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Old 27th July 2011, 11:23 AM   #2031
Mark Kravchenko
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Default This is going to be really cool!

horn air velocity.jpg

Now I get to play....

I'm thinking that this will end up being a very powerful piece of Hornresp.

Thanks David.
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Old 28th July 2011, 04:39 AM   #2032
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Quote:
Originally Posted by mwmkravchenko View Post
I'm thinking that this will end up being a very powerful piece of Hornresp.
Hi Mark,

Could you please let me know in due course if you do find the information to be useful, and if so, how it influences your horn design considerations. Many thanks.

Kind regards,

David
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Old 28th July 2011, 01:52 PM   #2033
Mark Kravchenko
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Me post test results? When?

I promise David. I have always posted test results. The problem with this concept is going to be able to measure the air flows.

Maybe there is a low enough cost anemometer that is USB plug-able or something like that.

Because I would really like to know when and at what power level I can design a horn path to reach a SPL point without packing up. If I could do that with the same degree of confidence that the rest of your program has given me....

Muhahahhaaaaa Rubbing hands together.....

One last question if you don't mind.

You have made reference to some of your work starting away back when. You have made reference to starting the Hornresp program on punch cards.

Mind me asking how old you are David?

Because you are one very productive gentleman. And I'm certain that you are older than I by quite a piece.

I remember punch cards. I never used then as there were the medium sized floppies when I took computer science.
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Old 28th July 2011, 06:45 PM   #2034
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Mark,

I am not sure if what we have been seeing is due to air velocities or not. I was thinking it could be related to that or, pressure, force or even acceleration perhaps. Maybe a combination. Another thing is how do we know it is happening at the throat. It makes sense that the highest stresses on the system and air inside the horn are there, but you never know.



Thanks for the addition David.
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Old 28th July 2011, 11:35 PM   #2035
Mark Kravchenko
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Default A little thinning

Velocity ends up being a function of speed of the air. If you have speed and a known volume of displacement off of the driver you can calculate the air pressure. That pressure of course diminishes as you go further down the horn path length. It should not be that difficult to calculate the pressure drop when you are down the path length of the horn.

My guess is that when a horn packs up the air pressure is too great. Therefore we get the distorted output. What has to be done now is the measurements and simulations.

What is to great of an air pressure or air velocity I do not pretend to know.

But I think that a little experimentation should be able to get some of those answers.


Mark
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Old 29th July 2011, 12:30 AM   #2036
jbell is offline jbell  United States
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Originally Posted by mwmkravchenko View Post
My guess is that when a horn packs up the air pressure is too great. Therefore we get the distorted output. What has to be done now is the measurements and simulations.
Mark, I want to throw out an alternate thought for you based on some of my mcm experiments. The exact same area (50cm2) in a 1/2" x 8" vs in a 2"x4" area sound COMPLETELY different, and when pushed the 1/2" x 8" 'packs up' as you call it, where the 2x4 doesn't.

Air speed may be one thing to be aware of, but I'm thinking that air friction (if that's the right description) may be even more relevant in small horns. Where hornresp doesn't take losses into consideration, I don't think there is a good way to model what I observed with the mcm's.

Thanks for the addition david.
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Old 29th July 2011, 12:56 AM   #2037
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More food for thought:
Quote:
Mark, I want to throw out an alternate thought for you based on some of my mcm experiments. The exact same area (50cm2) in a 1/2" x 8" vs in a 2"x4" area sound COMPLETELY different, and when pushed the 1/2" x 8" 'packs up' as you call it, where the 2x4 doesn't.
Is it a question of pressure over the cone or an area away from the cone where there is actually turbulence?

If I can take this one more step.

I'm thinking that in a well designed, linearly operating horn we have laminar air flow.

If that statement is correct then what is happening when a horn is over driven?

Is it a function of flow patterns?
As in an area where there is so much turbulence that is creates a type of stopper effect? A small high pressure area within the horn path where we get effectively a dead spot in the horn path?

Or are we pushing a driver to the point of non-linearity and we suffer the natural effects of oil canning?

A view port could prove or disprove that idea ( oil canning ) quite easily.

I have a Baumer laser distance measurement thingy magigy. I could insert it into a horn and measure the driver displacement as the distortion goes up.

The only part that is a little more difficult is finding a microphone that will survive the SPL close to the horns throat. I really don't know how loud it is that close. But I know that most horns are well above 100db at one meter before they start to misbehave.

Maybe a panasonic cartridge with the Linkwitz high SPL mod would survive. I have a few of those to give a shot at it with.

Still don't have an idea for the actual velocity measurement.

Crazy anemometers are not that cheap.

Oh well this kind of stuff never stopped me before.

It just slows me down for a while!
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Old 29th July 2011, 02:12 AM   #2038
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In the few horns that I have measured I can rule out driver excursion or oil canning. The plateau in output never occurs where there is a lot of excursion or even in the first octave of the useful response. Just from looking at some simulation data compared with the real world results the air velocity doesn't seem to match up that well either. In horns there is a pattern of high velocity and low velocity movement that will follow the driver displacement roughly. The plateau in horn output only appears in certain frequency ranges in my few limited tests and they don't seem to correspond well with a velocity or excursion maximum either one.
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Old 29th July 2011, 02:16 AM   #2039
Mark Kravchenko
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I think I have to make me a test horn. Preferably a straight one that I can do some performance work on.

I put out some feelers to suppliers of anemometers. Will see what I end up with.

I tend to agree with you Josh that the distortion effects are not due to driver over excursion. That is as long as the signal is within the passband of the horn.

This should prove to be interesting to say the least.

I don't know if there are any papers on the subject.

Time to get a digging.

Mark
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Old 29th July 2011, 09:12 AM   #2040
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Originally Posted by mwmkravchenko View Post
Mind me asking how old you are David?
Hi Mark,

Without giving too much away - I am old enough to have been happily retired for a number of years :-).

Kind regards,

David
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