WinISD Helmholtz resonance question

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IG81

IG81

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Joined 2008
#1
I am a bit concerned about how WinISD and the following formula don't yield the same results for the same metrics. Not just a few Hz, but 162Hz the former and 100Hz the later. And it's not a port volume inside or outside of stated V problem.

helmholtz.jpg

Is something else being taken into account by WinISD?

IG
 
#3
Inductor said:
Helmholtz is very straightforward and maybe you are missing some parameters.
Maybe this helps, post (your) results.
Résonateur de Helmholtz
http://www.diyaudio.com/forums/multi-way/169313-helmholtz-resonance-again.html#post2227318
Click to expand...

Thanks for the info. The formula I posted did not include the end correction factor.

So here's what I tried: 10 liter box with 60mm diameter vent, 120mm long, vent inside the box. Both techniques described in your link gave me 149.9Hz. WinISD still insists on giving me ~71Hz and does not seem to care for end correction factor changes.

I'm probably doing something wrong in WinISD, maybe there is a specific order for entering the numbers? I'm pretty sure I did OK with the formula in your link, but then again, I'm pretty sure the WinISD guys know their stuff too! :S

IG
 
#4
WinISD or its pro version? The former hasn't been very accurate IME, though the latter is OK for cube or low aspect ratio rectangular cabs. For higher aspect ratios you'll need MJK's MathCad software or maybe AkAbak to find the proper vent length empirically.

GM
 
#5
GM said:
WinISD or its pro version? The former hasn't been very accurate IME, though the latter is OK for cube or low aspect ratio rectangular cabs. For higher aspect ratios you'll need MJK's MathCad software or maybe AkAbak to find the proper vent length empirically.

GM
Click to expand...

WinISD Pro alpha 0.50a7. I assume it works with a cubic volume, as it won't allow me to input enclosure dimensions; "This feature is not yet available in this alpha release".

I assume that higher aspect ratios start to have a quarter-wave behavior at some point. I checked out Akabak a while ago, seems like it would be a lot to learn. Maybe too much before the cold sets in and I can't build anything anymore, but could be a good winter project!

IG
 
#6
Correct on all points. There may be some reasonably accurate rule-of-thumb way to calculate the 1/4 WL effect on vent length, but if there is I never figured one out over the decades I built tower/column alignments (now MLTL).

GM
 
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