Affordable portable speakers once relied only on the strength of tiny, powered drivers to produce sound. Thankfully, passive radiators are now the norm—they don't receive direct power like the drivers but vibrate in concert with them to create a greater sense of bass. Although they won't make you think there's a subwoofer inside, passive radiators handle the lows quite well. You might notice that some speakers have tiny rubber feet on the bottom; those prevent the passive radiators from propelling the speaker across flat surfaces.

It seems like mono (single-driver) speakers are more popular than in the past, thanks to how effective passive radiators are compared with a second driver. We don't think this is too big a deal because you can't get much stereo separation a few feet away from a small speaker, even if it does have two drivers.

Manufacturers, of course, want to sell you multiple speakers, however, so they often offer the option to wirelessly set up a stereo pair with a second unit. The advantage here is obvious: If you connect two speakers to your phone (usually via an app), with each handling either the left or right channel, you suddenly get a wide stereo field. Of course, most of these speakers cost more than $50, so you might have to stretch your budget past $100 to do this. Alternatively, the Creative Pebble Pro satellites connect to each other via a physical wire for a wider soundstage.

The battery range for most portable speakers typically falls between 8 and 12 hours per charge. It's always good to keep in mind that whatever number the manufacturer lists is the best you should expect. If you play your music loudly, revise your expectations downward.

Several speakers also have a built-in USB port for charging mobile devices on the go. This is useful if you're away from home and your phone or tablet runs low on juice. Remember that charging other devices takes away power from the speaker itself. The batteries in these speakers are also usually much smaller than those in dedicated battery packs, which you should consider instead if you have frequent battery life worries.

Some indoor speakers require you to plug them into an outlet via an adapter for power. These models avoid the battery issue altogether, so they are ideal as stationary fixtures throughout your home.