[Harp-L] nail polish, embossing, etc.

[Rick Epping]

Hi Vern, Hi Sebastien,

Sorry for the delay in responding. Vern, certainly the back third of the
reed undergoes very little movement compared to the rest of the
reed.  However, the degree of reed movement is irrelevant to the amount of
air leakage that can occur around the sides of the reed when the reed
closes the slot, and air leakage can occur just as much from around the
back of the reed as from the front. Of course, one can go too far in
closing the gap, potentially leading to some of the problems you
anticipate.  The increase in energy in the high overtones, however, can be
quite perceptible, and is something one takes into consideration when
deciding how closely to emboss.

On the subject of the high overtones, there is an interesting effect
exploited in accordions of the cassotto, or tone chamber variety.  If a
reed is played within a restricted space, energy is transferred from the
higher overtones, or partials, to the lower partials.  The result is more
volume in the low midrange for a warmer tone.  This same effect occurs when
one cups a harmonica with one’s hands.  If you make a recording of one note
on your harmonica starting un-cupped followed by cupped, then plot the
spectrum of a sample of each, you will see that not only has the amplitude
of the higher partials decreased in the cupped sample, but that the
amplitude of the lower partials has increased – even though the sound of
the cupped sample was blocked by the closed hands!

There is another aspect of embossing to consider besides its effect of
reducing the gap between the reed and slot.  Embossing reduces the gap by
creating a thin burr along the upper edge of the reed slot, which may have
a similar effect to that of reed chamfering (see my article on chamfering
here
<https://docs.google.com/document/d/1hHeMSL1Pt3MV2U9HWGoPBCYicfukRP6W09CpfVssinU/edit>).
A
similar design is used in a Bavarian-made jaw harp that William Galison
gave me some years ago.  The edges of the frame facing the reed are
scalloped, leaving them sharp and knife-like.  A thin or sharp edge on the
reed slot as well as on the reed tongue, both of which shorten the moment
that a reed cuts off airflow through its slot, is used both in accordions
and jaw harps to improve response and reinforce higher partials. Accordion
and concertina reed slots are often noticeably tapered, with their narrow,
upper surfaces milled after stamping to give them a straight, sharp
edge.  Some modern production harmonica reedplates have slots that are
nearly parallel, with sharp edges on both sides.  Slots on older production
reedplates are slightly tapered; wider on the entrance side facing the
stamping tool, with a rounded edge caused by the tool striking the
reedplate blank, and narrower on the exit side, with a sharp edge.  Reeds
were always attached to the exit side of the reed slot.  This sharp edged,
tapered design of the reed slot once again can improve reed response, and
is not unlike a harmonica reed slot that has been embossed.

Sebastien, I’m glad you’re happy with your current production
Hohners.  It’s true that a harmonica that is made with a close reed-to-slot
tolerance has less need of embossing than that of some older production
instruments.  However, that is not to say that they might be further
improved by at least some embossing, which will add that sharp burr to the
reed slot edge, as described above.

Regarding the suggestion someone made to use Brendan’s nail polish method
around the entire reed.  As Vern pointed out, the back third or so of a
reed tongue undergoes very little movement during playing, so will not
really benefit from the effect of a sharp edged burr on the reed slot edge,
but only from the reduction of the gap.  So the nail polish method should
work fine there.  The rest of the reed, however, undergoes most of the
movement during playing and benefits from a thin, sharp edge to the reed
slot.  Nail polish here would only be detrimental.

Best regards,

Rick