Circular plates (and circular membranes), like strings, vibrate in higher frequency modes, only not in even multiples of the fundamental frequency. See the link showing these same modes with a circular membrane. Keep in mind that the movement on a circular plate is very small compared to that on a membrane.
I have long thought that the fold at about mid radius of the Dobro cone and the webs at about mid radius of the spider bridge force the cone and spider to vibrate in the higher frequency 02 Mode, for improved treble response. I obtained a Quarterman QD2 cone without the mid radius fold and tested it against a standard Dobro cone. It is indeed mostly fundamental, missing many of the harmonics in the treble. I also removed the webs at about mid radius between the legs of a spider bridge, and tested it against a standard spider. The harmonics on the first two strings were missing. So, both the mid radius fold in the cone and the mid radius webs in the spider bridge contribute to the unique Dobro sound.
https://youtu.be/QksHbCwYngw?si=V8IO23wngy8uX5Q4
Edited by - SamCy on 11/01/2024 22:31:04
Hello,
Unfortunately, the YouTube video was for the tone resonance of a banjo head as different frequencies were subjected to it. I remember this video on Banjo Hangout. I doubt a spun cone would flex that much.
Thank you for sharing your findings. I went to a Beard Legend Cone in my OMI. I liked the improved tone it gave.
From the above post:
"Keep in mind that the movement on a circular plate is very small compared to that on a membrane."
Here is a demonstration with a circular plate, driven at the center and the outer edge free. See the sand settle in the circular nodes at the resonant frequencies.
