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Kef Reference 1 Meta Impedance Puzzle

Gang,

I’m still stuck on this speaker and it’s terrible and odd impedance curve. It’s a 2 Ohm speaker with no good reason.  I should point out, I don't own them and have no interest in buying them, it's a purely academic puzzle for me.

I’m wondering if someone can help me by measuring the impedance of the top and bottom sections separately? If you use REW this may be easy for you to do. A kind and generous soul (Erin’s Audio?) at ASR posted this, but it’s got me more curious. On top of the ludicrously poor (i.e. low) impedance for most of the bass and midrange it’s also not the impedance plot of a ported speaker. Ported speakers characteristically have 2 humps in the bass impedance. One at the port resonance and another at the woofer resonance This has one. What on earth?

Alternatively, if anyone can send me a picture of the crossover that would be a great start.

Comprehensive Measurements

erik_squires
erik_squires OP
16,039 posts
 

Who wants to send me one of theirs to analyze?  Pleeeeease? :D

russ69's avatar
russ69
3,497 posts
 

It’s a 2 Ohm speaker with no good reason.  

It's not a 2 ohm loudspeaker. KEF lists it at 4 ohms. Many loudspeakers dip down to 2 ohms, not that unusual. The phase angle is pretty manageable in the low impedance region. It happens. 

erik_squires OP
16,039 posts
 

Hey Russ, Take a look at the grey line. That’s the equivalent impedance given the phase angle. The current requirements of this amp are equivalent to about two Ohms from 1kHz on down. The high current and breadth of frequency is pretty breathtaking, and in my opinion, which is informed, hard to drive.

Also note the phase angle being negative. It’s highly capacitive in this range, when most speakers would be be a little inductive as the woofer impedance should dominate the bottom octaves..

These two items, plus missing two impedance humps make this a very unusual 3 way. In fact I’d say we are missing 2 humps, a mid/tweeter crossover hump and the port hump. After looking at maybe hundreds of speaker charts in Stereophlile over time and my own simulations and builds I would judge this as very unusual.

Based on that chart and the experience of audiogoners, the 4 Ohm rating is a deceptive guide for buyers.

My best guess right now is that there’s a poorly designed or implemented impedance compensation circuit in there.

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