[Harp-L] Nail polish and bubbles

[Rick Epping]

I don’t think there’s really any question that more air leaks through the
offset of the opposing, or opening reed than through the back third of the
primary, or closing reed.  It seems obvious to me and Vern’s bubble test
only confirms it. However, it also seems to me that more is at issue here
than simply how much air is leaking into or out of the reed cell while a
reed is playing.

Free reeds produce sound in a manner similar to that of a pneumatic siren,
by repeatedly interrupting an airflow, creating alternating rarified and
compressed pulses of air.  The more effective a reed is in rapidly and
completely cutting off the airflow that passes through its slot, the more
defined are these air pulses and the better the reed will perform.  Air
leakage around the opposing reed will affect airflow within the reed cell
but not perhaps the air pulses exiting the slot of the primary reed.  A
harmonica reed, when properly voiced, enters its slot along its entire
length at the same moment, causing a rapid interruption of
airflow.  Sealing the gap at the back of a reed should help to achieve a
more complete interruption of airflow through the primary reed's slot.
Conversely, a reed with a curvature such that the middle of the reed passes
through the slot before the tip does, or vice versa, will have a relatively
poor signal-to-noise ratio – the noise being that breathy sound that
accompanies a badly adjusted harmonica.  Because the airflow is never
completely and/or is not rapidly interrupted, the reed will perform poorly
in terms of tone, response, bending and overblowing.

I play regularly with an uilleann piper and we often discuss issues with
our reeds.   A pipe chanter uses a double reed made of cane, similar to an
oboe reed. The two slips of cane in this reed are slightly convex laterally
so that, while the two long sides of each slip lie flush against the other,
held together by the winding and by the bridle, the ends of the slips are
bowed apart to allow air to pass between them and initiate vibration,
similar to the offset of a harmonica reed.  The bridle, a small loop of
wire that goes around these slips, can be adjusted to increase or decrease
the amount of offset between them.  Sometimes the slips can warp
longitudinally, creating a gap somewhere along their long sides, rendering
the reed virtually unplayable. A gap in this location corresponds somewhat
to the gap under discussion at the back of a harmonica reed, though the
problem is much more serious in a chanter reed, perhaps because the one
reed must produce all the notes in the chanter.  I mention pipe reeds just
to show how important it is that when a reed closes, whether it's a free
reed in its slot or a beating reed against a surface, that the airflow
should be stopped as completely as possible.

I haven’t yet tried Brendan’s new method of sealing the gap at the back of
a reed, but it makes good sense to me and I look forward to giving it a go.

Best,

Rick