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The Sw10 is a passive subwoofer.  The woofer is a 10" Blaupunkt unit.  As might be expected, it is better suited to the automotive environment than a home theater.  The enclosure is a single ported banpass design.  Bandpass enclosures aren't necessarily more difficult to build than a ported enclosure, but special care must be taken to ensure that ALL joints are sealed.  After slapping the box together, I fired it up only to be highly disappointed by an incredible amount of whistling.  The problem turned out to be that air was rushing through the wire holes in the terminal.  A little silicone took care of that.  The enclosure only has a little over .3 cuft. of internal volume, which isn't much for a 10" woofer.  Combined with the woofers relatively high fs of 40 Hz, one would expect pretty miserable performance.  Herein lies the secret of the bandpass enclosure.  By manipulating the volumes and tuning of the enclosure, the output response can be altered quite drastically.  The unfortunate side to this is that efficiency takes a big hit.  This would lead one to believe that a 1000W amp would be necessary to get good results.  For some reason this isn't the case.  Under normal listening conditions, a puny amp will suffice.  I powered this sub with a 24 watt tube amp for a while, and could overpower the rest of my system with ease.  I would suspect that a good quality (true) 50W sub amp would give great results.

This sub design should really only be used for low bass.  By that I mean below about 70 Hz.  Bandpass designs aren't known for their quick attack, rather their incredible rumble.  This sub compliments any speaker that can handle bass down to around 50 or 60 Hz.  Teamed with the inductor, it doesn't produce sound any higher than about 125 Hz.  While not particularly accurate, it recreates the rumble of thunder or the impact of an explosion superbly (especially when placed right behind the couch).  Probably the best use for this sub is in a car.  With is small footprint, it fits in about anything (except behind the seat in your truck).  Because of the bass boost experienced in about every car, you will get even lower bass response.

Parts List
$ each
1 10" Blaupunkt paper cone woofer, foam surround, 150W
1 4.25 mH inductor
1 Terminal
1 3" or larger port (4" recommended)
1 Misc. (shipping, cabinet materials, etc.)