Every car needs a good amplifier. Unfortunately, not all amps are created equally. There is a lot to consider when shopping for an amplifier the size of your vehicle, the power that you need, the type of music you listen to are just some considerations, and especially the number of channels.

For this type of requirement, the best 4 channel car amplifier should be able to power your system well enough, but not too much. It is also important that the amplifier can drive all of the individual channels at sufficient levels without overpowering any one channel or underpowering another. And it’s important that it was designed with durability.

The car amplifier 4 channel needs at least two channels per speaker so you need to know how many speakers you are going with before buying an amplifier. Because if it does not have enough channels then there will be some.

In this blog post, we will provide information on the best car amplifier 4 channel available on the market so that you can find what’s right for your needs! and moreover… If your are in a Hurry? Here Are the Top 3 Best 4 Channel Amps for quick selection:


Alpine S-A32F S Series, Class D, 4 Channel amplifier


  • Variable low- and high-pass filters
  • Selectable bass boost
  • 80 Watts RMS x 4, 2 Ohms

Rockford Fosgate PBR300X4, Class AB, 4 Channel


  • Full Range Class BR Topology
  • Ultra-compact Size
  • MOSFET output stage

MTX Audio THUNDER75.4 Thunder, Class A/B, 4 Channel


  • Variable LPF and HPF
  • Surface Mount PCB
  • Small Foot Print Design

First, we know about:


The amplifier acts as a controller which regulates how much power flows from the alternator (or battery, if you’re not driving) to the speakers. The amplifier also boosts the power to a level that is good for your speakers – so that they play at their best.


A four channel car amplifier, also known as a full-range or monoblock power amplifier, provides the voltage to drive speakers. It does not have any input connections for other sources of audio such as CD players.

Instead, it has what is called speaker terminals where you would connect your factory radio outputs and then use connectors at these points to route the signal back into your stereo system’s wiring harness.

The average power output for this type of amplifier is between 300W and 600W per side if driven by an electrical current from 12 volts DC (direct current) battery pack or alternator that supplies up to 14 volts in automotive applications; though some can produce more than 1000 watts when used with a 24-volt electrical supply.

A 4 channel car amplifier can be powered by 12 volts of electricity, which is what your car battery produces. The voltage output from the amplifier will vary depending on what you connect it to and what type of power intake you have (i.e., whether or not you are running a low current through secondary wiring).

Music enthusiasts should consider buying an amplifier with at least two channels per speaker so they don’t end up with sound spilling out in undesirable places, but if too many speakers cause problems for your vehicle’s internal circuitry then this point may not apply as much to you.


A 4 channel car amplifier can be used to power a subwoofer or speakers. The signal from the radio is sent into what’s called an “in-line amplifier,” which boosts it enough for the speaker to function properly.

If there are no amplifiers present in your vehicle, then you won’t feel much bass coming out of your speakers because they just don’t have what it takes!

A 4 channel amplifier might also work if you want more than one pair of stereo speakers inside your car that produce sound at different volumes.

In either case, things will likely sound better with this type of equipment installed and powered up.

This article discusses how a 4 channel car amplifier may benefit any setup by simply providing the right power, volume levels, and much more. Our experts have found the 12 Best 4 channel car amplifiers for your perfect selection.

These are the best we could find with our many hours of research. Now we are presenting the quick ranking table according to the best sellers.

»>How do we review products«<


  1. MTX Audio THUNDER75.4 Thunder Series Car Amplifier

  2. Alpine BBX-F1200 280 Watt 4-Channel Amplifier

  3. Zapco ST-4X II 4-Channel 320W RMS Class AB Amplifier

  4. Rockford Fosgate PBR300X4 Punch 300 Watt 4 Channel Boosted Rail Amplifier

  5. Alpine S-A32F S Series 4 Channel Digital Amplifier 80 Watts RMS x 4, 2 Ohms

  6. TORO TECH – RX4, 65 Watts x 4 RMS @ 4 Ohm / 4 Channel Amplifier

  7. JL Audio JX400/4D 4-channel car amplifier — 70 watts RMS x 4

  8. Pioneer GM-D1004 400W 4-Channel GM Digital Series Class FD Amplifier

  9. Sony XMS400D 4 Channel Micro Amplifier (Black)

  10. 4-Channel High Power MOSFET Amplifier – Slim 2000 Watt Bridgeable

  11. Cerwin-vega Mobile CVP1200.4D CVP Series 4-Channel Class-D Amplifier (600W RMS)

  12. Pioneer GM-A6704 4-Channel Bridgeable Amplifier with Bass Boost, Black/red



Brand Name: MTX

Model: THUNDER75.4

Class: THUNDER75.4

No. of channels: 4

Dimensions: 14.43 x 7.5 x 4 inches

Weight: 4.5 pounds

Made in: China

This is one THUNDEROUS device. If you’re looking for the best car amplifier for sound quality, it’ll be hard to find something better than the MTX Audio THUNDER75.4 Thunder Series Car Amplifier.

The amplifier uses class A/B topology and has variable LPF and HPF settings, along with a small footprint design that provides excellent thermal distribution without overheating- a culprit that hampers other models on the market. Variable LPF and HPF allow you to filter out the bass under 80Hz when playing music at high volumes so that speakers don’t distort.

This device can be tailored to meet your need. It even provides an increased power handling capacity as well as improved sound clarity.

The wireless remote control will allow users from outside of the vehicle to navigate through features such as digital bass management adjustments which ensures that you have what you need whether at home or on the go!

The MTX Audio THUNDER75.4 Thunder Series Car Amplifier is perfect for cars with speakers and a small output capacity, or for installations requiring one amplifier per channel in any car or truck. A surface mount PCB design lowers the noise floor and reduces the temperature inside the box significantly.

The small footprint takes up little space in your trunk but still provides 75 watts of power per channel. Get all of this plus amazing customer service from MTX Audio today!


  • Really good for subwoofers
  • Never gets hot or shuts off
  • Compatible behind the speakers
  • Broad spectrum
  • Makes the factory Bose and Infinity stereo
  • No overheating, no protection mode discrepancies


  • Sometime, low care or loose wiring may cause heating

_Sample Customer Review: _

“I paired this 4-channel amp to two Alpine-S 6.5” speakers and two Alpine-S 6x9s. This combination brings a broad spectrum of mids/highs & lows to the vehicle. Makes the factory Bose and Infinity stereos in my other vehicles sound sub-par. This amp is money well spent, you won’t regret it!"



Brand Name: Alpine

Model: BBXF1200

Class: A/B

No. of channels: 4

Dimensions: 12 x 8 x 20 inches

Weight: 5 pounds

Are you looking for the class-leading power and performance of an Alpine amplifier in a small package? The Alpine BBX is perfect for bass lovers who want to take control. Its automotive design means it’s ready to handle all types of weather, from blistering heat to searing cold.

Designed with great bass frequencies in mind, it includes everything you need: very high output, incredible signal stability at 2Ω or 4Ω loads, sophisticated protection systems that protect from thermal meltdown, and speaker shorts – even sublime sound quality thanks to its Soft Start turn-on which reduces popping.

Alpine’s BBX amplifier has incredible signal stability at either its rated power or lower, making it ideal for automotive use or other cases where multiple channels are needed but limited space and/or high ambient temperatures pose problems. Alpine’s BBX amplifier is designed to supply Alpine sound quality, even in the harshest environments.

Alpine has class-leading power with a big performance, so it’s ideal for any type of music – from rock to hip hop or country tunes. Alpine’s Alpine BWX-M1200 and Alpine BBX models are made for bass lovers who want control over the high end sound experience in your vehicle, no matter what genre you listen to most often.

The built-in Bass EQ circuitry allows you to customize how much highs remain crisp and clear while supporting a strong low end without sacrificing either one; there’s even an RCA preamp output that will work with all types of external amplifiers, so you can build your own bass/amp combo that’s perfect for the Alpine sound.


  • Very good bass
  • crisp highs from the tweeters
  • No over heating
  • Great sound and build quality
  • Compatible with JBL GTO speakers (6.5 and 6×9) with excellent results
  • Very easy to install
  • Great sound quality for 6.5


  • PleaseConfirm in writing warranty before buying

Sample Customer Review:

“There’s separate inputs for the subs, made it very easy to customize the sound from the preamplifier.”



Brand Name: Zapco

Model: ST-4X II

Class: AB

No. of channels: 4

Dimensions: 14.9 x 7.4 x 3 inches

Weight: 6.09 pounds

Power @ 4Ω: 4 x 50 watts THD @ Rated Power 0.5%THD Power @ 2Ω: 4 x 80 watts Power Bridged @ 4Ω: 2 x 160W RMS.

Signal to Noise Ratio 95dB THD + Noise 0.5%

Channel Separation 60dB

Frequency Response 15Hz to 30KHz ±1dB

Input Sensitivity .25v to 5v

Dimensions in mm: 160(W) x 52(H) x 260(L) Overall: 160(W) x 52(H) x 302(L)

With the ZAPCO ST-4X II amplifier, you can load up your vehicle with high-quality audio that will shake everything! Keep things crystal clear by extending its 15Hz to 30KHz ±1dB frequency response. This product is not for beginners and definitely pushes a lot of power with 4 x 50 watts at 4Ω and when it goes into bridged mode 2 x 160w RMS.

It features variable bass boost control for more feels, auto-on speaker level inputs to simplify your life as well as variable input gain control. Is what you’re looking for giving you massive amounts of pow?

This is one component of their wide array of electronic equipment, supplies, and accessories. When it comes to amplifiers or speakers that are loud enough for the weekend. This device is exactly what you need for your vehicle – even if you’re the type to turn up your stereo a little too high!

With four channels, full-range class A/B components are complete with variable input gain control and variable electronic crossover to route the signal.

Where it needs to go as well as back again through extra protection features like auto-on when there are speaker level inputs established and a compact chassis plus an optional bass boost control turns those extras handsets from average.

It has RCA and Speaker Level inputs to accommodate any audio source and variable input gain control. This means you can play music at low volumes without sacrificing audio quality, perfect for quieter listening settings! You’ll be amazed by the sound output of each channel.

The variable electronic crossover lets you adjust frequency separation from 30Hz up to 300Hz effortlessly, giving you unprecedented control over your sound.

With auto-on with speaker level inputs turned on, this amplifier will turn on whenever there’s an incoming signal (saving precious battery life)! Finally don’t forget about that sleek compact chassis—you could easily put these amplifiers anywhere in your car or home.


  • High Power
  • Compact chassis
  • 4-Channel, Full Range, Class A/B
  • RCA and Speaker Level Inputs
  • Variable input gain control
  • Variable electronic crossover
  • Auto-on with Speaker level inputs
  • Variable bass boost control


  • Not Yet

_Sample Customer Review: _

“If you want amplifier for many years zapco is your amplifier you will not regret it is an amplifier q is even used in sound competitions is an amplifier q can be used to the extreme and yet give you clarity and incredibly last years and years what your competition can’t do. As long as I live, I will be a customer of ZAPCO and swbwoofers kicker.”

Related Article»> 12 Best Car Amplifier for Bass 2023



Brand Name: Rockford Fosgate

Model: PBR300X4

Class: AB

No. of channels: 4

Dimensions: 9 x 6 x 3.4 inches

Weight: 2.53 pounds

Power: 300 Watts-RMS Power Output: 75 Watts x 4 @ 4-Ohm (4-Ohm only)

The PBR300x4 Punch Amplifier sets the bar for amplifier efficiency with 300 watts of power without taking a lot of juice from your electrical system.

Powerful, compact, and efficient while providing big power – RMS Power Output: 75 Watts x 4 @ 4-Ohm (4-Ohm only) with features like high-level inputs and MOSFET output stage, this amplifier is perfect to use in speakers or drive upgrades on any car stereo system.

It also has variable 4-6 volt hi-level DC offset voltage input turn-on control to really customize the sound you want for your vehicle’s stereo equipment that is looking for smooth operation while being small enough to be tucked away when not needed or placed in a box when not in use.

Perfect for smaller installations and stealth fighters, the Stealth Ripper Bill is great to use on motorcycles or recreational vehicles.

The Stealth-Rip™ bill allows you to save time by quickly ripping your bills in half without a hassle!

This amplifier features a variable high-level turn input for any type of installation or mobile device and is perfect for boosting the power output to your factory speakers, driving upgrades, replacing amplifiers with higher efficiency designs where size constraints are an issue as well as adding more usable wattage to the Rockford Fosgate PBR300XB.

More features of the Rockford amplifier include an all-metal chassis that provides rugged durability in any environment, and overload protection to safeguard against accidental clipping or prolonged exposure to excessive levels of the input signal.

It also features thermal protection that automatically shut down the amplifier when high temperatures reach 25°C (77°F). The control panel also includes; Input Sensitivity selector.


  • Compact
  • Nice build quality – Super clear sound
  • Easy to install
  • Solid performer
  • Unbelievable sound for the size of this amp
  • Great sonic clarity
  • Small enough to fit in a batwing fairing


  • Check accessories before buying

_Sample Customer Review: _

“If your doubtful get the 500, dont make my mistake. This amp is great dont get me wrong , but i was looking for a little more power than it has.”



Brand Name: Alpine

Model: S-A32F

Class: AB & D

No. of channels: 4

Dimensions: 11 x 11 x 5 inches

Weight: 4.97 pounds

Voltage: 14.4 Volts

The Alpine S-A32F is an affordable, 4-channel digital amplifier that delivers 80 watts RMS x 4 to your car’s front and rear speakers with high fidelity. The amplifier features variable low- and high-pass filters, selectable bass boost, subwoofer level control, crossover network, phase inversion, and a frequency response of 20Hz to 200Hz.

The amplifier also offers 55 watts RMS per channel for each of your front and rear speakers. It has an 8" by 8" footprint and it’s just over 2" tall. This compact amplifier can be mounted behind the front or rear seats of most vehicles.

Power to the People! The Alpine S-A32F Amplifier has a max power output of 80 watts RMS x 4 for each of your car’s speakers, plus 55 watts x 4 at 2 ohms in its Class AB configuration and 90 watts x 4 at 4 ohms in its Class D configuration.

The S-A32F amplifier also boasts a MOSFET output circuit and immaculate sound quality, so you can feel the beat from your external speakers without worrying about distorted sound.

At Your Command. Alpine’s S-A32F features an easy-to-read front panel, which shows all controls and indicators for easy adjustment. You can also set the crossover to low-pass, high-pass, or off (full range) operation for each pair of front and rear speakers.

There are also bass boost and subwoofer level controls that allow you to improve your sound system’s performance in any vehicle with a speaker system.

Make Your Move. With the convenient phase control, you can adjust the phase shift of your front channels relative to your rear channels from 0° to 180° in 3° increments.

Many factory speaker systems are outfitted with woofers on both sides of the car’s interior, resulting in symmetrical left/right signals reaching your ears at different times due to the distance between them and their location within the vehicle.

When listening to a song, this may cause an unnatural sound, such as loss of bass or treble. Phase control eliminates this source of distortion by adjusting both front channels simultaneously so they are “in phase” with one another and allow for a more enjoyable audio experience in your car.

Keep It Cool. The amplifier’s slim, dual-layer design allows it to fit inside narrow spaces and still provide the excellent cooling performance you expect from Alpine. The exterior aluminum layer provides the amplifier cooling fins and protects the internal circuitry. The inner layer uses brushed aluminum for a clean, modern look.

Stereo RCA Preamp Inputs Give You Flexibility The S-A32F comes with two pairs of gold-plated stereo RCA preamp inputs that let you connect your CD player, satellite radio, or mobile audio device. Both inputs accept a wide range of signal levels, from 150mV to 10V (or 5V), so you can connect the preamp outputs from just about any external audio source.

The amplifier’s versatile design gives you plenty of mounting options: It comes with two pairs of 4-channel gold-plated wire harnesses and mounting screws, so you can install it behind your vehicle’s seat or place it in the trunk. It also has a 12V DC trigger and remote inputs for connecting Alpine PDX series power door speakers.

Note: When using both RCA preamp inputs, the variable low-pass filter affects only the front channels. The rear channels remain unaffected.

Note: The Alpine S-A32F includes mounting brackets and hardware for installation behind the vehicle’s seat. Not all vehicles have the same opening in the floor allowing for an easy installation of this amplifier. Please check your floor pan to ensure proper fitment before you begin with your installation.​

Check out the rest of the Alpine S Series Amplifiers.

Note: Alpine recommends that you install your amplifier in a location with adequate ventilation to prevent overheating. Ensure that there are no objects immediately behind the amplifier, and do not install it where people will be seated or potentially step on any portion of the amplifier for extended periods of time.

Do not place anything directly onto the top plate of this amplifier, including loudspeakers or enclosures. The rear enclosure is provided by Alpine and must be used when you install this part in your vehicle.

Note: Neither Alpine nor Crutchfield offers instructions on how to remove an existing factory radio and replace it with another type (such as a navigation receiver), nor do they offer instructions on how to adapt Alpine products to a vehicle with a factory system. If you have questions about these issues, please consult your Crutchfield Sales Advisor for additional information.


  • Sleek Design
  • Good power for a compact size
  • Fantastic budget amplifier
  • Awesome highs
  • Certified 98 watts @ 2 ohms x 4ch
  • Fantastic for powering 4 infinity 5×7’s in the doors of F150


  • Sometimes here’s no wiring harness with this amp

_Sample Customer Review: _

“The Alpine s-a32f 4 channel is exactly what I needed to power my mids and tweeters. I compared this amp with an amp from another manufacturer in the same price range, and thats when Alpine showed its true value!”



Brand Name: TORO TECH

Model: TORO TECH – RX4

Class: Class A/B Design

No. of channels: 4

Dimensions: 1.61 x 2 x 7.1 inches

Weight: 6.78 pounds

Size:RX4 – 65 Watts x 4 RMS @ 4Ω

TORO TECH’s RX4 provides you with the power to challenge your audio system and keep pace with today’s sound requirements. Each channel is designed around a 65-watt, JAN CLASS A/B amplifier capable of four-ohm operation and a powerful clip LED.

The variable low pass crossover lets you add a deep bass response emanating from the subwoofers while maintaining crisp highs from your speakers.

Executive style and features make this amplifier perfect for powering any part of an automobile sound system through factory-installed speaker systems or external amplifiers like TORO-powered subwoofers, powered car speakers, or RCA cable antenna amplifiers. An RCA output jack is provided for rear speakers.

This high-quality, 2ch amplifier will deliver crystal clear sound to your power-hungry factory-installed speaker systems and intelligently handle high volume levels without distortion.

The device uses a state-of-the-art three-phase noise reduction IC to eliminate the buzz associated with switch mode amplifiers. Each channel is equipped with a bass boost switch to allow you to focus more sound energy towards your subwoofers.

This amplifier’s simple layout and large gain knob make it easy to install AND adjust. The RX4 also features a variable low pass crossover that allows you to send frequencies below 80Hz out of your subwoofer and above 80 Hz through your system speakers for impressive, accurate bass response without unwanted distortion.

The TORO TECH power team worked hard to create a state-of-the-art audio amplifier that makes an immediate impact on the quality of sound coming from your factory-installed speakers or aftermarket amplifiers.

Unlike traditional stereo systems, this 2 channel amplifier provides 4ohm stable operation so it can be used effectively with 2-ohm to 8-ohm subwoofer amplifiers.

The amplifier is a true class A/B design that delivers a minimum of 65 watts per channel at less than 0.1% THD when driving 2-ohm loads with no clipping, making it perfect for powering subwoofers and aftermarket speakers in your car.

The circuitry is designed to be quiet when the volume knob is set below 11 o’clock on the rotary gain control; however, you can still hear the music loud and clear above this point without being drowned out by background noise created by the factory electrical systems or home entertainment center equipment.

In addition, TORO TECH has included its uniquely designed three-phase switching technology so system restoration will not be a problem.

The TORO RX4 is capable of driving up to four 8-ohm subwoofers in parallel with each channel providing 65 watts of stable power. This amplifier makes a great replacement for defective factory stereo amplifiers or can be used alongside your existing amplifier as an additional channel.

If you are looking for true hi-fi sound, and want the peace of mind that comes from owning a high-quality audio item, you should definitely consider the TORO RX4!


  • Cheap Price
  • Excellent value
  • Solid construction
  • Clean power
  • Solid performer
  • Good for adding wattage to mid/high range speakers


  • Solid build but annoying alternator whine that won’t go away

Sample Customer Review:

“So far its been a good amp i wanted class ab for my highs only thing i didnt like 1 time speaker contacts touched metal amp didnt go to protect just made squealing noise on speakers & started smoking surprisingly fixed speaker issue amp still working perfectly.”




Brand Name: JL Audio

Model: JX400/4D

No. of channels: 4

Dimensions: 12 x 9.5 x 4 inches

Weight: 5.85 pounds

The JL Audio JX400/4D has you covered. If you’re looking for power and a clean sound, the JX 400/4D is what you need.

With an impressive RMS Power Rating of 14.5V (at 4 ohms), this 4-channel amplifier will make your system come to life with 70 watts x 4 channels at 2 ohms or 100 watts x 8 channels at 1 ohm input, 160 watts x 4 channels bridged into 2 ohms, and 200 watts x 2 chanels bridged from one channel when connected in bridge mode.

The amplifier includes 3-way speaker protection circuitry; the thermal protection circuit prevents overheating of voice coil that could damage the unit’s internal components while overload protection circuitry prevents damage to the amplifier when driving 4 ohms or higher.

The amplifier also features a Bass Remote Level Control that allows you to adjust your subwoofer level remotely from the front of the vehicle. You can connect four (4) pairs of speakers and load them down with up to 200 watts per pair in 4 ohm operation at 20Hz to 20kHz with a dynamic range of 95dB.

This amplifier is equipped with speaker level inputs and outputs, allowing for a simplified connection to your OEM parts.

The amplifier also features an internal Bass Boost Control which you can adjust from 0-12dB/Octave (40 Hz – 250Hz) frequencies via the remote control included or control it with the included remote.

You can also adjust the phase of your audio signal between 0 and 180 degrees via the remote control allowing you to achieve just the right amount of bass frequencies in your system.

You’ll find both left and right channel speaker outputs on a pair of binding posts that will accept up to 8 gauge wire (8 AWG), which is enough power for 5 pairs of speakers at 4 ohms each.

The amplifier is rated at 60 watts x 4 channels into 4 ohms, 80 watts x 2 channels in 1 ohm bridged mono, 120 watts x 2 channels with greater than 1-ohm load, 160W @2 Ohms or 200W @1 Ohm for bridge operation. Like most JL Audio products.


  • Quality of the place where the wires connects to the unit are exceptional
  • Excellent Power
  • Sound great
  • Good amp for the price


  • Excellent amp, but not for smaller speakers



Brand Name: Pioneer

Model: GM-D1004

No. of channels: 4

Dimensions: 8.5 x 7 x 2.5 inches

Weight: 2 pounds

Class: FD Amplifier

This Pioneer GM-D1004 400W 4-Channel class FD digital series amplifier has power ratings of 45 watts per channel at 4 ohms, which is perfect for powering even the most demanding and difficult speakers. The installation takes only minutes with pre-punched mounting holes in the chassis and an included wiring harness ready to plug into your vehicle’s stereo or speaker system.

Owners will be pleased by this 1,400-watt RMS pioneer amp’s high performance specs that can put out 45 watts per channel at 2 ohms. You’ll get a frequency response from 10 Hz up to 40 kHz with distortion so low you won’t hear it through your speakers (less than 0.05%). Your Pioneer GM series d1004 amplifier also has built-in thermal, short circuit, and overload protection.

This 100W RMS pioneer amplifier features dual preamp outputs plus speaker-level input control for an easy hookup. The Pioneer GMD1004 amplifier is made with an aluminum alloy heat sink to effectively dissipate heat and ensure optimum performance.

Drivers are equipped with both high- and low-pass filters to ensure your sound is pure. You’ll hear clear highs and lows.

This 1,400-watt Pioneer digital amplifier has both high and low pass crossovers to enable the speaker output with the highest fidelity possible. It also features separate bass boost controls for each channel so you can balance out your highs and lows.

This amplifier has a frequency response of 50 Hz up to 40 kHz with total harmonic distortion levels at 0.05% and output power at 2 ohms of 80 watts RMS x 4 channels or 1,200 watts peak power. This may not be the most powerful class-D amplifier on our list, but it’s certainly one of the most affordable. Also, its rugged construction ensures that it can be used in many different types of vehicles.

This Pyle amplifier is best suited for systems that have dedicated channels for highs and lows to provide the truest sound reproduction possible. A built-in crossover network allows you to send the midranges and higher frequencies through your tweeters, while the woofer frequencies are sent through your subs.

This amplifier even has a subsonic filter that will reduce low-frequency information under 30 Hz to avoid speaker damage caused by ultra-low frequencies. To ensure the amplifier is protected from accidental power overloads, it comes with an inbuilt thermal and short circuit protection, as well as an AC spark-proof design.Pioneer GM-D1004 400W 4-Channel GM Digital Series Class FD Amplifier

In the event of a power surge, Pioneer’s GMD-1004 comes with a fuse that will blow to prevent harmful damage to your amp. The 4 gauge power and ground inputs are also well protected against accidental shorting out or overloading the system. This protects your speaker system and keeps them running smoothly.

When it comes to wiring up your speakers, this Pioneer amplifier has screw terminals for easy setup and installation. The speaker-level input makes the amplifier compatible with virtually any OEM or aftermarket speaker system. You’ll hear better bass and treble from the 3 RCA inputs, which can be used for CD players, satellite radio receivers, and more.

Each channel has an independent crossover knob that lets you adjust the highs (treble) and lows (bass). This allows you to not only adjust the sound output depending on the music being played but also customize it for your setup.

The high-pass filter eliminates lower frequencies below 80 Hz, while low-pass filters eliminate frequencies above 80 Hz. Even if you have never installed an amplifier before, the Pioneer GMD1004 4-channel amplifier is a great choice.


  • Tiny amp huge sound
  • Low price range
  • Quality sound from a small package
  • A simple way to add some oomph to your car audio
  • Not too shabby
  • Good Power


  • No Wireless Remote

Sample Customer Review:

“I’ll be honest, it’s been a while since I’ve been “in” the car audio game, and the last time I installed an amp in my own car it was one of those wired from the battery, under the seat affairs. Don’t get me wrong, it sounds great, but surely technology has advanced since then.

Well, I’m here to tell you, it has. This little box fit behind the head-unit in my wife’s 2017 Crosstrek, and after a lot of cursing and praying (mostly Subaru’s fault, not this amp) it sounds fantastic. I replaced the door speakers with some Infinity components, and running this through a line level converter it sounds fantastic. Rich lows, clear highs. Definitely worth the $90.”



Brand Name: Sony

Model: XMS400D

No. of channels: 4

Dimensions: 8 x 6.12 x 2.44 inches

Weight: 1.74 pounds

Class: D

Made in: China

The Sony XMS400D is a low-cost, high-quality amplification solution for professional users. With 45W per channel paired with a compact design, this amplifier is great for live performance or if you’re looking to expand your sound system setup.

Featuring many connection options and professional features like an LP filter and HP filter, the Sony amplifier ensures that your entire music experience will be harmonious.

Connections are easy: either hi-level sensing power on; high-level input connections/low-level input connections or wired in via RCA connectors–you have flexible options! With a line output and an input jack for bass, this amplifier is the perfect addition to your sound system.

Its DSP circuitry and EQ settings ensure that you get the best sound out of your music, whether you’re in the vehicle, at home, or in a club. The 4-ohm speaker terminals help you maintain a strong signal, reducing noise and improving your overall listening experience.

This versatile amplifier will meet all of the needs of your home sound system!

Flexible Connections When looking for an amplifier with flexible connections, you want one that can be used in live shows as well as other projects around the house.

Luckily, this Sony model offers both options to ensure that you have everything you need. There are RCA connectors included for quick installation–no matter what connection type is available on your stereo equipment!

You can also use these high-level sensing power on; high-level input connections if there aren’t any low-level inputs available from your stereo gear. With these features,.The XMS400D is an amplifier for anyone who values quality without paying top dollar.


  • Takes up very little space
  • Sound is amazing for the size
  • Very easy to install
  • Doesn’t require a large gauge power
  • Truly plug and play
  • No need for a secondary battery
  • Amp does not get warm even when pushed hard


  • No Wireless Remote

_Sample Customer Review: _

“I got this because I didn’t want to fill my trunk full of bulky, heavy, space eating gear.
All I was after was a little more kick to the sound of my Sony CDX G1200U I purchased a couple years back and this works very well.

It doesn’t pick up engine noise or get real hot when used for an hour or more.
It will let you know if your original recording has trash in it like hiss or pops because they will be more pronounced, but good clean original CDs or MP3 files sound great.

The radio sounds like a radio but better. The installation instructions are easy to follow and it comes with all the cords and plugs you need. If you are looking for a system that will rattle your windows and license plate this isn’t it, but it is a Sony product so the quality is there.”



Brand Name: Lanzar

Model: VCT4110

No. of channels: 4

Dimensions: 17.77 x 12.6 x 3.59 inches

Height: 4 inches

Weight: 8.43 pounds

Made in: China

If you’re looking for a cheap 4 channel car amplifier that will blow your mind, check out the Lanzar Vector VCT4110 Car Amplifier. This little guy can really pump out some sound and has plenty of features to make it worth every penny! We’ll take a look at everything from its sleek design to its ability to power an entire system in this review.

This is a 4-channel, high power MOSFET amplifier which delivers 2000 watts of peak power. The four channels can be configured as either mono or stereo with the ability to bridge two channels for increased output.

A slim design helps this amplifier fit in most vehicle applications while an RCA input and line output make it easy to connect your system’s preamp outputs. Best of all, this model comes at a very affordable price!

The Lanzar Vector VCT4110 is actually pretty powerful! This model can pump out 2000 watts of continuous power with a maximum power output of 4000 watts.

It can also deliver 1100 watts of RMS power on each channel with a frequency response of 20 Hz to 30,000 Hz. While this model does come in at 12 volts of power output, you should be able to get a pretty good sound solution for your vehicle and experience superior performance from the amplifier.

It comes with both an RCA input and line output. This makes it easy to hook up the amplifier to an existing preamp set-up in your vehicle. If you’re not sure what this means, don’t worry!

It just means that you can plug the amplifier into a line output on your receiver or existing speaker system and then connect it to your speakers with either RCA cables or common speaker wires.

This 4 channel model also features a bass boost control, adjustable crossover, and high pass filter. You can use these adjustments to tweak the sound of your vehicle’s system for more accurate performance.

It is pretty modern looking all around! It also features a black anodized aluminum heatsink cover and edge connector for corrosive resistance.

One of the coolest things about this amplifier is its ability to be mounted either vertically or horizontally. This makes it easy to work with this model no matter what type of vehicle you have! When it comes right down to it, you aren’t going to find a better 4 channel amplifier than the Lanzar Vector VCT4110. It is powerful, sleek, and works great with almost any vehicle system.

The Lanzar Vector VCT4110 car amplifier is a great choice for anyone looking for a high-performing 4 channel solution that doesn’t break the bank.


  • Easy to install
  • Professional Look
  • The sound is crisp n clear and loud
  • Great quality at a fair price


  • Spade type terminals are not included

Sample Customer Review:

“It is very sensitive. It has to be grounded properly or it’s gonna constantly go into protect mode. But it’s powerful. I’m using it to drive 2 8” mid, 2 tweeters, & bridge 2 channel to push a 12" double coil Sub woofer. Plays excellent!"



Brand Name: Cerwin-vega Mobile

Model: CVP1200.4D

Class: D

No. of channels: 4

Dimensions: 11.81 x 9.05 x 2.01 inches

Weight: 7 pounds

Made in: China

Cerwin-Vega Mobile CVP1200.4D is a Class D amplifier that comes with the power of 1200 watts and 4 channels to give you a clear sound quality. This powerful amplifier will give you an impressive bass without taking over your control.

It can also be used to drive other speakers like subwoofers, and active or passive speakers in any configuration. This amplifier has been engineered with the latest technology for high efficiency, reliability, and durability. This product has an auto protection breaker which gives you peace of mind against overheating, low voltage, and electrical shortage.

The CVP1200.4D uses Class D technology to give you a more refined sound with high power and low distortion. It has an RMS Power of 1200 watts per channel at 4 ohms.

This amplifier is equipped with 2 x 20amplifiers, built-in conjugate rise time circuitry, and a bandpass filter which helps for low distortion and a clean, precise audio quality.

The unit is also equipped with an internal high pass filter which delivers a good performance as well as contributes to the cool operation of the amplifier itself.

It comes with a membrane tactile power switch that makes it easy to access on the fly and ensures that you are not in danger when using a large number of subwoofers. The power is given through RCA and speaker terminal jacks for better installation.

The amplifier operates with a low impedance of 2Ω which provides clear sound quality at a high volume too. This unit gives you deep, accurate bass response from your speakers thanks to the built-in active low pass filter that has variable frequency adjustments.

The CVP1200.4D is compatible with a wide range of speakers, subs, and passive systems that help to improve the efficiency and performance of your system dramatically.

With this amplifier onboard, you can be assured of enjoying rich, full-bodied sound quality without breaking your bank or emptying your pocketbook.


  • Easy to install
  • Good sound quality
  • Tight and accurate bass
  • No overheating
  • Low voltage and electrical shortage


  • Not yet

Sample Customer Review:

“This is great for door speakers and maybe some little subs. But it RMS is about 125 watts per channel if anyone needs clarity on that, there is potential to get one DOA my first one was so don’t panick if it doesn’t work just trouble shoot it.”



Brand Name: Pioneer

Model: GM-A6704

No. of channels: 4

Dimensions: 14.1 x 8.5 x 2.4 inches

Weight: 4.9 pounds

The Pioneer GM-A6704 4-Channel Bridgeable Amplifier with Bass Boost, Black/red is a great car amplifier for you. It has 1000 Watts Max Power and can power up to four speakers at the same time.

Even if you will be running four speakers at the same time, this car amplifier will deliver 1000 Watts Max Power to all four speakers which means you can listen to your music or watch a movie without having to worry about the quality of the sound.

There are many advantages of using the Amplifier. The first advantage is that this product has 1000 Watts Max Power so it will power up to four speakers at the same time.

The second advantage is that this product uses automatic signal sensing and Turn-On so you won’t have to do too much in order to use your new car amplifier.

And finally, the third advantage is that the Pioneer GM-A6704 also has an adjustable bass boost so you can adjust the sound as best as possible for your music preferences.

The negative aspect about purchasing this amplifier is, that these car amplifiers can be costly. But if you are wanting to get one then you should definitely invest in this product as it has a lot of advantages and uses.

The best part about this car amplifier is that it was made by Pioneer who are always known to make great products.

If you are considering to purchase the best inexpensive car amplifier for yourself or even someone else as a gift then this is definitely the best choice for your needs and wants.

This car amplifier is best known for its bass boost and frequency adjustments which can give you the best sounding music you have ever heard.

It also has a very high Wattage power so it can be run in all types of weather while taking care of your needs. The best part about purchasing this best inexpensive car amplifier is that it comes with a year warranty just in case it did not last beyond one month.

If you are looking for a car amplifier that will give you Bass Boost then buy this best inexpensive car amplifier today. For your best interest, ensure that you have all the important information about purchasing the best inexpensive car amplifier before deciding to make such an expensive purchase of the best inexpensive car amp.


  • Sounds excellent
  • Very affordable high quality
  • No overheating
  • Bass & treble are very clear
  • Easy to install


  • Little bit costly

Sample Customer Review:

“Im running a complete pioneer audio equipment in my car and this was the last piece. Highly recommended. You wont regret it. Also it for those who don’t know, it needs a 4 gauge power supply. Install gear has a good amp kit that pairs nicely with this.”


As you have read that I have described what is a 4 channel car amplifier in the intro. Now before going to the product reviews, let’s dive in for consideration for choosing the best 4 channel car amplifier.


The power supply voltage is directly related to how long your speakers can play at a given volume before blowing. If you’re using a low voltage receiver, make sure that any stereo or multi-channel home theater amplifier you purchase has circuitry designed for low voltages.

Otherwise, it could damage your speakers, endanger your hearing, and even destroy your receiver.

The voltage output rating tells you how much power it can supply under various circumstances. If an amplifier has the same voltage output rating (for example, a 100 watt/channel RMS), the only difference is in its ability to output that power at different frequencies or loads (8 ohms and 4 ohms).


An amplifier’s peak power rating tells you how much total electrical energy it can deliver for short periods of time at high volume levels with no distortion or clipping.


The greatest difference most people will notice between amplifiers of different power outputs is in the volume they can achieve since that’s related directly to the amount of electrical energy they can supply at a given impedance and musical demand.

RMS refers to the root mean square average voltage of electrical current measured over a given period of time. It is also called DC value, which is the typical voltage for audio signals sent by the head unit.

The majority of amps are stable at RMS wattage or 4 x (peak) watts because they were designed for that range of energy input.

But some feature two modes with different peak power ratings; one mode for low-impedance subwoofer channels and another mode set higher for use with speakers having low impedance with respect to their recommended operating resistance rating [4 ohms or 8 ohms]. Most amplifiers specify the RMS power rating at 4 or 2 ohms and some also mention the peak power that can be used.


SNR is related to how quiet the unit is when it’s running, but it isn’t directly related to sound volume. A high signal-to-noise ratio is a vital feature of an amplifier.

If the signal-to-noise ratio is low then there will be unwanted noise in your music, which will make you believe that sound quality has been compromised. The signal-to-noise ratio should be higher than 90 dB.


If you’re going to use the amplifier in a car, find out how much power it draws from the battery when it’s turned on. Huge amounts of current can cause an under-equipped alternator to overload and blow a fuse or even burn out wires and other electrical connections inside your vehicle’s wiring harness.


The best 4 channel amplifier will have power and protection circuitry designed to avoid putting stress on your components or blowing out speakers with electrical overloading or voltage spikes.


Most amplifiers are designed for powering two, three, or four channels (speakers) at a time. Some can power a single channel (for example, a subwoofer), while others have multiple sets of outputs that allow you to wire in additional channels at the time of installation.



The peak power rating is determined by multiplying the RMS rating by 1.41 (or sometimes 1.34). A 500 watt RMS amplifier with a peak rating of 1000 watts is capable of supplying 500 watts RMS for extended periods and bursts up to 1000 watts.


You can choose car amplifier classes between a class A/B or a class D amplifier. Though the class ‘D’ amplifiers are more efficient and less expensive to run, they offer better sound quality than the older ones.

The advantage of using a class ‘D’ amplifier is that it delivers large amounts of power and in this case, your speakers will sound clear. Moreover, class ‘D’ amplifiers are more efficient when it comes to power consumption as compared to a class A/B amplifier.


Before choosing the right amplifier for your car you need to know what kind of power it is. If you are a first-time buyer then you might not be aware of this aspect. The wattage per channel should be known by the user as there is no point in investing in an amplifier with low wattage even if it has other good features.

You will have to choose the power of your amplifier according to the speaker’s quality. The impedance level should also be considered as it is directly related to its power handling capacity and efficiency.

The higher the impedance, the greater the wattage needed in order to drive this speaker properly otherwise you will face difficulties in listening to clear sound.

The impedance measurement is given in ohms so that you can easily calculate the wattage requirement by multiplying it with the speaker impedance.

8-ohm speakers need a minimum of 50 watts per channel and 4-ohm speakers will need 75Watts and 2-ohm speakers require 150Watts per channel. If your speakers are of 1-ohm impedance, then you need a minimum of 200Watts per channel.

The higher the power rating is, the more expensive it will be but this does not mean that just because your amplifier comes with a bigger wattage, it will produce better quality sound and give you value for your money.


The next thing you have to check is the compatibility of your car audio amplifier with your car stereo. The amplifier must be compatible with your receiver and it should also match the speaker impedance.

You can choose between a class A/B or class D amplifier through Class ‘D’ is a better option. Class ‘D’ is preferable because it uses digital technology and so the quality of sound will be better than class A/B. Also, they are more efficient in terms of power consumption.

For instance: a 40-Amp 4-channel amplifier that comes with 2x50Watt channels plus 2 x 150 Watts channels is great for smaller cars. If you have a car with a lot of space, then it will be great to get an amplifier that comes with 2 x 50Watts channels plus 2×200 Watts channels.

Also, check if the amplifier has RCA preamp outputs and subwoofer outputs so that you can play your music loud without any trouble.


fuse is a safety feature that comes with all car audio amplifiers. The fuses in amps are usually of two types: slow-blow and instantaneous.

Slow blow fuses are designed to melt gradually if there is an overload on the system or if there is some problem in the amp so that the system can be shut down in a safe manner.

The other type is instantaneous which melts completely within a fraction of a second if there is an overload, thereby stopping supply immediately and preventing damage to your car stereo.


Sound quality is also very essential when choosing the right amplifier for your car stereo system. You should make sure that you do not compromise the sound quality of your amplifier. If the amplifier is of excellent quality, it will give you value for your money and last longer.

Since there are two types of amplifiers available – class A/B and class D – you can choose according to your requirements as well as budget.

14. LOOK

A good amplifier must have well-designed circuitry along with high-quality materials so that there are no problems such as heat generation and interference while running the unit at constant levels for hours.

Amplifiers run continuously even if we do not listen to music and produce heat which can cause malfunctioning if proper design quality was not considered while making the unit.


In order to do this, you need to connect the electrical circuit (the sound) from your audio source with an amplifier, and then you must connect the terminal amplifier with 4 speakers or subwoofer, depending on whether we’re using a 2-channel or 4-channel amplifier.

16. SIZE

The size of your amplifier is another important factor while choosing the right amplifier. If you are driving a big vehicle and you want to buy an amplifier for it, then you should select one that has two channels and can deliver at least 150 Watts of continuous power per channel. The size of the amplifier should be such that it does not take up too much space in your car.

For example, if you have a sedan-type of car and you are buying an amplifier for it, then you should never go beyond 3 channels [2 + 1] because each channel in a 4-channel amplifier will take up about 10 cubic inches. If you buy extra channels, even though they won’t be used, your amplifier will be bulky and take up too much space.


So that it can be heard by everyone in the comfort of the car’s room. Installation of the amplifier and car subwoofer box in…

The Amplifier size and the available space for installation are two factors that should be evidently looked at and considered by any auto enthusiast who would like to install a good sound system in his vehicle. The amplifier is one of those parts that one has to…

Considering this, one cannot just use any car subwoofer box that can fit perfectly in the trunk area of one’s vehicle. There are still other important factors to consider for the sake of achieving a good car audio or sound system setup.

The rule is that if the amplifier is too big, then it will have to be mounted on top of the car subwoofer box which will not make it possible for the car subwoofer to deliver the kind of sound quality that one is expecting.! Car amplifier size vs the installation space

A lot of people who are new to auto sound systems installation usually end up buying smaller amplifiers just because they can easily fit inside their vehicle.

But then, their speakers have small woofers which are not that capable of producing loud levels of bass.

One should know that the amplifier power is directly proportional to the woofer speaker size and cone area. If you put a small amplifier in a car with small subwoofers, then you will realize that there is just not enough space for installing larger amplifiers.

The last thing you want to do is install an amplifier that will not be able to power your subwoofers.

If you want to get the best possible sound out of your car audio system, then this should be one factor that you have to think about and prepare for ahead of time. Always remember that installing a good car subwoofer box in your vehicle.


One of the most important things to consider when choosing a speaker system is how sensitive the speakers are to certain frequencies.

Speaker Sensitivity is the percentage of the volume that the sound output will vary for a given input volume setting. In a vehicle, the speakers are designed to maintain a speaker sensitivity rating of 90 dB. A vehicle with a lower speaker sensitivity rating will make a louder sound at equal or lower volume settings.

However, if you’re really into music and want to enjoy it to the fullest, you might want to go for speakers with a high sensitivity.

But remember that a high sensitivity means less volume and bass. The lower the sensitivity, the louder and deeper the bass. If you want the best of both worlds, you’ll need to balance the sensitivity of your speakers.


Another thing to consider is frequency response, or how well the speakers react to different frequencies. As you can see, the frequency range for speakers in your car is pretty narrow, which is why you need to choose carefully.

Medium frequencies are measured in KHz, or kilohertz. High frequencies are measured in megahertz, or millions of cycles per second. Finally, mid-range frequencies are measured in hertz.

Now I’m going to keep this short and sweet so let’s explore some of the best 4 channel car amplifier options available.



A lot of car audio enthusiasts want to know the difference between 4 channel amplifier and 2 channel amp. This article hopefully gives a better understanding of it.

Firstly, we need to understand the concept for each type of amplifier:

4 Channel Amp: This kind of amplifier is connected to four separate speakers in order to get good sound quality.

2 Channel Amp: This kind of amplifier is connected to two separate speakers in order to get good sound quality.

Now that we know what the difference is, let us look at some facts about 4 channel amplifier versus 2 channel amp.


When you want to get the best from your car audio sound system, and you have four speakers in your car, then a 4 channel amplifier is what you need for maximum performance.

Since it’s connected to four different speakers, this will maximize the quality of output sound with clarity and high performance. A 4 Channel amplifier is designed to power four speakers – two on the front and then two more in the back.


2 channel amps are more cost-effective and readily available. Having two speakers in your car, this kind of amplifier is suitable for you, especially if you don’t want to spend too much money on your sound system. Is there any difference between 4 channel amplifier and 2 channel amp, other than the number of channels?

Yes, there is a slight difference in power. A 4 channel amplifier generates at least 80 watts per channel. On the other hand, a 2 channel amp only generates 60 watts per channel. In conclusion, if you are using four speakers on your car audio sound system, then the best choice is the 4 channel amp. If you don’t have four speakers, then a 2 channel amp is what you need.


One of the challenges when it comes to choosing the best 4 Channel car amplifier is that there’s no clear-cut answer. There are many factors, but if you have an abundant budget and want something with powerful performance, MTX Audio THUNDER75.4 is your best option on the market today – for those who can afford it!

If not though, don’t fret; each category has its own noteworthy amps worth considering in addition to this one such as Alpine BBX-F1200 which offers great value and versatility all around.

If you’re looking to power your speakers and subwoofer, then the JL Audio JX400/4D is an excellent choice. And if you only want one amp for everything without breaking the bank? The Alpine S-A32F S Series will do just fine!

Choosing the right amplifier power for good sound-Now that you know about all factors while choosing an amplifier, it is important to understand what RMS watts are.

An amplifier’s output is expressed in watts and we need to choose one according to our vehicle’s power requirement so that there is no damage to any part of your car audio system.

For example, if you have four 6-inch speakers installed in your stock stereo system with a 50 Watt peak/300 Watt max head unit, then you should go for at least 300 Watts RMS which will give you clear sound without damaging your speakers.

We hope this article helped you find the best amplifier for your car. Our goal is to help you make an informed decision by presenting all the information about amps in one place, and we want our articles to be as helpful as possible. If there are any amplifiers or questions that were not covered in this article, please post a comment here.


1. How to wire 4 channel car amplifier?


To wire your amplifier to provide 4 channels of amplification, you will need a “left-right” stereo Y adapter. This adapter will get two input signals from the sound deck and then distribute these signals in an “X” manner to four amplifiers (2 left channels, and 2 right channels).

2. What is the maximum number of speakers that I can connect to a 4-channel amp?


You can use two speakers to each channel, so that gives you four speakers in total. In most cases, connecting two or more speakers to a 4-channel amplifier should allow you to run up to 8 speakers.

This is typically true if the amplifier has a 2-ohm setting, which pumps out twice the typical RMS. If your 4-channel amplifier is bridgeable, then you’ll be able to connect two subwoofers together.

3. Is a 4-channel amp strong enough for subs?


A 4-channel amplifier is strong enough for subs if it has enough output power that you don’t clip the amps. If you’re using an amplifier and your bass driver is making high-frequency noises, then your amp clips, and all of its power isn’t applied to either low or high-frequency ranges.

The more speakers in a system, the less total output power per speaker is required to give them all clean, loud sounds. So with four speakers at 12 watts each (total 48 W) maybe you can get away with a 120-watt receiver but if you have six speakers at 12 Watts each (total 72 W) something like 500W of amplifier might be called for.

4. Class A/B or Class D amplifiers: Which is better?


The Class D amplifiers have rapidly been replacing Class A/B because they consume less power. In addition, the design structure of a class D amplifier is such that it can generate nearly any number of phases to create different waveforms with little lag or overlap.

The reason for this is that Class A/B uses a feedback loop which will cause an additional delay in getting output as compared to a digital amplifier.

This could be harmful when there is a need to process fast-changing signals like when using them in audio amplification applications where you want to get it as close as possible to real-time reproduction. As such, the trade-off of higher efficiency and lower cost would make class D more favorable over time.

5. What’s the difference between a 4-channel amp and a 2-channel?


A 4-channel amplifier has four independent channels, whereas a 2-channel amp has just two. That makes it more versatile as you can use them to connect a few speakers in stereo mode, or just one speaker with a subwoofer.

In short with a two-channel amplifier, you’ll have the ability to fully power two speakers. A four-channel device can power up to four speakers.

6. Can I Connect An HU 2 Channels To A 4-Channel Amplifier?


Yes, you can connect an HU which has only two channels to a 4 channel. You’ll be able to do this with pair of RCA Y adapter cables.

7. What does bridgeable mean in car amplifiers?

This means that two channels of sound can be connected to power a single speaker in order to produce more volume. Many amplifiers have these features, and some also have bass boost or crossover features that can be used on two out of the four channels.

8. What is signal-to-noise (SNR) ratio?

Signal-to-noise ratio (SNR) is the ratio between the signal strength and the noise. SNR is also called signal-to-noise power ratio or just power ratio.