As we continue our look at how car audio amplifiers work, let’s discuss how the classic Class AB amplifier output stage works and explain why it’s still the benchmark for high-end audio systems.

How Does a Class AB Output Stage Work?

We recently looked at the power supply, the input stage and how Class D output stages work to allow your car audio amplifier to reproduce music. If you go way back to the beginning of high-power car audio amplifiers, you’ll find the Class AB design.

A Class A amplifier uses a single output transistor to add current to the output signal to drive your speaker. When no music is playing, the output device is halfway on and gets very hot. Think of the output as a resistor. If you put two small resistors in series across your power supply, a lot of current would flow through the load. A Class A amp works the same way.

Class B amplifiers use a pair of output devices and split the voltage delivery duties between each device. When no music is playing, both devices are turned off and no voltage is produced at the speaker. The problem with Class B amps, as the guys at BestCarAudio.com discussed in their Class AB Amplifier Distortion article, is that there a dead zone that occurs as the voltage across one of the diodes in the transistor is biased on. The result of not compensating for this roughly 0.7-volt bias requirement is called crossover distortion.

Class AB Amplifier Output Stage

The Class AB amplifier is a Class B amplifier with a small bias voltage applied to the output devices to get them ready to play music. Different amplifier designs use different amounts of biasing to balance between efficiency and silky-smooth operation.

Amazing High-Frequency Extension

One thing that high-end Class AB amplifiers are known for is their extended high-frequency performance. Many top-end amps can play beyond 80 kHz with ruler-flat, low-distortion performance. If you are building an audio system that is compatible with high-resolution audio, this extended high-frequency response is crucial.

Low Output Impedance

As compared to Class D amplifiers that use inductors and capacitors on their outputs, Class AB amplifiers, except in configurations with variable voltage power supplies (often called Class G or Class H designs), don’t need these devices. The result is less variance in output voltage relative to load impedance and more predictable response.

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Efficiency versus Performance

At low to medium power levels, Class AB amps are not as efficient as a Class D amplifiers because the output devices act like resistive voltage dividers across the power supply rail voltages. As such, AB amps need larger heatsinks to ensure their reliable operation. As you approach the upper limits of an AB amplifier’s output capabilities, their efficiency becomes similar to that of a Class D amp. The output devices are close to being all the way on or off.

Experience the Ultimate in Car Audio Amplification

If you are determined to assemble the best possible audio system for your vehicle, visit your local specialist mobile enhancement retailer and ask about using Class AB amplifiers. Yes, you’ll need to find room for them in your vehicle, but the amazing clarity and detail they provide is well worth the effort.

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.

Our series on the tools that are important to test and configure car audio system upgrades moves to the topic of the real-time audio analyzer, also known as an RTA or spectrum analyzer. This important tool helps installers measure the acoustic response of your mobile audio system, and it can be a fundamental component in testing a complex factory sound system to ensure that the integration process goes smoothly.

What Is an RTA?

In the simplest of descriptions, an RTA tells the technician how loud specific audio bands are relative to one another. Depending on the resolution of the RTA, the bands may be divided into full octaves, half-octaves, third-octaves (the most popular) or, on some computer-based analyzer solutions, as fine as 1/48th of an octave. For an audio system to sound realistic and believable, the transition from band-to-band (depending on the resolution) needs to be smooth and free of peaks or valleys that can detract from the listening experience.

RTAs can be used with a microphone for acoustic measurements of your system, or they can be used with an adapter to measure the output of a factory radio or amplifier, so your installer will know if an equalizer or interface is required to make your system sound its best.

If you’re thinking to yourself that you’ve seen something like this before, some radios and under-dash equalizers had spectrum analyzers built into them many years ago.

Types of RTAs Found in Car Stereo Shops

When you’re shopping for a retailer to upgrade the audio system in your car or truck, one of the things we recommend is that you ask for a tour of their facility. During that tour, feel free to ask about the tools they use. When it comes to RTAs, they may use a classic stand-alone solution like the older AudioControl SA-3055 or a modern computer-based interface like the AudioControl DM-RTA or Audison bitTune.

Some computer-based solutions allow for more complex measurements than a stand-alone solution can produce, but at the very least, knowing that your technician has a way to look at the acoustic performance of your vehicle is paramount.

Tuning Digital Signal Processors

We’ll make it abundantly clear: If you’re having a digital signal processor added to your vehicle, your technician needs to have an RTA. In the same way that you can’t look at a glass of water and tell what temperature it is, an installation technician can’t listen to an audio system and know which frequencies need to be adjusted and by exactly how much. The RTA is the car audio equivalent of a thermometer for that glass of water.

Before you commit to an audio system upgrade, make sure that your local mobile enhancement retailer has the tools required to complete the task efficiently and reliably and the training needed to ensure that the proposed benefits and improvement in performance will be delivered to you, the customer.

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 continue our look at how at how car audio amplifiers work, we need to discuss what has become the most popular design on the market today: amplifiers that use a Class D output stage. In audiophile realms, Class D designs often carry an unfavorable reputation. Do their drawbacks outweigh their benefits? Let’s have a look!

How Does a Class D Output Stage Work?

Once the input stage has handled any signal processing needs, the audio signal is passed to the output stage so that it increases in voltage and the MOSFETs can provide adequate amounts of current to drive our relatively low impedance speakers. In a modern Class D amp, the MOSFET output devices are fed by a driver IC that handles the conversion of the analog signal into a pulse width modulated signal.

What is a Pulse Width Modulated Signal?

Imagine, if you will, an incandescent lightbulb. We hook the bulb up to a power source and insert a computer-controlled switch in series with the circuit. If we leave the switch off, the light stays off. If we turn the switch on, the light illuminates to full brightness. However, if we turn the switch on and off very quickly, and the switch is on for as long as it’s off, the bulb will glow at half of its possible brightness. This variation of on-versus-off time is called duty cycle. When the on-vs.-off time is equal, that’s a 50% duty cycle. Using a square wave signal with different duty cycles is called pulse width modulation (or PWM for short).

The Class D driver analyzes the audio signal at extremely high speeds (some as fast as 800kHz) and creates a relatively low-voltage PWM signal that feeds the output devices. The output devices switch all the way on and all the way off very quickly. Because the devices spend very little time in a partially on state, they present very little resistance and, subsequently, consume very little energy. The best Class D amplifiers on the market offer overall efficiencies that exceed 92% at full power. This excellent efficiency is in contrast to Class AB amplifiers that turn between 35% to 50% of the energy fed into the amp into heat.

Compact discs use a version of PWM where the duty cycle of the output pulse is stored in a 16-bit digital word. This gives us 65,536 possible amplitude levels. Unlike modern Class D drivers, our audio is stored at 44,100 samples per second. This is still more than enough to reproduce the entire audio spectrum.

Class D Circuit Arrangement

Lastly, Class D amplifiers typically have their output devices arranged in a Class AB configuration, where one device drives the negative part of the waveform and the other drives the positive. As such, Class D describes how the output devices are used, rather than their electrical orientation in the circuit.

Drawbacks of Class D Amplifier Designs

If you have read the BestCarAudio.com articles on distortion, then you know that a square wave AC signal is made up of a large number of high-frequency harmonics. You’ve likely heard this phenomenon in your home if you have a dimmer on some of the lights. The filament in the lights will occasionally ring, depending on the level of the dimmer. Since we only want to pass an audio signal back to the speaker, amplifier designers add a passive filter network to the output of the MOSFETs. This network includes an inductor in series with the load as well as a capacitor and resistor in parallel and acts as a low-pass filter to remove this high-frequency switching noise.

One drawback of a Class D design is that these output filter components interact with the frequency-dependent variations in load impedance to alter the frequency response of the amplifier. While the effect is minute, it can give Class D amps a different overall tonal balance than you’d get from an AB design. Of course, a little manipulation with a digital signal processor (DSP) will get that back in check in a jiffy.

Another issue with all this high-frequency energy is the potential for electrical interference with other systems in the vehicle. Most commonly, AM or FM radio reception can be washed out or dramatically reduced. While the better amplifier manufacturers do everything possible to mitigate radio-frequency interference, problems can still occur — the best plan to keep the amplifier as far away as possible from the radio antenna.

Why Would You Want a Class D Amplifier?

The long and the short of it is that companies have invested in developing Class D amplifiers in an effort to shrink the physical size requirements of amplifiers, supposedly to make it easier for installation technicians to find mounting locations for them. The reality is, heatsinks for amplifiers are one of the more expensive single components in an amplifier. If the size of the heatsink can be reduced, so can the cost of the amplifier. The days of 40- and 50-watts-per-channel stereo amps with a footprint of more than a square foot are long gone, thanks to modern Class D designs. Now, you can get more than 1,000 watts of power from that same physical space.

Class D amplifiers are a good solution for subwoofer systems because they do offer increased efficiency over their Class AB counterparts, and almost all amplifier manufacturers have at least one series of Class D amplifier in their catalog. Your local specialist mobile enhancement retailer can help you choose a solution with the right power level, number of channels and features to make your car stereo 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.

If there’s one thing that can add emotion and excitement to your music, it’s adding a little more bass. Bass frequencies, especially those below 80 Hz, can be felt as much as heard at a higher volume level. The tingling in your amps and vibration in your back make a night at a club, your favorite concert or a high-end car stereo system some of the most enjoyable musical experiences available. The problem is, adding bass isn’t always easy. Let’s look at how many people do it and offer a few suggestions for enhancing the low-frequency performance of your car stereo.

Making Bass Takes Power

If you are an avid reader of our articles, then you know that it takes significantly more power to drive a subwoofer to an output level of 90 dB than it does for a set of tweeters. You can find out more about the physics behind that phenomenon here.

Unless the stereo system in your car has a dedicated amplifier with a switching power supply, it’s likely with 6.5- or 6×9-inch speakers as the largest size, it takes a lot of power to move the speaker cone enough to produce the bottom few octaves of our music.

Imagine “Thunderstruck,” “Bohemian Rhapsody” or “Yeah!” by Usher comes on Pandora and you can barely hear the bass line. Instinctively, you look for a way to turn up the bass with the tone control or EQ built into your car radio. More often than not, you are rewarded with a garbled mess that sounds less like music and more like the performer is munching on a rubber floor mat.

As much as this isn’t any fun, it’s really no surprise. That tiny little amplifier built into your radio is designed for moderate listening levels with fairly neutral overall tonal balance. That means, not a lot of bass relative to the mids and highs.

Problem defined. How do we fix it?

Does Adding Power Make More Bass?

What if we visited our local car stereo shop and asked to have a 75-watts-per-channel amplifier installed between the factory radio and the speakers? Now, any signal that comes out of the radio is amplified and we don’t run out of power when the bass line kicks in, right?

In the simplest of terms, sure, adding an amplifier to your factory speakers helps a lot. With that said, you are still limited by the small size of the speakers. Worse, you are asking those relatively tiny woofers to move really far to produce bass, as well as midrange information. Unless someone has come up with a way to defy the laws of physics, more excursion always results in more distortion.

Adding an amp added a little bass, but made the midrange sound worse.

Will Upgrading Speakers Add Bass?

Let’s say you skipped the amplifier idea and decided that upgrading to high-quality speakers was a better bet. Do better or more expensive speakers produce more bass than less expensive offerings? There’s almost no definitive way to answer that question in a single paragraph. Some speakers produce less midrange relative to the amount of bass they produce. There are also speakers that play lower than factory speakers. In both cases, the new speakers are typically less sensitive (require more power) than what’s already in your car or truck. In short, you may get the perception of more bass, but more often than not, you’ve ended up with less midrange.

The good thing about upgrading your speakers is that they can likely handle the power from an amplifier with fewer complaints and stress. So, if you upgrade your speakers and add an amplifier, your system might sound pretty good.

The Best Way to Add Bass is to Add a Subwoofer System

Imagine if there were a way to add an amplifier and speaker to your car or truck that was dedicated to reproducing bass. I know, it sounds far-fetched, right? Sorry, just kidding.

Adding a subwoofer and driving it with a dedicated amplifier, even if the selection is modest, will offer an impressive improvement in the reproduction of bass in your music. A powered 8-inch subwoofer that fits under a pickup truck seat or in the corner of your truck is a perfect starting point. Best of all, you can turn the bass settings on the radio back down and let the small speakers in your car do their job of reproducing midrange and high-frequency information. The result is a car stereo system that plays louder and sounds amazing.

Of course, there are an unlimited number of options for generic, vehicle-specific and custom subwoofer systems to add more bass to your car stereo. Your local specialist mobile enhancement retailer can help you choose a solution that will meet your needs. Drop by today and have a listen to what they have to offer.

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.