Strange Volvo wiring

[moe3152]

I'm trying to restore some old speakers from a 1997 Volvo 850. And the wiring totally confuses me. They're not coaxial but the tweeter is mounted right above the woofer and they're wired directly to each other. I've triple tested the polarity of each one with a 9 volt battery and have identified both pos and neg connections. Here's the confusion. The tweeter has the capacitor wired into the negative wire and the woofer has, what I'm guessing is a resistor(since the speakers is rated at 8ohms but when I measure thru the resistor it's 11ohms), also wired into the negative wire. How can this be? Every youtube video I've watched says a capacitor should be wired into the positive wire. Anybody have an idea what's going on? Thanks

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[Jimi77 5,000+ posts]

Probably an inductor/coil wired to the woofer functioning as a low pass filter. I'd guess you're wrong about which wire is the negative wire.

 

[moe3152]

That's what I thought over and over. And I just checked them again with 9 volts and the wires that cause the 2 cones to move outward do not have the capacitor or resistor wired to them - if I'm right in connecting the positive pole of the battery to the positive pole of the speaker. And there is no inductor on the woofer. I was able to look up the part number and it's a resistor. I'm thinking that they increased the impedance because these are rear shelf speakers that are wired in parallel with the 8 ohm rear door speakers and if they didn't increase it then the combined impedance would have been too low for the amp. Vaguely, I seem to remember that I read something a long time ago on a Volvo forum that the woofer and tweeters we're wired in series on these speakers. Would that explain it?

 

[Jimi77 5,000+ posts]

That's what I thought over and over. And I just checked them again with 9 volts and the wires that cause the 2 cones to move outward do not have the capacitor or resistor wired to them - if I'm right in connecting the positive pole of the battery to the positive pole of the speaker. And there is no inductor on the woofer. I was able to look up the part number and it's a resistor. I'm thinking that they increased the impedance because these are rear shelf speakers that are wired in parallel with the 8 ohm rear door speakers and if they didn't increase it then the combined impedance would have been too low for the amp. Vaguely, I seem to remember that I read something a long time ago on a Volvo forum that the woofer and tweeters we're wired in series on these speakers. Would that explain it?

You're doing the 9v test properly, but that doesn't mean the wire with the component is the negative wire; the postive wire could be hooked up to the negative terminal of the speaker, either accidentally or to counteract phase issues.

It would be really odd to wire a resistor into the circuit, especially since any HU or amp would be able to handle a 4 ohm load. If you're wired in parallel, then you would lose the ability to fade front to rear - is that the case?

 

[moe3152]

I did test the polarity by connecting to the braided wires coming off the coil and the wires we're connected properly. Which confirms they wired the capacitor and the resistor to the negative wires.

I unsoldered the resistor from the woofer and now it tests at 8 ohms instead of 11. At first I thought it might be some weird shaped capacitor for the woofer. But it has continuity, which a good capacitor does not, till a signal is sent.

Remember that 25 years ago all the amps we're rated at 8 ohms, along with the speakers. If an 8 ohm tweeter was wired in parallel with an 8 ohm woofer and wired again in parallel with the 8 ohm door speaker, my calculations show an impedance of less than 3. So I see the need for a resistor which would raise the impedance enough for the amp to handle it. And yes, I cannot fade them. I can fade the front door speakers to the rear.

I just came from the local Pick n Pull and checked a Volvo that was 2 years newer and no resistors and the capacitor is wired to the positive tweeter terminal. I guess they finally got smart.

 

[Jimi77 5,000+ posts]

I did test the polarity by connecting to the braided wires coming off the coil and the wires we're connected properly. Which confirms they wired the capacitor and the resistor to the negative wires.

I unsoldered the resistor from the woofer and now it tests at 8 ohms instead of 11. At first I thought it might be some weird shaped capacitor for the woofer. But it has continuity, which a good capacitor does not, till a signal is sent.

Remember that 25 years ago all the amps we're rated at 8 ohms, along with the speakers. If an 8 ohm tweeter was wired in parallel with an 8 ohm woofer and wired again in parallel with the 8 ohm door speaker, my calculations show an impedance of less than 3. So I see the need for a resistor which would raise the impedance enough for the amp to handle it. And yes, I cannot fade them. I can fade the front door speakers to the rear.

I just came from the local Pick n Pull and checked a Volvo that was 2 years newer and no resistors and the capacitor is wired to the positive tweeter terminal. I guess they finally got smart.

I was repairing amps 30+ years ago and car audio amps were rated at 4 ohms and quality ones could handle 2 ohm loads.

You can fade front to rear, but you cannot fade them - you can't fade rear to front???

Your impedance calculation is wrong. Because the tweeter has a crossover (aka cap) and the midbass driver has impedance rise, you are at 8 ohms on the front channel. I assume the rears aren't wired parallel to the fronts or you wouldn't be able to fade to the rear. The resistor would (presumably) be in the circuit to attenuate the driver, but 3 ohms on an 8 ohm driver = ~1db of attenuation, which is really odd.

 

[moe3152]

Let me update - Volvo stereos and amps we're made by Alpine and they we're all 8 ohms back then.

I've got 3 sets of speakers. The fronts are wired separately to the amp and the rears and decks are wired parallel to each other and then to the amp. So I can fade the fronts to rears/decks no problem. If the rears and the decks we're left as is, those two 8 ohm speakers would drop to 4 ohms, which I'm guessing was too low for an 8 ohm amp(and I'm not even taking into account what the 8 ohm tweeter on the decks might add) That's why it seems to make sense that they bumped up the deck speakers to 11 ohms with the resistor so the amp could handle it. My guess.

But that leaves the question of why the capacitor was wired to the negative terminal on the tweeter?

 

[Jimi77 5,000+ posts]

Let me update - Volvo stereos and amps we're made by Alpine and they we're all 8 ohms back then.

I've got 3 sets of speakers. The fronts are wired separately to the amp and the rears and decks are wired parallel to each other and then to the amp. So I can fade the fronts to rears/decks no problem. If the rears and the decks we're left as is, those two 8 ohm speakers would drop to 4 ohms, which I'm guessing was too low for an 8 ohm amp(and I'm not even taking into account what the 8 ohm tweeter on the decks might add) That's why it seems to make sense that they bumped up the deck speakers to 11 ohms with the resistor so the amp could handle it. My guess.

But that leaves the question of why the capacitor was wired to the negative terminal on the tweeter?

I ran and fixed alot of Alpines - a freaking ton of Alpine decks, they were 4 ohm stable. It's easier/cheaper to make power in a smaller package using low impedance high current designs. Maybe they made 8 ohm amps especially for Volvo. If the amp was a 4 channel bridged on the rear channel(s), then that might explain using a resistor to bring up the load to a level the amp would be happy with.

It doesn't matter what terminal the capacitor is wired to; I wire speakers out of phase all the time. It's AC voltage, not DC.

 

[moe3152]

Ok, but it sure seems strange that every other speaker I've ever seen has it wired to the positive, And they switched later too. It kind of goes with their history of doing oddball things that no one else does. Final question - The speakers are apart now and I can't remember, but could the deck woofer and tweeter have been wired in series to each other? And if so, would that have raised the impedance? Have you ever seen that before?