A "Standard Noise Source" for SPL meters. - diyAudio
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Old 12th July 2004, 07:48 AM   #1
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Default A "Standard Noise Source" for SPL meters.

About 30 years ago in the British mag "Wireless World" someone asked if anyone had any creative ideas about inventing a "Standard Noise Source". I have never seen if the request got any results. The idea was that if a suitable noise could be found people could do the claibration of their DIY SPL meters without the trouble of hunting up another calibrated meter. As I recall it the idea was that we should be able to make a noise that had the following features. (i) It has to be a known level (say for example 85 db). (ii) It had to be able to be reproduced consistently and (iii) it would be good if it was cheap and readily available to the average DIYer.
The sort of thing (just an example) that would be useful would be something along the lines of dropping a Volks Wagon hub cap from 3 feet on to concrete if that could be shown to be reproducible. Concrete and VW hub caps are readily available but I don't know if it would be acoustically acceptable!
Any thoughts?
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Old 13th July 2004, 03:18 AM   #2
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I realise that people won't be able to give a response without having time to think so I'll just "bump it" ocassionally so that there might be an idea or two over the next few days.
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Old 13th July 2004, 03:35 AM   #3
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Default What would Psmith say

I think I have read everything Wodehouse wrote !!!! (even have 'The Most of P.G. Wodehouse', a great compendium.)

standardized SPL -- today there are a lot of semiconductor pressure sensors today which could be pressed into service -- it's an interesting question. I have some motorola devices which we were going to use for an altimeter...
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Old 13th July 2004, 06:15 AM   #4
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Yeah, I'd grateful if you can can up with something. Good to see someone else appreciates the Great Man.
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Old 13th July 2004, 09:25 PM   #5
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It is early morning over on this side of the world so I guess on the other side the rest of the DIY community is just settling in for a long night of posting. I'll just put this up once or twice more as members may have had time to think about it over the last two days. I still reckon it is a good question. Has anyone measured a ballon being "popped" at STP (Standard Temprature and Pressure) or dropped a British Standard House Brick on the garage floor? There has got to be some ideas.
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Old 13th July 2004, 10:00 PM   #6
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Default I suggest

The opening of a standard 355mL (12oz) can of Coke that has been cooled warmed to room temperature of 20C (68F) and dropped from a height of 2 meters (78-3/4"). Microphone at 1 meter level with the top rim of the can. Operator flips the tab directly towards the mic and wears appropriate safety equipment like goggles and raincoat. Steps take to ensure the product has not been on shelf longer than 3 months.

This is relatively inexpensive and is available just about everywhere including Antartica (no word on the Int'l Space Station but I won't bet against it). Coca-cola is one of the most consistent products in the world so the chemistry and pressurization quality are highly predictable. The warming to room temperature ensures that all climates or remote locations can do this experiment without undue hardship. The 2 meter drop ensures that there is not just a pop but a fizz that lasts for more than 2 seconds. (This also makes it an ideal test for video as there will be movement and acted emotion that can be used to test the accuracy of the visual systems).

Although this is not an endorsement of one brand over another, this particular soft drink enjoys the largest global market share and is more likely to be available in rural areas.

:)ensen
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Old 13th July 2004, 10:19 PM   #7
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Great. Thanks, now that's more like it. And, with your permission, can I suggest that we call this "The brown noise standard" with a certain fluid quality it the mid--range perhaps?
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