Car Audio Amplifiers

To get the most out of your car stereo speakers, you need to send the proper signal to them. Many decks simply don't have the power output needed to make your speakers truly sing.

To get adequate power to your speakers, you should include an amplifier in your signal chain before your loudspeakers.

Here are four articles about Car Audio Amplifiers

How to Set Your Gans with a Piezo Tweeter

Getting the most out of your amplifier is a matter of matching the inputs of the amplifier to the outputs of the source unit. This article discusses how to use a piezo tweeter to set your gain control.

How to Set Your Amplifier Gains with a Piezo Tweeter

How to Set Your Amplifier Gains With a Digital Multimeter

Getting the most out of your amplifier is a matter of matching the inputs of the amplifier to the outputs of the source unit. This article discusses how to use a digital multimeter to set your gain control.

How to Set Your Amplifier Gains With a Digital Multimeter

Three Features You Need in a Subwoofer Amplifier (and Three Features That are Nice To Have)

When choosing a subwoofer car audio amplifier, you should make sure it has these three features

What Features Should I Look For In a Subwoofer Amplifier?

How to Set Crossover Points and Subsonic Filters With Test Tones and Your Digital Multimeter in 4 Easy Steps!

We need to tune our systems for optimum performance. After setting gains, we need to set our filtering properly to get the most performance out of our subwoofer.

How to Set Crossover Points and Subsonic Filters With Test Tones and Your Digital Multimeter in 4 Easy Steps!

Three Features You Need in a Subwoofer Amplifier (and Three Features That are Nice To Have)

Choose a subwoofer amplifier based on how well it can provide a signal to a large driver. This is the most important feature.

The rule of thumb when you set up your system is to send half the power to the subwoofer system. If you want to set up a 1,000-watt stereo in your car, 500 watts should go to the subwoofer. You have to move a lot of air to make bass that will keep up.

You should buy an amplifier that includes these three features:

• Mono design
• Low Pass Filter
• Remote Bass Knob

These are three features that are nice to have but not needed:

• Subsonic (or infrasonic) filter
• Bass Boost
• Clip Indicator

Mono Design

Low frequencies have a very long wavelength. We cannot localize lower frequencies as well as we can localize higher frequencies. We can localize higher frequencies because high frequencies have a short wavelength. If you were hiking in the wilderness and you heard a bird singing, you would look in that direction. Our brains can use the audio signals from a bird song to triangulate the location of the bird. The wavelength is shorter than the distance between our ears. The phase of the waves at our ears will be different, as well as the sound pressure levels. Our brains take the differences between the bird song at our ears to tell our eyes where it comes from.


Low frequencies don't have this feature. If a footfall causes a rumble, we generally don't know where it's coming from. We'll get the thud. If the rumble source is moving, our brain can triangulate that position. Since we're in a fixed position in the car and the subwoofer doesn't move, we can use a mono amplifier. It's one less channel to fiddle with so it's easy to match to your subwoofer impedance and power output.

Low Pass Filter

We do not want high frequencies to play through our subwoofers. We need to filter the high frequencies out of the signal sent to the subwoofer. The filter should be adjustable to better match up to your main speakers.

Remote Bass Knob

There are several reasons to want a remote bass knob. 

• You're not gonna go booming every time you get in the car. (It's true!)
• You want to listen to an audiobook or a podcast. A subwoofer tends to bring hard consonant sounds from P and B. Puh Buh, Buh Puh. It's distracting.
• You have small children in the car. Protect those young ears!
• You are listening to music where heavy, thumping bass takes away from the music. In my own experience, "Before you Accuse Me" on Eric Clapton's Unplugged CD includes a foot tap. The center frequency of this foot tap seems to be at most car interior signature frequencies. What should be a simple "pat pat pat" turns into a romping "thud thud thud" with a powerful car stereo. Using a bass knob can bring this down to a normal SPL.

You should use the knob to achieve balance from bass to treble.

Subsonic (or Infrasonic) Filter

If you have a ported enclosure, the subwoofer may not play much lower than the port tuning. You may cause the subwoofer to unload. A subsonic filter will cut the signal to the ported box for frequencies it should not try to reproduce. You won't need a subsonic filter for a sealed box. Like the low pass filter, you want to make sure the subsonic filter is adjustable.

Bass Boost

Bass boost has been a feature of car audio amplifiers since the early 1970s. Bass boost goes by many names. It boosts the signal around frequencies that make subwoofers fun. Most of these bass boost controls are adjustable in both frequency and intensity. You have to be careful with this feature. Bass boost can overdrive your amplifier. Overdriving the amp can introduce clipping and harmonic distortion. Both can damage your amplifier and your subwoofer's voice coils. It is a good idea to reset the amplifier gain after introducing some bass boost.

Clip Indicator

The clip indicator light could be on the amplifier chassis or on a remote knob. Some may include a light on both. The clip indicator is there to keep you out of trouble.

You can use a clip indicator light for setting gains. Play a test tone with the bass knob all the way up and the gain all the way down. Play a test tone at about 40hz. Turn the deck volume up until the clip indicator lights up. Turn the volume down until it turns off. Turn the gain up until the clip indicator goes on, then turn the gain down until it turns off.

The main selling point of a clip indicator is for demonstrations. When you have a large subwoofer system and you want to show it off to others, you want to make sure you take it to the limit. Taking it past the limit means equipment damage. You'll need a visual indicator to stay below that limit. The clip indicator is there to keep you out of trouble.

Final Thoughts

An amplifier was an amplifier in the past. It received a signal and then amplified that signal. Manufacturers included a gain control so you wouldn't go blowing things up. If one wanted filtering and signal manipulation, one would need equalizers and crossovers. Now we can get amplifiers with built-in BlueTooth and on-board Digital Signal Processors. This article narrowed down the list of features to three must haves for a subwoofer amplifier, and three features that are nice to have.

How do I Wire my Subwoofers? Wiring Multiple Subwoofers Explained

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!

7 Posts about Subwoofers

Feeling overwhelmed over the amount of information out there about subwoofers? Let's break it down by category.

This page simply curates other posts in this blog and is intended to help guide you to what you're looking for.

Here are seven posts on our blog about Subwoofers:

1. What is a Subwoofer? Subwoofers Explained!

This page breaks down what a subwoofer is, what it does and why you need one for your system.

What is a Subwoofer, Subwoofers Explained!

2. What is Voice Coil Impedance? Subwoofer Resistance Explained!

This page breaks down why 2 ohms isn't always 2 ohms. Sometimes it's 1.8 and sometimes it's 20.

What is Voice Coil Impedance? Subwoofer Resistance Explained!

3. Got Bass? A Beginner's Guide to Your First Car Subwoofer

This is a step by step guide to installing a subwoofer for the first time. We explain everything you need to install a subwoofer in your car, regardless of what pieces already exist.

Got Bass? A Beginner's Guide to Your First Car Subwoofer

4. How to Design Your First Ported Subwoofer Box!

Bringing '88 back: how we used to have to design subwoofer boxes, laying out all of the math by example.

How to Design Your First Ported Subwoofer Box!

5. How Do I Wire My Subwoofers? Wiring Multiple Subwoofers Explained!

This post discusses when to use series wiring, parallel wiring and when to combine the two wiring schemes to arrive at the perfect impedance for your amplifier.

How Do I Wire My Subwoofers? Wiring Multiple Subwoofers Explained!

6. Five 12 Inch Subwoofers for about $150: Two videos of HiFiVega Expertly Reviewing Budget Bangers!

HiFiVega reviews 5 budget 12 inch subwoofers, all of them available from between roughly $110 and $155 shipped to your door. He puts them through the paces. Which one does he like best?

Five 12 Inch Subwoofers for about $150: Two videos of HiFiVega Expertly Reviewing Budget Bangers!

7. Subwoofer Box Calculator

If you need to know how to calculate dimensions for a sub box, then you'll want to check out our subwoofer box calculator

Sub box Calculator

What is voice coil impedance? Subwoofer Resistance Explained

Impedance is a measure of resistance at frequency. 

But there's more going on inside of a voice coil.

In this guide, we'll discuss

• DC Reisistance
• Nominal Impedance
• Peak resistance at a driver's Fs
• Voice Coil Inductance
• Box Rise, or how an enclosure affects impedance
• The effects of passive filtering on a subwoofer's parameters

Voice Coil DC Resistance

DC Resistance is an easy parameter to measure. Simply set your digital multimeter to DC Ohms and probe the leads. For a 4ohm driver, the digital multimeter should read anywhere from 3.0 ohms up to 4.5 ohms, and anywhere in between. 

The DC Resistance is different than Nominal Impedance because that's a measure of impedance at zero ohms. There are methods for measuring impedance vs frequency, but that's a discussion for another day. But understand that there are free modeling tools we can leverage to discover a woofer's impedance curve. 

Nominal Impedance

Simply put, Nominal Impedance is how much resistance the subwoofer provides to the amplifier most of the time. A subwoofer's nominal impedance is a very basic and useful measurement for matching a subwoofer system to an amplifier. Nominal impedance will tell you what impedance to expect over the loudspeaker's useful range. If the nominal impedance is too low, the amplifier will go into protect or overheat since the amplifier's circuitry is designed to operate with a certain amount of impedance on the loudspeaker leads. You can use this number in place of resistance to compute series and parallel circuits to wire up multiple subwoofer drivers to an amplifier, too. 

We use "nominal" because that's how the subwoofer is expected to behave for a majority of frequencies in the driver's usable range. The impedance will go up and down across the frequency range for both mechanical and electrical interference reasons.

Peak Resistance at Resonance

A subwoofer is an electro-mechanical transducer, converting electrical signals into physical sound waves that travel to our ears. The mechanical part of the device has a resonant frequency. Resonant frequency is the "natural" frequency based on a woofer's cone and suspension. If you've ever tapped on a woofer cone, you can hear the low frequency "thud". That thud's tone is centered around the woofer's resonant frequency.

This thud is the equivalent of a cymbal's ring or the sustained sound from a plucked guitar string. It wants to keep ringing.

Just like the cymbal or guitar string, the woofer cone and suspension has a tendency to keep ringing. This tendency to continue ringing pushes voltage back through the woofer's motor assembly, introducing additional impedance to the voice coil around that frequency. If we were to use a tool like a woofer tester or set up a testing circuit to measure impedance at frequency, we would notice an incredibly high impedance at that resonant frequency, making a peak in the woofer's impedance curve. This impedance at resonance may be 10x the woofer's nominal impedance! 

Voice Coil Inductance

An inductor is also known as a "choke coil". It's a coil of wire that passively increases impedance as frequency increases. The inductor is used by loudspeaker engineers to curtail high frequencies sent to a loudspeaker as part of a crossover network. The inductor works by quadrupling the impedance for each doubling of frequency. The term for this is "-6 decibels per octave slope", as the output goes down -6db for each doubling in frequency. 

Each doubling of power would result in +3db. As such, each halving of power results in -3db. Doubling the resistance halves the power. Quadrupling the resistance (doubling again) results in -6db.

A subwoofer's motor assembly is a coil of wire surrounded by a magnet. As such, the motor assembly will exhibit properties of an inductor, causing the impedance to rise as the frequency increases. This will cause the subwoofer's impedance to rise as the frequency increases.

"Box Rise", or How an Enclosure Affects a Subwoofer's Impedance

An enclosure affect's a subwoofer's impedance in much the same way an enclosure affects the subwoofer's output. A sealed subwoofer enclosure will increase the subwoofer's overall resonant frequency and will also increase the "ring time" of the driver. Both of these properties will increase the impedance seen at the new resonant frequency.

If one were to include a port on the subwoofer enclosure, we would add an additional resonance to the loudspeaker system. This additional resonance is centered around the port tuning and adds an additional ringing. Just like the ring of a woofer adds resistance within the voice coil, this resonance at port tuning also adds resistance to the voice coil centered at that frequency. 

This port tuning adds an additional peak to the impedance curve, centered around the port tuning frequency. There are now two peaks in the subwoofer's impedance curve

When one adds another chamber and resonance to the enclosure (in the case of a sixth order band pass), one adds yet another resonant frequency peak, totaling up to three.

These additional peaks in the impedance curve are frustrating to SPL competitors who design a subwoofer system's output to dovetail into a vehicle's sonic signature and provide maximum boom at the "burp frequency", only to find the impedance at the "burp frequency" curtails the amount of power the amplifier can send through the voice coils. This additional impedance is known as "box rise". 

Box rise can be introduced through heat in the motor assembly during a long demo or a db drag race format. 

Effects of Passive Filtering on Parameters

Passive Filtering (like in the choke coil example discussed above) will change how the system reacts. Any additional components will introduce a bit of a change in the system. The addition of a choke coil to curtail higher frequencies from the subwoofer driver will introduce additional DCR. This additional DCR in the circuit will change the Qes parameter of the subwoofer driver, and then subsequently change the Qts parameter. This change will affect how the subwoofer driver will perform in an enclosure. The higher the DCR of the passive components in line with your subwoofer driver, the larger the change in Qes/Qts. A large shift in Qes will change the efficiency bandwith product. That will change what kind of enclosure your woofer will perform best in, shifting towards a sealed box.

This complication illustrates why it's recommended to use a dedicated subwoofer amplifier, instead of trying to drive all loudspeakers from a single amplifier with passive speaker-level filtering.

Some Final Thoughts on Impedance

A subwoofer's nominal impedance is only a rough estimate of how the subwoofer will present a resistance to the amplifier. The subwoofer voice coil, enclosure and external components will all effect how the subwoofer performs. Most of the time we don't need to worry beyond the nominal impedance matching up to the amplifier, but in some cases we should take it into consideration.

What is a Subwoofer? Subwoofers Explained!

A subwoofer is a type of loudspeaker. Subwoofers reproduce the lowest frequencies or tones audible to human ears. We use a subwoofer to reproduce tones your main speakers cannot reproduce.

In this guide, we're going to learn why we need a subwoofer and then dissect the parts of a subwoofer. What makes a subwoofer tick?

• Why Do I Need A Subwoofer?
• What Are the Parts of a Subwoofer?
• The Subwoofer Driver
• The Subwoofer Enclosure
• The Subwoofer Amplifier
• Final Thoughts About Subwoofers

Why Do I Need a Subwoofer?

You need a subwoofer because you have great speakers. Those speakers are straining to reproduce low frequencies with any presence. Drums, bass musical instruments, and sound effects lack authority. You may hear the main speakers strain when watching a typical Hollywood action film. The subwoofer will help your beloved main speakers sound their best! Subwoofers help by relieving them of the task of reproducing low bass. The mains speakers will not have sub-bass signals crowding out the power. They are free to reproduce vocals, winds, synths, cymbals, brass, and strings.

No single musical instrument can play tones throughout the spectrum of human hearing. In a similar vein, no single driver can reproduce all the tones that humans are capable of hearing. A typical floor-standing speaker consists of a woofer and a tweeter. Some of them will include a midrange for more vocal clarity. But few floor-standing speakers will play below 65hz, or the “deep C” on a piano (much less “pedal C”). 

Adding a subwoofer to an existing system can improve your listening experience. 

What Are the Parts of a Subwoofer?

A subwoofer system consists of a subwoofer driver and an enclosure. Some “powered” variants will include an onboard amplifier. 

The Subwoofer Driver

A subwoofer’s driver is usually larger than a typical home theater or stereo speaker main driver. The subwoofer driver will be 20cm (8 inches) or larger in diameter. Some engineers have designed smaller drivers, too. Engineers choose a cone, voice coil, and suspension to handle more power and play deep.

The Subwoofer Enclosure

A subwoofer’s enclosure helps shape the sound. These enclosures can be a simple “box” around the back of the woofer. They can also be well-engineered physical air manipulation devices.

Sealed Subwoofer Enclosure

The simple sealed enclosure isolates the rear wave from the front wave. This prevents any cancellation between the front and back of the speaker. It also serves as both a spring and a mass component for the cone. This property allows the engineer to adjust the system’s resonance for a given driver.

Ported Subwoofer Enclosure

The ported enclosure is more complicated than a sealed enclosure. You may see this listed as a "bass reflex enclosure". Ported subwoofers get their name from the port that allows the rearward wave to escape. But escape is only one part of the story. The port shifts the phase of the wave at a specific tuning frequency. Engineers can bake in a bit of distance to change when the rear wave exits the box. They adjust this to increase Sound Pressure Level (SPL) or to increase the depth. Changing the enclosure's net volume can do both!

A ported enclosure uses a simple round tube most of the time. Some ported subwoofer designs use a slot port. The engineers use the outer walls of the box as part of the port. The internal port walls also work as internal bracing for the subwoofer box! 

Other Subwoofer Enclosure Alignments

Other alignments increase a subwoofer system’s complexity. 

Bandpass subwoofers use more enclosure air spaces on either side of the driver cone. These spaces may or may not include ports. You may have seen one of these at an electronics store in the 90s. They generally had a plexiglass window. Engineers can tune these systems for an incredible low-frequency extension.

A quarter-wave pipe uses a column of air equal to the quarter-wave of a specific tuning frequency. This accomplishes one of two goals. 1) increase the low-frequency extension of the subwoofer; 2) or increase SPL at a specific band. The column of air's cross-section area is usually equal to the loudspeaker's cone area. These enclosures can get very large.

A horn-loaded subwoofer uses an air mass that feeds into a small “throat”, and then flares out. Think of how a tuba works. It is more efficient than other alignments, at the expense of space. These are generally used in pro audio and sound reinforcement. You may have seen a horn-loaded subwoofer at an outdoor concert.

The Subwoofer Amplifier

Marketing companies call home theater subwoofers either active subwoofers or powered subwoofers. This means the subwoofer system has an on-board mono plate amplifier. This provides your receiver some relief from attempting to play low frequencies. This helps like the large subwoofer driver relieves your smaller speakers. This further cleans up the sound reproduced by your main speakers. The amplifier is reproducing a smaller bandwidth for your speakers. 

Powered subwoofers are also starting to appear as an option for car audio systems. These serve as an easy upgrade for people who want to add a little boom to their existing factory stereo.

Final Thoughts About Subwoofers

Most stereo systems will sound better with a subwoofer. The type of subwoofer you choose will depend on your listening habits. You'll need to look at how much space you have. You'll need to think about the kind of listening you do. Music or home theater? You should arrive at a solution that improves your listening experience!

Further Reading: How To Design a Custom Ported Subwoofer

Subwoofers

Best Mono Amplifier For Subwoofer For Bass

In order for your car audio subwoofer to work properly, you need to provide a strong signal. A subwoofer doesn't need a stereo signal as the low frequencies are not localizable when compared to higher frequencies, so we can use a mono amplifier instead of a stereo amplifier. In order for the subwoofer to keep up with the rest of the stereo system, the subwoofer needs a lot of power to move the air needed to make impactful bass compared to higher frequencies.

You'll need some additional features to fully enjoy your subwoofer. Each of the mono subwoofers below includes a remote bass knob and a low pass filter. 

• Skar Audio SKv2-4500.1D
• Budget: Boss Riot R1100m
• DS18 FRX2.5k Pro
• Best Mono Amplifier by Power Rating
• Best 1200w: Rockford Fosgate Prime R2-1200X1
• Best 500w: MTX Thunder 500.1
• Best 300w: Rockford Fosgate Punch 300x1
• Best Mono Amplifier for Subwoofer by Price Point
• Under $300: Taramps Smart3
• Under $200: Skar Audio SKv2-1500.1D
• Best Bridgeable Stereo Amplifier: Rockford Fosgate Punch 300x2
• Best Mono Amplifier for Home Theater: OSD Audio SMP1000
• Best Mono Amplifier for Powersports: Rockford Fosgate Power TM750X1bd
• FAQ
• What is a subwoofer? Why does it need an amplifier?
• Why does a subwoofer use a mono amplifier? Why not stereo?
• What features should I look for in a subwoofer amplifier?
• Low Pass Filter
• Remote Bass Knob

Skar Audio Skv2-4500.1D Mono Amplifier for Subwoofer

The Skar Audio SKv2-4500.1D is a no holds barred competition subwoofer amplifier. It is built for "burps" but is clean enough to use for daily listening. This amplifier delivers a whopping 4,500 watts into one channel at 1ohm from 15-270 hz. The amplifier is "strappable", meaning you can use two of them in conjunction with one another to deliver a face-melting 9,000 watts mono into 2 ohms, if you've got the vehicle electrical system upgrades to deliver it. The amplifier accepts two 1/0 gauge wires each for power and ground.

Check Amazon for Pricing and Availability for Skar Audio SKv2-4500.1d Competition Mono Amplifier

Skar Audio Skv2-4500.1D Features

• 1-ohm Stable Car Subwoofer Amplifier
• Competition Grade Quality and Performance
• Low Level Input (Gain): 6V - 0.2mV
• RCA pass through
• Low Pass Filter at 24dB Slope: 35Hz - 250Hz
• Variable Bass Boost at 45 Hz: 0dB - 9dB
• Subsonic Filter at 24dB Slope: 10Hz - 50Hz
• Phase Shift: 0 - 180 Degrees
• LED Power & Protection Indicators
• Strappable
• Remote Bass Knob & Wire Included
• Dual 1/0 Gauge Power and Ground Terminals (2 of each terminal)
• Working Voltage: 8.5V - 18V
• Fuse Rating: 450 Amp
• Dimensions: 25.6" (Length) x 9.15" (Width) x 2.5" (Height)

Skar Audio Skv2-4500.1D Specifications

• RMS Power at 2 Ohms: 2,800 Watts x 1 Channel (14.4v)
• RMS Power at 4 Ohms: 1,500 Watts x 1 Channel (14.4v)
• RMS Power at 1 Ohm: 4,500 Watts x 1 Channel (14.4v)
• Peak Power at 1 Ohm: 7,400 Watts x 1 Channel (14.4v)
• RMS Power at 2 Ohms (Strapped): 9,800 Watts x 1 Channel (14.4v)
• Frequency Response: 15Hz - 270Hz

Budget: Boss Riot R1100m

This is the best selling mono amplifier on Amazon as of this writing, in Summer 2020. 

Let's get it out of the way: there's no way this $70 amplifier makes 1100 watts. It has a 30 amp fuse built in. The fuse will blow after it's making 360 watts for a period of time. In fact, a youtuber connected a Boss Riot R1100m to an amplifier dyno and found that it could barely push 200 watts dynamic burst. It wins in the budget category based solely on features for the money. When you get a Boss Riot mono amplifier, you get a feature-rich 200 watt amplifier, which is enough power for a small subwoofer added to a factory stereo or to enhance a "deck and four" aftermarket system.

Just be sure to scratch off the "1100 watts" emblazoned on the chassis. 

Check Amazon for Pricing and Availability for Boss Audio Systems Riot 1100m

Boss Riot R1100m Features

• Class A/B Topology. It's "old school" under the hood.
• Speaker level input
• RCA inputs
• Remote bass knob
• Adjustable low pass filter
• Switchable bass boost

Boss Riot R1100m Specifications

• Class A/B Monoblock, MOSFET Power Supply
• 1100 Watts @2-Ohms Max Power
• 825 Watts RMS @2-Ohms
• High and Low Level Inputs
• Variable Low Pass Crossover, Bass Boost
• Remote Subwoofer Control

DS18 FRX2.5k

The DS18 FRX2.5k mono amplifier is a no compromise 2500 watt monoblock car audio amplifier. It's not just a subwoofer amplifier, it will also play mids and highs with that full 2500 watts. If you plugged a guitar into your system, you could power a stack of Marshall amplifiers and put on an outdoor concert for all to hear. The DS18 can power more than just subwoofers.

Check Amazon for Pricing and Availability for DS18 Pro FRX2.5K Mono Amplifier

DS18 FRX2.5k Features

• One ohm stable
• Low pass, full range or high pass filtering
• Remote bass knob

DS18 FRX2.5k Specifications

• Channels - 1
• Frequency Response - 20Hz - 20KHz
• RMS Power - 2,500
• Impedance Range - 1-8 ohm
• Input Sensitivity - 6V ~ 200mV
• Bass Boost - 0-12dB
• Hi/LO Pass - 40Hz-4KHz
• Product Dimensions - 12" x 7.3" x 2.2"

Best Mono Amplifier for Subwoofer By Power

1200w: Rockford Fosgate R2-1200X1

Rockford Fosgate invented the modern car stereo amplifier in 1973. They've been pushing the industry forward ever since. Each iteration of their amplifiers builds upon the previous. Features found in that first "Power Punch" amplifier are found in today's Rockford Fosgate amplifiers, such as Punch EQ bass boost. This Rockford Fosgate Prime R2-1200X1 is the latest in a long line of Rockford Fosgate amplifiers, with their legendary build quality paired with new features like C.L.E.A.N. set up and 12db/octave low pass filters and even and adjustable infrasonic filter designed to protect your subwoofer.

Check Amazon for Pricing and Availability for Rockford Fosgate R2-1200x1 Prime Mono Amplifier

Rockford Fosgate R2-1200X1 Features

• Variable On Board PunchEQ
• C.L.E.A.N. Technology

Rockford Fosgate R2-1200X1 Specifications

• Rated RMS Power: 400 Watts x 1 @ 4Ω OR 800 Watts x 1 @ 2Ω OR 1200 Watts x 1 @ 1Ω
• Crossover Slope: 12dB/Oct Butterworth
• Crossover Frequency: Variable 50Hz-250Hz Low Pass
• Infrasonic Filter: Variable 15-50Hz
• Auto Turn On With Defeat Switch
• Cast Aluminum Heatsink
• Short Circuit & Over Current Protection
• Remote Level Control Included
• Dimensions: 1.9" x 6.8" x 11.3"

500w: MTX Thunder 500.1 Mono Amplifier

The MTX Thunder 500.1 is a small but powerful amplifier, delivering 500 watts into two ohms. It's a bare bones, no nonsense 500 watt amplifier that pairs well with the MTX Terminator Subwoofers.

Check Amazon for Pricing and Availability for MTX Thunder 500.1 Mono Amplifier

MTX Thunder 500.1 Mono Amplifier Features

• Class D Topology
• Variable LPF
• Selectable Bass Boost
• Small Foot Print Design
• Surface Mount PCB

MTX Thunder 500.1 Mono Amplifier Specifications

• 500x1 RMS into 2 ohms

300w: Rockford Fosgate Punch 300x1 amplifier

Rockford has been in the game since 1973. They invented the modern car audio amplifier and included a "Power Punch" circuit to boost the bass response in car. The current P300x1 is a spiritual successor to the original entry level punch amplifiers. This full range amplifier is useful for powering your subwoofer or for powering a center channel in a sound quality competition system.

Check Amazon for Pricing and Availability for Rockford Fosgate P300x1 Mono Amplifier

Rockford Fosgate Punch P300x1 Amplifier Features

• High level input capable with Auto Turn-On circuit
• RCA pass-thru outputs
• Features C.L.E.A.N. Set-up
• Optional remote Punch Level Control (PLC2) ready (w/ input clip indicator)
• 12dB/octave Butterworth crossover
• On-board Punch EQ with +18dB boost @ 45Hz
• Muted turn on
• Stealth top mounted control panel
• Cast aluminum heatsink
• Short circuit protection
• Over current protection
• 1 Year Warranty

Rockford Fosgate Punch P300x1 Amplifier Specifications

• Punch 300-Watt Full-Range Mono Amplifier
• Rated Power: 200 Watts x 1 @ 4-Ohm OR 300 Watts x 1 @ 2-Ohm
• 12dB/octave Butterworth crossover
• Power Wire Gauge: 8 AWG to 4 AWG
• Speaker Wire Gauge: 8 AWG to 18 AWG
• Optional Punch Level Control Ready (PLC2 sold separately)
• Recommended Fuse (not included): 50 A
• Dimensions (H x W x D): 2.38" x 7.76" x 9.86"

Best Mono Amplifier for Subwoofer By Price

Under $300: Taramps Smart 3

This is a single channel amplifier that produces 3000 watts into one or two ohms at a great price. It covers most of the spectrum of human hearing.  

Check Amazon for Pricing and Availability for Taramps Smart3 Subwoofer Amplifier

Taramps Smart 3 Features

• Crossover High Pass (Hpf): 10Hz ~ 90Hz (-12dB) Variable
• Crossover Low Pass (Lpf): 90Hz ~ 10KHz (-12dB) Variable
• Bass Boost: Freq.: 35Hz ~ 55Hz, Boost: 0 ~ +10dB

Taramps Smart 3 Specifications

• 1 OHM: 3000W RMS
• 2 OHMS: 3000W RMS
• 4 OHMS: 2000W RMS
• Input Sensitivity: 0.22V ~ 4V
• Signal to Noise Ratio: >90dB
• Frequency Response: 10Hz ~ 10KHz (-3dB)

Under $200: Skar Audio RP-1500.1D

A baby brother to our top rated SKv2- 4500.1D, this amplifier has many of the features at a power level consistent with a daily driver at a price we can agree with. The Skar RP-1500.1D can be wired to 4, 2 or 1 ohm. This amplifier is powered low enough where it would work with a stock electrical system.

Check Amazon for Pricing and Availability for Skar Audio SKv2-RP1500.1D Subwoofer Amplifier

Skar Audio RP-1500.1D Features

• Skar Audio RP-1500.1D Monoblock Amplifier
• 1-ohm Stable Car Subwoofer Amplifier
• Class D Monoblock Subwoofer Amplifier
• 4 Way Protection Circuitry: Thermal, Voltage, Speaker, DC
• High Speed MOSFET Power Supply
• Soft Turn on Circuit
• Bass EQ Switch: 0, +6dB, +12dB
• Low Pass Filter (Variable): 50Hz - 220Hz
• Subsonic Filter: Off - 50Hz
• Remote Bass Knob & Wire Included
• 4 Gauge Power and Ground Terminals
• Working Voltage: 8.5V - 14.4V
• Fuse Rating: 120 Amp
• Dimensions: 13.875" (Length) x 6.1875" (Width) x 2.25" (Height)

Skar Audio RP-1500.1D Specifications

• 500w into four ohms
• 930w into two ohms
• 1500w into one ohm
• Frequency Response: 20Hz - 250Hz
• Signal to Noise Ratio: 85dB

Two channel amplifier for subwoofer: Rockford Fosgate Punch 300x2

This Rockford Fosgate Punch 300x2 was chosen as our best two channel amplifier for driving a subwoofer because it produces 300 watts into a four ohm load when bridged. The amplifier features both a low pass filter and a high pass filter for system flexibility. The Punch series of Amplifiers includes top mounted controls to make it easier to set up after the amplifier is installed in the car. This was chosen to be your system's "starter amplifier" that you could use to power a small subwoofer for your vehicle's factory stereo system. When you would acquire a dedicated mono amplifier for your subwoofer, you could then use this two channel amplifier to power your front stage or rear fill. This amplifier is compatible with a Rockford Fosgate Remote Punch Level Control, sold separately.

Check Amazon for Pricing and Availability for Rockford Fosgate P300x2 Punch 300 Watt 2-Channel Amplifier

Rockford Fosgate Punch 300x2 Features

• Aluminum heatsink
• Top mounted controls (!)
• C.L.E.A.N. Setup
• Punch EQ
• High level inputs

Rockford Fosgate Punch 300x2 Specifications

• Punch 300-Watt Full-Range 2-Channel Amplifier
• Rated Power: 100 Watts x 2 @ 4-Ohm OR 150 Watts x 2 @ 2-Ohm OR 300 Watts x 1 @ 4-Ohm Bridged
• 12dB/octave Butterworth crossover
• Power Wire Gauge: 8 AWG to 4 AWG
• Speaker Wire Gauge: 8 AWG to 18 AWG
• Optional Punch Level Control Ready (PLC2 sold separately)
• Recommended Fuse (not included): 50 A
• Dimensions (H x W x D): 2.38" x 7.76" x 9.86"

Powersports: Rockford Fosgate Power TM750X1bd

There are unique challenges to a power sports installation. A car audio amplifier needs to withstand temperature extremes, vibrations and still just work day in and day out. An amplifier in a boat also needs to withstand temperature extremes and vibrations while still just working, but it also has to deal with mud, dust, fresh water, salt water, etc. And the owner will still expect it to just work, day in and day out. 

Rockford Fosgate has a number of compact power houses for power sports, but we chose the big 750w TM750X1bd amplifier for a subwoofer in a power sports application. Boats are noisy. UTVs are noisy. Side by sides are noisy. Motorcycles are noisy. You need to overcome all of that noise from wind and water and it needs to penetrate your helmet. You need power and lots of it.

Check Amazon for Pricing and Availability for Rockford Fosgate TM750X1bd Power Marine 750 Watt Class-bd 1-Channel Amplifier

Rockford Fosgate Power TM750X1bd features

• Dual fan cooled
• No RCA, uses a sealed four pin connector for input

Rockford Fosgate Power TM750X1bd specifications

• 500 Watts x 1 @ 4-Ohm
• 750 Watts x 1 @ 2-Ohm
• 750 Watts x 1 @ 1-Ohm
• Input sensetivity: 150 mV to 12 V

Home Theater: OSD Audio SMP1000

A mono amplifier for subwoofer in a home theater is designed for reproducing low frequency effects. This is the "point 1" in your home theater system's nomenclature. 

In some cases, the home theater subwoofer will also take the lower frequencies from smaller main speakers and play those, freeing up those speakers from producing frequencies they are physically incapable of reproducing. 

The room also plays a role in the home theater bass response. There are a number of unknowns when you shop for a home theater subwoofer, and modern technology has made it easier to fix any room anomalies. 

The best home theater subwoofer amplifier is the OSD Audio SMP1000. This amplifier includes an app-controlled DSP so you can easily tune the subwoofer for your home theater. This is a separate component that rests on a shelf, as opposed to a plate amplifier, so it sits with your other home theater components.

Check Amazon for Pricing and Availability for OSD Audio SMP1000 Mono 1000W Class D Subwoofer Amplifier

OSD Audio SMP1000 Features

• Class D topology for cool operation
• Includes speaker level inputs
• Includes RCA inputs
• Includes +12v trigger to turn on with receivers

OSD Audio SMP1000 Specifications

• 200w rms at 8ohms (500w max)
• 400w rms at 4ohms (1000w max)

FAQ

What is a Subwoofer? Why does it need an amplifier?

A subwoofer is a large loudspeaker driver designed to reproduce low frequencies. Low frequency reproduction needs more power than high frequency reproduction, since the has to move more air to achieve the same SPL. It is generally advised that your subwoofer should use half of the power in your system. If you're adding a subwoofer to a factory stereo, 300 watts is plenty. If you're building a super street competition system, you're going to need more than 1000w to be competitive. At that point you'll be upgrading your vehicle's electrical system.

Why does a subwoofer use a mono amplifier? Why not stereo?

A subwoofer uses a mono amplifier because of the wavelengths involved. Those frequencies are incredibly difficult for people to "localize". You can determine the location of a bird song because the wavelengths involved are only a couple inches apart and your brain and ears combine the different signals to triangulate the position of the bird relative to your head. Cool, huh? 

Contrast that with plucking the open string of the low E on a bass guitar. Doing so will produce a wavelength that's roughly 27 feet long. You can see how it would be difficult to localize such low frequencies, when your ears are just a few inches apart. Using two separate signals to two separate subwoofers in stereo is virtually indistinguishable from using one combined low frequency signal to power two separate subwoofers. So designing one signal path in the amplifier as opposed to two helps save money through a reduced component count, and the engineers can design the circuit around higher power components in a smaller chassis.

What Features should I look for in a mono amplifier for subwoofers?

Low Pass Filter

Just like your tweeters won't do a good job reproducing bass frequencies, your subwoofer is less than ideal for reproducing vocals or many musical instruments. Ideally you want an adjustable low pass filter, and not a "fixed" low pass filter. If your low pass filter is fixed at 80hz, but your existing speakers don't play well below 150hz, the system will be missing some midbass punch.

Remote Bass Knob

Not everyone appreciates a bass heavy system. Employing a remote bass knob to reduce the subwoofer's volume when you're not interested in bass is beneficial. If you're on a long trip and listening to an audio book, you don't want Ps and Bs to be emphasized. If you have children in the car you don't want to harm their ears. So having an easy way to turn it down when it's not needed is beneficial to everyone.

Speaker Level Inputs

Speaker level inputs are useful if you need to hook your amplifier up to a factory stereo that does not have line-level RCA inputs. Some of the amplifiers on the market are able to turn on the amplifier with this high voltage speaker level signal, so the installer does not have to tap into the vehicle's electrical system in order to find a +12v switched source for the amplifier's remote turn on.