Audio loudspeakers usually rely on resonance to get more strength, mainly in low-frequency range.

We are so used to them that it is what sounds normal to us. But is the enclosure always needed? Actually not.

If we get rid of the resonant box we loose its help but get clarity. Less power but less sound from the box.

We built a pair of such open-frame things.


They use speed instead of pressure and need a lot of available excursion to be able to move enough air. Special cones (but from standard, commercially available ranges).

Another side-effect is you loose low-range and it must be compensated by a low-boost filter (6dB/octave).

These speakers are fed by dual-amplifiers (separate channels for woofer and tweeter) and the cross-overs are at line-level. Advantage: you can use software for cross-overs, cone equalization, and maybe room equalization all in one.

Note: open frame speakers work on air speed, their interaction with the room is different. Usually they sound better far from back wall.

You can try it yourself: two cheap cones, one 20 mm wood sheet, not too big (cut it to roughly follow cones’ contours). Build just one. Use a stereo amplifier to feed the cones (mono). Use a software equalizer to get a flat response and feel how they sound different.