Answers to common questions about car amplifiers (2024)

Questions about amplifier power and configuration

Planning your system is the key to getting the right gear. These are common questions about knowing what kind of amplifier you need. Be sure to also read our Car Amplifier Buying Guide for more details.

Q: How many channels does my amplifier need to have? What are the options?

A: Each channel of an amplifier is a discrete source of power, intended to drive one speaker, sub, or a component set that uses a passive crossover. How many channels you need depends on your plans for your audio system now and in the future.

A 2-channel amplifier will be the practical solution when you only need to power a single pair of speakers – for people who like their music with a strong front stage and don't even use rear speakers.

Most people choose to use a 4-channel amp because they like rear-fill sound in their car and want to retain front-to-rear fade control. Most 4-channel amps can also be used in 3-channel mode – two channels to drive a pair of speakers and the other two bridged together to run a sub. This also gives you the option for future expansion of your system. Later on, you could use the 4-channel amp to run four speakers and add a separate amp for the subwoofer.

A 3-channel amp can take care of a single pair of speakers plus a sub quite effectively without any further modifications.

You may want to consider a 5-channel amplifier that can power your entire system from one convenient and compact package. It has four channels for your speakers, plus a fifth, higher-powered channel for your subwoofer.

6-channel, 8-channel, and 12-channel amplifiers exist, often with digital signal processing features, to handle newer OEM "premium" systems that have similar numbers of speakers.

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Q: Why is it best to use a mono 1-channel amp for my subwoofer system?

A: Bass needs much more power than higher frequencies in order to sound full and encompassing (which is what we want). Mono, 1-channel amplifiers are designed to power subwoofers. They feature much higher output power than multi-channel amps, and have tone controls and sonic filters specifically made to help reproduce bass that sounds (and feels) great.

Most subwoofer amplifiers can power two or more subs at a time, due to their large amount of wattage and their capability of handling the different impedance loads. (See our subwoofer wiring diagrams for more information. Also our "Ohms of impedance" Q&A below.)

Subwoofer amps only have one channel because stereo (2-channel) bass doesn't really exist. Our brains are good at locating the apparent position of high- and mid-frequency noises, but not low-frequency sounds. As far as bass goes, there is no left and right. Most single-channel amps have two sets of speaker output terminals, wired together inside the amp, to make it eaiser to hook up two subs to the same amp.

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Q: What's "bridging" an amp, and can I do it with mine?

A: Bridging combines two of an amplifier's channels into one more powerful channel in order to get more power to a single speaker, usually a subwoofer. For example, a 2-channel amp that puts out 75 watts RMS per channel at 4 ohms may be able to put out as much as 200 watts RMS at 4 ohms into one channel when bridged. Another example might be using a 4-channel amp to drive your left and right speakers with two of its channels, while driving a sub with its other two channels bridged together, saving you the need to buy a separate subwoofer amp. For more information, see our article, "How to bridge a car amplifier."

A limitation on bridging is that amps that can work with 2-ohm loads per channel in "stereo," non-bridged mode can only safely drive 4-ohm loads when bridged. When an amp tries to drive a load that's too low, it usually automatically protects itself and shuts down. And you can't bridge a mono subwoofer amplifier because it only has one channel.

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Q: What's a "high-current" amplifier? Or a "2-ohm" or a "one-ohm" amp?

A: An amplifier is considered high-current if it can handle a one-ohm load. Most amps cannot. (See the "Ohms of impedance" Q&A below.) The ones that can are usually "1-ohm capable" subwoofer amplifiers or "2-ohm stable when bridged" multi-channel amps. (See "Bridging" Q&A above.)

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Q: How much power should I get for my speakers?

A: This will depend on what speakers you have, or plan to get, and how loud you want them to play. Car amplifiers come in a few different ranges of power, depending on each manufacturer, to accommodate different applications and taste.

1. 25 – 60 watts RMS per channel. To hear music clearly over traffic and wind noises. Maximum appropriate power for factory speakers.
2. 65 – 80 watts RMS per channel. For aftermarket speakers. Music sounds full, with all details audible.
3. 90 – 120 watts RMS per channel. For high-performance speakers and components to play loudly.
4. 125 – up watts RMS per channel. For competition-level components and high volume music in a large vehicle.

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Q: How much power should I get for my subwoofer?

A: It takes more power to produce low-frequency bass than it does for the higher-frequency sounds, so your subwoofer needs a lot more wattage than the full-range speakers do in order for the bass to blend in well and sound musically balanced.

A good rule of thumb is to power a subwoofer with about ten times the amount of power that the full-range speakers get.

• If you're using your car's factory stereo – 100 to 250 watts RMS of power for the bass will do nicely.
• An aftermarket receiver – you might want 250 to 500 watts RMS of power for your sub.
• Amplified speakers with around 50 to 75 watts RMS per channel – plan on 500 to 750 watts RMS for bass.
• A 100 watts RMS or higher per channel system – you'll want at least 1,000 watts RMS for your sub.

To avoid damage, never connect an amplifier with a watts RMS output that's higher than the subwoofer's total RMS power input rating.

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Q: What are RMS and Peak power ratings?

A: RMS wattage (sometimes called "continuous wattage") is a measurement of power capacity used for comparing and matching components together. Peak wattage, often double the RMS value, is a description used by the marketing department of the amp's manufacturer to sell more amps. You should only use RMS ratings when designing systems and matching gear.

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Q: What's the most powerful amp I can hook up to my vehicle's factory electrical system?

A: Your car's alternator ampere rating will determine how powerful an amplifier you can install. You can find out what your vehicle's alternator rating is in its owners' manual specifications and printed or stamped on the housing of the alternator itself. There, you'll find three numbers labelled as "IL" (low-current – at idling speed), "IRA" (rated current), and "VTV" (voltage). Use the current-rated number (IRA) for your calculations. We’ve done all the math for the examples below, but you can figure that the maximum wattage your vehicle's electrical system can support is 11.7 times the alternator's current rating.

Examples:

• 60A alternator will support up to 702 watts RMS
• 90A alternator will support up to 1,053 watts RMS
• 120A alternator will support up to 1,404 watts RMS
• 160A alternator will support up to 1,872 watts RMS

Warning: When your alternator is unable to meet the demands of the electrical system, your vehicle can experience anything from dimming headlights to catastrophic engine, brake, and steering failures. Car audio competitors often replace their vehicle's factory alternators with heavy-duty upgrades in order to accommodate the massive power demands of their loud sound systems. (Also, see our Q&A about electric vehicles, below.)

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Q: What're the differences between Class A, AB, and D amplifiers?

A: Amplifiers are divided into different classes defined by how their internal circuitry works. In the car audio world, most amplifiers are Class D, because of their high-efficiency operation and compact size-to-power ratio.

• Class A amps are large, heavy, run hot, and are used in expensive high-fidelity home stereo systems and audio laboratories.
• Class AB amps are smaller, lighter, run cooler, and are used in less-critically accurate but still good-fidelity systems.
• Class D amplifiers can be smaller, run cooler, and in a more efficient manner than any other class of amp, with audio fidelity on a par with most of them.

For more details, check out: Which amplifier class is best?

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Questions about speakers and subwoofers

Here are a few common questions about connecting your speakers.

Q: Can I add an amp to power my vehicle's factory speakers?

A: If you like the tone of your factory speakers but just want more power and impact to the sound, you can add amplifiers to your system as long as you understand the limitations of such an option. Factory speakers can't take a lot of power — they're designed to play with "deck power," a receiver's 10 to 25 watts RMS per channel built-in amp, or a "premium" factory amplifier with no more than about 50 watts RMS per channel.

Crutchfield carries quite a few car amplifiers rated for 60 watts RMS and under that will work well with factory speakers. Another option is to add an amplifier with built-in digital signal processing (DSP) in order to improve the sound quality and fidelity of your music as well as its volume and emotional impact.

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Q: What are speaker and subwoofer "ohms of impedance" and what do they have to do with amplifiers?

A: Impedance, measured in ohms, describes the resistance to a flow of current. Amplifiers make speakers work by pushing voltage and current against the electrical resistance of the speakers' voice coils to produce cone movement, resulting in sound. The amplifier senses this resistance as a "load" on its output. The lower the speaker's impedance, the easier it is for the amp to drive it.

The way the physics and math work for this is that, for example, an amplifier that can send 100 watts through a 4-ohm speaker will be able to send up to twice that much power, 200 watts, through a 2-ohm speaker. Although there are featured exceptions (see "high-current amp" Q&A above), the minimum impedance load most car amplifiers can handle is 2 ohms on each channel or 4 ohms on bridged channels. For more information check out our article, Wiring Subwoofers — What's all this about Ohms?

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Q: Can I power speakers and a sub with one amp?

A: There are a few amplifier configurations that can take care of your car speakers and subwoofer at the same time. Refer to the at the top of this article.

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Q: How can I wire my sub to be 2-ohms, in order to maximize my amp's performance?

A: You can't wire every subwoofer to have any particular impedance you want it to have. For instance, you can't change the impedance of a single voice coil (SVC) subwoofer — the 2-ohm model has 2 ohms of impedance, the 4-ohm model has 4 ohms. It's when your subwoofer system has a dual voice coil (DVC) sub or multiple subwoofers wired together that knowing what wiring options are possible becomes important.

• One SVC 4-ohm sub can only be wired as a 4-ohm load
• One SVC 2-ohm sub can only be wired as a 2-ohm load
• Two SVC 4-ohm subs can be wired together as a 2-ohm or an 8-ohm load
• Two SVC 2-ohm subs can be wired together as a 4-ohm or a 1-ohm load
• One DVC 4-ohm sub can be wired as a 2-ohm or an 8-ohm load
• One DVC 2-ohm sub can be wired as a 4-ohm or a 1-ohm load
• Two DVC 4-ohm subs can be wired together as a 1-ohm, a 4-ohm, or a 16-ohm load.
• Two DVC 2-ohm subs can be wired together as a 0.5-ohm, a 2-ohm, or an 8-ohm load.

Wiring solutions for three- and four-sub systems can get pretty complicated, so we won't go into those here. For specific wiring options and schematics, check out our Subwoofer wiring diagrams.

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Questions about amplifier installation

These are a lot of the common questions we get about installing and connecting an amplifier. For help with installation problems, be sure to read our guide to troubleshooting your amplifier installation.

Q: How do you install a car amplifier?

A: For detailed step-by-step instructions, see our Car amplifier installation guide. You can also check out our short video How to install a car amplifier.

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Q: Can I install an amplifier in my EV (all-electric vehicle)? How about in a hybrid gas-electric vehicle?

A: You should not install an aftermarket amplifier in an electric vehicle (EV). There is no reserve electric power available for any aftermarket accessories in these vehicles. Hybrid-electric vehicles have some flexibility, but you can't push them too far. Read our article about installing gear in hybrid vehicles for more information.

That being said, there are some amplified audio upgrades available that are designed for specific models of all-electric vehicles. Alpine’s PSS-TSLA-22Y upgrade for a Tesla Model Y is one example. These upgrades include low-power multi-channel amplifiers that can handle the computer-controlled behavior of an EV's high-to-low voltage DC-to-DC power supply — which a standard amplifier couldn’t handle without needing additional power-surge resistors and possibly a relay.

Because of the complicated and dangerous nature of installing aftermarket electronic equipment in "smart" high-voltage electric vehicles, it is highly recommended that you employ an experienced professional installer to perform your EV upgrade. For example, just "disconnecting the battery" pre-installation involves elaborate window, seat, and electronic switch positioning, as well as partial disassembly of the whole car.

Some people get around this issue by installing a dedicated and isolated 12-volt DC power supply (i.e., a second battery) for the new amplifier to use without affecting the car's operation. This isolated second battery will need to be recharged separately from the vehicle's main battery with its own separate stand-alone 12-volt battery charger as well.

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Q: Where can I mount my amp?

A: An amplifier produces heat, which its heat sink absorbs and then dissipates into the air. Wherever you mount your amplifier, you need to leave a few inches of air space around each side so that it can stay as cool as possible, otherwise it may overheat and shut down. Also make sure there's enough room for you to connect the wiring and adjust the controls during installation and servicing.

Do not bolt or screw your amplifier directly to your car's metal chassis — that's inviting noise issues, like ground loops which hum or buzz. Most installers mount the amp on a wooden board or plastic panel and then attach that to the car body. Follow the manufacturer's recommendations for locating the amplifier and make sure it's mounted securely.

Since space is at a premium in most vehicles, two common locations are under a seat and in the trunk or hatch area. Under-seat mounting is space-efficient, keeps the amp hidden from view, and lets you run shorter cables to the receiver. A rear-mounted amp requires longer power and signal cables but makes it easier to get to the amp's controls.

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Q: What wiring do I need?

A: Car amplifiers don't come with the wiring necessary to hook them up. The wiring you need will depend on your amp's power rating and how you're connecting it to the stereo. Luckily, we offer a wide selection of amp wiring kits and input and output signal wiring that can provide everything you need to connect your amp. See the Accessories tab for the amplifier you plan to buy (or already have) for a selection of the proper wiring kits and speaker wire. For more details, read our amplifier wiring kit buying guide.

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Q: What's "Ground" and why is that connection so important?

A: The ground connection completes the system's power flow from the battery, through the amplifier, and back to the battery. The vehicle's metallic frame is the power supply's ground. That's what the negative terminal of the battery is directly connected to. Loose or badly located ground connections are responsible for more amp noise trouble than anything else, by far. Make sure your amplifier is grounded tightly to the chassis of your vehicle, with all the dirt and paint removed where contact is made.

Read our amplifier installation guide for more details.

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Q: Why do I need to install a separate fuse near the battery?

A: You need to install a fuse at the battery to protect the power wiring, your car, and yourself against fire. In the event of an accident, you do not want a live wire stretching throughout your vehicle overheating, melting, and then igniting. For more information see our Car amplifier power wire fuses article.

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Q: In my amp wiring kit, what's the blue wire for?

A: The thin blue wire is the turn-on lead and it must be connected properly in order for your amplifier to power up. It carries a 12-volt DC signal from your stereo to your amp, triggering an electronic switch inside the amp that powers on the amp whenever the stereo turns on. In the case of a factory stereo with no remote connection, you can tie into a switched 12-volt source (one that only comes on when the car is running) in the fuse box.

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Q: How do I power a multi-amp system?

A: You have to supply power from the battery to every amp in your system. You do this by running a lower-gauge (thicker) power wire from the battery to a power distribution block near your amps. From the distribution block, you run smaller power wires to each amplifier. You do the same thing for the ground wires.

Our amplifier wiring kit buying guide covers this in more detail.

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Q: How do I wire an amplifier into my factory stereo system?

A: In addition to running power, ground, and a remote turn-on lead, your amp hook-up will require input and output wiring.

• Most late 20^th century factory car radios have analog outputs, and you can connect the speaker wires coming from the radio's outputs directly to an amplifier that features speaker-level inputs. Or you can use a line output converter to ensure that the amp can handle the factory signal. The amp's outputs can then connect to the factory speaker wiring at the same location behind the radio.
• Cars today have amplified digital factory systems that make adding an aftermarket amplifier more difficult. The best way to install an amplifier while retaining your vehicle's factory audio features, like hands-free calling and controllable warning-chime volume, is to use a vehicle-specific amplifier replacement module and wiring harness.

See our article "Adding an amplifier to a premium factory system" for more information.

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Q: How do I wire an amplifier to my aftermarket stereo system?

A: Normally you use RCA patch cables to send the signal from your receiver to your amplifiers. Presumably, the receiver will already be installed with the interface wiring necessary for all the factory audio functions to operate connected correctly. Most receivers have three sets of preamp outputs to provide signal for your front speakers, rear speakers, and subwoofer amp channels. You may have to use Y-adapters to provide signal for a multi-amp setup, or use amps with built-in preamp outputs that allow you to daisy chain the signal from one amp to the next. You then send the amps' output signals back through the factory speaker wiring harness or run new speaker wires throughout your vehicle.

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Q: What's amplifier "gain" and how should I set or adjust it?

A: A car amplifier's gain control adjusts its input sensitivity to match the output level of the receiver or other source unit it's connected to. This is done so that the signal the amp works with isn't so weak that we hear the system's ambient background noise, nor is it so strong that the signal "clips" and the sound distorts.

You can think of this essential amp setup procedure like it's a "Goldilocks" adjustment so your system won't sound too loud, won't sound too soft; but will sound just right.

To set amp gain, first you play a familiar piece of music, then turn the gain up until the music sounds distorted. Then turn it back down until the music sounds clean. For more details about setting amplifier gain see How to set amplifier gain using test tones.

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Q: What're "high-pass and low-pass filters" and how should I set or adjust them? How about "bandpass" and "subsonic" filters?

A: In car audio, electronic crossover filters — high-pass, low-pass, bandpass, and subsonic filters — divide full-range input signals into discrete frequency-limited ranges or bands of sound so each of the different kinds of speakers can play just what they were designed to handle and deliver clean output without distorting — tweeters playing high frequencies only, subwoofers low bass, etc.

• A high-pass filter — sometimes referred to as a "low-cut" filter — removes the notes below the filter's frequency setting so tweeters and midrange drivers won't try to play bass notes that they weren't designed to play without distorting.
• A low-pass, or "high-cut," filter removes the notes above the filter's frequency setting so mid-bass woofers and subwoofers won't try to play high notes that they weren't designed to play without distorting or muddying the pure bass tones.
• A bandpass filter employs both high-pass and low-pass filters so midrange speakers can play cleanly with the very high and very low notes kept away.
• A subsonic filter, sometimes called an infrasonic filter, is used to remove the extremely low bass notes (often below the range of human hearing) that the amplifier would otherwise waste energy trying to reproduce. Subsonic filters are also used with ported subwoofer enclosures to reduce the unwanted loud booming notes around the box's resonant frequency.

An easy way to set up high- and low-pass crossover filters is to start with an approximation, setting both filters at 100 Hz., and then fine-tune by ear.

1. You play a favorite, well-known song or test track. With the sub turned off, you adjust the high-pass control so no low-frequency bass sounds play through your midrange speakers and tweeters.
2. Then, with the "full-range" speakers turned down or off and the subwoofer turned back on, you listen to the music coming out of your sub alone and slowly adjust the low-pass filter until all the high- and mid-frequency notes disappear. The low-pass filter lets you filter out the cymbals, strings, vocals, and guitars while keeping the bass guitar, synths, low tom-toms, and kick drums.
3. With all the speakers and subs playing, you can tweak the controls the small amounts needed to smooth out any high and low bumps in the sound.

Crossover filters control the amounts of power going to different elements in a sound system — they should not be used as tone controls. That's the job of an equalizer or sound processor.

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Q: What's a "bass boost" and how should I set or adjust it?

A: An amplifier's bass boost is a tone control that increases the volume of the bass notes, usually around 42 Hz., a popular bass drum tuning as well as the bass guitar's and piano's low E. To adjust a bass boost, slowly turn it up and listen to the bass beat. Applying just a little boost will bring up the kick a lot. Be careful with any boosting — this is where distortion is often introduced into a system. When you add bass to the signal, you'll need to readjust the amp's gain downward to prevent distortion.

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Q: Why won't my amplifier turn on?

A: The most common problems are:

• Bad ground connection – this is the most common cause.
• A missing fuse – either on the amp or on the power wire at the battery.
• The remote turn-on lead isn't connected properly or it doesn't have enough power available for multiple amps in the system.

For more, see Troubleshooting your car amplifier installation.

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Q: Can I call Crutchfield and talk to a real person for help and advice?

A: Yes, you can.

For help choosing the perfect gear for your system, Crutchfield advisors are available via phone or chat. They will help guide you through the maze of product and accessory options and reach your goal of getting a great-sounding car audio system.

After receiving your new amplifier, or any product from Crutchfield, you can call Crutchfield tech support if you need help solving any issues you encounter with your new audio gear setup.