You are presented with a number of ways to wire up your subwoofers when you have multiple subwoofers or if you have subwoofers with dual voice coils. This guide will help you choose the correct wiring method. We'll go over some wiring basics and then explore different ways to match an amplifier to a group of subwoofers with different wiring schematics.
In this guide we will go over the following:
- When should I wire multiple woofers?
- How Do I Match My Subwoofer Wiring With My Amplifier's Ratings?
- What is Series Wiring?
- What is Parallel Wiring?
- How can I combine series and parallel wiring to best match my amplifier's specifications?
- Case Studies
- Can I wire three 4 ohm subwoofers to a 1 ohm stable amplifier?
- If I have four 2 ohm subwoofers, how can I wire them to match my 2 ohm stable amplifier?
- Final thoughts
When Should I Wire Multiple Woofers?
You should only wire multiple copies of the brand and model of woofers together. Combining different brands and different sizes and even voice coil impedances will result in both constructive and destructive interference at multiple frequencies across the subwoofer spectrum. The woofers may be in phase electrically, but mechanically they will be out of phase enough where it matters.
For example, when you mix and match subwoofer drivers, a Low E on a bass guitar played through this mismatched subwoofer system may sound crisp and forceful, but moving up to an F or G in the same recording will sound fuzzy and weak on these mismatched drivers.
This phenomenon is sometimes referred to as a "comb filter effect", where the frequency response graph resembles a comb instead of a flat line or smooth curve.
If you have space for 4 woofers, make sure they're all the same brand, model and voice coil configuration before continuing. It helps with troubleshooting down the line.
We want to make sure our woofers are a good match for our amplifier, so shoot for a group of woofers whose total RMS power handling will equal that of our amplifier's RMS power output. We can give or take a few watts either way.
How Do I Match My Subwoofer Wiring with My Amplifier's Ratings?
Simply put: one does not wire their subwoofers to a lower impedance than what their amplifier is rated for. If the amplifier says it is 2ohm stable, then wire the amplifier to 2ohms or more. Wiring below 2 ohms causes more current (amperage) to flow through the circuit than what the circuit was designed to handle.
At best, wiring subwoofers with impedance rated below the amplifier's rated impedance sends the amplifier into protect or it blows a fuse.
At worst, wiring subwoofers with impedance rated below the amplifier's rated impedance catches your car on fire.
What is Series Wiring?
Series Wiring is where you wire multiple speakers one right after another. They could be "daisy chained" together, where one woofer connects to another. One woofer's positive terminal goes to the positive terminal of the amplifier, then a wire connects from that woofer's negative terminal to the next woofer's positive, and this wire from one woofer's negative to the next woofer's positive is repeated until you're out of woofers. The final woofer's negative terminal connects to the amplifier's negative terminal.
You'll compute the final impedance by multiplying the impedance of one coil by the number of coils.
Final Impedance = coil impedance * number of coils.
If I have 3 woofers with single 2 ohm coils, I have a final load of 6 ohms, thusly:
Final Impedance = 2 ohms * 3 woofers
Final Impedance = 6 ohms
What is parallel wiring?
Parallel wiring is where you wire all of your woofer's positive terminals to the amplifier's positive terminal and all of your woofer's negative terminals to your amplifier's negative terminal. If you were to lay out your amplifier and woofers on a table to wire them all up, the schematic would resemble a ladder, where negative and positive leads would make parallel lines and the amplifier and woofers would make the steps between those lines.
You'll compute the final impedance by dividing the impedance of one coil by the number of coils.
Final impedance = coil impedance / number of coils
If I have three woofers with single 8 ohm coils, I have a final load of 2.66 ohms, thusly:
Final impedance = 8 ohms / 3 woofers
Final Impedance = 2.66 ohms
How can I combine series and parallel wiring to best match my amplifier's specifications?
If you have at least four subwoofers (or at least 2 dual voice coil subwoofers) to wire up, you can combine series and parallel wiring to arrive at a a given impedance.
If you have four 4 ohm subwoofers, you can series-wire up two pairs of speakers each into an 8 ohm load and then wire those two loads into a parallel load, returning to a 4 ohm final load, presenting an easy load for most class AB amplifiers.
Case study: Can I wire three 4 ohm subwoofers to a one ohm stable amplifier?
Let's say we have a subwoofer enclosure with openings for three subwoofers. We have three subwoofers of the same brand and model. The subwoofers all have single four ohm voice coils. If we wire the speakers in series we would have a 12ohm final load. This of course is safe for just about any amplifier on the market, but because of Ohm's Law, the amplifier simply won't produce much power.
If we wire the subwoofers in parallel, is it safe for the amplifier? Remember, the formula looks like this:
Final impedance = woofer impedance / number of woofers
Plugging our numbers into the formula:
Final Impedance = 4 ohms / 3 woofers
Final Impedance = 1.33 ohms.
1.33 ohms is safe for our theoretical 1 ohm amplifier.
Case study: If I have four 2 ohm subwoofers, how can I wire all four of my subwoofers to my 2 ohm stable amplifier?
If we wire four 2 ohm speakers in series, we end up with an eight ohm final load.
Final Impedance = woofer impedance * number of woofers
Final Impedance = 2 ohms * 4 woofers
Final Impedance = 8 ohms
While this is certainly safe to wire up to a 2 ohm stable amplifier, it is going to produce only 1/4 of the rated power. Nobody wants to lose 6db because of impedance.
Now, if we wire four 2 ohm speakers in parallel, we end up with a half ohm final load
Final Impedance = woofer impedance / number of woofers
Final Impedance = 2 ohms / 4 woofers
Final Impedance = 0.5 ohms
A half ohm load is not safe to wire up to an amplifier that is only 2 ohm stable. You risk damaging the amplifier and even your car.
So what are we to do? We wire two pairs of 2 ohm speakers in series! Then we have a pair of 4 ohm pairs. Now we can wire that pair of 4 ohm pairs in parallel to achieve a single 2 ohm load, a perfect match for our two ohm amplifier!
Some Final Thoughts about Wiring Car Audio Subwoofers
Please understand that your amplifier's rated minimum impedance should be treated as a hard and fast rule. If it says 2 ohms mono, please do not attempt to wire it at 1 ohm. You could damage the amplifier and possibly start a fire.
You can wire your subwoofers at a higher impedance if you'd like. There isn't anything stopping you from wiring to 8 ohms if you find that it's just too loud at 2 ohms. But then that is better handled with a remote bass knob control.
However you choose to wire your subwoofers to your amplifier, make sure you include your safety and the safety of others in your decision.
Happy subwoofing!
