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Bending mid horns

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Topic: Bending mid horns
Posted By: gen0me
Subject: Bending mid horns
Date Posted: 12 February 2017 at 12:28pm
Does anyone has experience in bending horns. Im thinking about horn going to 3-4kHz. Very long horn. How far can I bend it?



Replies:
Posted By: ceharden
Date Posted: 12 February 2017 at 1:29pm
You could bend it but it's unlikely to sound good.


Posted By: VECTORDJ
Date Posted: 12 February 2017 at 1:31pm
Horns below 500 hz can be bent or folded. Lots of models on the market that sound good. Horns from 500 Hz to 5000 Hz should not be bent or folded. Not many folded or bent mid horns that sound good. Bent mid horns may sound like a paging horn. If you must make a bent mid horn make the curve as smooth as possible.
 


Posted By: gen0me
Date Posted: 12 February 2017 at 1:55pm
I understand that option 2(with straight walls) is failure.
How about option 2? Lets say the horn canal would be drilled so the shape could be any. Any chance of reaching at least 3kHz? to connect it to nice 1" driver? I want to try some more HiFi crossover range.

Or only straight horns like Unity can go so high?

Any examples of bend horns? Good or bad.


Posted By: Thomas Hosker
Date Posted: 12 February 2017 at 5:56pm
Why does the horn need to be so long, to need to have a fold? Whats the intended lower cut off?



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WWW.T8Audio.Com


Posted By: gen0me
Date Posted: 12 February 2017 at 7:14pm
To reproduce everything over basses. Right now Im in the middle of making one playing to 1kHz. Im curious if it is possible with different HF driver. If this one sounds good.


Posted By: odc04r
Date Posted: 12 February 2017 at 7:33pm
As long as the horn expansion is always smooth and continuous, in theory a bend should not matter. But when you get into it the radius of a bend vs frequency will probably begin to have an effect.

You can see the effect in an impedance plots when the peaks that due to horn transmission are damped in magnitude as you go up in frequency, walls are absorbing the sound.




Posted By: gen0me
Date Posted: 12 February 2017 at 8:00pm
What can be the radius?
Can I simulate bend in akabak?


Posted By: bitSmasher
Date Posted: 12 February 2017 at 8:50pm
Have a look at the DR**0 horns by Bill Fitzmaurice for ideas

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https://www.instagram.com/batteryacidsoundsystem/


Posted By: SouthwestCNC
Date Posted: 12 February 2017 at 8:59pm
what effect will the bend have on directivity? Out of interest.


Posted By: gen0me
Date Posted: 12 February 2017 at 9:30pm
I checked them(DR200) but cant find any info how high is crossover. Only size of HF horns could get ROUGH idea. What are recommended speakers?

On intuition the directivity should be dictated by shape of bend end and exit of horn. Ofc bend should be narrow to keep similar patchlengths. Now I see where DR shapes came from.
Am I right? Whats DR directivity?


Posted By: _djk_
Date Posted: 12 February 2017 at 10:48pm
"You could bend it but it's unlikely to sound good"

http://www.youtube.com/watch?v=fYhpRlY_EfM" rel="nofollow - https://www.youtube.com/watch?v=fYhpRlY_EfM

A straight horn sounding like S*it.

http://www.youtube.com/watch?v=wNFK4w9NgoM" rel="nofollow - https://www.youtube.com/watch?v=wNFK4w9NgoM


http://www.youtube.com/watch?v=wNFK4w9NgoM" rel="nofollow -



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djk


Posted By: Mark James
Date Posted: 13 February 2017 at 12:33am
i personaly cant see any reason to bend/fold a horn playing down to 1khz i mean that needs to be like less than a ft long? at most id imagine [too drunk to do exact maths atm but im sure its less than a foot?] do you realy need to bend it?
not saying you dont need to just asking


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me so horny me love you long throw
horn loaded for her pleasure


Posted By: SouthwestCNC
Date Posted: 13 February 2017 at 9:46am
Originally posted by gen0me gen0me wrote:

I checked them(DR200) but cant find any info how high is crossover. Only size of HF horns could get ROUGH idea. What are recommended speakers?

On intuition the directivity should be dictated by shape of bend end and exit of horn. Ofc bend should be narrow to keep similar patchlengths. Now I see where DR shapes came from.
Am I right? Whats DR directivity?


By narrow you mean remain conical also. Id imagine an exponential bend may have some effect on directivity even if only narrow.

Most of the bent horns ive seen are fully exponential, no good for arraying so I understand. Just wonder how a conical transition is possible in a bend and immediately after if your aiming for constant directivity.


Posted By: DMorison
Date Posted: 13 February 2017 at 1:28pm
Originally posted by Mark James Mark James wrote:

i personaly cant see any reason to bend/fold a horn playing down to 1khz i mean that needs to be like less than a ft long? at most id imagine [too drunk to do exact maths atm but im sure its less than a foot?] do you realy need to bend it?
not saying you dont need to just asking
 
You're also too drunk to do exact reading at the moment apparently Wink
 
OP wants their mids to play from whereever their basses cut off up to 3-4kHz, not down to 1kHz.
 
 
 
 


Posted By: DMorison
Date Posted: 13 February 2017 at 1:32pm
Originally posted by gen0me gen0me wrote:

Does anyone has experience in bending horns. Im thinking about horn going to 3-4kHz. Very long horn. How far can I bend it?
 
Have you looked at Peter Morris's DIY 3 ways on soundforums.net?
He reckons that a 12" mid horn cab get up to about 600Hz usefully with a single bend, and used BMS coax compression drivers to reach down to meet that. 
Probably a lot more practical than stretching the (low)mids another 2.5 octaves higher.
HTH,
David.


Posted By: SouthwestCNC
Date Posted: 13 February 2017 at 4:00pm
Ive heard its possible to get down to 370hz with a bms4590 and a straight horn just 350mm in length. Will find out soon as im making one.

Think genome is looking for longer throw.


Posted By: gen0me
Date Posted: 13 February 2017 at 8:10pm
Originally posted by SouthwestCNC SouthwestCNC wrote:


By narrow you mean remain conical also. Id imagine an exponential bend may have some effect on directivity even if only narrow. 

Ofc exponential bend will have bigger patchlength differences but its not only "S bend entry" that counts but the whole design.
Originally posted by SouthwestCNC SouthwestCNC wrote:


Most of the bent horns ive seen are fully exponential, no good for arraying so I understand. Just wonder how a conical transition is possible in a bend and immediately after if your aiming for constant directivity.

Do you think it will move the center of bend exit?

Originally posted by DMorison DMorison wrote:

Have you looked at Peter Morris's DIY 3 ways on soundforums.net?
He reckons that a 12" mid horn cab get up to about 600Hz usefully with a single bend, and used BMS coax compression drivers to reach down to meet that. 
Probably a lot more practical than stretching the (low)mids another 2.5 octaves higher.
HTH,
David.

Yes thats an option but... thats basicly mine current design. Instead of 12" is 8" predicted +-100Hz to +-1kHz. So Instead of the current 3"VC 2" throat I could put there coaxial BMS. I wanted something else.


Posted By: SouthwestCNC
Date Posted: 13 February 2017 at 9:11pm
Originally posted by gen0me gen0me wrote:

Originally posted by SouthwestCNC SouthwestCNC wrote:


By narrow you mean remain conical also. Id imagine an exponential bend may have some effect on directivity even if only narrow. 

Ofc exponential bend will have bigger patchlength differences but its not only "S bend entry" that counts but the whole design.
Originally posted by SouthwestCNC SouthwestCNC wrote:


Most of the bent horns ive seen are fully exponential, no good for arraying so I understand. Just wonder how a conical transition is possible in a bend and immediately after if your aiming for constant directivity.

Do you think it will move the center of bend exit?

Originally posted by DMorison DMorison wrote:

Have you looked at Peter Morris's DIY 3 ways on soundforums.net?
He reckons that a 12" mid horn cab get up to about 600Hz usefully with a single bend, and used BMS coax compression drivers to reach down to meet that. 
Probably a lot more practical than stretching the (low)mids another 2.5 octaves higher.
HTH,
David.


Yes thats an option but... thats basicly mine current design. Instead of 12" is 8" predicted +-100Hz to +-1kHz. So Instead of the current 3"VC 2" throat I could put there coaxial BMS. I wanted something else.


I retract my statement, I received an xt1465 horn today and that is completely exponential yet its cd is good. contrary to what ive read. I'm just learning about this stuff hence my questions. Comsol might shed some light on it.


Posted By: SouthwestCNC
Date Posted: 13 February 2017 at 9:20pm
Here is a image courtesy of teunos which would suggest it is possible if from the exit if not smoothly terminated due to reflections and I would hazard a guess to say this may happen if the bend is too tight or un smooth ie one horn is then transitioning into another but could be wrong.



Posted By: gen0me
Date Posted: 13 February 2017 at 10:25pm
Oh thats beautifull visualisation.
Whats the program?


Posted By: _djk_
Date Posted: 14 February 2017 at 1:15am
http://www.youtube.com/watch?v=jPhONWr1Njo" rel="nofollow - https://www.youtube.com/watch?v=jPhONWr1Njo

WE32A, as in the Altec Model 15

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

Meyer Sound 833 (patented)

http://medias.audiofanzine.com/images/normal/meyer-sound-833-834-553021.jpg" rel="nofollow - http://medias.audiofanzine.com/images/normal/meyer-sound-833-834-553021.jpg

(foam in the bend)




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djk


Posted By: odc04r
Date Posted: 14 February 2017 at 10:45am
Originally posted by gen0me gen0me wrote:

Oh thats beautifull visualisation.
Whats the program?


Comsol


Posted By: gen0me
Date Posted: 14 February 2017 at 8:43pm

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

Meyer Sound 833 (patented)

[/QUOTE]
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" rel="nofollow - 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?


Posted By: Teunos
Date 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" rel="nofollow - 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" rel="nofollow - 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.


-------------
Best regards,
Teun.


Posted By: SouthwestCNC
Date 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


Posted By: odc04r
Date 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.


Posted By: SouthwestCNC
Date 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


Posted By: gen0me
Date 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?


Posted By: odc04r
Date 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.


Posted By: gen0me
Date 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


Posted By: Teunos
Date Posted: 09 March 2017 at 9:53pm
Mouth = exit, throat = start.


-------------
Best regards,
Teun.


Posted By: gen0me
Date Posted: 09 March 2017 at 10:30pm
Ao - throat ofc



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