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Message: <blockquote data-quote="GrnEydDvl" data-source="post: 4539667" data-attributes="member: 568270">I was eying some Digital Designs subs this weekend which led to me looking over their box designing page. I've never owned or even heard a DD sub.For those that might not know, they recommend a certain amount of airspace, port area, and to tune to 40hz, due to the way they design their subs. According to their site they design the subs somehow to specifically benefit from the cabin gain in automobiles and give good response when tuned to 40hz, as opposed to a more common tuning range of 30-36hz. <a href="http://www.ddaudio.com/dd/caraudio/enclosureInfo/boxSize_hiEff.asp" target="_blank">Link to their site for more info</a>I took their numbers and ran them across at least 6 online port length calculators. None of them matched the port lengths found on the DD site. Most gave answers that did not equal the other calculators as well - a multitude of "correct" port lengths even though all other variables were kept constant.Looking over threads here and on other sites, the general consensus is the online calculators are just wrong.Does anyone know why this is?If they are all wrong, which is shocking (why build a calculator that cannot handle the basic function it is designed to do), then what is right?Do any of you test the boxes you have built to see how they perform as far as port tuning? I understand a car is not an anechoic chamber and that the common tools we have to measure with are not terribly accurate. But we should be able to get a general idea if the tuning is close enough to what we had intended.Does winISD get port calculations right? The tutorial here by Noah uses winISD.I imagine DD has it right, as they would have tons of upset customers who built to their specs with poor performance if they were wrong.</blockquote>

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