novice needing advice on amp install please - Page 3 - BMW Forum

320de46m47 · 12-03-2007, 03:17 PM

Thanks to your help I've come a long way
but if i forget the infinity basslink (which is a bit on the large side!!) can i adequately power a sub using the alpine amp somehow?

da_bull · 12-03-2007, 07:12 PM

I was thinking it has a built in amp. If not, there is a different way to wire the amps.

320de46m47 · 12-04-2007, 02:46 AM

Yes the basslink has a built in amp, but its a little large. can i put 4 speakers in to two channels (would mean no fader?) and then bridge the remaining two for a sub (smaller than the basslink)?

da_bull · 12-04-2007, 06:11 AM

The specs show that its 200w. That should be a pretty close match for your four channel midrange amp. You usually want a ratio of 3:1 or 4:1, sub power to midrange power. A sub requires much more power to get moving than a typical midrange speaker, for a number of reasons. One, it typically has a larger voice coil; two, as the frequency drops you require more amp to retain the same volume; three, the sub is typically place the furthest from your ears more power is required to overcome distance, there is more but you get the picture, all of which require more power. You Alpine is rated at 50x4, so your sub amp should be right on the money. Plus, Infinity has a good R&D department, they gear the sub, enclosure, and amp to all work together well. Bridging that Alpine will net you about the same power as what Infinity provides (+/- 10%, not enough to hear a difference. I saw where they have a 25A fuse on there, you'll probably want another piece of 8ga. for that amp as well, again fused at the battery at around 30A.

320de46m47 · 12-05-2007, 03:35 AM

the problem with the basslink is really that its physically too big and will take up around a fifth of the boot space when seats up (e46 touring). this in itself wouldnt be too bad but when seats are down the whole flat load area is, well, no longer a whole flat load area. i had wanted to put it underneath the large panel and above the spare but the space is about 2 inches too shallow!! arghhhh! i made a mistake in my calculations. mind you it was only £46.

da_bull · 12-05-2007, 06:03 AM

Lol, this is the way my mind is working this morning. First thought was to make a false floor 2" higher all the way up to the back seat, so it would again be flat back there, but when you fold the seat down, it would drop 2" in front of your new floor. I'm not sure if you could take the sub out of its enclosure, reloacte the amp, build an enclosure similar to the one you showed earlier, and go that route.

320de46m47 · 12-05-2007, 10:36 AM

interesting idea. i too thought about raising the floor panel on a frame around the edge underneath. dont really want to re-arrange the basslink components...might just sell it instead. ah well!

320de46m47 · 12-05-2007, 01:57 PM

ive decided im going to look for another amp and sub. so what am i looking for...ideally 200watts rms you say? 2 channels? and a 10inch or 12 inch subwoofer or two? (the alpine is 4 x 40rms). what i think will do is cut out a sheet of mdf the same size as the original floor stick a hole in it build on to the back of it and then carpet it. that way if i ever want to sell the car i can just put the old panel back in.

320de46m47 · 12-05-2007, 02:34 PM

the ratios 3:1 and 4:1 you mentioned....is that each speaker? i.e. as with 200w RMS (basslink) : 40 w RMS (alpine per channel)

da_bull · 12-05-2007, 09:24 PM

Yeah, the ratio is right (3-4 times the power for your sub than the mids). 200 RMS would be a nice setup for like a single 10 or 12". Just seal the MDF to the steel floor really well, so it doesnt leak air anywhere.