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.

Our series of articles on what tools are important to test and configure a car audio system upgrade moves on to the oscilloscope. Tools like digital voltmeters, real-time audio analyzers and, of course, hand tools such as screwdrivers, side cutters, wire strippers and a socket set each have their place and importance. When it comes to analyzing the amplitude of electrical signals that change with time, only an oscilloscope can provide an installation technician with the information he needs.

What Is an Oscilloscope?

An oscilloscope is a device with a screen that displays the amplitude of a signal relative to time. The screen has several calibrated squares, each representing an adjustable time base or voltage level. Controls on the scope let the user change the time base and voltage ranges for the type of signal that is under inspection.

Why Is It Important for the Shop I Choose to Own an Oscilloscope?

If you are having an audio system installed in your car or truck, especially if an equalizer or digital signal processor is in the audio signal chain, having a scope is a sure-fire way of setting the amplifier sensitivity controls so they can achieve maximum output without significant distortion. Proper configuration ensures the highest possible signal-to-noise ratio, so hiss and background noise are kept to a minimum.

An Oscilloscope is an Important Tool

A scope is also useful for testing the wiring in the car for audio and data signals to confirm that each electrical connection will function as intended. Some installers try to use a digital multimeter set to the alternating current (AC) voltage setting to perform these tests. While the meter may show some amount of information, there is no way to know the shape of the waveform to determine if the signal is digital or analog.

Finding a Quality Mobile Enhancement Retailer

As you search for a shop to work on your vehicle, we recommend that part of the process include a tour of their installation facilities. The install bay and fabrication area need not be spotless if they are working on vehicles, but they do need to have the right tools and supplies. Ask them what they use to set the sensitivity controls on the amplifiers you intend to buy. Hopefully, they have invested in the right tools and they own and know how to use an oscilloscope.

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.