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A Detailed Look at the Speaker and Subwoofer Xmax Specification

Speaker Xmax

For car audio enthusiasts who’ve invested time studying the Thiele/Small parameters of speakers and subwoofers, you’ll know there is a specification called Xmax. This variable, typically expressed in millimeters or inches, is intended to describe the one-way excursion capability of the driver. Put another way, it’s the distance the cone can move forward or rearward from its rest position before distortion overwhelms the signal being produced.

Mechanical Xmax Calculations

The simplest way to calculate the Xmax specification is to subtract the thickness of the top plate from the height of the voice coil winding and divide it by two. This calculation describes how far the woofer (or midrange or subwoofer) cone can move forward while keeping the voice coil inside the magnetic gap. If and when the coil attempts to move out of the gap (determined by the thickness of the top plate), the strength of the magnetic field is dramatically reduced and the output of the speaker becomes non-linear. If the audio signal being produced by the speaker isn’t the same as the signal sent from the amplifier, significant distortion is being added to the signal, and your music won’t sound right.

Speaker Xmax
The parts of a Hertz MP 300 D4.3 PRO subwoofer.
Speaker Xmax
The Rockford Fosgate T2S1-13 Power T2 Series subwoofer has an Xmax specification of 34 mm in each direction and is rated for 2,000 watts RMS.
Speaker Xmax
The Hertz ML 2500.3 Legend is a sound-quality subwoofer rated at 700 watts and features an Xmax of 17 mm.
Speaker Xmax
The Black 12 subwoofers from ARC Audio offer amazing output and low-frequency extension with an Xmax of 16 mm and 500 Wrms power handling.

It’s worth having a baseline for values that are considered normal and impressive in terms of Xmax. Tweeters seldom have an Xmax specification, but that doesn’t mean it’s not a value that can be calculated. For example, a linear excursion of plus or minus 0.2 mm (0.0079 inch) would be an excellent specification for a tweeter. For a small 3- or 4-inch midrange driver, an Xmax of plus and minus 2 mm would be good, and greater than 4 mm would be excellent. For a 6.5-inch mid-woofer intended for a door speaker application, an Xmax value of 4 mm would be good, and anything above 8 mm would be exceptional.

Subwoofer excursion capability increases dramatically as the price of a driver increases. For entry-level 10- and 12-inch subwoofers, rated for 300 to 450 watts, an Xmax of 10 to 12 mm is good. Stepping up to mid-level woofers with power ratings between 500 and 600 watts typically results in the Xmax spec jumping up to 14 or 16 mm in each direction. The cream of the crop in subwoofers offer Xmax capabilities beyond 18 mm, with some drivers capable of more than 24.5 mm (1 inch) of excursion in each direction. Shallow-mount subwoofers typically scale these values down a bit, with mid-level drivers capable of 8 to 10 mm of excursion and premium solutions capable of more than 15 millimeters.

Speaker Xmax
An example of a driver with the cone and voice coil at rest position.
Speaker Xmax
The Sony Mobile ES XS-W104ES 10-inch subwoofer has an Xmax of 6.5 mm and is rated for 450 watts per the CTA-2031 standard.
Speaker Xmax
The Helix Q 10W is a 750-watt subwoofer with an Xmax of 14 mm.

Those who care less about sound quality and are interested only in achieving maximum sound pressure levels can continue to increase the power to a speaker beyond the Xmax value. In this scenario, peak SPL measurements are typically all that matter, so sound quality and accuracy take a back seat.

Xmax Isn’t Always a Calculation

A second way to specify the Xmax parameter involves using acoustic test equipment and laser-based cone excursion measurement. Using this method, a signal is fed to the driver being tested at an increasing level until the speaker’s output reaches a distortion level of 10%. These performance-based measurements are crucial as they take into account non-linearities caused by limits in the compliance of the speaker’s suspension components.

For example, if a driver has a 16 mm top plate and a 32 mm voice coil height, the calculated Xmax would be 8 mm. Suppose the surround on the driver is very narrow or stiff and starts to limit cone travel at an excursion level of 5 mm. Once again, the output audio signal won’t replicate the signal from the amplifier, and significant harmonic and intermodulation distortion will be added to the output. The speaker also won’t play any louder. The surround or the spider can cause compliance-based excursion limiting, and these characteristics are usually the limiting factors in how loudly a speaker or subwoofer can play. In the car audio industry, very few manufacturers use the Xmax+10% specification method as investing in the test equipment is very expensive.

Speaker Xmax
A subwoofer at its maximum linear forward position. Note that the bottom of the voice coil winding is flush with the bottom of the top plate.

Though it isn’t as common as it was years ago, another mechanical measurement affects how loudly a speaker can play. If the bottom of the voice coil former runs into the bottom plate of a speaker, you’ll hear a very sharp snapping sound. Of course, this limits excursion and can damage the former very quickly. This situation happens when the suspension components aren’t stiff enough or if the driver is designed to be extremely shallow and there isn’t adequate space at the bottom of the driver.

Speaker Xmax
A subwoofer at its maximum rearward position. Note that the top of the voice coil winding is flush with the top of the top plate.

One Last Thought on Xmax Specifications

If you’re shopping for a subwoofer, the Xmax spec isn’t the be-all, end-all in determining how loudly the subwoofer system will play. The way the driver interacts with the enclosure plays a huge role in determining the audio system’s effective efficiency and low-frequency extension. Check out our articles on speaker specifications and subwoofer enclosure designs for more insight into this topic.

When it’s time to choose the right subwoofer for your car or truck, drop by your local specialty mobile enhancement retailer and talk with them about your expectations and the speakers and subwoofers that are the best for your application. Be sure to audition one of their demo vehicles to see if the subwoofer solution meets your performance goals.

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.

Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

A Close Look at Class-D Car Audio Amplifier Efficiency

Class-D Efficiency

For car audio enthusiasts, especially those interested in competing in SPL competitions, amplifier efficiency should be one of their primary concerns. In this first of three articles on efficiency, we take a close look at the Rockford Fosgate M5-1000X1 Class-D subwoofer amp and analyze how well it makes use of power at different output levels.

What Is Car Audio Subwoofer Amp Efficiency?

In the case of car audio amplifiers, or this specific analysis of a Class-D subwoofer amp, some of the voltage and current from your alternator and battery are converted into heat. This is wasted energy. Don’t fret, and it happens with every electronic device – even if the heat produced is minuscule.

When we talk about efficiency, we look at how much power is sent to the load (speakers) compared to how much is consumed by the amplifier. We set up the Rockford Fosgate M5-1000X1 that Dave MacKinnon reviewed for BestCarAudio.com in early 2021 on the bench. First, we used our D’Amore Engineering AMM-1 to confirm that we had a 1.0-ohm resistive load. Next, we measured output voltage, input voltage and input current at 60 points between idle and an output level of 800 watts where the CLEAN circuit put the amp into protection.

Class-D Efficiency
Efficiency of the Rockford Fosgate M5-1000X1 relative to 800 watts of output in 1 ohm.

A few things to note. The amplifier idles at about 1.5 amps of current. That’s the power it takes to drive the circuitry without the amp producing any power. At output levels below about 1 watt, this idle current significantly outweighs the current required to deliver power to the speaker. As such, the efficiency in this range is well under 5%.

If you analyze the graph above, you can see that the efficiency increases very quickly to over 70% by the time the amplifier produces 140 watts. At this level, the current draw is 17.45 amps. Beyond that, efficiency increases to a maximum of 76% while delivering 400 watts. The current draw at that level is 49.78 amps.

Graphs like this have been floating around the car audio industry for many years and are often combined with a graph of a Class-AB amplifier to highlight the efficiency benefits of the Class-D design. One problem with this way of looking at the data is that the power delivery scale is linear. In the real world of reproducing audio, we know that we need to double the power to a speaker every time we want to increase the output by 3 dB. That’s a logarithmic requirement. Let’s analyze this same data with the percentage of maximum power on a logarithmic scale.

Class-D Efficiency
Efficiency of the Rockford Fosgate M5-1000X1 relative to 800 watts of output in 1 ohm – logarithmic power scale.

Suddenly, our amplifier doesn’t look quite as efficient. The numbers haven’t changed, though; it’s just the way we’re analyzing them. You may only need 5 or 10 watts to drive your subwoofer at very low volume levels. At these levels, the amplifier wastes a LOT of power as heat. The efficiency in this range is only 18 to 27%. This means that around a quarter of the power going into the amp is going to your speakers; the rest is running the amplifier’s signal processing and is being converted to heat.

How Manufacturers Specify Efficiency

When you’re looking at amplifier efficiency specifications, the odds are very good that they’ve been taken with the amp at full power. In almost every case, this is the level at which a Class-D amplifier makes the best use of the power it’s drawing from your electrical system.

What matters much more in the real world is what the amp is doing at 10% or 25% of its rated output. This is where 95% of users spend most of their time listening to music. More efficiency in this range means less draw on the electrical system. Efficiency is paramount for marine applications where we might be running on batteries for several hours. It’s not uncommon to find one amplifier that draws half as much current to produce the same output as another model with worse efficiency, especially when the amplifier is loaded down.

Efficiency and Load Impedance

One last item we’ll look at is efficiency versus the current required to produce power in the load. It would be impossible to count the number of times we’ve heard someone suggest loading an amp down with additional speakers or the use of lower impedance speakers to produce more power. If the power supply in the amp can deliver the current, sure, you get more. The question is, is there a cost to this power? Let’s see how our test amp behaves in terms of efficiency when driving a 2-ohm load.

Class-D Efficiency
A comparison of amplifier efficiency: 1-ohm load, blue; 2-ohm load, red.

As you can see, the amp makes better use of power when connected to a 2-ohm load. The peak efficiency is up to 84.7% at an output level of 691 watts, with the amp drawing 58.1 amps of current. Compare that to the 1-ohm load, and the amp was drawing 71.5 amps to make the same power. Those extra 13 amps of current are wasted as heat.

It’s also worth noting that the amp produced more power in this 2-ohm load configuration before the CLEAN output distortion indicator was illuminated. Instead of 800.3 watts, it produced 865.3 watts. That’s 8.1% more power, for free, with less current draw and less heat. Sooo … if the amplifier you’ve chosen is rated to produce the same or even remotely similar power levels into 2- and 1-ohm loads, please don’t load it down.

Does Amplifier Temperature Effect Efficiency?

While we had the Rockford back on the bench, we took one more set of measurements. We wanted to know if the amplifier would become less efficient as it got hotter. Now, it’s crucial to keep in mind that this particular test will be specific to this amplifier from this company. There’s no way to predict if other designs work the same way. So we started the 2-ohm testing with the amplifier’s heat sink at 19 degrees Celsius and measured its efficiency. Then, we repeated the measurements as the temperature rose to 45, 50, 55 and 60 degrees. We’d have gone farther, but our load resistors were starting to make some strange crackling noises.

Class-D Efficiency
Amplifier efficiency versus chassis temperature.

If someone had asked us to predict how the amp would behave, we’d have put all our chips on predicting that efficiency would decrease as the amp heated up. It only makes sense as wires, components and traces on the circuit board would increase resistance with temperature. The findings are very interesting and say a lot about the work the designers at Rockford Fosgate put into their products.

With Great Power Comes Increased Efficiency

There are three takeaways from this experiment. First, if you need a small amplifier for your midrange speakers or tweeters, choose one that only makes as much power as you need. A 150-watt amp is overkill when you’ll only use 10 or maybe 20 watts on a midrange driver. Second, if you compete in SPL competitions, choose a speaker load impedance that balances power production with amplifier efficiency. You may be throwing away power in the form of heat by loading your amplifiers down too much. If the limiting factor in your audio system is the ability to feed the amp, choosing the most efficient solution is crucial.

Last and certainly not least, amplifier efficiency depends on output level. Our testing shows that efficiency increases as power output approaches the rated output level when it comes to name-brand Class-D car audio amplifiers. Posting a single value on a website or in a brochure (do companies still make brochures?) doesn’t tell you much about the design or how efficient the amp will be when used at low power levels.

When it comes time to shop for an amplifier for your car or truck, drop by a local specialty mobile enhancement retailer and talk with them about the options for your vehicle. They’ll help you choose the right solution and integrate it into your vehicle so that it sounds excellent and functions reliably for many decades.

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.

Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

Do All Car Audio Amplifiers Double Their Power When Loaded Down?

Double Amplifier Power

If you’ve been around the car audio scene for a few decades, then you’ll recall a time when almost all amplifiers doubled their output power when the load impedance was halved. For example, an amplifier might have been rated to produce 75 watts per channel into a 4-ohm load and 150 watts into a 2-ohm load. It wasn’t unheard of to see low-power amplifiers like the infamous Orion 225 HCCA continue to double their power, right down to 0.5 ohms per channel. Do modern amplifiers behave like this? If not, why?

Making Power from an Amplifier

Let’s start with the basics. Your amplifier is designed to boost the voltage of the signal coming from your radio. By way of an example, let’s say you have a 1-volt RMS signal and you want the amplifier to produce 50 watts of power into a 4-ohm load. The signal would need to be increased to 14.14 volts out of the amp. That’s a signal gain of just over 5 decibels.

Because car audio speakers have a relatively low voice coil impedance (4 ohms), the amplifier will also deliver a significant amount of current to the speaker. In our 50-watt, 4-ohm example, the current flowing through the speaker is 3.536 amps.

One last piece of math. We’ll call this hypothetical amplifier a Class-D design and say that it has an overall efficiency of 80% when driving 4-ohm speakers. To produce 200 watts of power, the amp will need to consume 250 watts of power from the vehicle electrical system. If there’s 13.5 volts at the amplifier power terminals, it will draw 18.52 amps of current from the alternator and battery.

Double Amplifier Power
Power, current and voltage measurements for our 200-watt, four-channel amplifier scenario.

Old-School Amps Were Huge

Back in the day, nobody cared if a 200-watt amplifier was 20 inches long, 12 inches wide and had to be mounted in the trunk. Today, installers want that power from a package that will fit behind the radio or under a seat. Why does the size of the amplifier matter? Well, in order for it to function reliably, the heat sink needs to be large enough to keep the amplifier cool while it produces full power. In this case, our amp needs to shed 50 watts of heat. This number is the difference between the 250 watts it consumes and the 200 watts it delivers to the speakers. Dissipating 50 watts isn’t a significant issue.

Double Amplifier Power
The compact KS125.2 BX2 amplifier produces 70 watts per channel into 4 ohms and 125 watts when loaded to 2 ohms.
Double Amplifier Power
The Sony XM-S400D is rated to produce 45 watts per channel into 2- and 4-ohm loads to ensure reliable operation.
Double Amplifier Power
The four-channel, DSP-equipped Audison AP 4.9 bit produces 70 watts per channel at 4 ohms and 130 watts at 2 ohms.
Double Amplifier Power
The Punch Boosted Rail-Series PBR300X2 amplifier delivers 150 watts per channel into 2 ohms and 100 watts per channel into 4 ohms.
Double Amplifier Power
The DSP-equipped M Four DSP from Helix produces 100 watts per channel into 2- and 4-ohm loads.

Let’s add a second speaker to each channel of the amplifier so that we have a net load impedance of 2 ohms. The amplifier will still attempt to produce 14.14 volts on each output, but it will now flow 5 amps of current to each pair of speakers. We’re up to a total output current of 20 amps from our 14.14 amp draw at 4 ohms. When you load an amp down, its efficiency drops. Let’s say this Class-D amp offers 72% efficiency when driving 2-ohm loads. If the amp is to produce 50 watts to each of the eight speakers (400 watts), it needs to draw 555.6 watts from the car. At 13.5 volts, that would entail 41.15 amps of current flowing into the amplifier. The heat sink will need to dissipate 155.6 watts of thermal energy. That’s a LOT of heat.

Double Amplifier Power
Power, current and voltage measurements for our 400-watt, four-channel amplifier scenario.

When designing this amplifier, the engineer will need to come up with a way for it to manage this 155.6 watts of heat without allowing the components inside the amp to overheat. If the amp has to be very small, this might be a significant problem. Large heatsinks help radiate thermal energy into the air that surrounds the amplifier. Another cooling method is to add a fan to the amplifier design. Fans can dramatically reduce the size of an amplifier and help ensure that they run at cool temperatures. If you choose an amp with a fan, make sure it flows air across the heatsink where the output and switching devices are located. Blowing air into the middle of a circuit board does almost nothing.

The last option, and one that has become quite common, is to limit the amount of current the power supply will pass. Limiting current directly limits the amount of heat energy the heatsink needs to manage. Let’s reverse-engineer how much power our amplifier can produce if we limit the heat sink’s thermal capabilities to 120 watts.

If the energy wasted by the amp is 120 watts at an efficiency of 72%, then the total power it can consume is 430 watts, with 310 watts going to the speakers. In this scenario, each channel is producing 77.5 watts of power and each of the eight speakers would be receiving 38.75 watts when everything running at its maximum output capability.

Double Amplifier Power

Is There Anything Wrong with Current-Limited Amplifiers?

As we’ve demonstrated, limiting current controls the maximum amount of power an amplifier can produce in order to ensure that it doesn’t overheat when pushed to its limits. Are there any drawbacks to a design like this? Not really. Simply, you don’t get as much power when you load the amplifier outputs down further. This design decision isn’t directly detrimental to sound quality, distortion or the addition of noise to the audio signal.

If you’re shopping for an amplifier for your vehicle, drop by your local specialty mobile enhancement retailer and ask them about the best solution for your system design and budget.

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.

Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

Car Audio Myths – You Can’t Ground a Car Audio Amplifier to the Battery

Battery Ground

It’s time to dispel another unsubstantiated car audio myth! This time, we’re talking about claiming that you can’t ground an amplifier directly to the battery in a vehicle. Perhaps it would add to the clarity of the statement to say that many inexperienced installers think the ground wire for the amp has to go to the chassis of the vehicle. Many of these statements also add, “Connecting directly to the battery will cause noise.” All of these statements are nonsense. Let’s check them out.

How Electricity Flows

Whether you subscribe to the conventional current theory that electricity flows from the positive side of a power source through a load and back to the negative terminal, or to the electron theory that holds that electrons flow from negative to positive, what matters is that an electrical circuit is a loop. Your load, be it a light bulb, radio or amplifier, needs to have two electrical connections. Power flows from the electrical source through the load and back to the source again. The current in both conductors is equal.

Our vehicles have two power sources: the battery and the alternator. The battery is there to start the vehicle. It feeds a high-torque electric motor that spins the engine when you turn the ignition key to start. Once the engine starts, the alternator takes over the operation of the vehicle. Technically, you can remove the battery from the car and it will continue to run. Don’t try this, though, as many new vehicles monitor current flow in and out of the battery to control the alternator’s function. Once the engine is running, the alternator recharges the battery.

Battery Ground
Your installer needs to know how to work with battery ground connections that include a current sensor.

Having an Amplifier Installed in Your Vehicle

In the “good old days,” installing an amplifier in a car or truck involved having your installer run a large-gauge wire from the battery’s positive terminal through a fuse holder or circuit breaker to the positive terminal of the amplifier. The wire from the amplifier’s ground terminal would be bolted to the chassis of the vehicle.

Until about a decade ago, most cars and trucks were built with steel, and the chassis or unibody components were spot-welded together. As a result, there was often enough surface area to allow current to flow from the ground of the amp back to the negative terminal of the battery or alternator.

What’s Wrong with a Chassis Ground?

A few things could go wrong when using the chassis as a ground point for a high-power amplifier. First, the connection to the chassis needs to be secure and reliable. Second, your installer needs to brush or grind away any paint, rustproofing or undercoating from the metal before they drill a hole to make the connection. Third, the chassis may not be a direct electrical return path to the battery.

Battery Ground
The JL Jeep Wrangler body features steel, aluminum, magnesium, Quiet Steel and glass-fiber reinforced polyester panel construction to save weight and reduce noise.

The ground connection needs to be secure. Because the cable is of a reasonably large gauge, it can experience moderate loads during acceleration and braking and from the vibrations associated with regular driving. This stress can loosen the connection and cause intermittent behavior or damage.

You’d think removing paint, primer and coatings would be easy, but the number of poor grounds we see is amazing. In some cases, especially with cars that are painted silver, some primers and corrosion-resistant coatings can look similar to bare metal.

In many modern vehicles, lighter metals such as aluminum are used in vehicle construction. These materials don’t conduct as well as steel. What’s more concerning is that many new vehicles are assembled with high-strength adhesives and even two-sided tapes from companies like 3M, Dow Chemical and Henkel. These materials are not electrically conductive.

Battery Ground
More than 121 feet of adhesive is used to assemble the 2019 Acura RDX. Image: Acura

Ohm’s Law in 20 Seconds

Whenever current flows through a device or conductor with resistance, a voltage is produced across that device. In the case of a piece of wire, the resistance is typically low, so very little voltage is wasted. When the current flow is significant, we can see several volts across the wire, and it will heat up. To calculate the voltage drop across a resistance, multiply the current flow (in amps) by the total resistance of the device (ohms). For example, 2 amps of current flowing through a 4-ohm resistor results in 8 volts being produced across that resistor.

Proper Amplifier Grounding

Feeding your high-performance amplifier with the power it needs means delivering as much voltage as possible to the power terminals. If the amplifier draws a significant amount of current, then your installer will need to use large-gauge conductors to prevent voltage losses due to the resistance in those conductors. This same logic applies to the ground return path. A test performed several decades ago by one of the engineers at JL Audio in Miramar, Florida, showed that most vehicle chassis have a resistance equivalent to a piece of four AWG cable. Modern vehicles are much worse.

Let’s say you have a good quality 1,400-watt amplifier like the ARC Audio ARC1000.4 DSP we tested a few months ago. This amp produced 1,406 watts of power (at 1% distortion) when provided with 13.37 volts at the power terminals. It drew 137.1 amps of current to deliver this power (at an impressive 76.7% efficiency). If your vehicle had a 16-foot run of all-copper, CTA-2015 compliant, four-AWG power cable to feed the amp, there would be a voltage drop of 0.588 volts across the length power cable. The ground return path (assuming it has the same resistance) would result in a similar loss of voltage at this current level. Your electrical system would need to be able to supply the battery with 14.546 volts and have a spare 137 amps of current capacity available. For a full-sized sedan or truck, these numbers are quite reasonable. So, you might be able to get away with using the chassis as a ground – if you know it’s all-steel from front to back.

Battery Ground
Assuming all four-gauge power is the same size is, sadly, a bad idea. Smaller wire has more resistance and wastes energy.

When Grounding Goes Wrong

Now, what happens when we run into a vehicle where the chassis isn’t a good ground? Perhaps it only has the current-carrying capacity of a piece of 12-AWG wire. At low to moderate volume levels, our amplifier won’t draw much current. If the amp is a modern Class-D design, it will likely have a driver IC that includes low-voltage support for start-stop vehicles. If so, the amp won’t shut off even if the voltage drops below 6 volts for a moment.

Let’s run the math again. We want about 1,400 watts and will attempt to draw 137 amps of current. With a chassis with the current-carrying capacity of a 12-AWG conductor, 3.74 volts would be lost across our chassis connection. The amp will likely stay on, but it certainly isn’t going to produce 1,400 watts when it only sees 10.8 volts. In our experience, aluminum and bonded-construction chassis have even more resistance, and the voltage drops are significantly worse.

The Parallel Ground

Going back to the testing done by the folks at JL Audio, they propose that your installer run what they refer to as a parallel ground. The installer can bolt the ground lead from the amp to the chassis, then run a conductor of the same size as the power leads to the battery’s negative terminal.

In this scenario, the worst-case condition is that the new ground wire carries all the current from the amp, and you have a minimal voltage drop. More likely, some current will also flow through the chassis to the battery, and this results in less voltage being wasted than if it wasn’t grounded at the rear of the vehicle.

Stop The Noise

We can’t fathom where the myth about grounding to a battery and getting noise came from. Perhaps there was an installation that had a ground loop of some sort. Ground loops can (and do) happen when the chassis is used for grounding.

Let’s dispel this myth with one sentence. Think of all the marine audio systems and stereos in Corvettes that you’ve seen over the years. Fiberglass certainly can’t be used as a ground return path. These vehicles don’t have any noise problems associated with how power is distributed.

Battery Ground
Car audio amplifiers installed in Corvettes require a ground wire to be run directly to the negative terminal of the battery.

When it comes time to have an amplifier installed in your vehicle, you can improve its efficiency by providing it with as much voltage as possible. This means minimizing voltage losses due to power cable or ground return path resistance. Upgrading to larger or better wiring and having the installer at your local specialty mobile enhancement retailer run a parallel ground is a great way to ensure that your system will function reliably.

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.

Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

Even the Simplest Car Audio Systems Need DSP Calibration

Car Audio DSP

Every professional audio system installation, be it for a church, dance club, home theater or your car, requires DSP calibration. Your smartphone, laptop and smart speaker use digital signal processors to optimize the sound you hear from the tiny speakers. Digital signal processors aren’t magic, and they aren’t complicated. They offer a reliable and straightforward way to calibrate what you hear so that voices and instruments sound the best they can.

Signal Processing in Car Audio Systems

If you look at any radio in the dash of a car or truck, you’ll see it has bass and treble controls. The treble control adjustment lets you fine-tune the output of high frequencies to calm speakers that are bright or add some sizzle when things seem dull. The bass control is often used when the speakers in an audio system don’t produce enough bass on their own. While this can lead to the addition of a lot of distortion if the volume is turned up, it remains a popular tweak. Nobody hesitates to adjust these controls when they get a new radio.

Even if you’ve chosen the very best speakers on the planet and had them installed in optimum locations in your vehicle, the confines of the car or truck itself wreak havoc on what you hear. Reflections from the windshield and side windows, the floor, roof, seats and dash all combine at the listening position to dramatically change the perceived frequency response of the audio system. It’s not abnormal to see peaks and dips of more than 20 dB across the usable audio range. Left uncorrected, these variations in frequency response detract from the realism of your audio system.

Car Audio DSP
Our friend Paul Bennet shared this photo of the frequency response in this car before tuning.
Car Audio DSP
The results of some fine-tuning with a DSP show a smooth frequency response that sounds absolutely amazing.

For about 15 years, vehicle manufacturers have used amplifiers that include electronic crossovers and multi-band equalizers to fine-tune the audio systems they deliver to customers. Even with inexpensive speakers, these systems offer smooth frequency response. However, they may still not have enough bass or play loudly enough, which is why there’s an aftermarket car audio industry.

Car Audio DSP
The DSR1 is an eight-channel DSP that includes factory audio system integration features powered by the iDatalink Maestro.
Car Audio DSP
The PSM from ARC Audio, with six inputs and six outputs, is compact enough to fit behind your radio or in the fairing of a motorcycle.

What Is a Car Audio DSP?

A car audio DSP is nothing more than a set of very accurate multi-band equalizers, adjustable electronic crossovers and signal delay processors in a single compact and efficient package. Unlike the bass and treble controls on your radio, these equalizers have as many as 40 bands of adjustment available to let your installer fine-tune the speakers’ output accurately across the entire audio frequency range. If there’s a peak at 1 kHz, it can be tamed. If there’s a dip at 350 Hz, it can be boosted.

The crossovers in a DSP are part of setting up your audio system. You don’t want deep bass to be sent to your door speakers if you have a subwoofer in the system, right? Your installer will set filters that ensure that only the correct information is sent to each speaker in the system. When done properly, each speaker will sound better and be able to play louder.

Signal delays are a tricky subject. In essence, they are used to compensate for different path lengths between the speaker installation location and the listening position. How these delays are configured depends on the goals of the system. If there will only ever be one person in the car, then everything can be set relative to the driver’s listening position. If the system is designed such that everyone in the car needs to be able to enjoy the music, then the settings change dramatically. Let the product specialist and installer at the shop you’re working with know your expectations before they design your audio system.

Car Audio DSP
The bit Ten from Audison has five outputs and includes processing to undo the equalization built into many factory-installed amps and source units.
Car Audio DSP
The AXDSP-X from Axxess Integrate has 10 channels of output and includes equalization, crossovers and signal delay adjustments.

The Right Tools for the Job

Two tools are an absolute necessity for setting up a car audio digital signal processor: a real-time audio analyzer and a way to measure path lengths between speakers. An RTA is a sound-level meter that shows the volume or output of an audio system at different frequencies. For example, your installer will be able to see how loud 1,000 Hz is relative to 800 Hz and 1250 Hz. Most RTAs divide the audio spectrum into 30 or 31 bands. This is called a 1/3-octave RTA. There are 10 octaves between 20 Hz and 20 kHz, so we have three measurements in each octave. It’s impossible to calibrate a DSP efficiently and accurately without an RTA.

You can download an RTA application for your smartphone if you want to see how they work. With that said, to set up an audio system, a microphone with a flat audio response from 20 Hz to 20 kHz is required. In short, don’t use your smartphone to try to adjust a DSP.

Your installer will also need a way to measure path lengths. Across the industry, installers use a multitude of DSP calibration processes. Some folks use a tape measure, while others use impulse audio tracks. As long as their process is repeatable and predictable, you’re in good hands.

Car Audio DSP
The DSP Mini from Helix offers four inputs and six outputs along with features like StageXpander and Augmented Bass Processing to improve the performance of your car stereo.
Car Audio DSP
The TwK-88 from JL Audio has eight inputs, eight outputs and a full suite of adjustments that allow your installer to configure and calibrate your car audio system.
Car Audio DSP
The H8 DSP from Hertz is the perfect upgrade for a system with a subwoofer, front and rear speakers that’s fed from a factory-installed source unit.

What Is a Simple Car Audio System?

We titled this article the way we did because many audio enthusiasts believe that including a DSP in an audio system is reserved only for the fanciest and most elaborate designs. The truth is, if you have a set of speakers in your car, your system is a candidate for proper calibration. In addition, if you add a subwoofer, then there’s even more reason to include one in your audio system upgrade.

Years ago, processors were expensive. Now, options from companies like Rockford Fosgate, ARC Audio, Audison, Axxess and many others are quite affordable. When you factor in the cost of the DSP, an hour or so of labor and a few extra RCA cables, this single component offers the most significant and cost-effective upgrade you can make to improve the performance of your car audio system. So drop by your local specialty mobile enhancement retailer today and ask to audition a car audio system that’s been calibrated with a DSP. We expect you’ll be impressed.

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.

Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

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