# Too many impedance peaks?



## kc999 (Nov 13, 2011)

Can anyone tell me why I’m seeing three impedance peaks instead of two on this Dual ported Dual driver design? Both test ports are of equal length 8 inches each. Changing port lengths does not reduce the two peaks only the tuning. Even if I remove one port and block the hole I still get two impedance peaks.
No matter what software I use to measure when I have both ports in and back sealed the result is the same the 3 impedance peaks.I should be seeing measuring two impedance peaks and one low frequency region:scratch:
Any help is appreciated.


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## fusseli (May 1, 2007)

What tuning frequency are you expecting? Does your midrange woofer have it's own internal enclosure.


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## kc999 (Nov 13, 2011)

THX for reply. Midrange and tweeter are not even connected. with two bass drivers in parallel and two ports I should be seeing two impedance peaks that are spread wider than if I were using a single port. the more ports you add the wider the valley will become but there shouldn't be additional impedance peaks I could be wrong about that but all simulation software out there confirms only two . So I don't know why I'm measuring/ seeing three peaks instead of only two.


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## fusseli (May 1, 2007)

Please answer my above two questions so I can advise. The cabinet tuning is measured by the lowest point in the saddle between impedance peaks for an ordinary ported system, what tuning you are expecting might help determine where the other one is coming from. Are you getting the same impedance measurement from either of the two?


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## kc999 (Nov 13, 2011)

Midrange driver does not have it’s own internal enclosure and it’s not connected at this point.
With two 8 inch long ports and port diameter of 2.635 which gives cross section 3.71 inches total, I’m expecting approximately around 28 to 31 Hz depending on if I fine tune for QB3 or SBB4 .
In that image the measured Frequency is approx. 23 Hz.


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## fusseli (May 1, 2007)

How is your internal bracing arranged? I wonder if the internal construction is inadvertently creating a double tuned bass reflex, there's a better term for it but it's escaping me at the moment.


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## kc999 (Nov 13, 2011)

just 3 double narrow bracing nothing to drastic or weird.


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## kc999 (Nov 13, 2011)

THX fusseli.Problem solved


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## dougc (Dec 19, 2009)

What solved the issue?


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## kc999 (Nov 13, 2011)

The problem was the mid driver which needs it's own separate chamber. I removed it and taped up the hole and run the measurement and that shows the normal two impedance peaks for dual driver, dual ported enclosure. 
So I have to make a separate chamber and install that.


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