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In Reply to: Re: From Wayne Parham - Re: Patentable claim posted by Mark Seaton on July 6, 2002 at 16:21:49:
Hello Mark!You wrote:
> > Wayne, I have to ask if you actually read through and gave any
> > thought to Tom's response in the post you are responding to here?( http://www.audioasylum.com/forums/HUG/messages/29609.html )
Yes I have. Tom has some interesting ideas. But I am not convinced of their implementation.
> > I wonder if you missed this portion of Tom's response, or chose to
> > ignore it:
> >
> > "When one drives a big conical horn from its apex, the driver
> > couples into a part of the horn where the expansion is very rapid
> > and so, such a horn has poor lf response compared to an
> > exponential of similar size. If one slices up a conical horn and
> > looks at each slice, what one finds is that the expansion rate is
> > greatly variable and that for example the same 16 1/2 inch mouth
> > conical horn that would only allow flat response down to ~1Khz
> > driven from the apex, now with appropriate drivers, connected
> > where the expansion rate is slower, can go down to 300 Hz."Yes, I've read it. It's an interesting idea, but my position is that the premise is wrong. Essentially what Tom is saying is that a conical horn with a 16.5" mouth provides response down to 1Khz if driven at its apex but it can provide response down to 300Hz if driven by an appropriate driver mounted somewhere nearer to the mouth.
He goes on to explain his ideas with the changing expansion rate analogy, but this can also be described as a throat discontinuity. Such a discontinuity is something that makes the horn less efficient, and it is my position that you can't go very far with this before you can't even consider the diaphragm to be horn loaded at all. The further the diaphragm is placed towards the mouth, the less the system is acting like the diaphragm is horn loaded at all.
> > What part of this explanation goes against the theory, or doesn't
> > make sense to you?To satisfy the conditions of the Webster equation, the horn must have constant pressure applied to its cross section. This means the diaphragm must be mounted in the apex, or the device isn't acting as a Salmon family horn anymore. Essentially, the conical horn must be driven at its apex or it isn't a conical horn. This is true also for catenoid, hyperbolic and exponential horns - all memebers of the Salmon family.
Now then, I'm not saying that a device that isn't built this way has no merit. It just doesn't fit the model. But this does mean that it has a throat discontinuity and that efficiency is reduced. I call them mal-formed horns, and they are appropriate for certain conditions - like perhaps yours. But I think it is important to call it for what it is, and this make plain the fact that the further out from the throat the drivers are placed, the less "horn loaded" they really are.
> > The key to the above explanation is in the realization that the
> > expansion rate and mouth dimension which defines the loading.
> > I am not sure if you are thinking in terms of only the angle and
> > mouth area, but you need to examine each segment as part of a
> > multi-way speaker. This could be further explained by breaking
> > each segment of the Unity Summation Aperture into separate,
> > discrete horns. In such a case, each segment would still operate
> > over the limited bandwidth each segment is responsible for covering.Actually, the diaphragms nearest the mouth are not really horn loaded at all. Those that are near the apex, but not at the apex, are less than optimal. And the size of the horn defines the range of frequencies where horn loading is accomplished the most - With a conical horn like this, you really can't expect more than about 10dB in a very narrow range of frequencies at its cutoff, and falling response after that. So the horn may be too large to be optimal for the compression device, even though it is at the apex. Above the horn's bandwidth, the device acts as a reflector or waveguide only.
> > Now rather than just blindly stating that "it doesn't work,"
> > please explain what specifically would not allow proper loading.I think I have done this above, yes? To provide horn loading, the device should properly satisfy the conditions of the wave equation.
Take care!
Wayne
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Follow Ups
- Re: From Wayne Parham - Re: Patentable claim - Wayne Parham 07/7/0202:08:32 07/7/02 (0)
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