A digital signal processor, or at the very least some type of equalizer, is pretty much a requirement when it comes to creating a car audio system that will have realistic tonal balance. There are dozens of methods to configure and tune these processors, and each has benefits and drawbacks. What seems to be an ongoing issue is the need to have someone with the proper training and tools execute the process. The so-called “Golden Ears” method doesn’t work. This article will look at some of the expertise required to complete this process, along with the equipment necessary to deliver accurate and reliable results.

Is It Tuning?

Describing the process of setting up a digital signal processor for a car has long been described as tuning. While technically correct, this term carries the implication that it’s an art form rather than a process. We think a better word to describe the process is calibration. The technician working on your car will take a measurement, perform an adjustment and repeat the process until the final goals are achieved. This process doesn’t require a unique skill set but does require proper tools and training.

The Engine Management System Analogy

If you’re into cars or trucks, then you’ve likely seen the thousands of options available to set up an electronic ignition and fuel injection system for a modern vehicle. At the most basic level, ignition timing and fuel delivery maps are required to let the engine know how much gas to squirt into the cylinders and when to fire the spark plugs. These three-dimensional tables aren’t much different from the signal delay, output level and equalization settings in a car audio DSP.

Start with the Basics

If you buy a stand-alone engine management computer for a project car, something like an AEM Infinity or Holley Terminator X, the starting point is to tell the system what it will be controlling. Your technician needs to set up the crank position sensor and confirm that it’s reading the true mechanical top-dead-center of your engine. Next, they’ll need to configure fuel injector information to let the computer know how much fuel they can flow. They will also need to set up any O2 sensors and a MAP sensor. If there are fuel and oil pressure, temperature, cam position and throttle position sensors, the list goes on and on. The tech will need to understand the calibration of each of these sensors and enter that into the software long before he or she tries to start the engine for the first time.

On a DSP, your mobile enhancement technician needs to set up the signal inputs and configure how those will be routed to the channels of the processor. Next, they have to set crossovers for each channel based on the speakers in the vehicle. This requires an understanding of the speakers’ capabilities, where they are installed and what drivers are being used in adjacent frequencies. They also need to understand what type of crossovers to use to deliver the smoothest frequency response while protecting the speaker from damage. On the latter, how loudly the system will be played has a significant role in setting filter frequencies.

The technician can now move to set signal delays. Whether they use a tape measure or an acoustic technique using impulse tones, these settings need to be close to right before the frequency response calibration process starts.

System Calibration Ensures Accurate Performance

Once the engine is up and running, it’s time to start making measurements and adjusting the fuel and timing tables. The engine or vehicle will need to be installed on a dynamometer to provide the engine with different loads at different speeds. The technician will work through the fuel map while reading from one of several wide-band oxygen sensors to calibrate the amount of fuel the injectors feed into the engine. At the same time, the ignition timing needs to be adjusted for a similar table to tell the spark plugs when to fire in each revolution of the engine. Getting these settings right works in conjunction with fuel delivery, as firing the spark plug at the wrong time might result in not all the fuel being burned. Too much timing or too much ignition advance can damage the engine. The technician will monitor power production in each table cell (engine speed versus load) to optimize the system.

Back to our audio example, once the system is up and playing, the technician will use a calibrated audio analyzer to examine the frequency response of each channel in the audio system. Again, they are looking to ensure that reflections and resonances caused by the vehicle interior haven’t changed the sound at the listening position.

Since it always happens, they use graphic or parametric equalization to compensate for these changes. But, just as with the engine management system, too much adjustment can also lead to speaker damage. Likewise, the technician needs to examine and fine-tune the interaction between speakers running in adjacent frequency ranges or on the other side of the vehicle. Those with the tools and training to do so will also measure the phase response of the system to further fine-tune the calibration. Properly configured phase response is part of what helps to produce “up front bass” in an audio system with a subwoofer in the cargo area or behind a seat.

Calibration Equipment is Crucial

You’ll note investment in equipment is required to complete either calibration process. On the engine side, a wide-band oxygen sensor and a dynamometer are necessary to evaluate how each change to fuel delivery and timing affects the engine’s performance.

A calibrated real-time analyzer and appropriate test tones are the primary tools on the audio side. In addition, an audio analysis system that includes a time-referenced measurement is necessary for more advanced tuning with phase evaluation.

What if someone tries to calibrate either system without these tools? Is the infamous “butt dyno” going to be able to pick out a deficiency in a particular cell of a fuel or timing map? Would ¼-mile timeslips let them know if day-to-day drivability is smooth? Tools are a necessity to ensure proper optimization.

Is It Right or Wrong?

In an engine management system, lack of optimization might reduce the maximum power that the engine can produce and reduce fuel efficiency. If it’s too far out of what’s ideal, the engine can overheat, or in the other direction, pre-detonation or knock might occur that can damage a piston. Ideally, the engine should run smoothly and deliver excellent power and fuel economy at all load conditions

If things aren’t configured properly in a car audio system, there is a chance that a speaker or number of speakers could be damaged by overdriving them. In most cases, the audio system won’t sound right. For example, voices might not sound realistic. They might be too bright or have too much bass information. If the delay and level settings aren’t correct, vocals and instruments may sound as if they are coming from the incorrect location on the soundstage, the sounds might be blurred, or there may not be a soundstage at all.

Choose an Expert to Calibrate Your Car Audio System

Just as you wouldn’t let an amateur calibrate a high-performance race car engine, it’s paramount that you choose a technician with the experience and tools required to design, integrate, configure and calibrate your car audio system. If you choose the wrong shop and technician, you may not get the most from your investment, and the system might not sound impressive. In a worst-case scenario, the speakers could be damaged if you turn up the volume. So make sure you audition several systems the shop has created and make sure they can deliver those same results in your car or truck before you agree to hire them.

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.

Whether it’s Black Friday, Christmas, Back to School or just a regular sale, many car stereo shops around the country offer subwoofer system upgrade packages that let you add bass to your stereo at an affordable price. These packages typically include a 200-300 watt amplifier, a single subwoofer, an enclosure and an installation kit. We’ve noticed a trend in the choice of enclosure included in these systems. We want to offer some advice on an upgrade that will dramatically improve performance and value.

Sealed Versus Ported Subwoofer Enclosures

The goal of these car audio subwoofer upgrade packages is to deliver an affordable way to add bass to your vehicle. As such, the products these systems include are typically chosen based on their price rather than their combined performance. Most options include a 12-inch subwoofer and a sealed enclosure. While this combination works well, it might not offer the best bang for your buck. Let’s look at an example.

Let’s use an ARC Audio X2-Series X2-12D4 12-inch subwoofer as an example. It’s not an entry-level subwoofer compared to some of the low-cost options on the market, but its performance, build quality and capabilities make it worth every penny. The sub is rated to handle 250 watts of power. Let’s model it in a sealed enclosure with a net internal air volume of 1 cubic foot.

As you can see, the response curve is nice and flat. By way of specifications, the system has a Qtc of 0.894 and an F3 frequency of 42 Hz. These numbers are ideal terms of delivering clear and accurate bass.

Less Subwoofer, More Enclosure

What if we switch things up a bit and go with a 10-inch subwoofer in a vented enclosure? This cost of the system might go up a little bit, but is it worth it? Let’s model the 10-inch version of that subwoofer in a vented enclosure with the same net 1-cubic-foot internal air volume. For this simulation, the enclosure has a tuning frequency of 33 Hz.

You’d think we knew what was going to happen before we started writing, wouldn’t you? The 10-inch sub in the vented enclosure is louder at all frequencies between 20 Hz and 75 Hz. How much louder? We made this chart below to show you.

If the two systems’ differences were less than a decibel, the comparison would be a wash. The 10-inch sub in the vented enclosure produces around 3 dB more output from 40 to 50 hertz. This increase in output level is significant.

System Efficiency and Power

Aside from getting more output for a similar investment, there’s another way to look at this. Let’s say you want to listen at a specific volume level. The subwoofer in the vented enclosure can produce that output with less power. This means the amp won’t run as hot, the subwoofer won’t heat up and the amp will draw less current from the vehicle electrical system. We’ll add a power comparison to our graph above to show you just how much less is required for the same output.

In the chart above, we compare the output of the 12-inch driver with 250 watts to the amount of power the 10-inch driver in the vented enclosure requires to produce the same result. At 45 hertz, the requirement is less than half the power. This equates to much less current draw on the electrical system in your car. It also means the voice coil of the subwoofer won’t heat up as much. This reduction in power to the sub can help reduce power compression and further improve the efficiency of the subwoofer system.

If you are wise with your purchasing strategies, you might ask if there are any drawbacks to using a vented enclosure instead of a sealed one. So long as the enclosure has a large enough vent and includes a smooth radius around the vent opening, there aren’t any issues. In addition, you can see that the overall shape of the response curve is similar to that of the sealed design, so the system will sound similar. In all honesty, it’s a win-win situation.

Upgrade Your Car Audio System with a Subwoofer

One of the best upgrades you can make to your car audio system is to add a subwoofer. So drop by a local specialty mobile enhancement retailer today to find out what’s available for your vehicle. If they have a subwoofer system package available, ask about upgrading to a vented enclosure. The improvement in efficiency will be worth every penny.

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 while back we published an article that discussed why aiming speakers in a properly designed car audio system was futile. As usual, we received a good deal of feedback about the piece. The comments ranged from the typical “that’s not how it works” to more scientific discussions about how even minor changes in placement had significant effects on imaging and soundstage position. So let’s dive deeper into this discussion to flesh out some of the finer details in speaker positioning.

Proper Audio System Design

The first thing we need to discuss is proper audio system design and component selection. To deliver the most realistic listening experience possible, you need to choose high-quality speakers. Speakers that add significant distortion will lack clarity and detail and render all other efforts futile. Forget the hype about anti-resonant baskets and fancy cones – the technologies that dramatically reduce distortion are motor upgrades like shorting rings and copper inductance-reducing caps.

Next, the speaker system needs to be designed and integrated into the vehicle in a way that ensures the even distribution of sound through the listening environment. This typically involves using a subwoofer, a set of woofers or midbass drivers, midrange speakers and tweeters. As our article on directivity explained, below a frequency where the effective circumference of the cone is equal to the sound wavelength, the sound is emitted evenly in all directions — as such, tilting a speaker up or down won’t change its perceived frequency. Keep this in mind, as we’ll circle back to it shortly.

Lastly, the speakers need to be chosen so that the high-frequency driver operating in the adjacent frequency range can play low enough to ensure that directivity doesn’t become an issue. Unfortunately, this statement confirms that using a two-way front stage with a 6.5-inch woofer is difficult, as most tweeters bundled in component sets can’t play low enough.

Speaker Placement Matters

When we talk about speaker placement for the front stage of our vehicles, the options are typically a stock location in the lower part of the front door, a location in the middle or upper portion of the door, the dash or in a custom pod on the A-pillar. It should come as no surprise that every location has a benefit and an equal number of drawbacks.

For midbass drivers used in a three-way front stage, the door location often works well. Some will go further with the installation and have custom mounting solutions created in the kick panels. If this driver is going to play up to 400 or 500 Hz, this “farther away” position can help with the perceived depth of the soundstage.

The same concept applies to midrange drivers. If they are installed in the doors, as would be found in many Porsches and BMWs, the soundstage can appear to span the car, but comes from a position that’s in line with the steering wheel. Mounting the speakers in pods on the A-pillars can move that soundstage deeper into the dash. Finally, speaker positions in the corners of the dash, right at the base of the windshield, are about as far away from the listening position as is possible and help to create a soundstage that seems to come from the rear edge of the hood. Some listeners don’t concern themselves with the sound source, while others weigh it heavily in their system design considerations.

The angle at which tweeters are aimed matters. Suppose you want to have any chance of hearing the highest of frequencies. In that case, tweeters need to be aimed toward the listening position or pointed up into the windshield so their output can reflect off the glass and “spray” into the vehicle interior. Tweeters mounted in sail panels can help to increase the perceived width of a soundstage – another consideration in where the music seems to come from.

What About Fine-Tuning Mounting Angles?

Much of the feedback on our article about speaker directivity was targeted at the fact that car audio system performance changed based on the angle at which the speakers were mounted. We don’t dispute this for one second. How a speaker performs in terms of directivity is a constant. How sounds reflect off of nearby surfaces plays a huge role in what we hear, even after setting signal delays and calibrating the system with an equalizer.

Let’s say you have a speaker mounted in an A-pillar, and it’s aimed directly across the vehicle. There will be immediate reflections off the windshield and, a moment later, off the side windows. Given their proximity to the speaker, these reflections may be almost as loud as the sound coming directly from the speaker cone. Another moment later, there may be a reflection off the roof and the dash. Vehicles are very complex and behave differently than a listening room or recording studio.

If we tilt the speaker in or out, up or down, we can change the path lengths from the edge of the speaker to the surfaces off of which the sound will reflect. Even a fraction of an inch will change how the sound these speakers produce interacts with these surfaces.

Let’s Look at An Example

Let’s say you have a Porsche 911 or Boxster with a midrange speaker location in the middle of the door. A number of 2.5- and 3-inch midrange drivers will perform excellently in that location. On the inside of the car, there is almost nothing near the speaker that will cause a significant reflection, other than the smooth surface of the door panel itself. In terms of delivering a predictable performance that won’t require significant equalization, this is as close to an ideal mounting location as is possible in a car or truck.

Is this the perfect location, though? What if you like the sound to appear to come from the windshield or dash of the vehicle, or even out on the hood? Will this speaker location offer that? It isn’t very likely. The soundstage is apt to seem very shallow. Tonally, the system may sound excellent, and the lack of nearby reflections should offer impressive clarity.

If we put those same speakers in small enclosures up on the dash, just as we described above, the sound will reflect off of every surface imaginable. We can make the system sound good with an equalizer, but the interaction of multiple reflections won’t deliver the same amount of clarity.

Balance the Benefits and Drawbacks

The goal of any speaker system design (i.e., the placement and configuration of the drivers in a listening application) requires balancing the benefits and drawbacks of each location. The specialty mobile enhancement retailer you are working with can help explain each location’s benefits and disadvantages. Together, you can choose a solution that will deliver the sonic performance and aesthetics you want from your upgrade.

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.

Have you ever looked at something and thought you were only getting part of the story? Many previous articles have discussed amplifier distortion at length but haven’t delved into how power output levels and frequency affect distortion measurements. If you’re looking for the best amplifier for your car audio system, especially for midrange drivers and tweeters, this information should be crucial to your purchasing decision.

Amplifier Distortion Specifications

If you’re browsing a car audio amplifier manufacturer’s website, you’ll see a single specification that’s intended to quantify the amount of distortion an amplifier adds to the audio signal. The CTA-2006-C standard requires that the total harmonic distortion and noise added to the audio signal be specified at an output level that is 50% of the maximum rated output for the amplifier. Of course, that power rating needs to comply with the CTA-2006-C standard as well.

Measuring Amplifier Distortion

When an amplifier is being tested for distortion, the technician or engineer will typically look at the harmonic information and noise added to a single test tone.

In the measurement above, you can see the test signal at 1 kHz at a level of 2.0 volts. The second harmonic (labelled with the pink 3) is at a level of -77.10 dBV, or 83.15 dB below the 6.03 dBV (2.00V) test signal. The third-order harmonic (labelled with the pink 1) is louder at an absolute level of -68.18 dBV and a relative level of -74.23 dB. You can see the pattern of even and odd harmonics continue well past 20 kHz. It’s worth noting that this is a good Class AB amplifier and not a poorly designed, inexpensive unit.

Sadly, this single specification is quite incomplete in terms of telling the whole story. Audio measurement and analyzer devices like those from Audio Precision and QuantAsylum can generate distortion graphs across a range of power output levels and frequencies. So let’s characterize this amplifier in terms of the amount of distortion it adds to an audio signal based on the amount of power it produces.

Before we dive into analyzing the data, we should explain that the horizontal X-axis scale is in decibel volts, known as dBV. This way of looking at voltage represents the amplifier output level using a decibel scale with 1 volt as 0 dB. Thus, the equation to convert dBV to a voltage is 10 ^ (dBV/20).

The output level of 6.03 dBV, where we measured %THD+N in the first chart, would be 2.00 volts. At the low level, distortion is at 0.075%. At an output level of 22.6 dBV, you can see that the distortion increased. This level is the point where the amplifier started to run into clipping. Maximum power output measurements are specified at the output level that corresponds to a THD+N of 1%. For this amplifier, that would be about 24 dBV, or 63 watts into a 4-ohm load.

At the other end of the scale, you can see that distortion increases as output power decreases. This performance is very typical for a Class-AB amplifier. At very low levels, the harmonic distortion content is buried in the noise created by the amp, which for this unit is at about -105 dBV. Crossover distortion at very low volume levels plays a significant role in adding unwanted information to the audio signal. As the output level increases, the audio signal passes through the transition between the positive and negative output devices at a steeper slope, reducing the time the signal spends in this transition region. As such, distortion decreases relative to the output level.

The CTA-2006 THD+N specification for this amplifier would be 0.02% at the output level of 21 dBV (-3 dB from the maximum power output level). This information doesn’t do a good job of describing how well the amp performs in a real-world application since most of the time, we’re only using a fraction of the power available to drive a speaker. For example, if we have a midrange speaker or a tweeter in a three-way system, we may only need 1/10 to 1/20 of the power a midbass speaker would need, or even less than a subwoofer. Played at high volume levels, a tweeter rarely needs more than a few watts.

So far, in all the TestDriveReview product evaluations we’ve published, the distortion has been specified at the same level as the signal-to-noise ratio. This would be at an output level of 1 watt in a 4-ohm load or 2.00 volts. From now on, we’ll include the Power versus THD+N graphs as shown above so readers can see the entire picture of how the amplifier behaves.

Distortion Versus Frequency Response

Another characteristic often overlooked is the amount of distortion an amplifier adds relative to different frequencies. We ran another test on this amplifier to characterize this. We used an output level of 1.95 volts (very close to our 2.00-volt number) and measured distortion at frequencies from 20 Hz to 20 kHz.

While the numbers don’t vary as much compared to output level changes, you can see that there’s more distortion added at higher frequencies compared to midrange levels.

In an upcoming article, we’ll start all over with a new set of measurements with the three amplifiers we used in the What Do Better Amplifiers Sound Like article a few years ago. We’ll throw in a Class-D amp or two to round out the mix, so you’ll have a benchmark from which to compare solutions.

In the meantime, if you’re interested in purchasing an amplifier for your car or truck, drop by your local specialty mobile enhancement retailer today and ask them about a high-performance solution that will make your music sound amazing!

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.