impedance spike... hmmm

[Etac 10+ year member]

ok i was mesing around with ISD and never realized how much the type of box changes impedance spikes....

and i was just wondering the affect this has on a speaker.. logically i figure it would be harder to produce a 32hz tone fi theres a 50ohms spike at 32hz.. but figured i would ask here before jumping to conclusions lol

cause lately i been trying different boxes.. went from small sealed to IB basically (not completely sealed but just trying it out) and loved how it sounded but one low note didnt seem right.. and like i posted before... winisd is showing a huge imedance spike at around 32hz.. in a ported box as im sure most of you know... had two spikes but ones at like 2something and the other is like 50 something leaving 30-40 clean... does this play a decent role in why ported boxes tend to get lower?

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[Immacomputer 10+ year member]

The impedance rise in an enclosure is the point where you have system resonances. The higher the order, the more poles you have in the transfer function and the more resonance points you get. These frequencies would not be "harder" to reproduce and pretty much the opposite of that idea. Since these frequencies are the resonance points, they actually have very high gain. In an IB situation, this will be the point of most excursion and below this, the speaker relies more on it's mechanical damping to control cone movement instead of electrical damping from the motor.

Well if these points are really resonance points, shouldn't they be louder than other frequencies? That would be true if it weren't for the damping of the amp (damping factor sound familiar?). The higher the damping factor of the amp, the more control the amp will have over the cone of the sub around resonance points.

Another thing that keeps those resonance points under control is the vehicle cabin. It offers a different transfer function that puts new resonance points into place. It basically adds acoustical damping and gain to the system (your sub/enclosure combo).