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horn stuff and a final post to Wayne

Posted by tomservo (M) on July 7, 2002 at 11:03:52

In Reply to: Unity Patent posted by str8aro on June 26, 2002 at 17:56:37:

I hope it was ok to rename the thread, I was having trouble keeping track of what was new etc.

You wrote:

>> I have been looking at a lot of old posts today, it seems that
>> you have made dozens and dozens if not more posts about the Unity
>> horn in the last year or so, you had made this a personal crusade
>> "to stomp this out".

Actually, there have only been two times I've given the Unity device a second thought. The first was a year ago,
when Mark Seaton wrote remarks comparing the Unity with my Professional Series four π loudspeaker system.
The second time was this week, when I was surprised to find that you had worked on patenting the thing.

I did not look to see who you were responding to only that there were a large number of posts by you attacking the idea when one did a search
on Unity horns etc. on this and on your forums.

I have written a lot of things in general about loudspeaker performance in the time domain; This is not necessarily
about the Unity, and my opinions in this matter are first documented in the 70's.

Maybe you feel I've been a "big meanie." Maybe my approach has been rude, and I'm sorry for that. I don't
honestly like "product bashing," and find it distasteful. So I don't like that this thread has taken this tone, and for my
part in it, I'm sorry.

Not a big meanie but rather someone who "will not" see.
I have to put this in my perspective for you, I have explained ideas and inventions of mine at countless audio trade shows in the last 20 years, I have presented a decent number of papers on loudspeaker innovations at many AES and ASA conferences, I been an invited speaker at a good number of scientific & acoustic conferences too (you know someone who they figure would be interesting enough so that they pay your way
etc). I have directed the efforts of engineers and scientists at literally "Rocket Science" and working on real rockets as well as loudspeakers which I love loved all my life. .
Some of them at times did not grasp the "leap frog" way they say I solved problems and were actually somewhat disturbed by it, but I can honestly say that ultimately they always understood what I was getting at.
I have not run in to someone like you ever and by a large margin and I have certainly spent more type on you than anyone ever and if it wasn't such a challenge I wouldn't have done it.

But I think the technical debate we've entered into has merit. I'd like to see it continue until it reaches a point of
conclusion, if that's possible.

>> In the end it is exactly the kind people I had wanted to Unitys to
>> go to that you have harmed, how many that were thinking about it
>> didn't get it because of your tirades.

You have yet to convince me that your claims have merit. My opinion stands, and with good technical grounds.

Your technical grounds do not encompass measured results in the real world but you are of course entitled to your beliefs what ever they are.

>> Those tirades driven because you felt threatened or something
>> and based on your misunderstanding of how things work and lack
>> of test equipment to find out for yourself.

Your explaination of your device doesn't square with existing theory. You have the extra burden of proof. I do not
misunderstand - I disbelieve.

Perhaps this is getting close, exactly what part of this does not hold together for you?
Given that the arrival time of each part can be measured and a configuration realized based on those measurements what part seems inconsistent
to you? Go take a quick read of Richard Heyser's "Determination of loudspeaker arrival times"

>> Just as bad, you harmed Nick's business, he is a nice guy and one
>> of relatively few places a DIY'r can get cool stuff, these are the
>> people that need support, not someone crusading against them,
>> especially someone who is wrong to boot.

And in an earlier post, you wrote:

>> You must imagine the world revolves around you I guess and that no
>> one has ever given any of this though before you.

See, Tom, now you're showing your arrogance. You see in others what is most evident within yourself. It is you
that appears to imagine the world revolving around you and "needing" your "revolutionary new explaination" of horn
theory to replace our existing ones. You appear to actually believe that you have broken all the rules and hit new
ground. So it is you that is predatory with your claims.

I don't care one bit if I break rules as long as the measured results back up what ever it is and in the case of the Unity, they do, not only that but other peoples measurements back it up as well. Synaudcon for example uses our boxes to teach horn array theory, would they do that if there was even a trace of VooDoo? no.
I would not have gotten a decent pile patents awarded in acoustics and electromagnetics if I was concerned about "not breaking rules".
As an inventor, the point is after all to find "New" things not to confirm the already known.

I'm not the only one that is building horn loudspeakers, and neither are you. You are not the only horn builder that
caters to the DIY market.

Perhaps you missed the point, I wanted to give the DIY people a chance to get something "new" at the beginning of its life span, not at the end like is normally the case.
How often do you see a commercial speaker company offer one of its newest inventions to the DIY crowd? not too often.
There was no intention of catering to the DIY area, only to make something available that they wouldn't normally have access to.

But you and your associates are the only ones saying that you have a single horn flare that is capable of providing
acoustic loading from 200Hz to 20Khz. You say that it is a perfect point source. Since the rest of us discuss our
systems using traditional horn theory, that puts us at a distinct disadvantage. We speak in terms of mass loading and
upper frequency cutoff, while you and your associates speak of ultrasonics from physically large horns. Quite a
difference, and shocking since your device is based on a Salmon family horn, same as most of the rest of us. These
are all fairly narrow bandwidth devices,
limited to a few octaves or so. Certainly nothing like two decades. So when you claim that yours is capable of
doing this, you are potentially hurting the business of everyone else.

...and you are wrong to boot.

You are making several errors here.
You refer to the conical horn as if it were a narrow band pass, in reality, when one uses a compression driver, the HF rolloff
IS NOT caused by the horn but rather the constant directivity of the horn reveals the true power response of the driver.
Even with the most exotic construction, a compression driver will have a hf cutoff at 4-5 KHz or below and a more normal 1" compression driver at about 2 - 2.5 KHz.
Again, this is not the fault of the horn but rather that the driver cannot produce a velocity response (constant acoustic power) above a few KHz. A Plane Wave Tube response chart shows the same thing.
Acoustically on the other hand the horn IS perfectly capable.

Point #1, the conical horn is in effect only a high pass filter who's cutoff is set by the expansion rate at what ever point one is looking.

Point #2, the HF roll off you allude to in several posts is NOT due to some "band pass" effect in the horn passage but rather reflects the power response of the driver.

Point #3 YES, all of this works at even ultrasonic frequencies it is just a matter of the physical sizes (acoustic size) of what's involved.

You are forgetting the roots of all this as well, my job at first at Intersonics was to design transducers for acoustic Levitation, this process uses
very high intensity sound to support or float objects in mid air.
The purpose of this was to make new materials which melted at such a high temperature that there were no suitable containers to hold it in, hence it is "Containerless Processing" My transducers and the electronics I built for this flew on several sounding Rocket flights, on the KC-135 Zero gravity plane and on two Space Shuttle flights.
An array of 6 of the transducers can produce over 173 dB at 21 KHz, a level sufficient to light a cigarette with acoustic friction. Some sources operated as high as 75KHz.
I needed a way to model what happens when you try to the sound to go through various shaped passages, while also going through a large
temperature gradient as in the furnace where the sample is was (as much as 1600 degrees C.)
Under NASA contract, I assigned a mathematician to develop a transmission line modeling program which could model any shape passage one could describe. After several years, he had one which gave predicted results very close to what was measured.
From then on, I removed the temperature gradient parts and made it much more "speaker friendly" and it remains my primary acoustic modeling tool and as long as it continues to be able to make predictions which are very close to measured results, it will continue to be useful.

>> You insist that the Unity doesn't work but will not or cannot
>> answer any of my questions related to getting you to explain on
>> what grounds you base your insistence.

I have made my grounds very plain. I'l reiterate them here:

1. I do not believe that the Unity device acts as an acoustic transformer, i.e. provide horn loading over the
two-decade bandwidth claimed.

As I explained, the compression driver is what rolls off, not the horn, above the low cutoff of the horn, it is a constant with
increasing frequency. If one could make a driver that would do it, a conical horn with a 60 foot square mouth could go up to 100 kHz if desired.
As there has been much more work done in RF with such horn shapes, you might want to look into antenna theory too, a good book to start with
is "Antenna's" By Krause.

I sense a misunderstanding about what you see.
Are you familiar with why a curved wall horn narrows its radiation pattern with increasing frequency?
Do you know why with the same driver a curved wall horn can be flat where a conical show hf roll off?
For example did you know that at 20 kHz, ALL of the acoustic transformation that can take place (reaching the flat part of the radiation resistance curve) has taken place well within the driver?.
It is because the active region of the horn is an "acoustic size" which means it has a different physical dimension at different frequencies.
This radiation resistance plateau is the one reached when the mouth is 1 WL in circumference or larger btw.
How big is the active transformation part of a 20 kHz horn? answer: transformation stops when the mouth is about 1 wl in circumference or about the diameter of a .22 cal bullet.
Continuing the horn past that point does not change the radiation resistance but for some additional length, does govern directivity (rule of thumb for dimensions /frequency / angle defined in the manta ray paper).
AS the math shows a 1 inch driver's exit is already SO large it can have no more than about 90-100 degrees of dispersion at 20 KHz.
If one had a 90 degree conical horn, one would have a case where there would be NO difference in efficiency and little difference in the primary pattern with and without the horn.
In any horn, this these control points move up the horn with increasing frequency and the dispersion narrows as defined by the wall angle at that point if it is a curve wall horn
Above the power roll off of the compression driver (say 2 KHz) the curved wall horns narrowing dispersion can on axis "EQ" out the power roll off by concentrating the falling acoustic power into a proportionally smaller angle. With a proper match of horn and driver, one can even make
the SPL on axis "Flat" even though at 20 kHz the acoustic power is down say 16 dB.
A horn like a 311 / 511 / 811 is an interesting compromise, it is a constant directivity horn in the horizontal plane (above some F) but has a close
to complimentary narrowing of the vertical such that the response is reasonably flat, at lest a lot flatter than the acoustic power response.

When you see your compression driver rolling off on a CD horn, it is NOT the loading of the horn but rather the declining power output of the driver you see.

I cannot extend the flat power corner of off the shelf compression drivers but one can devise a crossover that EQ's the response so that one has a flat power response.
That limits one to a maximum sensitivity set by the compression driver and horn angle at the highest frequency you want to
be flat to.
The needed slope is the inverse of that caused in the driver by its moving mass and then a second knee near 10 kHz which is the series
inductance of the VC.
With normal Pro sound compression drivers, it is not a problem to make the power response flat to say 18-20KHz depending on the driver but
at a sensitivity of say 104-106 dB 1w1m (because that is the sensitivity of the driver on that (60X60) horn at that frequency)

2. I do not believe the Unity device manages to correct the movement in time over the span of frequencies
delivered by its subsystems in this two-decade bandwidth, such that it acts as a point source. You have said,
"generally a first or second order crossover gives the best results" in this design. This very statement means that you
had not figured out how to make this thing work when you wrote it. Not only that, but the midrange drivers have
wavelength-scale distances between them and across their diaphragms, and they enter a common chamber.

No driver is "perfect" in time, all have some amount of time variance (in addition to an basic delay) over there operating band and until I can get back to making new kinds of drivers, that is a problem which is unsolved (and described nicely by Heyser) and common to all loudspeakers.
The important thing about the Unity is that in the frequency regions where an upper and lower sets of drivers are interacting, that the physical positions and the phase shift on the horn side of the drivers is offset by the inverse produced by the electrical and electroacoustic response.
The result is that there is simply no apparent "splice" upper and lower sections when Amplitude, Time, Phase and polar
plots are measured.

>> I suspect you are feeling like you took a good long Whiz into a
>> campfire and now are finding having to stand in the "steam"
>> unpleasant.

Touche! That's so funny!

But you appear to have become unbalanced and defensive. If your argument has merit, then it should be easier to
explain than this. One would think you would have quantified it better by now.

I thought it was funny too.

>> An array of sources that are small acoustically (less than 1/4 wl
>> in size) can combine totally and coherently IF they are less than
>> 1/4 wl (1/3wl if some directivity is acceptable) apart, center to
>> center. In the range they operate in, the mid driver exit holes
>> and horn dimension are less than 1/4 WL and load the horn as a
>> pressure (being too small acoustically to make a beam).

If that were true, I could accept this. But at high and middle audio frequencies, 1/4 wavelength is pretty small.
How are you managing to get multiple midrange drivers packed within the space of less than 4 inches? A quarter
wavelength at 1Khz is only 3.4 inches, and I expect you are running the midrange diaphragms even higher than this. If
they are crossed over with a low order filter, then the regions of interest are pretty wide and wavelength scale gets
very small.

I'm am glad "you could" accept this, the dimensions ARE small enough, Mark and I have said that many times.
Where the mids combine is in fact less than 3 inches across and where ever any transition is made from an upper and lower frequency range, that
dimension is also "small enough" (~1/3 wl or less at the highest F).
While I have thrown out the clue several times, there is more here than the electrical filter action too, as I have mentioned there is an acoustic "low pass" filter associated with each cone driver and a high pass slope associated with the flare rate, the result is much more than the the electrical filter alone.
Also, while textbooks teach math for 1st, 2nd, 3rd order filters, one must recall that that there is a world between each integer order and that in addition a filter system may have more than one slope depending "if" one needed a specific phase response "for some reason". One can even make a flat amplitude but have a changing phase such as in an all pass filter or even make combinations of them.

So what are your dimensions and frequencies, exactly? Please quantify the scale instead of speaking in generalities
and put this issue to rest.

Sure, on a horn like the one Nick was selling, the dimension at the mid drivers is about 3 inches, the crossover is at 1150 Hz.
Remember that if one can stand some small amount of directivty perpendicular to the sources, up to a 1/3 wl spacing is usable, in this case that directivty would be on axis with the horn.

We've discussed the time alignment issue quite a bit. So let's move to another issue that is perhaps even more
telling. I've read your claims about wideband loading by putting diaphragms in the walls of your conical horn. It's
always left me scratching my head. The rest of the world puts their diaphragms in the apex, and often with a
compression chamber. This is always done to increase efficiency, and having constant cross section area is required
to satisfy the conditions of the Webster equation.
Failure to do this has been shown to reduce the effectiveness of the horn, and is what I sometimes refer to as
"mal-formed horn."

It would hard to put into words how little I care about what others do especially when it does not do what I'm trying to accomplish.
I figure that basic math is nice but as long as my computer program predicts the results I measure, than that is more like what I am concerned
with.
Also, who says there is not a compression chamber? That compression chamber btw is usually a "low pass" filter which can extend the hf
response.
With the exception of our very first product, the cones do not show.

Most of your peers feel pretty good when we can get linear response from a horn over three octaves. Please don't
simply show what you do, or discuss the phenomenon with the analogy of the "changing flare rate." Another way to
describe this is a "large discontinuity" in the throat for the drivers mounted closer to the mouth. Some of my designs
have this too, but I've always called it a mal-formed horn - a compromise - 'cause that's really what it is. In those
designs, it's better than nothing, but it is used for economy of size and complexity, and not for performance.

So please expand on the mathematical model you've used to derive the wideband performance of your horn.
Maybe you can discuss how it relates to the Webster equation.

Like I said, the computer model can deal with any driver, any shape passage, even with a large temperature gradient if desired, it is not simply Websters, it is far far more, think of it as a spice simulator for physical acoustics and electrodynamics.
More importantly there is a history of products designed with it and hundreds and hundreds of cases of a careful physical measurement compared to the predicted results which gives me some confidence that when I see something in the model, I know if I build it exactly the same, that it will measure very similarly.
This obviously has save a lot of trees.
Look up the AES journal issue from about 10 years ago about horn modeling and you can read the paper Dan wrote about the computer
modeling of horns and drivers which resulted from this NASA funded work.
You may wish to look at commercial program called AKABAK which can also model arbitrary shapes and combinations of acoustic and
electrical circuits. Since you are up on Spice, you would probably get up to speed on it in a short time and it seems to be VERY powerful.
Cheers,

Tom

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