Amplifier

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An amplifier or amp, as it relates to the car audio hobby, is a piece of hardware the boosts an audio signal. Typically the audio signal will enter as a pair of RCA wires from a CD player or computer. The amp then boosts the signal and sends it out to each individual speaker thru standard speaker wire; one positive and one negative. An amplifier usually takes lower voltage AC input from the RCAs and amplifies it to send out high voltage AC signals to the speakers.

[edit] Picking an Amplifier

One of the most asked questions on the MP3Car.com forums comes when a user needs to determine what amp to go with to power their speakers.

Picking out an amplifier can be a bit intemidating considering that there are many paramaters that need to be considered.

To keep things simple, we'll just start off with your full range speakers. We'll talk about subwoofers in a bit.

Let's say you have 4 speakers and would like to power all of them on an amplifier. The safest and easiest way of doing this is to find a 4 channel amplifier. This means a channel for each speaker.

If you have a set of seperates (where the midrange driver and the tweeter are mounted seperately) you don't necessarially need to add in more channels of amplification. That's where the crossover network that comes with seperates can be used.

Wiring up subwoofers can get a little trickey, and for the purposes of this article, we're trying to keep things simple. After reading this entire article, if you still have questions on how to wire up your subs or which amp to go with for your subs, you can ask it here: [1]

[edit] Speaker Wiring

In general, the number of channels refers to how many speakers the amp can run. One channel is one speaker. You can also wire up multiple speakers to one channel. There are various ways to do this.

If you have just one speaker, you can match the speaker to your amplifier and you're all done!

Most of the time though, you will have more than one speaker especially when we're talking about subwoofers.

There are three ways to wire up your subs. The key is to choose a wiring method which best matches the impedance of your sub combination to the optimum or recommended inpedance of your amplifier. If you amp wants to run 1000 watts at 4 ohms, chose a sub combination that gives you a 4 ohm load. It's that simple!

[edit] Series

When you wire speakers in series, you add up the total ohm load. For instance, if you have two 4 ohm speakers wired in series, your total ohm load is then 8 ohms. If you have three 4 ohm speakers wired in series, your total ohm load is 12 ohms.

The wiring for this will be as follows:

Lets say you have four 4 ohm speakers that you need to wire in series, this would give you a total ohm load of 16 ohms.

The wiring for this will be as follows:

The equation for this is as follows:

Z_total = Z_{speaker a} + Z_{speaker b} + ... + Z _{speaker z}

[edit] Parallel

When you wire speakers in parallel, the equation isn't as simple as with series wiring.

This is what it looks like when you wire up two speakers in parallel:

This is what it would look like if you were to wire up four speakers in parallel:

OR

The equation for this is as follows:

1 / Z_total = 1 / Z_{speaker a} + 1 / Z_{speaker b} + 1 / Z_{speaker c} + ... + 1 / Z_{speaker z}

For 2 speakers (namely a and b) the equation simplifies to:

Z_total = (Z_{speaker a} x Z_{speaker b}) / (Z_{speaker a} + Z_{speaker b})

Note: multiplication on top and addition on the bottom of the fraction!

[edit] Combination

You can also wire speakers in a combination of series and parallel.

If each speaker is 4 ohms, this combination will give you a total of 4 ohms impedance for the circuit.

Left two speakers are in series: 4 + 4 = 8

Right two speakers are in series: 4 + 4 = 8

Left pair and right pair are in parallel: (8x8)/(8+8) = 4

[edit] Wattage Ratings

Amplifier ratings can be trickey. Many times, the consumer is bombarded with outrageous power claims. One way to get past all of the numbers and hype, you can look for the following symbol:

This logo will ensure that the ratings that the manufacturer are claiming are true and accurate. This is not to say that if a manufactuer doesn't have this logo that their raitings are false.

The main determining factor to the wattage output of an amplifier comes from Ohm's Law.

[edit] Ohm's Law

This is where Ohm's law comes into play and will be crucial to your understanding of power raitings.

P = Power in Watts

E = Voltage - The voltage in your car will be anywhere from 12v (at idle) to upwards of 14.4v

I = Amperage - The current raiting is usually indicated by the fusing (either internal or external) on the amplifier. If there are miltiple fuses, you will need to add up all of these fuses.

R = Electrical Resistance in Ohms

SQR = Square Root

[edit] Basic Formula

This formula is the most basic form of the equation.

P = I x E

or

E = I x R

[edit] Voltage

If you know the wattage and the amperage, you can determine the voltage requirement.

E = P / I

or

E = I x R

or

E = SQR (P x R)

[edit] Current (Amperage)

If you know the wattage and the voltage, you can determine the amperage requirements.

I = P / E

or

I = E / R

or

I = SQR (P / R)

[edit] Power (wattage)

If you know the voltage and the amperage, you can determine the wattage output.

P = I x E

or

P = E2 / R

or

P = I2 x R

One thing that these formulas do not account for is the amplifier efficiency. The efficiency numbers are listed above under each amplifier type. To adapt these numbers you should use the basic equations as follows:

P = I x E x efficiency

[edit] Amplifier Classes

Amps come in a variety of sizes and configurations as well as classes. Class D amps are designed for powering subwoofers while class A or B are for door speakers. Analog amplifiers are cataloged by how much current flows during each wave cycle. Measured in degrees, 360º means current flows 100% of the time. The more current, the more inefficient and the more heat generated.

[edit] Class D amplifiers

A power amplifier that employs a pair of transistors that are connected in push-pull and driven to act as a switch, and a series-tuned output filter, which allows only the fundamental-frequency component of the resultant square wave to reach the load. These amplifiers are highly efficient. However, because of this, they are also regarded as having poor soundquality.

These amplifiers are usually 85% efficient.

[edit] Class A amplifier

The amplifier conducts current throughout the entire cycle (360º). The Class A design is the most inefficient and is used in low-power applications as well as in very high-end stereo. Such devices may be as little as 15% efficient, with 85% of the energy wasted as heat. However, they also are known for being exceptional when it comes to sound quality.

These amplifiers are usually 50% efficient.

[edit] Class B amplifiers

The current flows only 180º for half the cycle, or two transistors can be used in a push-pull fashion, each one operating for 180º. More efficient than Class A, it is typically used in low-end products.

[edit] Class AB amplifiers

An amplifier in which the grid bias and alternating grid voltages are such that anode current in a specific tube flows for appreciably more than half but less than the entire electric cycle. A transistor amplifier whose operation is class A for small signals and class B for large signals. Combines Class A and B and current flows for 180º to 200º. Class AB designs are the most widely used for audio applications. Class AB amplifiers are typically about 50% efficient.

These amplifiers are usually 60-70% efficient.

[edit] Class T amplifiers

A Class T amplifier is an audio amplifier product developed by Tripath Technology. It is based around a Class D amplifier, but uses digital signal processing to reduce distortion. While it is called a digital amplifier because of its use of pulse width modulated switching, this does not mean that it accepts or outputs digital audio.

[edit] Setting Your Gains

Tuning an amp: read the instruction manual carefully first. Typically the low pass filter will filter out any frequencies higher than what you set it too. The high pass filter will remove any frequencies lower than it's setting. To get the cleanest possible sound from the system, oversize the amps and turn the levels back down to correspond with the speakers. This is referred to as 'overhead'. Generally, the less an amplifier has to work, the better it will sound.

For more info on amplifier wiring see: How To: wire an amp.

[edit] Bridging An Amplifier

Bridging an amplifier is a means of combining the power of two channels to drive one speaker. Typically this will double the power of a single channel (i.e. two 50 watt channels would combine to become one 100 watt channel) although some of the top amplifiers will actually quadruple the power of a single channel (i.e. two 50 watt channels would combine to become one 200 watt channel). This is usually the most desirable and you can plan this into your overall design. For example, if you have two subwoofers in your system and you want to drive each of them with 100 watts you can do one of the following.

A. Drive each speaker with its own stereo channel of 100 watts

OR

B. Wire both speakers to a bridged amplifier that produces 50 watts in stereo or 200 watts in mono

Choosing option B will give you the same power but at a lower amplifier cost (lower dollars/watt). You may need to adjust the impedance of the speakers you buy when doing this. If your amplifier is only 2 ohm stable then you will only be able to bridge it to a 4 ohm load. So you must either buy two 8 ohm woofers and wire them in parallel or buy two 2 ohm woofers and wire them in series. Again, this is why you must plan your system before you start buying equipment.

[edit] Resources

Basic Car Audio Electronics - [2]

Answers.com - [3]

CarAudioBook.com - [4]