Primer on horns

Since horns are so efficient, you have to have an amp that runs pure Class A or is at least biased pretty highly. Since horns take such low power to play at reasonable levels, you will hear the low level switching on many Class AB amps. Many low powered tube amps are run strictly in Class A, making them free from switching distortion. Hence, they compliment the characteristics of horns quite well. The switching noise is what tends to make horns sound "grating" or "harsh". That and the fact that many metal based horns ring like crazy. Plastic horns do the same thing, but at a different frequency range. Knowing that, one can easily damp or minimize the effect of the horn throat itself and cure much of the problem.

With all of that in mind, i would look for older gear and begin to tinker. You have the PERFECT opportunity to do that here. Spend a little bit and learn to "upgrade" components on your own. Not only will you see first hand what it takes to make things "tick", you'll be rewarded with a system that blows smoke for pennies on the dollar. You will also be able to say with as much pride as you can muster "i built this".

Don't let a prior lack of "hands on" scare you away. There are TONS of good DIY websites and kits out there with plenty of people willing to help. Try checking out the bottlehead and tube forums over on AA. As "Clueless" mentioned, there are also many other forums dedicated to tube / horn combo's, so you've got plenty of info and research ahead of you. If you do take the type of approach that i mention, you'll be in for some of the best music and most fun that you've ever had with hi-fi. Sean
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Absolutely check on "Pi" speakers: http://dsb.8m.com/pipics/pipics.htm For more info also visit AudioAsylums "pi" forum for discussion with the owners of these horn based speakers.

Class A isn't necessarily any better than Class B, and "Class" A/B isn't really a class but an amp the flip-flops between the two. "Class" A/B will always have more distortion than a well optimized Class B, all other thing being more or less equal. And between the A and B, alot of it depends on how well its done. I've seen Class A with 10% THD and class B with .0005% THD at most frequencies. Not to mention all the other variables of an amplifier like slew rate, intermodulation distortion, damping factors, etc. While the switching distorion found in Class B (and technically A/B) is the most offensive type, its levels can still be designed so low that the audible difference between the two classes is negligiable. Randy Slone from Seal Electronics puts it ok in his FAQ:

7. How about Class-A audio power amplifiers? Don't they sound better than Class-B designs?
To make the statement that one amplifier sounds better than another poses the requirement that the differences in sonic reproduction be discernable to the human ear. It has been proven that the human ear is capable of detecting high-order odd harmonic distortion as low as 0.3%. Crossover distortion, as produced by Class-B operation, is the worst kind of distortion, being high-order odd harmonics across the entire audio bandwidth and existent at virtually all signal levels. The worst-case conditions for crossover distortion is at very low volume levels at high frequencies (i.e. close to 20 kHz). Even under these extremes, several of the amplifier kits in this catalog are typically capable of THD levels better than 7 times lower than the minimum audible level. Therefore, in these or similar designs, it is quite impossible to detect a difference between Class-A and Class-B operation based on human perception, as long as all other performance variables are identical.

In summation: you can use a Class B amplifier, or any amplifier designed for home audio, with horns and still get very good sound if its a well designed amp.

Wow: Ezmaraldo, fascinating post (as always) and now onto the thread. Pete: Your space seems a bit small to optimize traditional horn systems unless you can place them near the short wall and be seated approx. 3', or so, from the opposing wall (most horn systems require a greater listening distance, than traditional dynamic speakers, in order to bring "things" such as coherency together). This is one of the reasons that "horns" have a modern love/hate persona as many people do not incorporate them properly into their systems/rooms (near field horns - gimme a break). This said, if you can accommodate 12' (or more) of distance between the listening position and the speakers, go for it, it will sound "OK" throughout the room, but the sweet spot will be sweet indeed. Instead of experimenting with this or that (as far as tube amps go) take the leap and work with "single ended" and/or "single ended triode" amps only which is what horn type speakers were originally used with in the beginning (instead of push/pull configurations). Screw distortion spec's, etc., (other than component matching specs) as they mean very little in this realm and the sound/realism is what "walks the walk". If your listening distance needs to be less "than the above" then maybe figure out efficient dynamic speakers in a "near field" configuration, again with a SE or SET amp. The amps (decent ones) start @ around $500, or so and go up (way up). I have used push/pull tube amps for over 30 years, but recently (a year or so ago) went with SET and there is no comparison when these amps are used properly within a system/room. You are definitely on the right track, so hang in there. Please, feel free to email me directly on this subject if you like. By the way, I am not an artist, but a collector (currently short on funds:-).

Ezmeralda, my comments were talking about AB amps that were "richly biased". I'm talking about amps that stay in Class A for at least several watts. You can typically tell these from other SS amps as they tend to run hot even at idle. Most amps that are labeled AB and don't get hot unless you're standing on the throttle are not biased very richly. As such, they operate more in Class B than they do in Class A mode.

Most efficient horn based systems under "dynamic" listening conditions will never leave the "first few watts" region of operation. As such, switching distortion is basically non-existent in a high bias AB or pure Class A design. Hopefully, the rest of the amplifier design is up to snuff also.

If one is trying to do a "wall of sound" approach, a higher level of bias ( an amp that stays in Class A longer before switching over to Class B ) or "pure" Class A operation would be more appropriate if worried about crossover distortion. All you have to worry about in that situation is how to dissipate all of the heat.

As to the general content of your post, i can't argue with most of it. One can find poorly constructed and designed products to use as examples regardless of how they are labeled and / or categorized and marketed. This includes, but is not limited to, amps that operate in ANY class of operation.

However, i would keep in mind that these comments come from ( or are at least attributed to ) someone trying to sell you something. Presenting "facts" that support one's own ideas, products or agenda is typically considered "marketing" and should be considered as such. Sean
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