RE: XB-40 in C: high notes squeaking?

["Rick Epping" <REpping@xxxxxxxxxxxxx>]

- -----Original Message-----
From: "Laurent Vigouroux" <laurent.vigouroux@xxxxxxxxxxx>
To: "Harp-L" < >; "harponline Timler" mail@xxxxxxxxxxxxx
Subject: Re: XB-40 in C: high notes squeaking?

> Is it only a technique problem or can I do some tweaking (gapping?) to

> improve the response?

The range of notes easily obtainable on an XB-40 is determined at its
upper limit by the resonant frequency of the highest chambers relative
to the frequency of the reeds occupying those chambers.  The smaller the
air space within a reed chamber, the higher its resonant frequency will
be and the higher pitched will be the reed that can be effectively
played there.  The chambers in the highest holes of the XB-40 have been
designed as small as possible given the clearance requirements for the
reeds and valves as well as the requirements of the injection molding
process by which the comb is manufactured.  

Difficulty begins to arise when the resonant frequency of a reed exceeds
that of its chamber and the lower frequency of the chamber begins to
pull the oscillating frequency of the reed downward in a phenomenon
known as mode locking or frequency pulling.  The greater the disparity
between the frequency of a reed and the lower frequency of its chamber,
the more difficulty there will be in obtaining good performance.  It's
for this reason that the key range for the XB-40, like that of the
chromatics, is set lower than that of the standard, single-reed
diatonics (C/C# is the highest chromatic key while high G is the highest
diatonic key).  The highest reed in a Hohner Richter 10-hole model, the
g4 reed from hole 10 of a high G harp, would play flat and with some
difficulty if set over a 270 or 280 chromatic's highest chamber, which
is larger and has a lower resonant frequency than that of the hole 10
Richter chamber.  The difficulty would be greater still were that same
reed set over the highest chamber of an XB-40, which is actually a
double chamber - the inner valve chamber combined with either the upper
blow reed chamber or the lower draw reed chamber, depending on the
direction of airflow.  While hole 10 in the lower XB-40 keys plays
easily, the notes in the highest keys, where the resonant frequency of
the reeds is well above that of the hole 10 chamber, become increasingly
difficult.  

Technique can to some extent minimize this problem.  For high notes on
harmonicas with small reed chambers, the player's tongue can be
positioned both forward in the mouth to create a resonant frequency in
the reed chamber/mouth cavity matching that of the reed being played or
down and back in the mouth to avail of the higher partials of the full
vocal tract.  On the higher keys of the XB-40 however, the player might
not be able to position the tongue forward enough to reach the resonant
frequency of the reed being played, resulting in an unintentional bend
or a choked note.  If the tongue is instead positioned back in the mouth
to create a fundamental resonant frequency one octave lower than that of
the reed, the second partial of this larger mouth cavity will then match
that of the reed and allow it to play.  From this position the tongue
can be shifted upward and forward for a bend.  Using this technique, the
notes in hole 10 on an XB-40 in the key of C are playable though still
somewhat stiff.  

In short, while the notes in hole 10 on the lower keys are quite
playable they are unavoidably less so for the key of C and progress
effectively beyond the practical range in the highest keys of Db, D and
Eb.  

Best regards,

Rick Epping
Hohner, Inc.