Marine Audio Glossary
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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). For more information, see our amplifier articles.
Anti-corrosion features enable a marine audio unit to resist rust and the corrosive effects of salt water. Examples of anti-corrosive features include 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 player (CD, MP3, cassette, or MiniDisc) to the receiver. The input jack can be either Mini or RCA.
BlueChart maps are an exclusive line of marine cartography from Garmin International, Inc. These digital maps (available on data cards or CD-ROMs) can be read on-screen like a paper map. They are compatible with all of Garmin's new line of navigation equipment. You can find other maps available for other navigation systems as well as for Garmin systems.
Heavy-duty capacitors act as a buffer zone between your amp and your boat's electrical system. They store up a reservoir of power, which can supply the amplifier's peak demands (like a kick drum beat) without having to get additional current from the battery. All amplifiers have built-in capacitors, though high-performance amps use larger, more effective ones. External capacitors connect to the power cable just before it reaches your amplifier.
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.
A crossover is like an audio "traffic cop", directing high and low frequencies to the proper drivers. Crossovers come in two basic categories: active and passive. You install an active crossover between the in-dash receiver and the amplifier in the signal chain, while a passive crossover hooks in between the amplifier and the speakers (or subwoofer). The passive crossover usually costs much less than an active crossover, but its inefficient design wastes more power. For more information, see our crossover articles.
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 that Crutchfield offers come with a detachable face.
You can put several sizes of receiver into your boat. You'll find the most common sizes below.
- DIN A "Euro DIN" receiver (or "E" fit) is the most common size of receiver for both car and boat applications. It has a rectangular chassis that measures about 7" wide by 2" high (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 will need to cut a hole in a panel to fit your new receiver.
- ISO-DIN The "I" and "J" fits are essentially the same dimensions as the DIN receivers, but they do not mount through the mounting sleeve. Instead, they attach directly to the side support system of the factory receiver location. If you do not already have a factory receiver location on your boat, you shouldn't purchase an ISO-DIN size receiver. "J" fit receivers have a slightly wider faceplate than do "I" fits. Mounting an "E" or "I" fit receiver into a "J" size hole would leave a slight gap on either side of the faceplate.
- Double DIN Double DIN receivers are two times the height of DIN-size receivers. Double DIN receivers are also shallower in depth and slightly wider. In some cases they house both a cassette deck and a CD player. These receivers are a good choice if you have a shallow mounting location, or if you prefer a larger faceplate.
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.
A free-air rated subwoofer saves valuable space, but you must place it in an airtight compartment or enclosure. Free-air systems also have flat frequency response, for clean, crisp bass. To get the best results, the sub must be specifically designed for free-air use.
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.
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.
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-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.
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.
In most cases, the navigation system comes in the form of a separate box, like a CD changer, that's installed under a seat or in a compartment and connected to your receiver via a special cable. But, some all-in-one, portable navigation systems are designed to be mounted on your boat's dash, and some are all contained within a single unit that you install just like an in-dash receiver. For more on navigation systems, check out the Crutchfield Advisor article How to Choose a Navigation System.
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, guaranteeing the speaker holds up in all weather conditions.
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.
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.
Besides playing your musical sources (CD, radio, 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. For more information, see our receiver articles.
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.
Two companies, SIRIUS and XM, each provide over 130 channels of radio programming, which is broadcast via satellite and is available to the user for a monthly fee. To get satellite radio, you must have some special hardware, namely a tuner and an antenna. Satellite radio systems come in lots of different flavors. Some will connect to your factory radio, and some require that you install a new receiver. For a detailed description of what's on satellite radio, and what you need to get it, see our Learning Center's Satellite Radio articles. CD receivers with satellite radio controls operate same-brand external satellite radio tuners. A specialized antenna and service subscription are also required (in addition to the tuner) to receive the satellite radio signal.
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 audio system, when it comes to how things actually sound. They're can be located just about anywhere on your boat. Most vehicles come with four speakers, but some come with six or even more. If you want to make a big difference in the sound of your factory system without spending much money, try replacing the speakers first.
Many speakers can be powered right from your receiver. But some models require more power than an in-dash receiver can provide, and you'll get them to perform their best by powering them with a separate amplifier. For more information, see our speaker articles.
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. In most cases, a subwoofer is mounted in a specially designed box. (Some subs can be mounted in what's called a (link) "free-air" application — that is, no box is required.)
Bass frequencies need a lot of power, so you can't hook up a subwoofer directly to your receiver — you have to have an amplifier. Subwoofers sometimes come with their own amplifiers built in (that makes for a simple installation); others require a separate amplifier. For more information, see our subwoofer articles.
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.
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.
Have you ever noticed that there is no such thing as UV-proof? The sun is so powerful that while out on the water, you can only partially protect yourself from its harmful effects. Yet, this protection is vital to your survival. The same goes for your electronic gear. UV (ultraviolet) rays can cause your products to bleach out, crack, and overheat. Be sure to invest in UV-protected gear.
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.
The wakeboard tower is the tall crossbar found on many sportboats to which the wakeboard tow line is often attached. You can mount several audio components to this tower, such as marine 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.