Hello

[Pooge]

The question of throat angle vs exit angle of driver is one of the aspect of horns I want to know more about. I understand that they should match but say you have a 2" horn and a 1" exit on the driver with given exit flare. How to optimize that throat flare? I'll chat up Bjorn on the subject, see if I can learn something.

You just transition with the lowest rate of change of slope as possible. But then you have to take into consideration that the transition is part of the horn. Actually, everything from the diaphragm forward is part of the horn, so you want the correct expansion rate through the phase plug, any coupler, and through to the mouth.

Horns were always mostly about pattern control. I think the early work by Western Electric scientists, who invented and formalized most of the basics, came out of the mindset of network engineers. They were trying to optimize acoustic impedance matching for power transfer like the WE engineers did for telephone lines and 600 ohm studio lines...but the first theater amps were two watt PP 205Ds!
With cheap watts, who cares anymore?
Martin from Azura is a cool guy. Ask him what he can do.

I don't know about "always mostly about pattern control." They certainly played with it, as in rectangular horns, and later, diffraction horns. But since a horn is mostly about being an acoustic impedance transformer, and minimizing impedance discontinuities.

Waveguides, as designated by Geddes, is more about pattern control. They aren't flat, though, and require equalization. Not a big deal, though going low in frequency is not their forte, since they don't load well.

Azura sells molded horns. They aren't likely to build a mold for every client; at least not at a reasonable cost. I'd rather put that money into a CNC routed wood horn.

Last edited by Pooge on August 8th, 2016, 9:07 pm, edited 1 time in total.

[Pooge]

Another option for a LeCleach horn is to build a petal style round horn, made up of nine or more petals of identical dimensions. They can be very beautiful, and perhaps easier to find a CNC machine to mass produce the petals. I have a spread sheet by LeCleach that will output the exact dimensions of each petal if someone wants to experiment with building one out of stiff paper. I haven't heard if the flat petals compromise the sound vs. a real round horn, but the more petals, the closer it is to round.

[Roscoe Primrose]

Make the petals out of 1/8" ply, then once it's assembled you can fiberglass the outside and have a very solid structure.

Roscoe

[Cogito]

Again from Altec literature:

A characteristic feature of the sectoral horns is a beam width in the horizontal plane that is constant through the middle and high frequency range. Other horn types (except the multicellular horns) passes beams that become progressively sharper as the frequency increases, and generally cover a narrow area at the high frequencies.

Probably directionality of the higher frequencies is the reason almost all the direct radiating speakers have very small sweet spot for soundstage imaging.

I am not suggesting that sectoral are better than other horns or speakers of any other kind. Just trying to understand. What sonic characteristics of sectoral (not just 511Bs) horns is considered flawed?

In diffraction horns, diffraction is used to "spread" the sound. However, a diffraction is an impedance discontinuity. It causes reflections that reach the listener at different times, smearing the image, just as sharp edges at the edge of a baffle do. Impedance discontinuities also cause reflections back to the diaphragm and what that entails. If looking for controlled directivity as a priority, the Geddes OS waveguides or Minphase horns offer that with the least amount of diffraction.

The same goes for the horn's mouth. Large roundovers minimize impedance discontinuities. They will be delayed longer when reflected back to the diaphragm. However, according to Geddes, impedance discontinuities (changes in slope) near the throat are more detrimental to creating High Order Modes (HOMs) that are basically sound waves that, by bouncing around in the horn, take a longer path to your ear.

Thanks a lot for taking time to explain. This has been an educational thread ho me.

Any hypothesis on why Altec engineers intruoduced diffraction into 511s which are designed for large areas and not in 32s which are designed hor home music reproduction? What sonic effect are they trying to achieve ?

[Pooge]

Make the petals out of 1/8" ply, then once it's assembled you can fiberglass the outside and have a very solid structure.

Roscoe

I think plywood would be too hard to bend at the mouth. LeCleach horns have lips that circle all the way around on themselves. But you could do the same with a good thickness of poster paper.

[Pooge]

Any hypothesis on why Altec engineers intruoduced diffraction into 511s which are designed for large areas and not in 32s which are designed hor home music reproduction? What sonic effect are they trying to achieve ?

They wanted broader patterns to cover a a larger area. Not as important in the home, where the listening zone may be only the width of a sofa. Still, it's desirable to have enough breadth of pattern so as not to sense beaming and rapid change of image position with head movement. Crossover points should be selected so as to get around beaming problems.

[brombo]

The following link might be of interest to those wanting to fabricate speaker parts using CNC -

http://www.techshop.ws/arlington.html

Also from examples I have seen 3d printers have more than enough resolution for the horn throat region. I think it would take a very expensive (large) printer to do the entire horn. Of course with 3d printing you could make pieces to glue together into an entire horn.

[J-ROB]

You just transition with the lowest rate of change of slope as possible. But then you have to take into consideration that the transition is part of the horn. Actually, everything from the diaphragm forward is part of the horn, so you want the correct expansion rate through the phase plug, any coupler, and through to the mouth.

Yes, designing from scratch, but I can see a lot of options and pitfalls with real existing drivers and horns that don't have smooth equal flares and I can speculate on a variety of options on the best way to couple them, but I am just guessing.

I'd like to see some trends via sims.

As for the other question, pattern control was certainly at the forefront from the earliest PA and theater horns, the earliest "scientific" horns, as it were. In 1927-28, there were folded horns in Victor Credenza phonographs, an impedance transformer to get a mechanical phono diaphragm to move some air (licensed by WE), and long exponential trumpets for PA...also pattern controllers, what was later called a "long throw horn." Amps were 1.2W battery powered.

The earliest theater horns, the WE snail horns c.1927 were 13 ft long for the Z transform and load on the driver, but the dispersion was also controlled as a design feature---wide vertical, quite narrow horizontal, just like theater rooms with balconies. Add more horns for more horizontal coverage...or use two sideways for wide horizontal if you didn't need the vertical

By the third generation of theater horns, c. 1934, there were a variety of controlled coverage multicellular horns depending on the solid angle of coverage desired.

The story continues with the late 40s WE auditorium speakers like the L-9 and the voice of the theater Altecs, where a short midbass horn was used to narrow dispersion to approximate that of the midrange horn at the crossover point. VOT cabs were initially built into large flat baffles, so the waveshaping began at 60hz, became cardoid at 300-500hz, and the horn picked up with 50 or 90 degree horizontal from there.

Hints of this approach began to show up in the early 1930s WE LF baffles with integral short C horns. Largely forgotten now. And modern constant directionality horns just throw out this whole notion of controlled narrowing as function of frequency to reduce crossover discontinuities.

Both aspects occur at the same time but once PA and theater sound came along, the controlled coverage aspect is foregrounded in the practical literature. Maybe for the Bell Labs guys who designed the horns using impedance models, they were impedance transformers foremost, but not for anybody down the chain.

By the way, I heard all of the horns above, including a pr of Victor credenza horns with an adapter for a WE 555 driver, and most are better than 511s. No lie.

Martin build some weird one offs for himself. So did Jeffrey Jackson. He has a huge CNC now, but he didn't then I'd ask these guys and see what they recommend.

[Pooge]

Jackson made the beautiful petal horns I was referring to earlier. When I spoke with him a while back, he wasn't taking on new clients. I'm sure they'd be out of my price range, anyway.

[J-ROB]

Jackson has a gig that is only partially audio. He's working with a guy who is trying to set up a tourist hot spot in an old mill and they want to sell fancy doorknobs and such made right there in the mill. The speakers he's making, drivers and all, are insanely nice but also insanely priced.

I have heard L'Cleach horns sounding very good but I don't know if it is the only game in town, even though the paperwork behind them is convincing and the man himself was worthy of intellectual respect. But they are available at semi-reasonable prices, which is a plus.

One of the best small horns I've heard is the Klangfilm tractrix from the Eurodyn 2 way. I measured one with a WE 594A driver and it was dead flat, I meanflat, no ripples even, from 450-9k. It also sounds like the voice of god. And that is a prewar design! This design was in use by Siemens until the 1970s!

I'm trying to scam a pr from Suzuki at GIP who copied it at my suggestion. All I need now is some great 2" drivers and my begging for "loaners" to be rewarded. It would be useful to make up a 2"-->1" adapter maintaining the catenoidal expansion down to 1".

If I get the horn, maybe I can make a plaster mold and run off some papier mache or even plaster copies.