Car Audio

Developing a speaker requires that the designer and engineer balance many different aspects, such as the application, cost and desired performance level of the end product. For the consumer, navigating the thousands of different speaker offerings on the market can be difficult. Two speakers can measure similarly regarding efficiency, power handling and frequency response, but still perform completely differently because of different distortion characteristics. Cone, dust cap and suspension resonance, motor non-linearity, and enclosure/application requirements play a crucial role in determining how the end-product will sound once installed in the listening environment. This article scratches the surface of looking at the benefits and drawbacks of choosing speakers by comparing coaxial and component speaker designs.

When Choosing Speakers, Define the Design

Component (or separate) speakers are a set of speakers that includes a set of dedicated midrange drivers and dedicated tweeters. Each of those four speakers requires a dedicated mounting location. By contrast, a coaxial speaker features a midrange driver with a tweeter mounted in the center of it. In most cases, the tweeter is on top of an extension post connected to the pole piece. Other coaxial designs use a bridge or mesh grille to suspend the tweeter over the midrange. These are sometimes called coaxially mounted components by marketing departments.

Benefits of Coaxial Speakers

In most cases, coaxial speakers are the less-expensive options in a product lineup. This pricing is due to the chosen target customer and not because you can’t make a high-quality coaxial speaker. Less-expensive magnets, baskets, cone materials and suspension components, and wider tolerances that allow for faster production with fewer rejected assemblies, all help reduce cost. The benefit is, if you need an inexpensive speaker, coaxials are a good solution.

Coaxial speakers can be installed faster, so they are less expensive to install. The integrated tweeter saves a lot of time during the installation process. Most coaxial speakers have integrated crossovers of some sort that don’t require special wiring or mounting. The net result is that your installer can get them up and running in your vehicle in about half the time it takes to install a component set, which means your labor charges will be reduced.

Benefits of Component Speakers

Most component speakers are made from better materials and have higher performance goals. High-end components can cost more than $5,000 for a set and often include premium passive crossover networks, elaborate installation accessories and – of course – amazing speakers. The sound that component speakers produce, when installed and tuned properly, can be amazing!

When a good set of components is tuned properly, most of the sound can appear to come from the tweeters. Having a separate tweeter allows your installer to mount it high in the vehicle – at the top of the door, on the dash or in the A-pillar. The combination of proper tuning and placement puts the music out in front of you, essentially at eye level. This higher soundstage is similar to what you would experience at a concert, listening to the band performing in front of you.

Many factors contribute to where and how your installer mounts the tweeters – your budget, your performance goals, and how much modification you want or will allow to your vehicle. All locations have their benefits and drawbacks. For example, a tweeter mounted on the dash or A-pillar is very near the windshield. The hard surface of the windshield can cause significant reflections. Alternatively, a mounting location in the upper section of the door may reduce these reflections, but may not raise the soundstage as high, or could make it appear to come from somewhere closer to you than the dash or pillar location.

A component speaker doesn’t have any of its output blocked by the tweeter, which eliminates some minor reflections . Likewise, with a coaxial speaker that uses a tweeter post, a component speaker can have a full dust cap. The dust cap moves with the cone and increases the driver cone area. Additional cone area increases the driver’s efficiency.

The Huge Role of Crossovers

Whether you choose a coaxial or component speaker set, you are going to need a crossover to handle splitting up the frequencies. In the most basic of speakers, a capacitor is used on the wire going to the tweeter to block low and midrange information. The midrange driver is allowed to roll off naturally – ideally, there are no significant high frequencies resonances that will affect the sound.

As you progress up through the quality of a speaker set, you will see steeper filter networks on tweeters. These steeper networks allow the tweeter to play to a lower frequency and then be stopped to protect it from excursion damage. At the same time, filtering the high-frequency output of the midrange is common in mid- to high-end crossover networks. Speaker manufacturers construct the most elaborate of crossover networks with premium components for both the high- and low-pass portions of the network. Adjustability is often built into the crossover for tweeter level. Small components can be overdriven and saturated, reducing their effectiveness. Large amounts of distortion can cause the tweeter cap to overload and explode.

The Option of Coincident-mounted Coaxial Speakers

The radiation pattern of a speaker is a sphere in its standard operating range. As frequency increases, this output pattern becomes more directional. When a tweeter is mounted at the base of a midrange, a phenomenon occurs called Intermodulation Distortion. As the cone of the midrange moves up and down to reproduce music, this moving surface modulates the reflections of the tweeter.

It is worth noting that the same thing happens when a single speaker cone is asked to reproduce high frequencies: The source of the high-frequency sounds moves forward and rearward as the speaker cone attempts to reproduce lower frequencies. This modulating effect is known as Doppler Distortion. These distortions, combined with the narrowing of the radiation pattern as frequency increases, are some of the many reasons why we have to use different-sized speakers to reproduce music accurately.

When shopping for a coaxial speaker, you will want to choose one that has the tweeter mounted low enough not to interfere with the installation of a grille or trim panel over top of the speaker. You should also look for a tweeter that has a small waveguide that prevents the output from bouncing off the midrange cone.

Shopping for Speakers

We could spend years discussing the different aspects of speaker design and performance. Suffice it to say that you should seek out the assistance of a seasoned and reputable professional for purchase and installation. Be sure to quantify as much of the purchase process as possible – your financial limits, cosmetic preferences regarding installation and performance goals for the system. You will want to use music you have listened to many times when auditioning speakers.

You may want to listen to both a set of more- and less-expensive speakers to help quantify the price point you have chosen. Finally, talk with the salesperson and, if possible, the installer about how and where the speakers will be installed. Be sure to ask about sound deadening, spacers, wiring and anything else that can affect the performance of the installed speaker.

Speaker shopping is a lot of fun, and getting new speakers for your car, truck, boat or motorcycle can be very exciting. Be patient – take your time and be thorough. You will enjoy your new purchase all that much more when you choose a great-sounding speaker and a skilled installer.

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 speakers in your mobile entertainment system are one of the most critical components in determining how your system sounds. If you choose poorly designed speakers that have distortion issues from poor cone, suspension or motor design, no amount of signal processing can make your system sound great. The methods used to install your speakers are as important as the design of the speakers themselves. In this article, we are going to look into some of the common mistakes that occur during speaker installation and how to maximize the performance of your speakers.

Speakers Need A Stable Foundation

If you want to listen to a record player, you want the unit to be on a solid table or stand. You’d never try to hold the turntable on your lap – the needle would jump and bound all over the place. When it comes to speakers, you want all the energy from the motor to move the speaker cone and not the basket. Why would the basket move? Newton’s Third Law of Motion states: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

When the voice coil pushes the speaker cone out, the inertia of the cone is also pushing back on the fixed magnet. If the speaker isn’t mounted securely, it will buzz, vibrate and otherwise move around. These vibrations cause all manner of distortion.

Look at a set of high-end home audio speakers. Years ago, Linn had a set of narrow floor-standing speakers that used a pair of small midrange drivers, roughly 4.5 inches in diameter. The front baffle of the speaker enclosure was 1.5-inch thick MDF. If you knocked on it with your knuckles, it sounded like concrete. And yes, those speakers sounded excellent!

Speaker Installation – Consider Mass

To combat the forces generated by the moving speaker cone, you will want to consider beefing up the mounting surface. In the case of a subwoofer enclosure, an extra-thick front panel can help. Vertical braces on either side of the speaker mounting surface help even more. The best solution is to run full-size braces from the front of the enclosure to the rear. Full depth braces lock the front and rear panels together and add dramatic strength to the speaker mounting surface. These braces also control vibrations in the rear panel to improve performance further.

For a smaller speaker such as midrange or midbass driver in a door, adding strength is a little more difficult. The most common practice is to add a layer or two of butyl damping material (sound deadening) to the metal around the speaker. You can even add a layer or two on the inside of the door skin if you are concerned about thickness. Damping materials with an aluminum layer add a little extra mass.

If your installer is constructing a set of speaker mounting adapters, then ask if they are using a material that has some mass to it. HDPE and ABS are good; acrylic is even better. A material like Corian – the DuPont countertop material – is fantastic. You can easily cut and shape Corian and glue parts together with Cyanoacrylate (Crazy Glue). You may want to use thread inserts or t-nuts with all of these materials. While it is readily available and easy to work with, don’t use wood for speaker adapters inside doors – it will get wet, swell up and deform. It can also hold water and get moldy.

Speaker Installation – Location Matters

If your audio system is going to use factory speaker locations, most of the time these are acceptable to provide an unobstructed output path to the listening area. The last thing you want to do is block the output of the speaker by putting something in front of it. Keep magazines, books, paper and other objects from piling up in front of, or on top of, your speakers.

For subwoofers, the location of the sub has a dramatic effect on how it sounds. You want the energy from the subwoofer to be able to mix with the sound from your midbass speakers as easily as possible. For this reason, hatchbacks and SUVs are great for bass. If you have a sedan, then firing the output of your subwoofer through a ski pass-through works well. You can get away with firing subs into the trunk of a sedan, but you will want to ensure that your midbass drivers can play fairly low – say 75 Hertz or so – to ensure that you don’t lose impact and dynamics.

Back-Wave Cancellation Problems

We use speaker enclosures for two primary reasons – to limit the movement of the speaker cone and to prevent the sound coming from the rear of the speaker cone from canceling out the sound coming from the front. You need to prevent the rearward sound from mixing with the front. For midrange speakers, this means building good quality mounting adapters. Your installer can also use sound-deadening materials to seal up openings in the interior skin of your door panels. You will get better speaker performance with proper back-wave management than you will just buying better speakers.

Weather Protection Ensures Longevity

When mounting speakers in a door panel, it is inevitable that the back of the speaker will get wet. The interior of doors are not completely watertight, and this poses a challenge for installers. Creating an enclosure out of a water-resistant material would be the perfect option, but there is rarely enough mounting depth and it is difficult to create an enclosure that is large enough not to affect the performance of the speaker. For many years, installers have used foam ‘hats,’ cut in half to protect the top of the speaker from direct exposure to drops from the window seal. These are a good option. A thick foam gasket mounted behind the speaker mounting surface can also help. Companies like SoundSkins and F.A.S.T. Rings have ready to apply pre-cut solutions.

There are dozens of other considerations when it comes to having your speakers installed. The most important task for you is to partner with a retailer that does high-quality work and has an excellent reputation. Choosing great speakers for your car audio system is a lot of fun. Hearing them perform up to their potential is even better.

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.

Adjusting or modifying audio signals is nothing new. Analog signal processors have been around recording studios and live performances for decades. Everything from equalizers to crossovers and compressors were conceived back when vacuum tubes were popular. As technology advanced, the size, cost and complexity of signal processors decreased. Now, many car audio source units contain more processing power than early recording studios. This article looks at digital signal processors (DSPs), what they do and why you need them.

A Hostile Environment

If we were to take a full-range home speaker into an open field and measure the frequency response, we’d see a fairly flat and smooth response curve. If you take that same speaker into a small room and measure the response again, you will see peaks and dips at various frequencies. This change in frequency response is not caused by the speaker, but by the room itself. Reflections cause nodes and anti-nodes (peaks and valleys) that dramatically affect the perceived frequency response of the speaker system. To maximize our enjoyment of that speaker, we need to apply signal correction to the speaker so what we hear is similar to what we would have experienced in that field.

In a car, we are very rarely able to sit directly in the middle of the left and right speakers. The driver is usually twice as far from the right speaker as from the left. We hear the output of the left speaker first and it seems as if that speaker appears to be playing louder – because it is closer. Keep this in mind as we discuss digital signal processors (DSPs).

Speaker Limitations

No single speaker can reproduce the entire audio spectrum from 20 Hz to 20 kHz with accuracy, detail and even dispersion of sound. Even if there were one that could do this, the distortion levels in the midrange and high-frequency sounds would still be high because of the excursion requirements of the speaker at low frequencies. Because of this, we make use of several different speakers to cover the audio band. Woofers or subwoofers cover the bass, and typically play up to 80 or 100 hertz. Midrange drivers cover the range from 100 Hz to around 4,000 Hz. Finally, we use tweeters to cover the remainder of the frequencies above 4,000 Hz. While these are approximations, they are common crossover points for these speakers.

A crossover is a device that limits the passing of audio signals. There are two common types used in car audio: high-pass and low-pass. Their name describes their function. A high-pass crossover allows frequencies higher than the crossover point to pass through, and a low-pass allows frequencies below the crossover point to pass. A high-pass crossover would be used to keep the deep bass out of a small door or dash speaker, while a low-pass crossover is used to keep midrange and high-frequency information out of a subwoofer. We can combine both kinds of crossovers to produce what is known as a bandpass crossover – we limited the low- and high-frequency information. We would use this on a midrange speaker when combining it with a woofer and a tweeter. (We will discuss crossovers in detail in another article.)

In car audio, we use both active and passive crossovers. Passive crossovers are a combination of capacitors, resistors and inductors that we connect to the speaker wires between the amp and the speaker. The behavior of the components, and how they are configured, limits what frequencies are allowed to pass through to the speaker.

An active crossover is an electronic device that affects the frequency response of the signal before the amplifier. The benefit of active crossovers is that it is easy to adjust them to different frequencies. Most, if not all, crossover components have to be replaced to adjust the crossover frequency of a passive network.

This information gives us a basic understanding of why we need signal processing. For decades, the mobile electronics industry survived and thrived using analog processing. Companies like AudioControl, Phoenix Gold, Rockford Fosgate and Zapco made equalizers and crossovers, and enthusiasts flocked to them like moths to a flame.

As computing power advanced, we saw products like the Rockford Symmetry appear. The Symmetry was an electronically controlled analog processor – a fantastic creation that allowed users to make many adjustments from a single computerized control panel.

The next evolution in signal processing was to do everything in the digital domain, instead of analog. How does that work?

Building Blocks

A DSP is a powerful audio signal processor with hardware and software that is optimized to perform high-speed processing in real time. Some of the less-expensive processors include the analog-to-digital and digital-to-analog converters within the chip itself. On the higher-end units, the analog converters are external components. Better D/A converters offer increased resolution and improved signal-to-noise ratio performance. Once the audio signal is in the digital domain, one DSP doesn’t vary much from another. Algorithms are written in a similar fashion for filtering, equalization and time alignment.

Why would we want a DSP and not an analog processor? In a DSP, there are no associated concerns about component tolerances or temperature variations that will affect the response of the processing. With the right interface, users can access different system presets quickly and store an unlimited number of configurations on their computers. Most DSP units don’t include any analog adjustments, like potentiometers or switches, which can get dirty or wear out over time. Vibrations that could lead to component failure in an analog system rarely affect DSPs.

Features of Digital Signal Processors

Once an analog signal is converted to digital, the available signal processing is limited only by the software that is written for the chosen unit. The limit on the features of the software is typically determined by the available memory of the processor itself. It takes space to store the program, and additional space to store the converted analog information as the processor works with the information. When you see one processor with more features than another, the difference is usually a memory limitation.

Inputs And Signal Summing

Most DSP units on the market can combine and adjust the level of audio signals on the input to the DSP. If you have a radio with front, rear and subwoofer outputs, you may want to maintain all of these channels discretely as you process the audio signal.

What about when you are trying to integrate with a factory amplifier? Perhaps you have a front door midrange and tweeter output from an amplifier that you need to use for your new front speakers. Most digital signal processors will allow you to combine signals from multiple inputs to facilitate applications like this.

Since different sources have different peak voltage levels, the inputs to your DSP have adjustable sensitivities. Just like the gain control on an amplifier, we want to set the input gains on our DSP to maximize the signal-to-noise ratio of the processor.

Crossovers And Filtering

As we mentioned, different size speakers are designed to focus their performance within different audio ranges. A 3-inch midrange will not play the same frequency range as a 1-inch tweeter or a 6.5-inch woofer. We use the crossovers in the DSP to divide up the frequencies sent to each output and speaker.

A benefit of doing all the crossover processing in the digital domain is that many digital signal processors offer different crossover filter alignments and roll-off slopes. The alignment describes the shape of the roll-off around the -3 dB point. This shape also affects how signals sum back together acoustically. Options are Butterworth, Linkwitz-Riley, Chebychev, Bessel and more. It’s not that one is better than another, but that each is distinct and different. We could write an entire article about crossover alignments.

The crossover slope describes how fast the audio stops playing as a signal moves away from the crossover point. Because it’s all digital, most digital signal processors offer slopes from -6 dB to -48 dB per octave, in steps of 6 dB or 12 dB, depending on the chosen alignment. In most cases with DSPs, 24 dB/Octave Linkwitz-Riley filtering works quite well, but there are dozens of different tuning approaches, so use what works well for you.

Time Alignment And Signal Delay

One of the coolest features of a digital signal processor is its ability to store the audio signal for a variable amount of time before sending it to the speaker. This storage ability allows a properly trained installer to delay the signal going to the speakers closest to the listener so the sound from created by them arrives at the listening position at the same time as the rest of the speakers. For four-way systems (subwoofer, midbass, midrange and tweeter), this setup and fine-tuning can take a little time.

Equalization

The ability to fine-tune the frequency response of each speaker in an audio system is a huge key to making that system sound amazing. We have to measure the response of each speaker at the listening position, then adjust the equalizer so each speaker produces a smooth response. There are many ways to achieve this.

Graphic equalizers typically offer 31 bands of equalization per channel and are spaced 1/3 of an octave apart. This spacing usually provides enough frequency resolution to resolve response issues. Graphic equalizers are easy to understand: You pick the desired frequency band, then boost or cut the signal by the amount of your choice.

Parametric equalizers are much more powerful, but can be a little more difficult to configure. In a parametric equalizer, the user can choose the frequency, bandwidth and amount of signal boost or reduction. Understanding the selection of frequency is simple, but understanding filter Q factor is more difficult. When it comes to Q, the basic concept is that a higher number means that the band adjustment affects a narrower range of frequencies. A low number, like 0.7 or 1, covers a wider range of frequencies. Setting up a parametric equalizer accurately takes some practice. That said, some software applications will provide setting information automatically after you measure the frequency response of the speaker or system.

Output Level And Remote Controls

Having the ability to tune the output level of each speaker finely is critical to the performance of an audio system. To achieve an accurate and balanced soundstage, the amplitude (level) of each speaker in the system must be adjusted very accurately. Output level control is also quite important to matching the efficiency of the different speakers.

Many DSP units have the option of a remote control. These controls can be used to adjust the overall system volume and adjust the subwoofer output level, and can typically load presets for the processor. More advanced controllers give you access to some of the system tuning features, allowing you to make adjustments without the need for a laptop computer. Displays on these remote controls vary from simple single-color dot-matrix LCD panels to full-color OEL displays that are easy to see in bright sunlight.

Digital Signal Processor Tuning – Art Or A Process?

There are many schools of thought about how to configure a DSP. Whether you do it using instrumented measurements or different acoustic techniques, we want to achieve proper protection for the speakers, smooth frequency response from both channels of the audio system and aligned arrival times from each speaker.

Many car audio manufacturers train their dealers in different methods of achieving a great “tune” on their customer vehicles. If you are looking to improve the sound of your mobile entertainment system and already have great speakers and amplifiers, visit your local car audio professional. They would be happy to demonstrate the benefits of DSPs, and provide you with the information you need to make an educated decision about buying one.

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.

When people are looking at purchasing a car audio amplifier, the specification they check most often is how much power it can produce. Power is rated in watts – a universal unit of measurement of power. In this article, we explain what a watt is, and how it is measured – both the correct and incorrect way.

Dictionary Time!

Let’s get the formal definition of a watt out of the way first. A watt is an SI (Systéme International) unit of the measurement of power. The power does not have to be electrical. In fact, the unit watt was named after James Watt and created to quantify the work a steam engine could do. In that kinetic application, a watt was the work done when the velocity of an object was moving steadily at 1 meter per second with a force of 1 newton opposing it. When referring to an electrical motor, 1 horsepower equals 746 watts.

As much fun as talking about horsepower is, we are car audio enthusiasts, so let’s get back on track with an explanation of the electrical watt.

In electrical terms, a watt is a transfer of 1 joule of energy over a period of 1 second. The next logical question is what is a joule? A joule is yet another SI unit of measurement, and it defines the amount of work required to move a charge of 1 coulomb through an electrical potential of 1 volt. Yes, the question now moves to the coulomb – what in the world is that? A coulomb is a unit of electrical charge – and is equal to -6.242 x 10^18 electrons.

Lost yet? Don’t fret; we are just appeasing the math and measurement nerds among us. Let’s break this down to what matters.

When we want to use electricity to do work, we have to flow electrons through a device like a filament, motor or voice coil. The result will be, in the case of a speaker, that the magnetic field created by the flow of electrons will cause the voice coil to be attracted to or repelled from the fixed magnet in our speaker. When we flow more electrons, more work is done, and the speaker moves farther toward or away from the magnet.

Power Math

Here is where we start to talk about power equations. There are three common methods of calculating the power in a circuit – but we need to know the values of other variables such as voltage, resistance or amperage. Any two of these variables can be used to calculate the power done in a circuit. Here are the equations:
If we have a circuit with a resistance of 4 ohms and we apply a voltage to it with a potential of 10 volts, then we have 25 watts of power. Increasing that voltage to 20 volts means the power available is now 100 watts. We can substitute and rearrange the variables in the equations above to figure out any other variable – it’s simple algebra.

Measuring Power

When a technician has an amplifier on a test bench and wants to measure power, the technician typically connects the amp to a bank of high-power load resistors, then measures the output of the amplifier when the signal has reached a distortion level of 1%. The measurement taken is voltage. Most often, we assume the load is not variable. Let’s say we measure 44 Volts RMS out of an amplifier and we have the amp connected to a 2 ohm load. That works out to 968 watts. It’s very simple and very repeatable – but it doesn’t work in the real world. Let’s look at why.

Resistance versus Reactance

This is going to get a bit technical. Audio signals are alternating current (AC) signals. AC signals are required to make the speaker cone move back and forth from its rest position, but they make power measurement much more complicated. The way conductors and loads react to AC signals is different from direct current (DC) signals.

Because AC signals change direction, the polarity of the magnetic fields they create also changes direction. Trying to change the polarity of magnetic fields wreaks havoc with the behavior of current flow. Once current gets flowing and sets up a magnetic field, it doesn’t like to stop. Imagine a DC voltage – all the electrons are moving in the same direction all the time. They are happy and have no complaints. When it comes to AC signals, though, that flow of electrons has to change directions. With a 20 k Hz signal, the change of directions happens 20,000 times a second. Electrons are lazy – they like to keep doing what they were doing. Because of this, they oppose a change of direction.

An inductor is truly nothing more than a coil of wire. We see inductors in passive crossover networks and the filter stages of Class D amplifiers. When electrons are flowing through an inductor, they set up a strong magnetic field. When you take away the voltage source, the electrons try to keep flowing. In fact, if you have seen a relay with a diode connected to it, that diode is there to give that flow of electrons somewhere to go, other than back into the circuit that was controlling the function of the relay.

When we apply an AC signal to an inductor, the higher the frequency, the harder it is to change the direction of the flow of electrons. The resistance to the flow of alternating current is called inductive reactance. Think of it as resistance, but only applicable to AC signals. Inductors oppose a change in current flow. If we disconnect our alternating current source and measure the DC resistance of an inductor with a multimeter, the number we see on the screen is the resistance. To measure the reactance of an inductor, we need a device that can apply an AC signal and measure the effective voltage drop across the inductor.

The formula to calculate inductive reactance is Xl = 2 x pi x F x L, where F is the frequency of the applied AC signal, L is the inductance value of the inductor measured in henries and Xl is the inductive reactance in ohms. You can see that inductance increases with frequency, as we mentioned earlier.

The voice coil of a speaker is and acts as an inductor.

Current and Voltage

We have more bad news for you. Because an inductor opposes the change in current flow, a timing error arises. Timing of what, you ask? The relative time between the AC voltage across the inductor and the AC value of the current flowing in the inductor. In a perfect inductor (one with no DC resistance), the current through the inductor lags the voltage across the inductor by 90 degrees or ¼ of the frequency of the signal being passed through.

Let that sink in for a second, then think back to our equations for power. Power is voltage times current. But what if the current peak isn’t happening at the same time as the voltage peak? We can’t simply multiply the two numbers together to get the power in the circuit. Worse, the amount of time that the current lags voltage depends on the DC resistance of the inductor and the inductive reactance – for most car audio speakers, the DC resistance is usually somewhere between 2 and 8 ohms. The inductance is in between 0.04 mH for a high-quality tweeter to more than 5 mH for a big subwoofer.

There’s one more challenge: The inductance changes depending on the drive level of the speaker and the position of the speaker cone.

We’re sure you agree – It’s all very complicated, but don’t give up just yet.

How do we measure the real power in an AC circuit? There are a couple of ways. We can measure instantaneous current and voltage at a very high sampling rate and multiply them together. The sampling rate would have to be 20 or 30 times the frequency we measure to be reasonably accurate. We can also use conventional meters to measure the amount of current and voltage in the circuit, then use a Phase Angle Meter to find the relative relationship between the two. Pretty much none of us have a standalone phase angle meter in our toolboxes. What we can’t do is just multiply voltage and current times each other.

Those SPL Guys And Watts

If you are reading this, then you likely roam the Internet with some frequency. You have undoubtedly seen SPL enthusiasts attempt to measure the power produced by their amplifiers by “clamping”’ it. They connect a current clamp to one of the speaker wires coming out of the amp and put a voltmeter across the terminals of the amplifier.

This creates three problems:

1. They should connect the voltmeter to the speaker terminals. Because of the high current flow, the resistance in speaker wire can waste a measurable amount of power.
2. With a voltmeter and current clamp, we don’t know the phase relationship between the current flowing through the voice coils and the voltage across the voice coil.
3. They typically perform these tests at extremely high power levels. The massive amounts of power heat up the voice coils quickly. This heat also increases their resistance quickly. This increase in resistance will cause the current flowing through the speaker to decrease. If the connected current clamp is in “peak hold” mode, it will store a peak reading of the initial current flowing through the voice coil. The reduction in current flow eases the load on the amplifier power supply and allows it to produce more voltage. As current decreases, the voltage out of the amplifier may increase, giving a false reading to the voltmeter in peak hold mode. This heating and resistance increase can happen in a matter of seconds.

If you thought our definition of the watt was complicated, then explaining how to calculate power in a reactive load would push you over the edge, so we won’t explain it all. That’s a topic saved for college or university courses on AC power. What we will do is provide a solution for making complicated power measurements.

The reality is when it comes to measuring power out of an amplifier while connected to a speaker, getting accurate results is very difficult. A few companies produce car audio power meters. The most popular unit is the D’Amore Engineering AMM-1. The AMM-1 is a handheld meter that simultaneously measures current and voltage, and calculates the phase angle between them to provide an accurate power measurement. The AMM-1 will show you how much real-world power your amplifier is making. (Please don’t cry if it’s less than you thought.)

The AMM-1 can also show volt-amps. Volt-amps are calculated by multiplying current times the voltage. You can also see the phase angle of the load on yet another screen. If you are serious about measuring power when an amplifier is driving a reactive load like a speaker, then this is the tool you need.

What You Need to Know

When you are shopping for an amplifier, the numbers you usually see quoted are measured into resistive loads. Most amplifiers have no problem with driving reactive loads, so you can trust the published numbers, as long as the distortion specification is clearly defined.

The CEA-2006A (now called CTA-2006A) specification for power measurement defines the maximum signal distortion during measurement as being 1%, and no more than 14.4 volts can be supplying the amp. Comparing power specs using this standard has leveled the playing field in the car audio industry.

We will look at some other very important amplifier specifications in another article. These other specifications may, in fact, be more important to choosing the right amp for your system than how much power the amp makes. Until then, drop into your local car audio specialist retailer to find out about the latest amplifiers available for your system. There are some amazing new amps on the market with a lot of cool features.

Happy listening!

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.