I’ve been practising getting the high octaves on a D whistle. High D, high E and high F# are fine. High G is a bit wobbly (sometime I get it clear and sometimes not), but damned if I can ever get a clear high A or high B. It seems like to get even close requires a LOT of breath pressure and it happens at the start but can’t be sustained. In addition, it’s LOUD!
Is it possible that some whistles fail once they reach this region or, as I suspect, it’s just a matter of technique and it really does require that much welly to get those notes? Are high A and high B ever played in a sustained manner in tunes or are they typically short sharp notes? I’m afraid listening to Mary Bergin’s tutor CD isn’t any help as it sounds effortless to her and although the pitch goes up, there’s really not that much increase in volume.
Access to the upper second octave varies from whistle to whistle, particularly across whistle brands. The design and voicing of the whistle has a a big effect on the way the top notes will play. So some whistles are harder, more finicky than others.
While there are common techniques that can be employed to hit the notes it is still a matter of sorting out what your whistle wants. Most players will mention starting the note by tonguing the note - sort of spitting at the note to start it off. Others will mention covering the bottom two or three holes to start the note off. But in the end it is a matter of familiarity with the whistle and time spent playing up there to become comfortable hitting those notes.
So why is that? Well high notes on a whistle require more velocity of the air jet coming off the windway to generate those notes. You have to blow harder. The highest notes will always be louder than the lower notes. It’s a matter of the physics - but the overall difference can be managed in voicing. If the sound mechanism is inefficient or the voicing heavily favors the first octave you will feel like you are blowing your brains out to hit those notes. The shape and position of the plug in relation to the blade has a lot to do with this. Voicing can change on some whistles as they get carried about. The Clarke original is a regular offender there. The position of the blade can be effected if you carry one about unprotected in say a backpack full of heavy books and such. Tonehole sizes have a bearing too. Larger toneholes (relatively) allow the high notes to speak easier.
Better whistles will have better dynamic balance and a smoother more predictable breath pressure curve across the octaves.