How to match subwoofers and amplifiers
Find the right amp for your sub or sub for your amp
In the 1950's, I'd take the family television's vacuum tubes down to Willow Grove Radio and TV Repair, check them with the giant tester machine, buy new replacement tubes, and reassemble the repaired television, so my mom and dad could enjoy their precious, respectively, Dean Martin and Red Skelton shows. In the 1960's, I studied radio and electronics at the Franklin Institute in Philadelphia. After college, in the early 70's, I joined a rock 'n roll band as the soundman, learning how to operate the electronics that make music sound good. Then, I worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems and components for recording studios, nightclubs, and touring bands. I moved back to Charlottesville permanently in 1984 and opened a little demo recording studio. I also attempted to put to practical use the creative writing degree I had picked up along the way. In 2006, I finally came to my senses and got this job at Crutchfield where they actually pay me to ramble on, rant, and explain the things I love about music, electronics, and getting good sound.
More from Buck Pomerantz
In a Nutshell
A subwoofer has impedance (measured in ohms) which represents the "load" an amplifier will sense on its output. An amplifier will put out different amounts of power (watts RMS) based on the impedance load it "sees."
Getting the right sub for an amp, or the right amp for a sub, is like solving a puzzle where the amplifier's capabilities (X watts RMS into Y ohms) needs to match the subwoofer's specifications (Y ohms and can handle X watts RMS). Your goal is to get those two variables to match for both the amplifier and the subwoofer.
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.
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
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:
- Infinity Kappa K1000 — 700 watts RMS x 1 at 4 ohms
- JL Audio HD750/1 — 750 watts RMS x 1 at 4 ohms
- Kicker 43CXA1200.1 — 600 watts RMS x 1 at 4 ohms
- Memphis 16-PRX1000.1 — 1,000 watts RMS x 1 at 1 ohm
- Pioneer GM-D8601 — 800 watts RMS x 1 at 1 ohm
- Rockford Fosgate Power T1000-1bdCP — 700 watts RMS x 1 at 4 ohms or 1,000 watts RMS at 1 ohm
- Rockford Fosgate Punch P1000X2 — 1,000 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 amp listed above, the Rockford Fosgate Power P1000X2, is a 2-channel amp that happen to work with these two subs when bridged into 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.
Kicker CXA1200.1 subwoofer amplifier
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 sub||DVC 2-ohms||SVC 2-ohms |
DVC 4 ohms
|SVC 4-ohms |
|2 subs||SVC 2-ohms |
|SVC 4-ohms |
|SVC 2-ohms |
|3 subs||(1.3 ohms)* |
|(3 or 2.7 ohms)* |
|(6 ohms)* |
|4 subs||SVC 4-ohms |
|SVC 2-ohms |
DVC 4 ohms
|SVC 4-ohms |
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.
You have a Memphis Audio SRX500D.1 amplifier and you want it to drive two subwoofers
The amp is capable of 350 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:
- Alpine SWA-10S4 10" — SVC 4-ohm, 250 watts RMS
- Memphis SRX125S4 12" — SVC 4-ohm, 250 watts RMS
- JL Audio 12W0v3-4 12" — SVC 4-ohm, 300 watts RMS
- Kicker 44CWCS104 — SVC 4-ohm, 300 watts RMS
- Rockford Fosgate R2D2-10 10" — DVC 2-ohms, 250 watts RMS
Kicker CompC 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.
If you have neither amp nor sub, and want help in deciding how to begin:
Check out our other article, All About Subwoofers.