Not too long ago, we took a look at how speaker-level line output converters worked. We discussed the difference between passive and active devices and explained what features to look for. If you have a vehicle with a premium factory-installed sound system, those interfaces might not be adequate to provide your amplifier with a signal that will sound good with new speakers. So let’s look at some of the intelligent car audio speaker-level interfaces available and why they’re the best choice to upgrade your stereo.

Factory-Installed Audio Systems are Complex

While modern factory-installed sound systems might not use the best speakers and are often limited in power delivery, the signal processing included in them can be pretty complex. Companies like Bose, Panasonic and Harman (the brand behind JBL, Infinity, Lexicon, Mark Levinson, Bang & Olufsen and Harman Kardon) know a LOT about optimizing their products to sound the best they can. So while an aftermarket system might sound better with larger subwoofers, better speakers and more powerful amplifiers, these companies and their technicians are masters when it comes to system configuration and calibration.

A prime example of the capabilities of these companies is the Mark Levinson system in the Lexus LS. There are 23 speakers, including four in the ceiling. The system has a state-of-the-art upmixer that takes a stereo audio track and creates left, center, right, left side, right side, left rear, right rear, front overhead and rear overhead channels. The signals going to each channel are unique, so the system reproduces audio as though you were in a live venue with the stage in front of the listening position. In addition, the system has 2,400 watts of power, so it gets good and loud.

Upgrading these audio systems is complicated. It requires careful planning and accurate measurement of the audio signals that will be used for the upgrades and testing of signal routing for different frequencies and audio sources. This isn’t something you’d want to undertake in your driveway.

Intelligent Line Output Converters

In a more conventional factory-installed audio system, upgrading is less involved but still complicated. Crossovers, equalization, all-pass filters and signal delays are expected on systems with door and dash speakers in the vehicle’s front. Thankfully, a few companies have created line-output converters with built-in digital signal processors that can undo these features and provide a reasonably wide bandwidth signal that’s phase-coherent – like you’d get from an aftermarket source unit.

When the technician upgrading your audio system completes the wiring, these processors require a calibration step. Most include an audio track to be played through the system while the software analyzes the audio signals being produced. Once the measurement step is done, they analyze the information and configure the digital signal processor to undo equalization and signal delays, and combine signals from multiple channels. Once complete, your installer can move on to configuring your new system.

What Happens if You Don’t Undo Signal Processing?

Some upgrade methods work from what the OEM audio system offers. In those instances, you’ll need a digital signal processor with dedicated inputs for each channel from the factory amp. In addition, the system will need to use similar drivers and stock locations. For example, suppose you want your installer to build new A-pillar pods or use speakers that operate in the frequency range where a crossover existed in the factory stereo. In that case, intelligent line-output converters (or a DSP with these features) are necessary.

Let’s look at a simple example of combining two audio signals where one has been delayed from the other by a few milliseconds. This would be akin to using an active line-output converter to combine door and dash speaker signals.

The graph above shows the frequency response of our original signals in red. I applied a 0.6-millisecond delay to one signal, then combined the two to produce the orange trace. As you can see, the frequency response is a disaster. That curve is what’s known as a comb filter, as it looks sort of like a comb you’d use to straighten your hair before work or school. Signal delays are just one of the reasons why it’s crucial for the installer working on your vehicle to understand what’s happening in the time domain and the frequency domain for each channel of your sound system.

Choose Your Upgrades Wisely

If you’ve read this and think, “I have no clue what they are talking about,” that’s 100% OK. This is where you need to choose a professional mobile enhancement retailer to help you upgrade your car audio system. You’ll want to ask them what test equipment they have to measure the frequency and phase response of the factory-installed audio system before you let them work on your vehicle.

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.

It seems like everything to do with car audio installations has something to do with managing voltages. For starters, your electrical system needs to produce enough voltage to keep your radio and amplifier going. And amplifiers need to increase the voltage to drive speakers. When adding an amplifier to a factory-installed audio system, your installer will need to measure the voltage that the radio or amp produces. Chances are, they’ll need to use a line output converter to reduce that voltage so it’s compatible with a new amplifier. Let’s look at how these converters work and some of the options they include to make upgrading your car audio system easier.

What Is a Line Output Converter?

These simple integration devices go by several names. They’re sometimes called high-to-low or hi-lo converters, speaker input adapters or line level converters. Their task, however, is relatively simple. They take an audio signal intended to drive a speaker and lower the voltage so that it can be connected to the RCA preamp input on an amplifier or signal processor.

Most amplifiers want to see a maximum input voltage of 4 to 6 volts. Beyond the rated maximum input voltage, the signal can overdrive the input circuitry and cause clipping and distortion. Yes, you can clip the input to an amplifier with too much voltage.

Even a modest car radio can produce about 6.5 volts (peak to peak) output on the speaker wires. A small amplifier rated at 45 watts can deliver 13.4 volts. A subwoofer amplifier integrated into a factory-installed audio system could easily produce more than 30 volts.

How Do Line Level Converters Work?

There are two common types of converters on the market. The least expensive incorporates small audio transformers to reduce the voltage. The input winding on the transformer might have two or three times as many turns as the output, lowering the voltage by 50 or 60%. These devices are often passive in that they don’t require a power and ground connection to function.

The second and most popular converter adds circuitry to provide a low-impedance output to the new amplifier. These devices require a power, accessory and ground connection to function. They can also serve as a line driver to increase the output voltage relative to the input. If you have a modest source unit that can only provide 1.5 or 2 volts of output on the preamp, adding a line driver to bump that voltage to 4 or 5 volts will let your installer turn down the sensitivity control on your amplifiers to improve the signal-to-noise ratio of your audio system.

What To Look for When Shopping for a Line Output Converter

If you’re in the market for a quality line output converter, you’ll want to know how much voltage it can accept on the speaker-level inputs and how much it can increase or decrease that signal, and you’ll need to know the output impedance on the preamp side. Most good-quality converters can accept up to 40 volts on the inputs and have an output impedance of no more than 200 ohms, though lower is better.

You’ll also want to check the frequency response of the device. Entry-level transformer-based converters may not pass deep bass or high-frequency audio information as well as the active units. Accordingly, a frequency response spec of at least 10 Hz to 40 kHz with a tolerance of 1 dB is a good benchmark.

Since these are audio signal processors, noise and distortion specifications are also worth checking. A total harmonic distortion (THD) spec of no more than 0.05% is good and noise should be quieter than 110 dB.

Remote Turn-On Detection Features

One of the most common features of a line output converter is providing an amplifier turn-on output signal. Let’s say you’re having a subwoofer amplifier added to a factory-installed sound system. There likely won’t be an easily accessible wire that goes to 12V when the radio turns on. Many output converters have several ways to detect when the radio is on and produce this trigger. First, they can monitor the speaker wires for voltage. Once it detects an audio signal, it turns itself on and generates the remote output. The drawback of this option is that the unit might be fooled into turning on when a car door is closed. If the vehicle is relatively airtight, closing a door or the trunk can momentarily pressurize the interior, causing the speakers to move. When that happens, they produce a voltage and sometimes this tricks the converter.

The second way these devices can trigger an output is to monitor the input connects for a DC voltage on the speaker wires. For example, most radios use a speaker output device configuration called BTL, or bridge-tied load. There will be a few volts on the speaker wires when the radio turns on. The converter will sense this voltage and activate the output. If the source in your vehicle works this way, this is the best option for your installer to use.

Bonus Line Output Converter Features

Many line output converters come with additional features. One of the most common is a remote level control. If you’re having a subwoofer added and want to adjust its volume relative to the rest of the system, this is a great option.

Another popular feature is an equalizer. Your installer may find that the lowest audio frequencies from the factory source are attenuated. Adding a little boost to that missing information is a great way to deliver bass with good extension and impact.

Many of the better processors include speaker load simulators. Most Class-D amplifiers used in factory audio systems need to see a speaker connected to their outputs to function. As such, if your installer is adding an amplifier to drive those speakers, a relatively low-impedance load needs to be added to the speaker wires.

Channels and Signal Summing

The last topic we should discuss is understanding how many channels are needed for the line output converter. As we mentioned, typically, these are used when adding a subwoofer amplifier to a factory-installed source unit. That doesn’t mean that they aren’t also common for adding an amp to drive front and rear speakers. Many branded audio systems (like Bose, JBL, Fender, Infinity, Lexicon, Mark Levinson and B&O) that come with new cars and trucks are easily upgraded using multi-channel line output converter interfaces. Your installer can feed the output of the converter to a digital signal processor and new amplifiers, speakers and subwoofers.

Many multi-channel line output converters can sum signals together from multiple inputs. These days, using this feature is a risky proposition unless your installer has confirmed that the audio signals are in phase at the crossover frequency. For example, let’s say the front speakers in your car include a woofer in the door and a small midrange speaker in the dash (what many call a middler). If there is signal delay applied to the woofer, summing the signals together in a line output converter can result in the audio signal having an unusable frequency response. The summing circuits on these devices work perfectly, but the signals coming from a factory amplifier may not be compatible. So everything has to be tested. We’ll talk about signal summing processors in another article soon.

If you plan to have an amplifier added to a factory-installed audio system, chances are you’ll need a line output converter. It’s even more likely that you’ll need one that can provide a remote turn-on signal for that new amp. Drop by your local specialty mobile enhancement retailer to find out about the solutions that are compatible with your vehicle to deliver great sound.

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 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.

A while back we published an article that looked at the issue of intermodulation distortion from coincident coaxial speakers. As the woofer cone moves forward and rearward from its rest position, it acts as moving waveguide for the tweeter. While the phenomenon is measurable, there are other considerations in a coincident speaker design that offer dramatic performance benefits not found in other designs. To balance the universal car audio karma state, let’s take a look at why coincident coaxial speakers can sound absolutely amazing.

Point-Source Speaker

You’ll often hear coincident coaxial designs described as a point-source speaker. While not 100% accurate, they are about as good as things get in the real world. In a true point-source speaker, every frequency would emanate from exactly the same infinitely small point in space. Because speakers need to move relatively large amounts of air to be efficient, we have to deal with cone diameters that are more significant. As with everything to do with audio reproduction, there are benefits and drawbacks.

Where a point-source speaker really shines is that the distance between the woofer and the tweeter remain constant no matter where the listener is positioned. This can be a stark contrast to a component speaker set, where the tweeter might come much nearer or farther as we move our heads around the listening environment. Why does this matter? Phase. Phase matters.

What Is Phase?

Any time we have two signals containing similar content, there will be a relationship between the peaks and valleys in those signals. If the peaks and valleys align, then the signals are described to be in phase. If the peaks from one source align with the valleys from another source, and the levels are the same, the signals cancel. Drop a pebble into a large puddle and watch as the waves ripple outward from the center then reflect back from the edge. Very quickly, you’ll see complex patterns emerge.

When a passive crossover is designed or the technician working on your vehicle sets up a filter in a digital signal processor, the settings are correct for a single-phase relationship between the midrange driver and tweeter. If one component changes distance to the other, then the settings don’t work as well.

Even under perfect conditions, there is some unwanted summing and cancellation between a woofer and a tweeter as the phase relationship changes between the sounds they produce. This phenomenon can cause changes in sound level that are referred to as lobing. As result, there can be more energy at some frequencies than others depending on where the listener is positioned.

When most car audio systems were built using passive crossovers designed in simulation, the need to keep the woofer (or midrange) and tweeter as close as possible to each other was crucial. With a DSP, those rules have changed. The inclusion of signal delay capabilities has opened up a suite of entirely new installation options.

Keep Everything in Time

If you are having the car audio system in your vehicle upgraded, and you plan on having the system configured for driver and passenger enjoyment, it can be quite beneficial to implement a speaker solution that uses a coincident coaxial design. With this design, the distance from the listeners to both the woofer and the tweeter is consistent, ensuring good tonal balance and realism. Drop by your local specialty car stereo shop to find out about coincident coaxial speaker upgrades that can make your mobile audio system 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.