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[ JBL T150 Subwoofer picture - front ]
JBL T150 Subwoofer - front
The subwoofers used in my car audio system are a pair of JBL T150 15inch subwoofers. This horrible graphic is supposed to represent the front of the picture, but I currently have no photos of the front. Below is a picture of the rear of one of the subs mid-way through installation.

JBL produce brilliant automotive and home / club speakers, some of the best of which are their subwoofers. These aren't the top of the range GTi model, and don't boast a thousand watts as the GTi's do. The are rated at 125 watts RMS and currently get wired to a 2 x 200 watt RMS amp, which has the gain turned down. I currently have the subwoofers mounted in an isobarik box in the back of the BMW being powered by the Annihilator HA400C amplifier, one of which is wired out-of-phase to produce a push-pull effect.

[ JBL T150 Subwoofer picture - rear ]
JBL T150 Subwoofer - rear
The box is 3 cubic feet with a sloping rear back constructed [ very solidly ] of 1inch and 0.75inch thick MDF. You can see the screws in the front of the box in this picture, spaced an inch above around all surfaces. This was combined with PVA wood glue and glass fibre matting around all internal edges to provide a completely solid and air tight sealed box.

The subwoofers are fed only a mono signal from the Phoenix Gold crossover to the amplifier which powers the sub. This is a must as minor differences in the left and right channels of the sound would reduce the sub's sound quality and possible damage them. The Annihilator could be bridged for the subwoofers and they could have been wired in series, but as this type of isobarik box needs one speaker wired out of phase, both channels of the amp are used, one for each speaker. The t/s parameters used to design the box are in the table below but as the speakers were both bought second hand, they're isn't a lot of manufacturers information about them.

[ technical specification ]
Features
Die cast precision machine aluminium frame 30 - 300hz Frequency response
15inch (380mm) woofer size 125watt RMS power handling
Mechanical Parameters Electrical Parameters
Fs = 32 hertz Qes = 0.419
Qms = 9.560 Re = 2.5 ohms
Vas = 7.700 cubic feet Le = 0.8 mH
Cms = 0.037 in/lb Z = 4.0 ohms
Mms = 4.184 oz. BL = 11.9 N/A
Rms = 5.501 lbs/sec Pe = 200.0 watts
Xmax = 0.280 in Qts = 0.401
Sd = 133.0 sq.in nO = 1.700%
Dia = 13.0 in Sens = 99.56 dB (2.83V)

All trademarks and copyrighted images / icons are acknowledged and accepted.
JBL   Phoenix Gold Corporation
Annihilator® [possibly Earthquake]   BMW

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