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Teunos View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 15 February 2017 at 7:51am
Originally posted by gen0me gen0me wrote:


http://www.audioheritage.org/vbulletin/attachment.php?s=891d6879c4ffbfc7010196f507fa82c7&attachmentid=53177&d=1317961911

Meyer Sound 833 (patented)


How does it sound? What is comparison to straight horn and what is the high freq cutoff?
Unity comes into mind.

Hmm i think I saw HF drivers mounted like this:



Originally posted by _djk_ _djk_ wrote:


http://medias.audiofanzine.com/images/normal/meyer-sound-833-834-553021.jpg
(foam in the bend)


What is foam in the bend for?
So something like this
Originally posted by SouthwestCNC SouthwestCNC wrote:




wont happen?[/QUOTE]

Let me put a bit of perspective into this image.
What you see here is one quarter of a very simple diffraction slot opening into a horizontal horn. The throat is a simple 2'' circle and the diffraction slot itself is 30mm wide(so 15mm can be seen here) and around 100mm wide IIRC (so 50mm is seen here).

What i wanted to know is how different diffraction slot geometries influence horn performance.
From these sims we can see what we expected to see in a diffraction slot. The rapid jump in expansion rate causes a discontinuity in acoustics impedance which causes reflections back down the horn. This is something that can also easily be seen mathematically by inspecting the general horn equations (webster). If you measure the frequency response of such a horn, you might see some sharp peaks and dips in it accompanied with slight wiggles in the phase response. Measuring the CSD and directivity of of such a horn will prove much more insight into why the peaks and dips are there.

Horn design is often very challenging and it is something that is greatly underestimated by the main DIY community. Some have found ways that work for them through empirical experimentation and it can definitely be done.
But a bent horn sounding good up to a few kHz is something i really do not see happening and here is the main phsyical argument for why;

In general,(however the exact behavior is dependent on more things such as expansion rate, horn profile etc.) a horn can propagate sound above its natural resonance frequency. So, no biggie right, only a lower limit? 
Well, no, not really. If we consider a rectangular pipe with diameter d, the upper limit for plane wave propagation is equal to f=c/(2*d) or re-arranging d = c/(2*f).
Above that frequency, also higher order modes can exist in the horn in the direction not aligned with the center of the horn but perpendicular to it as well as combinations of these higher order modes.
If you do not bend the horn and it expands quickly enough, this is generally not a problem since these modes are unfavorable assuming the walls are rigid enough not to resonate. When you start to bend the horn however, sound will not travel down the horn along its center axis and higher order modes are unavoidable. The result will be a lot of unwanted resonances in the horn, no matter how rigid you make it. And as we know resonances are typically decaying on a long time scale since they do not dissipate energy as quickly as propagating waves, they will mess up the intelligibility of the sound. Hence why earlier a comparison was made to paging horns.

I am not saying you should not try it, because above anything, experimentation is golden and i love to see people building things. But even though i have never personally heard such a spiral horn as the one DJK quoted to, i have a hard time believing it will sound very good up high.

So, i would stick to the advice given, and refrain from bending horns above a few 100Hz. just for fun; calculate what a typical dimension of the upper limit of plane wave propagation is at this frequency.

edit: punctuation.


Edited by Teunos - 15 February 2017 at 7:53am
Best regards,
Teun.

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SouthwestCNC View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post Posted: 15 February 2017 at 9:12am
all good points there teunos

is horn length / horn throw logarithmic? Ie surely it will Plato out at some point where driver power becomes the limitation, I wonder what length of horn is required to get where throw is maximised or would we be talking of a ridiculous length in which case can throw be calculated to be matched with subs etc

Edited by SouthwestCNC - 15 February 2017 at 9:39am
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odc04r View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 15 February 2017 at 9:40am
Directivity is a function of the horn mouth size/how the sound is directed leaving it + wavelength dependent effects. The SPL at the mouth is the volume velocity of air moving through it multiplied by the acoustic impedance of the air it is delivered to (again depends on wavelength too).

Then if your horn is non-ideally terminated there are mouth reflections due to impedance mismatches as Teunos says to account for too.

It is a complicated question, and it is also heavily frequency dependent.

You maximise 'throw' for a given frequency by confining the horn radiating solid angle and putting as much power in as you can. It is easier to direct higher frequencies.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote SouthwestCNC Quote  Post ReplyReply Direct Link To This Post Posted: 15 February 2017 at 10:23am
Originally posted by odc04r odc04r wrote:

Directivity is a function of the horn mouth size/how the sound is directed leaving it + wavelength dependent effects. The SPL at the mouth is the volume velocity of air moving through it multiplied by the acoustic impedance of the air it is delivered to (again depends on wavelength too).

Then if your horn is non-ideally terminated there are mouth reflections due to impedance mismatches as Teunos says to account for too.

It is a complicated question, and it is also heavily frequency dependent.

You maximise 'throw' for a given frequency by confining the horn radiating solid angle and putting as much power in as you can. It is easier to direct higher frequencies.


I see, Learnt something about spl there thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 15 February 2017 at 9:25pm
Originally posted by Teunos Teunos wrote:

If we consider a rectangular pipe with diameter d, the upper limit for plane wave propagation is equal to f=c/(2*d) or re-arranging d = c/(2*f).



You are talking about standing waves but why it is the upper limit?

Originally posted by Teunos Teunos wrote:

Above that frequency, also higher order modes can exist in the horn in the direction not aligned with the center of the horn but perpendicular to it as well as combinations of these higher order modes.

Originally posted by Teunos Teunos wrote:

Measuring the CSD and directivity of of such a horn will prove much more insight into why the peaks and dips are there.

Standing waves peaks? Why directivity? to have view in 3D or rather x, y?

How about those?
Will they be seen on directivity on the angle according to red length?



So DR200 should have some peaks in response according to green length?


On the simulation bend is not continous. Whats the math describing impedance? Or calculation "on paper" are useless due to 3 dimensions? Only simulation.


Originally posted by Teunos Teunos wrote:

just for fun; calculate what a typical dimension of the upper limit of plane wave propagation is at this frequency.

so for 1kHz:
340/(2*1000)=17cm
What does it says to me? It should be somewhow connected to minimal radius of the bend at this frequency.

There is one thing I cant beat for longer not getting directly into horn theory. Ofc the group delay characteristics is not flat. Does it mean that speed of sound in horn is dependent from sound frequency so not 340m/s?

Edited by gen0me - 15 February 2017 at 9:27pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 16 February 2017 at 8:43pm
It is the circumference or perimeter of a horns cross sectional area that determines the limit of frequency reinforcement I recall not the width or height.

Generally horns are all about cross sectional area, and how it varies with length. This is highly related to the flare rate also.

To work out how a horn works from first principles in a model I think the way I would try is to use a 2 port matrix analysis with a matrix for each conical segment approximation and then connect that to the usual electro-acoustical model of driver and any other chambers. Terminate it with the acoustical impedance of the mouth radiating into free air for which there are a few models floating about for rectangular mouths. There are some good papers on the subject, there is a real classic by Leach which shows you how to model a Salmon horn with Spice simulation. Makes a change from HR. Probably easier to start with a sealed box first though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2017 at 9:00pm
A(x)=Ao * e^(k*x)

Is k a flare rate?
Ao - mouth surface
A(x) exit surface
X - length
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2017 at 9:53pm
Mouth = exit, throat = start.
Best regards,
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Post Options Post Options   Thanks (0) Thanks(0)   Quote gen0me Quote  Post ReplyReply Direct Link To This Post Posted: 09 March 2017 at 10:30pm
Ao - throat ofc
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