When designing a car audio subwoofer system, the Product Specialist and Installer you’re working with have two options for mounting subwoofers in your enclosure. There is, of course, the typical method with the motor assembly and basket inside the enclosure. With that said, many installations have the subwoofers mounted upside down, or as many call it, in an inverted fashion. There are benefits and drawbacks to this installation method – let’s talk about it!

Benefits of Inverted Subwoofer Installation

The most significant benefit of having your subwoofers installed such that the motor assembly and basket are visible is cooling. The heat generated in and around the voice coil and magnet can easily escape into the air in the vehicle. Access to all the relatively cool air in the vehicle can dramatically improve thermal power handling, especially compared to an acoustic suspension (sealed) enclosure.

The second benefit of an inverted subwoofer installation is mounting depth. With only the cone inside the enclosure, you can install deep subwoofers in locations with minimal mounting depth. Yes, you’ll have a large woofer protruding from the enclosure’s front, which may affect your vehicle’s cargo carrying capacity.

Extending this same philosophy regarding depth, another small benefit of inverted subwoofer installations is increased enclosure volume. Subwoofers with large baskets and motor assemblies can easily displace 1/10th of a cubic foot. Thus, your installer can reduce the size of the enclosure or use that extra airspace to improve the low-frequency output of the subwoofer system. The difference isn’t likely to be dramatic, but more deep bass is always a good thing!

Drawbacks of Having Your Subwoofers Upside Down

There are some drawbacks to inverted subwoofer installations. First, it’s challenging to protect the rear of the subwoofer and the wiring from damage caused by cargo. This isn’t the sort of installation you’d choose for a daily driver that’s also used to get groceries or go on vacation. On the other hand, it might be great for a company demo vehicle or a show car where there’s a conscious and consistent effort to keep things safe.

It can be tricky to come up with a way to keep the wiring to the subwoofer’s voice coils looking tidy. Inside an enclosure, so long as the electrical connections are solid, few care how the wiring looks. When the wiring is visible, then terminations and wire routing become a genuine consideration. Protecting those connections from damage or from objects that might short the terminals is also an issue.

The next drawback is a minor reduction in efficiency. No, the operation of the subwoofer doesn’t change, but the effective cone area might be reduced. When the woofer is mounted conventionally, you have the entire cone surface available to pressurize and rarefy the air in the vehicle. When mounted upside down, the area of the cone inside the voice coil may not contribute to moving air. This effect depends somewhat on the design of the woofer. If there’s a vented pole piece, the change will be minimal.

Lastly, and perhaps the most significant drawback of having a subwoofer mounted in an inverted fashion, is the chance for unwanted noise. Not all voice coil cooling systems are quiet at high excursion levels. Airflow around the coil, top plate and in and out of vents may add unwanted huffing and chuff at high output levels. There is also a chance that tinsel leads can make noises if they come into contact with the cone when played loudly. Unfortunately, if you have a subwoofer that makes these kinds of noises, there’s typically no easy way to remedy the issue. It’s best to mount those subs in a conventional cone-out installation. Your installer can test the subwoofers by applying a signal to them and listening for noise without any enclosure. Be careful not to bottom out the woofer, though.

Balance the Benefits and Drawbacks

As you can see from the images we’ve included in this article, sometimes the only option is to mount the subwoofers such that the motor assembly and basket are visible. You can discuss your inverted subwoofer installation options with the installer before work begins on your car or truck to ensure that you’ll be happy with the results.

Lead-in Image: Thanks to Matt Schaeffer from Musaic Audiophile Design in Lewes, Delaware, for sharing this installation of a pair of Focal subwoofers in the back of a ZL1 Camaro.

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 the ’80s and ’90s, the target demographic at a car stereo shop was men ages 18 to 24. Guys would work to upgrade their cars with subwoofers, pull-out CD players and lots of speakers in hopes of having the loudest audio systems in their group of friends. Not coincidentally, during that time magazines ran advertisements for products with outrageous cosmetics, promoted by scantily clad women. Fast forward a few decades, and the typical client is likely the same person, but their goals and expectations have matured significantly. So let’s look at the typical client for a reputable mobile enhancement retailer today.

Drivers Want Safe Ways To Use Their Phones

One of the most common types of client visiting car stereo shops these days has a 10- to 20-year-old vehicle and wants to upgrade the technology in that car or truck. It might be a Chevy Monte Carlo, Ford F-150 or a Porsche 911. In almost all cases, they want to add a Bluetooth hands-free solution that will let them make phone calls without having the phone in their hands.

Another popular upgrade is multimedia receivers that include Apple CarPlay and Android Auto smartphone integration. Along with hands-free calling, these technologies allow the driver to send text messages using voice commands. They can also search for navigation instructions to a destination almost anywhere in North America using Waze, Google Maps or Apple Maps (the latter only when using an iOS device). Finally, of course, streaming audio is another popular source of music these days. CarPlay and Android Auto include dedicated apps for Spotify, Amazon Music, Pandora, iHeartRadio and Tidal, to name a few.

In most cases, installing a new multimedia receiver is the solution to these upgrade requests. We’ve covered the basics of buying a new radio in our Car Radio Buying Guide. That guide includes details on radio sizes, features and functions. If there’s a single takeaway from the article, it’s that we recommend that before you buy a radio, test it on a display board. All models aren’t as quick to respond to commands, nor do all of them have intuitive interfaces. Oh, and make sure you connect your phone to the radio to test smartphone integration, as well as Bluetooth hands-free calling and audio streaming. Unfortunately, not every phone is compatible with these technologies.

A few companies, such as AIS and ZZ-2, offer smartphone integration upgrades that will work with the factory display and controls in your vehicle. Check with your local retailer about whether these products are available for your vehicle’s year, make, model and trim level.

Raising the Bar for Realistic Sound

Back in high school, most of us had a Walkman or, for the slightly younger crowd, a Discman. It was rare to see someone who had upgraded the headphones that came with these devices to something that offered better performance, but it did happen. These days, high-end headphones are a multi-million-dollar industry. As such, more and more people have a higher benchmark for what their music should sound like.

The philosophy around wanting better sound from our entertainment systems hasn’t changed, but the customer has. The younger crowd is less likely to visit a stereo shop for an upgrade and more likely to try to do it themselves. The results vary from “Hey, nice work!” to “How is your vehicle not on fire?” Partnering with a specialty mobile enhancement retailer is the best bet for those who want predictable results from their investment. These shops have the products, integration solutions and, most importantly, the training to ensure that you get the best performance possible from the upgrades you choose.

A proper audio system upgrade will start with the installation of sound deadening material to reduce noise transfer into the vehicle. Just like treating the listening room in a high-end home audio or theatre system, this is a crucial step in delivering great sound.

The next step in a great audio upgrade is to choose a subwoofer system to help reinforce the bottom octave or two of the music you enjoy. Even the most premium factory-installed sound systems from Bose, Bowers & Wilkins, Bang and Olufson, Lexicon, Burmester or Mark Levinson have difficulty playing music below 35 or 40 hertz. That’s an entire octave (or more) that you’re missing out on. As such, synthesizers, drums, a timpani or purely computer-generated sounds will be missing, and you may find the audio system lacks emotion and impact. Can you imagine watching a movie without feeling the bass impact from an explosion or a helicopter landing? The same goes for listening to your favorite music.

Subwoofers come in all shapes and sizes, and a reputable retailer can design a solution that delivers the bass you want without taking up valuable storage space in your vehicle. The subwoofer system can be configured to blend in with the rest of the speakers in your car or truck and provide the extension you want. They don’t have to be set to wake the neighbors or rattle the rearview mirror.

Seeking Clarity Through Upgraded Speakers

Once you’ve addressed adding a subwoofer system, the next step is to upgrade your speakers and add an amplifier. New speakers reproduce audio signals with improved clarity and, when powered by a high-quality amplifier, allow you to play the audio system at higher volume levels. When buying speakers, or more importantly, picking from the options on the display at your local car stereo shop, be sure to audition them. Yes, they’ll sound different when installed in your vehicle, but that doesn’t mean you shouldn’t make sure they sound great. Harshness, unnatural tonal balance or too much midbass emphasis is only going to be exaggerated once the speakers are integrated into your car or truck.

They Care Enough To Include System Calibration

Digital signal processors are a necessity when it comes to delivering great sound in your vehicle. The acoustics in our cars, along with unequal path lengths to speakers, wreak havoc on imaging and staging. Having your audio system configured and calibrated using a DSP by someone intimately familiar with the process is crucial to experiencing your music the way the engineer who mastered the recording heard it. Proper instrument and performer placement on the soundstage, along with neutral and accurate tonal balance, are only achieved when the equalization, signal delay and crossovers are set properly.

They Seek Perfection in Design and Integration

Another observation about today’s car audio upgrade landscape revolves around system design and integration. Many car audio shops can install a set of speakers or replace a radio. Fewer have the skills to design a proper custom subwoofer enclosure. Even fewer again have the tools and training to configure and calibrate a digital signal processor properly.

Finding a shop that can do this all properly and execute the installation in a way that makes the upgrade look like a part of the vehicle rather than a bolted-on afterthought is, well, truly rare. Our point: You’re going to have to have to shop for the right company to work on your car or truck. You want it to be treated with respect while it’s in their bay, and you’ll want an audio upgrade that sounds magnificent and functions reliably. The process may take some time, but partnering with a genuine professional is worth the effort.

They Crave Precision in Speed Trap Detection

For those with a heavy right foot, upgrading a vehicle with a radar detector and laser defense system is an excellent investment. The latest technologies offer exceptional long-range sensitivity to all types of police radar. At the same time, their digital processing helps to reduce or eliminate false alarms from adaptive cruise control and collision avoidance systems. Of course, you have many options when it comes to having these systems integrated into your vehicle. The display and control panel can be attached to your dash or center console, or you can work with an expert who can create custom mounting solutions that make these a part of your vehicle interior. The same goes for laser shifters. Vehicle-specific acrylic mounts help to conceal these pods and make them nearly invisible.

They Want Their Vehicle Treated with Respect

We could go on and on about how installing a remote car starter is crucial to its reliability and how the wiring for a dashcam should be run carefully around airbags. We think you get the message that high-quality car audio and accessory upgrades are now something a more mature client is after. Invest the time in choosing the right shop that offers the right products and solutions to work on your vehicle.

Lead-in Image: Thanks to Shon Besharah of 6Thirteen Auto Design near Ottawa, Ontario, for sharing this image of a custom vehicle interior and subwoofer system he created.

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.

A few weeks ago, we were browsing a few car audio related Facebook groups and Reddit subreddits. We saw the same question come up time after time: “I have two dual 2-ohm voice coil subs; how do I show the amp a 1-ohm load to make max power?” It wasn’t just once or twice that this question was asked – we saw it and versions of it at least a dozen times in less than an hour of browsing. Clearly, this is a topic that consumers struggle to understand. Subwoofer wiring configuration is crucial information if you’re shopping for an amplifier to mate to an existing set of subwoofers, or vice-versa.

Subwoofer Voice Coil Impedances

We’ve talked about single- and dual-voice coil designs in the past. In essence, they exist to provide the Product Specialist designing your car audio system with different wiring options so that they can maximize the performance of your subwoofer amplifier.

We’ll be clear: A single voice coil subwoofer isn’t “better” than a dual voice coil sub, or vice versa. The only benefit of a DVC sub is that the coils can be wired in series, in parallel, or each can be fed directly to an amplifier channel. There are benefits in terms of installation flexibility, but the number of connections to the voice coil doesn’t improve the driver’s performance or sound quality.

In subwoofers available from professional mobile enhancement retailers, you’ll typically see either single 2-ohm or single 4-ohm drivers and dual 2-ohm or dual 4-ohm offerings. There are some unique offerings as well. The JL Audio W7AE drivers have a single 3-ohm coil, so three drivers can be wired together to present a 1-ohm load to an amp. Audiotec-Fischer has some quad 3-ohm-coil woofers designed to extract maximum power from its line of non-bridgeable amplifiers.

When you get into some competition-level subwoofer products, you may see some dual 1-ohm coil configurations. If we think long and hard, we seem to recall hearing about a quad 0.7-ohm coil competition-level subwoofer. Nevertheless, there are a lot of options available.

Picking the Final Load Impedance

When it comes to wiring subwoofers to an amplifier, your installer has a few wiring options: parallel, series and series-parallel. The voice coils of a single dual-voice-coil woofer can also be wired in series or parallel. The goal of the options is to present the amplifier with a net impedance that allows it to make the best use of the available power.

You see, most subwoofer amplifiers produce more power as the load impedance drops. If we look at an amp like the ARC Audio X2-1100.1, it’s rated to produce 350 watts into a 4-ohm load, 600 watts when connected to a 2-ohm load and 1,100 watts when the subwoofers are wired to present a 1-ohm load. If you’ve purchased this amp, it only makes sense to present it with a 1-ohm load so that you get the most power available for your investment.

Here’s a small aside about amplifiers: Many subwoofer amps don’t make more power into lower impedances yet are still designed and listed as capable of running these loads. For example, the Rockford Fosgate T1500-1bdCP is rated to produce 1,000 watts when connected to a 4-ohm load, then 1,500 watts when wired to a 2- or 1-ohm load. The same goes for the Hertz Mille Power 1. It produces 600 watts into a 4-ohm load and 1,000 watts when connected to a 2-or 1-ohm configuration.

We highly recommend wiring these amplifiers to 2 ohms. The higher impedance will improve the amplifier’s efficiency, allowing you to deliver more power to your subwoofers with less draw on your electrical system.

Subwoofer Wiring Options

Let’s start by looking at wiring pairs of subwoofers to an amplifier. The simplest would be two 4-ohm single-voice-coil subwoofers wired in parallel. Two identical loads wired in parallel present a single load that is half of the single-load impedance. In this case, two 4-ohm subwoofers present the amplifier with a net 2-ohm load.

If you have an amplifier like the Rockford Fosgate T1500-1bdCP that we’ve used in the drawings that include a pair of terminals, you can wire one sub to each terminal. The two positive terminals are wired together inside the amp, so are the negative terminals. Having two sets of terminals can help keep the wiring neat and tidy in installations like this.

In both of the above scenarios, the load the amp “sees” is half of the impedance of one woofer. The chart below shows you the net load for common subwoofer options.

A less common configuration is to use low-impedance drivers and wire the subwoofers in series. Series wiring results in the sum of each voice coil impedance being added. For a pair of 4-ohm woofers wired in parallel, the amp would “see” an 8-ohm load.

A quick note about wiring subwoofer voice coils in series: Sometimes it’s necessary when multiple drivers are involved. With that said, there is a small drawback. The inductance of the individual voice coils adds and can result in a very reactive load for the amplifier. This configuration can cause instability in lower-quality amplifiers and reduce mid-bass performance from the system. The latter can result in difficulty getting the sound from the subwoofers to blend with the midbass woofers so that the bass appears to be coming from the front of the vehicle. It’s more important to present the amplifier with the correct load, but keep this in mind.

Dual Voice Coil Subwoofer Wiring

Let’s start by looking at the options to wire a single DVC subwoofer to an amplifier. We have the choice of wiring the individual coils in series or in parallel.

Wiring multiple dual voice coil subwoofers to a single amplifier presents a whole gamut of options. For example, we can wire all the coils in series, all in parallel, or mix them in a combination of series and parallel. It’s crucial to note that each DVC subwoofer in the system needs to be wired the same way. If one has its coils wired in series, all of them need to be wired in series. The same goes for wiring them in parallel. We’ll explain with a few examples.

Let’s start with an example of two dual-voice coil subwoofers with all four coils wired in parallel. This is a common configuration for dual 4-ohm subs wired to an amplifier optimized to make power into a 1-ohm load.

In this example, the load seen by the amplifier is one-quarter the value of each coil. So, for 4-ohm voice coils, the amp will see a 1-ohm load.

It is also possible to wire all four voice coils in series. This might be an option for drivers with very low impedance coils, like a dual 1-ohm design. Just as with our single voice coil subwoofers, wiring in series adds the impedance of each coil. This is a very unlikely configuration in a car audio system.

Now that you’ve had a taste of how subwoofers and their voice coils can be wired in series or parallel, let’s combine both to create what is easily the most common configuration: two dual-voice-coil subwoofers with their coils wired in series, and both drivers wired in parallel with each other. In this configuration, the amplifier “sees” a load that’s equivalent to the impedance of a single coil.

You can wire more than just two subwoofers together in series, parallel and series-parallel wiring. Four, eight or even 16 subwoofers can be driven from a single monoblock amplifier, so long as the net impedance is correct.

Two Amplifiers on a Single Subwoofer

If you have a dual voice coil subwoofer and would like your installer to use two amplifiers or all four channels of a four-channel amplifier, the electrical connections are quite easy. In either scenario, your installer will need to use a digital scope with a voltage readout or a high-quality digital multimeter to ensure that each coil is receiving exactly the same voltage. In addition, the subwoofer will need to be chosen such that each coil’s impedance maximizes the power available from the amplifier.

If you want to use a four-channel amp, then the connections to the subwoofer are the same. One coil will be wired to channels one and two in a bridged configuration and the other coil to channels three and four when bridged. In almost all cases, a four-channel amp will want each pair of bridged channels to see a 4-ohm load, so a subwoofer with dual 4-ohm voice coils is the only choice.

A Few Rules To Keep in Mind

There are a few guidelines to keep in mind as you and the Product Specialist you’re working with discuss your system design. First, all subwoofers connected to an amplifier should have the same impedance. For example, you can’t use a dual 2-ohm and a dual 4-ohm sub on the same amplifier.

The second rule is that all the voice coils of a DVC or quad-coil subwoofer must be used. If you need a 2-ohm load but have a dual 2-ohm subwoofer, you need to change the amp or the sub in the system design. Using one voice coil changes all the parameters of the woofer and doesn’t promise good sound or reliability.

Last, all the subwoofers should be installed in enclosures with the same air volume. We once heard a “story” where a vehicle owner told us one 12-inch sub was in a small enclosure for fast bass, and the other was in a large enclosure so it would produce deep bass. No. Just No. Please don’t do this. They all need to have the same amount of air behind them in the enclosure to deliver predictable results.

Oh, I suppose we should mention that mixing different size woofers or different models of woofers in one system is also less than ideal. That whole “fast” and “deep” stuff is silly. If you want to use some smaller woofers for midbass, that makes complete sense. This is popular in system applications where high-efficiency PA-style speakers are being used. With that said, very few car audio subwoofers are designed to play up to 250 or 300 Hz without some significant amounts of cone resonance distortion.

Anyway, please don’t mix and match different size subwoofers in a single system. We recommend saving your money and having the subwoofer system designed and installed properly. Your local specialty mobile enhancement retailer can help you choose the best amplifier and subwoofer combination, then design an enclosure that will make the best use of the space in your vehicle, so your stereo system sounds amazing.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

For car audio enthusiasts who’ve invested time studying the Thiele/Small parameters of speakers and subwoofers, you’ll know there is a specification called Xmax. This variable, typically expressed in millimeters or inches, is intended to describe the one-way excursion capability of the driver. Put another way, it’s the distance the cone can move forward or rearward from its rest position before distortion overwhelms the signal being produced.

Mechanical Xmax Calculations

The simplest way to calculate the Xmax specification is to subtract the thickness of the top plate from the height of the voice coil winding and divide it by two. This calculation describes how far the woofer (or midrange or subwoofer) cone can move forward while keeping the voice coil inside the magnetic gap. If and when the coil attempts to move out of the gap (determined by the thickness of the top plate), the strength of the magnetic field is dramatically reduced and the output of the speaker becomes non-linear. If the audio signal being produced by the speaker isn’t the same as the signal sent from the amplifier, significant distortion is being added to the signal, and your music won’t sound right.

It’s worth having a baseline for values that are considered normal and impressive in terms of Xmax. Tweeters seldom have an Xmax specification, but that doesn’t mean it’s not a value that can be calculated. For example, a linear excursion of plus or minus 0.2 mm (0.0079 inch) would be an excellent specification for a tweeter. For a small 3- or 4-inch midrange driver, an Xmax of plus and minus 2 mm would be good, and greater than 4 mm would be excellent. For a 6.5-inch mid-woofer intended for a door speaker application, an Xmax value of 4 mm would be good, and anything above 8 mm would be exceptional.

Subwoofer excursion capability increases dramatically as the price of a driver increases. For entry-level 10- and 12-inch subwoofers, rated for 300 to 450 watts, an Xmax of 10 to 12 mm is good. Stepping up to mid-level woofers with power ratings between 500 and 600 watts typically results in the Xmax spec jumping up to 14 or 16 mm in each direction. The cream of the crop in subwoofers offer Xmax capabilities beyond 18 mm, with some drivers capable of more than 24.5 mm (1 inch) of excursion in each direction. Shallow-mount subwoofers typically scale these values down a bit, with mid-level drivers capable of 8 to 10 mm of excursion and premium solutions capable of more than 15 millimeters.

Those who care less about sound quality and are interested only in achieving maximum sound pressure levels can continue to increase the power to a speaker beyond the Xmax value. In this scenario, peak SPL measurements are typically all that matter, so sound quality and accuracy take a back seat.

Xmax Isn’t Always a Calculation

A second way to specify the Xmax parameter involves using acoustic test equipment and laser-based cone excursion measurement. Using this method, a signal is fed to the driver being tested at an increasing level until the speaker’s output reaches a distortion level of 10%. These performance-based measurements are crucial as they take into account non-linearities caused by limits in the compliance of the speaker’s suspension components.

For example, if a driver has a 16 mm top plate and a 32 mm voice coil height, the calculated Xmax would be 8 mm. Suppose the surround on the driver is very narrow or stiff and starts to limit cone travel at an excursion level of 5 mm. Once again, the output audio signal won’t replicate the signal from the amplifier, and significant harmonic and intermodulation distortion will be added to the output. The speaker also won’t play any louder. The surround or the spider can cause compliance-based excursion limiting, and these characteristics are usually the limiting factors in how loudly a speaker or subwoofer can play. In the car audio industry, very few manufacturers use the Xmax+10% specification method as investing in the test equipment is very expensive.

Though it isn’t as common as it was years ago, another mechanical measurement affects how loudly a speaker can play. If the bottom of the voice coil former runs into the bottom plate of a speaker, you’ll hear a very sharp snapping sound. Of course, this limits excursion and can damage the former very quickly. This situation happens when the suspension components aren’t stiff enough or if the driver is designed to be extremely shallow and there isn’t adequate space at the bottom of the driver.

One Last Thought on Xmax Specifications

If you’re shopping for a subwoofer, the Xmax spec isn’t the be-all, end-all in determining how loudly the subwoofer system will play. The way the driver interacts with the enclosure plays a huge role in determining the audio system’s effective efficiency and low-frequency extension. Check out our articles on speaker specifications and subwoofer enclosure designs for more insight into this topic.

When it’s time to choose the right subwoofer for your car or truck, drop by your local specialty mobile enhancement retailer and talk with them about your expectations and the speakers and subwoofers that are the best for your application. Be sure to audition one of their demo vehicles to see if the subwoofer solution meets your performance goals.

This article is written and produced by the team at www.BestCarAudio.com. Reproduction or use of any kind is prohibited without the express written permission of 1sixty8 media.

For car audio enthusiasts, especially those interested in competing in SPL competitions, amplifier efficiency should be one of their primary concerns. In this first of three articles on efficiency, we take a close look at the Rockford Fosgate M5-1000X1 Class-D subwoofer amp and analyze how well it makes use of power at different output levels.

What Is Car Audio Subwoofer Amp Efficiency?

In the case of car audio amplifiers, or this specific analysis of a Class-D subwoofer amp, some of the voltage and current from your alternator and battery are converted into heat. This is wasted energy. Don’t fret, and it happens with every electronic device – even if the heat produced is minuscule.

When we talk about efficiency, we look at how much power is sent to the load (speakers) compared to how much is consumed by the amplifier. We set up the Rockford Fosgate M5-1000X1 that Dave MacKinnon reviewed for BestCarAudio.com in early 2021 on the bench. First, we used our D’Amore Engineering AMM-1 to confirm that we had a 1.0-ohm resistive load. Next, we measured output voltage, input voltage and input current at 60 points between idle and an output level of 800 watts where the CLEAN circuit put the amp into protection.

A few things to note. The amplifier idles at about 1.5 amps of current. That’s the power it takes to drive the circuitry without the amp producing any power. At output levels below about 1 watt, this idle current significantly outweighs the current required to deliver power to the speaker. As such, the efficiency in this range is well under 5%.

If you analyze the graph above, you can see that the efficiency increases very quickly to over 70% by the time the amplifier produces 140 watts. At this level, the current draw is 17.45 amps. Beyond that, efficiency increases to a maximum of 76% while delivering 400 watts. The current draw at that level is 49.78 amps.

Graphs like this have been floating around the car audio industry for many years and are often combined with a graph of a Class-AB amplifier to highlight the efficiency benefits of the Class-D design. One problem with this way of looking at the data is that the power delivery scale is linear. In the real world of reproducing audio, we know that we need to double the power to a speaker every time we want to increase the output by 3 dB. That’s a logarithmic requirement. Let’s analyze this same data with the percentage of maximum power on a logarithmic scale.

Suddenly, our amplifier doesn’t look quite as efficient. The numbers haven’t changed, though; it’s just the way we’re analyzing them. You may only need 5 or 10 watts to drive your subwoofer at very low volume levels. At these levels, the amplifier wastes a LOT of power as heat. The efficiency in this range is only 18 to 27%. This means that around a quarter of the power going into the amp is going to your speakers; the rest is running the amplifier’s signal processing and is being converted to heat.

How Manufacturers Specify Efficiency

When you’re looking at amplifier efficiency specifications, the odds are very good that they’ve been taken with the amp at full power. In almost every case, this is the level at which a Class-D amplifier makes the best use of the power it’s drawing from your electrical system.

What matters much more in the real world is what the amp is doing at 10% or 25% of its rated output. This is where 95% of users spend most of their time listening to music. More efficiency in this range means less draw on the electrical system. Efficiency is paramount for marine applications where we might be running on batteries for several hours. It’s not uncommon to find one amplifier that draws half as much current to produce the same output as another model with worse efficiency, especially when the amplifier is loaded down.

Efficiency and Load Impedance

One last item we’ll look at is efficiency versus the current required to produce power in the load. It would be impossible to count the number of times we’ve heard someone suggest loading an amp down with additional speakers or the use of lower impedance speakers to produce more power. If the power supply in the amp can deliver the current, sure, you get more. The question is, is there a cost to this power? Let’s see how our test amp behaves in terms of efficiency when driving a 2-ohm load.

As you can see, the amp makes better use of power when connected to a 2-ohm load. The peak efficiency is up to 84.7% at an output level of 691 watts, with the amp drawing 58.1 amps of current. Compare that to the 1-ohm load, and the amp was drawing 71.5 amps to make the same power. Those extra 13 amps of current are wasted as heat.

It’s also worth noting that the amp produced more power in this 2-ohm load configuration before the CLEAN output distortion indicator was illuminated. Instead of 800.3 watts, it produced 865.3 watts. That’s 8.1% more power, for free, with less current draw and less heat. Sooo … if the amplifier you’ve chosen is rated to produce the same or even remotely similar power levels into 2- and 1-ohm loads, please don’t load it down.

Does Amplifier Temperature Effect Efficiency?

While we had the Rockford back on the bench, we took one more set of measurements. We wanted to know if the amplifier would become less efficient as it got hotter. Now, it’s crucial to keep in mind that this particular test will be specific to this amplifier from this company. There’s no way to predict if other designs work the same way. So we started the 2-ohm testing with the amplifier’s heat sink at 19 degrees Celsius and measured its efficiency. Then, we repeated the measurements as the temperature rose to 45, 50, 55 and 60 degrees. We’d have gone farther, but our load resistors were starting to make some strange crackling noises.

If someone had asked us to predict how the amp would behave, we’d have put all our chips on predicting that efficiency would decrease as the amp heated up. It only makes sense as wires, components and traces on the circuit board would increase resistance with temperature. The findings are very interesting and say a lot about the work the designers at Rockford Fosgate put into their products.

With Great Power Comes Increased Efficiency

There are three takeaways from this experiment. First, if you need a small amplifier for your midrange speakers or tweeters, choose one that only makes as much power as you need. A 150-watt amp is overkill when you’ll only use 10 or maybe 20 watts on a midrange driver. Second, if you compete in SPL competitions, choose a speaker load impedance that balances power production with amplifier efficiency. You may be throwing away power in the form of heat by loading your amplifiers down too much. If the limiting factor in your audio system is the ability to feed the amp, choosing the most efficient solution is crucial.

Last and certainly not least, amplifier efficiency depends on output level. Our testing shows that efficiency increases as power output approaches the rated output level when it comes to name-brand Class-D car audio amplifiers. Posting a single value on a website or in a brochure (do companies still make brochures?) doesn’t tell you much about the design or how efficient the amp will be when used at low power levels.

When it comes time to shop for an amplifier for your car or truck, drop by a local specialty mobile enhancement retailer and talk with them about the options for your vehicle. They’ll help you choose the right solution and integrate it into your vehicle so that it sounds excellent and functions reliably for many decades.

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.