Held Bends [A `bit' long!] HarpL Archives

Other web Sites
Harmonica Blues Harmonica Amps
Harmonica Links Harmonica Pages

• Archives Home

• Years
· 1992 · 1993 · 1994 · 1995 · 1996 · 1997	· 1998 · 1999 · 2000 · 2001 · 2002 · 2003

Ebay Searches:

Amps:
Microphones:
Effects:
Harmonicas and Gear:
Harmonica Music and Instruction:

Harp-L Archives

[Previous Message] [Next Message]
[Next in Thread]
[Start of Thread] [End of Thread]

From: Bobbie Giordano
Date: Wed, 14 Jan 1998 05:31:15 -0500 (EST)
Subject: Held Bends [A `bit' long!]

Sorry, Harp-L.... Got a tad carried away....
I'll try not to write anymore for a few days!! :)

Douglas Tate asked Mike Curtis about sustaining bent notes. It seemed to
me he was wondering what are the dynamics involved that maintain a bent
note, and how and why are they different from those we employ when just
sounding a note by activating a harmonica reed with normal breath?

As he said...

> >....if a bend / overblow etc is achievable by a mouth position, then
> >why is it not sustainable?? Or is it bcause some notes are only
> >obtainable during a dynamic shift between positions

To this, I felt Mike Will was coming close to my theories on the subject
when he stated:

> Certain bends on a diatonic are relatively unstable... and there is more
> to getting the note than mouth position... sometimes the note fights
> back a little...

Close, I said. :) He made reference that there is more to bending a note
than just mouth position, but even stronger, I feel that bent notes are NOT
as strongly affected by mouth positions at all; in fact, I have to disagree
with numerous accepted notions that ~certain~ mouth positions are even
necessary to produce bent notes in the first place. I suppose that sounds
rash to some, but I enjoy examining this phenomenon and have reached some
conclusions through experiments and study that have molded my thinking on
this issue.

I will say that many vocal tract manipulations are useful to aid in the
production of the best quality tones from all notes generated by vibrating
reeds, including bends and overbends. The shape of the various parts of
the vocal tract can surely affect the notes' resonance, loudness and
intensity by interacting with soundwave factors such as superposition and
constructive or destructive interference of the soundwaves, reflection,
absorption and harmonic overtones. These are elements of fashioning the
resonant cavity in which the notes sound their best...hopefully! But they
do not, IMO, "cause" the reeds to gyrate and speak.

The one major influence on the vibration of the reeds is the relatively
constant flow of air across them, by which tight eddies and currents of
turbulence are induced as they flex back and forth across and through the
slot in the reedplate. For each reed, according to its size, plasticity,
shape, and perhaps other factors such as material, there is a natural
frequency at which it responds best to passing air, and it may thereby be
stimulated into action, chopping the air, and sending forth a compression
wave, which may become audible with a strong enough air flow. What I do
believe is that this air flow can be altered in several ways which will
cause the reed to oscillate in uncharacteristic ways, resulting in pitch
changes. In a dual reed system, there is another reed sharing the chamber
with the reed that may also be so induced to vibrate at the same time.
And furthermore, the combined vibration of these two reeds would seem to
set up additional turbulence between them resulting in sympathetic vibra-
tion akin to, and perhaps in reality, a form of mechanical resonance. Play
a regular diatonic some time and check with a tuner as you dampen the less
involved reed in the hole you choose to play, and watch the pitch alter
before your very eyes. There is quite a bit of interaction.

This activity is what would be called a driven oscillation system, wherein
the driving force is the air flow, which when aimed correctly at the reed,
will cause the reed to move, until it snaps back and is moved again, etc...
setting up a turbulence, which, due to the reed's regular response of back
and forth to the air flow, has a particular frequency. This frequency can
be altered with changes in the air flow's intensity, direction to the reed,
air pressure, and maybe other factors. The reeds themselves have their own
natural frequencies, which when met by similar driving force frequencies,
begin to oscillate, and if the two types of frequencies equal each other,
the reed vibrates at maximum efficiency. These frequencies are called the
resonance frequencies of the system, but they refer to the match between the
natural frequencies of the reeds and the frequencies of the driving force,
the air flow.

Reeds, however, are of such a form that they possess numerous resonance
frequencies beyond their natural one, just as in bronze bells, guitar and
violin bodies, a car door, one's skull! And when a driving force can be
made to match these other frequencies [recalling that pitch is a measure of
soundwave frequency,] the reeds can be made to vibrate at different pitches
than their normal pitch. I believe these other pitches are however elusive
because they are located in different areas of the reeds, perhaps explaining
why the vibratory appearance of reeds as their notes are bent or overbent
have a different appearance from usual, aside from the usual look of opening
or closing reeds, that is.

This brings me to the fact that we DO alter our mouth positions when bending
notes. I do as well. But, it is my feeling that performing the dynamic
shifts of positions that perhaps Doug was referring to in order to cause and
maintain extended bent notes smoothly, in truth, is actually connected to
the unique manipulations of the air flow I mentioned, which, in turn, is the
real factor determining how the reed responds. One thing we all do to bend
a note is constrict some part of our vocal tract, whether for a blow bend or
draw bend. The lower bent notes sound better to most when the deepest parts
of the throat are constricted. On overbends, some of us learn them by
constricting near the front of the mouth, as also with blow bends. The wide
opening of the mouth and throat improves the resonant qualities of the air
cavities to match the lower notes, and we cup our harps with big, rounded
shaped hands to improve the sound and enhance the lower harmonics. Then we
do the opposite for higher notes. But these are enhancements, not causes of
the bent notes themselves. Yet, as enhancements, they involve creating the
best resonant environment for the note... sort of like finding the best room
in the house to experience one's singing voice or harp or CD/stereo. Some
areas augment the sound better than others.

The recent comparison to whistling and bending are examples of what I'm
saying here. Whistling is essentially making your mouth into a Helmholz
bottle, but there is no reed involved there. If you try whistling a note
and then while doing so bring a harp to your mouth to play a distinctly
different note, you will mainly notice that the harp reed begins and right
away the whistle note disappears... it can be done however, and you can see
that the whistle and reed play completely separately... one has really
nothing to do with the other. And that's for whistling in while drawing on
the harp, too. [I whistle both ways, partly to save breath and partly cuz
the draw whistle tends to be about a semitone higher and I can count on it
in moving from one note up or down - kinda cool... but I digress! sorry!]

My point is that the constrictions we use to initiate bends are altering the
air flow which alters the note. As you constrict the vocal tract somewhere,
you cause the air to speed up to maintain the same driving force of the air
flow. This also results in the Venturi effect, which means that as the
speed of a fluid [or air flow] increases the pressure drops in the area of
constriction, but, also, as you increase the velocity of the air flow, even
ever so slightly that you may not even notice it, the pressure in the vocal
tract drops in general. It is these changes [for the most part] in air
pressure and velocity of the air flow [driving force of the oscillating
system] which I believe has the primary impact on the change in frequency
[pitch] of the bending reed... different resonant frequencies between the
reed and the air flow are being matched.

As for why then overbends go up in pitch instead, I have some ideas on that
too but this is way too long already. Suffice it to say for now, the reeds
are opening not closing reeds, and after all, everytime you do regular bends
in dual reed systems, you're also overbending a little too! But for now, I
just wanted to try to make a distinction as I think of it between "cause and
effect"... and I think I have some proof, as well. :)

In a couple weeks, I'll be heading to LA to meet and greet a slew of harpers
and related folks, as will Douglas, primarily with the intent to introduce
some new people to a few Rennys. But.... I will also bring along a little
demonstration I worked up, and with it, maybe a chance for others to test
and see for themselves that things may not always work the way we assume
they do. It's a deceptively simple experiment, but I find it intriguing.
Hope to see a number of you H-Lers there! Maybe at NAMM, in fact! [This is
how I make sure Vern will be there! heehee!!!]

Harp on, y'all!!

__________________________________________________ _-/==============\-_
:::BOBBIE:::::::::::::::::::::::::::::::::::::::: |##HARP SPOKEN HERE##|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~================~~