We recently talked about the difference between good and great speakers. In a nutshell, when you choose great speakers, you get more power handling, the potential for more output and dramatically improved clarity, thanks to a reduction in distortion. In this issue of Bang for Your Buck, we are going to look at two car audio speaker technologies that reduce distortion. This article will be a true behind-the-scenes look at how speakers work.

Current Flow and Magnetic Fields

According to Lenz’s law, when current flows through a conductor, a magnetic field is created around the conductor. At the same time, when we move a conductor through a magnetic field, a current is created in the conductor.

The diagram above shows a conductor (in grey) with a current flowing through it. The green lines show the direction of the magnetic field around the conductor.

In a speaker, the voice coil is a coil of wire wrapped around a bobbin or former. Current from our amplifier flows through this conductor and sets up a magnetic field around the voice coil. We use this property to move the speaker in and out of the basket. When the polarity of the magnetic field is the same as that of the fixed magnet, the similar magnetic fields repel each other, and the speaker moves forward. When the polarity of the magnetic field reverses, the speaker is attracted to the magnetic field and the speaker moves rearwards.

Unfortunately, when it comes to dealing with alternating current, the behavior of magnetic fields can work against you. When the polarity of the current reverses, it has to fight against the magnetic field it created. You can think of it as momentum. If marbles are rolling across the floor, it takes energy to make them change direction. This opposition to the change in the flow of current is called inductance. The electrical momentum resists the desire to set up a new magnetic field of the opposite polarity.

Managing Voice Coil Inductance

The amount of inductance in a speaker voice coil is determined by several factors. The size of the voice coil conductor, the geometry of the conductor, the number of layers in the voice coil and the proximity of the voice coil to the top plate and the pole piece – just to name a few.

So, how does inductance cause distortion in a speaker? As you can see in the diagram above when the voice coil winding (in red) is at rest, it is centered on the top plate (in green). As the cone moves down, more of the voice coil is beside the magnet (in blue) and the pole piece (in pink). Conversely, as the come moves outward, less of the cone is near the pole. In a conventional speaker design, the changes in proximity to the steel pole piece cause changes in inductance. As the inductance decreases, there is less opposition to the flow of high-frequency current and an increase in high-frequency performance. Changes in performance based on the position of the speaker cone result in distortion.

The image above shows the inductance of a voice coil relative to its position in the speaker. The red curve is the inductance graph of a conventional speaker. The blue curve is the inductance graph of a speaker that includes an aluminum shorting ring at the bottom of the T-yoke. As you can see in the image above, without the shorting ring, the speaker has dramatically different inductive characteristics depending on the position of the cone.The graph above shows the frequency response of a speaker without a shorting ring (in red) and that of a very similar speaker with a shorting ring (in blue). As is clearly evident, the inclusion of a shorting ring dramatically improves the high-frequency performance of a speaker. Further improvements in linearity can be achieved by including a copper cap on top of the T-yoke.

When you are shopping for great speakers, look for inductance-reducing caps on all speakers (subwoofers, midrange drivers and tweeters), and in larger speakers (subwoofers and midrange drivers) where the room is available in the motor assembly, look for the presence of a shorting ring.

Comparing Inductance Numbers

If we can’t determine whether a speaker has a design that mitigates changes in inductive characteristics, can we simply look at the specifications? They most certainly do provide a hint. A 6.5-inch woofer without a cap or shorting ring may have an inductance of 0.7 to 1.1 mH (millihenries), whereas a speaker with these technologies will be closer to 0.1 or 0.2mH. In terms of how they sound, all other design criteria being equal, the driver with the lower inductance will have better high-frequency performance and produce less distortion.

Speaker Suspension Nonlinearities

The purpose of the spider (also known as a damper) is to keep the voice coil laterally centered in the air gap between the top plate and the pole piece and to help return the cone to the resting position when the audio signal is removed.

Picking the perfect damper stiffness (compliance) for a given cone mass and desired resonant frequency is one of the biggest balancing acts involved in designing a speaker. If the spider is too stiff, the resonant frequency of the speaker may be too high for the desired application and its efficiency may suffer.

A variety of materials are available, as well as different sizes and different geometries. A spider is a spring. Some spiders are designed for linear compliance and some are progressive. More importantly, because of variances in voice coil winding height and basket design, some spiders include an offset mounting lip. This is called a cupped spider. This cup or spacer allows the spider to attach to the voice coil former above the winding, then connect to the chassis while keeping the voice coil vertically centered in the magnetic gap.

The above graph shows the suspension compliance of two different 6.5-inch diameter speakers based on the position of the cone. The graph in red shows the compliance of a speaker that uses a cupped spider. You can see that at 6.5mm of inward travel, the suspension is 25 percent stiffer than at 6.5mm of outward travel. The blue graph shows a similarly sized speaker with a flat spider. Though the overall compliance is different, the behavior in the forward and rearward directions is nearly identical.

What To Look For in a Spider

Ultimately, we want the spider to exert the same amount of force on the cone and voice coil as it moves forward or backward from the rest position. The amount of force should not change based on the direction of cone travel. Imagine the distortion created by a speaker playing a sine wave where the cone doesn’t move as far rearward for a given amount of current as it moves forward. As such, try to avoid speakers that use cupped spiders.

Hear Different Car Audio Speaker Technologies In Person

The next time you head to your local mobile enhancement retailer to listen to new speakers, choose two wildly different price points and listen to the same portion of a song on each speaker. Listen to them at a reasonably loud volume level, and position yourself across the room. Switch back and forth until you determine the differences.

Then, add a third speaker option, priced and featured somewhere in the middle. Make the same comparison with this new speaker and the expensive speakers. Once you have listened to the speakers, ask to look at a sample of each and see if you can correlate some of the design characteristics we have discussed with their performance. It’s not only a great way to audition products but to learn about what makes one car audio speaker technology or design better than another.

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 should be no surprise that your choice of speakers has the biggest impact on the sound quality of your car audio system. With that said, many consumers simply don’t understand what separates one speaker from another in terms of performance and value. In this installment of Bang for Your Buck, we are going to talk about car audio speaker upgrades and the performance benefits of buying premium speakers.

How Do Speakers Work?

In the simplest terms, a speaker has a cone, a motor and a suspension. The cone is a rigid surface that moves to produce sound. The motor is a voice coil and a fixed magnet. When alternating current from your amplifier creates a magnetic field in the voice coil, the assembly attracts itself toward or repels itself away from the magnet. Finally, the suspension’s job is to keep the voice coil and cone centered in the speaker basket and control how far the cone moves at low frequencies.

Many engineers have made it their life’s work to try to perfect the performance of a loudspeaker. Advances in computer simulation are responsible for great leaps in performance, thanks to models of magnetic fields and finite element analysis of cone and suspension assemblies.

Why Aren’t All Speakers Perfect?

It’s simply impossible to design a perfect speaker. Just as with a source unit or amplifier, each component in a speaker is responsible for some minute amount of non-linear behavior that changes the way a speaker sounds. Cone and dust cap resonances cause distortions at mid and upper frequencies. Non-linear suspension geometry can cause harmonics at low frequencies and high excursion levels. Uncontrolled magnetic field changes in the voice coil, top plate, magnet and T-yoke increase inductance and cause distortion at higher frequencies.

In spite of this, don’t think for a second that the speakers available for your car, truck or SUV aren’t great upgrades over what came from the factory. Remember: Better speakers offer better performance.

The Speaker Quality Analogy

Cameras are a good analogy for speaker performance. An inexpensive digital camera hanging on a peg in a big-box store will take a picture of anything. You’ll be able to discern the content of the photo without any problem.

When you move up to a premium point-and-shoot camera in the $400 range, the photos the camera takes will be more accurate. The focus will be improved, and the images will have more detail. It’s still the same picture, but the accuracy is better.

Finally, if you move to a digital SLR camera with a premium lens, the accuracy and detail increase even more. The subtlest of nuances in the content are captured with exemplary detail. You can see each hair in a person’s eyebrow or the smoothness of the finish on an automobile.

Whether we’re talking about great photographs or great music, the resulting experience has as much to do with the equipment as it does with how it’s used. A good photographer knows how to compose an image to evoke emotion and tell a story. It’s not just a matter of pointing the camera at an object and pressing the shutter release. In our cars and trucks, how equipment is installed and configured plays a huge roll in the quality of the listening experience. We’ve talked about the importance of proper equipment installation in the past. When it comes to speakers, doing things right is crucial.

Better Speakers Can Play Louder

Let’s compare 6.5-inch component woofers designed for use in the door of your vehicle. Right off the bat, we can look at the Xmax specification to determine how far the cone can move. Cone excursion directly relates to the maximum output possible from a speaker. The Xmax specification describes the geometry of the motor assembly. A speaker with a rating of 5mm (one-way) can move forward or rearward 5mm without any changes in the amount of voice coil winding that is within the magnetic gap. Beyond this measurement, distortion in the output increases quickly.

A basic 6.5-inch speaker may have 2 or 3mm of one-way excursion. A better speaker will have numbers in the 4 to 5 mm range. Finally, the very best designs may offer as much as 9mm of one-way excursion. Though not deliberately included in this discussion, many 6.5-inch subwoofers have an Xmax specification around 9mm.

Better Speakers Handle More Power

As you spend more money on a speaker set, their power handling capabilities increase. We should make it clear: More power handling does not relate to better performance from a speaker. It’s just one of the many aspects that need to be considered during the evaluation and purchasing process.

Power handling in a speaker is determined almost exclusively by the diameter of the voice coil. Just as with a radiator or intercooler in a car, more surface area allows for the dissipation of more heat. If you overheat a voice coil, the adhesives used to bond the winding to the former will fail and the winding will unravel – usually with smelly and crunchy consequences.

With some exceptions, there are some general guidelines for the relationship between voice coil diameter and power handling. A 1-inch (25mm) voice coil can usually handle about 60 watts of continuous power. Moving up to a 1.25-inch coil (32mm) increases continuous power handling to about 80 watts. Finally, 1.5- to 2-inch voice coils can handle between 100 and 150 watts of power.

The absolute power handling numbers depend on many factors, including the diameter of the voice coil winding conductor, the proximity of the voice coil to the T-yoke and top plate, and the presence of any cooling vents in the motor design.

Why Is Power Handling Important?

For years, high-quality speakers were considered fragile. They were made with lightweight components, supposedly to help improve their transient performance. The problem was, many people like to listen to their music at high volume levels. It was unfair that speakers that sound great couldn’t handle large amounts of power. In the last decade or so, this contradiction has gone away. Premium speakers not only sound great, but they also offer good excursion capabilities and can handle lots of power.

Better Speakers Produce Less Distortion

Sadly, very few companies talk about distortion when it comes to speakers. In fact, the entire topic of distortion in the mobile electronics industry is often overlooked because it often reveals that products people think are great actually aren’t. A manufacturer needs to be confident in his (or her) product design to reveal every detail of its performance.

While output capabilities and power handling are important aspects of speaker design, distortion, or the lack of it, is the most important of all. To the untrained eye, it’s difficult to determine the quality of a speaker by looking at it, but there are often some hints. More information can be provided by looking at a high-resolution frequency response graph of a speaker. Here, cone, dust cap and surround resonances reveal themselves to give some insight into the design of the speaker and how it should be integrated into a system.

How is Distortion Measured?

Speaker distortion is easy to measure, for those with the right equipment. Just as with an amplifier or signal processor, a known signal is sent to the device under test. The output of the device – in this case, the speaker – is compared to the input signal.

A concept that is hard for many to grasp is how distortion manifests itself. If you feed a 1kHz, 2-volt RMS sine wave to a well-designed speaker, you get a 1kHz tone back. In a speaker with design issues, you get that 1kHz tone, plus other sounds. These extra sounds are distortion. Sometimes the sounds are harmonics of the 1kHz frequency.

Better speakers produce less distortion. That is to say, less additional information is added to your music. As such, your music sounds clearer, instruments and performers are easier to identify and the sound is more realistic. The most important thing to consider – once that distortion is created, it can’t be removed from the system.

How to Shop For Car Audio Speaker Upgrades

It can take years to train yourself to identify subtle differences in speaker performance. With that said, listening to two or three music tracks again and again on different sound systems will help you identify the benefits and drawbacks of those system designs and installations.

When it’s time to go speaker shopping, visit your local mobile enhancement retailer and ask for a demonstration. Whether the source is on a display board or in a demo vehicle, listening is the fastest way to quantify the performance differences between speakers.

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.

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.