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

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Valued Member
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.
Pillar of the Community
United States
744 Posts
 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.
Bedrock of the Community
10045 Posts
 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.

Bedrock of the Community
10045 Posts
 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
Pillar of the Community
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.
Pillar of the Community
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

Pillar of the Community
United States
4000 Posts
 Posted 01/24/2011  9:43 pm  Show Profile   Bookmark this reply Add Scooby Due to your friends list Get a Link to this Reply
Very interesting read. Thank you!

How about some '82 zinc vs. copper comparisons.

Bedrock of the Community
Australia
17629 Posts
 Posted 01/25/2011  06:27 am  Show Profile   Bookmark this reply Add sel_69l to your friends list Get a Link to this Reply
samboyyellowsub:That's interesting.

Australia used to have sliver florin coins in circulation prior to the introduction of decimal currency in 1966. Coins made before 1946 were .925 fine, those after that were .500 fine, but had the same mass and diameter.

The alloys for .925 fine were silver 92.5%, copper 7.5%,
and for .500 fine were silver 50%, copper 40%, nickel 5%, and zinc5%

That means the .925 silver coins were thinner and denser that the .500 ones.

This resulted in the two alloys having different ring tones, naturally. The ring pitch of the .925 coins is lower.

I had always assumed that due to greater inertia resulting from the greater density of the .925 coins, the ring tones for for these coins must be lower.

I guess that if you have clad coins rather than a homogeneous alloy, the ring characteristics would be altered in a different way than by the assumption that I have indicated above.

Although my observations are true, my assumptions may be wrong. Can you make a comment about my assumptions?
Valued Member
United States
113 Posts
 Posted 01/25/2011  09:40 am  Show Profile   Bookmark this reply Add samboyellowsub to your friends list Get a Link to this Reply
sel_691,
If the mass is the same, actually, the inertia is the same. Although, I get what you're thinking about density affecting inertia. Say you have an inflated birthday party balloon, and a coin that is the same mass. What you're perceiving is that the coin has greater inertia for its size, than the balloon, which it true. But they have the same inertia if they have the same mass.

In two similarly sized objects, the thing that affects the pitch the most is not necessarily the density, but the speed of sound in the material. Copper is less dense than silver but carries sound (mechanical vibrations) faster than silver in all respects. This is not always the rule though. For instance tungsten is nearly twice as dense as silver, and it carries sound much faster than silver.

The speed of sound is proportional to a material's elasticity. An easily perceptible mechanical property related to elasticity is probably malleability versus springiness, the easier a metal "gives" without the tendency to return to its undisturbed state, the lower its elasticity and the lower the speed of sound and the lower the ring pitch. Like gold, it is softer than silver and as you might expect it carries sound slower.

Hope that helps.
Valued Member
United States
113 Posts
 Posted 01/25/2011  09:45 am  Show Profile   Bookmark this reply Add samboyellowsub to your friends list Get a Link to this Reply
forgot to add, that yes, a clad coin will change things quite a bit. The chunk of zinc inside the penny will act almost completely independently of the copper cladding. The reason for this is that there is a boundary between the copper and zinc and sound reflects off of boundaries in materials. Not to say that some sound doesn't transmit between boundaries, because it does. But that is why it doesn't sound as sharp, because its two resonant systems; the filler and the cladding and they do compete with each other for sonic real-estate!
Pillar of the Community
Canada
595 Posts
 Posted 01/25/2011  6:40 pm  Show Profile   Bookmark this reply Add North of 49 to your friends list Get a Link to this Reply
Very impressive , thanks.
Bedrock of the Community
Australia
17629 Posts
 Posted 01/25/2011  11:44 pm  Show Profile   Bookmark this reply Add sel_69l to your friends list Get a Link to this Reply
samboyellowsub. Before, I did not have enough background knowledge. Now I have a reason. It seems that the lattice structure of atoms in a metal or an alloy has a lot to do with elasticity and sound transmission. Some alloys are certainly harder, and that is why alloys are preferred to pure metals in circulating coins.

Sukria. ('thankyou' in Urdu)!
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Canada
9379 Posts
 Posted 11/23/2011  9:42 pm  Show Profile   Check SPP-Ottawa's eBay Listings Bookmark this reply Add SPP-Ottawa to your friends list Get a Link to this Reply

Quote:
I dropped the coins on my hardwood floor on which I rested my laptop


I would like to see a repeat of your test, but with the coins dropped on a piece of marble. That is what the Royal Canadian Mint used to use to "ring" their silver coins, 'odd' sounding coins were rejected, which could have been a bad alloy mix of silver, or other flaws like cracked coins.

http://www.liveleak.com/view?i=677_1293705960 (you can fast forward to 8:03 of this archive video)

Also, that is why vintage cash registers also used to have a marble slab above the cash drawer, to ring the coins if they were suspect of being a cast counterfeit of other metals or lower silver content.


"Discovery follows discovery, each both raising and answering questions, each ending a long search, and each providing the new instruments for a new search." -- J. Robert Oppenheimer

Content of this post is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License. See: http://creativecommons.org/licenses...0/deed.en_US

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Edited by SPP-Ottawa
11/23/2011 9:46 pm
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