How to match subwoofers and amplifiers

The secret to great bass is making sure your subwoofers and amp are evenly matched and will properly work together. And this article will help you figure out how to do just that — match amplifiers and subwoofers. We cover the important basics of power-matching, impedance, and planning for the number of subs you want, and we approach the situation from both sides of the system:

• Part A: You have the subs, which amp should you get?
• Part B: You have the amp, which subs should you get?

Start with either part you want, but they're both worth a read.

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Part A
You have the subs, which amp should you get?

The subs need to be the same
Multiple subs wired together must be the same coil type and impedance. If they’re not, the power won’t divide evenly between them, and some subs would probably be over-powered while others get under-powered. If you want to run different types of subs in a system, each type needs to have its own separate amp.

Step 1: How much power? Find out the “watts RMS” rating of the sub

Then, multiply the number of subs you have by the RMS rating of each, to get their total RMS rating. You want to make sure the amp you choose is capable of supplying from 75% to 150% of the sub system’s total RMS rating.

Step 2: What impedance? The results of combining coils and subs

Figure out the possible total impedance(s) that the subs can be wired together to form.
(SVC = single voice coil, 1 pair of terminals; DVC = dual voice coil, 2 pairs of terminals.)

• 1 SVC 2-ohms can only have 2 ohms of impedance
• 1 SVC 4-ohms can only have 4 ohms of impedance
• 1 DVC 2-ohms can have 1 ohm or 4 ohms of impedance
• 1 DVC 4-ohms can have 2 ohms or 8 ohms of impedance
• 2 SVC 2-ohms can have 1 ohm or 4 ohms of impedance
• 2 SVC 4-ohms can have 2 ohms or 8 ohms of impedance
• 2 DVC 2-ohms can have 2 ohms or 8 ohms of impedance
• 2 DVC 4-ohms can have 1 ohm or 4 ohms of impedance
• 3 SVC 2-ohms can have 6 ohms of impedance
• 3 SVC 4-ohms can have 1.3 ohms of impedance
• 3 DVC 2-ohms can have 1.3 ohms or 3 ohms of impedance
• 3 DVC 4-ohms can have 2.7 ohms or 6 ohms of impedance
• 4 SVC 2-ohms can have 2 ohms or 8 ohms of impedance
• 4 SVC 4-ohms can have 1 ohm or 4 ohms of impedance
• 4 DVC 2-ohms can have 1 ohm or 4 ohms of impedance
• 4 DVC 4-ohms can have 2 ohms or 8 ohms of impedance

 For more combinations of subs and their impedances, see Subwoofer Wiring Diagrams.

Step 3: Pick an amp that can do both — X watts at Y ohms

Look for an amplifier that can put out power within the RMS wattage range you’ve figured in Step 1, at an impedance load the subs can be wired to form, from Step 2.

Estimating amp power at the odd impedance values:

• 8 ohms — figure on the amp putting out half the power it would at 4 ohms
• 6 ohms — figure on the amp putting out three-quarters of the power it would at 4 ohms
• 3 ohms — figure on the amp putting out the average of what it would at 2 ohms and at 4 ohms
• 2.7 ohms — figure the same as for 3 ohms, and add a few watts
• 1.3 ohms — use the 1-ohm spec and take away a few watts

Example:
You have two Alpine Type R SWR-8D4 8" subwoofers and you want the right amp for them.

They are DVC 4-ohm subs rated at 350 watts RMS each.

Two 350 watts RMS subs together need a total of 700 watts RMS, but an amp putting out from 525 to 1050 watts RMS will do. (75% of 700 is 525; 150% of 700 is 1050.)

Using the chart in Step 2, 2 DVC 4-ohm subs can be wired together to form a 1-ohm, a 4-ohm, or a 16-ohm load.

The last is too high a load to be practical, so you’ll look for an amp that can put out from 525 to 1050 watts RMS into either a 4-ohm load, or a 1-ohm impedance load:

• (525-1050) watts RMS x 1 at 4 ohms, or
• (525-1050) watts RMS x 1 at 1 ohm

Among Crutchfield’s selection of amplifiers you’ll find:

• Alpine MRX-M110 — 650 watts RMS x 1 at 4 ohms
• JL Audio HD750/1 — 750 watts RMS x 1 at 4 ohms
• Rockford Fosgate Power T1000-1bdCP — 700 W RMS x 1 at 4 ohms or 1,000 W RMS at 1 ohm
• Focal FPS 2300RX — 530 watts RMS x 1 (bridged) at 4 ohms

Any one of these high-quality amplifiers would work well with those subs. It doesn’t matter which impedance an amp plays through — 600 watts RMS through a 4-ohm load produces the same volume as 600 watts RMS through a 1-ohm load.  Notice that the Rockford Fosgate Power T1000-1bdCP can play that pair of subs at 700 watts RMS or 1,000 watts RMS, if you want it louder, just by wiring them together differently.

Rockford Fosgate T1000-1bdCP subwoofer amplifier

The last two amps listed above, the Focal 2300RX and the Rockford Fosgate Power T600-2, are 2-channel amps that happen to work with these two subs when bridged in 1-channel mode. But multi-channel amps are typically lower-powered than mono subwoofer amps, and usually can’t drive loads lower than 4 ohms when bridged.

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Kicker DXA1000.1 subwoofer amplifier

Part B
You have the amp, which subs should you get?

Step 1: What can the amp do? Find the RMS ratings of the amp at different loads

Find the amp’s power, expressed in “watts RMS”, at 4 ohms, at 2 ohms, and, if it can, at 1 ohm. Pick the power you’d like to achieve. The load impedance (ohms) of that rating will be what you want your subs’ total impedance to be.

Step 2: How many subs do you want?

Divide the power you picked in Step 1 by the number of subs you want. This number is the target RMS rating for each of the subs you’ll choose.

• Divide that target number by 1.5. This is the lowest RMS rating per sub that will work.
• Divide that target number by 0.75 for the highest RMS rating per sub.

Step 3: What impedance does each sub need to be and how many voice coils?

Using the impedance you picked in Step 1 and the number of subs from Step 2, cross-reference the possible coil configurations that you can use: 

	1-ohm	2-ohms	4-ohms
1 sub	DVC 2-ohms	SVC 2-ohms DVC 4 ohms	SVC 4-ohms DVC 2-ohms
2 subs	SVC 2-ohms DVC 4-ohms	SVC 4-ohms DVC 2-ohms	SVC 2-ohms DVC 4-ohms
3 subs	(1.3 ohms)* SVC 4-ohms DVC 2-ohms	(3 or 2.7 ohms)* DVC 2-ohms DVC 4-ohms	(6 ohms)* SVC 2-ohms DVC 4-ohms
4 subs	SVC 4-ohms DVC 2-ohms	SVC 2-ohms DVC 4 ohms	SVC 4-ohms DVC 2-ohms

* Estimate amp power at the odd impedance values like in Part A, Step 3, above.

Step 4: Pick a sub that works for both — (SVC or DVC) X-ohms, Y watts RMS)

Look for subs that are rated within the wattage range you figured in Step 2, and are configured as you found in Step 3. This might sound confusing, so let's walk through an example and it'll make sense.

Kenwood Excelon X500-1 subwoofer amplifier

Example:
You have a Kenwood Excelon X500-1 amplifier and you want it to drive two subwoofers

The amp is capable of 300 watts RMS x 1 at 4 ohms and 500 watts RMS x 1 at 2 ohms.

Let’s say you choose to maximize the amp’s potential and want the system to put out 500 watts RMS. This means your subs have to be wired to form a total impedance of 2 ohms.

Two subs on a 500 watts RMS amp will want about 250 watts RMS each.
250 divided by 1.5 is 167; 250 divided by 0.75 is 333. So you’ll look for subs each rated between 167 and 333 watts RMS.

Using the chart in Step 3, for two subwoofers, a final 2-ohm load can be achieved with either two SVC 4-ohm subs or two DVC 2-ohm subs.

So, you’ll look for two subs that are either SVC 4-ohms or DVC 2-ohms, rated between 167 and 333 watts RMS each:

• 2 SVC 4-ohms, (167-333) watts RMS, or
• 2 DVC 2-ohms, (167-333) watts RMS

Among Crutchfield’s selection of subwoofers you’ll find:

• JL Audio WXv2 Series 10" — SVC 4-ohm, 200 watts RMS
• Infinity Reference Series 10" — SVC 4-ohm, 275 watts RMS
• Kenwood Performance Series 10" — SVC 4-ohm, 300 watts RMS
• Kicker CompD 10” — DVC 2-ohms, 300 watts RMS

Kicker CompD 10" component subwoofer

All these subwoofers will sound their best when amplified with the proper amount of power. Differences in size have more to do with tonal qualities and frequency response than with power performance. And optimizing performance is the point of matching subs and amps together.