subIt may look like some weird coal-powered throwback to the industrial revolution, but you won’t see nasty black smoke coming out of this chimney. What it emits is lots and lots of very low bass. Yep, this is a subwoofer, but it’s a sub with a difference.

For a start you bury it in the garden with nothing but the smokestack – maybe I should call it a periscope – visible above ground. Crank it up and add in a couple of decent regular outdoor speakers and what you have is serious music alfresco, great for dancing.

Now outdoor speakers come in various shapes and sizes but the problem with subwoofers is that to go seriously low they have to grow seriously large – there’s no beating the laws of physics. The usual approach is to disguise them as other things. So there are subs that look like great big mushrooms that people can sit on, especially if they enjoy a vibrating seat, and there are subs disguised as rocks, except it’s a pretty crook disguise because how many rocks have a rather obvious grille at the front?

This one is a sub you bury. It’s made by Tru Audio, an American company that specialises in outdoor speakers – mostly rock look-a-likes but hey a change is as a good as a holiday.

Inside that fibre-reinforced plastic box there’s a 25 cm long-throw polypropylene driver, but unlike most subs there’s no amplifier, so power will have to come from an external amplifier located wherever you happen to put it. The advantage of this is that the sub doesn’t need a power supply, it only needs the speaker cable from the amplifier, so you won’t have to get electricity to it.

It can be driven by any amplifier with rated power output between 20 and 250 watts but the manufacturer of course recommends its own TRUS350 single-channel 250-watt amp ($1145). Once pumping the sub goes as low as 30 Hertz, where deep bass is as much felt as heard, handing over to the higher-range speakers at 180 Hertz.

You’ll need a substantial hole. It’s 48 cm long, 42 cm wide and with the periscope, 73 cm high. You don’t realise how large such a hole is until you start digging. You’ll also need $1995.

The cap topping the periscope is a soft curve shape that disperses that sound evenly and horizontally, not straight back into the ground like some outdoor subs do.

The thing about outdoor speakers is that they have to be more than just weatherproof. They have to stand up to sprinklers, hoses, spiders, worms, sunshine, ambitious roots, insects, mould, cricket balls, dogs with full bladders, birds relieving themselves, whippersnippers and, the biggest problem of the lot, whippersnappers. Children can be hell on speakers, but the Sub Terrain is a reassuringly strong piece of kit that can take a fair old hiding before anything goes wrong.

That’s the interesting thing about outdoor speakers; they’re built so tough they often outlive plenty of cosseted indoor speakers.

Published February 2014