View Full Version : Speaker 101

09-24-2013, 11:11 PM
Here is where I show my true lack of understanding:

In my old setup and new desired setup I want to run 2-way components up front (150w RMS / 300W peak) and coaxial in rear & subs off mono. I plan to run a 4-channel amp (JL 300/4). If I do not want to run anything off the HU power (not sure why not except unconfirmed thinking that it will be under-powered) how does this work? I had a local shop do the install so I am not certain that the rears were not run from HU.

Idiot math is 6 speakers and only 4 channels - so is there any reason not to have the rear speakers run from HU power? Can those channels be bridged as well to double the power going to each speaker?

Also, my subwoofers are 4 ohm - are typical components and coaxial 2 ohm or 4 ohm?

I just picked up a second JL 300/4 for next to nothing and I know the theory is to get one (1) 4-channel amp that has the necessary watts per channel, but can these two (2) be wired to mimic one amp?

I have researched the upgrade for a HO alternator (270a) and larger battery along with proper ground wires (Big 3 upgrade) and will do that before anything goes in my truck so as to not strain my electrical (subs are four (4) JL 6W0 powered by JL 500/1) - but will this setup work? It is still only 1100 total watts at full tilt - but can it be that inefficient not to consider it?

Please provide insight. Really appreciate it. Even if I don't do the work myself, sounding like I know what is going on is half the battle.

09-25-2013, 02:00 AM
you need to first verify what the shop did for wiring.

simply adjusting the fader and balance on your head unit will tell you what they combined on each input/output. what head unit do you have?

did they use factory wiring for the speakers? where did they intercept them?
what car make/model/year/trim?

rear speakers are just for "fill" and should be MUCH quieter than front. in fact, you shouldn't even tell they are on from the front seat. for that reason, they can sometimes be ran from the head unit as long as they are the only "rear" channels used. this means the JL amp has to get it's signal from the front output of the HU (and possibly dedicated sub output if the HU is capable).

you can wire front and rear in parallel but that is silly because you want the fronts louder.

coaxial are typically 4 ohm.

channels 1 and 2 of the amp will be stable to 2 ohms stereo so they can technically power front and rear, left and right.
channels 3 and 4 of the amp will be stable to 4 ohm bridged so they can power a single sub easily.

09-25-2013, 02:02 AM
a 270A alt is overkill for the system, but it shouldn't be an issue. note that some H.O. alts in some cars may require reprogramming of the ECM in order to not throw codes. we ran into that when putting a 240A in a 2005 Scion tC. not to say you shouldn't get a larger alt, it is a good idea if you don't expect issues.

the big 3 and a good AGM battery are definitely good items to consider.

wiring methods are a huge determination of power transfer "efficiency". grounds are vital and usually overlooked.

share pics of the shop's install. show all connections, power, ground, speaker at the amp. show connections made at the speakers (if you feel comfortable removing them to inspect the work done). we can likely give you ideas for improving their installation (such as improved seals at speakers).

09-25-2013, 02:19 AM
↑ What he said.

As for your math... component speaker systems come with passive crossovers that filter highs from the mid bass drivers and lows from the tweets & the amp doesn't see the impedance of the speakers, it sees the impedance of the crossover. So, even though there are two speakers connected to each channel in that scenario, it is still a 4Ω load on the amp... presuming the component set is 4Ω.

And if you want to find out if the rears are connected to the head unit or the amp, unplug the RCAs (with the system OFF) running the front channels and listen to it. If only the rear speakers and sub are playing, then the rears are connected to the HU. If only the sub is playing, then the rears are connected with the fronts.... which is doubtful.

09-25-2013, 08:56 AM
I cannot share pictures because I have sold that car and removed the equipment prior. The HU was a Pioneer AVIC F90BT and the speakers were JL XR 6.5" 2-way components in front & JL XR 6.5" coaxial in rear. Subs were run off seperate JL 500/1.

I was in the planning stages of the upgrade for my new truck and was going to start with the speakers. I have settled on the PHD FB 6.1 Pro for the front and the PHD MF 6.1C for the rear. I was looking to recycle the amps until I can upgrade. They power ratings are higher than the JL's so I was planning on running two (2) seperate JL 300/4 (since I have them already).

The ultimate goal is to have clean LOUD musical reproduction - not just noise.

09-25-2013, 07:49 PM
ok, so you described what you had, not what you have. there lies the confusion.

fell free to run both 300/4.

trucks have no purpose for rear speakers. you can put them in but they will add to the noise factor, not musical reproduction. more speakers is barely louder but noticeably less accurate.