[Emilime75]

You don't seem to understand some really basic things here. No offense meant, we've all got our things.

You shouldn't have to lose stereo by bridging your 4 ch amp to 2 ch. Use the appropriate input for chs 1+2 as your left, and chs 3+4 for your right...or front pair/rear pair, which ever way your amp handles inputs - outputs when bridging.

The 35w minimum rating does not mean they need 35 watts to make sound. It's a useless spec and you can pretty much ignore it. How loud a speaker will play is directly proportionate to how much power is provided, and the speaker's efficiency/sensitivity rating. EG, a speaker rated at 90dB/1w will play louder than a speaker rated at 87dB/1w, if all else is equal.

Does your head unit have any crossover functions? If you're planning on running your door speakers with the head unit amplifier, you're going to want to high pass them. You don't want bass going to them, they will distort and likely blow up.

[sir_bacharach]

Oh my after market head unit and door speakers will both be matched at 50 Watts RMS (150 peak) and 4 ohms, I'm not sure what the BMW factory speakers were but the new ones will be 4 ohms. I imagine replacing them even if it's just with these 50Watt ones will be better than having just the standard ones in. I've been trying to look into how Ohms and Wattage interact already, but I do find it quite baffling. I understand that if you get it wrong you can put strain on either the amp or the speakers depending on which way you go. I'll read the link you sent though too.

I was just concerned that with it having a minimum Wattage figure (even though my head unit exceeds it) that it wouldn't power it to its full 50 watt potential and that the actual decibels (if that's the right terminology) will be to the max that 50 Watts RMS can put out. I imagine I sound very stupid, but like I say, I am quite new to the audio thing and trying to learn. I'll definitely read the link you sent.

[sir_bacharach]

Thanks for that Emilime75, that clarifies things. I'll be able to get the speakers I was looking at, then when the time comes I will swap them into the back and get some components in the front, unless I'm happy with the sound. I imagine you guys are extreme audiophiles compared to me, but as long as I get somewhere where I'm happy without spending crazy amounts, that'll do me. Just happy to have under the seat subs rather than a big fat bass box in the boot. I do have a space saver in there though, which sucks, it was either that or run flats. Trying to strap it up against the back seats to tidy things up a bit and keep space for luggage. It's one of the posh white alloy wheel ones from BMW. I thought they'd not take up much space, but when you plonk em in your boot, you realise how big they are.

[sir_bacharach]

I've just been thinking....

The stock head unit is 2 ohms, and I read that the original door speakers are 4 ohms as is the sub under the seat, but the way they're wired together makes them 2 ohms. Is this correct? Because I also read that the resistance of the speakers shouldn't be lower than that of the amp, so if my head unit has higher ohms and the default speaker set up is 2 ohms, is this going to put strain on my head unit and damage it?

I'm guessing if this is the case I really need to get the subs replaced and amped as soon as possible so that the door speakers will be 4 ohms to match the head unit and the subs will be 4 to match the amp.

I think with the help you guys have gave me I'm starting to get a bit more of an understanding.

I think I read that it's ok to have a higher resistance on the speakers than the out put of the amp but not the other way round.

[ctuna]

Head Unit aren't rated in ohms .
There is a minimum resistance/impedence that any amp
will drive .
This is called the stability factor and amp that is 2 ohm stable
will drive a 2 ohm load .
Head Units typically aren't rated this way.(watts per channel)
Amp output for cars is rated in watts at a given voltage(power supply voltage)
usually two are given one for battery voltage and one for alternator
voltage with the car running.(12.5 and 14 something volts)

You need to find some stereo 101 material and read it.

If you put a big load on the head unit meaning more or bigger speakers
the output drops proportionally until you have none and you damage
the output chips and or it goes into protection mode.

If you read the friggen links it tells you what the resistance and impedence
is for each speaker location.


Base audio

The "base" audio system has been around since the early days, although it only made it to the US in 2010.

It uses four channels of deck power (yes, that's right, good old 50Wx4 when lightning strikes, 18Wx4 if you're charitable, and 12Wx4 if you do the actual 12V math into 4 ohms and 1% THD).

The front channels drive:

- 6.5" woofers underseat in 8" frames and molded plastic enclosures. The underseat enclosures are identical for all systems. There is uncertainty regarding whether the duct connecting the enclosure to another chamber in the frame is actually a tuned port, or simply a funny-shaped sealed box. The woofer is not crossover-filtered. The only things taking mids and highs out of the audible output are the driver's own mechanical rolloff, and the acoustic filter formed by the seat and your rear end.

-4" mids in the door. These have a capacitor on them, acting as a high-pass crossover filter and also making the two-speakers-in-parallel a load the deck can handle.

The signal is heavily equalized to the front speakers, and has a subsonic filter around 40 hertz.

The rear channels drive only a pair of 4" mids in the back. This channel is high-pass crossover filtered around 160 Hertz, so connecting a subwoofer to it is a disappointing experience. It is also heavily equalized.

There is a low-current-output remote turn-on present with base audio systems, but it's not controlled by the radio play state. It turns on when the doors are unlocked and stays on for a while after ignition is turned off.

http://www.e90post.com/forums/showthread.php?t=352586

http://www.e90post.com/forums/attach...2&d=1266451970

http://www.e90post.com/forums/attach...2&d=1260829447

4 channels
6 loudspeakers
• 2 mid-range loudspeakers, front 100 mm
• 2 mid-range loudspeakers, rear, 100 mm
• 2 bass loudspeakers, 160 mm
Bandwidth: 50 Hz to 14,000 Hz
Max. acoustic pressure 98 dB
Amplifier power: depends on radio,
radio: 4 x 15 W (4 Ω)
M-ASK: 4 x 40 W (2 Ω)
CCC: 4 x 25 W (2 Ω)

BMW does not give the power rating on these speakers but
they can't be more than 40 watts.

[sir_bacharach]

Thanks for all that, that makes it a lot clearer.

I've read the links and another link that was given about ohms law, my heads farting a bit to be honest, I know once you understand it it must be second nature, but I think it's linking the names of the values to the idea of what they are, pressure, flow and impedance.

I'm getting there, a bit slowly, but I'm quite fatigued and it does get in the way of my thinking at the moment.

The info you linked about the speakers set up is ideal, because it tells me there's capacitor that stops the 4" door speakers from being damaged by lower frequencies, which is not something my replacements will have and my replacement speakers only rang from 66hz, so those lower frequencies wouldn't be filtered out as they don't have a capacitor on them.

So I'll probably just not swap the door speakers out just yet and wait till I do the sub and amp, so I can run the replacement door speakers direct from the head unit using the filters on the head unit to filter out lower frequencies, then I'll amp the new subs for under the seats and low pass filter those and have a bit of overlap, I think I read 20hz is a good figure for overlap, but I'll experiment.

I know I'm being a massive pain in the arse, but I am reading the stuff you're giving me too, just having a hard time getting it all to sink in at the mo, I'll keep reading it over though.

I've come a long way for me though, at first I was just shitting myself thinking the only way was to buy one of these £1000 kits with all the drop in speakers, when I really couldn't afford to be spending that kind of money and probably didn't really need that kind of power from my system.

I think so far and hopefully I'll be satisfied, I've spent about £320 on a couple of second hand SWS-8 subs, a second hand amp to power them, some elcheapo 50w nominal 4" speakers, adaptors to put those in as well as wiring adaptors for both sets of speakers so I don't have to change the BMW wiring and I already had the wiring kit for the amplifier as well as the phono cables from the head unit to amp, so I'm happy with that.

If I'm not happy after that, I'll throw those 4" front door speakers into the back doors and then get some components to put in the front and hopefully that will do the trick.

[ctuna]

In any setup worth having the parallel connecton between
the doors and floors is split and each location is run on
a separate amp channel at which point no capacitor is needed.

[sir_bacharach]

Dear all!!

I've today fitted the replacement front door speakers, so one step closer to the final goal.

I was wondering where to earth the amp, it's going to be in the boot near the battery, so I'm wondering if it's ok to earth direct to the negative of the battery or whether you know of a better earthing point in the boot. My seats don't go down on my saloon, so the trim might be different to some peoples. I've read a lot and people say that you get interference earthing direct to the battery, but I don't really understand why that would be the case.

Oh and do I need to disconnect the battery before removing the seats because of airbags etc, or can I get at the subs just by tilting the seats out the way once they're unbolted?

Cheers in advance.

Rob.

[Emilime75]

Under seat subs can be replaced by unbolting and tilting the seats back, but you may still have to disconnect the plugs due to cable length.

Always disconnect the battery negative any time you work on anything electrical in these cars.

Using the battery negative as your ground connection is OK.

[sir_bacharach]

Thanks very much. I appreciate the advice. Will disconnect the battery as you say and I might just get the seats out and give it a government if I have to take the wires off. Thanks again.

[ctuna]

The part in this where I did the under seats might be of some
help

https://www.e90post.com/forums/attac...3&d=1329017429

If you are putting the amp in the factory location a lot of people
use the wheel well ground point. The kit I got has you run wires
all the way to the battery for both sides.(plus and minus)

electical e90 pdf
http://www.google.com/url?sa=t&rct=j...,d.cGU&cad=rja
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU
http://www.google.com/url?sa=t&rct=j...85464276,d.cGU

First electrical pdf lists the factory ground points.

[sir_bacharach]

Ah, perfect. My amp is quite large and has a fan on the bottom, but I'll open up that area, mine has a cd changer there, but i'll see if I can get in and measure it up, I'd much prefer everything concealed, so this is a great help. Thank you.

[sir_bacharach]

Well the amp fit in the cubby where the factory amp did, but I had to remove the massive cd changer and bracket it was mounted on. It's not compatible with my after market head unit anyway. Was really pleased with the fit, took me all day to do though but I'm still not well.

Started at about 11am and finished up at 830pm
Just wanted to do bite sized chunks so was gonna just remove all the boot lining and wire up the amp.

Ended up dropping a part of the negative battery terminal down the back of the battery and it slid under the non removable battery tray. Weak as piss at the moment, which makes me clumbsy but that makes jobs twice as hard because I drop things in shit places. The battery weighes a million ton and has a thousand connections to it so had to dismantle all those then use strength of the bear to get the battery out then used a tie wrap to rummage about that welded in battery tray through some luckily placed holes to push the bit of metal out I lost.

Then back to it again, I thought I might as well feed the wires through the chair, once that was done I didn't see the point in stopping so removed the passenger chair and the side trim and fitted the left sub, fed the remote blue wire and phono cables up into the glovebox and then was gonna call it a day and go in for some dinner, but the weather was holding out so I fitted the driver side sub too, all that remains now is for me to plug in the 3 wires to the head unit and refit all the trim.

Left the boot trim out too as I didn't have time to refit and also I thought I might want good access to the amp for now so that I can tune it before I cover it all up.

Couldn't have done this without all the help an guides I've received from you guys so thanks.

Will see how it sounds tomorrow. I didn't think the factory sub would be doing much, but when I turned on the ignition to move the car, there's currently no sub at all and the speakers in the doors sounded absolutely terrible, like a 1980s wireless.

Excited for tomorrow though when I get to test it all properly.

[sir_bacharach]

So I've wired it all up and it sounds good, but the left sub seems to be farting at lower volumes, I have a feeling it's something to do with the clearance between the sub and the carpet. Does anyone cut some carpet away under these circumstances?

Seems a bit odd how the standard subs speaker faces down, but these Earthquake SWS-8s face upward toward the carpet.

I'm a bit pissed because I'll have to whip the seat out again and mess about, but that's a job for another day, the subs are second hand, so I'm hoping that one's not just knackered. I don't seem to hear it when I turn it up.

Sounds better than standard though, but I haven't ramped it up yet as I don't want to piss off the neighbours, gonna put all the boot lining back in first and then go from there.

[kaigoss69]

Originally Posted by sir_bacharach

So I've wired it all up and it sounds good, but the left sub seems to be farting at lower volumes, I have a feeling it's something to do with the clearance between the sub and the carpet. Does anyone cut some carpet away under these circumstances?

Seems a bit odd how the standard subs speaker faces down, but these Earthquake SWS-8s face upward toward the carpet.

I'm a bit pissed because I'll have to whip the seat out again and mess about, but that's a job for another day, the subs are second hand, so I'm hoping that one's not just knackered. I don't seem to hear it when I turn it up.

Sounds better than standard though, but I haven't ramped it up yet as I don't want to piss off the neighbours, gonna put all the boot lining back in first and then go from there.

Could be some dirt on the cone.

[sir_bacharach]

I'll whip it up when we get back from our jollies and have a look. I have a feeling it's the BMW connector resonating off metal of the car at certain frequences. I did tie wrap it down but might pop some sponge in to keep it still.

Sounds a million times better though and love that it's all concealed.