Horn Loudspeaker Design -Theory And Practice
By Randy Bankert of O. S. Services,
and North American Distributor Of
Purpose Of This Article
1. To briefly explain the history of horn loudspeakers.
2. How and why horn loudspeakers were replaced by
conventional direct radiator loudspeakers in most consumer applications.
3. How and why horn loudspeakers are becoming popular once
4. The benefits of horn loudspeakers over conventional direct
5. How and why Zingali horn loudspeakers differ from both
conventional and other horn loudspeaker designs.
State Of The Horn
Recent developments in vacuum tube amplifier design and
improved components have renewed interest in single-ended triode amplification,
and many different brands and models of low powered tube amplifiers are
currently available. The resurrection of the directly heated triode vacuum tube
for audio usage has been accompanied by renewed interest in highly efficient
loudspeakers, so that the magical characteristics of accurate harmonic tonality,
immediacy, transient detail and micro-dynamics, and involving presentation of
single-ended directly heated triodes can be heard at higher levels than would
otherwise be possible.
Nutshell History Of Triodes And
The invention of the triode tube in 1923 enabled an
electrical signal to be amplified to greater levels than had been possible, and
the triode could produce an audible output when used to drive a rudimentary
headphone device known at the time as a "receiver." The receiver
consisted of a fixed coil on an iron anchor which produced vibrations in a metal
diaphragm close to the coil. The first horn speaker was basically a horn
attached to a receiver, and although the sound quality was quite bad it was
better than what had been possible prior to the invention of the triode output
Due to the low power output of the triode, high efficiency
loudspeakers were required to produce sound pressure levels sufficient to be
heard in a room, which happened in 1927 when two Bell Laboratory engineers,
Wente and Thuras, invented the compression horn driver, commonly known as a
driver. Their driver used a field coil to magnetize the pole pieces (permanent
magnets at that time did not have a practical strength/size ratio to be of
practical use) and incorporated an under-hung edge wound aluminum ribbon voice
The diaphragm was an inverted aluminum dome attached to a
self supporting voice coil. The Wente and Thuras driver also had a phase plug; a
device placed between the diaphragm and horn throat which enabled the sound
waves from the diaphragm to merge into a coherent wave front in the horn throat.
Direct Radiator Drivers
As time went on, Rice and Kellogg "invented" the
direct radiator speaker (conventional driver). Horns began to disappear from the
scene, being big and unwieldy. Soon after World War II, more powerful push-pull
pentode amps began relieving the humble triode of its duties. Later on, the
ultimate power/dollar rating transistor amps arrived. As the need for high
efficiency loudspeakers diminished, manufacturers began cutting costs by using
low efficiency smaller magnets in their drivers. Although horns no longer had a
major share of the market, they survived in movie theatres, PA applications, and
other applications where their high efficiency and low distortion outweighed
their typically large cabinet volumes.
Drawbacks Of Conventional
Direct Radiator Loudspeaker Designs
While horns offer a dramatic increase in dynamic capability,
image size, and presence, with harmonic distortion less than one quarter of the
value found in audiophile direct radiator systems, most direct radiators
severely compress dynamic contrasts and reduce image size. In addition, many
direct radiator designs suffer from dynamic compression coloration, where the
highs and lows are rolled off at high SPL's, resulting in a perceived midrange
boost. Many direct radiator designs are not efficient enough to be used with
low-powered single-ended triodes, and even with high-wattage and high-current
amplification, these loudspeakers sound polite and uninvolving compared to high
efficiency loudspeakers. Single-ended tube amplifiers need not apply, for
obvious reasons (low wattage).
Special Qualities Of Horns
What special qualities do horns have that endear them to
enthusiasts besides having very high efficiencies? The horn may be viewed as an
acoustic impedance transformer. When a diaphragm vibrates, pressure waves are
created in front of it. This is the sound we hear. Coupling the motion of the
diaphragm to the air is not an easy thing to do due to the very different
densities of the vibrating diaphragm and air. This can be viewed as an impedance
mismatch. We all know that sound travels better in high density materials than
in low density materials, and in a speaker system, the diaphragm is the high
density (high impedance) medium and air is the low density (low impedance)
medium. The horn assists the solid-air impedance transformation by acting as an
intermediate transition medium. In other words, it creates a higher acoustic
impedance for the transducer to work into, thus allowing more power to be
transferred to the air.
A horn is a tube whose cross-section increases exponentially.
The narrow end is called the throat and the wide end is called the mouth. The
transducer is placed at the throat. When the diaphragm moves near the throat, we
have a high pressure with a small amplitude in a small area. As the pressure
wave moves towards the mouth, the pressure decreases and the amplitude
increases. Excellent natural efficient amplification.
As mentioned earlier, horns have very special properties,
including lower distortion than conventional drivers, faster transient response
than conventional drivers, and are easier to drive at high SPL's than
Lower distortion at a given SPL: For an equivalent SPL,
horns require a smaller diaphragm, and since distortion is directly proportional
to the size of the diaphragm, a large diaphragm electromechanical transducer
(conventional driver) has to move much more than a horned diaphragm in order to
create the same SPL (sound pressure level). The larger the excursion, the worse
the distortion. So, for a given SPL, a horn loaded system will generate much
lower distortion than an electromechanical transducer.
Faster transient response: Since the diaphragm is
smaller, it is lighter and thus it accelerates and decelerates faster. This, in
the real world means superb, fast snappy transients. As the excursion of the
diaphragm is very small as compared to an electromechanical transducer, the
voice coil is much smaller and again, this translates to a lower moving mass and
again, results in fast transients.
Higher SPL's with a given input wattage: Small voice
coils also take full advantage of the flux in the pole piece gap. This increases
the efficiency of the transducer allowing the amplifier to work with greater
ease. Since the amplifier has more headroom and the driver handles peaks and
high outputs more efficiently, horns are able to produce much higher SPL's
before they distort.
Thus, in the normal operating range, horn designs are faster,
more dynamic, have a better transient response, have less distortion, and are
easier for an amplifier to drive than conventional driver designs.
Horns Have Impact!
You feel the music, you become part of the music, and the
music becomes part of you. The full-range phase coherent wave front of horns
produces a solid image and presentation, as opposed to the phase impaired,
smeared, and diluted imaging of typical low efficiency conventional driver
designs. Horns will never sound veiled or compressed. The performers will be
there, in your room, performing for you in the same way and location as the
original recording venue. If the performer was six feet from the microphone
during the recording session, he will be six feet away from you when the
performance is reproduced through your system, not fifteen feet behind the
speakers. Why would one want the performers to be fifteen feet behind the
speakers if that was not how the material was recorded? We want the performers
to be in the same room we are in, in front of us, so that we can feel the music,
front row center.
Due to their inherent benefits of low distortion, high
efficiency, fast and accurate transient response, and wide dynamic range, horn
loudspeakers provide a pure, un-adulterated musical presentation, a more organic
and natural recreation of the acoustic event. As a result, each different
musical selection is portrayed with its own character and life, not that of the
How Zingali Horn Loudspeakers
Differ From Other Horn Designs