Just like CD/DVD players, amps, and preamps, speakers often look nice on the outside but have low-quality parts inside that limit the sound quality. (Nobody looks in there anyway, right?)

The crossover (shown at the bottom of the picture at left) is a circuit board inside the speaker that directs high frequencies to the tweeter, middle frequencies to the midrange speaker, and low frequencies to the woofer.

Crossovers can often sound dramatically better with higher quality capacitors, resistors, and inductors. For example, replacing cheap electrolytic capacitors with polypropylene ones can greatly improve tweeter and midrange performance. Air-core inductors sound better than iron-core ones. Internal wiring can be upgraded, too (often it's no better than lampcord).

Mechanically, speaker cabinets can vibrate too much, muddying the sound. Damping the speaker cabinet with acoustically dead materials can improve clarity and accuracy.

Speaker drivers (tweeter, midrange, and woofer) can often benefit from similar damping material on stamped-steel driver baskets and magnet housings.

Not all speakers lend themselves to these modifications — some are made in such a way that getting inside the box is virtually impossible. However, if yours permit upgrading, you could be getting substantially better sound from the same boxes, at far less cost than buying new speakers. Check pricing here.

photo courtesy Thiel Inc.