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thepersonunknown View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thepersonunknown Quote  Post ReplyReply Direct Link To This Post Topic: horn beaming
    Posted: 09 March 2013 at 7:43pm
just a question i was pondering which i thought might bring up a bit of interesting conversation. excuse me if its a little basic, but at least im quite sure its not a topic which has poped up much if at all (seeing as thats the pet hate of the month)Tongue

what makes a horn beam as the frequency rises. with a cone driver its quite simple as i understand it as just a relationship between the diameter of the source and the wavelength of the frequency being reproduced, but what actualy happens with a horn?

with HF horns there are so many using different techniques from slots to vanes that it may become a little hard to generalise in a single coherent thread, but im thinking more about mid range horns

lets say a tipical conical or exponencial flare, what exactly causes them to beam in the higher frequencies and how can this be predicted/countered?
They keep telling me life is short, but its the longest thing ive ever done!!!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote b grade Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2013 at 10:18pm
It is the same basic principles as why cones beam.  The horn is an extension of the radiating surface and the larger that radiating surface is, the more directional the sound becomes as the frequencies rise.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote duck1 Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2013 at 10:46pm
Simply put, if the diameter of the radiating area is larger than a wavelength at frequency X, then it will be directional at frequency X and above. Once you droop below a wavelength the source becomes omnidirectional.

This obviously doesn't apply to any DSP controlled arrays. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2013 at 12:34am
Quote what makes a horn beam as the frequency rises. with a cone driver its quite simple as i understand it as just a relationship between the diameter of the source and the wavelength of the frequency being reproduced, but what actualy happens with a horn?

with HF horns there are so many using different techniques from slots to vanes that it may become a little hard to generalise in a single coherent thread, but im thinking more about mid range horns

lets say a tipical conical or exponencial flare, what exactly causes them to beam in the higher frequencies and how can this be predicted/countered?.

It is the shape of the horn that determines the directivity while the size that determines the frequency range over which it has control of the directivity. Not all horns beam as the frequency rises.

Quote It is the same basic principles as why cones beam.  The horn is an extension of the radiating surface and the larger that radiating surface is, the more directional the sound becomes as the frequencies rise.

How do you account for constant directivity horns where the directivity is independent of the frequency over its operating range?

Quote Simply put, if the diameter of the radiating area is larger than a wavelength at frequency X, then it will be directional at frequency X and above. Once you droop below a wavelength the source becomes omnidirectional.

To be pedantic, once the horn is acoustically small it has no control over the directivity.

Quote This obviously doesn't apply to any DSP controlled arrays.

Why obviously?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote duck1 Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2013 at 12:49am
Originally posted by Steve_B Steve_B wrote:

Quote

[QUOTE] This obviously doesn't apply to any DSP controlled arrays.

Why obviously?


Because you can manipulate dispersion using multiple (small) sources and DSP.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2013 at 12:59am
The OP was asking about how horns affect dispersion not multiple small sources, but say you had 8 small sources what DSP settings would you use to obtain a 60 degree dispersion angle over say 2 octave range?
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thepersonunknown View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thepersonunknown Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2013 at 4:57am
which horns dont beam, and how can this be done?

if the horn has a low cross sectional area (in the case of a large phase plug, spreading the expansion into a narrow ring rather than a simple horn where the cone-shaped cross section is much larger than a wavelength) does this help to keep the dispersion constant to a higher frequency?

i guess not as the radiating surface is the same at the mouth, but seeing as their is just so much variation with the dispersion of different horns leads me to believe that its not so straight forward as with the cone, and there must be ways of controling this....

come on gurus, lets get some more brains into the mix here.Smile


Edited by thepersonunknown - 10 March 2013 at 5:05am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2013 at 12:10pm

It depends what you mean by beaming. The generally accepted definition usually refers to a horn whose directivity increases as the frequency rises. If you mean why don’t horns radiate omni-directionally it is because the walls of the horn constrain the sound to a smaller angle. This is usually a desirable thing but it is possible to design a horn that radiated omni-directionally if required.

So why do horns confine the radiation pattern? Because they have solid walls that stop sound waves passing through (yes I know there will be a little transmission).  The sound waves therefore have to radiate at an angle dictated by the horn shape.

At low frequencies the horn loses control over the radiation pattern. This is due to diffraction. The mouth of the horn can be considered an opening through which sound passes. Where the opening is small compared to the wavelength the radiated sound is spherical. The following diagram illustrates what happens.

When the horn becomes large relative to the wavelengths most of the sound just keeps going at the angle of the horn.

Exponential horns and others with curved walls have a radiation pattern that narrows as the frequency increases. The best way to explain this without the use of maths is to start from what we said above; that the sound is constrained by the walls of the horn. If you flip that the other way round then if the sound can’t feel the horn wall it has no control over the radiation pattern. If you now imagine the sound wave as a bubble whose diameter expands until it is equal to one wavelength of the frequency. If the dimension across the horn is greater than that dimension the bubble loses contact with the wall. Lower frequencies see more of the horn and radiate at the angle set near the mouth whereas higher frequencies only see the section close to the throat where the wall angle is less.

At very high frequencies, where the throat dimension is comparable with the wavelengths involved, the horn becomes largely irrelevant.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote hond Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2013 at 5:15pm
http://www.synaudcon.com/site/articles/understanding-horn-directivity-control/

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TONY.A.S.S. Quote  Post ReplyReply Direct Link To This Post Posted: 10 March 2013 at 5:55pm
ASS HF Horns have been generally large, and my starting point for these designs was to make sure that the size of horn would be large enough to encompass the lowest frequency wanted. That way, everything that came out of the horn would be controlled by the dispersion angles. The same applies to mid horns as well, although I found when making practical horns, that I could only make them a size to control frequency down to the point where coupling didn't seem to matter much. I had always observed that hf was the last thing you want to couple because of the in and out of phase situation, but as you go  lower down the frequency scale, coupling matters less right down to the point where coupling can become an advantage, as in Bass.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Keen Quote  Post ReplyReply Direct Link To This Post Posted: 11 March 2013 at 1:59am
Originally posted by TONY.A.S.S. TONY.A.S.S. wrote:

down to the point where coupling didn't seem to matter much.
approx where is this point?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TONY.A.S.S. Quote  Post ReplyReply Direct Link To This Post Posted: 11 March 2013 at 6:52am
I've never been sure of the actual frequency. I think it differs because coupling from a reflex cab would be different than from a long horn Bass cab. all I know is it must be there, because, with a line of Bass Bins, advantage is created because the waves seem to combine to re enforce the sound, and the further you go up the scale, coupling has an adverse effect, to the point of serious combing effects with HF. I'm not talking about whether something is time aligned. Time alignment has little to do with acoustic coupling and its effect.
I think that logically, the crossover point would be somewhere in the lower mid band.
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