Jim Chambers

For those who have missed my self-created audio mess, a quick summary.
Car came to me with CD2 without a code, a "wrong" 4 channel Blaupunkt amp and evidence that at one time it had a serious aftermarket audio system.
I wanted OE system (silly me!). Bought a working CD2 with code, bought a 6 channel amp. Stefan at SW stereo checked them out and both were good.
Fired them up in my car after replacing some plugs on chopped speaker wires for 2 channels at the amp. Plugged speakers in according to WSM wiring diagram. Got great cd sound from the door speakers, almost no sound from the rear (poor radio all around, but that's another story). Following the advice of SQLGuy, I pulled the right rear speakers for a look. And what to my wondering eyes should appear, but after-market MB Quart speakers (4 ohm) in modified OE plastic rings. Even a little "can opener" body work behind the B pillar woofer. Some wires were chopped with a Quart crossover. I can't figure out how to get the rearmost speaker grill off to examine that speaker.

Now what? Any and all suggestions appreciated. I want decent sound from the rear.

auzivision

Either need OE speaker or a bigger amp to power the MB Quarts.

If you do decide to replace your speakers, don't toss those Q's... they still probably have pretty decent street value.

MB Quart Q series are fairly high end speakers... especially the ones manufactured in Germany.

Jim Chambers

Are you saying that the reason I get very muted sound from the rears is that the stock amp will not drive them?

auzivision

Yes, the MB quarts are great speakers when driven hard... but that may not be you only problem with the system. Those cross over’s and extra capacitors in the circuit could also be contributing

I'm not an expert on the OE system, but I believed it was based on 2 ohm speakers (this is impendence, not exactly the same as resistance), so it’s already at a disadvantage.

VehiGAZ

Specifically, the Quart crossovers are to blame - they are well known to sacrifice efficiency on the altar of sound quality. You need to run more power into them than for other speakers

If they are truly almost inaudible, though, you likely have other issues in the wiring.

Good luck!

VehiGAZ

And now to actually answer the question you asked...

I suggest to leave the rear-most speakers where they are and disconnect them. Use your rear amp channels to run the rear speakers (under B pillars), which will have more-or-less the same impedance load as the fronts, so they will produce more-or-less the same sound level as the fronts, producing a more balanced sound. If you get that sorted out, you can try adding another 2-ch amp to drive the rear-most speakers over the wheel arches, but that will effectively drag your sound stage backwards.

Hmm... re-reading your post, I am not clear if the B-pillar speakers were just very quiet compared to the front, or are they not working at all?

Jim Chambers

Very, very quiet. There is barely audible sound.

Jim Chambers

Can someone tell me a bit about "crossovers"? What is their function? The WSM diagram shows direct wires to the B pillar "woofers", with the other rear channel on that side going to the crossover located with/behind the woofer and then on to the two smaller rear speakers on that side.

Alan

Crossovers split the speaker output up by frequency bands low/mid frequencies to the woofer and only high frequency to the tweeters.

You can have active pre-amp crossovers that have variable element gain and frequency and type selections (variable: cut, pass & band modes) these go before the amplifiers

OR (as you have)

passive crossovers that go in the speaker outputs of the amplifier and split the feed to different speakers. These are not usually variable and are usually matched to a specific set of speakers and made by the same manufacturer.

Make sure these are the right matching crossovers for your speakers and connected the right way around: woofer outs to the woofers and tweeter outs to the tweeters.

Alan

Jim Chambers

Thanks Alan. The OE system with the 6 channel amp appears to feed the B pillar woofer directly. The other two rear speakers (tweeter and midrange) appear to be fed by the crossover. I now seem to have a MB Quart crossover feeding a MB Quart tweeter. Not sure about the midrange as I can't figure out how to remove the grill on that one.

mickster

That capacitor is functioning to cut out a frequency in addition to the crossover. Most likely it is cutting out the bass. If it has failed then it may end up cutting out everything. You could jump a wire over the capacitor to see if the sound comes back; if it does-it's a bad capacitor (not surprising). Also the crossover is made up of at least capacitors if not coils/transformers. It's passive (not powered) so it really relies on the right signal.

Based on the wiring be sure that the signal (aka the wires from the amp) are not designed to go to the bass; ditto that everything is connected correctly. That crossover basically knocks down sound 12 db/octave. Give it just bass signal and you won't hear a thing...

Good luck!

Michael

Jim Chambers

As the car came to me, two of the 4 rear speaker channels were unused, plugs cut off (can't be sure now which, the woofer wires or the wires to the OE crossover, I will check tomorrow). Apparently the system was using only 4 channels and 2 of them were running to the MB Quart speakers using the crossover and capacitor. I will trace things tomorrow and determine what goes where. Clearly I can't directly hook my OE 6 channel amp to the bastardized rear speaker system/wiring, regardless of the fact that the rear speakers are likely far superior to the missing OE speakers.

Jim Chambers

Another question: What is the consequence of having 4 ohm speakers being fed by the OE amp which originally fed 2 ohm speakers?

mickster

Roughly 1/2 the power (so 100 watts per channel would be only 50).

If these speakers are, however, more efficient by 3 dB, then they would "sound" about the same in terms of audio level.

I have a feeling you only have part of the system powered. Getting to those midranges and any other parts connected to them, is key.

Wild Bill

As the Ohms go up, you get less output... you need to make a decision, either ditch the OE stuff (my suggestion) or go back to all stock components that were designed to work together. You have a big hack job now.

The MB Quarts are TOTL speakers, but you need a real amp to drive them... Nothing huge, I'm feeding 25 wpc to mine and they work great. Also, don't worry about the rearmost speakers as they serve little purpose. More about marketing than anything else.

Go to www.crutchfield.com for some basic car stereo info... how-to guides and stuff.

Good luck and have fun with it.