![]() 04/22/2020 at 10:46 • Filed to: shitpost | ![]() | ![]() |
I created a new speedometer overlay for anyone who wants to use it. If you need a higher range, let me know.
“But officer, I was only going 4
0...”
[Update]: Thanks to JimZ for pointing out that speed is an amplitude quantity and should be represented as 20*log and not 10*log, which is for power quantities.
![]() 04/22/2020 at 10:54 |
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As in decibels? Is this submariner wizardry? Legal trickery? Please explain!
![]() 04/22/2020 at 10:56 |
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How do I wear that?
![]() 04/22/2020 at 10:56 |
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Something something about dB being on a logarythmic scale ...
![]() 04/22/2020 at 11:00 |
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Sewn on the front, or I suppose you could implant it in your chest like Stark.
![]() 04/22/2020 at 11:00 |
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https://knops.co/magazine/if-a-cars-speedo-was-expressed-in-decibels-youd-be-cruising-at-10000-mph/
The concept is right, but the details are wrong in this article I found
Edit: Correcting the details
1 MPH is the reference for 0 dB
10 dB = 1 x 10 = 10mph
20 dB = 1 x 10 x 10 = 100mph
![]() 04/22/2020 at 11:06 |
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It should start at 0, not a -infinity, otherwise you would need a -scale too.
![]() 04/22/2020 at 11:07 |
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er, something you want to tell us?
![]() 04/22/2020 at 11:10 |
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speed/velocity is an amplitude quantity, so shouldn’t you be using 20log(V2/V1)?
![]() 04/22/2020 at 11:13 |
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Nope.
10* log10 (0) = 1
10* log10 (-inf) = 0
![]() 04/22/2020 at 11:15 |
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It’s in decibels. 10* log10 (V /Vr) where Vr is the reference speed (1 MPH). I work in acoustics and we use decibels a lot.
![]() 04/22/2020 at 11:17 |
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“Can I get one?”
“Sorry, we only have one. The German subcontractor who printed it shuttered the factory after the prototype was done and we don’t have another $3B to purchase new equipment to start over.”
“Didn’t you have any financial or forecasting plans ?”
“BEAN COUNTERS RUIN ALL THE FUN!”
![]() 04/22/2020 at 11:23 |
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I believe you are c orrect. I actually did give this some thought and briefly looked for an answer. I couldn’t find anything decisive (in my 2 minute search) so I went with 10*log. But some further research suggests it should be 20*log.
Thanks for the tech review!
![]() 04/22/2020 at 11:27 |
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10*log is for power quantities. SPL is a power quantity. Voltage is an amplitude quantity and would be 20*log.
![]() 04/22/2020 at 11:27 |
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20? Hell, my car shimmies at 10...
![]() 04/22/2020 at 11:32 |
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Fixed! Thanks again for pointing that out.
Everything I do is SPL so I’m always using 10*log. I vaugely remember in an intro course using 20*log to solve intensities and convert to SPLs or something, but I’ve obviously brain-dumped all that since I don’t ever actually do it in the real world.
![]() 04/22/2020 at 11:35 |
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Thanks I hate it.
![]() 04/22/2020 at 11:36 |
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I will never not post this meme
![]() 04/22/2020 at 11:45 |
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I’ll own it.
![]() 04/22/2020 at 11:47 |
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oh shit I think I just got it.
![]() 04/22/2020 at 11:52 |
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An unfortunate naming collision.
![]() 04/22/2020 at 11:57 |
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A brapometer! Nice.
![]() 04/22/2020 at 12:14 |
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This explanation is appropriately rigorous for me.
![]() 04/22/2020 at 12:43 |
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Excuse me, I believe this is an engineer’s speedo:
![]() 04/22/2020 at 13:10 |
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That’s hilarious. Engine speed should also be in Hz.
![]() 04/22/2020 at 13:19 |
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That or rad s/sec.