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In the Forum: Horn-Loaded Speakers
In the Thread: Aporia - Silbatone Acoustics speaker

Post Subject: Point/no pointPosted by Joe Roberts on: 2/9/2009

First off, I will point out that neither Silbatone nor I claim or agree that the Aporia horn is a point source, because clearly it is not. The sound comes from two "areas" but even that is not a particularly useful notion.

Although some do make that claim and I may have alluded to it in the deep past, I would argue that the notion of point source is not the important thing about single driver speakers. Once the sound is excited beyond the surface of the driver, it is no longer a "point" in any way, but rather occupies a 3-D solid shape whose included angles vary as a function of frequency. This is the point of Jean-Michel's paper, earlier raised in the writings of G.A. Briggs in the 1960s.

Furthermore, in a world of walls and reflections, sound does not reach us from a "point" and when there are two speakers in stereo, the relevance of the point source argument further evaporates into a world of complexity.

Nor are microphones usefully considered as point sources (or point receptors) because in stereo recording and even mixdowns to mono, arrays of microphones are typically employed. They are variously directional in a frequency dependent way also. Simplification of the model to "point source" denies the inherent complexity.

As I argued above, the potential advantage presented by single driver speakers is that the sound comes from a single source. This advantage rests in the that problems with matching different types and configurations of drivers and horns or whatever are sidestepped. It is hard to get a compression midrange to mate with a direct radiator cone woofer for example.

The brain can blend different sound sources of different character to some degree, but I find that this can be hard work and subliminally fatiguing or unnatural. Depends on the specific implementation in question. This can be made to work.

Single drivers, especially in back horns, are not immune from frequency related differences in character. Many Lowther-type systems vomit out bass that is not "like" the midrange, perhaps due to distortions in the horn and problems of vibrating horn cabinets.

Where Le'Cleach's paper takes me in this discussion is that single drivers can more accurately capture the narrowing angular dispersion of sound with rising frequency compared with certain horns whose design is such as to engineer wide dispersion into the design. This concern in horn design comes from sound reinforcement considerations.

Ideally, a multi-horn system would include the notion of narrowing radiation into its execution, but the problem is complicated by the fact that various instruments present different patterns of dispersion narrowing--it is not purely a function of frequency. This is discussed in Briggs.

That said, the narrowing dispersion of a single driver can perceptually be too sharp, as as to strike the ear as unnatural. This is why, in my reading, Silbatone put a diffusor on that Manger driver.

Here again I would argue that the ear is the best judge of a successful implementation. If something sounds markedly unnatural, it is bad. If it strikes the ear as natural, it is good--or good enough.

Theory and speculation, even with a stack of physics books on the shelf, only gets you so far. Direct listening experience is key. That is a very serious argument in my book.

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