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General Horn Design Questions
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Disco Stu View Drop Down
Old Croc
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Joined: 03 March 2005
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    Posted: 11 November 2007 at 6:36pm
Ok I have spent ages messing about in hornresp and I am getting a bit frustrated with not being able to get the results I want so I wonder if anyone can answer the following questions
 
1) Is there a formula for mouth size and/or horn length for determining a specific cutoff frequency of a horn? I would at least like to be able to say as a starting point for Hornresp for example to have a mouth of XXXX to give me a cutoff frequency of XXHz providing the horn is long enough.
 
2) Has anyone used the new Hornresp feature of designing a horn with a ported rear chamber? It seems to be good at controlling excursion of the driver better, but can anyone point out potential disadvantages, perhaps due to path length differences etc.?
 
3) What would be an acceptable limit for a compression ratio for a "bandpass horn" like the HD15?
 
Stu
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LostGrayCat View Drop Down
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Points: 1053 		Post Options Post Options   Thanks (0) Thanks(0)   Quote LostGrayCat Quote  Post ReplyReply Direct Link To This Post Posted: 11 November 2007 at 7:32pm
Wasn't the mouth to be 1/4 the wavelength of intended frequency? Or something like that anyway.
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Look at Keele's papers, specifically those about optimum mouth size. i think traditionally 1/4 wavelength of the lowest frequency you want to reproduce should be equal to the diameter of a circle with the same area as the mouth of your horn, though it might be a 1/2 wavelength.

Hang on....just found this in keele's paper 'the mouth is small where  2pi/wavelength*mouthsize << 1)

Hope that helps!
Tom
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tb_mike View Drop Down
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1) the CIR box in hornresp shows how many wavelengths fit around the mouth from memory.

2) There must be some disadvantage.Id think that the group delay wouldnt be as good, and excursion will increase greatly below cutoff because theres no air cushion anymore.

3)Acceptable compression ratios for basshorns seem to be below 4:1.


Horn Loudspeaker Design Part 1, PDF, 881KB

"Horn Loudspeaker Design", by J. Dinsdale
Reprinted from Wireless World, Mar 1974, pp. 19-24.
© Copyright GM Media Corp., 5201 Blue Lagoon Drive, Miami, FL 33126, USA. All rights reserved.

Horn Loudspeaker Design Part 2, PDF, 1426KB

"Horn Loudspeaker Design - Part 2", by J. Dinsdale
Reprinted from Wireless World, May 1974, pp. 133-138.
© Copyright GM Media Corp., 5201 Blue Lagoon Drive, Miami, FL 33126, USA. All rights reserved.

Horn Loudspeaker Design Part 3, PDF, 971KB

"Horn Loudspeaker Design - Part 3", by J. Dinsdale
Reprinted from Wireless World, Jun 1974, pp. 186-190.
© Copyright GM Media Corp., 5201 Blue Lagoon Drive, Miami, FL 33126, USA. All rights reserved.



His ideas about using tractix for bass are silly but the rest is gold IMAO.



The Show Horn

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Reprinted, with permission, from Speaker Builder, Issue 2, 1990, p.p. 10-12, 14, 16-20, 22-23, 75, of Speaker Builder magazine.
© Copyright 1990 by Audio Amateur Corporation. P.O. Box 876, Peterborough, NH 03458, USA. All rights reserved.

The Monolith Horn

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Reprinted, with permission, from Dr. Bruce Edgar and Speaker Builder, Issue 6, 1993, p.p.12-14, 16, 18, 24-25, of Speaker Builder magazine.
© Copyright 1993 by Audio Amateur Corporation. P.O. Box 876, Peterborough, NH 03458, USA. All rights reserved.



http://users.ece.gatech.edu/~mleach/

http://# W. M. Leach, Jr., "On the Specification of Moving-Coil Drivers for Low-Frequency Horn-Loaded Loudspeakers," Journal of the Audio Engineering Society, Vol. 27, No. 12, pp. 950-959, Dec. 1979.
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Disco Stu View Drop Down
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Thanks folks, mike the GD plummets to about -500 at one point in the design I am working on but its outside of the horns operating bandwidth so I am guessing its not going to hurt too much. It seems like a very worthwhile tool, something that worries me a bit though is that judging by Rogs stasys X cab which seems to use a similar technique it looks as though the ports are just as long as the horn to keep them in phase would that make sense? Maybe I need to make sure of this also, which kinda rules out a long horn although this is what I would like ideally, maybe I just need to look into it some more and build a prototype at some point.

Stu
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LostGrayCat View Drop Down
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How about take the front of a horn and the back of a scoop, make the path lengths equal.
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tb_mike View Drop Down
Old Croc
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Well the old Wbins used ports with success,and that was with 18"s and relatively large rear chambers. Im not too worried about phase since the wavelengths are so long its much easier.
Plus youd be able to tell if the port was out of phase with the horn output,the SPL wont increase much at cutoff with the port working or closed off.
 
 
 
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JaKe View Drop Down
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How about porting into the throat of the horn at well below cutoff of the horn?

JaKe
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Disco Stu View Drop Down
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Originally posted by JaKe JaKe wrote:

How about porting into the throat of the horn at well below cutoff of the horn?

JaKe
 
Thats sort of the idea, only you cant model it, anyone know what the difference would be of porting the box into the throat rather than porting the box into the mouth?
 
Stu
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Sensitivity + Power Handling - Power Compression = Max Output

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jsg mashed View Drop Down
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Originally posted by Disco Stu Disco Stu wrote:

Originally posted by JaKe JaKe wrote:

How about porting into the throat of the horn at well below cutoff of the horn?

JaKe
 
Thats sort of the idea, only you cant model it, anyone know what the difference would be of porting the box into the throat rather than porting the box into the mouth?
 
Stu
 
I've modelled this. It has the advantage that the port output goes through the horn and can potentially get amplified by the horn. It has the disadvantage that some of the front-cone output will disappear through the port. Basically the same breaks as a series 6th-order bandpass.
 
The thing that makes it interesting to me is that the horn segment's path delay applies equally to the port output and driver output, and the latter two should be in-phase for the same reason as they are with a reflex cab.
 


Edited by jsg mashed - 12 November 2007 at 5:03pm
...because Good is Dumb.
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Disco Stu View Drop Down
Old Croc
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Yeah so far I have modelled just the straightforward HD15 using dave slaters conical approximation, then have tried different port diameters and lengths
 
What you get is 2dB lower sensitivity but a flatter response and a bit more extension
 
This is the first step, I am starting simple but basically its looking like you need a relatively high sensitivity driver on a shortish horn or a lower sensitivity driver on a long horn to make it work - kinda like the same principle as tapped.
 
What happens to the sound if the group delay has a massive spike into the negative?
 
Stu
All you need to know is:
Sensitivity + Power Handling - Power Compression = Max Output

My acts:
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www.myspace.com/scheisseelektronisches
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JaKe View Drop Down
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I have modeled it (in Hornresponse) as a horn with a large chamber in rear of the driver and also modeled the output of the front of the driver with no throat but with a vented box on the rear.
The driver front side of the driver in the horn looks a bit like a Weems pipe.
I haven't found a way to model the combined response but the Horn response method isn't far off.
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