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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,

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