With regards to amplifier power and amplifier types used on horns:
My speakers are horn hybrids, using a high efficiency pair of 15" woofers, which limit the efficiency to 98 db.
If I push the system hard, I am really challenged to clip a 30-watt amplifier. But I prefer 150 watts if I can get it, even though I will never use the power. In my case, because I am using OTLs, the amps have no issues at low power: the less power, the less distortion, quite similar to SETs.
The system plays very clean and is devoid of loudness artifacts. The only way you can tell how loud it is playing is if you try to talk to someone sitting beside you or if you have a sound pressure meter.
Amplifiers like the kind I am using (zero feedback) tend to make more distortion following a curve where the distortion becomes more pronounced as you approach clipping. Distortion is where loudness cues come from- the result being that while I can get satisfying volume from the 30-watt amp (and right now I am playing a pair of type 45-based P-P amps that only make 5 watts), the simple fact of the matter is that there are less loudness cues when I use the bigger amps.
(FWIW, the Trio is only horn speaker I know of where the designer intended it to be used with transistors. This is reflected in the crossover design, or lack of it, which consists of capacitors to roll off low frequencies for each driver. This results in an impedance curve that is nearly 19 ohms in the bass horn, but only about 4 ohms at the tweeter frequencies, even though the individual drivers are all nearly the same impedance. No low power tube amp is going to drive this right as the speaker is what I call a Voltage Paradigm technology, whereas most low power tube amps and other horns are Power Paradigm technology. see http://www.atma-sphere.com/papers/paradigm_paper2.html for more info.)
In a case where the speaker is 10 db more efficient than mine, the need for power does get eroded; 15 watts is a lot of power on such a speaker but IMO you do this to reduce loudness artifact from the amp. Horns tend to be very reactive loads and so are often shouty and shrill if the amp used has a low output impedance, particularly if that low output impedance is due to loop feedback in the amp (the back EMF tends to get into the feedback loop, causing the feedback signal to contain false information). This is one reason why horn users who get good results rarely use transistors, and a major reason why many people think that horns are for PA, not hifi. In a nutshell, its an equipment mismatch.
My speakers are horn hybrids, using a high efficiency pair of 15" woofers, which limit the efficiency to 98 db.
If I push the system hard, I am really challenged to clip a 30-watt amplifier. But I prefer 150 watts if I can get it, even though I will never use the power. In my case, because I am using OTLs, the amps have no issues at low power: the less power, the less distortion, quite similar to SETs.
The system plays very clean and is devoid of loudness artifacts. The only way you can tell how loud it is playing is if you try to talk to someone sitting beside you or if you have a sound pressure meter.
Amplifiers like the kind I am using (zero feedback) tend to make more distortion following a curve where the distortion becomes more pronounced as you approach clipping. Distortion is where loudness cues come from- the result being that while I can get satisfying volume from the 30-watt amp (and right now I am playing a pair of type 45-based P-P amps that only make 5 watts), the simple fact of the matter is that there are less loudness cues when I use the bigger amps.
(FWIW, the Trio is only horn speaker I know of where the designer intended it to be used with transistors. This is reflected in the crossover design, or lack of it, which consists of capacitors to roll off low frequencies for each driver. This results in an impedance curve that is nearly 19 ohms in the bass horn, but only about 4 ohms at the tweeter frequencies, even though the individual drivers are all nearly the same impedance. No low power tube amp is going to drive this right as the speaker is what I call a Voltage Paradigm technology, whereas most low power tube amps and other horns are Power Paradigm technology. see http://www.atma-sphere.com/papers/paradigm_paper2.html for more info.)
In a case where the speaker is 10 db more efficient than mine, the need for power does get eroded; 15 watts is a lot of power on such a speaker but IMO you do this to reduce loudness artifact from the amp. Horns tend to be very reactive loads and so are often shouty and shrill if the amp used has a low output impedance, particularly if that low output impedance is due to loop feedback in the amp (the back EMF tends to get into the feedback loop, causing the feedback signal to contain false information). This is one reason why horn users who get good results rarely use transistors, and a major reason why many people think that horns are for PA, not hifi. In a nutshell, its an equipment mismatch.