Vinther Labs' Horn-Loaded Speaker
Article By Alvin M. Foster
Winter 2012 Boston Audio Society Volume 34, Number 4
president Robert L. Miller (RLM) asked if anyone had a high sensitivity
120dB-range voltmeter for an upcoming series of preamp and amplifier S/N tests.
It was unclear, however, why the extreme sensitivity was required. A few said
they would get back to Miller if they could locate such a meter.
Stephen H. Owades reported that the number of new cars
offering HD radios was limited, and that HD Radio sounded better than analog FM.
He purchased a BMW 328-series mainly because it came with a nice Harman HD radio
that plays DVDs/CDs and generates surround with Lexicon's Logic 7 algorithm.
Gordon Vinther, Vinther Labs
Vinther: The Ultrahorn (patent pending) loudspeaker, unlike
most horn systems, has a small footprint (40" x 24"). It is a 6'-tall
full-spectrum horn. All drivers use the same sound path and therefore produce a
single coherent soundwave and create a realistic, three-dimensional listening
experience. The design pays special attention to time-domain parameters. Vinther:
The shape of the horn is conical by choice and by necessity of construction. A
conical shape offers the smoothest rolloff and lowest inband distortion. By
combining and conducting multiple driver outputs within a common path, a single
coherent wave is produced for all frequencies. Multiple-driver sound systems
exhibit comb filtering due to driver separation. This horn exhibits none of
these effects and sounds good no matter where the listener sits.
A prime consideration in driver selection is mass. Ideally a
driver would have an effective mass and compliance equal to that of the volume
of air moved. This is approached only by membrane drivers, which usually do not
contain the back wave and are generally beamy at high frequencies. Horn loading
allows the conversion of a large low mass to a small high mass at the driver and
thus ameliorate the mass problem of dynamic drivers. Horn loading also raises
the impedance of its drivers, eliminates the low-frequency resonant peak, and
makes the driver phase-linear.
The woofers are two 8" carbon-fiber drivers. They seem to work
better than 12" drivers tried earlier. When a dynamic speaker is used in a
compression chamber the upper cutoff is limited by the distance the wave travels
from the center of the driver to its rim and back. The shorter dimension in 8"
drivers allow a cutoff at 2 kHz, while a 12" driver cuts off at 750 Hz.
The tweeters are Heil air-motion drivers purchased on eBay.
They are also available new from ESS Labs. Vinther used the Heil driver because
it can go down to 500 Hz without distortion and is naturally phase-linear. With
phase-linear drivers it became obvious that a completely phaselinear speaker
could be built.
Initially he used a simple first-order crossover. However
after blowing several Heil diaphragms while playing a very loud concert one
evening, he decided to us a subtractive crossover with the high slope on the
Heil. (However, the Heil was probably blown by a high Vdc-offset in the amp.)
Modern steep-slope crossovers and their resulting time distortion greatly reduce
the impact of music. This is only gradually becoming apparent to speaker
John S. Allen asked if he had measured the phase. Vinther
replied that he had, and the step response measurements were very good.
Following up on Vinther's statement that the impedance was constant, someone
asked if there was interaction between the woofer and the tweeter pressures that
might cause audible IM distortion? The possibility, according to the questioner,
might exist because all the drivers share the same horn space. Vinther replied
that he had not measured for the phenomenon but concluded that his speaker's IM
distortion was extremely low.
Foster noted that considerable thought went into the
construction and materials used in the speaker. He said that when Vinther
arrived that afternoon the speakers were, for the most part, unassembled. The
multiple panels were light enough for one person to carry. Within one hour the
speakers were up and sounding very good.
Vinther started the listening session by playing his favorite
mixture — old jazz, popular, and vocal recordings. Several members played
selections from their CDs that spanned the musical gamut of classical to rock. A
member asked Vinther about the ideal speaker placement. Vinther replied that the
speakers should be positioned close together, that wide footprints work less
Vinther expects the price will be ~$12,000 when they come on the market around October 2012. [Nothing seen online thus far. DRM] The Vinther Lab speakers were well received, and most concluded that the time, effort, and research produced a very good-sounding horn loudspeaker.
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