Extremely high resistance, WTF?

soiset

Just got a pair of use PSB Bronze Stratus in like-new condition. Even the packaging is like new. The guy said he used them for surround only.

I hooked them up, and they sounded like there was a blanket thrown over them. Running them biamped, Rotel RB-971 (70 watts) and RB-987 (130 watts) The 971 goes to the upper binding posts, that connect to a mid and the tweeter, for 500 Hz and up.

I got out my Fluke, and measured across the posts: 3.9 ohms on the bottom pair, and a whopping 430 kohms on the top (no, I did not misplace the decimal point). The other speaker measured over 600 on the top!!

What the fudge is this all about? Also, from one of the mids I hear a tinny zing every so often, that sounds like something vibrating.

Any ideas?

I should add: I think the speakers may have never been biamped or biwired before, as the jumpers were there, the plugs for the banana holes were still in, and the mid-hi posts were locked down so tight I had to use pliers to get them started.

phuz

Un-bi-amp, and see what results you get.

Also - and I could be wrong - but I'm not sure that you should bi-amp with amps of different wattages/specs.

jcaut

I'll have to think about it for a bit, but I think the resistance measurement sounds reasonable. If the top pair of posts connect to the portion of the crossover that feeds a midrange and a tweeter, there's going to be a capacitor in series with both drivers. You're measuring DC resistance, which on a capacitor, should be very high.

Jason

seeclear

any chance you broke something in loosening those posts?

ben62670

Blown tweeters most likely. What you are probably reading is some resistance in the crossovers. Take the tweeters out, and test them.

killerb

jcaut wrote: »

I'll have to think about it for a bit, but I think the resistance measurement sounds reasonable. If the top pair of posts connect to the portion of the crossover that feeds a midrange and a tweeter, there's going to be a capacitor in series with both drivers. You're measuring DC resistance, which on a capacitor, should be very high.

Jason

i agree.

treitz3

Sounds to me like you received a dicked set of speak's. Return if possible.

jcaut

I thought about this a little more (long day) and I'm certain that high DC resistance, measured across the top pair of binding posts is not anything to worry about by itself. It's the result of series capacitors that block the low frequencies from reaching the mid and the tweeter. If anything, 430-600K Ohms seems a little low to me. I guess it depends upon the crossover layout.

I grabbed the nearest bi-amp capable speaker I have, which happen to be a set of Polk RT55i's and measured resistance across the posts: 4.2 Ohms on the bottom posts and in excess of 30M Ohms on the top posts (that's the top range on my meter). Like I mentioned before, a capacitor (at least a good one) should have extremely high DC resistance- approaching infinity. I think you'd find the same thing on most any bi-wire/bi-amp capable speaker, if you measure the posts that go to the bandpass/highpass section of the crossover.

I don't know what's wrong with the sound of your speakers. Pulling the tweeters to test them wouldn't be a bad idea, and neither would taking a look at the crossovers to see if anything looks burned.

Jason

disneyjoe7

You're right on Jason, good call.

soiset

Yes, Jason, after some research I'm sure you are right. When I get back in town, I'm going to pull the tweeter and the mid and check resistance across them. It is puzzling though that the problem seems to be nearly identical on both speakers.

I was using this setup to biamp my Energy C-8's and it worked well. Then, I switch to active biamping with an electronic crossover on a pair of Polk LS50s from which I removed the xover. Both sounded great. The improvement to the Polks was very noticeable.

I would want to actively bi, or possible triamp the PSBs, but I want to know that they work well otherwise. I haven't tried running them with the jumpers from a single amp, but will try that when I get back, too.

The seller has been very apologetic and is ready to take them back, but I really want these speakers if I can get them to perform properly.

Thanks for the responses, and I'll let you know what I learn.

soiset

I reconnected the jumpers, and tried them with a single amp: no improvement. I pulled the crossover out (it is huge) and nothing looks burnt. I read 5.1 ohms across the tweeter, and 7.1/7.2 across both of the mid-woofers. A guy at PSB suggested some kind of 9-volt battery test with the tweeters. Anyone know what that is about?

soiset

Also, I tested across the jumped binding posts, and read 4 ohms. Now, there is a crossover with a capacitor on both the bottom and top binding posts, so why do I read 4 ohms across the bottom (and of course when they are jumped) and a billion ohms across the top? Shouldn't the capacitors on the bottom crossover also cause a high-resistance reading?

Systems

Have you tried just the tweeter and its crossover section without the mid/woofs hooked up?

Systems

soiset wrote: »

Also, I tested across the jumped binding posts, and read 4 ohms. Now, there is a crossover with a capacitor on both the bottom and top binding posts, so why do I read 4 ohms across the bottom (and of course when they are jumped) and a billion ohms across the top? Shouldn't the capacitors on the bottom crossover also cause a high-resistance reading?

You are reading the DCR of the parrallel woofers.

soiset

GV#27 wrote: »

You are reading the DCR of the parrallel woofers.

I'll tell you the config and you tell me if that makes sense:

There are two identical woofers and a tweeter. One woofer, connected to the bottom posts, operates from 2k down. The other woofer, also connected to the bottom posts, operates from 500 to 2k. The tweeter is the only thing connected to the top posts, and it is 2k and up.

Oh yes, and the upper xover is 24 dB, the 500 Hz xover is 18.

I AB'd a pair of LS50's right beside them, and it's like night and day. Definitely something amiss. The tweeters are "working" and not crackling. Could they be blown anyway?

Systems

Yes it makes sense.With the jumpers in place or just on the bottom posts with the jumpers removed you will be reading the DC resistance of the 2 woofers and series inductors.On the top posts with the jumpers removed you will get a hi reading correct?

soiset

GV#27 wrote: »

Yes it makes sense.With the jumpers in place or just on the bottom posts with the jumpers removed you will be reading the DC resistance of the 2 woofers and series inductors.On the top posts with the jumpers removed you will get a hi reading correct?

Yes, that is correct. Could damaged tweeters manifest in this fashion? Wouldn't they be tinny or crackling, and not just muffled?

Just did the battery test on a tweeter, and it makes little noises like I guess it should. Seems to be down to the xover. Any tests I can do with a multi-meter?

Systems

Not likely if there are no burnt components in the crossover and each tweeter measures the the same DCR without the crossover attached and there are no signs of distortion.Could it be that they are just a very laid back sounding speaker and you are used to a brighter sounding one?It may take some time to get used to its down tilted balance.

btw.If you are brave and very CAREFUL you could check the tweeters voice coil for damage.

soiset

GV#27 wrote: »

Not likely if there are no burnt components in the crossover and each tweeter measures the the same DCR without the crossover attached and there are no signs of distortion.Could it be that they are just a very laid back sounding speaker and you are used to a brighter sounding one?It may take some time to get used to its down tilted balance.

btw.If you are brave and very CAREFUL you could check the tweeters voice coil for damage.

I pondered for a minute if I was just used to a brighter speaker, but I rejected that idea. They just sound like crap. Even my wife thinks so. I've heard a pretty wide range of speakers, and nothing sounds like this above $30/pair.

So, what is the voice coil test?

WilliamM2

Readings are normal, I get the same thing with my CSi40 on the tweeter circuit.

soiset

I know manufacturers use the same parts for different speakers, and simply mod them, but I'll ask this anyway: The top xover has two white ceramic resistors. One is rated 4 ohm, the other 30, and they test that way. But the left side of both does not connect to the circuit board, as though 1/8" of the wire were cut out. Would this be typical?

Systems

To check the voice coil you have to remove the tweet from the baffle and disassemble it.There will be either 3 or 4 screws nearer the dome that holds the front plate on.If you remove those srcews it will allow the front to be removed.Be careful not to damage the dome.Then the voice assembly can be carefully lifted out of the magnet gap.Then visually inspect it,the coil should have a copper colour not be blackened.Although there should be a dark fluid (ferro fluid)on the coil which is normal.If it looks burn't then you need to replace it.

Systems

soiset wrote: »

But the left side of both does not connect to the circuit board, as though 1/8" of the wire were cut out. Would this be typical?

Not sure what you mean,is the one end of both resistors not connected to anywhere or each other?is it the same in both speakers?

soiset

GV#27 wrote: »

Not sure what you mean,is the one end of both resistors not connected to anywhere or each other?is it the same in both speakers?

Two resistors per xover. The same end of the same resistor in each xover is cut.

I am wondering if the drivers could be out of phase. The connections are all the same size, so they could have been assembled improperly. I'll swap them tonight and have a listen.

soiset

GV#27 wrote: »

Have you tried just the tweeter and its crossover section without the mid/woofs hooked up?

I missed this suggestion. No, I haven't tried that yet. I tried reversing the phase on the tweeter, and it just got worse. So, once again I started to doubt my conclusion that something must be wrong, even though I found the sound very dissatisfying. I put an Energy C8 on, and oh yeah, there is definitely a problem.

I know the tweeters work, and I don't know what I am supposed to listen for with the test above, but I'll go try it now.

soiset

I tried it, and the tweeters are definitely very weak. They don't crackle or anything, and seem to hit the notes, but the volume is very low. Could they be "worn out?"

Systems

soiset wrote: »

Two resistors per xover. The same end of the same resistor in each xover is cut.

This is very odd the resistors should be connected at both ends.Is it possible that they broke loose from their connection points during shipping?Can you post a pic?

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soiset

GV#27 wrote: »

This is very odd the resistors should be connected at both ends.Is it possible that they broke loose from their connection points during shipping?Can you post a pic?

That's why I was thinking it is probably the same xover used in the Stratus Silver and Gold, wherein perhaps it is connected. So, can tweeters just be "worn out?"

Systems

soiset wrote: »

So, can tweeters just be "worn out?"

Only if abused the voicecoils can be damaged,but normal useage without being overdriven they should last for decades.
My guess is it those resistors need to be connected somewhere.

soiset

All three capacitors check for capacitance and resistance. The only suspect thing on the crossovers is that both of them have their 30 ohm resistors disconnected. It looks like a pretty obvious cut, but my options have been reduced to that, or bad tweeters.

I can test the tweeters outside of the xover by using one of my electronic crossovers, so I guess that's next. But that will only be a subjective listening eval. But I suppose if it is substantially louder outside the circuit, then I can conclude it must be the xover.