[EffectOne]

Hi all,

My 2007 E92 had the base stereo system. I have recently upgraded as follows:

- Xtrons PE9690BPL head unit (front L/R RCA, rear L/R RCA + mono sub RCA);
- MB Quart QM200 (2x subwoofers, 2x midwoofer door component speakers, 2x tweeters);
- MB Quart QM100 (2x rear panel speakers); and
- Pioneer GM-D8604 amplifier.

Being my first audio upgrade/install of any kind, it took me and a mate about 8 hours to install, including lots of question marks over wiring loom locations, etc...

I have attached a diagram showing how it is wired up (apologies for the crudeness). You can see that the front/left RCA pair is connected to channel A on the amp normally. The sub output from the head unit is a mono RCA out, which is connected to the red input only on channel B. The channel A left and right speaker outputs are connected to a crossover in each door, which then runs separate cables to each midwoofer and tweeter. Speaker cables are run from the left and right on channel B to their appropriate subwoofers directly. The upgraded rear speakers are left running on the canbus, using the old speaker connections. The amplifier is properly powered and grounded.

The Problem

The left subwoofer isn't firing at all. This will probably seem obvious to some of you, given that it is a mono RCA sub output going into the amp (we assumed the amp would duplicate the single incoming signal across both outputs). To rule out component damage, we have hooked up each subwoofer individually to L and R on both channels A and B, and got sound from them on every channel. So there appears to be no damage to either the left subwoofer or the amplifier which could be the cause of the problem.

We next tried plugging a y-splitter into the mono RCA output from the head unit, and running both red and white RCA cables into the channel B input on the amp. That had no effect and the left subwoofer was still 'dead' (which surprised us!).

Does anyone have any suggestions on what I could do to get both subwoofers firing? The obvious answer is to use the unused rear L/R RCA outputs on the head unit to connect to channel B, instead of the mono sub output. However, if I do that, I will lose the ability to control bass levels in isolation in the EQ menu on the head unit (a separate 'sub' slider controls the sub output in isolation to the rest of the RCA outputs). Also, if I solve the problem by doing that, I won't be able to add a second 2 channel amp to the setup in future to power the rear speakers (I don't want to leave them plugged in through the canbus/quadlock connection forever).

Thank you, and apologies for length of post!

[ctuna]

!)Did you split the parallel connection for the Front Doors
and floors in the door sill.
2)What is the exact amp you have.
3)Do you have a volt/ohm meter? The resistance to each underseat
and each door speaker should be the same when measured from the amp
connector.

And exact model number of your amp is necessary for and intelligent discussion. Pictures always help.

You could swap the left and right channels for the underseats at the amp and see if the problem follows the channel swap in which case if would be the amp or if it didn't then it could be a speaker or speaker wiring.

[EffectOne]

Hi ctuna. Thanks for the reply. Most of the info you've asked for is in the first post I think. The amp is a pioneer gm-d8604. I've already switched subs and channels around to ensure that the components aren't damaged. Both subs definitely work, all speaker cable is definitely fine and all channels on the amp definitely work (at least individually, or when used with the door speakers for channels a and b both left and right). The door speakers on both sides work perfectly. The only issue is the left subwoofer not receiving a signal, presumably because the amp is only receiving a right signal from the mono sub rca output at the head unit. A y splitter to duplicate the signal did not solve the issue.

I do have a volt meter and the speakers that are working all show the same resistance.

The front speaker sets are no longer connected to the bmw original internal wiring looms. I cut the wires as they exited the door connector hosing and ran longer cable lengths directly to the amp I installed in the boot.

[ctuna]

Why are you not running the underseats in stereo if you
have a 4 channel amp?

"I do have a volt meter and the speakers that are working all show the same resistance."
Does that mean the one that isn't doesn't?

The way your diagram is drawn it shows one channel
to each of the front speaker locations.

Did you split the parallel connection in the factory wiring ?(for both the left and right side)

[EffectOne]

I would like to run them in stereo (and they are connected up that way - see below), but I can't run them in true stereo because the head unit only has a single subwoofer output rather than a dual RCA pair, and therefore the amp is only receiving a single subwoofer output to the red input on the B channel. I've attached a table showing how the connections daisy chain. I was hoping my diagram would show this but it must not be very clear!

As you can see, there is a single subwoofer RCA output from the head unit, which goes into the red input connection of channel B on the amplifier. Then, the appropriate left and right +/- outputs go to the left and right subwoofers. Only the right subwoofer is firing, and it must be because the amp is only receiving a single (red) input into channel B, instead of a stereo (red + white) input.

The subwoofer which isn't working shows nothing on the volt meter when there is a current passing through the system. The one that is working does. I have already tried switching the subs and channels around in various different ways to ensure that: 1) both speakers and their cables are working; and 2) all outputs on the amplifier are working.

I don't know what you mean by split the parallel connection in the factory wiring. However, the new subwoofers don't use the factory wiring at all. They have new speaker wire connected to them which runs straight to the amp. The original factory subwoofer connectors are taped up and unused.

[ctuna]

So you are not using the factory head unit?
It has no subwoofer out.
You didn't say you had an aftermarket head unit
that I noticed so that threw me off.
(not reading carefully my bad)

The underseats are not actualy subwoofers .
In the sense they go from 50 hz down. more like mid bass.

IN which case you would use a Y splitter on each of the front (you need two one for left one for right)
left right channel Inputs at the amp to provide a and b right with the right
front channel and a and b left with a left front channel. And run it in the 4 channel switch position.
In a 6 channel amp this is handled internally.
The amp manual says it has a 2 channel switch but it seems a little unclear if this splits the Input such that both the channel A and channel B set get the same signal in the the 2 channel position.

https://www.bestbuy.com/site/metra-m...?skuId=9855367

just and example above you should be able to find this at most stereo or electronics shops.

If you read the base system descriptions you will find that in the original factory configuration the front door and floor speakers are run in parllel with one channel from the from the head unit running each left/right door speaker combination. When adding an amp you want to split this connection such that there is a seprate channel driving each door and floor.

If you ran new wiring you bypassed this problem most tap into the factory wiring at least for the doors.

If you continue to have problems and you verify the speaker good by switching sides , You verify the cabling good with the ohm meter . You verify the amp good by running each channel on a known
good speaker and wire.

"The front speaker sets are no longer connected to the bmw original internal wiring looms. I cut the wires as they exited the door connector hosing and ran longer cable lengths directly to the amp I installed in the boot."

Did you do the same for the under seats in terms of wiring ?

[EffectOne]

Hi ctuna. No, I replaced the factory head unit with the xtrons unit in my first post. It has 2x front rca, 2x rear rca and a single sub rca out.

Every single speaker in the car that is connected to the amp has new speaker wiring. None of the original wiring is used.

Is there no way to convert the single sub rca out into two channels? I assumed a y-splitter would work, but when I tried I still only got sound through the right sub.

[ctuna]

I think you have another problem with that particular sub.
or something in that channel .
If you where going to hook up just a mono signal to the under seats
you have to bridge the two channels and the speakers must be hooked
up in series. And you still need a splitter to feed the mono signal at the
amp I believe . At least that is the way it works on a JL amp if I remember correctly .

I think its a mistake to do that though.
You throw away a lot of the frequency's with that setup. And you get no stereo out of the floors .

You could try disconnecting the door speakers for a test and running those channels into the floor speakers to see if anything comes out different.

https://www.google.com/search?q=sub+...nt=firefox-b-1

https://www.google.com/url?sa=t&rct=...9QCdj9xo0AQbcO

Google two speaker in series diagram.

https://www.pioneer-car.eu/uk/

call pioneer and see if you can get some support.

[EffectOne]

I spoke with Pioneer after sales today. They think that using a y-splitter on the mono output to create two input signals to the amp should work. Therefore, it appears that either the splitter I tried is faulty, or the amp is faulty.

I'll update once I've tried a new splitter tonight!

[ctuna]

Do you have the speakers wired in parallel or series and do
you have the channels going to the under seats bridged if
in series?

[EffectOne]

Each sub is independently wired to the amp. They do not share any cabling. The left sub is wired to the left channel B output, and the right sub is wired to the right channel B output.

I could wire them in parallel as a last resort, but I am hoping to avoid that (mainly because it would involve pulling up even more central trim and carpet)..

[ctuna]

Actually if you decided to rewire it could all be done at the amp. If its working the way you have it there
is no need to change things around.

[EffectOne]

The replacement splitter solved the problem. The splitter I bought originally was faulty. Everything is now fully working! Wohoo.