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Old 9th October 2011, 10:36 AM   #1
ODougbo is offline ODougbo  United States
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Default Isobaric Lovers Only

hence the 4 drivers. Those boxes are long gone and thinking 3 drivers, mag to front configuration (tunnel) would be interesting e.g. [>>>]

I could use all 4 in a tunnel, which would be easier to wire up – back to 8ohm.

I started gluing up 2 - 15” square boards (1 ½”), will cut them, and glue up/laminate stacks as needed. This is a 2 sheet MDF and glue project ~ $60 bucks total.

Suggested box size for 1 driver - CONNOISSEUR BOX = 160L, PORT = 100 x 400mm, F 17Hz.

831857 12" POLYPROPYLENE WOOFER
Parameters: Free air Common Baffled
Nominal impedance Zn (ohm) 8
Minimum impedance/at freq. Zmin (ohm/Hz) 6.3/124
Maximum impedance Zo (ohm) 46.9
DC resistance Re (ohm) 5.5
Voice coil inductance Le (mH) 2.8
Capacitor in series with 8 ohm
(for impedance compensation) Cc (μF) 24
Resonance Frequency fs (Hz) 24.0 22.9
Mechanical Q factor Qms 3.72 3.90
Electrical Q factor Qes 0.49 0.52
Total Q factor Qts 0.44 0.46
F (Ratio fs/Qts) F (Hz) 50
Mechanical resistance Rms (Kg/s) 3.25
Moving mass Mms (g) 80.2 88.2
Suspension compliance Cms (mm/N) 0.55
Effective cone diameter D (cm) 25.7
Effective piston area Sd (cm²) 520.0
Equivalent volume VAS (ltrs) 210.0
Force factor Bl (N/A) 11.6
Reference voltage sensitivity
Re 2.83V 1m at 124 Hz (Measured) (dB) 89.3
Voice coil diameter d (mm) 39
Voice coil length h (mm) 26.0
Voice coil layers n 4
Flux density in gap B (T) 0.99
Total useful flux (mWb) 1.52
Height of the gap hg (mm) 8
Diameter of magnet dm (mm) 134
Height of magnet hm (mm) 22
Weight of magnet (kg) 1.28
Power handling:
Long term Max System Power (IEC) (W) 220
Max linear SPL (rms) / by power (dB/W) 110/170

ROCK BOX = 80L, PORT = 100 x 200mm, F 33Hz.

THEATER BOX = 120L, PORT = 100 x 220mm, F 25Hz.

CONNOISSEUR BOX = 160L, PORT = 100 x 400mm, F 17Hz.
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Old 11th October 2011, 02:48 AM   #2
60ndown is offline 60ndown  United States
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HWK15


do it.
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Old 11th October 2011, 09:53 AM   #3
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by ODougbo View Post
..I could use all 4 in a tunnel, which would be easier to wire up – back to 8ohm..
Hi,

Back to 8 Ohm saving cone area:

b
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Old 11th October 2011, 05:16 PM   #4
ODougbo is offline ODougbo  United States
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Can any of the Isobaric lovers suggest a box size/tuning frequency using 3 - 831857? I have 4 of these laying around, collecting dust and been planning on building a box.

I made a clamshell (1 pair) once, it was okay, but ended up building 2 sets; I might ~ that looks like a better plan than I had.
I remember reading about the death box, e.g. the speaker baffle board moves up and down for tuning.
$20 bucks plans wouldn’t be bad at all, however, not sure if my 12” woofers would work. The chambers would have been the right size. It would require some engineering.
Wouldn’t take long to build; a box with holes, PVC and baffle boards (sliding I guess).
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Old 11th October 2011, 05:29 PM   #5
60ndown is offline 60ndown  United States
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Quote:
Originally Posted by ODougbo View Post
I might ~ that looks like a better plan than I had.
I remember reading about the death box, e.g. the speaker baffle board moves up and down for tuning.
$20 bucks plans wouldn’t be bad at all, however, not sure if my 12” woofers would work. The chambers would have been the right size. It would require some engineering.
Wouldn’t take long to build; a box with holes, PVC and baffle boards (sliding I guess).
Ive built most of decwares subs, the housewrecker is one of the best, imo.

4 x 12s would be really good.
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Old 11th October 2011, 10:25 PM   #6
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ODougbo

I've never tried a triso-baric or quadso-baric. I tend to like the clamshelled rather than tunnel; I don't have to build a tunnel, I get the cones closer together, and I like the symmetry. I clamshelled some JBL 18's, mostly because the ideal cabinets were just unmanageably huge. Sold them a few years ago.

Yes isobarics are inefficient, yes you can achieve better results in a bigger box with non-isobaric mounting, yes it is often possible to make a better single driver with characteristics similar to an isobaric pair, yes the driver costs are doubled compared to a big-box solution.

I tend to like sealed isobarics in a low-Q system, as I get usable output well below resonance. I don't mind using EQ. I don't like the space the port tube requires. But your choice of bass-reflex is equally valid.

But for a given box size and reasonable driver budget, few things are more impressive than a little isobaric dense-pack kicking out low bass like a big box, except perhaps a bunch or a stack of isobaric dense-packs. Or perhaps a big tapped horn with more extension, more bandwidth, and FAR better efficiency. Yes, there are some new long-displacement drivers that go really low coming out of the auto sub industry, but the cost is usually outrageous.

I've now got 20 reasonably-matched 12" poly drivers I picked up for a good price (since I was about broke at the time): 10 used and 10 new; and I've done simiilar math. I'm contemplating clamshelling pairs and mounting them in sealed cheap knocked-down flat-pack enclosure kits that make wedge-shaped PA enclosures. I'll probably brush on marine epoxy, inside and out. I'd stack 2 cabinets on each side for the home stereo. Maybe use the spare cabinet in another room or for bass guitar. My particular drivers are no longer available, so the last 4 drivers are really spares, but the cabinets are cheap so I'd might as well load them up for now.

Luckily I have plentiful and well-endowed (lots of FETs) power amps.

My first problem is that the drivers I want to clamshell don't really have a gasket for mounting their faces to a baffle-board; they're meant to front-load with a gasket behind the lip.

My next problem is re-wiring enough electircal circuits to plug in all the power amps.
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Old 12th October 2011, 12:34 AM   #7
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Sounds like you want flat response. I can't get Bjorno's thumbnails readable. I don't really care about flat response, just so it's smooth, since I have decent EQ available, decent power available, and all those voice coils can collectively dissipate the power associated with using a lot of EQ. Using ported enclosures you have to be careful to make sure the cones won't ever exceed xmax, so plot cone displacement against frequency for some output level if you have the handy-dandy software available. Even then, you'll probably need a high-pass filter or the cone(s) might be uncontrolled (unloaded) really low, where my sealed system is still putting out something (with EQ boost). Just one man's prejudices; can't really make any recommendations without knowing yours too.

Sounds like you already know what you want, which is the sound of a 160 L. box shrunk down to 80 liters via isobaric or a 53.3 liter trisobaric? The bigger the original box the more the cubic volume savings isobaric (or trisobaric) provides.

Diminishing returns vs. cost and efficiency as you go from isobaric to trisobaric to quadsobaric etc. I would have thought that for 4 drivers 2 cabinets with 2 drivers in each would seem like a natural choice.

You have some big class-d switching-mode amps?
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Old 12th October 2011, 03:38 AM   #8
GM is offline GM  United States
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Quote:
Originally Posted by ODougbo View Post
Can any of the Isobaric lovers suggest a box size/tuning frequency using 3 - 831857?
Well, a T/S max flat alignment would be ~105.6 L net tuned to ~20 Hz, but requires a TL length vent unless stuffed to the point of might as well seal it up, so a folded, inverse TQWT is the way to do it.

GM
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Old 12th October 2011, 02:18 PM   #9
ODougbo is offline ODougbo  United States
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Originally Posted by cyclecamper View Post
Sounds like you want flat response. I can't get Bjorno's thumbnails readable. I don't really care about flat response, just so it's smooth, since I have decent EQ available, decent power available, and all those voice coils can collectively dissipate the power associated with using a lot of EQ. Using ported enclosures you have to be careful to make sure the cones won't ever exceed xmax, so plot cone displacement against frequency for some output level if you have the handy-dandy software available. Even then, you'll probably need a high-pass filter or the cone(s) might be uncontrolled (unloaded) really low, where my sealed system is still putting out something (with EQ boost). Just one man's prejudices; can't really make any recommendations without knowing yours too.

Sounds like you already know what you want, which is the sound of a 160 L. box shrunk down to 80 liters via isobaric or a 53.3 liter trisobaric? The bigger the original box the more the cubic volume savings isobaric (or trisobaric) provides.

Diminishing returns vs. cost and efficiency as you go from isobaric to trisobaric to quadsobaric etc. I would have thought that for 4 drivers 2 cabinets with 2 drivers in each would seem like a natural choice.

You have some big class-d switching-mode amps?
Yes , exactly, trisobaric: 1/3 of the 160L box, I would have to add back in the size of the tunnel, (1cf or more).
As far as flat, I tend to increase the lowest part of the curve, the bass is disappearing anyway.
Don’t have any D class amps, only large A/B, typical stereo amps, 200wpc.
I've been tempted to sell off the A/B, maybe a D class might be the way to go.
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Old 12th October 2011, 03:00 PM   #10
GM is offline GM  United States
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OK, then net Vb = the trisobaric driver's Fs doubling in a sealed cab is theoretically the most mechanical/acoustical compliance balanced or ~48.64 L/20 Hz based on the posted specs. Again, due to the long vent required, an inverse TQWT layout is the way to go.

GM
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