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Old 02-28-2003, 06:14 PM
goldstone's Avatar
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Location: Dutchess County, New York
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Question Ohmmmmmmmmm

Why do I need to move the fader on my new head unit significantly toward the front speakers [+5 on a scale that runs from -7 to +7] to properly balance the soundstage in my '89 420SEL?

Facts

1) No fader or external amps in use (I bypassed the stock setup and connected 4 new sets of speaker wires directly to the speakers);

2) Stock speakers (all in great condition);

3) Head Unit has a 4x25W Max output internal amplifier;

Assuming the amp in the head unit is okay, I suspect it has something to do with resistance and sensitivity of the front drivers vs. the rear, but I just don't understand enough about the electronics to quite figure it out... yet!

For those not familiar with the '89 126 speakers, the rears are comprised of 6.5" drivers flanked by two 1" tweets each (total of 6 drivers). I'm assuming they're 4 ohms, but I haven't removed them to check (anyone know this for sure?) The front doors contain a 7" sub rated at 2 ohms, and the dash has a one-way 4" speaker rated at 6 ohms.

So, if I probe my very limited electronics knowledge, Ohm's Law tells me that the front components (which are connected in parrallel) create [1 / (1/6 +1/2)] or 1.5 Ohms of resistance in total. And, if indeed the rear drivers are all 4 Ohms, then they should present [1 / (1/4 + 1/4 + 1/4)] or 1.333 Ohms of resistance.

Does this small difference in resistance explain the reasons for needing to shift the fader so far front to attain proper balance, or is it something even more arcane
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1991 560SEL-Euro (185,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)
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Old 02-28-2003, 07:18 PM
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Your math is excellent. However, most aftermarket headunits are stable into loads in excess of 4 ohms. Running a 4, 6 or 8 ohm speaker per channel would not present a problem. A 1.5 ohm load would draw too much current for the headunit's internal amp and 'fry the deck'. There must be a passive crossover attatched to each of your speaker channels. That crossover would allow higher freqs to be routed to your smaller speakers and lower freqs to be directed to the larger speakers. Each specific freq would represent a particular load. For example in your front stage: 4,000 hz would be directed to your 4" and present a 6ohm load to your amp. 70 hz would be directed to your 7" and present your amp with a 2 ohm load. A 2 ohm stable amp would not have a problem with this scenario. Regardless of this I also bias the majority of my sound to my front stage because it sounds more natural. I am not used to hearing music come from behind me. That would be like going to an acoustic non-amplified jazz performance and turning your back on the stage. Check out the hyperlink. It has information that you might enjoy. Also contact SCLJA he has all the Mercedes specific info not found on the hyperlink site.www.eatel.net/~amptech/elecdisc/caraudio.htm
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1986 420SEL. 200,000 miles plus.
1991 Cutlass Supreme
1980 VW Vanagon (Old Smokey)

Last edited by zla39fj; 02-28-2003 at 07:27 PM.
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Old 02-28-2003, 08:11 PM
goldstone's Avatar
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zla39fj,

You're my hero! Thanks for the continuous stream of insights. Thanks also for the weekend homework assignment

Best regards,
Eric
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Eric

1991 560SEL-Euro (185,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)
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Old 02-28-2003, 09:06 PM
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goldstone
That site will be more than a weekend homework assignment it is massive and it goes deep, really deep. Goodluck!
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1986 420SEL. 200,000 miles plus.
1991 Cutlass Supreme
1980 VW Vanagon (Old Smokey)
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Old 02-28-2003, 10:58 PM
zla39fj's Avatar
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goldstone
Just a thought.

www.audionutz.com/a7.htm
No pressure mind you.
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1986 420SEL. 200,000 miles plus.
1991 Cutlass Supreme
1980 VW Vanagon (Old Smokey)
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Old 03-05-2003, 07:57 PM
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goldstone
How was that weekend homework assignment? Pretty enlightening stuff, huh?
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1986 420SEL. 200,000 miles plus.
1991 Cutlass Supreme
1980 VW Vanagon (Old Smokey)
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Old 03-05-2003, 09:01 PM
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Join Date: Oct 2002
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Thumbs up You're making me dangerous!!!

What a GREAT recommendation! The site is really jam-packed with information--as you promised.

I'm starting at the very beginning and using it as a mega-tutorial. Most of the stuff I've gotten to so far is pretty basic, but I peeked ahead and know there's a lot of sophisticated (even esoteric) content to come.

Thanks for quenching my thirst for knowledge on this topic. Don't think I'll ever be a moderator of this group; but who knows !!!

Regards...
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1991 560SEL-Euro (185,000 miles)
1989 420SEL (Retired from daily use at 325,000 miles; Use as donor vehicle)
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