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Old 30th August 2012, 10:23 PM   #141
MaVo is offline MaVo  Germany
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while you can use a th higher than two octaves from the low corner and the response is alot cleaner than hornresp suggests, its still less than ideal sound quality wise. see the impulse spectogram (ctrl+h in spl response window) to see what i mean. compare it to a closed box for giggles. just from experience, i didnt mind using my 30hz th's up to 200hz, they measured fine too, but listenening to them alone did sound slightly weird "hollow" with higher tones.

also, you set the segments to PAR, which should be quite difficult to realize. i prefer conical for the straight walls.
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Old 31st August 2012, 07:18 AM   #142
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also, you set the segments to PAR, which should be quite difficult to realize. i prefer conical for the straight walls.
Hi MaVo,

Just to clarify, if a rectangular cross-section horn segment has two parallel straight walls and two non-parallel straight walls, then the actual area expansion will be parabolic not conical. It is therefore more accurate to specify Par rather than Con in this case.

Kind regards,

David
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Old 31st August 2012, 11:16 AM   #143
MaVo is offline MaVo  Germany
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thanks

then i have to say, it doesnt seem to matter, since i did it wrong with several tapped horn subwoofers and didnt realize it, despite measuring alot. i guess room modes >> build accuracy, even in nearfield.

edit: let me use this opportunity to say thank you for your amazing program and your support! both has helped me so much with this hobby.

Last edited by MaVo; 31st August 2012 at 11:22 AM.
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Old 31st August 2012, 01:34 PM   #144
DrDyna is offline DrDyna  United States
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IMO, the resulting schematic from parabolic is much easier to fold.
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Old 1st September 2012, 06:16 AM   #145
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Hi MaVo,

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Originally Posted by MaVo View Post
then i have to say, it doesnt seem to matter, since i did it wrong with several tapped horn subwoofers and didnt realize it, despite measuring alot.
With slowly flaring horn segments, the predicted responses for Con, Exp and Par expansions will be quite similar.

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Originally Posted by MaVo View Post
let me use this opportunity to say thank you for your amazing program and your support! both has helped me so much with this hobby.
Thanks for the thanks :-).

Kind regards,

David
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Old 2nd September 2012, 08:02 AM   #146
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Quote:
Originally Posted by David McBean View Post
Hi MaVo,

Just to clarify, if a rectangular cross-section horn segment has two parallel straight walls and two non-parallel straight walls, then the actual area expansion will be parabolic not conical. It is therefore more accurate to specify Par rather than Con in this case.

Kind regards,

David
David,

Could you please clarify why the area expansion is parabolic?
If S is the cross section area and a (constant) and b (linearly expanded) are the rectangular dimensions, then: S=a*b. If b=k*x (where k is a constant and x the horn axis) then S=a*k*x, but a*k is also a constant so it appears to me that S expands conically?
What I am missing?
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Old 2nd September 2012, 09:06 AM   #147
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Could you please clarify why the area expansion is parabolic?
Hi ConExp,

Sorry, my mistake - I was not thinking too clearly at the time :-).

It is the equivalent axisymmetric radius that has a parabolic expansion rate, not the area.

The plane cross-sectional area of an axisymmetric parabolic horn will expand conically with axial length - the same as for a rectangular horn segment having two parallel straight walls and two non-parallel straight walls. This is why I suggested using Par rather than Con.

My apologies for any confusion caused.

Kind regards,

David
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Old 3rd September 2012, 04:50 AM   #148
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Originally Posted by David McBean View Post
The plane cross-sectional area of an axisymmetric parabolic horn will expand conically with axial length - the same as for a rectangular horn segment having two parallel straight walls and two non-parallel straight walls. This is why I suggested using Par rather than Con.
To clarify further.

Attachment 1 shows how the plane cross-sectional area of a conical horn varies non-linearly with axial length.

S = S1 * (x ^ 2)

Where S is the area at distance x from the cone origin or vertex, and S1 is the area at distance x = 1 from the origin.

Attachment 2 shows how the plane cross-sectional area of a parabolic horn varies linearly with axial length.

S = S1 * x

Where S is the area at distance x from the parabola origin, and S1 is the area at distance x = 1 from the origin.

Kind regards,

David
Attached Images
File Type: png Conical.png (79.2 KB, 414 views)
File Type: png Parabolic.png (79.5 KB, 406 views)
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Old 3rd September 2012, 09:05 AM   #149
AndrewT is offline AndrewT  Scotland
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David,
my head must have got twisted back to front when I pulled on my pull-over this morning.

Could you explain that for me.
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Old 3rd September 2012, 05:15 PM   #150
jwmbro is offline jwmbro  United States
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Originally Posted by AndrewT View Post
David,
my head must have got twisted back to front when I pulled on my pull-over this morning.

Could you explain that for me.
Just do the math yourself. If you have a conical expansion (think: traffic cone) the area is pi*r^2. And the radius increases linearly as you move along the cone. So if at the peak, where the radius is, say 2cm, the area is 4pi cm^2. If you move down along the cone to where it gets bigger, where the radius is 4cm, the area is already 16pi cm^2. Move down again by the exact same distance, and the radius is now 6cm, but the area is already 36pi cm^2.

As the area of your conical horn increases by a linear factor of the length in x dimesion, and in y dimension, the area increases by a multiple of this, therefor a quadratic factor of the length.

In order for the area to increase linearly, you have to decrease the rate of expansion the further out you move, in an (inverse) parabolic fashion. As hornresp simulates the horns as having circular cross sections, you need this parabolic expansion (that is: width expands with length^0.5 and height expands with length^0.5, leading to a total expansion rate constant with length^1).

Another way to achieve this expansion rate is to have one dimesion (eg height) expand linearly with the length, but keep the other dimesion constant (width of the horn stays the same). Total area expansion is then still linear. Therefore to have the same rate of area expansion for these typical horns with 2 parallel sides, you need to simulate them as Par.
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