Design of acoustic enclosures

Acoustic Enclosure Design - What are Passive Radiator Enclosures?

Reading time: 3 minute

Author: Eng. Aurelian Mateescu
Year of publication: 1985

This topic is widely debated by lovers of music and high fidelity equipment everywhere, the various types of enclosures on the market having followers sometimes as radical as football fans, ready to defend or vehemently deny one enclosure or another. as their preferences evolve.

But where does this diversity of technical achievements come from?

The most plausible explanation is related to the construction of the human ear, to the fact that, at the same "technical solution" applied by nature, the perception of sound in all its complexity, is different from person to person. So, "it's not beautiful what's beautiful, it's beautiful what I like!". Overcoming the exaggerations that glorify one achievement (an enclosure), to the detriment of another, we must say that the only proven truth remains the proverb!

Enclosures closed

Closed enclosures are known before the 50s. In 1949, Harry Olson and J. Preston patented the acoustic suspension. Edgar Villchur and Henry Kloss founded "Acoustic Research", the company that used this technical solution, the AR-3 enclosure becoming a classic.

Henry Kloss broke away and founded other successful companies that popularized this project, "KLH" and "Advent". In 1972, Richard Small published the most complete design data for indoor enclosures.

Bass enclosures

The open enclosures (bassreflex) are not new either. In 1932, AC Thuras described in his patent the interaction between the speaker and the opening made in the enclosure. In the 50s, a number of researchers, including Branek, Van Leeuwen, de Boer, Lyon, Locanthi and Novak, published articles detailing mathematical models analogous to open enclosures, "pass-up" filters.

An important contribution to the definition of the mathematical model and to the establishment of the terms for design is made by the works of AN Thiele from 1961, even if his works do not include a systematic calculation of the losses inside.

R. Small's articles published since 1973 deal with the problem of on-premises losses and their effect on the linearization of the response curve, a problem repeated by Robert Bullock, which contributed to the increase in the accuracy of the design tables.

Passive radiator enclosures

Passive radiator enclosures were first described in Harry Olson's patent "Speakers and Methods of Sound Propagation", published in January 1935. Olson also published a paper on the same project in 1954, and more recently in 1973 and 1974. Nomura, Kitamura and Small have also published articles on this topic.

Enclosures with transmission line

Transmission line enclosures are based on achievements dating back to the 30s, when the acoustic labyrinth was studied and made by Stromberg and Carlson. Later, AR Bailey (in the 60s) and AT Bradbury (in 1976) published articles on their research on this technical solution.

We can thus say that there is "nothing new under the sun" in terms of technical solutions adopted by various companies building acoustic enclosures. The technical novelties are related almost exclusively to the introduction of new materials, used primarily in space, military, etc., and we refer to adhesives, membrane materials, acoustic insulators, etc. These materials have properties that improve the performance of transducers (speakers), without having reached an ideal solution in their construction.

Materials such as kevlar, ultra-light alloys, plastics, metal foams or materials with a three-dimensional structure, frequently used today in the construction of speaker membranes, could not replace the majority use of cellulose membranes (paper), even if it was reinforced with carbon fibers or polymers.

If in the above we referred exclusively to enclosures equipped with dynamic speakers, we did it because this type of enclosure remains by far the most widespread.

Enclosures equipped with electrostatic transducers, although they have remarkable performances and a number of followers who defend them fervently, also have their shortcomings and imperfections.

The materials presented in this paper represent, perhaps, the most complete design guide for acoustic enclosures published so far in our country (until 1985), including a large amount of data and calculation formulas for all components of an enclosure.

Add a comment

Your email address will not be published. Required fields are marked with *

The maximum upload file size: 2 MB. you can upload: image, audio, video, document, spreadsheet, Interactive, text, archive, queues, Other. Links to YouTube, Facebook, Twitter and other services inserted in the comment text will be automatically embedded. Drop files here