If, for some strange reason, you've been kept under a rock, and don't know what a subwoofer is, then I strongly recommend

For everyone else, you will identify a subwoofer as a big, bad-ass bass speaker that makes your car shudder and rattles your floorboards. For those who are into music with a bit of 'doof doof', a subwoofer is much more a necessity than it is a mere luxury.

A typical subwoofer driver - in this case a 'Lanzar Vector' unit

Appropriately named 'Earthquake' driver

I decided I was 'bad-ass' enough to own a large subwoofer unit. The first step was to find the central component - a driver.

After drooling over some $200 'Lightning' brand drivers, I settled for an 12 inch 'Earthquake' brand driver from the USA for $50. This particular unit was capable of 200W RMS power.

Of course, for any loudspeaker to work, one needs an amplifier. In the case of a subwoofer, an additional piece of circuitry to filter out the high frequencies is required so that only low frequencies are fed into the driver.

If this is not done, serious damage to the driver is easily possible because the mechanism is simply not designed for high frequency vibration.

The low pass filter I decided to use was directly from a kit sourced from Dick Smith Electronics, and afforded the extra ability to change the cut-off frequency, adjust the roll-off curve etc.

Low pass filter/processor unit

40W RMS dual channel amplifier unit

I realised that if I was to put the subwoofer in my room, 200W was going to be complete overkill (probably knock over the walls). Thus I decided on an amplifier with an output of about 40W RMS. This was again purchased in kit form - it just saves all the trouble of circuitry design, particularly difficult for power amplifiers.

This is a picture of an extremely messy installation inside the sub box... this picture was taken during a repair operation in 2006 when it mysteriously failed. Upon opening the box and seeing how ruthless I was in mounting everything made me wonder I ever expected this to work for more than a few months.

Anyway it turns out the repair operation was successful - the problems due to loose connections (hardly a surprise).

Completed subwoofer unit!

All loudspeakers need some sort of box to enhance the desired frequencies. Generally speaking, the lower the frequency output, the larger the required enclosure.

There are online calculators which assist the layman in working out the required dimensions of a box based on the sound output requirements and the driver attributes. Of course, if you like to get technical there is always the odd sound engineering textbook around!

After a while I decided that the wood I had used for the enclosure looked slightly tacky at the very least.

As a result, a rejuvenated subwoofer was born, with a coat of glossy silver paint and aesthetic adjustments to the equalizer panel.

Rejuvenated subwoofer unit (coke can for scale)

Here is a view of the driver behind black acoustic screening - the final touch added to provide a bit of dust/insect protection.

Notice the two vent holes in the bottom. As this was an open-box design, these vent holes were required to stop the box from exploding when the sound pressure is too high.





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