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Author Topic: Flare Rate Transitions  (Read 5829 times)

Michael_Elliston¶

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Re: Flare Rate Transitions
« Reply #10 on: August 07, 2005, 07:42:19 pm »

Peter wrote on Mon, 01 August 2005 17:33

Any discontinuity in the horn is a potential point that will cause a reflection, but its related to the wavelength, the discontinuity has to be large in comparison to the wave length to cause a problem.

The biggest discontinuity is the mouth exit, the usual way on minimising these problems is to use a mouth where the exit angle is quite large, approaching 180 degrees, or tractrix like in profile.  The trick is to minimize reflections and maintain the desired pattern control for a HF horn.

I think that most of the discontinuities in the LAB will not cause problems in the intended operating range. ---  distortion is not consider a problem with the LAB ---  

The only problem with the LAB is that you need so many of them, less than 4 to 6 of them in half space does not have enough mouth area and there will be a 1 / 4 wave length resonance, which is probably a good thing despite the distortion – you trade a little LF resonance for LF gain when you don’t have enough boxes.

Peter


There are some java animations some where (??) on to the web that demonstrates how waves travel around corners at different frequencies and the related reflections.



Do you prefer one large horn of 3200Litres volume? Wink
Remember that High Q resonances are less audible than low Q ones -from the articles Ive read.

http://www.diyaudio.com/wiki/index.php?page=basshorn

Two Davids


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[ Loudspeaker Discussion Area ]



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Written by W.H.Geiger at 17 Jul 2003 17:33:17:

As an answer to: Re: Horn Flare vs. Segmentation written by mike.e at 16 Jul 2003 22:00:08:

ME,

David McBean has produced an excellent piece of work.
And, you get it for free! This phenomenon seldom occurs in life.

For some horn simulations in real time, see the work of David Burners

Thesis Defense
http://www-ccrma.stanford.edu/~dpberner/Defense/pres.html

Also his other publications may be of interest.
http://www-ccrma.stanford.edu/~dpberner/downloads.html

Note, that in this setting, resonances rule supreme.

Regards,

WHG

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Peter Morris

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Re: Flare Rate Transitions
« Reply #11 on: August 08, 2005, 12:54:17 am »

Thanks Mike....

Bigger is always better, is it ???

The resonance issue - its not so much the Q but where it is in this case.  With the LAB its around 30Hz so its not that critical, at those frequencies its more about energy than defining the timbre of an instrument, but if it was at 80Hz then it would be an issue.

FWIW I did actually model (I had to pay for it) my 18 inch version of the LAB with a program that I guess you could say is like a finite element acoustic model – is capable of predicting a lot of things including directivity at various frequencies and will take into account anomalies in the horn  - The poor computer has to think for about an hour or so per run, anyway it agreed with what McBean simpler model had predicted.

BTW that nice power point presentation with all that math assumes plane waves propagating down the horn, which is what you would expect from the second order differential equation that describes the wave propagation in a horn – the problem is they’re not quite ... hence the problems with models.
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Wayne Parham

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Re: Flare Rate Transitions
« Reply #12 on: August 09, 2005, 01:11:47 am »


I agree with the direction you're going here.  As the horn approaches an infinite horn, it becomes less resonant.  But as it is made smaller and smaller, it acts more like a tuned pipe.  There was a discussion similar to this in a thread on AudioRoundTable.com called "Basshorn or Transmission Line."  You might check it out and throw in your 2
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Wayne Parham
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Michael_Elliston¶

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Re: Flare Rate Transitions
« Reply #13 on: September 15, 2005, 10:44:30 pm »

Peter wrote on Mon, 08 August 2005 16:54

Thanks Mike....

Bigger is always better, is it ???

The resonance issue - its not so much the Q but where it is in this case.  With the LAB its around 30Hz so its not that critical, at those frequencies its more about energy than defining the timbre of an instrument, but if it was at 80Hz then it would be an issue.

FWIW I did actually model (I had to pay for it) my 18 inch version of the LAB with a program that I guess you could say is like a finite element acoustic model – is capable of predicting a lot of things including directivity at various frequencies and will take into account anomalies in the horn  - The poor computer has to think for about an hour or so per run, anyway it agreed with what McBean simpler model had predicted.

BTW that nice power point presentation with all that math assumes plane waves propagating down the horn, which is what you would expect from the second order differential equation that describes the wave propagation in a horn – the problem is they’re not quite ... hence the problems with models.



Yes at LF its different WRT Q and audibility. The investigations by HARWOOD etc revealed Q=1 resonances in the midrange,and panel colourations needed much improvement.


Ive heard about FEA/FEMM having high price tags for the moment. As it becomes more common place it should reduce.

On a related note, cheap parallel computing is easier too through linux and cheap PCs.

Your saying that the waves arent quite plane waves? Are they generally distorted? Does it make an audible difference? Geddes has done some AES work on this too.
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