tw2

I have searched many threads and not found the answer, it is even more difficult since "sub" is too short for the search engine and no one uses subwoofer. Anyway from what I can ascertain, the dual voice coil sub is run off both of the rear speaker wires. When I tested the front speaker wires they were normal 4ohms as expected.

When testing the rear speaker wires they were 5.4 ohms. How do you get approx 5.4 ohms from two 4 ohm devices? (both of the dual coils are 4 ohms each)

My other question is that when I looked at the wires on the sub itself they almost look out of phase. The pink wire appears positive but the brown with white stripe on the other side is hooked up to positive also? Obviously mercedes would not have wired them out of phase so what am I missing?

Sub wires


Left side of sub


Right side of sub

phister

Looks like its a DVC (dual voice coil) sub and they wired so it sounds like a two subs instead of one. It doesnt look like its brigdged. Heres a diagram of what it maybe setup like.

tw2

Yes it is DVC but there is no amplifier specifically for the sub, it is driven from the rear speaker wires ie from the head unit.

phister

It probably uses a hi/lo converter of some sort. Or the HU has a built in amp.

amdeutsch

Depending on where you are taking that measurement you are most likely reading through the crossover as well. That would introduce an additional DCR value.

Glyn M Ruck

Note - it is wired out of phase!

https://mbworld.org/forums/c-class-w...rear+subwoofer

tw2

Thanks for the link, I had read that thread a few times. The problem is halfway through they go off on a tangent and never really get to the bottom of it. I can't believe a auto maker would accidentally wire out of phase which makes me think we are missing something.

I might just cut those wires and make a short loom to my aftermarket amp in the trunk. That would solve the problem.

I might take the resistance at the sub and speakers just to confirm. Otherwise the only way you can get 5.3ohms is if both rear speakers are 8ohms and the sub voice coils are in series.

Glyn M Ruck

It is wired out of phase due to the orientation of it's mounting i.e. upside down to the interior of the car - makes perfect sense. Send Wardsweb a PM. The impedance you are reading includes the X-Over caps.

tw2

Thank you for the reply. I have no trouble understanding that the sub is wired out of phase from the rest of the speakers because it is mounted upside down. I agree this makes perfect sense.

What I am having trouble understanding is that the two coils of the sub appear to be wired out of phase of each other. ie the white wire is negative on one coil and the pink is positive on the other coil and generally both are positive colors for the rear speakers. Or does this not even matter?

Wardsweb

This may help:



My sub install is found here:
https://mbworld.org/forums/c-class-w...pictorial.html

Glyn M Ruck

I'm sure someone at Becker/Benz has done some in-car measurement & found this set up to give the flattest response. I'm sorry I was not fully appreciating your question. I'm reluctant to believe that the twin voice coils are out of phase to one another or destructive interference would take place. The dual coils simplify impedance matching for simple wiring of multiple speakers while not presenting difficult loads to the amplifier. It would be interesting to see the full wiring diagram Benz is using. Anyway - easy check. Feed a mono thump, thump, thump bass frequency into the head unit - identical in both channels. Swing the balance from one channel to the other and put your finger on the back of the woofer cone & check the phase. Does it suck in for both channels due to mounting orientation? If it does not I would believe that the reason for out of phase wiring is to damp max cone excursion by achieving a null which is a bit tacky.

See:

http://mobile.jlaudio.com/support_pages.php?page_id=163

and this simple pdf.

Wardsweb

It is easy to get confused because you would think the brown wire would be the same for both coils. It is not. Take a close look at the picture above. It is positive on one coil and negative on the other. So, it is wired in phase. If it were wired out of phase, the two signals would cancel each other out.

Glyn M Ruck

Thanks Told him to speak to you!

tw2

Thanks, I will see if 66wrms to each coil will destroy it.
This is the part I was confused with. The positive terminal on the sub is the one closest to the camera for both sides. On the left it is a pink wire on the right it is brown/white stripe. Typically brown/stripe is a negative, so it is actually positive despite its color?

tw2

Update, the way we think it is wired is wrong. I ran the sub with an aftermarket amplifier. I ran the dual voice coils in parallel. I wired the pink(tan looking one) and the brown/white stripe one to positive and the brown/pink stripe and white to negative. You can barely hear it up on full. I then wired pink + white to positive and both brown with stripe to negative and it is normal volume.

The white is positive. If you treat it as negative the coils work against each other and effectively cancel each other out.

irokwrx

What is the size of the sub? Also has any one replaced it with a real sub(jl,mtx)

tw2

I have not measured it but it is either 8 or 10". There are lots of threads about putting new subs in, in general.

If you mean putting one where the stock sub goes then I know of at least one install. The only problem is that you need a sub that works well in an infinite baffle. Also the weight of most aftermarket subs is quite a lot to support with the metal of the rear deck.