I still haven't decided what I'm doing to the stock system this spring. I just want to confirm my basic understanding of how an amplifier fits into my plan.

I will be installing a new head unit with front and rear outputs going to an amplifier that will drive front components speakers and a sub in the trunk. Probably won't be going over 100 watts in power.

Am I correct in my understanding that a 4-channel amplifier will allow me to power the front components using the two front channels, and power a sub by bridging the rear channels?

All the amps I am considering have built in crossovers. High Pass or Full Range for the front, and High Pass, Low Pass and Full Range for the rear. Second question: Would I select High Pass or Full Range for the front components? (85 Hz crossover frequency)

Thanks.
-golfpro

 

If your new HU has Sub out, then you should connect front RCA pair and Sub out to your 4-channel amp.

If your amp has adjustable crossover you should set it at around 50-55Hz, if it has fixed crossover at 85Hz, then you should select High Pass to prevent frequencies below 50Hz driving your components.

 

is there any benefit to overlapping your crossover frequencies, say, setting the low pass sub at 80Hz and the high pass front channel crossover around 50-60Hz?

 

I expect it will, and the head unit will have bass controls as well. I referenced 85Hz as that was the spec on the amp I was looking at last night.

Thanks for the info.

 

Will and GolfPro, by setting the high pass at let say 50Hz and the low pass at 80Hz you will have 30Hz of region where door speakers and the Sub will be working. Turns out because of the filtering in this region the door speakers and Sub may not operate "in phase". Hence, they may be actually be "out of phase" and cancel each other out. This would be very similar to the BOSE noise cancellation headphones.

If the sub is indeed "out of phase" with respect to the door speakers, then you could reverse the positive and negative terminals of the sub. However, with both sets of speakers now "in phase" you may experience a "bump" in response between 50-80Hz. Basically, 50-80Hz will be louder than anything above or below those frequencies. This becomes a personal preference issue in my mind. Some people like the bumpiness factor, but others prefer for a flat response across frequencies.

Hope that helps,
Jimmy

 

Thanks. I understand the filtering issue and will be sure to keep the speakers in phase. I will be going for more of a flat response.

Back to the initial question: Can I essentially turn my 4-channel amp into a 3-channel amp and divide its power between my front components and the sub?

 

yes. there should be two seperate crssovers on the amp. one for channels one and two and the other for channels three and four. I'd switch the front crossover to all pas and the rear to low pass for your sub at around 50hz

 

Thanks, man. I knew I was on the right track.

 

Pick your sub carefully. Most 4-CH amps are not stable down below 4-ohms bridged. You will probably need an SVC 4-ohm sub or a DVC 2-ohm sub, so the coils can be wired for a 4-ohm impediance.

Check out the Hifonics Titan 8800. I am running it in my S now, and its a great amp at a decent price. It pushes 110wrms to the doors and 440wrms to the sub. It has adjustable HPF and LPF as well. I got it for under $200 shipped to my door. Good SQ as well.

John

 

Thanks, John. I'll pay close attention to all the specs. I'm probably looking at something at 100 watts, or less and most likely an 8" sub (SVC). I don't need much thump. Just looking to put together a listenable system that doesn't eat up too much of our limited storage space.