the nature of the rooms adjacent to the home theater. Standard Construction Typical, non-acoustically rated construction is adequate for rooms adjacent to the home theater where the noise level is low, and the adjacent room is not noise sensitive. This would be appropriate for rooms such
