Is this the start of an overblow?
I've noticed that the high end on my Manji is very touchy to proper embouchure technique. Sometimes while going through David's "Rollin' Rhumba" lesson, the sound on the high end is very squeally on the blow side. Adjusting my embouchure (opening up and dropping my tongue) fixes the problem. I've noticed I can get this to happen on my Special 20s as well - although it is a little harder to do.
I can purposely make the sound happen. Sometimes it is preceded by a metallic popping sound.
My questions:
1. Will purposely (or accidentally) doing this harm the reeds? It doesn't sound healthy, especially with the reeds popping.
2. Is this the start of an overblow?
It kind of makes a crinkly ping or pop, as though the reed is bending the wrong way and popping backward through the slot. I guess that's the best way I can describe it. This is usually accompanied by the squeal or ringing sound, but when the pop/ping occurs, the reed seems to stick and the sound stops (no sound at all happens then). I have quickly stopped doing it when this happened, as I'm concerned I might be bending the reed to the point of breakage.
Actually, if the reed bends backwards it bends *away* from the slot. Which is what happens during overblows and with the responder reed during a regular bend (such as with Blow 4 reed when you are bending Draw 4). But that by itself will not cause a popping sound.
The pinging crinkly sound makes me wonder if there is some small amount of contact between the reed and the edge of the slot. Suzuki warns that the reed slot tolerances on their new diatonics are extremely tight and that embossing could cause them to bind. Inserting a fine swage - lik the thin metal sheets from an antihteft tag as detailed in another post - might give you an idea of whether you have some amount of contact between reed edge and slot.
the squeal might be associated with close tolerances. But if you can get it to go away with a change in embouchure, then I'd cultivate that embouchure.
I'm pretty sure if you're playing a Manji you're bending too far. The Suzuki reeds will do that. When I played the Manji A it would make that squeal in the 2 draw bend if I was going too far. I might recommend getting a tuner and adjusting your tongue position until you hit the note. Good luck.
Squealing or ringing sounds are signs that you are giving a reed energy that it can't properly radiate as normal vibration. I've noticed that students who produce these sounds usually break reeds for awhile until they learn to eliminate those sounds.
I'm wondering what you mean by metallic popping. Can you describe it in greater detail?
As you noted, correcting your embouchure - which changes or neutralizes the resonant frequency of your oral cavity - will make these sounds go away. That's good for your technique, good for the sound you get, and good for the reeds.
As to the overblow question.
Overblows occur in Holes 1 through 6 on a standard-tuned 10-hole harp, so getting these sounds while blowing in Holes 7 through 10 are not, at least in those holes, the beginning of overblows. (In Holes 7 thru 10, you get overdraws.)
To work on overblows, you should first have a strong command of bending blow notes down in pitch in Holes 7 through 10. You can then apply what you've learned to getting overblows in Holes 6, 5, and 4. When you first try to apply the bending-down technique while exhaling in those holes, you may experience something like the following sequence:
1. the note bends down by a tiny amount
2. You hear no notes, just rushing air
3. You et squeals and complex noise as the reeds are thrown into a chaotic state
4. A clear single overblow note emerges.
In the third item above, you may experience squeals. These are byproducts of trying to focus your oral cavity resonance and air pressure until you find the right combination to sound the overblow note.