The 'laws' of Physics change every day, if not more often. Fermi went to the grave not knowing if the electron was indeed the smallest sub-atomic particle; that didn't make him any less of a physicist. Huygens made observations and assumptions based upon them according to what he had to work with at the time. That didn't make him any less of an audio engineer either. If you sincerely think he had it all figured out and there's no room to go beyond what he did, then fine.

I've gone to the trouble of building horns according to Huygen's model and my own, and mine pass high frequencies on the order of two to three octaves higher than the Huygens models do. I feel safe in saying that you haven't done so. When you have ring me up again and we'll compare notes.

If you really must hinge your opinions on art that's at least 20 years old before you'll believe in it take a look as US patent #4790408; I'm not the first to tread this ground, just the latest. If the internet had existed when this was published what I'm saying now would be old news.

I think these guys are talking about Christiaan Huygens, a mathmatician/physicist who proposed wave theory. I don't know if that's the same Huygens you are talking about or not.

I understand the point you are making. Curved ducts and flares pass sound through them if the ducts are dimensioned as to work as a waveguide.

You can actually take a vacuum duct and bend it in a variety of ways and still clearly hear voice spoken in the other end. The curves and bends don't attenuate the sound, and that's the principle you are using in your horns. That's how the wave passes through them at frequencies where the duct acts as a waveguide.

I also know from experience that angled reflectors are effective at high frequencies. The trick is positioning the reflector to direct the wavefront. If horn folds are angled so that reflected energies are directed towards the mouth, then the folds don't attenuate high frequencies, and instead, sound is directed outward.

Most basshorns don't use reflectors because only low frequencies are wanted. The folds attenuate high frequencies. At low frequencies, wavelengths are large enough that the folds don't act as reflectors and the energy passes right through. As frequency rises, the walls at each fold become reflectors, but they don't reflect sound towards the mouth, so it is attenuated. It literally bounces back and forth inside until the energy is dissipated.

Wayne

It seems to me two thing are fair to say:

1. Huygens model describes the behavior of a plane wave, essentially of a single frequency since the diffraction and reflection effects will vary with the relative magnitudes of wavelength and obstruction. While useful as far as it goes, it's hardly "complete" in the real-world sense. Idealized plane waves are hard to come by.

2. You can't argue with the empirical result. You don't need a model for wave propagation to explain a meter reading (though it certainly helps to improve the meter reading).

However, what Huygens did not address was the question of using a reflector versus a rounded bend. With a flat reflector segments of the incoming wave intersect with segments of the outgoing wave at various degrees of phase, with attendant dips and peaks in response; at higher frequencies the dips outwiegh the peaks to the point of serving as a low pass filter. Huygens made the flat reflector work as well as possible. However, a rounded bend, and not just a rounded bend but one with a rounded inner corner of relatively wide radius compared to the wavelength being passed, ideally allows the wave to pass without being reflected at all. If there are no reflections there are no interactions between an incoming and outgoing wave. This is what is seen in your vacuum duct analogy.

The rounded pathway is not perfect by any means. It suffers limitations because the relationship between wavelength and bend radius is an inverse one; the higher the frequency the larger the bend radius required to pass the wave. Once the horn gets to a size adequate to pass a 5kHz wave without attenuation, for instance, the horn mouth is so large that the off-axis response is drooping anyway. Still, it is a better method of allowing high frequency waves to pass through a bend than a flat reflector, with the additional benefit of working just as well in a 180 degree bend as in a 90 degree bend.

"The main principle Huygens is famous for, at least as far as folded horns is concerned, is the topology of a 45 degree reflector, as you state."

Huh? Huygens is known for pendulum motion, centrifugal force, gravity and wave motion. He is famous for a lot of things.

"However, a rounded bend, and not just a rounded bend but one with a rounded inner corner of relatively wide radius compared to the wavelength being passed, ideally allows the wave to pass without being reflected at all."

A large bass horn is many wavelengths across at midrange so inside walls are reflectors. Midrange sound bounces all around in there. Get a clue.

Somehow I don't think basshorns were on Huygens mind. Don't think they had speakers back then.