January 2001

Book Review: La Progettazione Dei Diffusori A Tromba
(Horn Loudspeaker Design) Project Editor: Luciano Macrì
Review By Dick Olsher
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  This is a cool little book that should appeal to those in search for basic information on horn loudspeaker design. The book's main reason for being is to reintroduce Jack Dinsdale's classic horn articles to a wider audience. Dinsdale's articles, originally published in Wireless World in 1974, have long represented an authoritative and informative summary of horn knowledge and practice, and were written with sufficient passion and clarity to qualify as a basic reference on the subject. 

The book is laid out in bilingual fashion, in double column format, in both Italian and English, which might give you a chance to pick up a bit of Italian vocabulary on the side. The author is well aware of the work of Voigt, Wilson, and Klipsch. The basic theory of both exponential and tractrix horns is described. It may surprise some to learn that even in the early 70s, on the basis of listening tests, the tractrix was supported as the optimum horn contour. The scope of the articles includes a detailed discussion and guidance about folded horns. This is essentially an art form, since as Dinsdale puts it: "As soon as one departs from the straight horn of circular cross-section, the scientific design principles described cease to be relevant and become more of an approximate value…" this follows on the heels of Wilson's admonition: "It cannot legitimately be assumed that a horn incorporated in a cabinet has the precise characteristics of any particular type of straight horn, whether exponential, hyperbolic, catenary or tractrix, even though their dimensions have been used as guides in its construction. The multiple changes of direction, coupled with reflections and absorptions and internal resonances, are always such as to destroy any legitimate comparison. Every internal (horn) enclosure construction must be judged on its own merits as revealed by measurement and by listening tests." I bring this up because, due to space (and cost) constrains, almost all commercial horn designs are of the folded variety. The final two articles consider in detail the design of two horn systems: a "mini-horn" and a "no compromise horn." 

Following the Dinsdale articles is a short but entertaining discussion by Paolo Viappiano, Director of the Italian magazine "Costruire HiFi," of recent developments in horn praxis. The contributions of both Richard Small and D. B. Keel are briefly mentioned, as are some computer program resources. 

A computer program that automates horn design, written by Giampiero Matarazzo, is included on a floppy disk. The program will need to run under a DOS window on Windows based personal computers. I didn't receive a copy of the program so I can't really comment on its utility.

The book's final section contains a large number of schematics and pictures of various horn designs, including the plans for several Lowther enclosures (e.g., Opus One, Academy, and Acousta 115) as well as the Mauhorn type 4 and 5. This should give the reader a glimpse of the great variety and ingenuity inherent in folded horn designs.

All in all, this is book would make a worthwhile addition to any serious hobbyist's reference library. I certainly enjoyed revisiting a subject that is dear to my heart. The book is nicely edited and packaged. It is published by Audion Magazine and is available directly from the publisher, Luciano Macrì:

Demidoff Editore
C.P. 6599
50127 - Firenze - Italy

Website: www.audion.net
E-mail: info@audion.net