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January 2013
Enjoy the Music.com Boston Audio Society The BAS Speaker Magazine

Beranek's Acoustics
Completely redone!
By Beranek and Mellow.
Winter 2012 Boston Audio Society Volume 34, Number 4

 

 

  Nonagenerian Dr. Leo ("Acoustics") Beranek (Leo Beranek; the home-page image is of the Tokyo Opera City concert hall, Japan, whose acoustical design consultant was Beranek) is still involved in enhancing our knowledge of acoustics with ACOUSTICS: Sound Fields and Transducers (Academic Press; ISBN: 978-0-12-391421-7), an update of sorts co-authored with Tim Mellow (engineer, audiophile and musician; Mellow Acoustics). This 720-page tome is "focused on electroacoustics with the needs of a broad range of acoustics engineers and scientists in mind" (from Elsevier website). This book covers the latest in microphones, electrodynamic and horn loudspeakers, box and bassreflex enclosures, transmission-line enclosures (e.g.: Bose Wave Music System), crossover filters, cellphones, soundfields in small enclosures and in large rooms, rooms for loudspeaker listening, plus radiation and scattering from all sorts of surfaces mounted in finite and infinite baffles. Lumped circuit elements are employed at low frequencies and exact equations at high frequencies. The text ends with state-variable analysis of circuits. The book assumes knowledge of electrical circuit theory. It is directed toward experimenters, hobbyists, and audio-equipment engineering designers.

Contents:
1. Introduction and terminology
2. The wave equation and solutions
3. Electro-mechano-acoustical circuits
4. Acoustic components
5. Microphones
6. Electrodynamic loudspeakers
7. Loudspeaker systems
8. Cellphone acoustics
9. Horn loudspeakers
10. Sound in enclosures
11. Room design for loudspeaker listening
12. Radiation and scattering of sound by the boundary value method
13. Radiation and scattering of sound by the boundary integral method
14. State variable analysis of circuits
APPENDIX I Frequency-response shapes for loudspeakers
APPENDIX II Mathematical formulas
APPENDIX III Conversion factors
Index
Design Summaries

 

The eBook and print editions can be purchased from the Academic Press Elsevier bookstore.  The print edition is $104 at [Mellow's website considers this book to be less a Beranek update and more a Mellow project with Beranek's 1954/1986 reference as a starting point. In Mellow's own words:

"

A few years later, ...I was thinking that what the world of engineering acoustics needed was a text book that covered everything from lumpedelement theory using circuit analogies, as covered in Leo Beranek's book, to wave theory and sound radiation/scattering problems. However, I could not cover the fundamental principles any better than Leo had already done and I did not want to plagiarize anything. The idea of writing an updated version of ACOUSTICS suddenly hit me like a thunderbolt. It seemed like completely the right thing to do even if it would involve a huge amount of work....

I wrote to Leo Beranek who amazingly wrote back informing me that he held the copyright and that I could use anything I liked. However, he was not keen on being a coauthor because he was too busy contributing to the current literature on concert hall acoustics, even if I wrote all the new material and he simply reviewed it. This was hardly surprising since at the time since I was completely unknown with only a handful of published papers to my name. However, as time went on, Leo became more enthusiastic about the project and contributed much new material, including two whole chapters on sound in enclosures and rooms for loudspeaker listening.

I was certainly delighted when he eventually decided he would like to have his name on it as that was the best possible endorsement of all the hard work involved....

Leo paid particular attention to the ordering of contents and specifically asked me to include a new section on transmission-line loudspeakers because so many had asked him about how the Bose Wave system worked. He also requested a new chapter on cell phone acoustics because he was curious as to how so much sound could be produced by something the size of a deck of cards and felt that it would bring the book right up to date.

A new version of ACOUSTICS had to include the work of Neville Thiele and Richard Small. They proposed just six parameters to completely describe the low-frequency behaviour of a loudspeaker, which are now commonly known as the Thiele-Small parameters, and Small showed how to obtain them from the input impedance. Also, they produced tables/charts which enable anybody to choose a frequency response shape for a given drive unit and engineer the cabinet and bass-reflex port accordingly. Leo is rightly proud of the fact that these authors used his book as their starting point and that it led to the development of smaller loudspeakers using the acoustic suspension principle."

[Something appears partly misemphasized in this last assertion about Thiele/Small, ports, development of smaller speakers, and acoustic suspension (which was famously the work of Edgar Villchur in the 1950s). -- DRM]

Also from the new book: "The audibility of phase distortion has provoked a lively debate over the years, but why not design the loudspeaker correctly in the first place so that there need not be any doubt about its accuracy? As we shall see in the next section, the solution to this problem need not be complicated if we approach it holistically and take into account all the factors that affect the response of the loudspeaker, including the baffle effect."

[Loudspeaker phase has been demonstrated for decades to be audibly unimportant, and in any case the term does not appear in Beranek's original index. Finally, Mellow's website also contains not only an audioXpress reprint of his article about a d-i-y output-transformerless tube amp but a 15-page PDF document listing more than 300 errata for this new Beranek/Mellow book. Admittedly, most of the errata appear to be typographic, editorial, and/or simple re-incrementations of the sort ‘replace chapter 5 with chapter 4'. Still, it does little to solidify a slightly sketchy feel to this whole Mellow project. DRM.]  

 

 

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