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RESOURCE LIBRARY

Product Spotlight: Rockford Fosgate P3D4-12 Car Audio Subwoofer

Rockford Subwoofer

If you’ve been into car audio for as long as I have, you’ve likely had a memorable experience with a Rockford Fosgate subwoofer. I vividly remember being in one of the Korbon Trading (the Canadian distributor of Rockford Fosgate in the ’80s) Blastro vans. This GMC Safari had four 18-inch Punch subwoofers powered by a pair of Power 1000 amplifiers. It was the first time a car audio system left me breathless. Fast-forward 33 years and Rockford Fosgate is still a leader in developing car audio subwoofer solutions that get loud and sound amazing. Let’s take a close look at the flagship of the Punch Series 12-inch drivers – the P3D4-12.

Rockford Fosgate Punch P3D4-12 Features

The P3D4-12 is a dual voice coil subwoofer constructed with each coil having an impedance of 4 ohms. The sub is available in a dual 2-ohm model called the P3D2-12. Both are based around a custom-tooled four-spoke hybrid stamp-cast aluminum basket. The main vertical supports and the mounting lip are stamped. There is a cast cooling insert at the base of the basket around the voice coil. Underneath the basket is a 96-ounce double-stacked ceramic magnet assembly that is concealed with a protective PVC rubber cover. The bumped T-yoke is visible through the bottom of the cover, exposing the vented pole piece and eight additional small cooling vents under the voice coil former. These extra vents also allow air pressure to be released from inside the motor as the driver moves rearward, thereby improving linearity and reducing distortion at high excursion levels.

Up top, the additional cooling and ventilation are provided by vents below each window in the basket. These allow hot air to escape from under the spider, helping to keep the motor assembly cool and reduce power compression. All the cooling features combine to ensure that these subwoofers continue to sound great without losing efficiency, even after hours of play time.

With Rockford Fosgate’s FlexFit basket, instead of eight fixed holes in the mounting lip for fasteners, eight slots allow your installer to align the subwoofer perfectly in the enclosure. An aluminum ring is included to finish off the installation and conceal the mounting hardware for a classy and tidy look.

Rockford Subwoofer
The heavy-duty hybrid stamp-cast aluminum basket ensures a solid foundation for this impressive subwoofer.

Voice Coil and Moving Part Features

The cone of the P3D4-12 is made from aluminum, as is the inverted dust cap. Both have an anodized finish, and Rockford Fosgate is screened on the cone. At the top of the cone is a Santoprene rubber surround that is attached to the basket with Rockford Fosgate’s VAST design. In essence, VAST moves the surround closer to the outer edge of the basket and increases the effective cone area of the driver.

Rockford Subwoofer
An aluminum trim ring conceals the FlexFit mounting hardware for a clean and tidy appearance.

At the base of the cone are a pair of tear- and fatigue-resistant linear poly-cotton spiders mounted face-to-face to reduce nonlinearities. Four 16-AWG tinsel leads are sewn into the spiders to ensure that they won’t make noise at high excursion levels. The 2.5-inch voice coil former is made of anodized aluminum so that it can withstand extreme temperatures. The driver uses a four-layer voice coil winding. A spun-laced NOMEX reinforcement collar adds strength to the connection between the cone, the voice coil former and the spiders.

Electrical connections are handled by four nickel-plated spring terminals. The terminals push inward toward the voice coil and wire up to 10 AWG in size is inserted from below. While it seems inconsequential, this vertical wiring method helps keep everything organized during installation.

Rockford Subwoofer
The bottom-entry terminals on the P3D4-12 accept up to 10-AWG cables and keep the wiring out of the way when installing the subwoofer.

P3D4-12 Specifications

The P3D4-12 subwoofer is rated to handle 600 watts of power continuously and up to 1,200 watts maximum power. The driver has a total weight of 20.9 pounds (9.48 kilograms). Mounting depth is 6.66 inches, and the driver requires a cutout size of 11.25 inches.

In terms of electromechanical specifications, Rockford Fosgate specifies the driver as having a resonant frequency (Fs) of 27.7 hertz, an equivalent volume compliance (Vas) of 2.04 cubic feet and a total Q (Qts) of 0.52. The maximum linear excursion (Xmax) is listed at 0.547 inch in each direction.

The owner’s manual suggests a sealed enclosure with a net internal volume of 1.02 cubic feet to produce an F3 frequency of 42.2 hertz and a system Q of 0.78 – which should be well-controlled and impressively musical. If you want to increase low-frequency efficiency, they suggest a 1.79-cubic-foot vented enclosure with a tuning frequency of 40 hertz. This should result in an F3 frequency of 32.8 hertz and a lot more output. If you have the room, we always suggest the vented enclosure.

Rockford Subwoofer
Predicted frequency response of the P3D34-12 in the factory-spec enclosures: red, sealed; yellow, vented

If you want a little more rumble from the sub, ask the Rockford Fosgate retailer you’re working with to build the vented enclosure with a tuning frequency of 30 Hz. You’ll lose some of the 50-60 hertz efficiency, but pick up more output below 35 hertz.

Rockford Subwoofer
If you want to trade some boom for more rumble, drop the enclosure tuning frequency from 40 hertz (yellow) to 30 hertz (green).

Upgrade Your Car Audio System with a Rockford Fosgate Subwoofer Today

If you’re searching for a high-performance subwoofer that’s designed to sound great while delivering impressive amounts of bass, drop by your local authorized Rockford Fosgate retailer. You can find a shop near you using the dealer locator on the Rockford Fosgate website. Be sure to follow Rockford Fosgate on their Facebook page and Instagram feed and check out the awesome videos they produce on their YouTube channel.

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.

Filed Under: ARTICLES, Car Audio, Products, RESOURCE LIBRARY Tagged With: Rockford Fosgate

Digital Signal Processors Take Your Audio System To The Next Level

Digital Signal ProcessorsAdjusting 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

Digital Signal ProcessorsIf 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.)

Digital Signal ProcessorsIn 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

Digital Signal ProcessorsMost 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

Digital Signal ProcessorsAs 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

Digital Signal ProcessorsThe 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

Digital Signal ProcessorsHaving 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.

Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

Product Spotlight: Sony XAV-AX8100 Media Receiver

Sony XAV-AX8100

When it comes to floating-face or T-style radios, there are more options than ever. The Sony XAV-AX8100 combines all the most sought-after features with an 8.95-inch screen that will look perfect in your dash. Whether it’s staying connected with Android Auto and Apple CarPlay smartphone integration or having support for all your favorite digital media files to entertain you on a long drive, this solution has all the bases covered.

8.95-inch Floating Face

The center point of the XAV-AX8100 is its large 8.95-inch color touchscreen. The display has a resolution of 800 by 480 pixels and has been treated with an anti-glare coating to help ensure that its graphics are clear in bright sunlight. At the base of the screen are eight physical buttons that provide quick and easy access to source selection, volume control, track selection and voice recognition features. As with all Sony multimedia receivers, the styling and colors are specifically designed to create a look that’s right at home in the dash of your car or truck.

One of the big upgrades to the XAV-AX8100 over its predecessor is the inclusion of an HDMI input jack on the bottom of the display. Located just under the volume control rocker switch, the input allows you to connect a laptop, game system or media player to access while the vehicle is parked and the parking brake is set.

Sony XAV-AX8100
An HDMI input on the bottom of the display makes it easy to connect a media player or laptop.

Smartphone Integration Technologies

Apple CarPlay and Android Auto smartphone integration remain at the top of the feature list for the 8100. Using the voice recognition features of your smartphone and its internet connection, you can make phone calls, send text messages or request navigation directions without having to enter information on the screen. Instead, press the voice button on the radio and ask for what you want. Your phone will take care of the rest.

The Sony XAV-AX8100 also includes support for Weblink. When installed on your Android or iOS-based smartphone, Weblink allows you to display images from many popular applications on the radio screen. In addition, touchscreen commands from the system are relayed back to your smartphone if the application is compatible, so navigating app menus is intuitive and seamless.

Sony XAV-AX8100
Apple CarPlay and Android Auto smartphone integration allow you to use voice commands to control your phone.

Sony XAV-AX8100 Audio Features

This media device includes an AM/FM receiver and one USB port for your smartphone or a USB memory stick. The system will play MP3, WMA, AAC, WAV and FLAC audio files, along with MP4, WMV and MKV video files (when parked). Bluetooth hands-free calling and audio streaming are also built in, and the integration features provide direct access to iHeartRadio, Pandora, Spotify and Tidal streaming services. In addition, your authorized Sony retailer can add an SXV300 SiriusXM satellite radio receiver to deliver non-stop entertainment from coast to coast.

The XAV-AX8100 has a four-channel amplifier that can deliver up to 20 watts of power to each speaker. The front, rear and subwoofer preamp outputs are rated at 5 volts and include adjustable electronic crossovers. In addition, Sony includes their EQ10 10-band equalizer, the Extra Bass loudness feature and Digital Soundstage Organizer (DSO) processing to let you fine-tune the sound of your car audio system.

The radio is based on a single-DIN chassis, which will fit in vehicles that weren’t previously compatible with double-DIN aftermarket radios. Your installer can adjust the screen angle, extension and height so that the radio looks great and is easy to use. From an integration and safety standpoint, the XAV-AX8100 is compatible with most steering wheel audio control interfaces, and it includes a backup camera input with a reverse trigger wire.

Sony XAV-AX8100
The compact single-DIN chassis allows the XAV-AX8100 to be installed in applications where a double-DIN unit won’t fit.

If you’re looking for a reliable, high-performance radio upgrade for your car or truck, drop by your local authorized Sony car audio retailer and ask for a demonstration of the XAV-AX8100. Be sure to bring your smartphone to experience the voice command features. For more information about this radio and the other fantastic car audio upgrade products from Sony, visit their website. Also, be sure to follow them on Facebook page, Instagram and YouTube for the latest updates and new product releases.

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.

Filed Under: ARTICLES, Car Audio, Products, RESOURCE LIBRARY Tagged With: Sony

Product Spotlight: Rockford Fosgate M5-1500X Marine/Powersports Amp

Rockford Fosgate M5-1500X5

Whether you have a Jeep that gets muddy, a side-by-side that thinks it’s a part-time submarine, or a boat that’s always getting swamped, Rockford Fosgate’s M5-1500X5 powersports amplifier can be the heart of an impressive audio system upgrade. This five-channel amplifier can deliver the power your speakers need to reproduce audio with amazing clarity while driving a subwoofer or two to give your music impact and warmth – all from a single chassis. If you agree that this sounds like the perfect upgrade for your mobile sound system, read on to learn more about this fantastic amplifier.

Rockford Fosgate M5-1500X5 Specifications

The M5-1500X5 amplifier is rated to produce 100 watts per channel from the four main channels and an impressive 600 watts from the subwoofer channel. The front channels can drive 2- or 4-ohm loads while the subwoofer channel is optimized to produce that power into a 2- or 1-ohm load. The sub channel makes 400 watts into a 4-ohm load. If you have an application where you need huge power for a set of tower speakers, the front and rear channel pairs can be bridged to drive a pair of 4-ohm loads with 200 watts to each speaker. Of course, all of the specifications for the amp are compliant with the CTA-2006 standard, so you know you can trust the ratings. Based on our experience with the M5-1000X1, the numbers are likely conservative.

The front, rear and subwoofer channels each have a dedicated sensitivity control, Punch EQ control and a crossover that’s adjustable between 50 and 250 Hz. The Punch EQ allows up to 18 dB of boost at 45 hertz on the subwoofer channel and combines that bass attenuation with treble boost centered at 12.5 kHz on the front channels. The crossover on the front channels can be run in high- or low-pass modes or defeated completely. The adjustable subwoofer channel crossover is always on and limits high-frequency information. Your installer can connect an RCA cable directly to the RCA input for the sub channel, or set the Sub Input Switch off and let the amp combine the signals from the front and rear channel inputs. The subwoofer channel has a fixed -12 dB/octave infrasonic filter that’s set to 30 hertz to protect your subwoofers and optimize their output. There’s also a two- or four-channel switch on the end of the amp by the input connections. Setting this to two-channel mode copies the signal from the front channel inputs to the rear channels.

Rockford Fosgate includes their C.L.E.A.N. input and output monitoring circuit, making it easy for your installer to maximize the signals going into the amp and set the output level controls to deliver maximum performance. They’ve also included a PRESET switch for level and crossover settings for use with their vehicle-specific Motorsports stage kits. These settings can be invoked by activating the PRESET switch on each channel.

Rockford Fosgate M5-1500X5
Your installer has easy access to settings and adjustments for each pair of channels right from the top of the M5-1500X5 amplifier.

The amplifier makes use of several technologies found on other premium Rockford Fosgate amplifiers. The NOMAD protection circuitry guards against short circuits on the speaker connections. The Class-AD and Class-BD designs help to ensure good efficiency to maximize the capabilities of the magneto or alternator and battery on your boat or side-by-side. Likewise, the lightly regulated P.O.W.E.R. technology for the power supply design allows the amplifier to maximize output power when it’s fed with more voltage. Finally, the Maximum Efficiency Heat Sink Application (MEHSA) heat sink design helps to ensure that the amp keeps running when pushed hard by spreading thermal energy throughout the chassis.

Rockford Fosgate M5-1500X5
The Rockford Fosgate M5-1500X5 includes speaker-level and RCA preamp input harnesses to make the amp compatible with all manner of signal sources.

Five-Channel Powersports Amplifier Layout

The M5-1500X5 is based on a 4.25- by 1.7-inch extruded aluminum chassis that’s 12.3 inches long, including the cast aluminum end-caps. The connections for input signals, along with speaker and power output, are made via pigtail harnesses that attach to each end of the amplifier. The harnesses are held in place with screws and feature gaskets to ensure that everything is watertight.

The controls are on the top of the amp on the left side and are protected by a removable cover once set. As you’d expect, the cover includes a rubber gasket to keep water, dust and debris out of the amp. The combination of these waterproofing features gives the amp an IPX6 water and dust intrusion rating. Rockford Fosgate calls this their Element Ready design, and it includes testing for prolonged UV exposure as well as corrosion resistance.

Rockford Fosgate M5-1500X5
The controls on the top of the amp are protected by a watertight removal cover that maintains the IPX6 water intrusion rating.

Upgrade Your Adventure with Rockford Fosgate

Your local authorized Rockford Fosgate dealer would be happy to design an audio system upgrade for your boat, side-by-side, off-roader or Jeep using the M5-1500X5. You can find a dealer near you by using the Dealer Locator on their website. To keep up with the latest new product release, cool events and amazing vehicle features from Rockford Fosgate, be sure to follow them on Facebook, Instagram and their YouTube channel.

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.

Filed Under: ARTICLES, Car Audio, Products, RESOURCE LIBRARY Tagged With: Rockford Fosgate

Watts Are Watts, Or Are They? A Detailed Explanation for Car Audio Guys

WattsWhen 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!

WattsLet’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:
WattsIf 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.

WattsWhen 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.

Watts

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.

WattsThe 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.

WattsThe 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.

Filed Under: ARTICLES, Car Audio, RESOURCE LIBRARY

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