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Old 3rd September 2011, 12:40 AM   #2231
GM is offline GM  United States
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Quote:
Originally Posted by Jmmlc View Post
Hello GM,

Every exponential horn of finite length is truncated and the Altec one you show is such.

I guess you are referring to Keele formula for the optimum mouth diameter.
Greets!

Actually, it's listed on the Lansing Heritage website as a Jim Lansing/Westrex/Ampex theater horn depending on the label stuck to it. Regardless, we must have a frame of reference to decide from which end [or both] to truncate from, so while you’re right referenced to an 'infinite' expansion it seems an impractical one, at least for the purposes of this thread topic.

Not really, Keele wasn't around when I learned that the pioneers of audio had long since concluded before I was born that a 1 WL mouth area of the desired LF response was the practical limit that the horn in the picture represents. Didn't know he even existed until folks started referring to his work decades later on the joelist and still haven't gotten around to reading any of his published work. Ditto BK's thoughts on horn theory. Thanks for the link though!

When someone on the joelist referenced Keele's thoughts on mouth size, I just assumed he subtracted out the mouth end correction which at a glance seems a reasonable thing to do, but my own experiments had already concluded that the 1 WL rule was fine for mid-bass, lower mids horns out to ~600 Hz, so was probably overkill for [sub] bass horns, though haven’t actually done any experimenting with < 70 Hz 1 WL mouth areas.

Since you don’t seem to agree with the < 1 WL reference to define being truncated from the mouth, where do you think it should be?

GM
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Old 3rd September 2011, 06:36 AM   #2232
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Default Optimum Horn Mouth Size

As far as designing a horn loudspeaker system in Hornresp is concerned, for those flare profiles that have a defined cutoff frequency, from a practical perspective you can't go too far wrong if the following mouth size conditions are met:

For Exp, Hyp and Obl: Cir = 1 or greater
For Sph and Tra: Fta = 90 degrees
For Lec: Fta = 180 degrees

For Con and Par flare profiles choose a mouth size such that Cir >= 1 when the flare is changed to Exp.

Kind regards,

David
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Old 3rd September 2011, 07:34 AM   #2233
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Quote:
Originally Posted by dirkwright View Post
Which is why, in the old days, men used to demolish their living room wall and make the new wall opening the mouth of a horn, extending the horn out to the back yard...
Hi dirkwright,

Not just in the old days... :-).

Kind regards,

David
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Old 3rd September 2011, 12:57 PM   #2234
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Just wondering about something. When I use your system designer, the window that pops up with the low frequency cutoff and high frequency roll off are filled in. I was wondering how Hornresp comes up with these numbers?
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Old 4th September 2011, 07:12 AM   #2235
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Quote:
Originally Posted by dirkwright View Post
When I use your system designer, the window that pops up with the low frequency cutoff and high frequency roll off are filled in. I was wondering how Hornresp comes up with these numbers?
Hi dirkwright,

For the System Design With Driver tool:

f1 = Int(fs / 1.125)
f2 = 10 * f1

Where fs is the driver free-air resonance frequency in hertz.

For the System Design From Specifications tool:

f1 = 40
f2 = 10 * f1

Bear in mind that these are empirical default settings only, intended to act as a suggested starting point. They can be altered by the user as desired.

Kind regards,

David
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Old 4th September 2011, 08:20 AM   #2236
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With f1 and f2 choosen, T is the parameter to be adjusted for achieving reactance annulling.

This strictly follows Leach´s formulas.

Another way to do it(as in my spreadsheet) is to decide f1 and T and then accept/find f2.

It would be great to have the opportunity to decide if inputting T or f2 together with f1 in the "System Designer".
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Old 4th September 2011, 01:43 PM   #2237
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Quote:
Originally Posted by revintage View Post
With f1 and f2 choosen, T is the parameter to be adjusted for achieving reactance annulling.

This strictly follows Leach´s formulas.

Another way to do it(as in my spreadsheet) is to decide f1 and T and then accept/find f2.

It would be great to have the opportunity to decide if inputting T or f2 together with f1 in the "System Designer".
Is T the same as "M" in the Bruce Edgar articles? For Hyp-Ex horns, M=0.7 was a good value as I recall.

Also, choosing F2 was a function of the chosen driver, or one would chose a driver to achieve the desired F2, based on the high frequency mass rolloff number. For example, the 12PE32 has a mass rolloff of 537Hz, so 500Hz is practical as F2. Back when I designed my first horn 20 years ago, I used the EVM15L driver, with a mass roll off around 500Hz.
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Old 4th September 2011, 03:43 PM   #2238
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Don´t mess it up! f1 and T are essential. Horntresp will show you topend-response whatever the published "mass rolloff" is. If f2 is essential, do some "trial&error". If f2 is of most importance to you, Hornresp is perfect.
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Old 6th September 2011, 04:17 PM   #2239
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I have been using Hornresp for a couple of years now. I am very impressed with it

I am now working on a LeCleac'h horn for a 1" compression driver. Group delay, acoustical impedance and polar map are useful. Spl response is not so useful though

May I suggest a few improvements? I have not read through all 224 pages, so forgive me if this has already been suggested.

I would like to be able to model the phase plug as the first section, the exit of the driver as the second section, an angle adapter as the third section (a spline perhaps as suggested by LeCleac'h himself) and finally the LeCleach horn as the fourth section.

Also entry and exit angles for each section would be useful.
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Old 8th September 2011, 07:44 AM   #2240
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Quote:
Originally Posted by more10 View Post
I would like to be able to model the phase plug as the first section, the exit of the driver as the second section, an angle adapter as the third section (a spline perhaps as suggested by LeCleac'h himself) and finally the LeCleach horn as the fourth section.

Also entry and exit angles for each section would be useful.
Hi more10,

The way that Hornresp has evolved, massive changes would be required to implement the functionality you are seeking. Sorry, but it is not going to happen. The best that you can do is to specify a chamber and throat adaptor using parameters Vtc, Atc, Ap1 and Lpt - see attached screenprint.

To check the throat adaptor half-angle, double-click on the Ap1 input box in edit mode and then press the Calculate button to display the Fta value.

The horn throat entry half-angle is given by AT on the main input screen.

In the example shown, the throat adaptor half-angle has been made equal to the horn throat entry half-angle.

Kind regards,

David
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