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Horn-Loaded Speakers
Topic: Some Horns propaganda

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Posted by Romy the Cat on 07-04-2004

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This is an article from Thomas Dunker's site (available in my Links Section) and presumably written by him. Although I slightly disagree with some of the statements he made about the horns “imaging”  and some others but generally it is very good article for the beginners and I highly encourage you to familiarize yourself with it.

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“Why Horns?”  by Thomas Dunker


So why would anyone want to use horn speakers today, when we can have 100W amps at low costs? As I hinted in the previous paragraph, horns DO have other special qualities than just high efficiency. Okay, it's necessary to understand a few basic things about HOW HORNS WORK in order to say WHY they do some things better than other speakers. (You'd be amazed at how many people who simply refuse to believe that horns can be used for serious music listening because somebody told them so or because they think horns all sound like megaphones.)

A horn can be viewed as an acoustic impedance transformer. Turning mechanical motion (a vibrating diaphragm) into sound waves in air is in many ways a difficult thing to do. The most fundamental problem, which has a lot to do with the issue of efficiency, is that the difference in DENSITY between a paper or metal diaphragm and AIR is huge. There is a tremendous impedance mismatch. This fact explains that sound travels very far through denser media like metal, water or rock. In a speaker-air situation, the speaker diaphragm can be seen as a high impedance source (solid material) and the air being a low impedance medium (the air does not easily load down solid moving objects). There is a reason why humans can't fly by waving their arms!

What the horn does is to help the transducer couple its radiated energy into sound waves in air by means of an impedance transformation. What this means is that it creates a higher acoustic impedance for the transducer to work into, which means that more power is transfered. (Analogous to putting an antenna on a radio transmitter, which seems like an obvious thing to do!) Basically, a horn is a tube or conduit with increasing cross-section along its axis. The narrow end (where the driver sits) is called the horn throat, and the large end (which opens into the room) is called the horn mouth.

Sound pressure is defined as pressure change per unit area. In a horn, the wave front is restricted by the inner walls of the horn, and the area across the horn increases as the wave front approaches the horn mouth. So what happens here is that at the throat we have a small area and high pressure with small amplitudes, efficiently loading the diaphragm. As the wave fronts travel towards the horn mouth, the pressure drops, while the amplitude and the area increases.

A horn also has the property of directing the sound into a narrower beam, which increases the on-axis sensitivity (SPL/1W/1m). Increased directivity combined with high electric-acoustic conversion efficiency means that horn speakers are very easy to power, even with very small amplifiers.
What does all this really mean, then? In what ways does the horn 'help' the driver/transducer. And how does all this make horn drivers a bit different from direct radiators? I will try to sum this up in a few points:

-Improved energy conversion means that for a given SPL, a horn loaded diaphragm will have to move less than a direct radiating diaphragm of equal size. For any electromechanical transducer, the distortion generated by the driver itself will be proportional to diaphragm excursion magnitude. Thus, for any given SPL, the horn loaded speaker will have lower distortion than the same size direct radiator.

-A smaller diaphragm on a horn can be used to generate the same SPL as a larger direct radiating diaphragm for the same excursion amplitude. This means that you have a smaller mass to accelerate for the same acoustic output when you horn load a driver. This helps the transient response of the speaker regardless of what Fourier said. Subjectively, horns will be noted for their effortless, snappy handling of transients.

-The smaller diaphragm excursions allow the use of short, underhung voice coils (reduced mass again) taking full advantage of the flux in the pole piece gap. This increases the efficiency of the transducer, allowing the amplifier to work with more headroom and greater ease. Horn drivers need to have powerful magnets and tight magnetic coupling because of the high pressure they are asked to produce when sitting in a horn throat.

-Because the amp has more headroom, and because the driver handles signal peaks and high outputs more ideally, horns will be able to produce much higher SPLs than comparable direct radiators before distortion becomes objectionable. In short, there will be room for more dynamics, at lower distortion, with better transient response, with less stress on the amp.

Since this is an enthusiastic pro-horn text, I have not emphasized the problematic aspects of horns. One thing I haven't mentioned is that the lower the frequency one wants to reproduce through a horn, the larger the horn must be. The size of a horn quickly multiplies when you go down a few octaves. Bass horns can be next to impossible to fit into a normal home. This really shouldn't be a problem to a true enthusiast, but even I have had to postpone any dream of a bass horn until I get a bigger place to live.

Some people say that horns have 'horn sound'. I'm not sure but I think what they mean is a sort of megaphone-like quality to the sound. A good horn should not have any of this. Unfortunately, many bad horn designs have led people to think that this is how horns 'are supposed to sound'. To the true horn fan, 'horn sound' will be a compliment that means, clean, dynamic, 'fast', physical, detailed and present sound.

Admittedly, there are a few things that horns don't always handle quite as well as your typical small direct radiator speakers. Particularly the much hyped concepts of 'imaging', 'neutrality' and 'transparency'. Horns will often lean towards a more 'solid' (as opposed to 'transparent') presentation with more 'body'. (Less ghost-like if you will!!) And horns will definitely not sound laid back! The music will jump at you rather than shyly hiding some place far behind the speakers.

Anyhow, horns have their problems like any kind of speaker, and can be extremely sensitive to the room and the rest of the system. The enthusiast would say that the advantages outweigh the disadvantages and that the problems are challenges.


Posted by Romy the Cat on 07-07-2004

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Another particle of a good Horn Propaganda. It was published in Sound Practices in 1994 and written by Joe Roberts. I disagree with quite many of the author’s statements but his strategic view that the majority of the horns and the horn installations are very horrible is very accurate. Mr. Roberts’ explanations are very truthful that the horrible horn results are no intrinsic to horn topology but exist only because the very specific numerous mistakes people do as well as very crappy particular implementations. This article is also recommended to the horns skeptics or to the horns-beginners.

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Reconsider, Baby! - The promise of horns in the contemporary situation

by Joe Roberts

For being a totally out of the blue concept, single-ended triode amplifiers enjoyed a relatively easy ride to respectability. The stuff is cool, no doubt about it, and that doesn't hurt a bit. In fact there are lots of people who are big fans of triode amps who never heard them - they got whipped up into a frenzy just thinking about it. Many others who viewed these fleapower amps with suspicion were won over by the experience of good triode amps.

Triodes do all the things the mainstream audio institutions say good audio amps have to do extremely well. You want imaging, soundstaging, back wall, yak yak yak? Look no further. The triode is your best friend if 3-D is your illusion of choice. But the lesson in triode amps for the "high-end" is that there are a few things that the general run of audio amplifiers does not do, things that we don't even have words for yet. The way good triodes play music leaves many jaded audiophiles speechless when they hear it.

Then the project of building a system around one of these fabulous amps runs you right into the question "What do I use for speakers?" Good question, one of the eternal questions in audio regardless of whether you're running two watts or two thousand. It gets a bit trickier when you leave behind the established power and sensitivity norms of the industry and enter the domain of "experimentation." With five watts, you're on your own looking for speaks, homes - at least as far as the high end speaker world is concerned.

Believe me, eight watts from a 300B will play many available speakers to at least medium listening levels. People are more or less happily running ProAcs, Ensemble Reference 3As, Spica TC-60s, etc. After all, all of these people running around raving about SE amps are listening to them on something, no? As reported by CG in Stereophile, my two watt 45 amp played loud and proud on a pair of ProAc Studio 100s.

The subjective sense of power that a triode amp can deliver far exceeds expectations. It is not unusual to hear reports that this or that >10W amp sounds louder, fuller, and weightier than this or that 100W transistor amp or p-p pentode amp. Whether a particular speaker will work on a particular amp is a question for empirical research. A high and flat impedance and >90 dB sensitivity helps.

From my listening chair, I say power ain't nuthin but a number as far as musical and emotional impact are concerned. But my chair is in front of a huge pair of high-efficiency speakers: 15" Altec woofers, Edgar midrange horns, Gauss compression tweeter. The listener with 8 watts and an 88dB speaker will encounter limits. How constraining these limits are depends on your needs. If you really like to crank up your stereo now and again or large scale orchestral music is your passion, the speakers you already have probably won't really shake the rope on three watts.

Triode amps sound great turned up to realistic SPLs, which makes the whole situation even more tragic.


ENTER HORNS

Thanks to the collective search for good high efficiency loudspeakers to use with low-powered amplifiers there's a lot of curiosity afoot about horn loudspeakers, probably the most unfashionable topic known to the modern high-end. Even 8 track gets more (and better) press than horn speakers in the US specialist mags.

Once upon a time, in the post WWII era, the earliest balls out hi-fi systems were constructed from recycled theater gear. Through the 50s and into the 60s, swanky top-of-the-line home hi-fi speakers featured arrays of horn-loaded squawkers and tweeters. A lot of this plastic horn and phenolic diaphragm stuff is a bit rough on the modern audiophile ear, but it sure was cool to be a "horn man" back then. Ain't that way now.

The need for high sensitivity dwindled as transistor power multiplied. Designers focused on ribbons, electrostats, and miscellaneous cones in sealed boxes intended to be driven by banks of steaming transistors or big hog parallel 6550 amps. The pioneers of the "high-end" as we know it had a different listening program and horns didn't fit. Quite a switch from the McIntosh and JBL 1950's upper crust hi-fi mentality. The horn ceased to exist in the mind of the modern US audiophile, except as a bad joke.

This is where triode amps and horns differ: single-ended amps are something totally new in the Western audiophile cosmos, horns have been tried and rejected. Nothing does more damage to music than a bad horn system and everybody knows it.

You can get a lot of music out of a good triode amp and a good horn. But, of course, it's not that easy. One minor problem is that good horns are extremely uncommon. Most horns are totally unlistenable in a serious music listening context. In my opinion, the bad reputation horns have endured among latter-day audiophiles is largely deserved. Most horns are junk.

But it is obvious that the kind of sensitivity a horn can provide would sure come in handy when you've got three watts and some change to burn. Plus the kind of crazy romantic audio nuts adventurous enough try a single-ended amplifier just to see what it can do are just the type who would gamble on horns too. So, here we are giving triodes and horns, the cutting edge technology of the thirties, a try in the Pentium age.


THE RISK OF TRIVIALIZING THE ISSUE

Because most horns are awful beyond description, if the goal is to pick up a few tricks which will lead us toward more perfect reproduction systems, we must be very selective. Most horns will be a total waste of time. If it looks like a cheap piece of junk, it is. Any horn made out of thin cheap plastic or cast metal that rings like a bell is going to be a problem. After all, how many cheap thin plastic or cast aluminum musical instruments can you name?

Our forebears figured out that most of those bottom of the line Jensen and EV $6.98 horn tweets were junk back in the fifties. We don't need to go through that discovery procedure again. Because horns vary so wildly in quality and performance, there is a real risk in thinking a "horn is a horn" and leaving it at that. While an "average" triode amp still sounds pretty decent, an "average" horn will DESTROY MUSIC.

Only the top 10% of the horn population is worthy of consideration for serious music listening. A few lesser horns are okay to play with for fun and may do some really interesting things, but they will have at least one dire failing which will have them in the garage after a few weeks playing time. Leave the junk in the airport paging systems where it belongs.

In recent attempts at covering the "Horn and Triode Scene," whatever that is, one big reviewer hooked up some cheap and junky squawk boxes with popularly priced SE amps and, in essence, reported that "Wow, this is better than I thought it would be but it's not that great, really." The writer was obviously having a good time, which is fine by me, but I don't think that he exhausted the possibilities of the horn genre with that experiment.

Screwing around with some funky cheap speakers is great recreation - I do it every chance I get - but it will not provide a lasting contribution to the goal of achieving real magic in the listening room.

What is needed is a profoundly deviant mindset. We have to search for something way better than what we've got to get trivializing the issue. A serious dialogue on horns, centering on open-minded evaluation of the finest of the species and reevaluation of our present-day goals and achievements, might get us to new and exciting places.


Horns and Mainstream Aesthetics

One day I was discussing the marketplace realities of horns with Peter Qvortrup of Audio Note UK. He evaluated the situation thusly: "There is so much suspicion about horns in the marketplace that listeners will be against the product before they even hear it. If you go out on the market with a product that doesn't do what they want and expect, you'll get destroyed".

Come to think of it, there is a bit of a party line regarding what constitutes "good" in the audio mainstream, a standardized aesthetic program. So what if horns do some musically relevant things better than cone and planar "high-end" speakers? Even the very best horns I have heard do not do some things on the 1994 Official Audiophile Speaker Criteria List.

Peter's findings were that horns do not give you "hall sound" and he predicts that reviewers will freak out if there is no "hall sound" regardless of how right the speaker is otherwise. Minus this critical performance factor, there could be PR problems ahead for our old friend the horn speaker.

I personally think "hall sound" is a cool illusion. Hall sound, as I understand it, is a recreation of the original acoustic space in which a recorded performance took place. This is, of course, partly a matter of the quality of a stereo recording, but a reproduction system has to be tuned in the right way to furnish an illusion of the original recording space. It's become a given that good systems do all this "hall sound" stuff right and a lot of contemporary audiophiles like this phenomenon. Most, I am sure, never questioned the issue since it sounds so good on paper.

Granted that hall sound is a neat illusion, isn't it strange that when we are supposedly trying to get to the sound of live music, we evaluate what we hear in terms of "soundstaging" and "imaging"? These concepts are strictly audio geek notions, totally irrelevant to the experience of live music. The language some people use to talk about reproduced sound suggests they are more concerned with questions of architectural acoustics of the hall than the music on the stage.

While it is nice to sit in a great hall and hear some unamplified acoustic music, it is unnatural to focus on the hall sound while you are there. You came to hear the music, right? Nobody talks about music that way and, as far as I can tell, live music doesn't even do most of the 3-D stuff that audiophiles insist on from their systems.

Furthermore, the effect of imaging is contrived and fake even when done well. I loved my Spica TC-50s but there wasn't any way they could reproduce any music except solo mandolin with a realistic sense of scale. Would you accept what passes for good hall sound in your speakers as good sound in an actual hall? No way, Jose.

Far from being an absolute part of listening to music, all this a soundstage jazz is an acquired taste and a rather obscure one at that. I like it quite a bit myself, but it took me a lot of magazine reading back in the Seventies and Eighties to even figure out what the writers were talking about.

Concepts like "dial in the soundstage with some Shun Mook ebony root pods from Mother Africa" are not intuitive. Ever notice how your non-audiophile friends never volunteer that your imaging is superb or remark, "Wow, I never heard the back wall on that recording before."

If you have to learn how to hear this stuff and learn that it is important, this suggests to me that hi-fi is not directly realistic despite the claims of the orthodox ideology. What we consider "real" is a matter of agreement rather than anything "absolute". There are codes and styles in reproduced sound just as there are in "realistic" visual art.


They are HERE

Contrary to popular folklore, horns can project three dimensional images. They are still "better" images than you get live. Big weighty images that grab you with presence and impact, just like real music, rather than relying on unnatural levels of hot top end "detail". 3-D is no problem for good horns.

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. True, the "soundstage" illusion of reproducing the original hall sound is skipped over as a consequence. After a few years of listening to horns, I strongly prefer the "right here in the room" sound of horns to the "looking into the room from a hole in the wall" sound I used to get with mini-monitors.

My real complaint about most soundstage projecting speakers, and I haven't heard them all, is that they can't rock out. Sometimes I just gotta listen to some old Funkadelic and whatnot. Stage boundaries are irrelevant in this context.

Maybe there is some grand cosmic tradeoff between dynamics and soundstaging. I think a lot of the hall sound master speakers create that unitary soundspace illusion by flattening out the dynamics somewhat and confining the presentation to a small listening window.

How can a 6" cone and a dome tweeter produce a powerful and spatially grandiose recreation of an orchestra? Most of the instruments you are trying to reproduce are way bigger than these dinky boxes. How can you expect "real" sized piano presence or the visceral growl of a bowed cello in front of a 6" plastic cone? Forget it. Getting the dynamics right and a larger sense of scale creates a stronger illusion for me than fake soundstage information, even on well-miked acoustic music.


In Search Of The Perfect Jukebox

Horn lover and audio philosopher Dennis Fraker nailed it down in a recent phone chat: "What audiophiles want is a really good jukebox, except they don't know that's what they want because they never been exposed to it and people are telling them that they want something else. But when they hear it, they know that's what they really want. You know, the right jukebox in the right bar can be magic..."

Whew, that phone call went off on a wild tangent, but he had a point there. Back when I was a snobby, sweater-wearing "high-end" salesman I often used the word jukebox as a term of derision, as in "the IRS ain't nothin' but a rich man's jukebox." Years in the hobby later, I realize that the perfect jukebox is perhaps the loftiest goal a music listener can aspire to attain. And perhaps the most challenging and difficult goal as well. The perfect jukebox, think about it.

If you're looking for buying advice, I can't give you a turnkey horn package purchase recommendation yet. At this stage of my explorations, I have enjoyed glorious results with my enormous 3-way Edgarhorn based system and I found a few "parts" that demonstrate real promise for music listening. The Stage Accompany Compact Driver is one such intriguing "part" (see sidebar).

After unpacking a loaner pair of Compact Drivers, I popped them on top of my Altec 416/Onken bass cabs, connected a 10 mF Hovland MusiCap speaker cap in series to roll off the driver around 1 K, stuck a coil in the woofer line, and turned on some music. Nice! LOUD! CLEAN! That was easy. 10 minutes down and we were rocking.

You know how well done live amplified music has that immediate sound that you can't get in your home even though both both are products of amps and speakers? Well, the Stage Accompany sounds like a great sound reinforcement speaker. It's the kind of speaker you hope the jazz club has when you go down to hear Betty Carter and it can bring Betty into your home for your listening pleasure.

Reminds me of a discussion I read on the Internet one time. One sage hobbyist wrote something to the effect that "of course, blues music sounds great on paper cone speakers and tube amps - it was produced on paper cones and tube amps!"

Conversely, if your thing is music that went through a microphone or pickup at the live venue, maybe something like the Compact Driver is what you need. It is musically satisfying to listen to a speaker that can slice through ether the way a Hammond B-3 played through a Leslie cabinet does. Leslies don't "image" and "localize", they energize the whole room.

The ultra clean sound of the Compact driver really helped out acoustic music too. Listening to Ralph Stanley transported me right back to old Virginia. The banjo notes sprayed out like ice and the fiddle breathed and moaned. "Natural" is a good way to describe the sound of this ribbon speaker and I'm not using this word in the metaphorical audiophile sense here.

My experiments with the Compact driver really showed me some new possibilities in sound. What more could you ask from a component than a glimpse of the beyond? It may be years before you can go out and buy a "high-end" approved horn system. Might never happen. In the meantime, listen and grow.

1) One obvious solution to the power challenge is to BI-AMP, preferably with crossovers before the amps. Use that SE triode amp on the mids and/or highs and use your Jadis, ARC, VAC, Aragon, or whatever on the low end. I resisted the concept of multiamp systems for years because I thought it was too complicated to work. I was dead wrong. Using different kinds of amps in roles where they'll perform best makes sense to me and it gets around the low power issue entirely.


Posted by Romy the Cat on 07-10-2004

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It is difficult to talk with audio people about Horns. It is a constraint problems, and not only in audio, when the mistakes of a specific poor implementation or a chase of a mistaken tangentional notions might shatter an entire concept. The very same, very frequently happens with horn-loaded installations.

Most of the horn-loaded installations out there sound quite horribly. Dose that Horrible Sound, that some ignorant people labeled as “Horn Sound”, intrinsic to the horn loading itself or that Sound is a direct reflections of the faulty assumptions and bad implementations?

This thread will elaborate on this subject and will cover many foolishnesses of faulty horn-loaded implementations that pus make horns do not perform at the level where thy might. By initiations of this thread I would like to enumerate the basic problems and causes that unfortunately have a wide use among audio people and that assure quite negative results in context of the Horns-loaded installations. Feel free to shares your thoughts on the subject if you have any.

Rgs,
Romy the Cat


Posted by AOK_Farmer on 07-12-2004

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Hi Romy.

Have you tried a large cone high efficiency tweeter? I have used a Saba 4 inch diameter 'green cone' 99 dB/w without a horn and found it to be interesting. Have you tried some kind of horn loading with such a tweeter?

Steve


Posted by Romy the Cat on 07-12-2004

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I have seen those old Telefunken, Siemens and some other 4” cone direct radiation tweeters, but I never tried them. I do not know thier signature and I do not know thier characteristics. The reason why I never cared about them, although I might be wrong on it, because those type of the tweeters would be useable in situation when you need a long and deep midrange tail and would like to keep the crossover point relatively low. For instance if you use no-compression, no phase-plug driver loaded into mid range then run such a tweeter sitting at 7kHz might be a solution. If I have a half dozen of them then might try building a parabolic array… The only problem that I see in those drivers that they have relatively high cone mass and might require a high order filter because the drovers LF harmonics might be too “weighty”. This high order filter would be a direct contradiction to my religion…. :-(

The caT

PS: please name your posts distinctively


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