I've collected some info on 1 Oz AGEs ping frequencies some might find interesting.

[doug19]

These are from a quantity of 2008, 2004, 1993 and 2009 American Gold Eagles using the Pocket Pinger, a recorder, and software I wrote.  The numbers are in Hertz, First number is the center frequency, second number is the beat frequency. Sometimes called shimmer. It's why they don't have a pure tone. There is quite a variation in beat frequencies from coin to coin. Also, how much shimmer or beat you hear depends on where you tap the coin. In some places the same coin will produce almost no shimmer while in others it is quite distinct. However, the shimmer frequency is always the same for any given coin even while it's apparent level changes with tap location. The two frequencies combined can be used to identify a coin out of a large set of coins.

The main ping frequency varies by coin and year manufactured due to small changes the mint made. They range in this set from just below 4500 Hz to a bit above 4600 Hz.

AGE 2008
4551.3  12.9
4549.7  14.2
4548.2  22.5
4554.1  18.0
4553.2  23.2
4550.6  13.5
4550.9  12.6
4555.0  20.5
4554.7  13.4

AGE 2004
4549.9  31.4
4559.7  15.7
4556.0  10.2
4553.0  33.9
4559.4  33.3
4561.7  28.4
4562.9  27.6
4543.7  11.6
4556.3  24.0
4559.4  20.2
4544.1  26.6
4562.9  26.2
4556.9  33.2
4556.2  18.8
4556.6   7.7

AGE 1993
4612.1  26.9
4603.5  19.5
4614.3  23.1
4614.5  16.2
4605.2  27.9
4610.8  30.4
4607.3   5.1
4598.3   8.1
4601.6  14.1
4604.6   7.3
4612.0  22.2
4611.1  19.5
4611.5  17.1
4607.3  30.7
4606.1   7.3
4595.9  20.7
4598.6   8.6

AGE 2009
4498.8  13.4
4492.6  17.2
4504.3  20.2
4500.4  25.0
4501.6  27.3
4502.0  18.4
4503.7  22.4
4500.4  25.8
4498.5  24.7
4501.8  18.7
4502.2  28.7
4494.8  17.6
4505.0   9.1
4503.3  18.8
4502.0  26.3
4501.4  15.4
4505.2  13.9
4506.0  21.1
4506.2  23.0
4493.4  18.7