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Old 25th July 2010, 11:08 PM   #11
Xoc1 is offline Xoc1  United Kingdom
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Certainly I did not use any smoke and mirrors in my attempt. I calculated the path length thru the middle of the bends - not at 0.7 of the bend width which would give a lower response. When I first tried to design a similar cabinet I ended up with a box 700 X 700 X 600 That seemed a better compromise, but would use too much timber for this challenge!
I think that J Bells original simple tapered TH will be hard to beat for its LF response.
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Old 25th July 2010, 11:30 PM   #12
jbell is offline jbell  United States
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Originally Posted by djk View Post
The 'iron law' still applies to a TH enclosure.
I don't think 40hz and 100dB are possible from a 2' cube.
50hz, yes, 40hz, no.
#9 is a good example of that at 90dB at 40hz.
"in reality it goes lower"
With room gain, I might buy that. In 2Pi or 4Pi, no way.
This is not restricted to a cube, but to a 4x8 sheet -- A cube just happens to be the shape that lends itself to the taper I drew. I know I can get slightly more volume, and still get all the internal panels cut from a sheet -- but the folding/cut sheet is eluding me at the moment.

BTW -- leaving out the bottom panel and saying "just sit it on the floor" is cheating.....

One last: The cube achieves 100db. 98db@40hz and 103db@120hz -- in marketing lingo thats 101db +-3db from 40-140hz.

Last edited by jbell; 25th July 2010 at 11:38 PM.
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Old 26th July 2010, 12:42 AM   #13
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Originally Posted by djk View Post
The 'iron law' still applies to a TH enclosure.

I don't think 40hz and 100dB are possible from a 2' cube.

50hz, yes, 40hz, no.

#9 is a good example of that at 90dB at 40hz.

"in reality it goes lower"

With room gain, I might buy that. In 2Pi or 4Pi, no way.
the only way to know is to built it and measure, JBells cube measured about 5hz lower then the sim too.
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Old 26th July 2010, 12:53 AM   #14
djk is offline djk
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The form-factor (cube) doesn't really matter, it's the net volume you can come up with.

A 2' cube has at best about 180L net volume.

In the past, I've built well braced 12mm Baltic Birch cabinets for subs. I didn't think 12mm was adequate. I think 15mm is adequate, but 18mm is better. Formica (Melamine) on 15mm about doubles the strength, but adds a lot of expense.

I've got a nice Hornresp for the Eminence 4015LF that's 1.5dB from 40hz~150hz, and 100dB at 50hz. But it's 205L, not 180L. If you remove the external inductor and its DCR, it gives an almost identical response to yours.
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Last edited by djk; 26th July 2010 at 12:59 AM.
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Old 26th July 2010, 12:56 AM   #15
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Originally Posted by polviggen View Post
the only way to know is to built it and measure, JBells cube measured about 5hz lower then the sim too.
I'd like to see impedance response measurements for these systems that seem to go lower than what the HornResp sims predict.
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Old 26th July 2010, 01:00 AM   #16
soho54 is offline soho54  United States
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I would like to see live FR and Impedance graphs with a correctly dimensioned cab drawing.

Like the two posted here, most of the time the HR sim is not what gets built.
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Old 26th July 2010, 02:35 PM   #17
jbell is offline jbell  United States
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Oliver:
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I've been playing around with the fold you presented here, which I really like. If I can increase s2 some, that'll help down low... and then see if I can get it out of a single sheet of ply....
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Old 5th August 2010, 06:36 AM   #18
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Any progress with this?
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Old 5th August 2010, 09:57 PM   #19
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Originally Posted by soho54 View Post
I would like to see live FR and Impedance graphs with a correctly dimensioned cab drawing. Like the two posted here, most of
the time the HR sim is not what gets built.
Could you enlighten us?

I, for one, make every attempt to follow the HR sim. Of course I use CONICs and build Parabolics, but the error is small, and I know I'm off a few percent
in the corners.

When I can't follow the HR sim, I go back and update the sim with the as-built information. If the damage is too bad, I scrap the drawing.

Sims are sims, they are one dimensional equations simming a three dimensional world. We're lucky they even come close.
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Old 5th August 2010, 10:30 PM   #20
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I, for one, make every attempt to follow the HR sim.
The impedance plot is one way of determining how close you got to the HR sim.
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