When you go shopping for a new radio for your car, one of the many questions the product specialist should ask you is whether your existing radio has steering wheel-mounted audio controls. Almost every aftermarket radio has provisions to accept a signal that will give you steering wheel audio control functions like volume, source selection, tracking and power. Here’s how it all works.

Factory Control Functionality

There are two common types of steering wheel control interfaces. The first is resistive; the second is data. Systems that use resistors often have two wires connected to the switches. Each switch presents a different resistance value when pressed. The factory radio sees these different resistances as different voltages and the computer in the radio responds appropriately. There are usually two wires so a multitude of switches can have well-separated resistance values to ensure functions will never overlap.

A small computer is built into the steering wheel controls switches in vehicles that use data communication for the steering wheel audio controls. This computer has inputs dedicated to each switch and its function. When you press a switch on the steering wheel, the computer sends a digital communication to the computer in the radio. Often, this communication takes place on the vehicle’s CAN data network.

Connection to Aftermarket Radios

In North America, almost every radio is Steering Wheel Remote Control Ready. Being “Ready” means the radio has a connection on the back to accept a serial data communication signal. The communication language used on the radio connection is not the same as that used in the vehicle. Thus, you will require an interface module to make everything work. Companies like iDatalink, Axxess and Pacific Accessory Corporation (known in the industry as PAC) all offer interfaces that can be programmed to understand and translate the information from the vehicle to something that is compatible with your radio.

Steering Wheel Audio Control Installation

When your tech is installing the new radio in your vehicle, he has three tasks to complete to make the steering wheel audio controls work. First, he must wire the controls into your vehicle. In many cases, the installer will use a “harness saver” or “wire harness adapter” to connect a set of bare wires to the factory radio plug for power, illumination and speaker wire connections. This adapter usually includes the steering wheel communication wires from the vehicle.

Once the installer completes the electrical connections, the next step is to program the module to understand the commands from the vehicle. Some interfaces have software built into them to recognize commands from the vehicle automatically.

Another method of programming the interfaces uses a website that will allow the installer to select the year, make, model and trim level of the vehicle, and program the interface to recognize the correct commands.

Finally, the interface has to be programmed to send the correct commands to the new radio. Each brand of radio has a set of dedicated and unique command codes.

Additional Options

Over the past few years, many vehicle owners have chosen to upgrade their factory radios to add Bluetooth audio streaming and hands-free calling to their vehicle. New cars have telephone control buttons on the steering wheel, but older ones don’t. Several of the interface modules have the ability to send different commands to the aftermarket radio, depending on how long you press and hold the steering wheel buttons. For example, a quick tap on the Volume Down button will, of course, turn the volume of the aftermarket radio down. You can have the button programmed so pressing and holding it for a couple of seconds to tell the radio to answer an incoming Bluetooth phone call.

The list of compatible functions varies by vehicle and the make and model of the aftermarket radio.

Custom Applications

One unique feature of the steering wheel control interface is that your installer could build a set of custom controls for you. Let’s say you are building a custom car, and you want to add a nice sound system. In most applications like this, the builder will install the aftermarket radio in the glovebox, under the seat or in the trunk of the vehicle. But how can you control the radio if you cannot reach the controls? Your installer could mount a set of switches in the center console and then program the switches, through an interface module to control the aftermarket radio.

Some installers and fabricators have gotten quite creative with these switch installations. A power mirror adjustment switch, for instance, serves as a great solution for volume and tracking functions.

Your Retailer is Ready to Help

When it is time to install a new radio in your vehicle, drop by your local mobile electronics specialist retailer. They would be happy to show you the latest in car audio source units and explain how they can integrate it into 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.

For almost as long as there have been car audio enthusiasts, they have been adding amplifiers to their vehicles to increase the power available to drive their speakers. More power means we can turn the volume up higher without distortion. When it came to connecting amplifiers to speakers, the first power boosters connected to the speaker wires of the radio. Now, modern head units offer dedicated RCA preamp outputs to make things easier.

Manufacturers specify how much voltage their source units can produce on these preamp outputs. Most radios offer at least 2 volts of signal, but some offer 4 volt, 5 volt or even 8 volts. Does this preamp voltage matter? Does more voltage make your system louder? Read on to find out.

Signal Chain

When we install an aftermarket radio in your dash and connect it to the amplifier, we have to make at least one adjustment to ensure everything will work properly. We refer to this step as “setting the gains.” This procedure involves matching the output voltage limit of the source unit with power production capabilities of the amplifier to ensure that both achieve maximum output when the volume is cranked all the way up.

Adjusting an amplifier’s sensitivity is, in theory, a simple process. That said, there are many things to take into consideration. How loud is the source material recorded? Does the head unit distort at full volume? Has anyone adjusted the radio’s tone controls or equalizer? Does the amplifier have any tone controls? If any one of these criteria are overlooked, the sensitivity adjustment may not be accurate.

What is the drawback to an improperly configured sensitivity control? If it is set too low, then you cannot get all the power available from the amplifier to your speakers. If the sensitivity control is set too high, then you can easily distort the output of the amplifier. A second side effect of adjusting the sensitivity control too high is that you increase the noise produced by the amplifier. Nobody wants to hear a hiss in the background of their music, so setting things properly is critical.

What Does High Preamp Voltage Do?

Some intensive research among several of us “old” car audio enthusiasts revealed that there were even a few twin-shaft cassette receivers with high-voltage preamp outputs. Some sales and marketing folks decided that more voltage meant more volume. In the early ’90s, several head unit manufacturers started marketing their radios as having high voltage preamp outputs. If nothing else changed, sure – in theory, more voltage means more output. That said, if you swap from a 2 V source unit to a 4 V, and then readjust the sensitivity control on your amplifier down to compensate for the extra voltage, the maximum output level should stay the same.

If more voltage does not make your system louder, what is the benefit of this extra voltage? The answer is a reduction in gain of the amplifier and, thus, a reduction in potential noise. If your amplifier is set up to produce full power with a 2 volt signal and has a subsequent signal to noise ratio of 85 dB, then it is not unreasonable to expect that the noise would reduce by about 3 dB when we turn the sensitivity down by the same amount.

To the Test

We set up a premium consumer-grade amplifier on the lab test bench. It had an S/N Ratio specification of 89 dB when producing 1 watt of output and connected to a 4 ohm load. This is a pretty good rating these days. We set the amp up to produce 1 volt of output with a 1 kHz sine wave at a reference level for our function generator at -30 dB relative to full signal. We then took a long frequency response measurement.

The next step was to reduce the output signal of the function generator by an arbitrary amount – we chose 6 dB. We readjusted the sensitivity control of the amplifier so the output level was once again 1 volt and took another long frequency response measurement.

The results of the two measurements are shown in Figure 1.

In Figure 1, you can see the large spike in frequency at 1 kHz on the right side of the screen. We zoomed in to fill the screen with as much information as possible below this frequency. The gold line shows the background noise produced by the amplifier with the sensitivity control at the lower of the two settings. The green line shows the background noise when we increased the sensitivity of the amplifier by 6 dB.

Figure 2 shows the difference in noise level at 100 Hz. Not surprisingly, the difference in noise is just under 6 dB.

Conclusion

When it’s time to go shopping for a new source unit, among the dozens of cool connectivity features, options for display technologies and different brand names, paying attention to specifications is still important. If you are planning to add an amplifier to your mobile electronics system, make sure your source unit can produce at least 4 volts of output on the preamps. This extra voltage will allow your installer to reduce both the sensitivity controls on your amplifier and the background noise level of the system.

Visit your local mobile electronics specialist retailer today for more information on which source units have high-voltage preamp outputs.

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.