[BillB]

Over on the av123 forum someone was having a problem keeping the bias on his tube amp stable on his Minis. I told him to check DC resistance just to get a general idea if there was a problem with one of the drivers.

He could not get a meter reading but tried everything else he had and got what you would expect (around 6ohm for an 8ohm and 3.6 or so for a 4 ohm).

So several others tried to meter their Strata minis and no-one could get a reading until a fellow with a high quality meter tested his and found 4.5 meg-ohm!!

I did a search trying to come up with a reason for this and the only thing I could find speaker related is that the Polk sound bar reads 40meg when you meter it.

What causes this? How could DC resistance be so high when it usually closely corresponds with impedence?

Is this a good or bad thing?

[JoshK]

A series cap?  Open circuit?  Is it just the driver you are measuring or is it the whole crossover network + drivers?

[BillB]

Entire network.

Keep in mind it has a planar and a ribbon tweet too.

[JoshK]

Its probably the series cap for the high pass.  Is the sub/woofer driver seperately driven or biampable with disconnected jumpers?

[BillB]

The sub is amped and was disconnected for the check.

Do you think there is something to the architecture of the x-over that is causing this? Most can be read with the crossover without issue.

[JoshK]

Then the upper portion of the speaker is all you are measuring, which is high passed, meaning it has a series cap.  The series cap blocks DC, so you can't measure DCR.  The other gentleman who measured the DCR to be 4Mohms was probably using an auto range multimeter that actually gave him an AC impedance (say at some low hz freg) or it was an error.

[BillB]

It would be a mid driver, planar mid, and ribbon tweet.

Yet again though, I have measured many 2-way speakers without having this issue...or is it just reading the woofer side?

[markC]

It depends on the makeup of the x-over. If non-biwire, your measuring the woof cicuit, (in a 2-way). It will almost always have a series inductor rather than a series capacitor.

[JoshK]

It would be a mid driver, planar mid, and ribbon tweet.

Yet again though, I have measured many 2-way speakers without having this issue...or is it just reading the woofer side?

2ways are completely different animals here, because the 2ways have no high pass.  In a 2-way, when you measure the DCR the tweeter is invisible due to its high pass, you are measuring the woofer only.  With the ribbon speaks, the woofer is seperately amped and the speaker you are driving is high passed, so its DCR is also "invisible". 

[BillB]

This speaker probably has a low-mid, high-mid and high pass therefore all drivers have caps in series.

That would make sense.