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2nd April, 2013
9th January, 2013
HIFICRITIC Book Review:
A classic text unexpectedly revised:
Acoustics: Sound Fields and Transducers by Beranek and Mellow
ISBN-13: 9780123914217, Elsevier Science, 0/4/2012 720PP
I first encountered Leo Beranek’s book Acoustics while researching material for High Performance Loudspeakers which first edition was published in 1976/77, when Acoustics had been in print for some 20 years. Now, more than half a century later and encouraged by Tim Mellow, Beranek and Mellow have collaborated to produce a new edition of Acoustics, founded on the original classical fundamentals but with a modern slant more clearly focused on electroacoustics and carrying the sub-title, Sound Fields and Transducers.
Leo has enjoyed a long and distinguished career in acoustic design and consultancy, particularly at Bolt Beranek and Newman, BBN. He has published 13 books and has also been involved in broadcasting as well as the precursor technology to the internet. Tim graduated in 1985 in Electronics and Electrical Engineering at the University of Dundee and has published a number of papers on sound radiation. His enthusiasm for loudspeakers led him to the electrical circuit analogies for electroacoustic transducers in Leo’s book; (these associated with the radiation acoustics that complete the circuit from electrical audio currents to radiated sound energy). Tim enthusiastically proposed a new edition of Acoustics to Leo, which after some extended discussions, was agreed as a joint authorship project.
The 2012 edition of Acoustics runs to 704 pages. The first 4 chapters comprehensively deal with acoustical fundamentals, leading to microphone theory and practice in chapter five. Electrodynamic loudspeakers are covered in chapter 6, followed by loudspeaker systems and enclosures in chapter seven. Cell, mobile phone transducer technologies are introduced in chapter eight, leading to a strong chapter nine on horn loudspeakers. This includes an example of a rectangular 7.5cm by 3.9cm treble horn, +/-3dB, 1.5kHz to 10kHz, which provides a typical sound pressure gain of 16dB into a defined radiation angle, a welcome reminder of horn efficiency gains. Chapter ten covers ‘enclosures’, here the design of rooms and halls, followed by a brief look at listening room issues in eleven. From twelve onwards we return to theory where Mellow’s speciality, acoustic radiation and scattering from a variety of theoretical sources in particular situations, comes to the fore.
In chapter twelve the boundary value method is employed while in 13 one can see the contrast with the boundary integral method, here used more comprehensively. These many analyses include some of the issues faced when mounting a high frequency driver on a contoured section of a loudspeaker enclosure. Interesting and relevant examples include the radiation of a spherical cap on a sphere, and radiation from an infinite line source.
In Chapter fourteen, state variable analysis is applied to numerous loudspeaker equivalent circuits, facilitating computation from first principles. Finally, there are some useful appendices, tables, design summaries and conversion factors.
The book is aimed at electroacoustic students and engineers active in transducer and loudspeaker system design. There is an emphasis on understanding the fundamentals, providing sufficient classic example problems for the designer to apply to new product. It won’t tell you how to design a commercial hi fi loudspeaker, but if you have the skills it can explain much of the relevant electroacoustic behaviour from first principles. Designers will find numerous alignment tables, charts, graphs, formulas and worked examples in Chapter 7, for example the complete behaviour of a driven bass reflex enclosure including the higher modes, a useful starting point though understandably not including structural behaviour.
Proficiency in mathematics is a help; this reference work could be regarded as the counterpart to the advanced, computational acoustic engineering software such as Comsol now becoming popular, providing much of the grounding for these multi discipline, coupled modelling programs, while inexpensive math programs such as Mathematica may be deployed to calculate the extensive models supplied in the work
It is a welcome surprise to see Leo Beranek’s Acoustics so exhaustively revised while we also have to thank co author Tim Mellow for his deep commitment to the work.
Martin Colloms
Technical Editor HIFICRITIC Jan 2013
See us at Bristol Sound and Vision show 2013
12th September, 2011
HIFICRITIC: The Rhythm King DIY Loudspeaker
Designed in the first half of 2011 by Martin Colloms,
Christien Ellis (CE Electro-Acoustics, www.christienellis.co.uk) and Miles
O’Carroll (milesocarroll@hotmail.com) The Rhythm King has passed its
proving trials and is ready for demonstration at the National Audio Show
September 24/25. Room S15 with ticketed presentations on the design principles
involved.
This speaker is designed for wall boundary matching and a
neutral timbre.
Wilmslow Audio built the enclosure to drawings
created by Miles O’Carroll from design sketches by Martin Colloms and Christien
Ellis. Wilmslow Audio have agreed to
supply all the parts required including the exclusive supply of the Cotswold
Acoustics manufactured, BMR full range planar driver. The custom made
Multi-Contact terminated solid core internal and external wiring harnesses are
built by DNM Design and work with external,
easily updated crossover networks.
The
first working prototype crossover
This site has the first article describing the approach to
design form Vol. 5 No 1; the second concluding part will be published in September
2011, HIFICRITIC Vol. 5 No 3 and will
be copied to this site soon after.
Also see the comprehensive measurements, the crossover
circuit with preferred wiring topology and related illustrations, the full
enclosure drawings file and related material.
Please send questions and comments to the DIY speaker
section of the HIFICRITIC Forum which also has some early description.
20.08.2011MC
26th August, 2011
National Audio Show
HIFICRITIC Exhibits the DIY TRK Loudspeaker at the
National Audio Show 2011, Whittlebury Hall, Sept 24/25
TRK, The Rhythm King will be demonstrated at NAS, with ticketed presentations on the design process by Martin Colloms. The design team will be on hand to take questions. Co-exhibitors are Wilmslow Audio who supply the parts and DNM Design who supply the special cables, inside and out. HIFCRITIC will also have their usual stand in Brooklands with show discounts on subscriptions and back numbers and where tickets may be obtained for the design presentations. The concluding issue for the unique HIFICRITIC loudspeaker project will be on sale, hot off the press.
HIFICRITIC-Wilmslow-DNM ROOM: S15, 1st Floor
National Audio Show
HIFICRITIC Exhibits the DIY TRK Loudspeaker at the
National Audio Show 2011, Whittlebury Hall, Sept 24/25
9th April, 2011
The Spring Audio Show at the Heathrow Park Inn
27th/27th March 2011
