Re: [Harp-L] Re: Rick Epping: the Father of Embossing

[Vern <jevern@xxxxxxx>]

On Dec 28, 2012, at 9:36 AM, Rick Epping wrote:

> Hi Vern, David, Joe,
> 
> Vern, in answer to your questions,
> 
> Q. What is the best way to measure clearance?
> You might have some suggestions here!  I guess most embossers just learn to
> eyeball (with magnifying lenses) the amount of clearance that works best
> for them.

I have a 40x microscope with a reticle having .001" divisions.  That should work OK with a good backlight.

I don't emboss my chromatics because they seem to have more than enough high frequencies. I also assume that narrower clearances will make them more sensitive to obstructions. I made some spectrum analyses of about a dozen reeds and found that the 2x overtone was louder than the fundamental and the higher ones were also very strong.  

My digital hearing aids make a mess of harmonica tones because their sampling rate is too low for the higher overtones and aliasing occurs.  I have had the same problem with digital audio-effects processors.

> A. I studied reeds under the Hohner factory's CNC measuring microscope
> during the time we were working on specifications for new reedplate tooling
> and got something of a feel for the absolute values involved, but I can't
> say that it's all that necessary for good embossing.  I was also able to
> make rough measurements of clearance by measuring the projection of
> reedplates on the microfiche reader I had in my office.

I like your idea of a projector.     
> 
> Q. What is "compression" and how is it measured?  Is it the opposite of
> leakage?
> A. Correct - compression, as I understand it, is the opposite of leakage.
> But how best to measure it quantitatively?  The greater the compression,
> the less the breath pressure needed to make the reed play.

I have used a water manometer to measured the pressure under chromatic reeds on an air table.  I found that a gap that made the reed begin to speak at .5" of water pressure and not choke below about 12" was optimum. I usually think of normal playing at about 5" of water.  I'm guessing that an embossed reed would require as much pressure but less flow, making a lung-full of air last longer. I was not concerned with optimizing gaps for bending and overblowing.

Vern