Easiest way to get my sub working?

[hedges88]

Hi All,

ICE and car electronics is probably my weakest area in terms of my car knowledge I'm useless with it and I'm asking for a little advice.

I replaced the original head unit in my Mercedes Benz W169 with a nice Erisin android unit. It works perfectly, the fade effect for the driver's seat work's well etc and sounds great in general and definitely an upgrade on the OEM unit.

I find the standard speakers to be adequate but too much bass can muddy the sound so I thought rather than upgrade the door speakers which will be a heck of a job I'd simply add a subwoofer and allow the other speakers to do their job a little better. The Erisin unit has just ONE RCA output which I have looked into and apparently it's as simple as using a cheap Y splitter cable.

To keep with the OEM look and feel of the car, and because it came up super cheap I got an original Mercedes Benz subwoofer that goes in the spare wheel well. This was part of the Logic 7 Harmon Kardon option my car does not have and uses the MOST bus technology. I'm aware expensive MOST to analogue converter's are available but seeing as my car never had the Logic 7 option and therefore doesn't have the amplifier unit installed I would find this to be pointless.

At the end of the day a speaker is a speaker is my thoughts. My plan would be to simply unscrew the speaker (maybe drill a hole in the casing for direct wiring) bypassing this MOST crap and to then get that sub speaker somehow connected to the ERISIN head unit. My understanding is the head unit cannot power the sub alone and so I would need to connect speaker to small amp, get the amp neatly mounted and powered somewhere and then run the RCA cables to the ERISIN which should be capable of sending the low sounds only to the sub output.

So as someone with little knowledge of ICE my questions would be, is my plan viable? If so what sort of cheap little amp could I use to power just that little sub speaker? It's just one speaker and that's all. I have access to Mercedes-Benz software so can easily find a place to mount and power an amplifier with wiring diagrams to find a power connection.

Any advice greatly appreciated, but I do want to stick with that OEM unit even if it might be easier to get something else

I've attached a picture of the sort of sub for reference, if there is any easier way to connect MOST to RCA then that would be ideal but I don't think there is??

[defblade]

First thing you need to do is find out the ohms of the speaker - commonly 4 or even 8, in which case any amp might do; but if it's 2 or 1 you'll need to check specs carefully. Then you'll need to research the RMS power it can handle. You will probably also want an amp with a low pass filter, so that speaker only see the bass notes.

[hedges88]

defblade said:

First thing you need to do is find out the ohms of the speaker - commonly 4 or even 8, in which case any amp might do; but if it's 2 or 1 you'll need to check specs carefully. Then you'll need to research the RMS power it can handle. You will probably also want an amp with a low pass filter, so that speaker only see the bass notes.

So I've tried to find out by disassembly but there is no information anywhere I've searched on those numbers and looked everywhere to find out it's actual specs. One thing I was not expecting when I actually lifted the unit out having unscrewed. The very small grill was just how heavy and big this sub actually is in its own little way. Also why is it connected like that on both sides? It's heavy. I can tell you that for sure. The only thing I have ever heard about them is that the Harman kardon thing is a bit of a sham and that they do not actually make the speakers that go into the Mercedes Harman kardon logic 7 package for the car.

Is it possible to tell just from the look of the thing what sort of ohms and RMS power it's likely to have?? Then if I manage to get that far will I need a low pass filter amp because the erisin head unit knows that output is for the subwoofer and it does do a lot of stuff with software with regards to frequency control and stuff like that. In any case, I guess I'm stumped at this first hurdle of not knowing anything about the speaker and therefore not even having the slightest idea of what I'm supposed to pair it with

[defblade]

Well, it's dual-coil, so its load will vary depending on how it's wired.
https://www.crutchfield.com/S-dbcSPHQIkfC/learn/wi...
https://www.crutchfield.com/learn/learningcenter/c...
Also page 58 (menu on right) here: http://www.bcae1.com/

You may be able to play around with a multimeter and the wiring a bit and work out the ohms by how it varies when in series/parallel... but the ohm rating of a speaker is only nominal/minimal, so don't be surprised it the results don't make a lot of sense, sorry.

I've tried a bit of Google, and a few comments about 160 watts into the sub in various HK systems, but nothing specific. Several comments about them using a 2 ohm load though. Also tried the sticker numbers, but not sure if I'm reading them correctly.

Have you considered emailing HK? Some big companies can be amazingly helpful with polite queries! Not much to lose, anyway

[hedges88]

defblade said:

Well, it's dual-coil, so its load will vary depending on how it's wired.
https://www.crutchfield.com/S-dbcSPHQIkfC/learn/wi...
https://www.crutchfield.com/learn/learningcenter/c...
Also page 58 (menu on right) here: http://www.bcae1.com/

You may be able to play around with a multimeter and the wiring a bit and work out the ohms by how it varies when in series/parallel... but the ohm rating of a speaker is only nominal/minimal, so don't be surprised it the results don't make a lot of sense, sorry.

I've tried a bit of Google, and a few comments about 160 watts into the sub in various HK systems, but nothing specific. Several comments about them using a 2 ohm load though. Also tried the sticker numbers, but not sure if I'm reading them correctly.

Have you considered emailing HK? Some big companies can be amazingly helpful with polite queries! Not much to lose, anyway

Thank you for all the information you posted. I'm away from home at the moment but I think the best thing I can do is to use my access to Mercedes Benz electronic workshop manuals and load up the part numbers and wiring diagrams of the power sound option for the vehicle, which I believe is code 535 as opposed to mine being a 527. That would give me a better idea of what amp they used. However, that amp would have been not only to power the subwoofer but also the upgraded door speakers and also the central speaker in the dashboard that w169 and w245 models have as option codes as well as some of the C-Class, coupés, etc. I doubt Harmon kardon would want anything to do with an enquiry. They would probably consider it a Mercedes-Benz problem not there's and as I say I don't really believe that the system is manufactured by them but just carries their branding.

As soon as I get home and get access to the systems are upload the diagrams and the specifications. But in the meantime if someone could explain to me what a dual coil is that would be helpful. My whole life speakers have just been a positive and a negative powering a magnet. I said I wanted to stick to the OEM look and feel and I do but only if it's practical and reasonable, otherwise something that goes under the seat that's already to connect straight up to the head unit and would be easier to wire. Might just be the best thing to do?

[defblade]

hedges88 said:

But in the meantime if someone could explain to me what a dual coil is that would be helpful. My whole life speakers have just been a positive and a negative powering a magnet.

It is still just that.. but twice
(NB: the magnet is not powered! It's an electrical coli inside the magnet that's powered. It's an electric motor, but linear rather than rotary. Normally just the one coil inside the magnet; this one has 2.)
Just means you can wire it to give different loads.


Ultimately, if you wire it in series, then it'll be safe (ok, should be safe. There is a tiny, tiny, chance it may be dual 1ohm) for any amp, as it will give at least a 4ohm load; if it gives 8ohm, then it's still safe, but will not be quite so loud (in theory... in practise, the resistances are nominal minimums (as far as I understand it!) and so it may well not make as much difference as you'd think).





Suggestions on the internet that these subs run possibly 160w, and/or that the total system is around 600w - I'd be splitting that on the order of 100w per door, and 200w for the sub (or maybe 75/300). So if it was me, I'd be looking at an amp to provide around 200w or so @4ohm (either a mono amp, or a bridged 2-channel).
Speakers will be happier driven by an amp with "too much" power, but keeping a clean unclipped signal, than they will be being driven by "too little" power turned up into clipping to try and make it loud enough. I'd go so far as to say almost any amp above 200w would be ok, so long as you start with the gain turned right down and turn it up slowly while aiming to reach a balanced sound overall, and not to produce a bass monster.

Edited by defblade on Sunday 31st October 08:40

[hedges88]

defblade said:

It is still just that.. but twice
(NB: the magnet is not powered! It's an electrical coli inside the magnet that's powered. It's an electric motor, but linear rather than rotary. Normally just the one coil inside the magnet; this one has 2.)
Just means you can wire it to give different loads.


Ultimately, if you wire it in series, then it'll be safe (ok, should be safe. There is a tiny, tiny, chance it may be dual 1ohm) for any amp, as it will give at least a 4ohm load; if it gives 8ohm, then it's still safe, but will not be quite so loud (in theory... in practise, the resistances are nominal minimums (as far as I understand it!) and so it may well not make as much difference as you'd think).





Suggestions on the internet that these subs run possibly 160w, and/or that the total system is around 600w - I'd be splitting that on the order of 100w per door, and 200w for the sub (or maybe 75/300). So if it was me, I'd be looking at an amp to provide around 200w or so @4ohm (either a mono amp, or a bridged 2-channel).
Speakers will be happier driven by an amp with "too much" power, but keeping a clean unclipped signal, than they will be being driven by "too little" power turned up into clipping to try and make it loud enough. I'd go so far as to say almost any amp above 200w would be ok, so long as you start with the gain turned right down and turn it up slowly while aiming to reach a balanced sound overall, and not to produce a bass monster.

Edited by defblade on Sunday 31st October 08:40

See I wasn't lying when I said I know nothing about ICE and stuff

So I learned what dual coil is and I perfectly understand it I think. If you have a speaker in a central location, like the centre dashboard speaker or the rear sub it's no good to have one coil because it's got to offer sounds from both the left and right channels otherwise it would sound odd.

And thanks for letting me know how they work, for someone who's enjoyed music their whole life all I knew it had something to do with a magnet and vibration lol

The details on the AMP used are a bit sketchy, Harman MO series but yet again you don't get detailed information on them. They are fairly large with a fan and stuff for cooling. As this is just going to be powering one sub and the head unit is dealing with the other speakers I know I need a fairly modest amp and I've looked at the wiring diagrams you have shown me but still just a little confused about 1 or two channel amps. I take it that after using the RCA Y splitter from the Erisin head units single RCA output I'm left with a left and right channel. So do I then run that to a one channel amp but then have to bridge the speaker like in the diagram or do I use a two channel amplifier and then connect the left channel and right channel directly from that??

Once I know what amp I need and how to wire it I'll be okay I have to run and trim fit the reverse camera wiring as well so it's not a bother

[defblade]

hedges88 said:

See I wasn't lying when I said I know nothing about ICE and stuff

So I learned what dual coil is and I perfectly understand it I think. If you have a speaker in a central location, like the centre dashboard speaker or the rear sub it's no good to have one coil because it's got to offer sounds from both the left and right channels otherwise it would sound odd.

That's not why it's dual coil! The left and right channels should be bridged together in the amp (or even the pre-amp), the signal the sub will see will be mono, no matter how many coils it has. It's all to do with resistance choice in wiring. Single, dual, quad coils would all get the same mono signal.

hedges88 said:

I know I need a fairly modest amp and I've looked at the wiring diagrams you have shown me but still just a little confused about 1 or two channel amps. I take it that after using the RCA Y splitter from the Erisin head units single RCA output I'm left with a left and right channel. So do I then run that to a one channel amp but then have to bridge the speaker like in the diagram or do I use a two channel amplifier and then connect the left channel and right channel directly from that??

Once I know what amp I need and how to wire it I'll be okay I have to run and trim fit the reverse camera wiring as well so it's not a bother

With a single RCA out (and a quick google at the make), your output is already mono, designed for a sub (otherwise there'd be 2 RCAs).

So if you get a mono amp, you won't need a y-splitter at all. A mono amp may still have 2 RCA inputs, but that's to allow it to sum both channels when there's no dedicated sub output from the HU. It should say which of the plugs to put a single mono feed into. There'll only be one output from the mono amp, so no concerns regarding bridging.

A 2-channel amp will need the RCA splitter to give both channels inside a signal (even if it's the same signal, as it's mono not stereo), but then you will bridge the output so you still get a single output signal to the speaker.

I'm not entirely certain what would happen if you took a 2 channel amp and wired one voice coil of the sub to each channel, but I don't think it would be good...!

[hedges88]

defblade said:

With a single RCA out (and a quick google at the make), your output is already mono, designed for a sub (otherwise there'd be 2 RCAs).

So if you get a mono amp, you won't need a y-splitter at all. A mono amp may still have 2 RCA inputs, but that's to allow it to sum both channels when there's no dedicated sub output from the HU. It should say which of the plugs to put a single mono feed into. There'll only be one output from the mono amp, so no concerns regarding bridging.

A 2-channel amp will need the RCA splitter to give both channels inside a signal (even if it's the same signal, as it's mono not stereo), but then you will bridge the output so you still get a single output signal to the speaker.

I'm not entirely certain what would happen if you took a 2 channel amp and wired one voice coil of the sub to each channel, but I don't think it would be good...!

Well that just goes to show don't believe everything you read on the internet

So I just need a small mono amp, would this do the trick?

https://www.halfords.com/technology/car-audio/car-...la-1099322212692|crid:539816504853|nw:u|rnd:11223582183759661166|dvc:m|adp:|mt:|loc:9046046&gclid=Cj0KCQjw_fiLBhDOARIsAF4khR0r5d_P6b-nXkmZWhh5WrMjeBFd5eZCE0UhGssmRmP_0rOWlcK6RfgaAvGxEALw_wcB

It's not expensive and says it's for a sub

[defblade]

hedges88 said:

Well that just goes to show don't believe everything you read on the internet

So I just need a small mono amp, would this do the trick?

https://www.halfords.com/technology/car-audio/car-...la-1099322212692|crid:539816504853|nw:u|rnd:11223582183759661166|dvc:m|adp:|mt:|loc:9046046&gclid=Cj0KCQjw_fiLBhDOARIsAF4khR0r5d_P6b-nXkmZWhh5WrMjeBFd5eZCE0UhGssmRmP_0rOWlcK6RfgaAvGxEALw_wcB

It's not expensive and says it's for a sub

Should be fine... although I'd still want to try to find out the ohms of the coils - that amp does 400w @1ohm, 250w @2ohm and 170w @4ohm - so probably about 100w if you give it 8ohm (series wired). Be nice to parallel wire it to give 2ohm/250w if possible.