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WannaBdone
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| Joined: | Thu Mar 29th, 2007 |
| Location: | Boston |
| Posts: | 28 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | Architect! |
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Posted: Fri May 2nd, 2008 12:37 pm |
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I'm having the hardest time understanding this; hope someone out there can help me make sense of it.
Looking at Flashcard #613 (from the Archiflash set; it's a yellow flashcard):
"Inverse Square Law : Applies to sound and light intensity, which is inversely proportional to the square of the distance between the source and the receiver. In simple terms, doubling the distance cuts the intensity of light and sound to 25%. Note: Do not confuse the intensity of sound (I) which is measured in watts per cm (squared), with the more common Intensity Level (IL), which is measured in decibels. The IL is NOT proportional to the inverse square of distance."
What's the difference between sound intensity and sound volume?
Also, if doubling the distance cuts the intensity of light and sound to 25%, then why just subtract a flat figure 6dB, why not take .25% of the total dB?
I'm totally confused, thanks for any clarity!
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brudgers
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| Joined: | Thu Jun 1st, 2006 |
| Location: | The Moment |
| Posts: | 6601 |
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Posted: Fri May 2nd, 2008 01:36 pm |
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You're conflating two concepts.
The inverse square law means that if you double the distance you quarter the power.
2d = 1p/(2*2)
Separately, db is a logarithimic scale.
110db is 1/10 the power of 120db, and 60db is 1/10 the power of 70db.
The reason doubling the distance causes a 6db drop in power is that 1/4 = 10-0.6
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Steve Johnson
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| Joined: | Sat Jun 16th, 2007 |
| Location: | North Carolina USA |
| Posts: | 491 |
| Exams Taken: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Exams Passed: | PD, GS, LF, ME, BD/MM, CD, SP, BP, BT | | Describes Me: | I am uh r k tek |
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Posted: Fri May 9th, 2008 03:24 am |
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WannaBdone wrote: I'm having the hardest time understanding this; hope someone out there can help me make sense of it.
Looking at Flashcard #613 (from the Archiflash set; it's a yellow flashcard):
"Inverse Square Law : Applies to sound and light intensity, which is inversely proportional to the square of the distance between the source and the receiver. In simple terms, doubling the distance cuts the intensity of light and sound to 25%. Note: Do not confuse the intensity of sound (I) which is measured in watts per cm (squared), with the more common Intensity Level (IL), which is measured in decibels. The IL is NOT proportional to the inverse square of distance."
What's the difference between sound intensity and sound volume?
Also, if doubling the distance cuts the intensity of light and sound to 25%, then why just subtract a flat figure 6dB, why not take .25% of the total dB?
I'm totally confused, thanks for any clarity!
This was discussed quite a bit in a previous post that I started: http://www.areforum.org/forums/forum4/46828.html
I hope that helps. More importantly, don't get caught up in the math... just understand WHY it happens... the math is not a significant portion of this exam.
Last edited on Fri May 9th, 2008 03:25 am by Steve Johnson
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