Subwoofer Wiring Configurations

Chris,

It really depends on a couple of things.

1.  What is the minimum load that your amp is stable into in a bridged configuration?

2.  How low are you wanting to go with it?  And this matters the most. 

When you drop below about 1/2 an ohm, resistance levels can become very unstable.  What a voltmeter reads as 1/4 or 1/8 ohm, can actually be lower or higher when placed into a live audio circuit.  Also, the frequency that is generated (20Hz vs. 1kHz (yes, I know, you won't go as high as 1kHz, this is just an example) can actually cause a variance on the amp side, where it can see as little as 1 ohm to as much as 60 ohms, again, depending on the frequency that is being generated).

Also, don't forget, when bridging an amp, whatever the load is that is measured at the terminals (for example, you are putting the amp into a 1/2 ohm load), the amp will actually see one-half of the resistance level (in the case of a 1/2 ohm load, it would see a 1/4 ohm load) that exists on that circuit because of the physics involved.

The last thing to remember is airflow.  The lower the resistance level, the hotter the amp will get.  You absolutely MUST have adequate airflow, or the amp will go into thermal shutdown.  Do this enough, and you COULD damage the amp, and possibly the drivers since the heat can also travel along the speaker wire to the driver's voice coil.

So, to recap, check out the minimum resistance level (ohms) that your amp is STABLE into in a bridged configuration, don't forget about that bridged amp seeing half of the resistance existing on the circuit, and most importantly, make sure you adequate airflow.  If you follow all this, you should be fine.

Hey dyalden

You said that when bridging an amp the load the amp terminals see is half the rated load of the speaker.  Now I am confused.

I am installing a Rockford Fosgate P312D4 12" sub. It has two 4ohm voice coils and is rated at 500Watts RMS.  My plan is to wire the VC's in parallel to produce a 2ohm load.

My plan is to use a Hifonics Neptune amp rated at 500watts X 1 RMS into 2 ohms.  The picture of the amp has 4 speaker terminals (as far as I can tell see picture

Is this amp going to see 1ohm or 2?  Are D-class amps bridgable?  I am confused.

I don't know about having 2 sets of speaker terminals on that amp, I've never worked with it.  What Dyalden meant was that if an amp is 1 ohm stable in stereo it will be 2 ohm stable when bridged.  And a 4 ohm bridged load is the same as a 2 ohm load in stereo as far as the amp's concerned.  Make sense?  If your amp can do 500w x1 into 2 ohms, it should be fine running your sub wired parallel as a 2 ohm driver.

Chris Sr, if you haven't already left the building....use the parallel and series wiring calculators on the left column of this page to figure quad coil wiring.  If you were to use series/parallel wiring, the total load would be 1.5 ohms onto one amp (each sub's coils in series to 6 ohms and then four subs in parallel to make 1.5 ohms). 

This would be what it would look like:

Most mono amps have two sets of terminals, so you can wire two subs to one set and the other two subs to the other set.  The amp will parallel the pairs of subs for the same final result (see DYohn's response above).

If you intend to use two amps, use the calculators to find that you can make a 3 ohm load onto each amp.  You will still need to use mono amps because of the low impedance, and this choice might be more suitable if your single amp isn't able to handle such a low impedance as the 1.5 ohm shown above.  The power would be the same in either case, because 3 ohms is double the impedance of 1.5 and each amp would put out half the power that the single amp would into the 1.5 ohm load.  This solution, however, depending on the amp quality and the integrity of the MA coil measurements, will be easier on your system...sound better...and last longer.

The problem with this posted question is that it doesn't provide adequate info on exactly how many / what type of amplifier is going to be used.