The next thing you’d need after buying a subwoofer is getting a compatible amplifier for it.
But car audio is all about compatibility, and you can’t just pair up the subwoofer with any random amplifier. Doing so can cause the amp to go into protection mode or even permanently damage itself (due to overheating) in some cases.
This is not a difficult task though and, after doing some simple calculations, you can easily get a suitable amp for your sub(s).
How to Match a Car Subwoofer to Amplifier
First we’ll have to discuss some important concepts:
1. Find RMS of Subwoofer(s)
If we talk about speakers, the RMS indicates its power handling capability.
RMS value defines the amount of power speakers can continuously handle and dissipate as heat without getting any internal damage. Speaker manufacturers also list peak power handling value in the specs sheet, which causes newbies to confuse the two.
Peak power handling refers to the maximum amount of power a speaker can handle for a short burst of time, usually for a second or two. Since the RMS value indicates the power handling for a longer duration of time, it’s much more accurate.
If you have a single sub, its RMS value will be our final RMS value. If you have multiple subs, the total RMS value will be the sum of their RMS values.
For example, if you have two subwoofers with each having 300W RMS, the total RMS value will be 600W.
2. Find Power Range for Subwoofer
Once we have calculated the total RMS for our sub, we’ll find the Power Range. For the upper limit of this range, we’ll multiple the total RMS by 1.2 (720W); and for the lower limit, we’ll multiply total RMS by 0.9 (540w).
So, for our 600W RMS subs, the power range will be 540W-720W.
Then we’ll try to find an amp that provides power within this range.
In general, though, it’s always better to have a slightly overpowered amplifier (more than 600W in our case) as it gives us more headroom and the amp will run much cooler even under load.
An underpowered amplifier, on the other hand, will output distortion at the max output and can cause the subwoofer’ voice coil to get damaged due to increased heat.
So if you’re indeed going for an underpowered amp, make sure to avoid high volume levels.
3. Find Impedance of Subwoofer(s)
Like RMS, impedance is another important factor when it comes to subwoofers.
In simple terms, it resists the flow of electric current in the subwoofer and is measured in Ohms(Ω). A larger resistance means the load at the amplifier will be smaller which will result in less power output.
On the other hand, lower resistance means higher power output but will cause the amp to run hot. In simple terms, you don’t have to go for either extreme.
The impedance for each subwoofer is listed on its specs sheet.
In case you’re having multiple subs, finding the final impedance gets tricky as it depends on whether the subwoofers are single or dual-voice coiled, or whether they’re connected to series or parallel wiring.
If you have multiple single-voice coil subs connected in series, then the total impedance will be the sum of their impedances – e.g., RT = R1 + R2 + —–.
And if you have multiple single-voice coil subs connected in parallel wiring, the total impedance can be calculated using this formula: 1/RT = 1/R1 + 1/R2 + ——.
So if we assume that each of our 300W sub is a single-voice coil model with 2 Ohm impedance, we’ll have 1-Ohm and 4-Ohm impedance in parallel and series wiring respectively.
But since many amps are not rated to work at 1-Ohm load, we’ll go with the 4-Ohm option.
On the other hand, a dual voice coil sub comes with two voice coils that can be wired in series or parallel configuration – just like two single voice coil subs.
So if you have a single 4-ohm DVC sub, it’ll have a 2-Ohm impedance in parallel wiring and 8-Ohm impedance in series wiring.
I have listed impedances for some of the common subwoofer combos down below. In case you have any other combination, you can use the formula above to get your final result.
- 1 single voice coil 2-ohm sub will have 2 Ohm impedance.
- 1 single voice coil 4-ohm sub will have 4 Ohm impedance.
- 1 dual voice coil 2-ohm sub will have 1 Ohm (parallel) or 4 Ohm (series) impedance.
- 1 dual voice coil 4-ohm sub will have 2 Ohm (parallel) or 8 Ohm (series) impedance.
- 2 single voice coil 2-ohm subs will have 1 Ohm (parallel) or 4 Ohm (series) impedance.
- 2 single voice coil 4-ohm subs will have 2 Ohm (parallel) or 8 Ohm (series) impedance
- 2 dual voice coil 2-ohm subs will have 2 Ohm (parallel) or 8 Ohm (series) impedance
- 2 dual voice coil 4-ohm subs will have 1 Ohm (parallel) or 4 Ohm (series) impedance
- 3 single voice coil 2-ohm subs will have 6 Ohm impedance.
- 3 single voice coil 4-ohm subs will have 1.3 Ohm impedance
- 3 dual voice coil 2-ohm subs will have 1.3 Ohm (parallel) or 3 Ohm (series) impedance
- 3 dual voice coil 4-ohm subs will have 2.7 Ohm (parallel) or 6 Ohm (series) impedance
- 4 single voice coil 2-ohm subs will have 2 Ohm (parallel) or 8 Ohm (series) impedance
- 4 single voice coil 4-ohm subs will have 1 Ohm (parallel) or 4 Ohm (series) impedance
- 4 dual-voice coil 2-ohm subs will have 1 Ohm (parallel) or 4 Ohm (series) impedance
- 4 dual-voice coil 4-ohm subs will have 2 Ohm (parallel) or 8 Ohm (series) impedance
4. Find Compatible Amplifiers
Now that we’ve calculated the RMS and impedance values, all we need is to find an amp to deliver power within our RMS range at our calculated impedance load.
Since we have RMS at 600W and the series wiring impedance at 4-Ohm, what we need is an amp that can deliver 600W of power at 4-Ohm load such as the JL Audio JD1000/1 amplifier. It can give 1000W at 2-Ohm load or 600W at 4-Ohm load.
Monoblock amps are generally preferred for such tasks as they can connect multiple subs with ease.
Also, make sure that the amp you’re getting is CEA-compliant. This ensures that the power rating number numbers you see on the specs sheet are actual and are not inflated for marketing.