Re: [Harp-L] An Over-Blurring Of Over-Bends And Over-Blows

["john" <jjthaden@xxxxxxxxx>]

Overblows and unvalved blow bends share something huge:  they both recruit the draw reed, 
causing it to be sounded by blown air -- by an air stream flowing in the opposite direction 
from the  usual.  In musicological terms, it is made to behave as an opening free reed (by 
pressure that would initially open the gap further.  Harp reeds normally behave as closing 
free reeds.).  Opening reed behavior occurs even in the absence of a second reed in a 
hole and it causes the reed to vibrate at a higher pitch than as a closing reed -- anywhere 
from a rather flat half-step higher, up to probably more than a major third higher, depending 
on embouchure.  

So what does distinguish overblows from unvalved blow bends?  It's the contribution of the
normal blow reed.  As a player adjusts embouchure and pressure, a blow reed tuned lower 
than the draw reed (Richter holes 1-6) may bend down a bit, but also will readily choke off, 
partially blocking its slot.  This allows pressure to increase into the slightly higher range 
that favors opening-reed vibration of the draw reed:  the overblow.

A blow reed tuned higher than the draw reed (Richter holes 7-10 plus MB 365 holes 11-14) 
also may bend down a bit under player control, but here, if it does, its new pitch is liable to
be supported by vibrations of the lower-pitched draw reed as it starts its opening-reed 
behavior.The two reeds are able to match their vibration rates, to resonate together.  This 
can happen over a wide range of pitches, from the normal blow-reed pitch, down to the 
lowest opening-reed pitch of the draw reed (a flat half-step above the normal draw-reed 
pitch). The smoothly controllable result is what we call bending.

If the blow reeds in a chamber is tuned considerably higher than the draw reed, then 
the bent blow reed pitch may not be able to be matched by the draw reed, regardless 
of resonance.  In that case, the blow reed will be more inclined to choke off completely.  
The note will then jump immediately down to the preferred pitch of the draw reed 
(while vibrating in opening-reed mode).  Some of you may have experienced this on 
the 10th hole of a 10-hole diatonic, which has a minor-third interval, but it is far more 
evident on holes 11-14 of the Marine Band 365, where intervals are even wider. The
behavior of these 'blow bends' can be a lot more "overblow-like" than bend-like: they
"pop" in instead of slide in.

Lots of harp performance issues become pretty clear if you keep in mind the two 
behaviors of isolated harmonica reeds: as closing and opening free reeds.  If you 
haven't tried, I think its pretty interesting to tape over one or the other of the two 
reeds in various holes and see what sounds you can produce with the isolated
reed (and under what conditions it chokes off).  This is a quick way to learn
over-blowing and overdrawing.

Regards,
John Thaden    



======= At 2008-08-16, 16:39:11 Brad Trainham wrote: =======
>So then..., it's really a curiosity of the architecture of that harp which
>makes the blow-bends yield the same result as what we'd expect from
>over-blows? 
> (At this point, a "Huh???" response would be entirely appropriate and
>wouldn't offend me in the least.)

>
> On Saturday, August 16, 15:50, David Payne wrote
>>  The E blow is the higher one, right? Assuming that, what you're doing
>> isn't an overblow, it's a blow bend like you said. The limit of the bend is
>> a half-step higher than the lower, opposing reed. In this case, you are 
>> blow bending to it's natural limit, a half step higher than the B reed, 
>> which is this C. 

>> Prior to that, Brad wrote:
>>>  On A Hohner Marine-Band 365, in the key of c..., we find 
>>> holes 11 through 14 giving us...
>>> Hole 11 - e-blow b-draw
>>> Hole 12 - g-blow d-draw
>>> Hole 13 c-blow f-draw
>>> And hole 14 - e-blow a-draw...
>>>
>>> My question... When I blow-bend hole 11, I get... 
>>> Consistently a c, which is a half-step higher than 
>>> the draw pitch.   This would meet the requirements 
>>> for the "over-blow' rule, but surely, this isn't a true 
>>> over-blow? I get the same results with holes 12 through 
>>> 14 on this harp, that is, what we would expect from an 
>>> over-blow, a pitch a half-step higher than the draw.