about the corrected Helmholtz calculator

Ted Nightshade · Post by **Ted Nightshade** » Thu Feb 17, 2005 3:03 am

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!

knightfly · Post by **knightfly** » Thu Feb 17, 2005 5:13 am

Here ya go Ted, had to first verify that the one in Everest's last version wasn't ALSO corrupted... Steve

Ted Nightshade · Post by **Ted Nightshade** » Thu Feb 17, 2005 7:11 am

Thank you!!!

knightfly · Post by **knightfly** » Thu Feb 17, 2005 7:59 am

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...

lomky · Post by **lomky** » Wed Mar 09, 2005 12:37 pm

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

knightfly · Post by **knightfly** » Thu Mar 10, 2005 1:54 am

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

AVare · Post by **AVare** » Thu Mar 10, 2005 2:08 am

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