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04-21-2006 Post mapped to one branch of Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,486
Joined on 05-28-2004

Post #: 1
Post ID: 2324
Reply to: 2324
Some conical horns anti-propaganda

Steve Schell pointed to Bill Woods’ site aka RCAfan.

http://www.acoustichorn.com/

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: http://www.acoustichorn.com/about_conical.html )

 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.

Rgs,
Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
03-04-2009 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,486
Joined on 05-28-2004

Post #: 2
Post ID: 9945
Reply to: 2324
More conical anti-propaganda
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Bill Woods of the AH! Company:

http://www.acoustichorn.com

…. posted at his site a write up about  the advantages of his conical horns:

http://www.acoustichorn.com/news/index.php?id=8313229270608416105

I meant to post a reply at his blog and wrote a reply but it has a need to login in and I have no account there. So, I dump the reply in here.

 Bill Woods wrote:
Conicals keep the sound wave at 90 degrees to the wall of the horn at all times as the wave exits the horn (this defines a conical.) The sound wave is not disrupted by the walls of the horn. For these reasons, conical horns have the best sound of any horns for home HiFi Use.

Bill, this is absolutely incorrect statement. A horn transfers narrowing of dispersion into increase of pressure.  In a conical horn, as much as in any other horn, when a wave exits the horn then there is no more dispersion constrains and the wave is very much distracted.  I do see how you can make a statement of “best sound” based upon false derivatives. If you do not believe then make the smile experiment by squirting ink into submerged in bathtub micro-horns of different profiles and you will see where the ink go as soon it leaves the horn’s edge. I did it 5 year back and it was very convincing.

 Bill Woods wrote:
  The tractrix profile has been used in commercial products and in DIY. All exponential, and tractrix horns tend to beam as they go higher in frequency due to the squeezing of the side wall of the horn. This results in a "honky" sound and some of the high frequency information is lost, when listening off axis.

Incorrect again. The exponential and tractrix horns tend to beam when the large throat is used. However, the "honky" sound that horns might have has absolutely no relation to the beam and I have no idea why Bill put them together. Bill is knowledgeable person and I am sure that one but one of his experiences, I a sure, is that most of his horn users are Morons who would read words but have no brain-power to put them into meaningful sentences.  Very sad indeed that Bill desired to “merge” the beaming and honking into a same salad.

 Bill Woods wrote:
  I have experimented extensively with all types of horns, using absorbing materials, mouth geometry, adding a foam ring at the horn’s mouth, cutting slots, and also with acoustical lenses. (see photo) I have discovered that these devices have, at best, an ameliorating effect, often redistributing the anomalies they try to correct to other places in the passband instead of eliminating them. The acoustic lens holds the most promise.

Why? I still hear no convincing theoretical argument that would be free from rudimental mistakes and false pretenses.

 Bill Woods wrote:
  It is interesting to note that RCA acoustic laboratories analyzed the conical horn flare and mouth termination issues in the 1950's. I am lucky to be in possession of the very lab sample test horns, of which my work is based.

So, what? JBL I think experimented with conical at that time. The facts itself that RCA worked with conical gives absolutely no justification to the conical reported advantages.

 Bill Woods wrote:
I can, however, suggest a simple way to make some experiments for yourself, to see how horns differ from each other in a very rudimentary way. Choose a compression driver, and make a number of very short horns of only 4-5 inches in length ---really horn adapters-- for your driver.

Actually, it is incorrect experiment as in the proposed scenario the throat is improperly loaded by a horn.

 Bill Woods wrote:
  The most critical part of a horn is the first few inches. This is often over looked.

And the reason why it is mostly overlooked is because in most of the compression drivers the first few inches happen inside of the driver.

 Bill Woods wrote:
  Start with a section of straight pipe. Listen to that. It will be very loud, and very colored. Next, try an exponential horn of the same length, then a tractrix - they will be progressively less colored. Finally, try the conical section. It will be the most natural sounding and uncolored.

Sorry, not convincing, and particularly as you proposer improperly loaded horn.  I also disagree with the whole methodology you proposed: to recognize the coloration using pink noise. This is a bit tricky to get but the “coloration” is NOT what you think the colorations are. You observe static changes in tone but from a certain perspective is it irrelevant.

 Bill Woods wrote:
  Musical instruments such as trumpets and trombones are not conical. They are designed to produce harmonics, the very thing we try to avoid in a sound reproducing device. The more the horn is squeezed, the more the harmonics. On the other hand, voice producing devices such as megaphones are always conical.

Once again. It is a cheap reference to demagoguery idea that illustrates absolutely nothing. Are you saying that megaphones were made conical and this proves anything, are you sure that megaphones were made conical not because a cheap manufacturing and comfortable storage? Are you sure that anybody ever truly care how the voice would sound over a megaphones? When you heard a megaphone did you ever hears anything resembling a respectful sound worth to mention? This overly populistic methods of presenting the subject kind of begin to bother me…

 Bill Woods wrote:
  Horn design is always a game of balancing the factors of length, angle, directivity, low frequency cutoff. There are many ways to tweak a horn’s response. One is to add an exponential throat adapter to a conical horn. This colors the sound, but improves the measurements.

And the very same paragraph you try to prove the advantage of the conical horn by measurements…

 Bill Woods wrote:
  As you can see, designing horns is actually a very complex equation involving parameters that all need to be addressed so that an optimal design results. There is no such thing as an “ideal” horn. But certain basic flare profiles work vastly better than others if the best sound quality is the most desired result.

Well, no one argue with that but you are trying to present the case that conical is something that produce the best sound quality. I disagree with it. If you feel that it is the case then you need to find deferent ways to talk about it, not the level at which you expressed you thoughts so far.

Rgs,

Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
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  »  New  Why horn-loaded loudspeakers are bad...  Re: the converse can also be true...  Horn-Loaded Speakers Forum     9  51426  05-30-2005
  »  New  An Interview With Dr. Bruce Edgar..  An Interview With Dr. Bruce Edgar...  Horn-Loaded Speakers Forum     0  53480  07-10-2007
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