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Old 2nd September 2011, 06:33 AM   #41
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Its very simple to sim this kind of "box" in Hornresp.

Click the image to open in full size.

This is two B&C 15TBX100 in a 50% sd slot and a 1 m2 baffle.
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Old 2nd September 2011, 06:36 AM   #42
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The response-graph above is direct radiation only. The combined response is hard to calculate because of room-interaction and such.
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Old 2nd September 2011, 11:59 AM   #43
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Rudolf

What do you think of the dispersion pattern: OB - would you build it slot loaded?
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Old 2nd September 2011, 12:13 PM   #44
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by Circlomanen View Post
Its very simple to sim this kind of "box" in Hornresp.
don't forget one major advantage of a folded dipole like this
you can have many woofers, without having a huge box

with less woofers you get less SPL
so I would think that a boxed design would need much different woofers
that is if you mate it with a Lowther like Nelson

but kind of OT I would say
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Old 2nd September 2011, 02:20 PM   #45
sreten is offline sreten  United Kingdom
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Quote:
Of course one of the first things I did was haul them out into the room
to measure the response difference between front and back. Here is the
(smoothed) comparison measured near field on the woofer system after
the crossover network has been applied. What you see is about about
9 dB pressure difference, equal to my 9 dB thumbnail calculation.
Hmmm .... Oh dear .... in reality practically inconsequential .....

You cannot just use pressure to indicate SPL, you need to normalise it
by multiplying it by the radiating area, otherwise you get nonsense
like small ports being more efficient than large ones, they are not.

Yes, the pressure is higher as the area is less, inevitable measured
nearfield. Farfield there is no difference, there is no efficiency gain
with the arrangement. Volume displacement is the same front and rear.

rgds, sreten.
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Old 2nd September 2011, 03:06 PM   #46
oublie is offline oublie  United Kingdom
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I sort of concur with sreten on this ive been playing about with hornresp and come up with something that sort of models the design i also ran a baffle simulation and from what ive come up with the 'port' seems to be adding extra path length to the box in essence making a wide baffle but doesnt seem to improve spl.

first two graphs are what i think is a representatio of the slot loaded drivers i may be wrong. The second two are the same drivers on the same baffle without the slot. There is a slight difference in spl down low but this could just be the added baffle size.

I set both to have a path length difference of 120cm

My hornresp design may not be right though.
Attached Images
File Type: jpg slot1.JPG (43.4 KB, 1397 views)
File Type: jpg slot2.JPG (56.2 KB, 1368 views)
File Type: jpg slot schema.JPG (23.2 KB, 1356 views)
File Type: jpg ob1.JPG (46.2 KB, 1352 views)
File Type: jpg ob2.JPG (59.3 KB, 157 views)
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Old 2nd September 2011, 03:15 PM   #47
oublie is offline oublie  United Kingdom
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ive also modelled a slightly different design. better response but no realy gain in spl.
Attached Images
File Type: jpg slot1a.JPG (45.4 KB, 125 views)
File Type: jpg slot2a.JPG (56.3 KB, 91 views)
File Type: jpg slot schema a.JPG (23.2 KB, 89 views)
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Old 2nd September 2011, 03:24 PM   #48
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Quote:
Originally Posted by sreten View Post
You cannot just use pressure to indicate SPL, you need to normalise it
by multiplying it by the radiating area, otherwise you get nonsense
like small ports being more efficient than large ones, they are not.

Yes, the pressure is higher as the area is less, inevitable measured
nearfield. Farfield there is no difference, there is no efficiency gain
with the arrangement. Volume displacement is the same front and rear.
You are saying my whole fallacy is wrong, and Heil transformers obviously
don't work as described.

But it's a fact that air moving at a higher velocity carries more energy
and this shows up as greater pressure.

When I said near field, I did not mean that I was sticking the microphone
in the slot - it is true that the farther away you get and as the frequency
goes lower the effect is diminished. I find that the effect is perfectly
adequate for listening purposes.

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Old 2nd September 2011, 03:36 PM   #49
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Old 2nd September 2011, 03:42 PM   #50
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It seems like compression would find a way to do Something, especially if the front side has a "hornier" load than the back.

What if you added a deep box for the woofers with a front and rear array. The front array is mounted just like this project, the back array connected to the front array through a deep box opening well away from the OB and floor with no compression ratio. Make the front to back path something like 3 meters and apply a 9mS delay to the rear array drive. This would make about 90 degrees phase shift at 30 Hz and would somewhat reduce the needed box volume? Babble babble.

Last edited by Andrew Eckhardt; 2nd September 2011 at 03:47 PM.
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