Running an amplifier using existing BM54 (modified)

Discussion in 'General maintenance, upgrades and modifications' started by MrHooky, May 10, 2020.

  1. 10 May 2020 at 12:22 PM #1
    MrHooky

    MrHooky A mere Chipper

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    So I'm continually looking to improve on existing sound quality. What started as a small sound upgrade keeps evolving! I've had the BM54 unit upgraded by Carphonics to c.50w per channel with RCA pre-outs fitted to the rear. I've fitted Focal speakers in the front doors (component) and Focal coax in the rear parcel shelf.

    I'm now tempted to run a small 4 channel amplifier from the BM54 given I've had pre-outs fitted. My questions are:

    • Will this produce a better quality in sound? I'm not looking for more volume. The Carphonic upgrade has been a massive improvement, but the front door speakers still fee a little underpowered/underwhelming, which I think it down to limitations in the BM54 unit. Would connecting a dedicated amplifier rectify this?
    • How do I best connect the sounds outputs from the amplifier to the existing E46 wiring loom. The BM54 unit is connected to the amplifier via the RCAs, but do I then need to buy a converter for the large pin harness connected to the BM54 that talks to the head unit? I'm a little confused as to how to ensure the head unit, BM54 and external AMP all communicate properly. I was assuming some sort of adaptor/splitter that would ensure the head unit is still connected to the BM54, but the speaker connectors are being fed from the AMP outputs.

    Sorry for the noddy questions. This is all new to me, and haven't upgraded a car sound system since I was 17 (20 years ago!)

    Looking at spending sub £200 on an external AMP, like the look of the Focal ones, c.4x60 Watts per channel which I'm hoping give the front speakers a bit more depth. Bizarrely the rear Focals sound pretty good, but I'm guessing that's the way the existing BM54 works, by driving more sound through the rears, with the fronts being more 'in-fill'.

    Cheers
     
  2. 11 May 2020 at 11:23 AM #2
    ExCop530dT

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    Hi MrHooky,

    In a nutshell, no, adding a separate amplifier won't improve the 'Sound Quality'. The reason is follows; The OEM audio system has a factory pre-set Equalisation curve and is done with the other OEM modules and speakers characteristics. It's non changeable too. By changing the IC's in the BM54 unit, the difference is that there's now more RMS power output which translates into being 'louder' as the speakers are being driven with that increased power. There's not been an increase in Sound Quality as the same EQ curve is still the same. What has also happened, is given the new speakers are 'better' than the OEM ones, then they do sound different to them given they will have better frequency response and efficiency. That 'difference' will be described as 'sounding better' for sure however, it's usually mentioned for the bass response.

    To Improve SQ, you need to go a different route if you wish to keep the OEM setup. Two options come to mind

    1. Use a Sound processor - This will take all the output from the BM54 amp and in your case, you'd disconnect the speaker outputs and use the RCA's you've had added. You'd take that BM54 output (RCA's) and input into a sound processor. This will cleverly analyse the input signal and remove the factory EQ curve to then output an as acoustically 'flat' as possible signal. At the same time, it'll boost the signal voltage as well. You then take that 'cleaned/improved' audio signal and connect to the aftermarket amplifier of your choice and in turn, drive your Focal speakers.

    2. Use the Intravee setup along with one of the compatible Alpine Processors which also have an Equaliser (and more features) built in too. The output from the Alpine processor will then connect to the aftermarket amplifier of choice and then it will drive your Focal's.

    I'm not sure on your 2nd question. Confirm with Baris that if the BM54 amp is left as it is right now (driving the Focals) if the RCA outputs are 'live' and functional? I'm assuming it will be. You can then connect an amp to that RCA output and just disconnect the speakers.

    The ideal is to have as much SQ coming from the front speakers and the rear ones just need to be for a bit of 'rear fill'.

    To make the most of the route you go, I'd always suggest going with a subwoofer as well. You can get a compact solution that'll provide smooth, controlled, musical, tight, low and matched sub bass to then provide the full musical range of frequencies of the music. Currently, it sounds as though you don't have any sub bass in the car.

    Cheers, Dennis!
     
    Last edited: May 11, 2020
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  3. 12 May 2020 at 12:16 AM #3
    MrHooky

    MrHooky A mere Chipper

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    That's really useful Dennis and appreciate the detail here.

    My second question was around the fact that the harness plugging into the BM54 unit seems to be a 'one-stop' harness/connector, taking everything from headunit into the BM54, plus then the speaker output cables from it. Hence if I was to use the RCA pre-outs from the BM54 to take to an external amplifier, then how do I best re-wire the speakers from the existing BM54 connector to the new amplifier. I think my answer is to cut them out of the harness/connector and re-wire into the AMP.

    Understood re the sound processor. Not considered before but makes sense. Would the existing head unit bass/treble still adjust the sound if running an external sound processor?

    I guess I'm just looking to see where I can make some more noticeable improvements. Baris' initial upgrade was night and day. I then replaced the rear speakers with FocalAC165s and they make a big improvement - there is decent bass - which I think is them effectively use the boot space to create a bit of bass. I'm not a bass junkie to be fair. The fronts however sound a bit underwhelming in comparison. I'm not that fussed, but just a little disappointed when compared to the rears and I think it's just an inherent limitation of the BM54 unit still. I had looked at the slimline Focal under seat sub, that I was considering just having in the boot instead.

    It's night and day better than what it was, and for a small outlay I'm pretty chuffed (£200 on speakers) and a pretty modest amount on the BM54 upgrade. I'm just now thinking in for a penny in for a £, and seems a shame not to have premium Focal speakers working their best.

    One last question - and this is really daft - do people simply screw the subs/amps into the current boot floor. I don't really want to damage the existing floor so was thinking of perhaps putting some thin ply underneath and getting a new boot carpet to screw through!
     
  4. 12 May 2020 at 1:02 PM #4
    ExCop530dT

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    Hi MrHooky,

    The OEM harness 'into' the BM54 and the 'output' from it are the original wires as you've 'kept' the original setup design.

    You can't take the 'inputs' to the BM54 and connect to the inputs of the new amplifier - else the BM54, monitor, GPS computer will not work. The OEM setup is modular and each need to be interconnected.

    For those who wish to 'keep' the OEM setup, the ways to 'add on' to the setup is the two points I mentioned above.

    Now, if you were to use a 5 channel amplifier, you could put the 4 outputs from the BM54 and connect to the Sound Processor which will then 'clean' the audio signal as best it can. The outputs from that will go into the 5 channel amp and you then connect the Focal's for the cabin and the processor will provide a dedicated subwoofer output too.

    You could use the powered slimline sub route and mount it in the ski hatch area and it might provide enough output that suits you. I'd still recommend a proper small sealed enclosure with a 8/10 inch modest high quality brand subwoofer, but it's your choice.

    I'd not recommend screwing a sub enclosure directly to the boot floor metal. A small sealed enclosure and sub doesn't weigh that much and can be securely mounted to the trim without cutting or screwing into anything.

    Cheers, Dennis!
     
  5. 17 May 2020 at 12:31 AM #5
    jafbash786

    jafbash786 Wearing official underwear

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    im sure u can add an inline amp to the left and right channels to boost power to each audio component

    Like this

    Panasonic d1004 amp 4x 45w rms

    Check my video although its an aftermarket setup it works with factory headunits just some splicing worth a try for some serious added punch

    Carphonics mods will make it on par with aftermarket units for me this baby amp added atleast 20% more volume with no distortion

    This addition can hide behind your stereo

    Only £70

    https://youtu.be/_uFqMrkrFIc
     

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