Car Audio

Upgrading a factory audio system is not as easy as it used to be. In the late 1990s and early 2000s, connecting an amplifier and a new set of speakers to a factory source unit would yield impressive, if not amazing, results. As automobile manufacturers put more focus on the performance of factory-installed sound systems, digital signal processing (DSP) became more and more prevalent. Equalization and signal delay built into factory source units and amplifiers allow inexpensive speakers to sound acceptable. This tuning works well for such speakers, but not for a set of premium aftermarket speakers. In the past few years, it has become common practice for reputable mobile electronics retailers to perform a series of oem sound system measurements in a vehicle we haven’t worked on before to ensure we understand how the factory entertainment system functions. The results of the measurements will determine the best path to upgrading the performance of the audio system.

Measure Twice, Cut Once

What do we measure, you ask? We need to quantify three items before a system upgrade can be discussed.

The first is frequency response. We need to know if the signal coming from the factory radio or amplifier has been equalized or filtered in any way. Equalization can help improve the performance of inexpensive speakers and compensate for the acoustic characteristics of your vehicle.

The second is voltage. If you have a high-power factory amplifier, then the interface we choose for your system has to be able to handle all of the voltage the amp can produce. Not knowing how much voltage is present in the speaker wires can lead to a system design that distorts at high volumes. This distortion will damage speakers.

The last thing our shop will want to analyze is the type of signal present. In most cases, the output of the amplifier is a BTL (Bridge-Tied Load), though some are single-ended. There is no right or wrong type of signal, but the information is required to ensure that they will use the appropriate interface solution or amplifier.

Depending on the vehicle and complexity of the factory sound system, we may have to complete several other tests. Signal routing tests are critical, especially if there is a center channel in the vehicle. Chimes, navigation prompts, parking sensors, up-mixers, active noise cancellation and systems that inject “engine noises” into the audio path have to be taken into account before the system design is complete.

What if We Do Not Measure Your System?

Imagine that you want to improve the sound in your audio system. You go to a car stereo shop and buy an amp and a set of speakers, determined to install them yourself to save some money. Even worse, you want to try to save a few more bucks, so you buy the equipment online and have it shipped to your house. Saturday rolls around, and you tear into your vehicle. You run wires to the battery and try to connect to the factory amp. After an hour or two in forums or Facebook groups, you think you have finally connected to the right wires. When you turn the system on, it sounds dull and lifeless.

What happened?

Many factory amplifiers have dedicated outputs for tweeters and midrange drivers. Connecting to one or the other limits how much information goes to your new speakers. Working with an experienced mobile electronics retailer helps you eliminate situations like these. A retailer that doesn’t already have the information can measure the response of each channel of the factory source unit or amplifier and provide a way to manage work with that information.

A more-typical result is that the high-frequency output from the new speakers is overwhelming. Many factory audio systems use a woofer in the door and a small midrange in the dash. These tweeterless factory systems require a moderate amount of high-frequency emphasis to sound acceptable. When you add a tweeter that can do a good job of reproducing these frequencies, the boost inherent to the system becomes overwhelming. You may be able to turn down the treble control on the radio, but it’s likely that the adjustment only compensates for the highest of frequencies, leaving you with an annoying frequency response bump around 4 or 5 kHz.

What We Do with the OEM Sound System Measurements

After the measurements are complete, our shop can recommend a solution to help ensure the success of your new system. If you luck out and have a simple factory source unit, you may only need a voltage adapter, commonly called a line output converter, to send an appropriate signal to your amplifier.

If a large amount of equalization is present from the factory amplifier, then an equalizer or digital signal processor may be adequate to compensate for the factory tuning. A calibrated microphone and audio analysis equipment is required to set up the new system. These devices are expensive, and it takes time to learn how to use them correctly to achieve acceptable results.

If you have a factory amplifier that includes crossovers or time alignment, then your interface options narrow. Several system integration processors on the market can automatically undo equalization and time alignment, then recombine signals from the subwoofer, midbass, midrange and tweeter outputs. There are also integration modules that will replace your factory amplifier and provide connections that will feed a signal directly to your new amplifier. Unfortunately for the Do-It-Yourselfer, these amplifier replacement modules need to be programmed for the year, make, model and trim level of your vehicle. This configuration process is not something that you can do at home.

Inquiring Minds Want to Know

Performing OEM system measurements are like preparing to have a cavity filled. Before your dentist starts grinding or drilling, he or she will take a series of X-rays so that they know exactly what they are dealing with. The same philosophy applies to constructing a subwoofer enclosure. You’d never see someone start cutting wood without having measured the car accurately.

When it is time to upgrade your factory audio system, visit your local mobile electronics specialist retailer. Ask if they know how your factory audio system is configured in terms of signal processing. If they don’t know, find out whether they have the equipment to measure the factory audio signals in your vehicle. Once you are comfortable with their level of expertise, you can enjoy the process of designing a fantastic sound system for your vehicle. You will be thrilled with the results!

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.

The adage that someone could write a book about a subject certainly holds true when it comes to a discussion of loudspeakers and their parameters. In fact, there are dozens of great books already available about the subject. This article provides an overview of some of the most commonly discussed speaker parameters.

What are Speaker Parameters?

Speaker parameters, often called Thiele/Small parameters, are a set of electromechanical measurements that can be used to define the low-frequency performance of a transducer. Using these parameters and a series of calculations, your installer can predict the performance of that speaker in an enclosure.

What Can We Determine from these Parameters?

Perhaps the most important set of calculations we can create is the output of the system. When we discuss the “system,” we are referring to the speaker itself and the enclosure in which we intend to install the speaker. Every speaker enclosure acts as a high-pass filter and reduces the low-frequency output of the driver. We gain physical power handling in return for this diminished output. Using a set of calculations, we can predict how much low-frequency information the system will produce.

Another important calculation is power handling. As mentioned, we need to control the movement of the speaker cone to prevent distortion and damage. We can predict how much the cone will move for a given amount of power in our test enclosure.

Resonant Frequency of the Speaker – Fs

In terms of analyzing the moving parts of the speaker, we need to know the frequency at which the compliance (springiness) of the spider and the surround combine with the mass of the cone and dust cap to store the most energy. At this frequency, the system alternately stores and subsequently releases the most energy for a given voltage input. If you were to swing a weight on a string suspended from the ceiling, the natural frequency at which it oscillates back and force would be equal to the resonant frequency of a loudspeaker.

Equivalent Compliance Volume – Vas

To understand how stiff the spider and the surround are, we compare them to an amount of air that would exert the same resistance to motion. Because air is easily compressed, a high Vas specification would represent a very softly suspended cone. Conversely, a speaker with a low Vas would have a very stiff suspension.

Electrical Q of the Driver at Fs – Qes

Understanding the Q (Quality Factor) can be somewhat difficult because it is a dimension-less value. In essence, the Q factor describes the damping characteristic of a resonant system. A higher Q represents less energy loss relative to the total energy stored in a system. A pendulum suspended from a low-friction bearing will have a high Q. That same pendulum, submerged in water, will have a much lower Q. An important consideration is that high-Q systems have less damping and, therefore, vibrate longer. The Electrical Q specification describes how much damping the voice coil and magnet assembly invoke on the moving cone.

As the voice coil moves past the magnet, it produces an electrical current. This current reaches its peak value at the resonant frequency of the driver and counteracts the current being provided by the amplifier. The net result is a significant rise in impedance at the resonant frequency.

Mechanical Q of the Driver at Fs – Qms

Just as the electrical characteristics of a speaker cause an opposition to cone motion, we have a similar effect from the mechanical properties of the speaker. Qms describes the mechanical losses resulting from the spider and the surround. A high Qms value describes lower mechanical losses, while a low Qms value describes higher losses.

Total System Q at Fs – Qts

This unit-less measurement is a mathematical combination of the mechanical and electrical characteristics of the speaker. In simple terms, we calculate Qts by dividing the total stored energy of the speaker by the dissipated energy in the speaker at resonance.

Compliance of the Driver Suspension – Cms

The Cms specification describes the stiffness of the driver suspension in meters per newton. A stiffer suspension will move less distance for a given amount of force applied to it.

Effective Cone Area of the Driver – Sd

This parameter describes the effective “size” of our speaker. We all realize that the cone will move air for us, but we also have to take into account the addition of the surround. It is commonly accepted that we can use a value of half the surround as contributing to the output of the driver.

Mass of the Cone and Moving Parts – Mms

The Mms specification describes the mass of the speaker cone and part of the spider and surround. Unlike the Mmd specification, Mms includes the acoustic load caused by the air in contact with the cone. In most cases, the values are similar, but as the surface area of the cone increases, so too does the value of Mms, relative to Mmd.

Maximum Excursion Level – Xmax

This parameter is frequently misinterpreted as being the defining factor in the distance a speaker cone can move. Early calculations used a formula that subtracted the height of the voice coil winding from the height of the magnetic gap, then divided by 2. This calculation describes how far the speaker can move before the winding comes out of the gap.

Subsequent investigation shows that non-linear behavior elsewhere in the driver design could have a larger influence on the motion limits of the cone. This suggests that Xmax should be the one-way excursion distance that represents a distortion level of 10%. This performance-oriented specification is far more indicative of the useful operating range of a driver, but is much harder to ascertain.

Additional Parameters

In this article, we only describe the basic parameters that are commonly used in predicting the low-frequency performance of a loudspeaker. Other parameters, such as inductance, become more relevant at higher frequencies. Addition parameters such as Nominal Impedance (Znom), efficiency, sensitivity and the Efficiency Bandwidth Product (EBF) are derived through equations that use the specifications above.

Proper Design Requires Simulation

A woofer in an over-sized enclosure may bottom out and be damaged easily. A midrange driver crammed into a small speaker pod may have a significant frequency response spike and an associated distortion peak. The result is quite unfavorable.

Before you assume a subwoofer or speaker is suitable for the enclosure or mounting location you have chosen, it is worth asking your mobile electronics retailer to perform a simulation to ensure everything will function the way you want. They can work with you to ensure everything will perform optimally, and your system will sound great!

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.