Acoustic Horn Design – The Easy Way (Ath4)

mabat

A very clear answer and one that I completely agree with. Horns and waveguides are very linear devices, there is no amplitude modulation. They can have strong linear effects and usually do, but as you and I know these can be dealt with - minimum reflections and diffractions and you have a device that is as clean or cleaner than any direct radiator.
 
is it wrong to compare a horn/waveguide to a transformer?

In its grossly oversimplified version it is an "ideal" transformer with none of an electrical transformers limitations, but some others of its own. It's better to think of the compression ratio in the CD as a transformer, that is more accurate, but some simplified models in the past have used a transformer for the horn as well - but that kind of modeling is obsolete these days.
 
Hysteresis is a complex nonlinear phenomena that depends on the nonlinear magnetic characteristics of metals. It can happen in a motor structure, but not in anything acoustic since the medium is air, not metal.

In the transformer situation that you quote, the energy is reflected from the transformer itself. In acoustics it is reflected from the mouth or internal shape discontinuities and is one area where the transformer analogy just doesn't work.
 
For an amplitude modulation to happen, there must be a nonlinearity. So which nonlinearity are you refering to? I don't believe there is a nonlinear behaviour in OS waveguides, or horns in general, that could be clearly audible. And if there was, OS waveguides should not suffer that much. How can you be so sure? I'm sorry but it sounds as a random impression to me. It still may be a linear distortion you are in fact hearing (and I'll give you that you really hear it) but that would mean there's still a lot of to be improved in the particular implementation. I've heard many OS waveguides and wouldn't ever speak of an "amplitude modulation". To me it allways sounded as clear as I could imagine regardless the sound level. YMMV, of course.

I listened to an OS waveguide for hours and hours a day, for something like five years. Eventually I sold it, but that was simply because I didn't have the space to accomodate it. Once I bought a bigger house, in 2018, I went right back to waveguide speakers. And I've been working for the past year or so to shrink the footprint to something that's WAF friendly.

So I have a fair bit of experience listening to horns and OS waveguides.

My two gripes:

1) Personally, I prefer smaller compression drivers or even domes. This is a personal preference; I like the "sparkle" that you get when the tweeter goes all the way to 20khz. The DE250 in the Summa and Lambda Unity Horn doesn't go to 20khz. B&C Speakers

2) The center-to-center spacing on the Summa is something like 18". Due to the very wide spacing, there are prominent vertical off-axis nulls. Basically you have to be very careful about the height of the speaker. I wasn't aware of this when I bought them, I basically plopped them down on a stand that was probably too short for the speaker. (If the speaker is too high or too low, you're going to be listening with your head in a null, if you're not careful.) In my experience with the Summa, I always noticed that it sounded much MUCH better in a large room, and I think that was a side effect of those nulls. Basically the nulls are a much bigger issue if you're listening at a distance of two meters and you have the speaker at the wrong height.

Once you compensate for those two things, I think you're "good to go."
 
That's one of the reasons I'd opt for a larger driver that can be used lower in frequency. With a large mouth flare (doesn't necessarily imply a larger waveguide) there's almost no midrange narrowing and I don't think that the "sparkle" has any connection with a frequency response extension to 20 kHz. I'm willing to sacrifice in the top octave in exchange for a better midrange anytime. A dome tweeter goes to 20 kHz only on axis and because of the directivity of an outer ear you don't hear much of that anyway. You hear these frequencies mainly from reflections and there is usually a substantial attenuation in the room this high in frequency. My opinion is that there must be a different explanation for any "air" or "sparkle" being mentioned (whatever that means). Remember, there is actually more of high frequency (>10 kHz) energy output from a typical CD waveguide than from most other tweeters.
 
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Mabat - I'd mostly agree, except ...

I do think that the VHF direct sound from a dome could be audible, even without reflections and that this might be called "sparkle". With a direct radiating tweeter you can have a strong direct field, but with a CD waveguide you really can't. That's because, as you say, there is so much more reverberant field VHF energy from a waveguide that its direct field contribution must be lower to allow for a neutral sound quality. It's definitely going to be two slightly different sounds. Personally I can't tolerate a direct radiating tweeter, probably for this exact same reason.
 
I do think that the VHF direct sound from a dome could be audible, even without reflections and that this might be called "sparkle". With a direct radiating tweeter you can have a strong direct field, but with a CD waveguide you really can't. That's because, as you say, there is so much more reverberant field VHF energy from a waveguide that its direct field contribution must be lower to allow for a neutral sound quality. It's definitely going to be two slightly different sounds. Personally I can't tolerate a direct radiating tweeter, probably for this exact same reason.
I see what you mean and it may well be the case, provided one can really hear the direct sound - I'm not sure. Then cutting off these VHF should also turn-off this "sparkle". Does it happen? I don't know... I have only a very mild understanding of what it really means anyway.