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Spectrum Analysis Of Ring Test Of 50% And 80% 1967 Coins

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United States
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 Posted 01/23/2011  10:19 pm Show Profile   Bookmark this topic Add samboyellowsub to your friends list Get a Link to this Message
I've read a lot about the ring test and that people say there is a distinguishable difference in the tone of a known 80% quarter or dime and a 50% quarter or dime. The usual comments are that the 80% will ring higher (not completely correct) and and have more sustain (also partially correct).

Here's the shake down. I did a sound frequency spectrum analysis of the drops of some pre 67 and then '68 - meaning there was no question of the content. Briefly, for those that are not familiar, a spectrum analysis plots the amplitude over the frequency range. What I found was that the higher silver content coins had resonant peaks that were from 1.5 to 1.8 kHz lower than the 50% coins. If the numbers were removed, the plots for each type of coin would look very similar, because they are the same shape object (a disc). Some peaks would be higher than others, but they'd mostly all be there. However, the difference in numbers between the two types of coin was stark. This makes a lot of sense since the speed of sound in copper is a lot higher than that in silver, meaning, the more copper in the coin, the higher resonance frequencies it would be able to support.

Looking at the plots I also noticed, that with the 50% silver/copper, the sharpest peaks (the ones we perceive the most clearly - the ones with highest signal/noise ratio) was on the higher side of the frequency spectrum, and it was at the 13.3 to 14.2 kHz range (mostly around 13.6 kHz) for quarters and even higher for dimes (17-18 kHz), a range that a large population will lose as they get older. That is why the 80% silver one seems to ring louder with more sustain - its sharpest and most distinct peak is at about the 11.5 to 12.4 kHz range (mostly around 12 kHz) and is more in the middle of the sound spectrum that humans hear.
Most people throughout their life (again, MOST people) will not experience as great a loss of hearing damage closer to the middle of the human hearing range. So that's why the silver ones sound sweeter - because we can hear it better! The frequencies that resonate in the 50% coins that are more in the range that we can hear the best are the lower ones that do not have as high of a signal to noise ratio, therefore they sound deader. I think that's because they get muddled up in the sound of the coin clashing into whatever you've dropped it on.

Anyway, I'm really excited about this. I'm including an example of each type of coin. Picture1 is of a 50% 1967 quarter and picture2 is of a 80% 1967 quarter. Even though each quarters frequency plot was unique in its own way and even varied about 7% for each type, it was not at all difficult to tell the difference, there was never one where I was wondering, is this one or the other? I did not do a formal scientific analysis of the data, these are just rough observations so far. But the differences between the two types of coins is different enough that an "eyeball" test can even make sense of the results.




Edited by samboyellowsub
01/24/2011 12:10 pm
Valued Member
United States
286 Posts
 Posted 01/23/2011  10:26 pm  Show Profile   Bookmark this reply Add northwestseeker to your friends list Get a Link to this Reply
WOW, Science! very interesting find, very cool!
Valued Member
United States
113 Posts
 Posted 01/23/2011  10:39 pm  Show Profile   Bookmark this reply Add samboyellowsub to your friends list Get a Link to this Reply
I like when science works! Another interesting observation was that of the $9.00 face value of 1967 coinage that I tested, $4.40 tested as 80% and $4.60 tested as 50% which is pretty much statistically congruent to what was minted in that year!
Valued Member
United States
113 Posts
 Posted 01/23/2011  10:42 pm  Show Profile   Bookmark this reply Add samboyellowsub to your friends list Get a Link to this Reply
Also, I'd like to note that I did this with free software called Audacity that I downloaded to my computer from the internet.
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 Posted 01/23/2011  11:08 pm  Show Profile   Bookmark this reply Add DBM to your friends list Get a Link to this Reply
VERY interesting,thank you
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Canada
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 Posted 01/23/2011  11:22 pm  Show Profile   Bookmark this reply Add TwoCentsWorth to your friends list Get a Link to this Reply
Yeah, great work here. Glad you are with us!

Thanks
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 Posted 01/23/2011  11:42 pm  Show Profile   Bookmark this reply Add Bowfin to your friends list Get a Link to this Reply
Very cool indeed.

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 Posted 01/23/2011  11:53 pm  Show Profile   Bookmark this reply Add ikandiggit to your friends list Get a Link to this Reply
Great work!
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Canada
386 Posts
 Posted 01/24/2011  06:58 am  Show Profile   Bookmark this reply Add 1945V to your friends list Get a Link to this Reply
Excellent work samboyellowsub !!

I was wondering if you could describe your physical setup.

What type of surface did you drop the coins on ?
What type of microphone did you use and what distance was it from the drop zone ?
Valued Member
United States
113 Posts
 Posted 01/24/2011  09:25 am  Show Profile   Bookmark this reply Add samboyellowsub to your friends list Get a Link to this Reply
1945V,
the physical setup was quite crude actually. I dropped the coins on my hardwood floor on which I rested my laptop. I thought a hardwood floor was just hard enough but wouldn't resonate itself and cause a lot of noise. I used my apple powerbook's built in microphone. I dropped the coins about 2 inches (5cm) from the microphone from a distance of 7 inches (18cm) for the quarters and about 10 inches (25cm) for the dimes. I tried to keep this pretty consistent but, out of curiosity every now and then with the same coin i'd try several different drops from different heights and distances from the mic and get the same results anyway :) Even when the coin dropped on its edge instead of its face, certain peaks would have different heights, but they'd all be in the same place. I figured, as long as the microphone was the same throughout, it would serve my purposes regardless of quality. Thanks for asking.
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 Posted 01/24/2011  12:20 pm  Show Profile   Bookmark this reply Add Wild Bill to your friends list Get a Link to this Reply
I think it's really cool when someone thinks outside the box, I found this drop test thing very interesting. Thanks for your time.
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 Posted 01/24/2011  12:27 pm  Show Profile   Bookmark this reply Add DVCollector to your friends list Get a Link to this Reply
Wow...that's a fascinating read!
It would be cool if others could repeat your results.
Valued Member
United States
113 Posts
 Posted 01/24/2011  2:01 pm  Show Profile   Bookmark this reply Add samboyellowsub to your friends list Get a Link to this Reply
DVCollector,
Its easy to do the test yourself. you just need any microphone and download the program Audacity from your favorite trusted download source. Its public domain or at least freeware. Just record the coin drop and highlight the sound like I have on the second track in the screen shot. and then up at the top click plot spectrum from the analyze menu. If you have more than one track there, you need to mute them before recording like I did, or those tracks will play while you record. if all the existing tracks are muted, a new one will be created as you press record. you can also delete them by pressing X in the top left corner of each track if you don't need them anymore.

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 Posted 01/24/2011  2:08 pm  Show Profile   Bookmark this reply Add DVCollector to your friends list Get a Link to this Reply
Thanks for the tutorial--this will be interesting to checkout
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Canada
838 Posts
 Posted 01/24/2011  2:51 pm  Show Profile   Bookmark this reply Add bibd to your friends list Get a Link to this Reply
Very nice work! I always wondered if this drop test could be made quantitative somehow.

I feel like buying a bunch of 1967 silver at 0.650 to make some $$$. (But who would believe me. )

You definitely have the most useful 5 posts for a guy with only 4 posts.
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United States
3046 Posts
 Posted 01/24/2011  9:15 pm  Show Profile   Bookmark this reply Add yotie to your friends list Get a Link to this Reply
very cool I would think this would also work with a 90%/40% half dollar as well

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