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about the corrected Helmholtz calculator
Posted: Thu Feb 17, 2005 3:03 am
by Ted Nightshade
Hi,
I don't have the right software to use the .xls files so kindly provided, so I'm figuring this stuff longhand.
What IS the correct formula? After reading that incorrect formulas are all over the web, I want to make sure I'm using the right one.
Thanks!
Posted: Thu Feb 17, 2005 5:13 am
by knightfly
Here ya go Ted, had to first verify that the one in Everest's last version wasn't ALSO corrupted... Steve
Posted: Thu Feb 17, 2005 7:11 am
by Ted Nightshade
Thank you!!!
Posted: Thu Feb 17, 2005 7:59 am
by knightfly
You're welcome; just noticed that I'd left quite a bit of room between the 216 and the radical - just in case anyone's confused by this, the formula is 216 TIMES the value within the radical, sorry... Steve
CORRECTION TO COMMENTS IN DRAWING -
Other correction - in the included example, I used 0.125" for slot width, NOT .75" - actual values were
Slot width = .125"
Slat width = 6.0"
slat thickness = .75"
cavity Depth = 12.0"
Taking .125, dividing by 6.125, multiplying by 100, gives p = 2.04 - denominator inside the radical would be .75 x 1.2, quantity x 12 -
total value inside the radical, = .1888...
sqrt of that = .4346...
x 216 = 93.8765.... = Fo
Not talking down to anyone, just making sure my fuzzy brain is still semi-functional... Steve
Aw, crap - here's a newer version instead...
Posted: Wed Mar 09, 2005 12:37 pm
by lomky
Just want to confirm something:
i was looking through Modern Recording Techniques and the formula they give is:
f= 216 SQRT r/(d x D) + (w + r)
f = the frequency
r = the slot width
w = the slat width
D = the airspace depth
d = the effective depth of the slot (approx 1.2 x the thickness of the slat)
Just courious if this is the same as the corrected formula or not.
Or maybe this has been said before and I'm just making an @ss of myself.
Josh
Posted: Thu Mar 10, 2005 1:54 am
by knightfly
No; the formula you posted does not take into account the EFFECTIVE slat thickness (this is the 1.2 factor), and I'm too groggy after 12-hour night shifts to sort out the rest; you can plug the same values into both formulas, and if yours is one of the WRONG ones it will be nearly an octave away from the one I posted here, using the same sets of values... Steve
Posted: Thu Mar 10, 2005 2:08 am
by AVare
lomky wrote:Just want to confirm something:
i was looking through Modern Recording Techniques and the formula they give is:
f= 216 SQRT r/(d x D) + (w + r)
f = the frequency
r = the slot width
w = the slat width
D = the airspace depth
d = the effective depth of the slot (approx 1.2 x the thickness of the slat)
Just courious if this is the same as the corrected formula or not.
Or maybe this has been said before and I'm just making an @ss of myself.
Steve gave the correct formula in the post immediately before yours! You have in your post the infamous error that Steve is trying to correct! The addition operand should be a multiplication operand!
Andre