It’s not often that a group leaves the audience wondering exactly how they are making their own brand of racket, but a cappella all female quintet The Boxettes are rather a unique proposition. As soon as they hit the stage in a full to capacity Jazz Cafe equipped with naught but microphones and launch into "Hatty Hit the Rocks", necks are craned and heads are scratched in an effort to work where the beats, bass, and multilayered vocals could possibly all be coming from.

Much of the credit for this is due to current World Female Beatbox Champion Isabel 'Bellatrix' Ehresmann who underpins her band-mate’s more conventional singing with an awe-inspiring array of drum, bass line and scratching effects.

It is certainly a unique sound, all lush, complex harmonies and soulful leads with hip-hop, dubstep and R&B-inspired backing. And while this is not the first time that contemporary music has been created from voice alone - Björk’s Medúlla is almost entirely a patchwork of processed vocals as is Todd Rundgren A Cappella - The Boxettes are doing it live, and it is undeniably impressive.

They are certainly a talented bunch; flawlessly constructed harmonies and vocal techniques are all note, and beat, perfect. Song writing is not of such an exclusively high standard however. There are standout tracks, including signature song Free, but some of their set was rather more forgettable despite technical accomplishments and polish.

 This is perhaps a result of the inherent limitations (as stretched to breaking point as they are here) of the variety and depth of sound which five sets of vocal chords can possibly produce. The risk with any kind of self imposed limitation is that novelty supersedes musicality, and it was easy to wonder whether The Boxettes would benefit from some conventional instruments thrown into the mix now and again.

Not that the audience seemed to mind. The five piece are just plain fun live, requesting suggestions for a brief improvisation (which turned into a trip-hop-esque ditty on the joys of rioting), and pre-empting any accusations of backing track trickery with a tutorial on how to create your own rumbling bass lines (fart sounds are the secret apparently).

While it remains to be seen whether The Boxettes will move beyond the narrow confines of “best all-girl beat box and vocal group”, in the meantime, they are well worth checking out for a live experience as intriguing as it is enjoyable.