Although TwelveSouth has positioned it as an accessory that turns a MacBook, MacBook Pro and MacBook Air into a portable sound system, I've used it with a new 27-inch iMac, as well as a 13-inch MacBook. The BassJump works well with both, making the bass, well, jump.

The laptop's speakers are still tinny, but less so. And the speakers in the new iMacs -- much improved over their predecessors -- sound substantially better when paired with the BassJump. The TwelveSouth won't make the built-in speakers on any Mac seismic or room-shaking, but it delivers bigger, fuller sound and more rumble than you'd expect.

The BassJump software also serves up visual feedback in the form of two glowing, old-school analog VU-meters. A working mini VU-meter is placed in the Menu Bar for quick access to settings. Finally, the software allows you to customize the sound for your style of music: rock, pop, R&B, etc.

The portable subwoofer's sound and power comes from one single USB connection. Proprietary software -- which must be downloaded from TwelveSouth's web site -- blends the sound output of the BassJump subwoofer with the output of built-in Mac speakers for enhanced sound performance. You'll certainly notice a difference when listening to music, video games, streaming videos and Internet radio.

Is it for you? If you're constantly on the road with your laptop, yes (the BassJump comes with a travel case). If you sometimes use your iMac as your stereo, gaming system, TV or movie viewer, yes. If you use your iMac for hours at a time for any of these purposes (as I do), you're still better off investing in some high-end speakers.

Macsimum rating: 8 out of 10