Wrong Helmholtz formula!?

so.... what's the verdict (okay, it's been a year, but still)

The verdict should preferably have been written by someone other than me. From my point of view it would be best to disregard the recommended calculating spreadsheets. Here is a summary why this should be done: 1. Calculating a Helmholtz type of resonator without a mouth- or end- correction would be totally wrong, since air particles are not only moving inside the neck as a mass, but around the neck as well. 2. A mouth- or end- correction should not only be considered geometrically dependant but also frequency dependant. This was already derived and mentioned 50-60 years ago by Cremer, Ingard, Smits, Kosten, and others. Therefore a fixed mouth- or end- correction would be wrong. 3. The resonant frequency can also be shifted by the viscous losses of porous materials. However, the viscous losses by the friction of air at the edges of the neck, the viscous resistance of the hole surface and the viscous resistance at the neck needs to be considered as well. 4. Finally there should be a proof by comparing measured results vs. calculated results, which I have done before. This can also be found in the book of Cox and D’Antonio (Acoustic Absorbers and Diffusers) on page 178, though this article is considered very superficial/shallow. Will

Thanx for replying. Let's keep this threat active then. (whish I had the/some knowledge to challenge the formulas)

Take the slatted helmholtz formula from Everest's MHOA, page 224 (variables explained on p. 225), and move the part of the calculation (inside the radical) that converts decimal to per cent (X 100) to the OUTSIDE of the radical by changing the multiplier of 216 to 2160, and you have the formula used in the spreadsheet found in this forum. Only other difference I see is that the forum version also includes mouth correction; however, this is a fixed value of 1.2 which I agree with Will isn't likely to be optimum in all cases... Steve Oh, Will, I cropped your pic to forum specs so we didn't have to scroll sideways. (moved your copyright in a bit to fit)