BOOK REVIEWS P. L. Marston Physics Department, Washington State University, Pullman, Washington 99164 These reviews of books and other forms of information express the opinions of the individual reviewers and are not necessarily endorsed by the Editorial Board of this Journal. Editorial Policy: If there is a negative review, the author of the book will be given a chance to respond to the review in this section of the Journal and the reviewer will be allowed to respond to the author’s comments. [See ‘‘Book Reviews Editor’s Note,’’ J. Acoust. Soc. Am. 81, 1651 (May 1987).]
The Loudspeaker Design Cookbook, 5th Edition Vance Dickason Audio Amateur Press, 1997, Peterborough, NH 03458. xii 216 pp. (including 51 pp. advertising section). Price: $34.95. Loudspeakerr Design Cookbook was released 22 The first edition of the Loudspeake years ago. Accor According ding to the author, each succes successive sive edition edition reflect reflectss the current engineering trends in the ever-shifting field of loudspeaker design. The first two editions were published by the author himself, and then Audio Amateur Press took over the publication of subsequent editions. It is not hard to see why Dic Dickas kason’ on’ss tex textt enj enjoys oys brisk brisk sal sales es over 60 000 copies of the latest edition have been printed . He writes clearly, thoroughly, and provides much data necessary for speaker design. The target audience can range from amateurs who are beginning to learn the ropes to well-established designers who like to keep a reference manual on hand. The back of the text contains 51 pages of advertisements by suppliers of drivers, driv ers, parts for makin making g driv drivers, ers, elect electrical rical/elec /electron tronic ic compo components nents,, test equipment, computer programs to assist and evaluate design, various publications, and even complete speaker kits and assembled speaker systems. The format of the text follows a rather logical path, although the chapter numbering is slightly quirky. There are twelve chapters in all, but the first chapter is titl titled ed ‘‘Ch ‘‘Chapter apter 0,’’ effectively effectively causing the last twelfth chapter to be christened ‘‘Chapter 11.’’ Technical terms are carefully defined so that there should be no doubt in the mind of a novice as to what they mean. Dickason did not stint on providing tables and parametric curves that are used in desig designing ning speaker systems and predi predictin cting g the performance performance capabilities of components acting individually and in unison; and a fairly thorough, potentially valuable reference listing is given at the end of each chapter. Chapter 0 describes how electrodynamic loudspeakers work, the effect of gap/coil geometries, the real-world behavior of loudspeaker cones with their resonance modes, the necessity for dust caps, dome shapes in higher frequency drivers, suspension of the cone that is attached to the voice coil which, in turn, interacts with the speaker magnet, modeling of loudspeaker impedance, and speaker input power required on the basis of loudspeaker efficiency and room size. The simplest loudspeaker design is that of a closed box, which is the topic of Chap. 1. The closed box system, more suitable for low-frequency response, subdivides into two categories: the infinite baffle and the air suspension, pensi on, the latt latter er made popu popular lar in the 1950s by Acou Acoustic stic Research cofounded by Edgar Villchur and Henry Kloss. It remained for Richard Small Engineering g Society in June 1972 the to publish in the Journal of Audio Engineerin most definitive study of closed-box design. The Q-factor of the driver represents the interaction of the electrical, mechanical, and pneumatic factors of the woofer/enclosure combination in determining the system resonance and response curves. Computer simulation through the use of LEAP 4.0 ®, arguably the most sophisticated speaker design program available at the time, is used by the author to model a series of closed boxes with different values of Q. Performance characteristics such as group delay, cone excursions, impedance curves, etc. are shown to depend on physical parameters such as box size, woofer cone mass, free-air resonance, voice coil overhang, effective driver radiating area, reference efficiency, etc. Vented boxes constitute the subject of Chap. 2. Vented boxes carry the advantage of lower cone excursions near the box resonance frequency, thus providing higher power-handling capacity and lower modulation distortion,
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and they operate more efficiently. However, vented systems are considerably more sensitive than closed boxes to inappropriately chosen values of parameters param eters.. Mani Manipulat pulation ion of the total speak speaker-bo er-box x Q can be achie achieved ved by changing the volume of a closed box; vented enclosures are dealt with in terms of specific alignments, entailing adjustments of a number of specific parameters to achieve a more or less flat response. There are at least 15 well-esta well -establis blished hed alig alignmen nmentt catego categories, ries, such as SSB4 Super Fourth-Order Boom Box, SC4 Fourth Order Sub-Chebychev , QB3 Quasi Third-Order alignment, and discrete alignments such as the Fourth-Order Butterworth B4, Four Fourth-O th-Order rder Bessel BE4, and Butt Butterwo erworth rth Inter Inter-Ord -Order er IB4. The rather involved procedure of selecting a box size and relevant parameters is described descr ibed with a discu discussion ssion of box losses, use of accompanying accompanying design tables, tabl es, calcu calculati lation on of vent dimensions, dimensions, box tuni tuning, ng, and othe otherr param parameters eters.. Two drivers serve as examples of suitability for use in vented boxes, accompanied by a description of measurement parameters. Other topics in the chapter include box damping, the dual-woofer format, resistive and distributed vents, and electronically assisted vented designs, and vented rear chamber bandpass enclosures. Passive-radiator low-frequency systems, covered in Chap. 3, contain ‘‘drone ‘‘dr one cones’’ that substitute substitute for vents vents.. Whil Whilee they closely follow the vented loudspeaker design methodology, the passive-radiator systems carry the advantage advantage of lacki lacking ng vent pipe colo colorati ration on and can be used in small enclosures where the required vent lengths would exceed the box dimensions. The procedure of selecting a woofer is the same as that described in Chap. 2, and alignments are generally restricted to QB 3 , B4 , and C4 types. The determination of box size and relevant parameters are generally dealt with in the same manner as with vented enclosures. An additional factor is the so-called delta, the compliance ratio of the passive radiator. A section in this chapter also treat treatss passi passive ve radi radiator ator bandpass enclosures, enclosures, which can be best designed through computer simulation by the use of a speaker design program such as Speak ® by DLC or LEAP 4.0 by Audio Technology . The augmented passive-radiator APR, a double-cavity version of the customary drone cone design, is capable of most of the vented and passiveradiator systems alignment variations. While it requires more volume in the way of enclosure size, the APR yields higher power output and a 15%–25% 1
lower cutoff corresponding up to 2-octave extension. The layout for the APR consists of two unequal area passive radiators, connected back-to-back, with the front baffles joined to the inner dividing baffle. A special table Table 3.4 provides the requisite data for designing an APR system. In Chap Chap.. 4, the transmission transmission line TL lowlow-frequ frequency ency syst system em is described as a means of obtaining low cabinet resonance and strong deep bass. The design situation is somewhat murkier here, as there seems to be little agreement among TL enthusiasts as to what is the optimal system parameter Q. One computer program described in the text was specifically developed for TL design by Juha Backman, but it is not currently available. However, curves based on the use of LEAP, a program that does not model TL designs, yielded results that show similarity to the performance curves developed by Backman. The line length and damping material, tuning of a TL, the TL enclo enclosure sure configuratio configuration, n, and the selec selection tion of the woofer are discussed. An exhaustive listing of articles on construction of the TL enclosure is also given. Chapter 5 covers the topics of cabinet construction. The sphere is the best possible shape to provide the flattest frequency response, but obviously it is the most impractical to build and manufacture. However, the rectangular box, which is considerably less than optimum radiator, is the enclosure type most easily built. Standing wave modes depend on the enclosure shape and can be minimized by choosing appropriate dimensional ratios for the box. Nonparallel shapes can also attenuate standing waves. Box damping is
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© 1999 Acou Acoustic stical al Soci Society ety of Amer America ica
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needed in order to eliminate as much as possible the coloration that is retransmitted by most wood enclosures. Internal cabinet bracing, driving mounting techniques, enclosure floor coupling, and selection of wall materials are factors to be considered in damping an enclosure. In this chapter the emphasis is on enclosure features rather than cabinet construction ‘‘tips.’’ Chapter 6 shows how to determine the proper crossover frequencies on the basis of driver bandwidth and boundary orientation and to establish baffle locations for mid- and high-frequency drivers. Among the topics are two-way versus three-way loudspeaker formats neither one is inherently superior to the other , the effect of boundaries room walls and ceilings on the loudspeaker power response, boundary-induced interference patterns, driver separation and horizontal dispersion, midrange enclosures, and midrange and high-frequency baffle configuration. Attention is paid to attendant factors such as driver placement, radiation pattern of separate drivers, and zero delay plane ZDP. Other topics include crossover network power response. Two-way crossover characteristics are described, including those of first- through fourth-order Butterworth filters, second- and fourth-order Linkwitz–Riley filters, second- and fourthorder Bessel filters, second-order Chebychev filters, fourth-order Legendre filters, fourth-order Gaussian filters, and fourth-order linear phase filters. Design formulas are given for two-way and three-way crossovers. Examples are given for the low-pass filter, high-pass filter, and high-pass/low-pass summation. Driver load compensating circuitry, series notch filter, impedance equalization, driver attenuation circuits, response-shaping circuits, and inductors and capacitors in crossover circuits are also discussed. Passive crossover networks constitute the main thrust of Chap. 7. An excellent history of the development of crossover networks is rendered here, followed by a primer on the fundamental principles of crossover design. Rather than delving into the esoteric aspects of this rather complex subject, the author chose to maintain a cookbook format by treating examples of accepted methods commonly used in the loudspeaker industry. Active networks do not lie in the scope of this chapter, but a number of references on construction details of active filter circuits are given. Chapter 8 is an important one, since it describes loudspeaker testing. While it is not as comprehensive as Joseph D’Appolito’s Testing Loudspeakers Audio Amateur Press, Peterborough, NH, 1998, it contains enough information to conduct loudspeaker performance tests. Break-in of loudspeakers is recommended, and the procedures described are those for measuring driver resonance, impedance AC resistance, complex impedance, driver mass delta mass and delta compliance methods, driver suspension compliance, driver motor strength BL, and voice coil impedance. Formulas are included for calculating driver voice coil impedance, amplifier source resistance, and volume of air equal to driver compliance. Measurement procedures are given for driver Q, frequency response, phase, and enclosure vibration. Equipment for determining frequency response is discussed, and microphone types are examined. An important facet of testing, too often given short shrift, is that of measuring voice coil temperature over time—the description of measuring this parameter concludes the chapter. Chapter 9 is essentially a compilation of the software intended for loudspeaker design. While this is a useful listing, it was done in mid-1991 and much new hardware and later versions of software have been developed.
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While Chap. 9 is somewhat remiss with respect to its modernity, Chap. 10 deals with an area that is growing more popular—the home theater system that is intended to reproduce movie soundtracks rather than conventional stereo programs. It is pointed out that soundtrack recording techniques for conventional home listening and motion picture theatre listening differ considerably, with the result of less than optimal reproduction in the home. Because film soundtracks are not remixed for home playback, Tom Holman developed the THX Tomlinson Holman eXperiment home specification, essentially an equalization fix-up. Controlled directivity led to the specification of THX speakers, which call for additional channels. An overview is rendered of the home theater loudspeaker system, including as subtopics the placement of left/right front speakers, magnetic shielding of drivers which may need to be placed close to a video monitor , center channel speakers possibly the most important speaker in a home theater system, controlled vertical directivity, rear channel surround sound speakers, and subwoofers. Chapter 11 devotes itself to the special requirements of designing a loudspeaker system for automobiles. The automobile passenger compartment is essentially a closed-field environment. Sections of the car body tend to flex, so the acoustic situation becomes one of a ‘‘lossy’’ pressure field. Also, the relatively cramped dimensions of the passenger compartment tend to limit the wavelength response. Because the Thiel–Small predictions are based on free-field performance of the speakers, adjustments need to be made by establishing the impedance, cone excursion, and frequency response in a small ‘‘lossy’’ field by actual measurements. Computer simulation can also be achieved by using commercially available programs. Both predictions and actual performance are shown to correlate rather well for a couple of actual speakers and automotive interiors. A somewhat tongue-incheek discussion of the desirability of including center channel imaging is included with a set of generic installation rules for those who absolutely must have this feature. It was wise of Dickason to point out the most overlooked method of improving automotive sound quality, namely cutting down on the ambient background noise levels generated by engine operation and car motion. In summary, The Loudspeaker Design Cookbook merits a place on the bookshelf of every serious speaker designer, whether he/she be a professional or a hobbyist. All of its chapters are well done, although Chap. 9 lacks immediacy in its compilation of computer programs but the reader can easily update himself or herself by checking out the Internet or consulting advertisements in current issues of The Speaker Builder. Loudspeakers other than the conventional electromagnetic type, e.g., electrostatic and planar systems, are not treated in The Loudspeaker Cookbook. There is no index to facilitate easy location of particular subjects in the text, but the table of contents is sufficiently detailed to help in finding the subject of interest. DANIEL R. RAICHEL CUNY Graduate School Mechanical and Aerospace Engineering Department and the School of Architecture and Environmental Studies The City College of the City University of New York New York, New York 10031
Book Reviews
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