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Quad 12" Isobaric Ported Sub

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ceharden View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 02 August 2017 at 9:15pm

Four 12" drivers in isobaric pairs....


Edited by ceharden - 02 August 2017 at 11:14pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Risc_Terilia Quote  Post ReplyReply Direct Link To This Post Posted: 02 August 2017 at 10:45pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 02 August 2017 at 11:15pm
Try now, not sure why copying and pasting the original link from the address bar didn't work
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Post Options Post Options   Thanks (0) Thanks(0)   Quote flinnt45 Quote  Post ReplyReply Direct Link To This Post Posted: 22 hours 9 minutes ago at 3:54pm
Look at decware for a quad box

JAH Kreator Hi Fi
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 19 hours 7 minutes ago at 6:56pm
A little work in a box program with isobaric designs will probably have you changing your mind.

While you only lose 3dB in efficiency, you lose 6dB in maximum output capability (model it and see).

The Qts of the BMS suggests a small equalized and vented alignment (6th order) might work the best.

A 2 cu ft 2nd order sealed box with an F3 of 30hz can only be 0.18% efficient (84.55dB).
A 2 cu ft 4th order vented box with an F3 of 30hz can only be 0.36% efficient (87.56dB).
A 2 cu ft 6th order vented box with an F3 of 30hz can only be 0.90% efficient (91.54dB).

RCA was the first company to use equal-pressure coupling (isobaric) in a loudspeaker. They used a 12 coupled to a 15 to reduce the box size by a factor of 4x. The drivers were in series, and the inside 12 received more power (the penalty for a small box that went deep in the bass)

*******************************

RE: nope

    Posted by djk (M) on December 14, 2010 at 06:53:43

    In Reply to: RE: nope posted by Scholl on December 13, 2010 at 14:46:43:

You don't need any real math to understand what is going on here.

We have a fixed box size and cut-off frequency. Each box requires a different driver to be optimum for the box type (2nd, 4th, 6th). This can be seen as if you would convert a 2nd to a 4th the reference efficiency cannot change, but the 4th would go about 1/3 octave lower.

In theory we should be able to see about a 3dB difference in a 2nd vs a 4th if the box size and cut-off frequency are kept constant (which we do, 84.55dB vs 87.56dB).

What you need to ask is how the 6th can be 91.54dB, an increase of 3.98dB?

The answer lies in the optimum driver having a lower Qts which in turn raises the mid-band reference efficiency, but causes the deep bass to roll off. There is no such thing as a free lunch, and there isn't one here either. The deep bass roll-off is compensated for by the bass boost in a 6th order system, typically 6dB at the box tuning frequency.

That's cheating!

Well, sort of.

Comparing output at Fc (2nd order) vs Fb (4th and 6th order), the 6th order is only about 1dB more that the 2nd order, and is actually 2dB less than the 4th order (low Qts drivers have no low bass). But the mid-band reference efficiency really is 6.99dB more that the 2nd order, or 3.98dB more than the 4th order. The 6dB boost in the 6th order is mainly at Fb and drops off rapidly above there. An octave above Fb the boost has declined to only 1.5dB or so. Distorting is not excessive as the largest boost is at Fb and does not cause excessive cone motion. Levels of F1 in program material tend to be on the order of 6dB~10dB lower than F2 on most musical instruments, so the boost at Fb doesn't eat up all the power on real music.

The 6th order vented system looks to be a free lunch (violate the Iron Law), but as we see, doesn't. Keele's actual examples were for a 2nd order with a 15, 4th order with a 10, and 6th order with an 8!

See example 2 on page 29 of the pdf (which was pg.28 of the actual paper)

From examining various equations for efficiency and LF cut-off I have concluded the optimum driver for the highest efficiency and lowest cut-off would have a Qts=0.312 and be a 6th order system with an Fb=F3=Fs=Faux with the filter (Faux) having a Q=2.

I can address alignment jamming (using non-optimum drivers) if desired.

****************************

A 6th order Quad 12 (cat is optional). Eminence drivers with 8mm x-max, rubber edge, similar parameters to the BMS driver. 101dB/1W/1M (8Ω load), -3dB at 27hz (Q=2, 27hz filter). Will handle 1100W without exceeding the x-max, less than $100 a driver (USA).



Edited by _djk_ - 18 hours 48 minutes ago at 7:15pm
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