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Car Audio FAQ

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by: Gary Brikowski

Below are some of the most frequently asked car audio questions.  Auto audio knowledge is based on physics and audio engineering, but a fair amount pertains to common sense. Once you retain the answers to these questions, you are well on your way to becoming an auto audio expert.

What does CD signal-to-noise ratio mean?

The signal to noise ratio measures how well the CD player silences background noise. Higher ratings, in decibels (DBs), indicate less noise and crisper sound.

What are preamp RCA outputs?

Preamp RCA outputs allow you to connect 1 or more external amplifiers. The subwoofer output is an important feature as it provides you with much cleaner low frequencies for your subs compared to a standard front or rear set of outputs.

What is a subwoofer preamp RCA output?

A subwoofer preamp RCA output is an output that has a built-in low-pass crossover for specific connection to a subwoofer amplifier that powers a low frequencies driver (a subwoofer).

What is the difference between peak power and RMS power?

Peak power handling refers to the amount of power a speaker can handle during a brief musical burst. The RMS power range figure is a much more reliable rating for determining the speaker’s power requirements.  Speaker power is measured in watts, a unit of electrical power. One watt equals one volt times one amp, or one joule of energy per second.

What does the sensitivity rating tell you about the speaker?

An efficiency or sensitivity rating tells you how effectively a speaker converts power into sound. The higher the number, the more efficient the speaker and the louder it will play given the same input power. The more efficient sub gets more power out of the amplifier.

An efficient speaker helps you maximize your available power. Most sensitivity ratings measure the speaker’s output with 1 watt of input, 1 meter from the speaker. Some speakers’ sensitivity is measured with 2.83 volts of input instead of 1 watt.

Efficiency is not an accurate indicator of a subwoofer’s output capability and it should not be used as a comparison to other subwoofers to determine which one is “louder.” However, physics tells us that a 3 decibel drop (3 dB) in sensitivity doubles the amount of wattage required by a speaker to produce sound at the same volume. In other words, a 90 dB speaker will need double the amount of wattage as a 93 dB speaker if you want both speakers to produce the same volume.

What is sound pressure level (SPL)?

The SPL is measured relative to 0 dB, which is considered a constant number. 0 dB represents the smallest amount of sound pressure that is recognizable to human hearing. The speaker’s listed sound pressure level is usually a prediction the manufacturer makes based on the speaker’s weight, voice coil, magnet strength etc. The manufacturer SPL is only a prediction, and should mostly be ignored.

What is linear excursion?

Given two subs with equivalent surface area, the sub with larger excursion capacity will produce louder sound volume if adequately powered.

What does the speaker’s frequency response rating tell me?

The range of frequencies the speaker will reproduce, from lowest to highest. The wider the range, the better. The optimal range is 20- 20,000 Hz, which is the range of human hearing.

What does Xmax indicate about a speaker or subwoofer?

Typically measured in millimeters, the Xmax value is the measure of a speaker cone’s maximum excursion in one direction while still maintaining a linear behavior. This indicates a subwoofers' flex capacity, which usually correlates with bass reproduction.

What is impedance?

The load value in ohms that the speakers present to the amplifier, stated per voice coil. It is the amount of resistance to the current flow. This is a key specification as subs wired in parallel or low impedances can create problems with your amplifier and potentially void all warranties.

What is an ohm?

An ohm is a unit of measurement that quantifies the amount of impedance in a speaker. Impedance measures a speaker's resistance to the flow of current.

What are voice coils?

Voice coils receive an amplifier’s power signal and move the subwoofer cone in and out, producing sound. Dual voice coil subs have more wiring flexibility than single voice coil subs. However, single voice coil subwoofers are easier options for wiring multiple subwoofers in parallel or series. You may also run a dual voice coil (DVC) sub in parallel, series, or combination. A quad voice coil has four voice coils and is equal to two dual voice coil subwoofers as far as wiring goes.

What is the difference between wiring speakers "in series" and "in parallel?"

In series, each speaker you add will increase the resistance, or Ohm load, in the channel. Add up each speaker’s impedance to get the total impedance. So the sum of two 4 ohm speakers in series equals 8 ohms of total impedance. The higher the impedance an amplifier runs at, the smaller the amount of power flow. Many amplifiers can run at either 2 ohm or 4 ohm loads, but some are stable at 1 ohm loads for optimal RMS performance. To connect speakers in series, connect the positive lead from speaker 1 to the amplifier’s positive terminal, and connect the negative lead from speaker 1 to the positive lead of speaker 2. Connect the negative lead from speaker 2 to the amplifier’s negative terminal.

In parallel, each speaker you add will decrease the resistance in the channel. The sum of the inverse of each speaker’s impedance equals the total impedance. So two four ohm speakers in parallel is equal to ¼ + ¼ = ½ ohm. To decide on the wiring configuration, you will need to know your amplifier’s capability (can it be wired in parallel?) and ohm rating. You will also need to know your speakers ohm rating (usually 4 ohms) and the number of voice coils. Keep in mind that you should generally limit your amplifier usage to two speakers per channel. To connect speakers in parallel, connect each speaker’s positive lead to the amplifier’s positive terminal, and connect each speaker’s negative lead to the amplifier’s negative terminal.

What does it mean when you say an amplifier is clipping?

Clipping refers to distortion produced by an amplifier due to a lack of sufficient power. When pushed beyond its maximum powering capability, the amplifier produces square waves, which causes distortion or even worse, results in a fried amplifier.

What does CEA-2006 compliant mean?

An amplifier is CEA-2006 certified if it is tested by the Consumer Electronics Association. This certification means that the amplifier ratings are accurate. The amp is compliant with the CEA 2006 standard. The RMS rating and the signal-to-noise ratio are the two main ratings that are verified by the CEA 2006 test (though they test a few other specs as well).

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Written by Gary Brikowski