While participating in some brand-specific online discussion groups, we often encounter the question: “Is it better to use two good subs or one great one?” Are two 12-inch KICKER L7S subs better than a SoloX? Should you opt for two Hertz Cento CS 250 S4s instead of a Mille ML 2500.3 Legend? What about choosing a pair of Rockford Fosgate P3 twelves over a single T1? There are many factors to consider, including enclosure design, output, frequency response and efficiency. Let’s dive into science and math to find an answer.

Maximum Output Level – Part 1

For many car audio enthusiasts, achieving the most bass possible from a given investment is the top priority. So, is a great subwoofer louder than two good subwoofers? Let’s use the CompVR and CompVX subwoofers from KICKER as our first comparison.

We’ll start by setting aside the total enclosure size for now. While this will become important later, let’s first model a pair of KICKER CompVR CVR124 12-inch subwoofers using BassBox Pro.

KICKER recommends an enclosure volume between 1.75 and 2.25 cubic feet per driver for a bass reflex enclosure. We’ve split the difference, using two cubic feet per driver. We let BassBox Pro suggest a tuning frequency of 33 hertz. According to the simulation, the enclosure will produce 123.1 dB, with each subwoofer receiving 400 watts of power. Remember that this SPL number doesn’t account for the vehicle transfer function, meaning the output would be higher in a car or truck.

Now, let’s switch our focus to the CompVX cast-basket 12-inch subwoofer. This driver handles up to 750 watts of power and has an Xmax specification of 19.25 millimeters compared to the CompVR’s 16.5. Let’s see if this makes up for the output difference.

In this case, the single great subwoofer cannot match the output of the two good subs when driven by the same power.

One quick note about the KICKER simulations. KICKER doesn’t specify driver inductance. For this simulation, we left that field blank. The result is a flat response curve at midbass and midrange frequencies. In the real world, that’s not how the drivers would perform in that region.

Maximum Output Level – Part 2

Now, let’s consider a similar scenario with Rockford Fosgate subwoofers. This question initially prompted the article—are two P3 subwoofers better than a single T1? Let’s simulate this and see which setup produces more SPL.

We’ll start by simulating two P3D2-12 12-inch subwoofers in a 3.58 cubic foot enclosure tuned to 40 hertz. The Box Advisor on the Rockford Fosgate website suggests this exact design. Well, it suggested half that volume per driver, but the results are the same.

As the graph shows, this enclosure delivers a solid punch at 50 hertz. With 1200 watts of power, the peak output is predicted to be 125.7 dB SPL.

Next, let’s examine what a single Power Series T1D4-12 can do in its recommended enclosure.

The Box Advisor recommends a 1.75 cubic foot enclosure tuned to 33 hertz for the single T1 subwoofer. Based on the response graph, we agree with this design. The enclosure predicts an output of 119.1 dB SPL when driven by 800 watts of power.

Like in car engines, there is no replacement for displacement when attempting to produce maximum torque. Subwoofer cone area is crucial for maximum output in car audio systems.

Low-Frequency Extension Versus Enclosure Volume

What if your goal is to achieve the most low-frequency output possible from your subwoofer system? Many of the subwoofer upgrades we see perform better at upper bass frequencies due to large drivers being installed in undersized enclosures. If deep bass is your priority, moderately sized subwoofers in relatively large enclosures are the way to go. To illustrate this, let’s compare two Hertz subwoofer options at 30 Hz.

We’ll begin with a pair of 10-inch Hertz Cento CS 250 S4 subwoofers in a 2.5 cubic foot enclosure tuned to 30 hertz.

This system produces 113.9 dB SPL at 30 hertz. Now, let’s look at a single, better subwoofer in a larger enclosure—the Mille-Series ML 2500.3 Legend.

At 30 hertz, the single ML 2500.3 Legend delivers 114.5 dB SPL. Though the difference is slight, the difference would be very noticeable. Letting a single driver “breathe” in a larger enclosure maximizes low-frequency output.

Car Audio Subwoofer Sound Quality

This is where things become more complex. Sound quality and accuracy are not as tightly related to frequency response as you might think. We agree that a poorly designed enclosure with a narrow-band spike will sound inferior to a system with a broad response curve. However, a subwoofer in any high-end system should be equalized to a target response curve. Thus, any two enclosures equalized to the same curve will sound similar, though not identical.

Driver design features affect harmonic and intermodulation distortion in terms of accuracy. For instance, the Mille Legend subwoofers include an aluminum shorting ring that reduces inductance and, thus, improves midbass response. The Legend subwoofer’s inductance is specified at 1.05 millihenries, while the Cento subs measure 3.33 millihenries. Lower inductance means more midbass output, making blending the subwoofer’s output with midbass drivers easier.

Rockford Fosgate incorporates a similar feature between the P3 and T1 subwoofers. The T1 and higher subwoofers feature an Inductive Damping Heat Sink (IDHS) that acts like a shorting ring, reducing inductance. The T1’s dual four-ohm inductance is 2.4 millihenries, while the P3 is rated at 6.94. As a result, the T1 delivers tighter, punchier, and more accurate midbass.

Even without features like inductance management, less expensive subwoofers are still a great choice. However, upgrading to better products often provides more than increased excursion and power handling.

From a sound quality and musical accuracy perspective, the Mille and Power-Series subwoofers stand out as clear winners.

Space for Bass

As we’ve discussed in previous articles, producing deep bass requires that your subwoofers have adequate space. Trying to fit two 10-inch subwoofers in a one-cubic-foot enclosure won’t work as well as using a single eight-inch driver in a bass reflex design in the same volume.

Here’s a perfect example of optimizing an enclosure for subwoofer duties. A single 8-inch Audison APS 8 D driver in a one-cubic-foot vented enclosure delivers more output from 16 to 44 hertz than two 10-inch drivers in the same space. While two 10s might offer more output above 50 Hz, we prefer deeper extension to 35 Hz for a well-rounded sound and a little rumble.

Subwoofer Enclosure Simulations To The Rescue

In conclusion, if your goal is to maximize SPL, using two good subs will generally outperform a single sub. However, a single subwoofer in a larger enclosure may be the better option for low-frequency output. A subwoofer with advanced performance features will offer superior results for the most accurate and detailed bass.

If you’re curious about the best bass solution for your vehicle, visit a local specialty mobile enhancement retailer. They can measure the available space and simulate different subwoofer options to achieve your desired performance. They’ll also explain product features and how they improve sound accuracy and detail.

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.

Having music playing while driving is not only entertaining, but it can be very relaxing. Enjoying your favorite songs while stuck in traffic or on a long drive can help time pass much quicker. We recently received a question from one of our readers about the best way to manage a large music collection. Specifically, they wanted to know what features different radios offer that make accessing a specific artist, album, or track easier. This is a great question, so let’s explore the answers.

Radio-Specific Storage Limits

So, what would be considered a large music collection? One BestCarAudio.com team member loves collecting music. He has over a terabyte of music on his home server, comprising almost 65,000 songs. That’s way more than would ever be reasonable to take on the road with you.

In fact, most modern car radios can’t handle that many tracks. The Sony XAV-9000ES, for example, allows up to 25,000 tracks to be read from a USB storage device. The folder structure itself limits other brands. For example, we looked at the specifications for a Kenwood radio, which allows for up to 999 files per folder, 9,999 folders, and a maximum folder depth of eight layers. We also checked the owner’s manual for an Alpine multimedia receiver. The particular unit we checked lists a limit of 10,000 files and folders, including the root folder. We’ve seen marine radios with a limit of 999 songs and a maximum of 255 folders.

The takeaway is that you must research this specific aspect of the radio you are considering before purchasing. Many consumers assume their radio will recognize all their tracks and play almost anything. If you forget to check, please don’t complain about it afterward. The manufacturers can’t change these limits; they are often based on the amount of memory connected to the radio’s microcontroller.

Modern Factory-Installed Infotainment Systems

For real-world testing, we copied 13 GB of music onto a 64 GB SanDisk USB memory stick. There are 27 folders containing 683 files. This wouldn’t be considered a massive amount of music, but it will help us determine how different source units handle finding a specific track.

We connected the memory stick to the infotainment system in a staff member’s 2025 Mazda CX-70 Turbo Signature, equivalent to the US Premium Plus model. The radio displayed an error message saying it didn’t support the connected device. It turns out that the radio in this brand-new vehicle can’t read USB memory sticks formatted with exFAT. Storage devices must be either FAT or FAT32.

Panasonic manufactures the “radio” in this vehicle, Automotive Systems. Bose provides the amplifier and speakers. This is referred to as a silver box solution. The radio itself has no integrated interface. Visteon manufactures the screen on the dash. The “radio” has the AM/FM tuner, satellite radio receiver, GPS receiver, and the inputs for the pair of USB-C ports in the center console. The radio sends a data stream to the Bose amp under the passenger seat, which then handles the signal processing and drives the speakers and subwoofer.

We tried again after searching for an old 8 GB stick and hunting down a USB-C to USB-A adapter. Now, the radio struggled with the file formats. It wouldn’t play 88.1 kHz, 24-bit FLAC audio files. Remember what we just said about ensuring the radio will play what you want? Yeah, we figured that out by trial and error. After a third trip back to the computer and some work in Adobe Audition, the content was finally working.

Mazda CX-70 Infotainment System

So, how does the Mazda handle navigating extensive music collections? You can search through folders pretty easily. It’s just a few presses on the control wheel in the center console to select the Folder option. If you want to search for a specific track alphabetically, you can choose the Library option, then select from Artists, Albums, Songs, Genres, Composers, or Playlists. From there, you will be presented with a list of options based on your chosen criteria. You can toggle to the right, scroll through the alphabet, and select a song. It’s a lot of button presses, but it works well.

Next, we tested a 2023 Nissan Rogue with Bose speakers and amplifier. Just for clarity, Bose doesn’t make radios. Robert Bosch GmbH manufactures this particular unit. We connected the SanDisk stick to no avail, so it was back to the old 8 GB stick. If you want to carry around a lot of music on a USB drive, support for a large drive will be the limiting factor.

With our little USB loaded with a few hundred songs, we set off to run some errands. We recalled seeing some voice recognition features outlined in the owner’s manual—yes, some of us read the manual. We pressed the voice button and asked the system to play a song. It informed us that it couldn’t because of how our smartphones were connected. If you connect your smartphone using Apple CarPlay or Android Auto, it appears to override the built-in voice commands.

Sadly, our USB listening experience took a turn for the worse. After about 30 minutes of driving, the radio encountered issues updating the screen. The results are shown below. It seemed to work fine the next day, but we didn’t play it for long.

Sony Radio Music Management

We checked with our Editor-in-Chief to see what he had on the test bench. He’d just unpacked a Sony XAV-AX3700 multimedia receiver, so we asked him to try the same test on that. With a large memory stick full of music, the Sony could display all the tracks he’d copied and had no problem reading the exFAT memory stick or playing the high-resolution FLAC audio files. Specifically, the XAV-AX3700 will play FLAC, ALAC, DSD, and WAV high-resolution audio files.

Sony makes it very easy to choose songs from different folders when it comes to finding songs. Navigating to the root folder and selecting sub-folders was straightforward. It would be wise to remember this when copying files to the drive. Putting 200+ random songs in a folder likely isn’t the best strategy. Sorting them by artist, album, or genre while copying will make finding what you want easier when driving.

Smartphone Music Storage

Now that we’ve examined a few radio behaviors regarding music stored on a USB memory stick, let’s consider using a smartphone as your music storage device. Apple’s Siri and CarPlay, Google Assistant, and Android Auto make it incredibly easy to access music stored on the phone.

Let’s say you have purchased eight Aerosmith albums. These will likely include Permanent Vacation and Pump. If you want to listen to “Dulcimer Stomp,” activate the voice recognition feature and say, “Play ‘Dulcimer Stomp’ by Aerosmith.” The system will find the track and start playing it automatically. You can also ask it to “play the album Pump by Aerosmith.”

Cloud-Based Streaming

If you don’t have the song stored on your phone, another option is to subscribe to a service like Spotify, YouTube Music, or Qobuz. For about USD 11.00 a month, you can access music from virtually every professional recording artist you want. These services also offer discounts for two users or even family plans that allow up to six users. Spotify and YouTube Music also provide discounts for students.

Is streaming as good as playing a FLAC or WAV file on a USB stick? If your service offers a high-quality stream, the tracks will sound very good over a wired connection between your phone and the radio. However, any compression will remove subtle details. You might hear the difference if your car’s audio system is good enough. With the basic audio quality settings in Spotify, for example, you can detect a loss in quality on a basic six-speaker factory-installed audio system.

Test Your Music Collection Before Buying

What’s the takeaway from our testing? At first, the voice command capabilities of the Mazda seemed promising. Unfortunately, they didn’t work as expected. After that, the system required too many button presses and toggles to reach what we needed. In contrast, the Sony was simple, intuitive, and—best of all—worked seamlessly with our large memory stick and music files.

If you have an extensive music collection and want to enjoy it in your vehicle, always test the interface before making a purchase. This applies not only to aftermarket radios but also to new cars. Yes, we would absolutely avoid buying a vehicle if its infotainment system was difficult to use. You may recall that Ford CEO Jim Farley recently apologized for issues with their Sync infotainment system—this is the second time Ford has had to address these problems.

When shopping for a new car radio, visit a local specialty mobile enhancement retailer. Bring a USB memory stick or your phone and connect it to the radio you’re considering. Ensure it functions the way you want. If not, try a different model or even a different brand.

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.

A short while ago, while testing an amplifier’s maximum power output, we observed how significantly the power increased with higher supply voltage. This observation made us realize that we’ve never thoroughly examined the relationship between a vehicle’s battery voltage and a car audio amplifier’s maximum power output. It’s time to address that.

Why Does Battery Voltage Matter to Amplifier Power Production?

Today, most car audio amplifiers use loosely or completely unregulated power supplies. As a result, the positive and negative voltages available to feed the output devices become a fixed multiple of the supply voltage. For instance, if the battery rests at 12.5 volts, an amp might generate 500 watts. However, if that voltage increases to 14.4 volts, the amp might produce 600 watts.

Maximum Supply Voltage Limits

To ensure product reliability, companies typically set a maximum voltage limit, which prevents the amp from producing excessive power. But why is this important? All car audio amplifiers convert some of the power they consume into heat. The heatsink and cooling system must dissipate a specific amount of heat energy to control the amp’s temperature. Notably, as the power level increases, the heat that needs to be expelled also rises because amplifier efficiency remains constant at maximum power.

For example, consider an amplifier that is 80% efficient and produces 500 watts of power; it converts 125 watts into heat. If provided with more supply voltage, the amp might produce 600 watts, requiring the heatsink to manage 150 watts of heat. This is likely manageable. Now, if the amp could produce 700 watts at 16 volts, it would have to manage 175 watts of heat—a significant increase from 125 watts. Unless the chassis is massive or there are numerous 0.3 watts, stepping from 14 to 15 volts increased the output by 56 watts.

Why does the power level increase more with each voltage jump? Power is proportional to the square of the voltage divided by the load resistance, according to the formula V^2 ÷ R. Thus, a slight increase in voltage results in a moderate power increase.

How Can You Maximize Voltage to Your Car Audio Amplifier?

Without resorting to unreliable aftermarket alternators or maintaining battery banks, the simplest way to ensure your amplifier receives all the power your battery and charging system produce is to have the technician working on the vehicle install a high-quality, all-copper power cable large enough for the amplifier’s current requirements.

In a car audio installation requiring about 15 feet of power wire, we suggest the following cable sizes: 10-AWG for loads up to 22 amps, 8-AWG for loads up to 35 amps, and 6-AWG (if you can still find it) for loads up to 56 amps. For loads up to 88 amps, a 4-AWG cable suffices. If you must pass 218 amps of current over 15 feet, a cooling fans, this difference means the amp won’t run as long before overheating.

Moreover, increased supply voltage presents another issue: the maximum voltage ratings on components. For example, most amplifiers include filtering capacitors on the power connections, which might be 16-volt, 1000 μF units. To accept more than 16 volts, the manufacturer might need to upgrade to 25-volt capacitors. These higher-voltage capacitors are larger and more expensive. Additionally, diodes and other protection circuitry components might need upgrades to handle higher operating voltages, further increasing costs with little performance gain under normal conditions.

Testing Amplifier Maximum Power Output

We decided to test this further using a Rockford Fosgate Punch-Series P300X2 two-channel, full-range amplifier. Recently, we re-tested several amps with our new power supplies, and although this amp wasn’t on the schedule, we decided to test it anyway.

We set up the amp and connected it to a bank of 300-watt, low-inductance ceramic power resistors configured for a four-ohm load. Initially, we set the power supply to provide 16 volts to the amp, just under its maximum upper voltage limit. We then increased the signal to the amp until the output signal was within 1 to 1.05% THD+N. Afterward, we decreased the supply voltage and signal, measuring power output at 0.5-volt intervals until reaching the minimum power output of the power supplies. To comply with the ANSI/CTA-2006-D car audio amplifier power measurement standard, we measured power at 14.4 volts instead of 14.5 volts.

The difference in power output between 11.25 and 16 volts is substantial, as the chart shows. With an increase of 4.8 volts, the amp nearly doubled its power output. We simultaneously captured current draw measurements to calculate efficiency. This class-BD amplifier remained between 67% and 68% efficient throughout the entire range of measurements.

In our full Test Drive Review of the amplifier, our original maximum power rating was 360.1 watts at 14.15 volts. This time, we measured 398 watts at 14.4 volts. While you likely won’t hear the 38-watt difference, it’s worth noting that an amp rated to produce 300 watts made 400 watts. Rockford Fosgate fans already know they’re getting more than they paid for.

Plotting Amplifier Power vs. Battery Voltage

Let’s examine that chart as a graph.

Interestingly, while the relationship between the maximum power an amp can produce and the supply voltage appears linear, it’s not. The increase from roughly 12 to 13 volts yielded 48.3 more watts. The jump from 13 to 14 volts added 50-AWG power cable is necessary. For up to 289 amps, use a 2/0-AWG cable. Finally, if you have a massive amplifier or multiple smaller amps, 4/0-AWG cable over 15 feet is suitable for 422 amps. While these cables can undoubtedly pass more current, the voltage drop for these calculations is set not to exceed 0.35 volts over the entire length. Don’t forget to account for losses in the return path, which, if the cabling size and length are the same, would result in a 0.7-volt drop.

The Math on Power Output Versus Power Wire Size

To illustrate more clearly, for our 300-watt amplifier, losing 0.7 volts at the power terminals reduces the output by around 35 watts, roughly 10% of the rated power. If you think skimping on a power cable is a good idea, here’s the math to prove otherwise.

Consider this amp’s maximum theoretical power output with 15 feet of 10, 8, and 4-AWG cables for power and ground connections. Assuming the electrical system could maintain 14.4 volts at the battery, a 15-foot run of 10-AWG power and ground cable would reduce the voltage at the amp to 13.11 volts. With 8-AWG cables, the voltage would drop to 13.59 volts, while using 4-AWG cables reduces the drop to 14.08 volts. If you splurged on 0-AWG cable, the drop across the cable would result in the amp receiving 14.27 volts. You might have expected less drop across 30 feet of 0-AWG power wire, but that’s not the case.

If you’re curious why Rockford Fosgate overrates its amplifiers, it’s because most installations lack adequately large power and ground cables. If you waste a volt across the power wire, in the case of the Punch P300X2, the maximum power output drops by about 10%. You’ll still get all the power you paid for, but not as much as possible. Therefore, investing in larger power and ground cables is more cost-effective than buying the next-size car audio amplifier in a series.

Don’t Starve Your Car Audio Amp for Voltage

Even after an average of three and a half decades in the mobile enhancement industry, none of our team members recall anyone publishing similar data. It may have happened, but we haven’t seen it. This data highlights the critical need for adequately sized power cables. If you’re considering upgrading your car audio system with high-power amplifiers, ensure the wiring is sufficient to maximize the power output from your chosen amp. Visit a local specialty mobile enhancement retailer today. Choose an amplifier that sounds great and is efficient, then ensure it is installed with the largest power and ground cables you can afford.

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.

When 99% of car audio enthusiasts think about a digital signal processor (DSP), they associate it with equalizers, crossovers, and signal delays. In more advanced solutions, a consumer-grade car audio DSP might add the ability to include all-pass filters, an upmixer for a center channel and signal summing. However, at an engineering level, much more is available. Let’s look at a handful of DSP features that make audio systems at home, work, and on the road sound better.

What is a Digital Signal Processor?

Before we discuss some of the hidden features in digital signal processors, we should define them. A DSP is a microprocessor designed specifically to perform high-speed numerical calculations to process signals. Digital signal processors are used in video transmission, radio frequency systems, and audio systems. They are also used to interpret and manipulate sensor data in commercial, industrial, and research applications.

In short, a DSP can take a stream of digital data and manipulate or extract information from it extremely quickly. Our smartphones, smart speakers, digital cameras, drone quadcopters, smartwatches, and security cameras use this technology to provide the features, functionality, and performance you want.

Audio DSP Development

As a little peek behind the curtain, we want to introduce you to an audio DSP development suite called Analog Devices SigmaStudio. The technicians and engineers who develop car audio signal processors from scratch use this tool as part of the development process. It works like a flowchart. The designer can drag and drop elements into the project and then link them together. They would then write code in their interface to control the different elements in the DSP configuration. That’s a greatly simplified version of how it works, but you get the general idea. Writing a new DSP software package from scratch takes over ten thousand man-hours, making it a very expensive and time-consuming proposition. Testing that software also takes thousands of man-hours.

We are by no means experts in working with SigmaStudio, but its basic functionality is simple to follow. Looking at the image above, there is a stereo input on the left. One channel from that input feeds a volume control, which can be thought of as the gain. Then, the signal goes into a limiter, which we’ll discuss shortly. After that, there are three parametric equalization modules, followed by a filter module. Finally, we have an output. In theory, this setup would serve as a three-band equalizer and an adjustable crossover.

Hidden DSP Features – Audio Limiters

You might have noticed that the latest generation of factory-installed amplifiers in cars, trucks, and motorcycles are much less prone to damaging speakers. Is it that the speakers are now better? That’s part of why, but not the most significant factor. Many of these modern amplifiers have a limiter built in. A limiter will reduce the amplitude of a signal if it exceeds a certain threshold.

For example, if your installer turns up two bands of an equalizer with similar frequency centers, that might try adding 24 dB of signal at a specific frequency. A boost of 24 dB would take a 0.5-volt signal and increase it to 7.93 volts. That’s likely far more signal than an amplifier can accept.

We talked with our friends at Rockford Fosgate about the amplifier used on new Harley Davidson motorcycles. They incorporated several limiters into the design. As such, the amplifier won’t clip (overdrive) the outputs and add huge amounts of distortion, even if all the equalizer bands are boosted to their maximum levels. Similar features are integrated into some car audio amplifiers.

As a side note, anyone trying to measure power output on this amplifier with a device that looks for distortion will result in horribly inaccurate results. The output signal never reaches 1% THD, so units like the SMD DD-1 and D’Amore Engineering AMM-1 or AD-1 won’t accurately measure power. Audio analyzers like those from Audio Precision or QuantAsylum can measure output level and distortion. More importantly, these devices determine when the signal stops increasing in amplitude regardless of the harmonic and noise content.

Noise Gates

Many DSP solutions include a feature called a Noise Gate, which operates at the opposite end of the audio amplitude scale. A noise gate turns off the audio output circuitry when the signal drops below a preset level. This suppresses any background hiss or noise. As the music fades out, just when you might hear noise, the outputs turn off, leaving silence. Most modern recording studios use gating like this to help isolate a performer’s voice.

ARC Audio uses a similar approach to noise-gating with the LR1 remote level control in its signal processors. When the remote’s level is set to its lowest setting, the output devices are muted by a digital signal from the microprocessor.

Bass Processing

If you’ve been around the block for a while, you might remember the Waves MaxxBass processor. This processing algorithm analyzes harmonic content in an audio stream and then filters out the low-frequency information. Yes, that’s right—it removes bass information. It then modulates the upper bass and lower midrange frequencies to make it sound like the deep bass is still there. It’s a very cool way to produce the perception of deep bass from a small speaker with limited excursion capabilities. Smartphones and smart speakers—we’re looking at you!

If we can remove bass information, then could we not add it? If you’ve ever experienced the AudioControl Epicenter or Wavtech bassRESTOR, you know what we’re discussing. Imagine a system that can analyze the harmonic content of an audio stream and then add audio information that’s an octave or two lower. It would be like having a super-grand piano capable of playing a fundamental of 13.75 or even 6.875 hertz. Your subwoofers might not like it, but it would be fun to try! Subharmonic generators are easily added functions already built into the SigmaStudio.

Stereo Width Expansion

By now, you’ve realized that signal processors are capable of much more than just equalization and filtering. Way back in the day, many portable speakers—called boom boxes or ghetto blasters—had a switch that made the sound coming from them seem much wider. The SigmaStudio includes a stereo expander control as well.

Some research shows that Philips Semiconductors used to offer an IC called a Spatial, Stereo, and pseudo-stereo sound circuit. This was introduced in 1985, which coincides with our memory of these functions.

More Features Require More Space

The goal of this article is to provide some insight into how digital signal processors are used in different audio systems. Some devices you might think are simple are, in fact, quite complex in terms of audio processing. One that caught us off-guard is a smart speaker, of which the Apple HomePod is a perfect example.

Anytime you have microphones and speakers, you can measure the sound in the time and frequency domains. In the case of the HomePod, the unit can use its microphone array to evaluate the acoustics of the environment it’s used in. For example, if the speaker is 12 inches from a wall, frequencies around 283 and 849 hertz are likely to be attenuated.

Sound Reflections Can Cause Cancellations

Sound emanates from all speakers in a spherical pattern below the frequency where it starts to be directional. The audio information that bounces off the wall behind the speaker will eventually mix with the sound coming directly to the listening position. In our example, we have a total distance of 24 inches added to the signal path—the distance from the speaker to the wall, then back to the speaker. Where the audio wavelengths match, but are inverted, the amplitude (volume) decreases around those frequencies.

Now, back to the HomePod and its signal processing. The system will have a benchmark for the time it takes for the sound to leave its speakers, arrive at its microphone, and then be processed. Let’s call this two milliseconds, to keep the math simple. If we have the HomePod in the middle of a table, it might be the aforementioned 12 inches from the wall. It takes sound 0.0008886 milliseconds to travel 12 inches. As such, it would take 1.777 milliseconds for the sound from the speakers to bounce off the wall and return to the microphone. Let’s add that processing time, and the DSP might measure a delay of 3.777 milliseconds. The math, calibrated in controlled testing conditions, knows there will be a dip in frequency response at 283 and 849 hertz. It can then apply equalization to those frequencies to produce a much smoother overall response for the listener.

Automatic Equalization

The system will also be able to measure the frequency response of the sound it hears. If it detects a constant increase in bass frequencies due to room resonance, it could theoretically adjust for this. We’ve heard many times that HomePods sound mediocre for the first few minutes they play. Then, they mute the audio for a second, load new equalization parameters, and continue playing. Everyone who’s heard them says they sound exponentially better after they recalibrate.

Many car audio digital signal processors have have the ability to make measurements, or work with external hardware to automate the process of setting signal delays and equalization. This is achievable thanks to the processing modules available for the DSP chips. We will note, it takes a LOT more code to make these work well. Add another ten thousand man-hours to that software development time.

Vehicle Presets

A simple DSP feature is the ability to load an entirely new calibration quickly. This is the same as we described above with the Apple HomePod. For example, if you drive a newer Ford Mustang convertible, you might notice that the audio pauses for a moment as you are raising or lowering the convertible top. This is the system loading a new audio system calibration. Your music should sound similar, at least in the midbass, midrange and high-frequency ranges. However, the settings used to achieve what you hear will be very different with the roof up or down.

Real-Time Noise Cancellation

The last feature we’ll talk about is active noise cancellation. Many new cars and trucks come with an array of microphones integrated into the vehicle interior. The signals from these microphones are sent to a DSP for analysis. The DSP works out the frequency response of the sound from the microphones, then sends a signal with the opposite polarity to the audio system amplifier. When this new signal mixes with the road, exhaust, and wind noise in the car, it cancels. Again, the system is much more complex as timing is crucial to making this work. The result is a vehicle that’s quieter to drive, and that doesn’t incur weight penalties from massive amounts of sound deadening. Adding weight reduces fuel economy.

This same noise-canceling technology is used in headphones and earbuds.

DSP Features Improve Audio and Listening Experiences

We’ll step back to our discussion about car audio DSP features. Not all processors have all the technologies we’ve mentioned. Some solutions might use a chip that costs $5, while others might be $30. Every function added to a DSP increases the amount of memory required. As such, you might find that some inexpensive solutions have limited equalizer bands, whereas others have more than you might ever use. Further, you can’t just call a car audio company and say, “I know the Analog Devices chip can do this. Can you add this feature?” Having been on the other end of that, I guarantee it won’t happen quickly, if ever. It takes exponentially more time to develop and test the software than you can imagine. Even small changes require extensive lab and field testing. However, the lack of a feature is often attributable to parts costs and the coinciding lack of memory, or the fact that the company doesn’t develop their DSP in-house.

With that said, if your DSP has an upmixer for a center channel, bass restoration, automatic equalization, an RTA display, stereo width expansion or a whole slew of other features, you can thank the impressive processing power of modern digital signal processors.

Upgrade Your Car Audio System with a DSP, Today!

Digital signal processors are everywhere these days, often in devices we think are much simpler than they actually are. We hope learning about how digital signal processors work in general terms has been enlightening. If you are looking for a way to improve the performance of your car audio system, drop by a local specialist mobile enhancement retailer and ask them about adding a DSP to your audio system. Assuming the system is designed, integrated, configured and calibrated properly, the DSP upgrade will be stunning!

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