ScoobyK69

Hi all, I really hope someone can help.

I took my headunit out last night ready to replace with a D Din Alpine...and discovered some interesting wiring. I've got to the bottom of it, and in the boot, I have power, TWO sets of RCA leads, remote, two sets of speaker cable, and a single piece of speaker cable.

Behind the head I have the TWO sets of RCAs.

So, my thoughts are, one set of RCA to a 4 chl amp in the boot, to run a passive sub, and the two sets of speaker wires (which power the fronts).

BUT, why do I have a second set of RCAs, and a single piece of speaker wire in the boot....what could I do that I'm not seeing at the moment ?

Sorry - a secondary question - 12" Alpine sub, or 10" Focal ?!?!

Your advices appreciated

Regards

Glenn - Car is a 2007 GB 270

alcazar

iTrader: (2)

Not for a multi-changer?

Mine, a classic, has a little 10" Alpine under-seat sub, it NEARLY fits under the passenger seat, but makes a lot of difference to the sound.

ScoobyK69

Cheers mate, hadn't thought it could have been for a changer....didn't think people still had them ! Guess the head unit would power that just through the rca's so that's a possible ! My sub will have to be in the boot, only had 12" before so not sure whether the quality of focal is worth dropping to a ten inch....can't really go wrong with alpine I guess !

Dave Hedgehog

iTrader: (1)

Sounds like a completely standard 4 channel amp set up to me:
2 pairs of RCA's go back from the head unit - one pair carrying front speaker signal, the other set carrying sub frequencies to the other 2 channels on the 4 channel amp. The head unit can then take car of balance between sub and front speakers, and if it's a clever head unit can adjust crossovers and even phasing or digital time alignment.
The single speaker wire will be the "remote" which powers up the amp when the head unit puts +12v on it, so the amp is only on when the head unit is on.

Here's a system diagram to explain it a bit better:


As for the 12" vs 10" sub question, there is no hard and fast rule.

If you like Dub, Reggae, and Rap, I'd err towards the 12" for low down extention. If you like Electro, rock and faster paced stuff then go towards the 10".
Ported or sealed is a much more important consideration. There are 10" and even 8" subs out there that bang with the best of them, and 12" subs that aren't that lound and are all about balanced sound quality.

POund for pound a 12" sub will be louder off the same power as they tend to be a bit more efficient, and that's important if you have a saloon. Take the rear parcel shelf speakers out if you have a sub in the boot anyway.

ScoobyK69

Top man dave, thank you. So I do need both rca's, thank goodness it was raining tonight and I didn't strip them ! The single cable is from amp to sub, the remote wire is separate and I can see how to wire in on the amp, how do I attach to the head though ?

Dave Hedgehog

iTrader: (1)

there will be a blue wire in the loom at the back of the head unit or coming from the head nit itself - it might be labeled "remote" or posisbly "antenna". This gives +12V when the head unit is on - you can check it with a head unit. It is a 12V signal and NOT a power supply! And if you're being fastidious it should have a 1-5amp fuse in it. Anyway, connect a cable (the single length of speaker wire) from that blue wire back to the "remote" input on the amp. When the amp sees +12V on that line, indicating that the head unit is on, it will power up. Stops the amp being on all the time and killing your battery.

As an example, it's the one being held in this photo:


(Nb there's a subtle difference between antenna control and remote on - sometimes head units have one or other or both. With a powered (or amplified) aerial, you only want it up when the radio is on, not if you're playing CD's or whatever, so it gives +12V when tuned to the radio. IF your amp only powers on when the head unit is set to radio, then that's you're problem and you need to look for another blue remote line!"

ScoobyK69

Thanks dave, sorry, to explain, I have the remote wire from where the head unit goes in, pre wired to the boot for the amp....I can see where it goes on the amp, but can't work out how to attach this wire to the head unit ? I know I'm being thick, but I'm trying !!!!

Dave Hedgehog

iTrader: (1)

So one end of the wie is in the boot ready to connect to the amp?
Where is the other end? Up in the centre console behind he head unit? If so, connect it to the blue wire out of the head unit....

alcazar

iTrader: (2)

Dave: you appear to have a "Talkie Toaster"......