It's not extremely important yet because I'm not purchasing a sub yet, but:

I have an Alpine MRV-F345 that has dual RCA inputs (2xL, 2xR) and I only ordered one RCA cable, since I am only plugging my front speakers into my amp. However, I was under the impression that since I have four outputs (and I can bridge 3+4 for a sub), that I could plug my HU to Amp using one RCA (ch1+2) and that's it. From there, I thought I would run Ch1 and Ch2 to the front speakers, and bridge 3+4 to the sub.

When I do add the sub, will I need to run a second set of RCA cables from the HU to the Amp (to channels 3 and 4)?

 

Run a pair of cables now - I'd even run three.

The effort to run the three cables is expensive but the cables themselves is very cheap (you're not buying Monster Moon-Bat cables are you!). If you ever change to a 5/6 channel amplifier you'll already have all the connections from the headend run aft to the amplifier's location. Plus if you ever get a cable go bad you can use the "extra" cable already run saving you the labor of pulling another.

 

So are you saying a second set of RCA's is required for the sub? I'm only using one amp to power the fronts and the sub.

 

May as well run the cables while you have it open. If you don't want a sub, no need to do so, but if you're talking about a sub now you'll probably want one sooner or later, and running the second rca pair is easy and cheap.

First, check your amplifier (I'm not familiar with that alpine). It might have the ability to take the 1/2 input and sum or repeat it to your 3/4 channels. If it has something you can use, then you don't need that extra cable and this is all moot.

A head unit may have a non-fading sub output or even a separately attenuated output; either gives you more adjustability (though the amp may have a bass thingy) but you need to run the extra cable or pair.

First thing to do is get familiar with your amp. You could be all done if it has some decent features.

 

I have a feature that sents the signal at the input of 1/2 over to 3/4. It says this is for headunits that don't have two pre-amp outputs, only one. But my headunit has two.
Am I good to go though with the one RCA then?

 

im not trying to be an a$$ but out of the 5 threads you have started in the last 2 days every one of your questions can be answered by simply reading your manual for your sub or your amp or whatever the hell it will be next.

if the amp says that it can use 2 rca's to run all 4 channels then it can

 

I understand your frustration, but also understand that I have looked through the amp manual in detail, I'm just trying to fully understand everything before I install this system (tomorrow) and before I order a sub. I admit, I didn't look into the sub manual until now, but that is because I thought there was a technical specification on the main JL product page that I didn't know how to interpret.

 

fair enough, ive just had a shitty day.... my bad


most 4ch amps have the option to run off of one set of rca's if you choose

 

I'm going to run 2 set of RCAs even though I will only have 1 RCA going to front comps' amp for now and then 2nd RCA once I get the sub in few weeks... I will have to tape the 2nd RCA off until I get the sub, right?

 

Run as many cables as you can during your initial install, as Paul said above. Trust us, it gets tedious having to pull panels again and again.

As for RCA's, you are going to need 2 pair, one set for the fronts and the other for the sub. If you ordered the 4-Ch Install kit, you will get BOTH pairs of RCA's, so you should be good.

Alpine's description of the Input Selector switch in the owner's manual is really vague. If you are using 2 pairs of RCA cables, you definitely won't use the "1/2-3/4" setting. I really can't remember which setting to use (1/2 or 3/4), and it's frustrating me! If I had to make an educated guess though, I would say you use it on "3/4" so that you can control the sub.