Car Audio Tips

1. Plan your audio system to fit your needs .

First, examine what you want from your system: is it GIANT BASS?, is it an audiophile's dream system? Is it just an upgrade to a factory (original equipment) stereo? The list below might help you pinpoint your car stereo needs starting from the modest prices and going up to the most expensive price tags:

• a) install a basic stereo, like a factory system..AM/FM cassette with pair of speakers
• b) upgrade a factory system just slightly, adding speakers to get a bigger sound
• c) upgrade to a system with CD player, amps and more speakers for audiophile sound, but not HUGE in volume
• d) install a pounding audio system that will shake the car
• e) install a competition-quality system that will drive the neighborhood crazy

Now that the cost of CD is so modest (and most 4x4 come bundled with it anyway) cassette no longer makes sense. No matter how high of a quality amps, speakers or signal processors you have, you cannot overcome 20 dB of dynamic range, 15 dB of signal to noise ratio at the very least, or the 20-50 Hz and 18-20 kHz octaves (or frequency ranges to be technical) that is lost by having a cassette source unit. Source unit (AKA head unit) is the thing that sits in your dash (usually) that is what you control (i.e. Radio/Cassette/CD Players). If you save on source unit, your splurging on other units will be of no use.

2. Do some homework, learn what the gear does.

Learn what head units, amplifiers, separates (mids and tweeters), crossovers, equalizers and subwoofers do. Most of the head units that cost over a hundred bucks do pretty much the same thing, they tune in radio stations, play cassettes and offer presets for convenience. As we said earlier, go for in-dash CD player. A little more money and you can purchase a CD changer, but it won't affect your sound quality but is mighty convenient. Buy the best quality head unit you can afford and opt for a known brand

3. Power

The next consideration: are you buying more POWER? If you want Volume, count on buying amplifiers. The IC chips inside any head unit can only provide so much power, about 30 watts max, regardless what the chassis says. That is about enough to power a pair of 5" 2-way speakers efficiently. If you add speakers to that, you will be under-powering them and you'll get distortion. If you don't want it loud... this minimum-sized system will be okay. It's a basic factory stereo. If you want good, clean punchy music, buy the amps. For audiophiles: run about 100watts per channel into your mid and high frequencies, and another 200 watts dedicated to your lows ( subs ) pushing subwoofer speakers. With the right drivers (speakers), this system will sound like a studio monitoring system! For you guys who want to FEEL it in your gut... double or triple the bass power.

Midrange drivers (4 to 6 inches) and Tweeters (for high frequencies) don't require much power to get LOUD, so sixty watts or so goes a long way. The big money comes in when you want BIG BASS, meaning more watts driving more subwoofers. Many cars are pumping 800 watts and more into bass alone. Many pro installations cost $1,500. in gear, then another 1,000. to install. The big boys spend ten times that.

4. BEWARE of inefficient sound systems!

It's not uncommon to see a shop install a 800 watt system that sounds like a 100 watt system. They are usually following orders from the client, who insists on a big 15" sub in a space that doesn't allow it to work properly. Remember: 8" subs in the right enclosure will produce more bass pressure than 15" subs installed "where-ever they fit". Throwing more power at poorly-thought-out speaker systems will not save you! The best sounding systems use multiple amps to power separate frequency spectrums (bass, mids, highs), utilizing electronic crossovers to cleanly divide up the spectrum before sending each band for amplification. This way, each driver type is doing just it's job... efficiently.

In this way, you can power dome tweeters with 25 watts, mid range 4" drivers with 50 watts, 6.5" mid-bass with 100watts, and a 10" dual voice coil sub with another 200 watts... and you'll get a pounding, high fidelity system, worthy of a studio engineer!

Replace the sub/amp with 500watts and a pair of 12" subs and you are pounding the neighborhood and making enemies. Past that, the sky's the limit.

5. HINT for the Cost-Conscious

The quickest upgrade is to add a self-powered subwoofer to your factory system! In this way, your existing system only has to push mids and highs, so it's not taxed as much...you can turn DOWN the volume on your deck, turn up the volume, carefully, on the powered subwoofer, and the music FEELS loud without blasting your ears. You perceive it as volume. Most factory car stereos sound horrible when turned up because they distort from the strain of trying to produce BASS. Allow a self-powered sub to do that, and the remaining system usually sounds fine!

Glossary of Audio Terms

which are also commonly abbreviated "amp". In computation, the abbreviation for amps is commonly "I".

`V' is for volts, which is a measurement of electric potential. Voltages don't "go" or "move", they simply exist as a measurement (like saying that there is one mile between you and some other point).

`DC' is for direct current, which is a type of circuit. In a DC circuit, all of the current always flows in one direction, and so it is important to understand which points are at a high potential and which points are at a low potential. For example, cars are typically 12VDC (twelve volts direct current) systems, and it is important to keep track of which wires in a circuit are attached to the +12V (positive twelve volts) lead of the battery, and which wires are attached to the ground (or "negative") lead of the battery. In reality, car batteries tend to have a potential difference of slightly higher than 12V, and the charging system can produce upwards of 14.5V when the engine is running.

`AC' is for alternating current, which is a type of circuit in which the voltage potential fluctuates so that current can flow in either direction through the circuit. In an AC circuit, it is typically not as important to keep track of which lead is which, which is why you can plug household appliances into an outlet the "wrong way" and still have a functioning device. The speaker portions of an audio system comprise an AC circuit. In certain situations, it is indeed important to understand which lead is "positive" and which lead is "negative" (although these are just reference terms and not technically correct). See below for examples. The voltage of an AC circuit is usually given as the RMS (root mean square) voltage, which, for sinusoidal waves, is simply the peak voltage divided by the square root of two.

`W' is for watts, a measurement of electrical power. One watt is equal to one volt times one amp, or one joule of energy per second. In a DC circuit, the power is calculated as the voltage times the current (P=V x I). In an AC circuit, the average power is calculated as the RMS voltage times the RMS current (Prms=Vrms x Irms).

`Hz' is for hertz, a measurement of frequency. One hertz is equal to one inverse second (1/s); that is, one cycle per second, where a cycle is the duration between similar portions of a wave (between two peaks, for instance). Frequency can describe both electrical circuits and sound waves, and sometimes both. For example, if an electrical signal in a speaker circuit is going through one thousand cycles per second (1000Hz, or 1kHz), the speaker will resonate at 1kHz, producing a 1kHz sound wave. The standard range of human hearing is "twenty to twenty", or 20Hz-20kHz, which is three decades (three tenfold changes in frequency) or a little under ten octaves (ten twofold changes in frequency).

`dB' is for decibel, and is a measurement for power ratios. To measure dB, you must always measure with respect to something else. The formula for determining these ratios is P=10^(dB/10), which can be rewritten as dB=10log(P). For example, to gain 3dB of output compared to your current output, you must change your current power by a factor of 10^(3/10) = 10^0.3 = 2.00 (that is, double your power). The other way around, if you triple your power (say, from 20W to 60W) and want to know the corresponding change in dB, it is dB=10log(60/20)=4.77 (that is, an increase of 4.77dB). If you know your logarithms, you know that a negative number simply inverts your answer, so that 3dB corresponding to double power is the same as -3dB corresponding to half power. There are several other dB formulas; for instance, the voltage measurement is dB=20log(V). For example, a doubling of voltage produces 20log2 = 6.0dB more output, which makes sense since power is proportional to the square of voltage, so a doubling in voltage produces a quadrupling in power.

`SPL' is for sound pressure level and is similar to dB. SPL measurements are also ratios, but are always measured relative to a constant. This constant is 0dB which is defined as the smallest level of sound pressure that the human ear can detect. 0dB is equal to 10^-12 (ten to the negative twelfth power) W/m^2 (watts per square meter). As such, when a speaker is rated to produce 92dB at 1m when given 1W (92dB/Wm), you know that they mean that it is 92dB louder than 10^-12W/m^2. You also know than if you double the power (from 1W to 2W), you add 3dB, so it will produce 95dB at 1m with 2W, 98dB at 1m with 4W, 101dB at 1m with 8W, etc.

`THD' is for total harmonic distortion, and is a measure of the how much a certain device may distort a signal. These figures are usually given as percentages. It is believed that THD figures below approximately 0.1% are inaudible. However, it should be realized that distortion adds, so that if a head unit, equalizer, signal processor, crossover, amplifier and speaker are all rated at "no greater than 0.1%THD", together, they could produce 0.6%THD, which could be noticeable in the output.

An Ohm is a measure of resistance and impedance, which tells you how much a device will resist the flow of current in a circuit. For example, if the same signal at the same voltage is sent into two speakers - one of which is nominally rated at 4 ohms of impedance, the other at 8 ohms impedance - twice as much current will flow through the 4 ohm speaker as the 8 ohm speaker, which requires twice as much power, since power is proportional to current.

`PSRR' is the Power supply rejection ratio. This is a spec sometimes provided with amplifiers, but is not exclusive to amplifiers. It refers to the propensity for an AC signal present at the output of the power supply to appear somewhere in the signal path. A poor PSRR often leads to an increase in noise, distortion, and crosstalk.

`BJT' is short for Bipolar junction transistor. It is a very common type of transistor that is found in a multitude of circuits. Often times, amplifier manufacturers will specify that a certain amplifier utilizes a BJT output stage. This simply means that the major current-carrying output devices (the output transistors) are of the BJT variety rather than FET. Regardless of output device type, most discrete amplifiers will incorporate many BJTs throughout the entire amplifier.

Many people do not realize that `MOSFET' is an acronym, but it stands for Metal oxide semiconductor field-effect transistor. It is another common type of transistor, but of the FET class. This type of transistor operates in a different manner than BJTs. There's much debate about which type of transistor is more suitable for car audio amplifiers, but in the end it becomes a matter of personal preference for the designer. It's important to note that neither design has an inherent benefit in terms of sound quality. However, properly constructed MOSFET output stages are sometimes more durable and immune to damage produced by device failure or poor output protection circuitry, whereas BJT output stages can sometimes be slightly more efficient and cheaper. But both of these statements depend even more so on the circuit design and the transistor used.

`RMS' is the abbreviation for root mean-square. It is usually associated with power measurements, and refers to a calculation that consists of the following procedure: 1) square the waveform; 2) take the mean of the result; 3) take the square root of this number. If the waveform is a sine wave, the RMS value is .707 times the peak value. If the waveform is a square wave, the RMS value is equal to the peak value. Importantly, the RMS voltage of a signal multiplied by the RMS current of a signal will yield the signal's average power. Sometimes, average power is erroneously referred to by manufacturers and hobbyists alike as "RMS power". "RMS power" would require calculating the root mean-square value of a power waveform, which ends up yielding a different result than average power, but it's become almost an industry standard.

`DCR' is the DC resistance of a speaker driver (it is sometimes referred to as `RE'). This number is typically lower than the nominal impedance provided by the manufacturer. It specifies the resistive component of the speaker's impedance characteristic at a given temperature. Sometimes it's useful to estimate a speaker's impedance by measuring its DCR value with a simple ohmmeter. Typical DCR values for 4 ohm speakers are on the order of 3.2 to 3.5 ohms, and for 8 ohm speakers, usually over 5.5 ohms.

`Q' is typically known as quality factor, and tends to refer to the roll off behavior of a filter or group of filters. Values of Q are intimately related to the breadth of band pass roll off (eg. in equalizers), degree of overlap between filters, filter alignment, or loudspeaker/enclosure interaction. In general, the higher the Q, the narrower the pass band, greater the overlap, or steeper the slope (depending on what the Q is referring to).

 

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