However, the lack of direct control of the reed of a windcapped instrument renders these higher notes extremely difficult to access. Thus the normal range is limited to the simple fundamental sounds produced by successive opening of the holes giving a range of an octave and one note. Many larger surviving instruments have auxiliary holes that extend the range downwards to just over an octave. On modern reconstructions additional keys are provided to extend the range upwards by one to three notes. And there is some evidence to suggest that crumhorns were sometimes played without the windcap, possibly to facilitate the production of higher notes.
Crumhorns have a characteristically sharp attack which is very effective in an ensemble.
Depending on how their reeds are voiced, they range in tone from a gentle, somewhat nasal humming of a bumble-bee to a rich, resonant buzzing. The curve is decorative only, having nothing to do with the sound. The curved bell section of many surviving instrument is hollowed out to form a more or less conical foot, which has the effect of raising the volume. When the reed is blown through, it vibrates, causing a standing wave to develop in the bore of the crumhorn. Pitch is governed not only by the length of the pipe down to the open finger holes, but also by breath pressure, so that the crumhorns are played at a fixed dynamic level.