What is the reason for "common" wire -- (3 wires in a 2 channel audio setup) -- Becker

[Jlaa]

OK I have to sheepishly admit that I don't understand the wiring diagram for our cars here.

I have a basic consumer level understanding of this stuff --- meaning --- I understand that each channel of sound usually has two wires, like if you use RCA plugs in the back of your home amplifier, then each RCA plug is actually 2 wires - one wire for the "tip" and one wire for the "barrel".

So I was looking to grab sounds from *after* the factory fader wheel in our cars (to feed an aftermarket amp) --- and I don't understand this wiring diagram. For two channels of sound, why are there only 3 "wires"? One of the wires is "common" for the 2 channels of sound? What? Why is this done? And, what should I know about this if I tap these to get a low level signal? I have attached the wiring diagram here with arrows pointing to the areas in question.

Thank you.

 

[2phast]

Your trying to mix old and new technology which is just going to lead to major headaches.

Now its been while since I have worked on these sound systems but from my recollection, the head unit is a two channel unit that feeds into the fader which splits the signal into four channels.

So if you plan on pulling a signal to feed an external amplifier, you would need a hi/lo level signal converter, unless you happen to have a amplifier that accepts high level signals (doubtful). You won't be able to get anything usable from the trunk mounted amplifier either, as it supplies low frequencies to the door speakers.

Since your working with a common ground system, you can't really integrate a floating ground amplifier without rewiring everything.

IMO, leave everything as-is, pull out the head unit and all the speakers. Now run new speaker wire to all the locations, route to new amplifier, route signal cables up to head unit location, install new modern head unit. You can tap into existing head unit wiring, without damaging it or cutting off any connectors. You will end up with a much simpler system that sounds 110% better than the stock system. AND if you keep everything intact, you can replace the factory head unit and factory speakers when/if you decide to sell your car.

I wouldn't waste anytime with the door mounted subs, they have something like a 2" mounting depth and very few speakers will fit in this location, unless of course you wan't to pull it all apart and fab something that sits behind the door panel. AND these speakers fire into the sides of the seat, so even with a coax, the sound isn't very usable.

For reference: I run a Pioneer Premier DSP headunit with something akin to a Mosfet 50 internal amplifier (four channel) which feeds two dash mounted Infinity Kappa coax speakers (four inch) and two Infinity Kappa 5.25" in the rear deck. The Infinities have their own passive cross over to filter frequencies to the tweeters and the mid/woofer, but you can't really feed low level signals to these things, so I use the internal head units electronic cross over to filter out anything below about 150hz. The low level output of the head unit feeds a Infinity Basslink T sub mounted in the trunk. The Basslink T has a internal 250 watt amplifier, a single 10" sub and two passive 10" subs. It also has a rotary volume control which you can use to boost the low level output and is convenient vs. messing around with the internal head units EQ or bass settings. The DSP of the head unit allows you to tailor your sound stage, so for example, I have it optimized for the driver, which requires you to measure the distance from your head/ears to each speaker and input these measurements into the head unit, the head unit then applies time delay so that all sound arrives at your ears at the same time, thus eliminating the Haas Effect, which is directly related to you sitting off axis in the sound field.

This is as far as I should of gone, but I made my life more complicated by sourcing a set of Pioneer coax speakers to mount in the factory door locations. Not a quality speaker, but the only 2" mounting depth ones I could find that would fit the factory door pods. These are powered by a small ADS 25 watt amplifier mounted where the factory amplifier is. This was a total waste of time and added nothing to the sound stage, so I would bypass this altogether and just leave the factory parts in place and unmolested.

 

[Jlaa]

Your trying to mix old and new technology which is just going to lead to major headaches.

This is because I am lover of paper cones and cassette decks. And headaches. And the Becker BE1432 headunit. It is glorious. Actually for all of my 1990s cars (all two of them), I have ensured that they all retained only the finest of OE cassette decks in the dashboard.

Now its been while since I have worked on these sound systems but from my recollection, the head unit is a two channel unit that feeds into the fader which splits the signal into four channels.

So if you plan on pulling a signal to feed an external amplifier, you would need a hi/lo level signal converter, unless you happen to have a amplifier that accepts high level signals (doubtful). You won't be able to get anything usable from the trunk mounted amplifier either, as it supplies low frequencies to the door speakers.

I think the phrase "you won't get anything usable from the trunk mounted amplifier" only pertains to those w124s that used the "Active Bass system" which had ONE amplifier mounted in the trunk. See wiring diagram below. In this system, your memory is really something else! Trunk amp feeds the door speakers a low freq signal and the dash and rear deck speakers are driven through the fader, as you mention.



However, my 500E has TWO trunk mounted amplifiers as shown below. The trunk mounted amplifiers provide full range output via pins 2 and 4 in the connector. See diagram below:

Since your working with a common ground system, you can't really integrate a floating ground amplifier without rewiring everything.

May I ask why this is? I don't understand why with a common ground system at line-level, you can't hook up the line-level signal to an aftermarket amplifier. This is the crux of my lack of understanding.

IMO, leave everything as-is, pull out the head unit and all the speakers. Now run new speaker wire to all the locations, route to new amplifier, route signal cables up to head unit location, install new modern head unit. You can tap into existing head unit wiring, without damaging it or cutting off any connectors. You will end up with a much simpler system that sounds 110% better than the stock system. AND if you keep everything intact, you can replace the factory head unit and factory speakers when/if you decide to sell your car.

Yes that would yield the most sonically pleasing result wouldn't it? Except I am a neanderthal and I love the Becker 1432. Hence, I wish to keep it.

I wouldn't waste anytime with the door mounted subs, they have something like a 2" mounting depth and very few speakers will fit in this location, unless of course you wan't to pull it all apart and fab something that sits behind the door panel. AND these speakers fire into the sides of the seat, so even with a coax, the sound isn't very usable.

I think your comment about the uselessness of mounting coaxial in the stock door mounted locations is the whole point of the Jehnert Doorboards. Pics below. Jehnert allows you to more than double cone surface area by going from one 5-1/4" driver to two 6-1/2" drivers for plenty of bass... and installation depth goes up to 2.5" (65mm). And ONLY bass --- because Jehnert suggests mounting a midrange AND a tweeter on the dashboard. That means the door speakers would only be used for output around 300Hz and lower.

For reference: I run a Pioneer Premier DSP headunit with something akin to a Mosfet 50 internal amplifier (four channel) which feeds two dash mounted Infinity Kappa coax speakers (four inch) and two Infinity Kappa 5.25" in the rear deck. The Infinities have their own passive cross over to filter frequencies to the tweeters and the mid/woofer, but you can't really feed low level signals to these things, so I use the internal head units electronic cross over to filter out anything below about 150hz. The low level output of the head unit feeds a Infinity Basslink T sub mounted in the trunk. The Basslink T has a internal 250 watt amplifier, a single 10" sub and two passive 10" subs. It also has a rotary volume control which you can use to boost the low level output and is convenient vs. messing around with the internal head units EQ or bass settings. The DSP of the head unit allows you to tailor your sound stage, so for example, I have it optimized for the driver, which requires you to measure the distance from your head/ears to each speaker and input these measurements into the head unit, the head unit then applies time delay so that all sound arrives at your ears at the same time, thus eliminating the Haas Effect, which is directly related to you sitting off axis in the sound field.

I agree time alignment is super awesome. I'm done some time alignment of the front drivers before and it REALLY REALLY makes for an optimal front stage. As well, I want to ensure that stuff at 250hz or 300hz and higher is coming through the dash ---- so door mounted woofers would be just that --- woofers.

That's why I'm gonna copy @8899 who copied that ERASE guy on Banzworld (who I think is also GoldenEars on DIYMobileAudio.com) and use a ScanSpeak 12M for the dash midrange --- it is supposed to be a perfect drop-in and is supposed to sound very good. Picture of ScanSpeaks lying in my garage -- I picked them up new from eBay for a terrific price.

This is as far as I should of gone, but I made my life more complicated by sourcing a set of Pioneer coax speakers to mount in the factory door locations. Not a quality speaker, but the only 2" mounting depth ones I could find that would fit the factory door pods. These are powered by a small ADS 25 watt amplifier mounted where the factory amplifier is. This was a total waste of time and added nothing to the sound stage, so I would bypass this altogether and just leave the factory parts in place and unmolested.

Yeah I'm gonna learn from you and not have the door speakers spit out anything past 250/300hz.

This is my plan. Note I'm keeping the rear OE speaker set. For the rears, I algebraically subtract R from L (L-R) and play that through both rear speakers, delayed by about 20ms (and also band limited to about 7000hz tops). In my experience, that seems to really add yet-even-more-depth to a time-aligned front stage.

 

[Jlaa]

BTW @2phast, if you are interested, this is what I intend to do with the 500E. I did this to another car and basically:

1) The time alignment did wonders! Wowzers! The singer is standing right there on my dashboard. You are right with that time alignment stuff.
2) The addition of 20ms of delay for L-minus-R and band limited in the rear is another huge wowzers effect. The singer is now standing somewhere on my hood or front bumper and now I'm in a club, and the whole experience is really immersive.

 

[2phast]

We have two different opinions about cassette decks and paper cone speakers.

Common ground systems have the negative of the speaker grounded to the chassis. If you try to connect a floating ground amplifier's negative speaker leads to a common ground speaker arrangement, well, good bye amplifier. You should try a Google search on this topic as there are probably more experts and possibly some who have integrated the two systems or discovered workarounds.

In some situations, existing components can be integrated with aftermarket, but it can be quite challenging. Some Bose OEM speakers are 2 ohm for example and most aftermarket amps are looking for a 4 ohm speaker load, running a 2 ohm load can easily overload a amplifier or provide too much power for the OE speakers (which are matched for the OE amplifier).

In almost every situation, going with aftermarket is going to be less expensive, provide a better experience and provide a more feature rich system.

As for the Jehnert. That is a slick setup for MID-BASS. I would never use something like that for low frequency reproduction, a 6.5" isn't suitable AND you don't want to use the inner door cavity as a sealed enclosure AND there is no room to construct something out of fiberglass. Your going to end up Dynamatting the entire inside of the door skin just to deal with the rattles and vibrations. This solution also requires extensive modification of your OE door card. If you elect to run this arrangement, use them for mid base, limit your 4" dash speakers to mid range only. This arrange would require a combination of passive and active cross overs or preferably, a full active 4 way cross over network.

A low frequency speaker requires that the rear wave of the speaker be encased in either a sealed or vented enclose. Said enclosure needs to be a specific size based on the parameters of the speaker itself (google Thiele/Small). Most manufactures will provide this information and it can be input into one of the myriad of sub woofer enclosure design problems and will spit out what size the rear enclosure needs to be (volume) and if vented, what diameter and length your vent would need to be.

You can use a small sub in your trunk without compromising much space and surprising as it sounds, you don't really need to cut any holes in your rear deck to allow subsonic frequencies into the cabin. Investigate a self contained solution, something like this;

https://www.crutchfield.com/p_108BASSLDC/Infinity-BassLink-DC.html?origitemno=108BASSLIN

Personally, I wouldn't use those rear speakers, although I know they are primary just for "fill", I would match them up with your fronts for optimum sound quality and decibel level.

Also, when choosing speakers, pay close attention to the efficiency rating, which would be something akin to 93 db 1w1m, that translates into a efficiency of 93 decibels with 1 watt of power measured 1 meter from the speaker. The higher the efficiency, the louder they will be using less power. Keep this in mind, to increase SPL just 3 decibels, you need to increase the power by 100%. So a speaker with 91db efficiency with 40 watts of power applied to it is not going to be as loud as a speaker with 94db efficiency with the same 40 watts to power going to it. To match them up, you would need to double the power of the first speaker to equal the output decibel level of the 2nd.

 

[2phast]

BTW @2phast, if you are interested, this is what I intend to do with the 500E. I did this to another car and basically:

1) The time alignment did wonders! Wowzers! The singer is standing right there on my dashboard. You are right with that time alignment stuff.
2) The addition of 20ms of delay for L-minus-R and band limited in the rear is another huge wowzers effect. The singer is now standing somewhere on my hood or front bumper and now I'm in a club, and the whole experience is really immersive.

View attachment 85374

Yes, your spot on, although the actual amount of delay in ms will vary from vehicle to vehicle and person to person.

 

[8899]

As for the Jehnert. That is a slick setup for MID-BASS. I would never use something like that for low frequency reproduction, a 6.5" isn't suitable AND you don't want to use the inner door cavity as a sealed enclosure AND there is no room to construct something out of fiberglass. Your going to end up Dynamatting the entire inside of the door skin just to deal with the rattles and vibrations. This solution also requires extensive modification of your OE door card. If you elect to run this arrangement, use them for mid base, limit your 4" dash speakers to mid range only. This arrange would require a combination of passive and active cross overs or preferably, a full active 4 way cross over network.

Personally, I wouldn't use those rear speakers, although I know they are primary just for "fill", I would match them up with your fronts for optimum sound quality and decibel level.

Yes, while the Jehnert setup does a decent job of providing mid-bass, it is not a substitution for a sub. And I completely agree re rear speakers....they don't help ANYTHING. At all.

 

[gsxr]

Jlaa's plan looks good to me, if he can figure out the floating-ground thingy, or otherwise get the 1432 source into the JL 8-channel amp. Once the JL gets a proper signal, the rest should be all fixable with digital wizardry: crossovers, parametric EQ, time alignment, DSP, and rear fill processing.

I think the OE rear speakers get a bad rap because people expect more from them than is really needed. The system Jlaa is describing uses the rears for fill only; at lower levels than the front, and with a reduced frequency range. In this application, the stock speakers should be fine. Note this is for the "sound system" rears only, with dual tweeters. The standard rears are a single, smaller, full-range paper cone that is truly awful. If working with a car that has the dinky full-range rear, please upgrade that. But the dual-tweet setup with larger woofer is really not bad for rear fill duty. Again, this assumes you are designing a system to sound great for the FRONT SEAT occupants. If you want great sound for people sitting in the rear seats, that's a whooooole separate discussion.

 

[Jlaa]

Yes, while the Jehnert setup does a decent job of providing mid-bass, it is not a substitution for a sub. And I completely agree re rear speakers....they don't help ANYTHING. At all.

Perhaps contrary to conventional wisdom, I'm fan of form over function - for the same reasons I like the glorious Becker in the dash, I'd like to keep the car free of additional detritus (subwoofer box) in the trunk. I like the car as a rolling shrine to the 90s --- else why would I put up with that space-robbing telephone in the armrest or that stupid AMPS phone amplifier hogging that space in the bottom left of the trunk?

That said, did you re-use the Jehnert tweeters with the scan speak (and the Jehnert cross over) in the dash? How did you find that got along?

... or otherwise get the 1432 source into the JL 8-channel amp. Once the JL gets a proper signal, the rest should be all fixable with digital wizardry: crossovers, parametric EQ, time alignment, DSP, and rear fill processing.

All this DSP work to de-equalize (and then subsequently re-equalize and time align) is really new stuff. The JL Audio FIX's main function is to take whatever your car's OE audio system spits out - even speaker level outputs - and flatten everything to give you something to start with. I didn't realize such a thing existed until I was talking with some folks in the industry a few weeks ago. Apparently de-equalization is really necessary these days because with new cars, you can't just replace the headunit (the screen) or even find line-outputs on new cars ---- and car manufacturers equalize and time align everything like crazy so that they can get away with using inexpensive paper-cone speakers (hah) and get away with suboptimal speaker placement.

People really like to talk about the hardware because its tangible, but I think all this recently available SW DSP work confers equally great if not even larger benefits.

I think the OE rear speakers get a bad rap because people expect more from them than is really needed. The system Jlaa is describing uses the rears for fill only; at lower levels than the front, and with a reduced frequency range. In this application, the stock speakers should be fine. Note this is for the "sound system" rears only, with dual tweeters. ... If you want great sound for people sitting in the rear seats, that's a whooooole separate discussion.

After geeking out a while with DSPs, I realized that using the L channel and subtracting it from the R channel and THEN, spitting it out the rear speakers with an additional 20+ millisecond delay has a huge huge huge effect on your perception of the expansiveness of the sound. I don't even think this is possible with the DSP on most head units --- I think you need discrete DSP hardware to do that.

I checked out the Pioneer DEX-P99RS manual (page 75 here - https://www.pioneerelectronics.com/StaticFiles/Manuals/Car/DEX-P99RS_OperationManual0428.pdf) and they talk about maximum time alignment values around 11 millisecond (150 inches). I'm not talking about just time alignment, I mean time alignment AND THEN ON TOP OF THAT adding another 20 millisecond delay for the rears. That's like adding over 20 feet. I'm not sure that modern head units let you add more delay on top of [auto] time alignment.

L-R information is really everything in the two stereo channels subtracting what is common (i.e. the voice which is probably coming from the center). It sounds really goofy and funky if you just play it by itself --- it sounds like a ghost version of the music with no-one singing. So if you take you take that L-R difference and you band limit it to say, 5KHz or 7KHz tops and you make it come out the rear, albeit 20 milleseconds later -- wowzers, the effect combined with a time-aligned front is spectacular. The effect is a similar experience to listening to a movie in stereo on your home cinema for a while, and then pushing the button to listen to the same movie in Dolby Pro-Logic or Atmos or THX or whatever they use these days.

If you had a rear seat passenger it would be a super weird experience for them to listen to L-R delayed 20 ms .... in that case just turn all that DSP jazz off I guess. Normally if I have passengers in the car, I'm not listening to stuff nearly as intensely as if I'm alone anyways.

 

[8899]

That said, did you re-use the Jehnert tweeters with the scan speak (and the Jehnert cross over) in the dash? How did you find that got along?

Yes, but don't recall if I used the Jehnert supplied crossover or not. But, it all plays together nicely!

 

[Kyiv]

I've been selling home audio speakers, amplifiers and pre-amps from different brands for several years. From Klipsch, to Paradigm, to Kef, Marantz, Yamaha, Anthem, etc. I've seen, handled and examined many. So I'll add a few cents, on what I think lands in the general plane of the topic.

1. Generally speaking and chopping off extreme tails on either side of the bell curve, there's no difference in sound quality between properly engineered in-wall and in-ceiling speakers of the same size, across brands. A $400 MSRP speaker from a relatively mainstream manufacturer with good economies of scale, sales volume, say like Klipsch will be as good as a $1,000 Paradigm speaker. There's only one woofer and one tweeter to deal with and that's it. They all have perfect in-spec electrical components. The cone and tweeter (paper, copper, beryllium, titanium, aluminum) material makes no difference. I think it's just for looks. Same as some tire manufacturers design tire tread to look cool with no added benefit to functionality.

In-wall and in-celling are very high margin items. Usual mark-up from dealer cost to MSRP is about 250%. One gets a relatively low bang for buck with them if purchased at MSRP. It's always better to buy from a relatively mass market brand such as Klipsch for example, vs a boutique brand such as Paradigm in this respect

2. All properly engineered and in-spec amplifiers sound the same at identical volume. A $300 a/v receiver is as good as $10k amp - at the same volume.


What this means for our cars:

1. My guess is that original Mercedes speakers, unless damaged, are as good as any modern 2, 3, 4 hundred dollar ones

2. New amplifiers, unless original is worn/out-of-spec will not make any difference

3. Our car's sound system was, to the extent possible, optimized from the factory, given speaker cavity damping quality and size, and interior shape.

Unless one changed: cavity size, it's damping quality, increased speaker size and then fine-tuned crossover and DSP settings with the help of sound engineering laboratory - there will be no objective improvement. Actually, it's a-lot-more-likely-then-not that the sound quality will actually be worse, but louder

 

[Jlaa]

OK, here is my final post in this thread as I wish to close this thread (my pet peeve are threads on forums on the intrawebz that never seem to have any conclusion). I did some research and wish to close out this question.

Common ground systems have the negative of the speaker grounded to the chassis. If you try to connect a floating ground amplifier's negative speaker leads to a common ground speaker arrangement, well, good bye amplifier. You should try a Google search on this topic as there are probably more experts and possibly some who have integrated the two systems or discovered workarounds....

Jlaa's plan looks good to me, if he can figure out the floating-ground thingy...

Just to be clear, the Becker amplifier system in the "Sound System" package (mit BE1432) uses a common SIGNAL ground to feed the amplifiers from the fader. This is not to be confused with CHASSIS ground for electronic components, and, furthermore, not to be confused with whether or not CHASSIS ground is either floating or not.

You can see that pin 7 on the Becker amps is the common SIGNAL ground for the front signal (pin 3) and the rear signal (pin 9). This is a similar arrangement like on TRS headphone jacks, which are commonly used to send UNBALANCED stereo signals, as show in the attachments below.

I was just making a mountain out of a molehill because I was used to RCA connections, where L and R had separate SIGNAL grounds.
Further reading: Headphone Jack and Plugs: Everything You Need to Know - Headphonesty