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Should an Amp Be Bigger Than a Sub? What You Must Know

Sound experts would say that the secret to having a great bass is to match the right amp with the right subwoofer. But what does it mean to have a well-matched pair, and how do you make sure your amp and your sub work properly together?

An amp need not be bigger than a sub as long as its capabilities evenly match the sub’s specifications. However, it’s always better to get an amp that puts out a bit more power than your sub, especially if it’s a passive sub. If you have an active sub, you may not even need an external amp at all.

Read on and learn about sub specifications and how to match these with an amp’s capabilities. We will also talk about the difference between a passive subwoofer and a powered one, and their amplification needs. 

Big subwoofer

Does a Sub Even Need an Amp in the First Place?

All subwoofers need an additional power source since reproducing low-frequency sound signals requires large amounts of power. However, not all subwoofers need a separate amplifier. This is why it is important that you first know the type of sub you plan on buying or the one you already have. 

There are two types of subs: passive and active sub.

Passive vs. Active Subwoofer

A premium powered or active subwoofer draws power from a built-in amplifier, so you would no longer need an external amp for it. It is designed with the ability to sustain all the power it needs by keeping its speaker/amp configuration well-aligned. All it needs to work is an audio source.

A passive subwoofer, on the other hand, relies on an external amp or receiver as an additional power source.

It is ideal for larger spaces that need multiple units or if you need a more spread-out bass. It is also the wiser choice if you are setting up a custom home theater system or a recording studio.

If you have a passive sub, you will need to get an amp that generates enough power to sufficiently sustain the deep tones produced by your audio player.

An active sub, meanwhile, is easier to set up because it is already an all-in-one solution for homeowners who need optimal bass. And because it operates as a single and self-contained unit, it is the ideal pick for smaller spaces.

Can You Use an External Amp With an Active Sub?

You can connect an external amplifier to an active subwoofer if you think it would improve the sound. But people who connect the two do it mainly for data transmission purposes because other workarounds aren’t possible. 

In this setup,  the amp serves as the channel through which data passes between passive speakers and the rest of the sound system.  Testing out this kind of connection comes with a cautionary warning, though.  

You have to ensure that the specs of your devices are in line. Otherwise, too much power could cause damage to both your external amp and active subwoofer.

So, using an external amp with your active sub just to push the output to extreme levels is not ideal.

Matching Sub and Amp Together

It is crucial to correctly match your amp to your sub. But this task is tricky because matching involves knowing the specifications of your subwoofer and understanding how an amp fits into these specs, or vice versa. 

Through this, you will find out how big your amp needs to be in relation to your subwoofer. 

So, what specs are we looking into?

  • Impedance (Ohms). Impedance refers to the amount of load your sub transfers to an amp. The amp, in turn, puts out the amount of power based on this load. The number of impedance is expressed in Ohms. As such, the number of Ohms of the subwoofer needs to match with the power output of the amp.
  • Power Output (Watts RMS). A subwoofer’s power output is expressed as watts RMS (root-mean-square).  This measures how much power your sub can handle without getting damage or without distortions in sound.

In an amplifier, the RMS is the amount of power it can deliver. To get the best results out of your amp/sub pairing, pick an amp that is capable of delivering anywhere from 75 to 150 percent of a sub’s watts RMS. The amp also needs to match with the sub’s impedance value.

Related article: Can an Amplifier Be Too Powerful for Speakers?

Doing the Numbers Game

Remember that if you have or plan to have multiple subs and one amp in the room, the subs all need to have the same impedance (Ohms) or coil type; otherwise, the power won’t be distributed evenly. 

Now, get the Watts RMS rating of each sub, then multiply this by the number of subs you want to install. This will be the total RMS rating of all the subs. Your amp should be able to supply the total RMS rating for this subwoofer system.

Additionally, figure out the total impedance load that your subs could be wired together to form. It gets tricky when you need to factor in the impedance and the wiring. So, you may need to check subwoofer wiring diagrams or charts to look into the combinations of subs and impedances.

According to the chart, it is important to take note of the sub’s voice coil, the pairs of terminals, and the ohms. For example, you have two DVC (dual voice coil) 4-ohm subwoofers that are each rated at 350 watts RMS. 

After figuring out the watts RMS and ohms of your subwoofers, find an amplifier that can put out enough power at an impedance load they can be wired together to form.

Using the same example above, the sub wiring chart will tell you that a pair of DVC 4-ohm subs with a combined 700 watts RMS rating can be wired together to form a 4-ohm or 1-ohm impedance load. 

So, you need to get an amp that can put out up to 700 watts RMS (or slightly higher than 700 watts) into a 4-ohm or 1-ohm load. As an example, you can use an amplifier with specifications of:

  • 600 W RMS x 1 at 1 ohm
  • 700 W RMS x 1 at 1 ohm
  • 600 W RMS x 1 at 4 ohms
  • 700 W RMS x 1 at 4 ohms

If you are having a hard time understanding subwoofer wiring options, you can check out Crutchfield’s charts or diagrams. You’ll also get a guide on how to pick the right subs if you already have the amp first.

Most people, however, would only take note of the amp and sub watts RMS and match the two numbers. This is especially the case if we’re talking of a single sub setup.

Advantages of Getting a Bigger (or More Powerful) Amp

In an ideal setup, you would want to keep the RMS numbers of your amp and sub fairly close to each other. But many sound experts prefer to get a slightly bigger amp than a sub, or an amp that puts out slightly more power. 

This way, you can accommodate a subs upgrade in the future without getting a new amp. Moreover, with an amp that is more powerful, you don’t have to turn up the gain. Or you just need to keep the gain low so as not to overpower your subwoofer. 

Turning up the gain just to get more power out of your amp will result in clipped sound signals to your subs.

Final Thoughts

Subwoofers will sound their best or reproduce great bass when they are amplified with the right amount of power. 

The difference in the sizes of your amp and sub has less to do with power performance and more to do with frequency response and tonal qualities. 

So, the point of matching your amp and sub is optimizing performance.