Multi-amp wiring scheme

[Nelsonmd]

Ok, so this may be a common question, but I haven't been able to search it out.

I currently have a sub and single channel amp installed and wired up with a 4ga kit. I am finding my front door speakers to be a bit under-powered now, so I am thinking about adding a 2chan amp to power them. I am curious if it is acceptable to tap battery power off the sub wire for the 2nd amp to avoid running another wire through the firewall (which was a pain), and avoiding additional clutter in the engine bay.

Here is what I am running right now:
HU: Pioneer Premier DEH-6900iB (says 50Wx4 max)

Front Speakers: Pioneer TS-C160R 60W Nominal (250Max)

Rear Door: Stock, don't care about them

Sub Amp: JL Audio A1400
RMS Power Rating:
4 ohms: 320 watts x 1 chan.
2 ohms: 500 watts x 1 chan.

Sub: 1x Alpine R series SWR-1242D (4 ohm dual voice coil)

 

[Nelsonmd]

Aw come on, anyone?

 

[H1_VLTG]

Yes you can tap into the power you have coming through the firewall for the sub amp. But it all depends on how much amperes the two amps you plan on using will draw. Will the 4ga wire support the total ampere draw?

Additionally I would pick up a fused distribution block to route the power to both amps. It will be much cleaner install and add additional protection for the amps.

 

[Offroader5]

How far is the run on that 4g cable? Is your sub amp in the rear cargo area or under a seat? If it's in the rear cargo...you could be looking at 12-15 feet of cable run. If you're tapping into this cable at the rear near the other amp...personally I'd be thinking of larger cable (1g or 2g)...or of course running a seperate cable for the front amp. Here's why:

The amp you already have is recommending a 40A fuse.
4g cable should be fine for upwards of about 60A (but now you're adding another amp).
With a 12 foot run of 4g cable, you're looking at a voltage drop of around .4v by the time it gets to the amp.
With 15 foot of cable, you're looking at a drop of closer to .5v at the amp.

These voltage drops are assuming the 60A max of the 4g which means it'll likely be higher with two amps pulling load from the same cable especially when they want to pull max amps at music peaks or when the speakers demand more current at higher volume.

Voltage drop is one thing...but the physical size of the cable has a finite amount of current it can transmit...4g may not be enough by the time two amps are trying to feed from it.

IMO..for things like this, 2g is an absolute minimum when I do it.

 

[Nelsonmd]

Thanks for the replies. The sub amp is under the driver seat, so not that far. The other may end up under the pass seat, so not far again. I was mostly thinking I might get some distortion in the speakers because of the dynamic load the sub puts on the line. I don't really crank up the music, so I doubt I will ever be pushing the limits of either amp.

That's a good idea with the dist block. I will have to check those out.

 

[BrianSD_42]

Nelson,

2-Channel AMP:
I would get a 4-channel AMP instead of a 2-channel. A great place to buy is ebay, there are a lot of power sellers that sell brand new Alpine, JL and Infinity for 40% off and have 1500+ positive reviews.


POWER:
A single 4-gauge should be more than sufficient. I have been running over 700W RMS on 2 amps for several years using a 4 gauge setup.

I would wire it like this:

Single 4-gauge wire from the battery to a 4-G distribution block ($30 online) under the drivers seat, then a short 4G wire to the 4-channel AMP also under your drivers seat (AMP1).

Next run 4G(+) wire from the distribution block to the second amp behind the rear seat.

Run individual grounds from each AMP to different mounting points on the chassis. Scape away all the paint.

Do not use cables thinner than 4G for any of the cables and you will be fine.

Run L/R audio from your head unit to the 4-channel AMP under the seat and the mono cable all the way back to the SUB amp (AMP2)

Do you have quality 4G cables? Many cheapo cables are actually 6G claiming to be 4G. This has been well documented.

*****

If you haven't already bought the amp for the door speakers then be very careful ….

Not all amps are the same (duh) but you need to research because power ratings are not all that matters. A 50W RMS Jensen or Pioneer will not hold a candor to the sound of a 50W RMS JL-Audio or Alpine 4-Channel AMP.


Here is an earlier thread that might help:

http://www.toyota-4runner.org/3rd-gen-t4rs/94843-do-i-have-ty-sound-system.html


I just bought a new Head Unit myself and I will be posting it later on.

:beer:

 

[tylersphile]

Good advise so far.

The only thing I would do differently from Brainemc2's advise would be to ground the amps at the same location. This will reduce the opportunity for noise (ground loops) to be introduced into your system. I would choose a location for a ground that is closer to the sub amp (as it will most likely draw more power) and run a ground from the high-frequency amp to that location as well.

Also, remember that no electrons get "used up" within the power amplifier and the positive and negative wires must be the same size. (Electrons actually flow from the negative terminal of your battery and return to the positive, but that's not important).

I believe the HVAC fan is located under the passenger seat (if I'm not mistaken), so there won't be room for an amp there...

4 guage will be more than enough if you aren't cranking your tunes. The relationship between current draw and perceived volume is logarithmic in nature. If you want to hit 120dB, for example (pretty loud), lets assume you require 300 watts. For argument sake, let's say you listen to your music at 90dB (fairly decent listening volume for prolonged listening), the power required to do so is only about 1/2 a watt.

Ex:
120db requires 300 watts (for argument sake)
117db = 150 watts
114db = 75 watts
111db = 38 watts
108db = 19 watts
105db = 10 watts
101db = 5 watts
98db = 2.5 watts
95db = 1.25 watts
92db = 0.625 watts
90db = 0.4 watts

The perceived doubling of volume (to the human ear is 10db). So even if you listen to your stereo at 1/2 the volume, you are using less than 5 watts, relative to a full volume 300 watt amp.

Most people don't realize this relationship!

So yes, 4 gauge will be plenty if you're not rockin' it out.

Cheers