We’ve talked about car audio amplifier features and specifications at great length, but up to this point, we haven’t discussed how a car audio amplifier works. In this article, we’ll provide a simple overview of how the power supply in your mobile amplifier can take the 12 volts supplied by your electrical system and convert it into a much higher voltage to drive your speakers.

Making Power for Your Speakers

To supply enough power to your speakers to produce music at realistic listening levels, we need a lot of voltage. For standard 4-ohm speakers, it takes a peak-to-peak voltage of almost 60 volts to deliver about 100 watts to your speaker. In most amplifiers, this voltage is configured as +30V and -30V, relative to the ground reference voltage of your vehicle chassis. So, how in the world do we get plus and minus 30 volts from 12? That’s the job of the power supply.

How a Transformer Works

Power supplies couldn’t be created with any reasonable amount of efficiency without a transformer. A transformer is a simple device that increases or decreases alternating current (AC) voltages using two coils of wire wrapped around a magnetically conductive iron core. If you have a 1:2 transformer and feed 12V of AC signal into the primary, you get 24 volts on the output. The big green boxes out on your curb or the cylinders on the power poles near your house are step-down transformers that convert the 16kV feed that enters your neighborhood into 120- and 240-volt feeds to your home.

How Do We Get AC Voltage in a Car?

As you may (or should) know, the power supplied by the battery and alternators in our cars and trucks is direct current (DC). Left in that state and fed into a transformer, we’d see a small voltage spike when the signal was first connected, then nothing. The steady current flowing through the primary winding would simply heat it up and not produce anything on the output side of the transformer.

Since we need an AC signal, modern amplifiers use a pulse-width modulator to create a series of square waves that turn on a bank of MOSFETs (electrically controlled high-current switches) that pulse the supply voltage on and off very quickly. Many high-quality amplifiers have power supplies that switch at more than 300kHz.

In the simplest of terms, by switching the connection from the battery to the input of the transformer on and off very quickly, we create an alternating current signal. The voltage of the pulsed signal is increased through the transformer and then fed into a set of diodes and capacitors to smooth it back out to what we call the rail voltage. The rails are the positive and negative power supply sections of the amp that are connected to the output devices.

In application, the circuit is far more complex, but this is the basic operation of the system.

Energy Storage and Power Delivery

As the output voltage of a car audio amp increases, so to does the amount of current flowing to the speaker. The pulse-width modulation controller that manages the power supply can change the relative “on” to “off” time in order to increase the current supplied by the amp. More “on” time means that more current is fed to the transformer, which results in more voltage being produced on the output. Regulated back down to the required rail voltage, this extra voltage ensures that we maintain stable rail voltages.

If you look inside an amp, you will almost always see a toroidal transformer and a bank of energy storage capacitors. These large capacitors help smooth the output of the transformer and diode rectifier stage, and store large amounts of energy so that the amp can keep up with the current demands of the audio signal.

Learn How a Car Audio Amplifier Works

You should now have a basic understanding of how your car audio amp converts the 12V feed from your alternator into much higher voltages for the rails. In the next article, we’ll talk about the front end or input stage of a car audio amplifier and discuss crossovers, gain controls and the features and functions that make it easier for your installer to configure your car audio amplifier for optimum performance in your car or truck.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

As we slowly approach the end of our latest Understanding Specifications series, we want to take a look at car audio amplifier distortion ratings and explain what they mean. We should make it clear: No matter how or good or bad a piece of audio equipment is, every audio component adds some amount of distortion to the signal. The amount and type of distortion those audio products add matters a great deal. Let’s explain distortion, so you know what we’re talking about.

What is Harmonic Distortion?

Before we talk about distortion, let’s talk about harmonics. By definition, a harmonic is an overtone or multiple of a frequency or sound. For example. If you were to play a 1 kHz test tone through an amplifier and a speaker, harmonics of 1 kHz would be 2 kHz, 3 kHz, 4 kHz and so on until the information becomes inaudible because the amplitude is reduced or you have reached the limit of the recording medium.

Visual Representation of Harmonic Distortion

 

Intermodulation Distortion Explained

Another common distortion is intermodulation distortion (IMD). From a mathematical standpoint, where harmonic distortion results in multiples of a specific frequency, intermodulation distortion manifests itself as audible signals that are the difference between two frequencies.

The most common lab test for intermodulation distortion involves playing two test tones at the same time and looking at the resulting output. In most cases, 19 kHz and 20 kHz tones are used and the resulting distortion typically manifests itself as unwanted output at 1 kHz. This 1 kHz content is the difference between 19 kHz and 20 kHz (20-19=1). You will also see harmonic distortion present in the output signal on either side of the 19 and 20 kHz tones.

 

How Do We Perceive Car Audio Amplifier Distortion?

In the case of harmonic distortion, this typically manifests itself as adding an amount of “brightness” or “harshness” to the amplifier since it creates high-frequency content where none originally existed. Harmonic distortion reduces the clarity and realism of the music you are enjoying.

Intermodulation distortion, on the other hand, is responsible for adding unwanted low-frequency content to your music. In most cases, when someone describes an amplifier (or source unit or processor) as sounding “warm,” that is a result of the presence of audible intermodulation distortion.

Choosing the Right Amp for Your Car Stereo System

Of course, you will want to choose an amplifier that offers the lowest possible distortion numbers for your given budget. In the case of the three amplifiers we used in our good, better and best comparisons, you are looking at a dramatic difference in cost, with the cheap amp coming in under $100, the middle amp costing around $600 and the great amp having an MSRP around $1,500. With that said, the fact that an amplifier is expensive doesn’t automatically make it good. Your local mobile electronics specialist retailer can help you choose the right amp for your system and budget to ensure that your music will sound great!

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

Unlike buying and setting up a basic home audio system, having a new amplifier and speakers installed in your car or truck requires proper setup and tuning. At home, you can adjust the placement of the speakers and how much they are toed in to affect the focus of the soundstage and the bass response. In a car, your installer needs to mount the amplifier, wire it, then adjust the crossover and sensitivity controls to work with your source unit and the design of the system. Getting these settings wrong can have an audibly detrimental effect on the performance of your mobile audio system. Let’s look at why proper amplifier setup and tuning are so important.

Basic Car Audio Amplifier Setup

Once the power, ground and remote turn-on connections are made, and new speaker wires have been run to each location in the car, the last step is to connect your amplifier to the source unit in the system. Depending on the design of your audio system, you may have a very basic CD player with low-voltage preamp outputs, a premium multimedia receiver with 5-volt preamp outputs or you might be using a factory radio with or without an amplifier. The sensitivity (gain) control on your amplifier exists to ensure that your new amp can reach its full potential from any of these sources. Many shops use an oscilloscope or a distortion detecting device to ensure that the system is configured accurately and efficiently.

If you are adding a subwoofer to your vehicle, the basic process is the same, but your installer now has to balance the output of the sub to the other speakers in the car. He or she will also have to set the crossovers on the amp so that the output of the sub blends with the output of the smaller speakers. Many high-end shops use a real-time analyzer (RTA) to perform this task to ensure the output of the speakers blends perfectly. Setting up crossovers also needs to take into account the physical capabilities of a speaker. A small 4-inch midrange certainly can’t produce the same amount of low-frequency information as a 6.5-inch woofer and needs to be adjusted accordingly.

What if Things Aren’t Set Up Properly?

If the sensitivity setting is wrong, you may experience a lot of background noise or hiss in your system. At the opposite end of the scale, you may not be able to reach full volume. If the crossovers aren’t right, you run the risk of damage to small speakers or experience unwanted dips and peaks in the frequency response of the system around the crossover point.

Setting Up a Digital Signal Processor

The goal of adding a digital signal processor (DSP) to a mobile audio system is to produce accurate imaging and realistic frequency response at the listening position. Setting up a DSP properly requires training and an investment in tools. Beyond that, your installer needs to use a real-time analyzer to measure the acoustic performance of the system. While there are a variety of processes used to set parameters like signal delay and different theories on whether to boost or cut EQ bands, the person tuning the system needs to have a full and detailed understanding of how the adjustments he or she makes affect the amplifiers, the speakers and the resulting acoustic performance of the system.

What if Your DSP Isn’t Set Up Properly?

In the simplest of scenarios, your audio system may not be as optimized as it could be. There may still be frequency response, imaging or staging issues. If the settings are really far off, you run the risk of damaging speakers permanently, or the performance of your sound system might have been better off with no processing at all.

Choosing the Right Retailer to Setup Your Mobile Audio System

The easiest way to choose a shop to set up your mobile audio system is to ask to listen to one of their demo vehicles. If you like the sound of the system, it offers excellent imaging and staging and plays at a volume level that suits your listening preferences, they should be qualified to recreate something very similar in your vehicle. If you aren’t happy with the way the vehicle sounds, ask to listen to a client vehicle. If you still aren’t satisfied, look for another shop to work on your car or truck.

When a car audio system is set up and tuned properly, it can rival some of the best home audio and studio reference systems on the planet. Don’t short yourself on getting the most performance possible from your upgrade – make sure it’s installed and configured properly.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

We’re back in the lab and working on a few more articles about amplifier specifications in order to wrap up this series. This time, we’re going to talk about the amplifier stereo separation specification. In a nutshell, the stereo separation, or crosstalk, number tells us how much of an audio signal leaks from one channel of an amplifier to the other. Of course, for the number to exist, you need to be looking at a stereo amplifier and in most cases, one that will drive a full-range signal.

Understanding Amplifier Stereo Separation

The stereo separation specification is supplied in decibels and describes the amplitude of the signal produced in the adjacent channel. For example, if we have a stereo amp, and we feed a sine wave into the left channel, some of that signal will be reproduced by the right channel. The stereo separation specification tells us how much quieter the signal will be. A good number would be something about 70 dB.

A criterion required to better explain the application of this stereo separation value is to specify at what frequency the signal is tested. In most cases, you’ll see 1 kHz as the specified test frequency. The reason that the frequency needs to be specified is that some amplifiers, in fact, most amplifiers, have more crosstalk (signal leakage from one channel to the other) at higher frequencies.

Why Is Stereo Separation Important?

When trying to recreate a musical experience, one of the many criteria that people will quantify subjectively is stage width. If you are using an amplifier with a poor stereo separation spec, content from the left channel will be reproduced on the right output and vice versa. This has the effect of making the signal more monaural and effectively reducing the width of the soundstage. If you switch to an amplifier with amazing separation performance, the stage may seem to be wider.

Measuring Stereo Separation

To give you an idea of how a good amplifier compares with an inexpensive solution, we set up our QuantAsylum QA401 on the bench and took some measurements.

 

 

 

Stereo Separation and Frequency

As we mentioned, crosstalk and channel separation get worse as frequency increases. We took a series of measurements for each of the amplifiers in this test and plotted their channel separation versus frequency in the chart below.

The graph clearly shows that the signal leakage from one channel to another is very dependent on frequency. At 20 kHz, our low-quality amplifier outperforms the good amp. Since we can’t hear 20 kHz, this isn’t an issue.

What to Look for When Shopping for a Car Audio Amplifier

Very few manufacturers publish an amplifier channel separation specification. If you do find a spec, the higher the number, the better the amp will perform in terms of creating a wide soundstage in your vehicle. Your local mobile electronics retailer can help you choose a great amplifier solution and install it for optimum performance and reliability.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.