The "ALL Fun" Horn
The article outlines and details the design and construction of a back-loaded single driver horn using a new driver from Lowther, the DX3. The article's approach is of a practical nature, with emphasis on all practical steps of the design process, enabling readers to fully understand the underlying principles of this particular speaker, as well as completing a horn loudspeaker design of their own. The article has previously been published in SpeakerBuilder (now AudioXpress) magazine.
Follow these links, if you so please (Some of the graphic files (GIFs) will probably display a little strangely. Try saving them, and opening them again by double-clicking their names):
Single driver back-loaded horns, background, goals
The driver, general design, Throat area, lower cut-off frequency, Curvature (Horn contour)
Size reduction and compromise, The Cabinet, building
Listening impressions/experiences, Conclusion
Plans and pictures
I have now had these speakers in my living room for a year or so, and have fed them all kinds of musical genres and recordings. And, just for the record, if I thought that these speakers had turned out bad, this article would not have been written. So I'll leave all pretence of being objective and unbiased, and try to give an honest impression of what I'm hearing.
The good things:
Reproduction is very coherent throughout the whole audible range.
Bass notes through the bottom-most octave are reproduced with great clarity and definition, in spite of the steep frequency roll-off below 50Hz.
Voices and instruments in the mid-frequencies are reproduced with astonishing detail and liveliness.
Dynamic transients are very accurate.
Virtually no cabinet vibrations are noticeable from top and front of the enclosures.
The not-so-good things:
Room placement is critical. At one certain spot in my listening environment, a great deal of the deep bass is muted. Move 1 metre away from or toward the speakers from this point, and everything sounds right. Interestingly enough, this was not a problem with the "Big Fun" horns. This may be due to the lower cut-off of that design, or it may be an indication that size matters, after all.
The horns sound a little stressed when fed with complex material, such as symphony orchestra crescendos or massive electronic passages.
The goal of this design was to construct a horn loudspeaker with the aid of established rules of thumb, that was compact in size, had good bass reproduction down to 40Hz, and was easy to build.
The end result turned out very good, and it seems clear that all the employed rules of thumb are valid. Apart from the mentioned "dead" spot in the listening room, no surprising drawbacks were discovered.
Measurements correspond very well with expected results, and are also coherent with the listening impressions.
AESJ preprint #1250, "Low-frequency horn design using T/S driver parameters" by D.B. Keele Jr, and AESJ preprint #1251, "Suitability of low-frequency drivers for horn-loaded loudspeaker systems" by Richard H. Small
Strutt, J. W., Lord Rayleigh, "Theory of sound" Pt. 2, Macmillian, 1878
Bruce Edgar: "The Monolith Horn", Speaker Builder 06/93
AESJ preprint #1679, "Anechoic Chamber with Optional Boundaries" by P. Klipsch
Beranek, 'Acoustics', 1954, chapter 9, page 272.
Plans and pictures:
Figure 6 - Internal boards lengths and angles
Figure 7 - Panel positions and outer measures
Figure 8 - Outer panel layout and dimensions
Figure 9 - Divider panels shapes and dimensions
Large picture of finished speaker cabinet (94K)
Building - Side view before fitting side panel (95K)
Building - Close-up of first bend, from back of cabinet (80K)