introduction - brief discussion of horns, pros and cons

[Angelo]

horn loudspeakers, are there any disadvantages?

http://www.stevehoffman.tv/forums/ar...p/t-73546.html

Where have the horns gone?

http://www.audiokarma.org/forums/showthread.php?t=69121

Horn Loudspeakers - Advantages and Opportunities

http://www.audiocircle.com/index.php?topic=72549.20

[Angelo]

Special qualities of horns

http://www.hornspeakers.co.uk/horn_design.htm[center]

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 lifelike presentation with tremendous dynamic range, as opposed to "polite", compressed presentation of low efficiency conventional driver designs. Horns will never sound veiled or compressed.
Due to their inherent benefits of low distortion, high efficiency, fast and accurate transient response, and wide dynamic range, horn loudspeakers provide a pure, unadulterated musical presentation, a more organic and natural recreation of the acoustic event.

Synopsis

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.

Modern horn loudspeakers have utilize 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.
Modern horn 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 modern horn 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.

[Angelo]

Greg Boynton, "What about horns", Sound Practices Vol.1, #1

http://www.audiocircuit.com/index.ph..._Quo-O-A01.htm

"...But when you get a horn system set up right, the sound quality is amazing. The most obvious advantage is in the dynamic range and transient response of the horns. For me, the emotional impact of recorded music is in the dynamics. Most speakers just do not produce realistic dynamic constrasts. Horns do, and they do so with ease. They also excel in low distortion. The sound seems unusually clean even at high levels..."
"One of the major challenges in setting up a horn system is finding an amplifier which will work with the horns. High power solid state amplifiers sound best when mated to inefficient speakers. With horn speakers they tend to sound really awful. The efficiency of horns is so high that your average big hog solid state amp never really gets turned on. Likewise, big tube amps using banks of 6550s just don't sound that clean when operated in the milliwatt power range. Horns work best with low power tube amps."
Herbert E. Reichert, "The Science of Beauty: Audio Culture in the Nineties", Positive Feedback (The Journal of the Oregon Triode Society) Vol.5, #1

"At equal acoustic outputs, as compared to conventional dynamic or electrostatic loudspeakers, horns offer a dramatic increase in dynamic capability, image size, and presence. Harmonic distortion drops to a quarter of the value found in audiophile direct radiator systems. In contrast, most direct radiators severely compress dynamic contrasts and reduce image size to the proportions of a symphony on a table-top. These are bothsevere distortions for which there are no measurements. More importantly, these are distortions which reduce the fun and excitement of music.
When reproduced music lacks weight and body, when sudden transients fail to startle, and the lead singer is only two feet tall, what's left? Detail? Transparency? Tonal balance?
People often say that most horns "sound like horns" and are therefore "disqualified from audiophile consideration". To me, a 90% reduction in image size is a gross distortion, but owners of minimonitors talk endlessly about imaging and transient response. But without weight and body, the transients fail to startle and lose most of their emotional power.
A system capable of reproducing an enormous soundstage, that showcases dynamic contrasts, and presents music with realistic presence, weight and body will never fail to excite and arouse. These are the traits that the triode/horn systems use to communicate. These are the traits that stimulate our body and unconscious mind..."

Herbert E. Reichert, "Casual Reactions", Sound Practices, Vol.1, #4

"...If you have only heard nasty horns, you might find it hard to believe that a good horn system can be the best speaker PERIOD."
Jeff Markwart and John Tucker, "Altec Voice of the Theater speakers for Hi-Fi", Sound Practices Vol.1, #4

"...If you don't think a speaker can have explosive dynamics, wall-to-wall imaging, a seamless midrange that just won't quit, incredibly low distortion, a sweet, airy top end, and do all this without a hint of strain, you just haven't driven a good horn system lately!"
Paul Eizik, letter to "Readers' Forum", Sound Practices Vol.2, #1

"...Once horn speakers get in your blood nothing else will do. They put you IN the music in a way other types of speakers rarely do."
Joe Roberts, "Reconsider Baby - The Promise of Horns in the Contemporary Situation", Sound Practices Vol.2, #3

"...Horns have a very forward presentation. Back in the Seventies, "too forward" was a common criticism of speakers. What people were looking for was that backward sound, I guess.
The illusion horns provide is a "they are here" sound rather than the old "you are there" illusion. That is, the sound is so dynamic and alive that it sounds like the music is going on IN YOUR ROOM."

Paul W. Klipsch, "Speaker Power", Audio, October 1961

"The higher the efficiency of a loudspeaker, the lower the distortion. In the absence of weight-loading, the distortion may be expected to be inversely as the square of the efficiency. In the case of weighted diaphragms, the major penalties are the power required to accelerate the extra weight and the resulting looseness of coupling between the electrical power and the air being moved. Transient response has to do with peak power output available with linearity (freedom from amplitude distortion) and the ability of the speaker to produce sound pressures proportional to applied instantaneous power.
Much effort has been expended to reduce weight of moving parts such as the diaphragm, and so forth - even to the extent of using aluminum ribbon voice coils instead of copper. There is seen to be a premium placed on high efficiency. This significantly applies not only to speakers but to amplifiers.
High efficiency results in reduced distortion in the speaker and less demand on the amplifier."
Harry F. Olson, "Elements of Acoustical Engineering", Chapter 7 - "Horn Loudspeakers"

"The existence of subharmonics in direct radiator loudspeakers is well known. However, in horn loudspeakers the diaphragms are relatively small and quite rigid. Consequently, the conditions for the production of subharmonics is not particularly favorable."
"Toneburst", "Low-cost Horn Loudspeaker System - Details of successful experiments", Wireless World, May 1974

"As far as the ear can tell, consistently clean and spacious bass can be reproduced only by a driver unit coupled to a horn-type acoustic transformer..."
Jack Dinsdale, "Horn Loudspeaker Design", Part I, Wireless World, March 1974

"Although full-range horn systems are used today only by a small number of enthusiasts, most experts are unanimous in acclaiming their virtues as loudspeaker enclosures, especially their high degree of realism and "presence".
Abraham B. Cohen, "Hi-Fi Loudspeakers and Enclosures", Chapter 11 "Horn-Type Enclosures"

"The advantages of horn-loaded systems lie in the fact that it is possible in such systems to obtain relatively distortion-free output at the low frequencies because of the small motions of the diaphragm even when large amounts of acoustic power are realized. Secondly, the high efficiency of the horn-loaded systems means, of course, that for a given power output the system does not have to be driven as hard electrically as the direct radiator baffle. This naturally results in more conservative use of amplifier power with consequently reduced amplifier distortion and better linearity of response during peak bursts of power."
Paul W. Klipsch, "Loudspeaker Performance", Wireless World, February 1970

"In every case - woofer, squawker, tweeter - the horn offers "cleaner" sound at all practical levels of sound pressure output. Indeed the horn is about the only means for delivering extremely high sound pressure levels with reasonably low distortion."
"A crude analogy of the direct radiator loudspeaker would be a "baffled" piston on the surface of a lake. It could agitate the waters but it would not be much of a pump. But put a cylinder around the piston, and it becomes capable of lifting the water. This is analogous to the driver unit coupled to a horn. The cone is forced to work at higher pressures with lower velocity.
Another analogy is the gear ratio of the automobile which transforms the "low impedance" engine - low torque, high speed - to the "high impedance" drive wheels - high torque, low speed. The direct radiator speaker is a low impedance device - low pressure, high velocity. The gear box is an impedance transformer. The horn acts as a transformer to increase the pressure and reduce the motion of the driving system."
"Modulation distortion is directly affected by the amplitude of diaphragm motion, and would thus be greatly reduced by horn loading."
H.J.F. Crabbe, "Design for a Folded Corner Horn", Wireless World, February 1958

"...Another great advantage of horn loading is that it results in heavy damping of the cone movement and consequent elimination of resonances."
James Moir, "High Quality Sound Reproduction"

"A small diaphragm may be designed to be extremely rigid and to move as a piston up to frequencies much higher than can be achieved with a large paper cone; as a result, the variations in sound output over the frequency range will be much reduced. A properly designed horn presents a resistive load to the diaphragm that is high and constant over a wide frequency range and down to a much lower frequency than is possible with a direct radiator speaker. Transient oscillations of the diaphragm are thus largely damped, and this gives the reproduction from a properly designed horn a solidity and body unequalled by any type of direct radiator speaker."
Rick Steiner, "A Back-Loaded Wall-Horn Speaker", Speaker Builder 4/91

"These speakers' high efficiency and dynamic range provide an impact and realism to percussive sounds I haven't heard in many nonhorn systems."
Philip Newell and Keith Holland, "Round the Horn", Studio Sound, March 1994

"...The model proved highly successful and gave good correlation with measured results, which used a Community M4 as a signal source (capable of producing signals with less than 1% harmonic distortion, even at 150 dB).
James Nicholson, "A High Efficiency Mid & High Range Horn", The Audio Amateur

"The use of horn-loading provides, I believe, the best acoustic coupling yet devised, with superior transient response, smoother frequency response, and high efficiency, while the configuration improves the polar response of the unit."
Dr. Bruce Edgar, letter to "Readers' Forum", Sound Practices, Vol.1, #2

[Angelo]

Special Qualities Of Horns

http://www.enjoythemusic.com/Magazin...re/zingali.htm

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.

[Angelo]

http://www.soundstage.com/yfiles/yfiles200109.htm

Horned Subjects

To mimic the basic principle of horn loading, use your hands to create a trumpet-like bell in front of your mouth. Now talk into this shape. Your voice gets louder, but its character is altered too. Horn speakers can do much the same thing. Based on our example, it seems patently obvious that they can distort tonality and change timbre. Perhaps that's acceptable for PA roadies, sound-reinforcement gigs and other head-banging, lo-fi enterprises. But for superior reproduction of music at home, horns are clearly bad, right?

But maybe there is more to horn loudspeakers. Certain manufacturers think so, and Avantgarde is one of them. Jim Smith, the real-life proprietor of Avantgarde-USA, has been an audio fixture since the early days of ARC and Magnepan. He's run audio stores, recorded music and worked as sales manager for various audio firms. He was ready to call the audio business quits. Then a chance encounter with one of the first pairs of Avantgarde speakers in the US caused him to hop aboard a plan -- and plane. He headed for the Avantgarde factory in Germany and became the company's exclusive representative in the New World. His main argument in favor of horns cites the inability of most traditional speaker systems to replicate the tremendous dynamic range of live music.

Horns add considerable acoustic gain to the driver resulting in a loudspeaker of much higher efficiency than conventional designs. As a result, horn speakers are quite common in the world of sound reinforcement where high decibel levels are more important than high fidelity. Unfortunately, the colorations that can accompany these designs are also apparent too. British designer Phil Jones, creator of the award-winning Platinum Air Pulse 3.1 full-range horn speaker, confirmed Avantgarde's position: high-end horn applications should eschew high compression ratios to avoid tonal anomalies and timbral deviations. In sound reinforcement, high compression ratios allow output levels that would be acutely dangerous in a home environment, where they're neither required nor desired.

According to theory, the low compression ratios used by Avantgarde and other high-end firms avoid the cupped-hands coloration but still benefit from the basic advantages of horn loading. (Of course, transducers superior to coliseum hardware are essential as well.) All dynamic transducers are pistonic devices. As such, they operate with diminishing linearity when pushed to the outer limits of their range of motion. For equivalent output levels, a horn-loaded driver undergoes significantly reduced excursion from a directly air-loaded competitor. Ten to 15dB of acoustical gain means that, everything else being equal, a horn-loaded transducer never abandons its area of linearity -- even at high levels, it's barely moving. This also makes it measurably faster. For any given amplitude level, the excursion and rarefaction cycle of out/in motion spans a far shorter distance than that of a non-horn driver. The increased efficiency of horn loading naturally requires lower power levels. High speaker sensitivities, in upper 90s or low 100s, turn single-ended micro-power triode circuits into optimal mates.

Truth or fiction?

Srajan's friend -- Belgian audio salon proprietor Pascal Devillers of La Galerie du Son -- reminds himself what the real thing feels like.

Disregard for a moment our audiophile dream list of desirable attributes such as soundstage holography, midrange voluptuousness and bass slam. If we honestly compared our system to a live event, one area would likely pale: dynamics.

Most speakers placed in conventionally sized rooms end up in what a real venue would call the extreme nearfield. An 11-foot distance at home might look like the farfield, but in a jazz club it's front row. At that distance, a real-life drum kit is frighteningly loud, transient rim-shot explosions and cymbal crashes startlingly violent. When a diva goes full throttle, her voice singes hair in the first row of a symphony hall. When a pianist falls into the keys from two feet up, it isn't sweet but stridently metallic.

It's quite obvious that live music is filled with serious short-term bursts of powerful decibel levels, sharp leading edges and brilliant transients. The confounding part is how differently our hearing reacts to live music versus at-home playback. In an acoustic venue, dynamic peaks are exhilarating and hair-raising. In a living room, attempts at realistic replication are usually plagued by convulsions. Clearly, most stereo rigs go into nasty-sounding and distorted compression when we set average volume levels such that peaks approach real-life scale.

Only gluttons for aural punishment won't instinctively lower playback levels to re-enter a safety zone of pleasantness. And that's where, according to Avantgarde, we're missing out. Playing it safe means playing it boring. The oceanic roar of the original event is sadly diminished to a teapot tempest. The magical journey on the open aural seas is imprisoned on a tiny windjammer inside a bottle. No emotional devastation -- just bonsai audio!

Fancy words or fact?

Here are certain design aspects of the Avantgardes I'm especially curious about.

Controlled dispersion: Consider the subject of wide dispersion. Unless a speaker was specifically designed to have smooth and broad off-axis response, its direct and reflected response curves will be dissimilar. When combined at the listener's ears, room boundaries will induce peaks and suck-outs. To minimize room colorations with such designs, many audiophiles instinctively revert to room treatments that minimize side-wall reflections for clearer sound. Others place their speakers so far away from room boundaries that most interior designers and spouses throw fits.

Consistent performance: According to Avantgarde, the spherical shape of their precision-molded horns causes 85% of the sound to be aimed directly at the listener. Only about 15% is said to escape as reflection, albeit highly attenuated in output. Above the pass band of the active woofer section, this speaker should, in theory, remain less encumbered by room-boundary logistics than conventional speakers. The claimed controlled directivity or dispersion pattern should make them easier to place and (from room to room) less dissimilar-sounding than regular designs.

Avantegarde's Trio Classico

Crossover simplicity: Fewer electrical parts in the signal chain usually translate into enhanced transparency and ease if the mechanical/acoustical functions operate in a linear fashion. As a physical function of their so-called throats (the innermost area of the flare's narrowest portion), the respective lower cut-off frequency of the Avantgarde horn drops acoustically by 18dB/octave. The low-pass thus remains free from electrical crossover parts. The upper cut-off frequency is a combined function of mechanical driver roll-off, a first-order electrical network and augmentation from a small inner chamber that acts as secondary acoustical 6dB/octave bandpass filter. These acoustical and electrical first-order slopes combine to an effective 12dB/octave roll-off, but they preserve the phase-linear benefits of an electrical 6dB/octave network.

Back to reality

The ready availability of many patently colored horn speakers speaks loudly and very efficiently about their inherent challenges. Could Avantgarde's engineers marry their very real theoretical advantages -- controlled dispersion, high efficiency, economy of transducer excursion and concomitant low distortion figures, superior mechanical rise times, and potentially huge dynamic range -- with the kind of flat frequency response and tonal honesty we audiophiles demand?

The Avantgarde Duo is a dual-horn actively bass-amplified four-driver, three-way speaker system. The load is a nominal 8 ohms, frequency response a claimed 22Hz to 20kHz, and sensitivity 103dB. The Duo's high-frequency horn covers an ultra-wide bandwidth down to 900Hz, with the passive crossover point at 2kHz. The midrange horn extends to 170Hz, where it hands off to dual 10" powered and sealed woofers. Why not a bass horn? Horn diameter and depth are a function of wavelength. Even a folded horn -- or spiral, as in the Platinum Air Pulse 3.1 -- would require a positively gargantuan cabinet. Consider this: the Duos' larger horn diameter is 26.25". It covers second- and third-order low and midbass harmonics and all midrange fundamentals. The company's flagship adds 11", for three feet of width, just to lower the crossover point by a mere 70 cycles to 100Hz! Avantgarde's engineers obviously intended to keep their speakers as living-room friendly as possible.

[Angelo]

Why Horns?

By Dr. Bruce Edgar

http://www.enjoythemusic.com/Magazin...e/whyhorns.htm

I remember hearing a very good horn loudspeaker for the first time in 1978. It was sheer magic to my ears. I could not believe the incredibly realistic sound that seemed to radiate effortlessly into the room. But when I talk to other audiophiles about horns, the reaction I hear is usually one of disgust. Like a bad hair day, everyone seems to have had a "bad horn" day.

Rich Weiner of "Bound for Sound" recently described his "bad horn" day. "As a neophyte audiophile, I once had the horrifying experience of listening to a friend's horn-based speaker system. "Killer equipment. You've never heard anything like it," he promised. Indeed I hadn't. I found myself sitting about six feet from a pair of Klipsch corner horns driven by Phase Linear 700 amps. My friend was right. I have never heard anything like it, although I understand that standing directly behind a 747 during takeoff is quite similar. Since that time I have avoided horn speakers." (Bound for Sound '99CES Report).

But times are improving. In the same report, Weiner says, "Perhaps it's time to try horns again...Edgar's Titan (Horn) system was quite impressive...detailed and articulate..." Weiner's experience is not unique. Other reviewers and audiophiles are coming around to the concept of an acceptable audiophile horn system.

So you may ask, "What is the difference between the vintage horn systems and the new generation of horn loudspeakers?" I have been researching that question for the last 20 odd years. In the process, I founded Edgarhorn whose main goal is the design and manufacture of audiophile quality horn loudspeakers. But I'm getting ahead of the story. After I had heard my first good horn speaker, I began trying to hear other horn speakers and other pseudo-horns. Most of the ones I listened to didn't come close to that first system that I'd heard.

Eventually, I was able to analyze that good horn system to discover what made it tick. It belonged to a Senior Engineer at the aerospace company where I worked. At the time, I was a research scientist specializing in radio wave propagation and signals analysis. The design came from a group of amateur horn builders on the east coast lead by Ben Drisko in the early 50's. This system used a Drisko folded corner bass horn design, similar to the Klipschorn, and a JBL 375 compression driver on a Western Electric midrange horn. The component that made this system so good was the JBL 375 driver. My engineer friend recently bought a set of my Tractrix horns for his 375 drivers. When we tested them, I was astounded by their ruler flat response from 400 Hz to 10 kHz.

In the early 80's, I set about tracking down all the horn articles and papers and analyzing all of the published and underground designs. I was very disappointed. There was no clear way of horn design. What was even more depressing was the periodic regurgitation of wrong headed ideas of horn design in articles from year to year that has infiltrated into some horn design software that is marketed today. So I embarked on course of experimentation with horn design and construction. I figured that with my background in wave propagation, spectrum analysis, and experimental physics, it should be easy enough to arrive at a satisfactory design. Was I ever wrong. After 20 years of horn building, I'm still finding new ways of designing and building horns. It's the Edison experience of having to go through all the different combinations and permutations of drivers and horns. And my customers keep coming in with different requirements that change my views and shift the proverbial paradigm.

So back to the question, "What made the vintage horn systems sound bad?" There are a variety of problems. I have run into most of the horn problems either in designing my own horns or duplicating somebody else's horn.

The first problem is electronics. Weiner talked about listening to some Klipschorns with high power solid state amps. The amps were one source of the bad sound. Horn systems typically have sensitivities of 100 to 108 dB SPL with one watt input. Even at the loudest sound that you would realistically audition any speaker system (95-100dB), the amplifier is only delivering a watt or so to the horn system at peaks. Most of the time the amp is idling at 100's of milliwatts; yes, I said milliwatts. At this level many high power solid state amps have real problems with crossover distortion. For this reason, I tell people who buy my horn systems to try different amps with them along with their existing amp. The low power requirement of horns means that single ended tube (SET) amps can easily fill a room with sound. However, not all single ended tube amps are created equal. Some SET designs have relatively high levels of distortion that can be easily heard on the horn system. And of course, the horn gets the blame for the distorted sound.

A second problem with horn loudspeakers is that they are easily prone to resonant peaks in their response. I have heard some horn tweeters that made me think that I was being drilled between the eyes. Many horn midranges have a honky megaphone sound that comes from resonant peaks. I have measured many old horn midranges with high resolution spectrum analyzers and have found them loaded with high Q spikes that give each horn speaker its own characteristic coloration.

Bass horns have their own resonance problems. Typically, a well-designed bass horn that can go down to 35 Hz will have a total volume of 20 cu.ft. or more. A company's marketing department will say that it can't sell a big speaker like it. Moreover, the marketers say, "Keep the 35 Hz flare but make it smaller." So the horn length is truncated to make it smaller. The net result is long folded slowly expanding tube that sounds more like a resonant tuba than a wide band bass horn. The response plot looks as a series of harmonically related resonant peaks.

Some resonant problems are caused by structural defects. At the point where the sound comes out of the mouth of the horn, the edge of the mouth can vibrate in a bell mode. If you have seen some old style trumpet PA speakers, they were actually shaped like a round bell. A bell will resonate at a frequency whose wavelength can be wrapped around the circumference of the bell end. No horn is immune to bell modes, but proper damping and tension bracing can eliminate the problems.

A third problem is the use of improper drivers on horns. Good horn drivers require heavy magnets and light weight diaphragms. Most regular speakers used in typical box speaker systems have lower weight magnets and heavy diaphragms. The use of regular speakers on horns will, for the most part, yield restricted bandwidths and irregular responses. Recently, Speaker Builder featured an article touting an easy horn for your dome tweeter. I performed the experiment with a high quality dome tweeter on a 800 Hz Tractrix horn. Without horn loading, the dome tweeter went up to 20 kHz at a sensitivity of 88 dB. With the horn, the efficiency increased several dB, but the response rolled off above 10 kHz. With such a horn loaded tweeter, any listener would ask, "Where's the top end?" My survey of horn construction project articles has yielded many other examples of using the wrong driver on a horn.

As a corollary to the wrong driver syndrome, an associated problem is the use of PA horn systems in home stereo applications. For example, I find many horn enthusiasts over the world using variants of the Altec "Voice of the Theater" (VOT) speaker system. The VOT featured a compression driver on a metal mid horn and a 15" woofer on a front loaded 110 Hz midbass horn. The back of the woofer was loaded by a bass reflex ported enclosure. In general, I have found the Altec compression drivers and woofers to be good quality horn drivers, but the horn design can be improved with my Tractrix horns. And I have done this for numerous customers.

[Angelo]

Andy Lewis on Horns
(a short tutorial on horn loaded loudspeakers, and variants thereof)
10/20/07

http://www.acmebass.com/forum/andy_lewis_on_horns.htm

Is it possible to play bass using a so-called "folded horn" loudspeaker? Would you want to? Is there any advantage to this type of loudpeaker which would make it worth the trouble of hauling one around? Why don't any credible manufacturers still produce them, as they used to? Why have they all but disappeared from the scene, and remained exclusively in the realm of the hobbyist?

Friends and customers have asked me to comment on the operation and the viability of horn loaded loudspeakers, and variants thereof. There seems to be an interest in home-built variants of horn loaded speakers for bass guitar.

What is A Horn Loaded Loudspeaker?
Advantages and Disadvantages of Horn Loaded Loudspeakers
My Opinion(s) of Horns: I Love Them
Can Horns, and Variants of Horns, Be Useful for Bass Players?
The True Horn
The Horn Variant: A Midrange Horn
How Low Can it Go?
Behavior Below Horn Cutoff: When is a Horn Not a Horn?
Where Did All the Folded Horns Go?

What is A Horn Loaded Loudspeaker?

Horn loading is a technique whereby a speaker diaphragm is coupled to a column of air, which increases in cross sectional area as a function of distance from the diaphragm.

Effective horn loading occurs when two conditions are met: (1) the distance from the diaphragm to the mouth of the horn is equal to the wavelength of the tone being produced, or greater, and (2) the cross sectional area of the mouth of the horn is equal to, or greater than, that of a circle of a diameter equal to the wavelength divided by PI (3.14159). More on this later.

(These figures are actually conservative by a factor of 1.25, according to my ancient text.1)

Horns can be designed to have different "flare rates." In other words, some horns increase in cross sectional area faster than others. Common flare rates include conical, exponential, hyperbolic, and "tractrix," which is a combination of exponential and hyperbolic. Each of these flare rates, or shapes, has its advantages and disadvantages. Flare rate is chosen to control "radiation resistance" in the "throat" of the horn. The exponential horn is the most widely used, by far, because it's seen as a good compromise between the low-end extension and low distortion in the throat.

Advantages and Disadvantages of Horn Loaded Loudspeakers

Advantages of horn-loaded loudspeakers include greatly increased efficiency and decreased distortion when operating within their range of true horn loading. Another practical advantage is that a horn can be shaped to achieve a predictable dispersion pattern in the room, with resulting tight control of coverage. This is great for feedback avoidance, as in a public address system, and for "long-throw" applications, as in a deep rectangular room.

Disadvantages of horn loading include, ironically, their tight pattern control, which can be bad in a situation where wide dispersion is desired, and their large size. We will see that the size issue is what makes horn loading impossible to achieve in practical bass guitar systems.

Another disadvantage of the folded horn, in particular, is the coloration, the response irregularities, and the phase effects caused by the convoluted path through which the sound must travel before entering the listening area. An acoustic guitar or a human voice reproduced through such a loudspeaker will be greatly colored and distorted.

This is not to say folded variants of horn loaded systems can't "sound good," only that if they do, it's not because of their horn shape per se. And they're undoubtedly larger than they need to be to sound as good as they do.

My Opinion of Horns

In my opinion, horns are like any other family of loudspeakers. They have a place. They can be used correctly, or they can be used incorrectly. They can be well designed, or they can be thrown together or ill conceived. When they are used and designed intelligently, they can be fabulous. When they are designed or used inappropriately, they can be silly, obnoxious, and too big.

Some of my favorite loudspeakers in the world are horn loaded. Among the classics, of course, is the venerable Klipsch Corner Horn, which albeit huge, overcomes the size problem of the true bass horn by converting the entire corner of the room in which it is used into a horn mouth. Electrovoice actually produced a larger version, under license from Klipsch, called the Patrician, a four-way all horn loaded system. Didn't sound that great, but they had a mojo of Biblical proportions. I owned some of them at one time.

The classic Acoustic 360 and 370 systems are probably the most celebrated horn-variant systems in the bass guitar world. Although not true bass horns, they are very cool. I had an opportunity to hear one locally not long ago, and that old pig still sounded great! It had an 18" Vega in it, before they called it Cerwin Vega.

The Electrovoice ST350A is a personal favorite. A radial tweeter with a phenolic diaphragm, very sweet. JBL and Electrovoice have produced, and do produce zillions of great horns. I love the sound of the modern JBL's at the movie theater. I have a fondness for early fiberglass horns from Community Light and Sound. They made a straight bass horn called the Leviathan (in the Whole Earth Catalog- Google that, kids!), which was huge, and came in two pieces, which when fastened together, would put a horn with a huge mouth area in front of a pair of 15" woofers.

I would be remiss to not mention the Altec 311 Series. The 311-90 is a highly sought after, antique, cast metal exponential horn, said to have a low frequency cutoff of 300 Hz. It's approximately, I estimate from memory, 30 inches wide, and 16 inches high. Completely bodacious, and a thing of beauty. It has an Altec-size throat of 1.4 inches, as I recall, and is driven by the Altec 280 and 290 series drivers, with their 3-inch aluminum diaphragms. Killer! Collectible, valuable, and mostly in Japan by now...

Google some of my faves. You won't be disappointed.

Bottom line: I love horns, when designed and used correctly. I've built and used lots of them. I still own some.

Can Horns, and Variants of Horns, Be Useful for Bass Players?

Well, yes. Sort of. They can get you through the gig in an emergency, when you can't find anything smaller or with better low-end extension, or with less midrange distortion, and if you can find a goon to carry it in for you. Other than that, it's hard to recommend them.

To explain, allow me to divide what are referred to as "horns" into two categories: True horns, which can achieve horn loading at bass frequencies, and "variants," which cannot.

We will see that the former is nonexistent, and that the latter is impractical.

The True Horn

The lowest note on a 5-string bass, as some of you might know, is 30.87 Hz. Let us calculate the size of a 30.87 Hz truly horn loaded system from the above rules:

Wavelength at 30.87 Hz = 1120 feet per second divided by 30.87 Hz = 36.28 feet.

A Low B note has a wavelength of 36.28 feet. This has alarming implications for anyone who wants to achieve horn loading at this frequency.

To wit: From the above conservative guidelines, a bass horn would have to have a length of 36.28 feet, and, assuming a circular shape, a mouth diameter of 11.55 feet (33.28/3.14159).

The true Low B bass horn is about 36 by 12 feet. Anything with a mouth or length smaller than that cannot achieve horn loading at this frequency. I know it's alarming, but those are the conservative facts.

This first type of horn is nonexistent, in my experience. I think I'd remember a bass rig of that size it if I saw it. So would the singer, who would fire the bass player, and get someone a little less OCD for the next gig.

The Horn Variant: A Midrange Horn

So what about the second type, the horn variant, which fails to achieve horn loading at bass frequencies? Let's take a look at what it really is.

The key to understanding the horn variant is to recognize that it transitions from true horn to non-horn behavior at a much higher frequency than the true bass horn. Thus, there are two modes of operation, above and below this frequency, and a limited range in between, where it behaves progressively less horn-like as it transitions.

This horn variant, in fact, is a true horn. It is a midrange horn, but not a bass horn. It's too small to be a bass horn. There is a frequency below which it cannot operate as a horn, based on its size.

[Angelo]

How Low Can it Go?

It is easy to calculate the frequency at which the horn loading breaks down. How big is the mouth? How long is the horn?

What would be the lowest horn loaded frequency of a horn variant? Let us look at an example. Let us assume we built a so-called folded horn, in which the length of the horn was folded back on itself, or around, to manage a convenient shape.

Let's say we have a horn with a folded length of 6 feet, and a mouth of 2 by 3 feet, or 6 square feet. This would be similar in scale to the typical bass horn variant, and would not be considered a small load by anybody but a linebacker. How low would this horn "work?"

Based on the mouth size, there is a frequency below which the unit can't operate as a true horn:

This horn's 6 square foot mouth would be equivalent to a circular horn with a diameter of 2.76 feet.

This would, from the above guidelines, predict a horn cutoff frequency wavelength of PI times this 2.76, or 8.68 feet.

A tone with a wavelength of 8.68 feet has a frequency of 130 Hz.

Below 130 Hz, this is not a horn. Its mouth isn't large enough to permit horn loading.

But it gets worse. The ability of this midrange horn to behave as a true horn is also limited by its length of 6 feet, and in fact, is longer than what is to be found in most bass "horns" and kit plans for them. This horn can't behave as a true horn below the frequency whose wavelength is 6 feet. What is this frequency? It is 1120 feet per second divided by 6 feet, or 186.7 Hz.

This very large loudspeaker cannot operate as a proper horn below 186.7 Hz, which is more than two octaves above Low B. In the low bass, this horn variant isn't a horn at all, it's just a good way to fill up a van and break your back moving it around.

Behavior Below Horn Cutoff

Below the frequency at which the horn loading begins breaking down, the horn structure becomes "invisible" to the wave, as the frequency becomes lower, and as the horn becomes smaller in comparison to the wavelength. The cone movement is no longer controlled by the horn, and the dispersion pattern in the room widens to virtual omnidirectionality at low bass frequencies, exactly like a conventional vented or sealed enclosure- because that's what it is at low frequencies.

When the horn is inconsequential, at these low frequencies, the actual air in the vicinity of the throat has a significant mass, which is "dragged" by the cone. This mass loads the cone of the woofer just as a wad of silicone or modeling clay stuck to the cone would. The unit literally becomes a mass-loaded woofer in a small sealed enclosure- the horn is gone. At low frequencies, you carried that behemoth into the gig for no reason, other than to meet girls.

(Please see my piece on "Should You Download Your Woofer," in the Science section of this website. You will find, if you look, a detailed analysis of the addition of an air mass in a confined space to a speaker cone, and how it changes the effective parameters of the woofer. All of the math applies to a horn well below cutoff frequency. It's important to understand these principles when choosing a driver for use in one of these horn-variant systems. Qualified suppliers of kit plans should be able to explain these principles to budding home-builders.)

As the frequency falls below the horn-cutoff frequency, the distortion-reducing qualities of your horn disappear. Cone excursion increases as the unit transforms to simple mass-loaded sealed enclosure. As cone-escusrion increases at low frequencies, intermodulation and "doppler" distortion of the high frequencies increases as a result. In fact, the conventional vented system is able to control cone excursion much more effectively than the horn variant in the low frequencies, where it counts, and is able to reproduce the lowest notes with lower distortion as a result.

Where Did All the Folded Horns Go?

There was a time, primarily in the 1970's, when folded horn bass rigs were everywhere. Partly because of the great sound, and the success of the Acoustic 360 and 370, and the visibility of Jaco Pastorius, nearly all manufacturers took a stab at the folded horn for mass production. I remember, as a drummer, helping bassists lug around designs from Ampeg, Fender, Traynor, Peavey, Carvin, and others. They were everywhere. I built a few of them myself. Like everyone else though, I abandoned the idea over 20 years ago as goofy, gave my last folded horns away, and haven't touched them since. As a musician, while I was still playing gigs, I crossed a line after which I declined to help my fellows carry their ridiculous equipment, such as Yamaha Electric Grand Pianos, Hammond B-3's, Leslie speakers, and folded horns. "You're on your own, pal."

The market has spoken. Folded horns for use in sound reinforcement applications are still used, but for bass players, they have gone the way of the Stanley Steamer for obvious, stubborn, and irrefutable reasons.

Can you play bass through a folded horn? Of course you can. It's just been proven to be impractical. They're just too stinkin' big and heavy, and average at best in terms of sound reproduction. For decades now they've been pretty much gone from the scene. They won't be coming back.

Horns have always had a great fascination for loudspeaker hobbyists, because they're so "cool," and they probably always will. Horns are sexy, no doubt about it.

But it's basically a huge box that doesn't have the low end that a vented or sealed box of similar size would have. It has a high low-end cutoff as it loses horn "loadedness."

This is to say nothing of the issue of the distortion in the midrange caused by the bending of the folded horn. Musicians seem to be much more concerned about coloration now than they used to be. I believe this is because of the proliferation of home studios in the last 15 years, and the experience musicians have had in hearing their instruments reproduced with relative accuracy.

I will never build or recommend a folded horn for a bass player. It's a dumb idea, which has failed to pass the test of time. Folded horns have been relegated to the well-intentioned world of the loudspeaker hobbyist and to the landfill. So they shall remain. Take it to the bank.

1. Hi-Fi Loudspeakers and Enclosures. Abraham B. Cohen, Hayden Books, 1956.

[Angelo]

http://www.ossaudio.com/lothx/LothXhorninfo.htm

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 impedence transformer. When a diaphragm vibrates, pressure waves are created in front of it. This is the sound we hear. Coupling the motion of the paper to the air is not an easy thing to do due to the very different densities of the vibrating diaphragm and air. This is can be viewed as an impedence mismatch. We all know that sound travels better in high density materials than low density materials, and in a speaker system, the diaphragm is the high density (high impedence) medium and air the low density (low impedence) medium. The horn assists the solid-air impedence transformation by acting as an intermediate transition medium. In other words, it creates a higher acoustic impedence 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, summarized as follows: Less distortion generated. For an equivalent SPL, horns require a smaller diaphragm. 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), and 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.

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. 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, they are faster, more dynamic, have a better transient response with less distortion and stress on an amplifier.

Large enclosure size reduced by folded-horn design

Since the horn mouth size is exponentially proportional to the frequency one wants to reproduce, the size of the mouth increases to ridiculous proportions very quickly. Enter the folded horn. Here the horn is flared within a cabinet by creatively folding the horn within the cabinet. This allows for us to achieve low frequencies without taking up too much space. Unfortunately, the exponential equation used in conventional horns does not apply in a folded horn enclosure due to the folds. As a result, the expansion rate has to be compensated for and there is no fixed formula for this, thus, the standard horn formula is only used as a starting point and the rest of the folding/tuning is done by painstaking listening and measuring iterations. After 15 years of work, we have finally come up with our own formulae for our various cabinet folds.

Horns have impact!

You feel the music and 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 much hyped low efficiency speakers. 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 an feel the music, front row centre.

[Angelo]

J. Dinsdale - Horn Loudspeaker Design - Wireless World - May / June 1974

http://www.saturn-sound.com/history/...projects.htm#J. Dinsdale - Horn Loudspeaker Design