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Marine audio glossary

The terms to know when buying audio gear for your boat

marine audio glossary

In this article: Marine audio is to car audio what car audio is to home audio. For one thing, marine audio gear needs to be water-resistant. For another thing, there's, well, everything else. This glossary will help familiarize you with some of the key words and phrases you'll need to know before you start planning you boat's awesome new audio system

Click on a letter below to jump to that section of the glossary.



A subwoofer has to have an amp to power it, but regular speakers can run off the built-in amplifier of a head unit. So why would you want an amp for your full-range marine speakers if a receiver will work? Because with an amp you get more power, and with more power, you get more volume and cleaner sound. In the marine environment, getting enough power to drown out the ambient noise is a full-time job, and the amplifier is your best worker.

Amplifiers require some special installation considerations. To install an amplifier, you have to run a thick power wire directly to your boat's battery. You also have to run audio cables to your head unit's preamp outputs (or, in some cases, connect your speaker wires to your amp).

Marine amplifiers are designed to perform in the varying conditions your boat can experience. Some features to look for include conformal coated circuit boards (for improved water and dust resistance), corrosion-resistant power connections, gasket-sealed front covers, and stainless steel mounting hardware that won't rust all over your boat's gel coat or carpeting. Some amps also offer a UV-protected heatsink finish.

Anti-corrosion features enable a marine audio unit to resist rust and the corrosive effects of salt water. Examples of anti-corrosive features include conformal-coated circuit boards, plated connections, and a rust-resistant chassis.

Auxiliary audio input
An AUX input is a jack on the face or rear of the receiver that enables you to connect a plug-and-play satellite radio tuner or portable music player to the receiver. The input jack can be either Mini or RCA.

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CEA-2006 compliant
CEA-2006 allows consumers to be able to compare car and boat amplifiers and receivers on an equal basis. Manufacturers who choose to abide by the new standard can stamp their products with the CEA-2006 logo that reads: "Amplifier Power Standard CEA-2006 Compliant."

On May 28, 2003, the Consumer Electronics Association (CEA) published standard CEA-2006, "Testing & Measurement Methods for Mobile Audio Amplifiers." This "voluntary" standard advocates a uniform method for determining an amplifier's RMS power and signal-to-noise ratio. Using 14.4 volts, RMS watts are measured into a 4-ohm impedance load at 1 percent Total Harmonic Distortion (THD) plus noise, at a frequency range (for general purpose amplifiers) of 20 Hz to 20,000 Hz. Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of 1 watt into 4 ohms. This applies to both external amplifiers and the amplifiers within in-dash receivers.

There are several different ways to connect the cables from your receiver or amplifier to your speakers.

  • Spade connectors are compatible with most binding post terminals. A spade fits around the terminal's central threaded post, allowing you to then tighten the collar down on the spade for a snug, secure connection. But keep in mind, some electronics now have terminals that prohibit the use of spade connectors.
  • Pin-type connectors will work with both spring clip and binding post terminals. This is probably the best type for connecting a thick, heavy-gauge wire to a small spring clip connector. On a 5-way binding post, this slender pin will also fit the hole that's back near the base of the central post (see binding post illustration, below). You can then tighten the collar down against it.
  • Banana plugs will plug straight into the center of 5-way binding posts. They make a quick and convenient connection — nothing to loosen or tighten. Bullet-type and butt connectors also work well.

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Detachable face
A detachable face lets you remove the control panel of your receiver easily, and then take it with you when you leave your boat. The stereo is useless to thieves without the faceplate, greatly reducing the temptation to ransack your boat. Most marine receivers sold by Crutchfield come with a detachable face.

You can put several sizes of receiver into your boat. The most common, for both boats and cars, is the "single-DIN" size, which means the receiver has a rectangular chassis that measures about 7" wide by 2" tall (depths vary), and loads into the mounting surface from the front. DIN-size receivers slide into a metal or plastic sleeve that attaches to the front of the mounting location. However, your boat might require a different receiver size, especially if you need to cut a hole in a panel to fit your new receiver. Marine-rated receivers are now availabe in a variety of shapes and sizes, including round designs that can fit into standard gauge openings.

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Fold-down face
Despite slot-faced receivers' convenience, their displays are small. A fold-down face, on the other hand, hides the CD slot behind the control panel, and allows the receiver to include a larger display for greater legibility. Hiding the slot also increases the unit's reliability by reducing internal exposure to dust, dirt and, most of all, water.

Frequency response
Frequency response refers to the range of sounds (from bass to treble) a stereo component can reproduce. It's measured in Hertz (Hz), and a wider range is better — the bass will be lower and the treble will be higher. Humans can perceive sounds from 20 to 20,000 Hz. The lowest note on a bass guitar is about 41 Hz. Most male vocalists have a range between 100 and 500 Hz. Cymbals hit at about 15,000 Hz.

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Gauge-style receivers

These digital media receivers are designed to fit into a standard gauge opening. They're handy for smaller boats with limited dash space. Gauge-style receivers won't play CD's, of course, but they're terrific for standard AM/FM/Weather radio and playing music from your smartphone.

GPS, which stands for Global Positioning System, is a navigational system designed and operated by the U. S. Department of Defense (DOD). Your boat's navigation computer processes coded satellite signals from three or more GPS satellites every second, and then calculates the boat's velocity and geographical location.

Ground Fault Circuit Interrupters
Simply put, Ground Fault Circuit Interrupters are circuit breakers. When the resistance between ground and the ungrounded conductor drops below a certain level — that is, when you've not-so-wisely diverted the current through yourself — the Ground Fault Circuit Interrupter kicks in, stopping the flow of electricity and preventing your demise. While GFCIs may help in the protection of electrical devices, they work primarily to protect humans against shock.

Grounding and grounding plates
A ground fault is the shorting of an electrical device or circuit to ground at any location other than the structure's common grounding electrode, or plate. This can be caused by damaged or faulty wiring, or by the installation of a second grounding electrode (US and Canadian electrical codes require a common grounding electrode for all wires that enter a structure). Most boats should have one designated grounding plate.

In order for your system (as well as your entire boat) to be protected, if a ground fault exists it is highly recommended that you consult a licensed electrician as soon as possible. Most of the power protection devices Crutchfield carries have ground fault indicators.

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Magnetic shielding
You can contain a speaker's magnetic energy inside its enclosure via magnetic shielding. This is usually achieved by placing another speaker magnet back-to-back with the existing one so that the two magnetic fields cancel each other. Shielding may also be achieved by lining the inside of the speaker cabinet with metal.

Magnetic shielding is important for marine applications. If you place an unshielded speaker too close to your compass (within 1-1/2 feet) or any other device dependent on magnetism, the speakers' magnetic energy has the potential to distort or even permanently damage it.

Marine rating
Marine-rated, also marine-grade, products are designed specifically for the marine environment. Many automotive applications just won't work on a boat, because they either lack protection from the environment or the proper power requirements. Always look for marine-rated gear for your boat.

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Navigation systems typically use a combination of a GPS (Global Positioning Satellite) location and tracking system, an internal, self-regulating gyroscope, and an electronic connection to your boat's speed sensor. Some models also use WAAS. Not only will a navigation system help you plot your course from port-to-port, but once you get to unfamiliar destinations, it can help you get around accurately and safely.

NMEA 2000

NMEA 2000 is a "plug and play" communications networking protocol that allows devices as varied as receivers, chartplotters, GPS units, wired remotes, and wind instruments to function as one complete system. Developed and maintained by the National Marine Electronics Association, it's similar in concept to the CAN-Bus systems found in cars and trucks.NMEA 2000 replaced the old NMEA 0183 protocol. To learn more, check out our Nautical Networking with NMEA 2000 article.

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A very popular material for car speakers, polypropylene is fairly rigid, with good internal damping, and complete weather-resistance. Many marine speakers are made from this material or something similar, which ensures that the speaker will hold up in all weather conditions.

Power inverter
A power inverter converts low voltage DC (direct current) battery power to 115 volt AC (alternating current) household power. It allows you to use household appliances and electrical equipment on your boat. A power inverter allows you to take a video game console, a TV, or a toaster on vacation with you.

Preamp outputs
These are jacks on the rear of a CD receiver that allow you to use a standard RCA patch cable to add an external amp. Some receivers have two sets, which help if you plan to add a 4-channel amp or a second 2-channel amp. Some receivers have three sets, one of which is usually intended to be used for a subwoofer amp.

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Besides playing your musical sources (CD, radio, streaming audio, etc), the receiver has another big job: sending the audio signal to your speakers. Most receivers have built-in amplifiers, and can power speakers directly. Many receivers have pre-amp outputs, too — these send signals to an external amplifier, which boosts the signal before sending it to the speakers.

Marine-rated receivers are designed to withstand the extremes of a marine environment. Most marine receivers feature a conformal coating on the circuit board. This coating adds a level of water and corrosion resistance to the internal electronics, though it doesn’t make them waterproof.

If your receiver is going to be exposed to a lot of sun, look for models with UV protection. And if you go boating in salt water, consider receivers that meet the ASTM (American Society of Testing and Materials) B117 standard for salt spray and fog exposure. On the other hand, many marine receivers are built to work with marine wired remote controls, which allows you to install the receiver below decks and operate it from the cockpit

RMS power
Root Mean Square (RMS) power refers to the amount of continuous power, measured in watts, that an amplifier produces. The higher the RMS figure, the louder and cleaner your music sounds.

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Satellite radio
SiriusXM Satellite Radio is a subscription service that offers a wide variety of entertainment, including music, news, sports, talk, entertainment, traffic and weather services, and more. The signal is available coast to coast in the 48 lower United States (including Puerto Rico), and for boaters, the signal reaches up to 200 miles offshore. The signal is digital, so it's always clear and free of static. When you subscribe, you receive an entertainment package of over 130 channels, so you can enjoy music, sports, news, talk, and more when you're out on the water. Check out the SiriusXM channel guide to learn more.

To get satellite radio in your boat, you'll need some special hardware, namely a tuner and an antenna. Some marine receivers come equipped with a built-in SiriusXM tuner.

Signal-to-Noise ratio
A measure of how well a CD player silences background noise. Higher ratings, in decibels (dB), indicate less noise.

Your speakers are probably the most important part of your boat's audio system. They're can be located just about anywhere on your boat. Many speakers can be powered right from your receiver, but some models require more power than an in-dash receiver can provide, and they'll perform their best with a separate marine-rated amplifier.

When it comes to boat speakers, a set of old car speakers just won't cut it .Sun, salt, and spray will destroy car speakers in a season or less, so you need to look for marine-rated speakers designed for life on the water. "Marine-rated" means more than a coat of white paint on a black speaker. Features to look for include sealed motors, rubber surrounds on the woofers, and UV-resistant cones, surrounds, baskets, and grilles.

You'd never want to purposely submerse your electronic gear under water, but it's a good idea to protect it in case of a mishap. Currently, only waterproof products protect against submersion, and the definition of submersion can vary between manufacturers. Limits on time and depth under water will cause these variants. Check with the manufacturer to find out what kind of submersion protection they offer.

A subwoofer, or "sub", is a large (usually 8" or bigger) speaker that's designed to do just one thing: play bass. Most marine-rated subs are designed for free-air use, so you'll get outstanding bass when you mount the sub in a panel or bulkhead on your boat — no box required

When you're shopping for a sub for your boat, look for the same marine-rated features you'd want in a set of speakers. And also make sure you purchase a marine-rated amplifier.

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Tinned wire
Tinned wire is any connecting wire (usually copper) between devices that is coated in tin. Tinned wire is very important in marine applications. It significantly increases a wire's resistance to corrosion without impeding its flexibility or resistance. Marine-rated wiring is an essential element of any boat's upgraded stereo system.

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Universal cover
Universal covers are available for marine receivers, offering extra protection against water, wind, and sun. Most universal covers have a hinged, see-through plastic cover lined with foam or rubber to keep water from ever reaching the receiver. These covers take up little space and are a great idea for any boater worried about too much moisture reaching his/her audio system.

USB port
USB (Universal Serial Bus) is the "plug and play" interface between your iPod, iPhone, Android smartphone, or other device, and your USB-compatible marine receiver. You can also plug in a thumb drive and play stored music files.

Have you ever noticed that there is no such thing as UV-proof? The sun is so powerful that no matter how much sunscreen you apply before you leave the dock, you're only partially protected from harmful UV (ultraviolet) rays. You have to do the best you can, though,because your health depends on it. The same goes for your electronic gear. UV rays can cause your expensive stereo equipment to bleach out, crack, and overheat. Don't forget your sunscreen, and be sure to invest in UV-resistant marine audio gear.

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WAAS (Wide Area Augmentation System) is a network of 25 ground reference stations, ranging from the US to Canada to Mexico, that monitor GPS satellite information and create a GPS correction message. This correction message accounts for disturbances in the ionosphere, and for timing and satellite orbit errors. The WAAS-corrected signal can give your GPS unit a position accuracy of less than three meters (as compared to a typical 6-12 meters with the normal GPS signal). WAAS is ideal for open-water or flat terrain navigation, and is currently available in North America only.

Wakeboard tower
The wakeboard tower is the tall crossbar found on many sportboats to which the wakeboard tow line is often attached. You can also mount audio components to this tower, such as marine tower speakers.

Waterproof generally means that the product will work despite any amount of water thrown at it, even temporary submersion. However, different levels of proofing exist, and it's up to the manufacturer to choose a level. Limits on time and depth underwater create these varying levels. Waterproof marine audio components, though rare, are great for boaters who expect to douse them with a lot of water.

By far the most common protection against water damage for marine audio components, water-resistance is essential for any gear on a boat. While not as thorough as waterproofing, water-resistance can protect your electronics from splashing and light rain, as well as from certain levels of internal moisture. Automotive receivers generally aren't protected with coated circuit boards, rubber gasketed faceplates, or covered chassis, as are marine receivers. You won't find paper or metal drivers on marine speakers, either. Check the materials for all the audio components you buy and make sure they are at least water-resistant.

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