In a recent article, we discussed the features to look for when choosing a new source unit for your vehicle. In this article, we delve deeper into the source unit specifications manufacturers provide and explain what they mean, in hopes of helping you weed out a solution that performs the way you want. Charge up your calculators and pull a pen from your pocket protector: It’s numbers time!
Source Unit Specifications
In the good old days of car audio, print magazines (remember those?) would publish product test reports that included both listening and bench test information. While at least one these publications still exists, the plethora of numerical information simply isn’t disseminated the way it used to be. That means shoppers have to rely on specifications printed by the manufacturer. In most cases, these numbers are accurate and serve as a good foundation for comparing certain performance characteristics of a product.
One thing that numbers can’t easily describe is the sound of a product. We can look at frequency response graphs and distortion specifications until we are blue in the face – that information does not describe what the distortion looks like or what causes it. That makes it crucially important to audition each component of your system before making a purchase. This is where your local specialist car audio retailer can help. Most have display boards and demo vehicles set up to let you experience different products and see their installation teams’ capabilities.
Head Unit Power Specifications
Almost every head unit on the market has a built-in four-channel amplifier. These amplifiers vary in power product capabilities between 14 and 55 watts of power. That said, among the most-popular and misleading specifications found on most head units are their power ratings.
When comparing specs, you want to look for ratings that use an industry standard like CEA-2006 (now called CTA-2006). This specification outlines the criteria for the power measurements. Any specification using this standard requires a power supply voltage of 14.4 volts, a load impedance of 4 ohms and no more than 1% total harmonic distortion in the output signal. Comparing max or peak power ratings is like buying a sports car based on the largest number on the speedometer or the speed rating of the tires. That information simply isn’t relevant.
How Amplifier Power Works
Before we move on to the next subject, we should talk about how important deck power is. Let’s use an example of a speaker that is rated to produce 89 dB of output when driven with a 2.83 V signal, measured at a distance of 1 meter from the speaker. 2.83 V equates to 2 watts of power into a 4 ohm speaker. If we double the power to 4 watts, the output increases by 3 dB to 92 dB. Doubling power again takes us to 8 watts and 95 dB. Next, we get to 16 watts and 98 dB of output, then 32 watts and 101 dB. These numbers assume that the speaker is operating linearly and without any form of power compression (reduction in output due to heating effects). For most head units, the most undistorted output we are going to get from a single speaker is around 99 or 100 dB.
Because it takes logarithmically more power to increase output, small differences in amplifier power result in very small changes in perceived output. Let’s take for example the difference between a 14 watt and a 22 watt head unit. This increase in power represents an increase of less than 2 dB of output. Going from a 22 watt head unit to something that will produce 55 watts of power yields almost 4 dB more output.
Our point? Don’t nit-pick over one or two watts when comparing amplifiers of any kind. You probably can’t hear the difference. That said, if you aren’t going to buy a stand-alone amplifier for your system, you will want as much power as possible from the source unit.
Background Noise Specifications
For true music lovers, one important measure of a source unit’s quality is its ability to reproduce your music without adding unwanted background noise. When you look at head unit specifications, this characteristic is called the signal-to-noise ratio and is expressed in decibels.
Here’s how the specification works. Let’s say you are playing a test tone at a level of 2 volts into a 4 ohm load. If a device has a signal-to-noise ratio of 80 dB, this means that the background noise (hiss) created by the unit is 80 dB quieter than the 2 V signal.
It is important to know how these measurements are performed. Using the CTA-2006 standard allows for easily comparable specifications. It is worth noting that many companies still rate the noise their products add relative to the maximum output level of the device. This means an amplifier rated to produce 10 watts of power and having an S/N ratio of 80 dB when referenced to full power, the real signal-to-noise ratio is 70 dB when referenced to 1 watt (2 volts into a 4 ohm load). Keep an eye out for this when comparing specifications.
Pre-amp Output Voltage
Interestingly enough, pre-amp output voltage is tied directly to the signal-to-noise ratio measurement of the source unit and the amplifier you choose for your system. Having extra output voltage means that you can turn down the sensitivity of your amplifier while still being able to produce maximum power for your speakers.
Let’s use a fictitious amplifier example – one that offers a signal to noise ratio of 90 dB when driven at an output of 1 watt with the sensitivity control set to produce maximum power with a 4 volt signal. That noise from each device accumulates as the audio signal passes from one component to another. Do you choose a source unit with a 90 dB S/N ratio rating that can only produce 2 V on the preamp outputs or one with a rating of 87 dB that can produce 4 volts? You probably have to turn the sensitivity control up on your amplifier with the latter choice, resulting in roughly the same net background noise. Audio systems are a sum of their parts.
Tuner Specifications
Over the past few years, the perceived quality of radio tuners in aftermarket source units has decreased. Tuners are not as big a focus as they used to be. The Pioneer SuperTuner IIID, Clarion Magi-Tune+, Sony’s SSIR-EXA and the old Blaupunkt radios from the 1980s offered excellent sensitivity and selectivity.
Sensitivity specifications are rated in dBf units. The dBf describes signal strength in decibels relative to 1 femtowatt. Some specifications are provided in microvolts relative to a specified impedance. As with any specification, it’s important to understand the test criteria. Additional specifications are often provided.
Let’s look at an example tuner with a Usable Sensitivity specification of 9.3 dBf.
This specification describes the weakest signal that the tuner can capture and lock on to. Weaker signals (lower numbers) will not be recognized as a radio station. For the best sensitivity (ability to lock onto a radio station), look for lower numbers.
To fully understand this specification, you need a second number to quantify the quality of the audio signal that is produced. In the case of this unit, that specification is 30 dB. This means that when the unit is locked onto a signal with a strength of 9.3 dBf, the background noise will be 30 dB quieter than the information.
To complicate the discussion as much as possible, it should be noted that most people will find a signal to noise ratio of 30 dB to be quite annoying. 50 dB is a better number. To achieve this noise ratio, this tuner requires a minimum signal strength of 10.2 dBf. Sadly, different manufacturers provide their specs using different quieting (background noise) levels, so trying to compare apples to apples can be frustrating.
How Important are Specifications?
The way your audio system is designed will determine the importance of the varying specifications. If you always use SiriusXM or Pandora, then tuner quality won’t be a significant issue. If you are running external amplifiers, then internal amplifier power doesn’t matter, but the preamp voltage does. No matter how you design your system, noise and distortion specifications do matter – keep that in mind when you go shopping.
When it’s time to upgrade your audio system, pack up your favorite music and head to your local car stereo specialist retailer. They can help you sift through the myriad of products available to find a solution that meets your feature and performance expectations.
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 long time ago, a friend of mine told me always to ask a salesperson what I would get if I spent 10 percent to 15 percent more on an item I wanted to purchase. At the time, the discussion was related to a large tube-style television. Let’s say the TV I was looking at sold for $800. If stepping up to a $900 model resulted in a better picture, or the addition of a feature that I would enjoy, then it would be worth the investment. In the mobile electronics industry, or perhaps consumer electronics in general, few customers ask, “What do I get for a little bit more?” This article will be the first of many that discuss the true performance features of mobile electronics products. For this article, we’ll look at better source units. What do you get when you spend more and how you benefit from those feature or performance upgrades?
It should be no surprise that the majority of 
When you are shopping for a new receiver, you may want to consider asking about Apple CarPlay and Android Auto. These smartphone solutions use voice recognition technologies to make performing common tasks easier and safer. You can send a text message, choose the music you want to listen to or get navigation directions, all by simply talking to your radio. These technologies have associated hardware requirements put forth by Apple and Google, and include technology licensing costs. As such, they cost extra to purchase, but they are well worth the investment.
If you are passionate about your music, look for a source unit that includes crossovers. The ability to filter the signals created by the source unit will let you add a subwoofer to improve the performance of your audio system dramatically. Having simple bass, midrange and treble controls may be adequate to let you adjust your sound system. More elaborate 
Hooking things up to your radio is part of the fun of upgrading your vehicle. The most basic of source units may include Bluetooth, a USB port, an auxiliary input, a backup camera connection and preamp outputs for external amplifiers. As you move up through a brand’s models, you’ll discover functions like SiriusXM compatibility, multiple USB connections, support for more than one phone, multiple camera inputs, multiple video inputs, HDMI input, multi-zone outputs and more. Do your homework before you go shopping. Decide what functions you want before you leave the house. Your retailer can start with that to help you choose a solution.
Another important consideration is digital media compatibility. Most systems will play MP3 and WMA audio files. As you step up in features, you gain support for AAC, WAV and FLAC files. Upgrading even further gets you support for high-resolution audio formats that offer audio content beyond 20kHz. The second consideration for digital media compatibility is video. Determining whether a source unit will play video files is the first step. Second is the type of files. MPEG and WMV file playback is found on mid-level systems. Premium solutions add H.264 formats and often support MKV containers.
Almost every multimedia receiver includes a steering wheel control interface connection. This connection allows your installer to configure an external interface that will allow the audio adjustment buttons on your steering wheel to work with your new radio. If you are looking for advanced integration, the iDatalink Maestro RR interface allows bidirectional communication with the CAN bus in your vehicle and many applications, as well as compatibility with factory backup cameras, UBS ports and infotainment solutions like Uconnect and Ford Sync. Depending on the vehicle and trim level, climate settings can also be controlled through the Maestro RR.
If you ask someone in the mobile electronics industry what “source unit integration” means, they’ll probably tell you about making an aftermarket radio fit into the dash of a vehicle and allowing it to send audio to the speakers. For decades, this has been the extent of the task.
As far back as the early 1980s (and maybe further), automakers started including buttons on the 
As automakers evolve the functionality of their infotainment systems, the aftermarket has forged forward with ways to work with those features and technologies. Once climate controls, vehicle configuration settings and integrated entertainment solutions like Ford Sync, Chrysler Uconnect and OnStar became part of the “radio,” upgrading factory source units became exceedingly difficult.
The iDatalink guys are best known for their remote car starter systems and data interface solutions. Their expertise in working with vehicle data networks translates directly to integration with infotainment systems. Maestro launched with two product solutions: a steering wheel control interface called the SW and a data interface called the RR. SW stands for steering wheel and RR for radio replacement. The SW product is pretty straightforward, while the RR is quite complex. Let’s look at what RR offers.
The Maestro RR is like a steering wheel interface on steroids. The system provides bidirectional communication with various vehicle functions. When an RR is used with a compatible aftermarket radio, factory entertainment systems like Sync and uConnect become part of the aftermarket radio. The driver can adjust vehicle settings, including keyless entry options, lighting controls, factory remote control functions, door lock functionality and more. The specific features and functions depend on the vehicle and the make and model of radio you choose.
When you go shopping for a computer, it’s important that all the pieces work together to provide maximum performance and reliability. When you head out to upgrade your 
For decades, car audio system upgrades have followed the recipe of a new radio, front and rear speakers, an amplifier and a subwoofer. Lately, it’s becoming difficult or impossible to remove the factory radio from many vehicles. In these situations, your mobile enhancement retailer should be able to provide you with options to make use of the signal from the factory source unit or amplifier, then upgrade the performance of the system with new speakers, a subwoofer and an amplifier.
Shopping for an audio system upgrade is like cooking: You need to determine what you want long before you head to the grocery store. Do you want loud? Do you want incredible accuracy? Do you want something that does not affect the cargo capacity of your vehicle? What is your budget for the project? Do you want to do everything at once? Only once you have a plan in place can you get an accurate quote to upgrade your vehicle. You may learn or experience something new as you do your research. It’s certainly OK to change your plan.