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In the Forum: Horn-Loaded Speakers
In the Thread: Some conical horns anti-propaganda
Post Subject: Some conical horns anti-propagandaPosted by Romy the Cat on: 4/21/2006

Steve Schell pointed to Bill Woods’ site aka RCAfan.

I do not know the guy but the site looks attractive. Some of his old large horns are interesting as so on… however, what make me to wonder is the horns that Bill Woods makes. They are 17” aluminum conical horn with a cutoff frequency of 700Hz.  I like the horns but what I disagree is the rational that Bill uses pushing the conical horn agenda. I do not argue that conical horns are inferior or superior then other shapes but look what Bill Woods proposes:

(Here and below are quotes from the Bill Woods’ site: )

 Bill Woods wrote:
 The conical horn is the simplest horn shape. The cross-section increases linearly, like a cheerleader's megaphone. Compared with all other horn flares, conical horns have a precisely defined radiation characteristic. Conical horns, manifest a homogeneous radiation characteristic over a wide frequency range. There is no disruption to the wavefront as it moves out towards the horn mouth. The "horn sound" is nil with a conical horn. Because the wavefront has a smooth passage, it has perfect phase.

Ok, let to leave the cheerleader's megaphone alone. “The precisely defined radiation characteristic?”  Does it means that any other profiles of the horns have unknown or unpredictable radiation characteristic? I do not think so.  “Homogeneous radiation characteristic over a wide frequency range?” Yes and no. Any horn, no mater what profile it is has very screwed radiation patter over a wide frequency range,  not to mention that no one use horns over the “wide frequency range”: 3-4 octaves and it’s it. Conical horns have some Homogeneous radiation patter advantages in the lower frequencies but not at the frequencies over 1000Hz, or the frequencies where Bill market his horns.

 Bill Woods wrote:
Another advantage is that the cross-sectional area in the vicinity of the horn throat increases more rapidly than for exponential horns. This thus reduces the sound pressure in the horn as well as distortions due to the compressibility of air.

It is absolutely irrelevant argument. The conical horn has more rapid increase of cross-sectional area at the beginning. So what? It does not affect the throat reactance as in giver case we deal with HF horns. The mass of the air in the bell of the horn is negligible and therefore the throat reactance is negligible. Did you try to tube the back chamber of compression driver working against 1000Hz horn? It has practically no effect at least in context of Bill’s horns. If Bill Woods’s horns are 1000Hz then the drivers might be crossed at least 1.7 octaves higher, so I would say 1.7kHz…. At this frequency the throat affects deriving form pressure propagation are not there and if they even manifest themselves microscopically then they got severely overwritten but many other more important at this frequency factors: front chamber reflections, imperfection of phase plugs, mean cone’s resonance,  and many-many other more important factors

 Bill Woods wrote:
Since conical horns have no curvature, the ever emerging wave is not deformed as it moves from the throat to the mouth. This means that there is a linear pressure change throughout the horn.

Yes, but how it affects sound? I do not know and I do not think that Bill does. Can in such case it be attributed to an advantage of a conical horn?

 Bill Woods wrote:
When this condition is met, the horn will have very low 'air column' distortion, or distortion cause by squeezing the air at the throat. Conical horn also have good phase response, due to the reason stated above.

I commented about it above. It has no real relation to HF horns.

 Bill Woods wrote:
In short, the conical horn amplifies the sound, with the least disruption to the sound wave.

This is a loaded statement. No one knows anything about the sound wave. It is a myth that some kind of perfectly shaped sound wave sitting next to a horn’s throat and then after diving into the horn it got deformed and bent out of it’s shape. It is heavily deformed at the beginning (partially at HF) and it is heavily deformed what it leaves horns. Let do not speculate and do not bring the theoretical postulates where they are not applicable.  Did anyone ever was able to objectively measure/depict the shape of the front wave after it goes via horn? Any profile?  The electricians can objectively measure harmonic distortions and so what? Can we juts looking as the harmonic distortions ONLY to say anything about the performance of amplifier?

 Bill Woods wrote:
The sound of a conical horn system has very little trace of the "honky" sound usually associated with horn.

Hm, it does not sound appealing: has very little trace of "honk". To fix the problem it would be necessary to increase the crossover point as the driver overload the horn’s rate. However, to do so it would be very difficult and no one upper-bass driver will reach there…. So, the solution is to built not 17” conical but much larger conical driving the crossover point down, A conical that stars at 1” and end up at 500Hz will be huge, deep, with EQed out HF, will be beaming like hell, and will be very-very difficult to integrate in 4-ways system. the solution “might” be going for a Tratrix that would be much shorter, wider radiation, less beamy and with more HF… hold on! We are not in the Conic anymore… :-)

 Bill Woods wrote:
Because the horn has good phase response it can be crossed over with another horn or direct radiator very smoothly.

Hm, I do not even know how to comment on it!!!

 Bill Woods wrote:
Directivity is another positive feature of a conical horn. The sound goes where you want, cutting down unwanted room reverberation.

Oh, I will take the Fifth on it. I do not want to mock Bill but it is too mockable….

 Bill Woods wrote:
The end result of all of this is that when you hear a horn system, it has a very lifelike sound. Bells and horns sound like the real thing. Nothing comes close the sound of a cello (especially the Mercury recordings with Starker.)

… and probably it all comes from a 1000Hz horn, doesn’t it?

 Bill Woods wrote:
If you were to clap your hands together in an auditorium, you will hear the echo more clearly- you literally hear more information. This is due to a linear wavefront and linear phase.

Actually this is VERY funny as it was always my one of that “secret tests” for horns installations. I always consider that if I do clap my hands in a listening room and if I head ANY reflections form the horns than it is an undeniable indication that the horn installation is very poor.

Romy the Cat

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