Learning horn resp, need some advice. |
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1083 |
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Ah ok thanks.
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SouthwestCNC
Young Croc Joined: 27 November 2015 Status: Offline Points: 830 |
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And this goes for the new version of hornresp? How did you manage to identify the port tuning required was that of a 65hz wavelength to achieve an overall tuning of 35hz taking into account the horn is acting as a duct? Trial and error? |
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1083 |
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Very much trial and error, I built various test boxes that I could change panels to convert between 4th/6th order bandpass and reflex, using bricks and waste pipe to adjust tuning, followed the same method for the horn with blanking plates to change from internal / external vents and sealed rear chamber. First box was built approx 18 years ago.
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odc04r
Old Croc Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5482 |
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It's an odd one, I could easily see how in this case simulation would struggle to match reality. If the port doesn't terminate one end in essentially infinite space and the other in a chamber far enough from any walls, you need to start making end corrections. But worse than just end corrections is when they terminate into a region of the horn where acoustic velocity and pressure is far from normal. I guess the electronic analog would be boot strapping.
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SouthwestCNC
Young Croc Joined: 27 November 2015 Status: Offline Points: 830 |
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Might be a ridiculous idea but Could the port not be simmed as two seperate horns, as if the rear chamber became the front chamber with a throat port only applying a rear chamber that simulates the remaining volume in the horn. Then sim the correct chamber orientation of driver and combine the results?
Quite tempted to build one with a port tuning of 65hz to begin with and do the same. If only these could be 3d printed in miniature and tested.
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1083 |
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There are various ways to try and fudge aspects of it HR although probably just as quick to just build a test setup- straight horn with one expanding surface and a reflex box with adjustable port that can be clamped to the horn profile. Model as for a standard ported horn for a starting point.
I also tried modeling it with Akabak but didn't get anything useful although that could have been my understanding of the software. I will try and get some test results to upload but may be a few weeks before I get to do that, can't find any at the mo so will have to re test , all the old ones were not in ideal test conditions.
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SouthwestCNC
Young Croc Joined: 27 November 2015 Status: Offline Points: 830 |
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Id be interested to see. Ive been going exactly as I mentioned and fudging it in horn resp by simulating the port as s1/s2 then leading to the horn and it seems to narrow the possible frequency tuning range of the port and the horn takes over, Could need three tunings ie two different length ports to compensate. All rather complicated.
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fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1083 |
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Using multiple ports is one way to change the tuning, another would be to tune the rear chamber om the high side and then blank off part of the port to lower it.
As and when I get around to working on another version I will make a straight horn expanding from zero in one plane and adjust the position of the rear chamber / driver along the axis of the horn. I would also aim to have the port tuning half an octave or more below the horn cutoff frequency. |
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jaya000
Registered User Joined: 24 August 2008 Location: India Status: Offline Points: 59 |
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How to get high resolution image of yoiur post? |
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DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1649 |
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Right click & save the images, or pop them open in new tabs - they're not much bigger that way, but it is enough difference that you can read them.
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SouthwestCNC
Young Croc Joined: 27 November 2015 Status: Offline Points: 830 |
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Any revelations FreddiesCat? With 0 volume on the rear chamber 0 atc vtc and no port you are effectively simulating a tapped horn with horn flare extension on the front are you not?. Im thinking i have a tham 12 here, I should sim it as is, measure. Then sim with a horn flare extension and build the flare and stick it on the tham12 and re measure. Will at least give me an idea how accurate horn resp can sim this arrangement initially before trying any porting.
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SouthwestCNC
Young Croc Joined: 27 November 2015 Status: Offline Points: 830 |
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Just had a go at it and on second thought its probably a futile exersize, Can get some lovely improvements to response but group delay goes through the roof and and more worrying is even with a short horn extension it introduces sharp changes in phase inside operating range so just be measuring distortions thats unlikely to tell me much.
Edited by SouthwestCNC - 01 November 2017 at 1:34pm |
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