Hi Duffy,
Been messing about.
1. Have tried both options (removed resistor and cap in various combinations) but neither appeared to have an appreciable difference. The speed is difficult to measure but if you interrupt the beam by moving an object slower than about 2mm per sec then she fails to make a sound.
2. Got me a speaker, 4Ω I know you said 8Ω but this is all I have to hand at present. Nice and loud but it stays on all the time and has an annoying growl. I can set the pot to a point where the speaker is quiet but the minute the beam is broken once the speaker stays on.
3. As the speaker was noisy thought I would keep on experimenting with the piezzo buzzer. Thought that perhaps the cap C1 on your schematic may not be needed with the piezzo buzzer so I bypassed it coonecting the buzzer directly to Pin 5 of the LM386 and ground. Progress, now it does not matter how slowly the wheel turns as every hole sounds the buzzer.
The buzzer also it turns out, totally coincidental, has a sound that when the wheel is spinning rapidly it emulates the drag of a reel very nicely indeed.
The only problem with the buzzer is that when the wheel is turning slowly the buzzer volume is low. It is almost as if the velocity at which the beam is broken has some outcome on the volume. There are two volumes, soft and loud.
I blew the original LM386N-1, I had a different LM386 to hand which responds nowhere like the original component. The latest LM386 is nowhere as "clean". Where I was getting no signal when the beam was interrupted I now get a soft feedback squeal?
Any thoughts?
Cheers
Andrew