Horn Loudspeaker Design -
by Randy Bankert of O. S. Services,
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 again.
4. The benefits of horn loudspeakers over conventional direct radiator loudspeakers.
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 Horns
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 tube.
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 coil.
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
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 conventional drivers.
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 playback medium.
How Zingali Horn Loudspeakers
Classic horns have great advantages over conventional transducers, but also present a few anomalies in timbral accuracy and dispersion characteristics.
In 1995, following years of extensive research, the revolutionary OMNIRAY HORN was born. Of circular shape, the OMNIRAY HORN is carved on a piece of solid wood (Poplar). Its exponential curve characteristics as well as throat depth (Patented Worldwide) guarantee the most accurate reproduction of mid and high frequencies available today. With an OMNIRAY HORN, the acoustic image and the timbre of musical instruments is reproduced with uncanny fidelity, perfectly restoring the "live" scenery with all its dynamic qualities in a fashion never possible before.
According to Giuseppe Zingali, the founder and chief designer of the Zingali Loudspeaker company: "I created the Omniray technology for the first time and patented it in 1995. The only circular horns prior to the Omniray design were megaphones which merely amplified the human voice and were not suitable for use in high-end audio applications.
"The design elements which differentiate the Omniray horn from other horns is its proprietary exponential curve and the short distance between the throat and mouth, resulting in a rapid flare which disperses treble frequencies in a wide and uniform pattern.
"Another unique feature of Zingali horn loudspeakers is that the diameter of the horn mouth is the same as the woofer diameter: this is why the sound arrives as a phase-coherent wavefront to the listener's ears, as a homogenous and cohesive wavefront, not as two separate wavefronts from the woofer and the horn."
Lifelike and involving music is made possible by the combination of highly efficient and low-distortion horn loudspeakers and low-powered single-ended tube amplifiers.
Zingali loudspeakers have utilized classic horn design principles and improved upon them to provide a harmonically accurate, dynamic presentation which enables the music to come to life, in an emotional, involving way.
Many Zingali loudspeakers are capable of handling hundreds of watts if desired, making the line versatile and easy to use with a variety of associated equipment.
There is virtually no dynamic compression coloration with Zingali loudspeakers, the correct frequency response is obtained at all volume levels, unlike many conventional multi-driver dynamic loudspeakers, which roll off the treble and bass at high volumes.
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