12 inch Double Magnet subwoofer

Jaycar Part no: 2228 - Cost $279aus (5th May 2005)

Single coil driven Both coils driven in series
Znom Nominal Impedance 4ohm 8 ohm
Pmax Power Handling 150watts 250watts
SPL Sensitivity 85.5dB/watt@1m 88.5dB/watt@1m
Re Voice coil resistance 3.7ohm 7.2ohm
Fs Resonant frequency 24hz 24hz
Qms Mechanical Q 3.58 3.75
Qes Electrical Q 0.48 0.236
Qts Total Q 0.423 0.222
Vas Equivalent volume 75 litre 75 litre
Xmax Maximum excursion 5.5mm one-way 5.5mm
Sd Cone Area 487 sq cm

487 sq cm
EBP Efficiency Bandwidth Product 50 - sealed 102 - Best in ported

 

Here is my parameter file for this driver ( single coil driven ) for WinISD Pro ver 0.50a7

Here is my parameter file for this driver ( two series coils driven ) for WinISD Pro ver 0.50a7

They also list specs for a parallel connection, which I have omitted because the resulting 2ohm impedance is too low for their Home Theatre plate amps.

Suggested designs

 
Jaycar Design

45 litre sealed - single coil driven
My Design

100 litre box - single coil driven

 tuning freq 24hz Two 86mm ports 540mm long
My alternate design 100 litre box - both coils driven in series tuning freq 24hz Two 96mm ports 680mm long

Jaycar only gives a sealed box example

SPL

Jaycar design in red, driven by 150w into 4ohms using the 240watt amp

mine in blue driven by 150w into 4ohms using the 240watt amp

mine in green driven by 240w into 8ohms using the 350watt amp A little disappointing - I had hoped for at least 110dB

 

Cone excursion

Sealed unit has no problem. Vented unit can't be tuned lower than about 24hz without excursion becoming a problem. Starts to run into trouble below 18hz

 

Port air velocity.

Sealed unit has no port and is not shown.

Port flares would be required - see the note at the bottom of this page

 

 

Running the 2nd coil in the vented design gives a benefit in extension but no extra SPL and requires a larger amp. Some more SPL is available but only by going to a much larger box (400l)

 

Port Flares - calculated with Flare-it

For the dual 86mm port design:

I would recommend 15mm flares. If you have a full size router, you can use a 19mm rollover bit for routed flares. If you have a small router, you could get away with 13mm flares.

 

For the dual 96mm port design:

Firstly, the ports could be changed to 103mm diameter. This utilises commonly available pipe. The length becomes 790mm, and the peak velocity drops from 11m/sec to 9.5m/sec.

This would require 11mm flares, so a 13mm rollover bit for routed flares would be perfect

 

For either design:

You could use heat molded flares in 20mm or 25mm radius.

The intakes should be fitted with a donut ring . If you are using a heat molded flare, you could do a one-piece design with a 20mm flare on the inlet

Depending on the flaring options, you'll need to adjust the physical length so that the effective length is as shown above. The port flares page has a section on calculating effective length as well as some information on availability of commercial flares.

 
 

Last update to this page 10th December 2006

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