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Jaycar 12 inch Double Magnet subwoofer

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

Single coil drivenBoth coils driven in series
Z - Nominal Impedance4 ohm8 ohm
Pe - Power Handling150W 250W
SPL - Sensitivity85.5 dB/watt@1m88.5 dB/watt@1m
Re - Voice coil resistance3.7 ohm7.2 ohm
Fs - Resonant frequency24 hz24 hz
Qms - Mechanical Q3.583.75
Qes - Electrical Q0.480.236
Qts - Total Q0.4230.222
Vas - Equivalent volume75 litres75 litres
Xmax - Maximum excursion5.5 mm5.5 mm
Sd - Cone Area487 sq cm487 sq cm
EBP - Efficiency Bandwidth Product50 - Best sealed102 - Best 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

Box size Tuning frequency Port details
Jaycar design 45 litre sealed - single coil driven
My design 100 litre box - single coil driven 24hz Two 86mm ports 540mm long
My alternate design 100 litre box - both coils driven in series 24hz Two 96mm ports 680mm long



SPL graph
Jaycar design - driven by 150w into 4ohms using the 240watt amp
My design - driven by 150w into 4ohms using the 240watt amp
My design - driven by 240w into 8ohms using the 350watt amp. A little disappointing - I had hoped for at least 110dB

Cone excursion

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

Port air velocity

Velocity graph
All OK

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
See the Porting section for more detail on the design, construction and purchase of flared ports.


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