Impedence spike - LspCad (1 Viewer)

[Scott M]

I've been tooling around with LspCad for a Sonosub and I think I've arrived at a setup I like but there is a large impedence spike, over 70ohms, at about 36hz. I'm not sure I have all the inputs correct so I thought I'd if this is normal behavior.
This is my first DIY in speakers. It's based on the shiva, I'm using seperate supplies for each coil - 100W @ 8ohms each(I have an old amp). I'm not looking for high levels of output right now so I'll look for another amp once I get this thing going.
I'm looking at around 150l, 4" port tuned near 18hz. I'm still adjusting things so any other suggestions would be appreciated also.
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-scott

 

[Alan Rutlidge]

Scott,
The impedance peak that you are seeing is probably occuring at the same or near the fundamental resonant frequency of the driver. Check the specs for the driver and see if the free air resonant frequency is quoted. I'm sure it is going to be near the 36Hz you have quoted in your post. I stand corrected if I'm wrong on this point. Is there anything you can do about it? Not likely. Does it matter? Probably not.
Other comments from fellow forum members?
Cheers,
Alan

 

[DanWiggins]

Scott,
Don't sweat the impedance peak; it's supposed to be there! It's a direct result of the vented cabinet design. If you're not using a passive crossover, then it has zero effect on the system. If you are using a passive crossover, then it makes the crossover design more difficult, but is still a fact to be dealt with/expected.
Dan Wiggins
Adire Audio

 

[Scott M]

Thanks guys. Right now I don't have any plans for a passive cross-over but I keep that in mind for the future.
Dan,
It's always great to hear it from the horses mouth, BTW LspCad is a great tool for beginners.
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-scott