Every speaker, be it a tweeter, midrange driver, woofer or subwoofer, will have a sensitivity rating. Sensitivity ratings attempt to describe how much sound a speaker will produce for a given amount of power from an amplifier. There’s a common misconception that more efficiency is better. Longtime readers of BestCarAudio.com won’t be surprised to learn that multiple standards are used to describe speaker efficiency. It’s time to break speaker sensitivity specifications down to eliminate the confusion.

Understanding Efficiency

Efficiency in a mechanical or electrical system describes the amount of energy or work put into the system compared to how much you get out. To be clear, nothing is 100% efficient. A flashlight might waste 50% of the electricity from a battery as heat. An alternator might only convert 80% of the mechanical energy from a vehicle engine into electricity. Even an automobile engine might only convert 20% of the energy in the fuel that powers it into mechanical energy.

Calculating efficiency is theoretically simple. You divide the power out of a system or device by the power put in, then multiply by 100. For example, a high-quality car audio amplifier might consume 1,075.3 watts of power to produce 1,000 watts of output at the speaker terminals. This would represent an overall efficiency of about 93%. A poorly engineered amplifier might consume 1,750 watts to produce 1,000 watts to drive a subwoofer. That’s an efficiency of only 57%. In terms of the performance and longevity of car audio amplifiers, efficiency is an essential factor.

What Is Speaker Sensitivity?

We need a way to describe how much sound the speaker produces for a given signal from an amplifier. We’ll clarify that speaker efficiency numbers are, at best, horrible.

Let’s look at the two standard specifications used to describe speaker sensitivity. First, we have the 1-watt/1-meter standard. This should be the reference for all car audio speakers, as it negates concerns over speaker impedance. If you have a midrange speaker with a 4-ohm voice coil, a 2-volt signal from an amplifier will deliver 1 watt of power to the speaker. If the speaker has a 2-ohm voice coil, it only takes 1.414 volts. A 1-ohm speaker only needs 1 volt of signal to deliver 1 watt of power.

The second standard is the 2.83 volt/1-meter standard. This is a holdover from the old days of home audio. A signal with an amplitude of 2.83 volts would deliver 1 watt of power into a speaker with an 8-ohm impedance. Connecting a 4-ohm speaker to a 2.83-volt signal gives you 2 watts. That same voltage connected to a 1-ohm load delivers 8 watts of power.

Using the Efficiency Comparison Chart

The chart below shows how much higher a 2.83-volt efficiency rating is than a 1-watt rating. For example, if you have a specification of 82 dB @ 2.83 volts/1-meter for a 4-ohm speaker, the 1-watt/1-meter rating would be 3.01 dB lower at 78.99-dB SPL. If you were given a 2.83-volt rating on a 1.5-ohm subwoofer of 85 dB, the 1-watt/1-meter rating would be 77.71 dB @ 1-watt/1-meter.

If you’re looking at speaker efficiency numbers, make sure you know whether they’re using the 2.83-volt or 1-watt standard.

Sound Level and Distance from the Sound Source

Before we examine the benefits and drawbacks of each specification method, we’ll discuss what’s common to both: the 1-meter measuring distance.

If you live in the U.S., it’s worth explaining that 1 meter equals 39.3701 inches, or 3 feet and 3.3701 inches. Using either the 1-watt or 2.83-volt speaker efficiency specification method is equivalent to a microphone or listener 1 meter from the speaker cone. If you are 2 meters away, the amplitude will be 6 dB lower. The sound level will be 6 dB higher if you are at half the distance, 50 centimeters or 19.685 inches. Pay close attention to speaker efficiency specifications; some companies provide 1-watt at 0.5-meter numbers.

Speaker Sensitivity Measurements

Car audio manufacturers use two methods to generate speaker sensitivity specifications. The simplest is to place a microphone 1 meter from the speaker and perform a frequency response sweep at a specific voltage level. This will produce a chart that shows the driver’s output at each measured frequency. However, this doesn’t produce a single efficiency number. That said, the information is much more helpful in determining the suitability of a speaker for different applications. We’ll dive into extracting data from frequency response measurements another time. Most manufacturers will average the output of the above measurement to provide a single efficiency number.

The second method for specifying a speaker’s predicted efficiency is based on a formula using Thiele/Small parameters. The formula calculates the reference or “power available” efficiency, represented by the lowercase Greek letter Eta (H), which looks like an n with a longer right-side tail, and the subscript 0.

As you can see from the above formula, a higher equivalent compliance (Vas) value will increase efficiency. A higher electrical damping factor (Qes) reduces efficiency. Importantly, even a slight increase in the driver’s resonant frequency (Fs) dramatically increases efficiency as the value is cubed.

The graph above shows the predicted frequency response of a high-quality 6.5-inch car audio woofer in red. The orange graph is the same driver with a 10 Hz higher resonant frequency and a lighter cone. The yellow trace is the same driver with a 20 hertz higher resonant frequency, and so on. As you can see, the efficiency increases significantly, but the amount of bass the driver produces relative to the midrange decreases.

Subwoofers and Efficiency Numbers

It’s absolutely crucial to understand that a subwoofer’s efficiency number doesn’t directly correlate to the amount of bass it will produce. For example, if you cram a 12-inch subwoofer into a 0.85-cubic-foot sealed enclosure, an 8-inch subwoofer in a 0.6-cubic-foot ported enclosure is louder from 25 to 45 hertz with the same power. Comparison of subwoofer efficiency numbers is misleading, so simulation software is required to determine whether it will produce more output.

Should We Compare Speaker Efficiency Numbers?

In many cases, comparing the efficiency of similarly sized speakers based on efficiency is more likely to provide information about how little bass they produce than how loudly they can play. If your application doesn’t need much output below 200 hertz, a more efficient speaker is likely a good choice. However, there is a lot of crucial audio information below 200 hertz. Most male voices extend to 100 Hz, with some like Johnny Cash, Leonard Cohen and David Draman of Disturbed being much lower. If you want to hear their voices clearly, you need speakers that play lower frequencies louder.

Every specification in a speaker design interacts with all the others to produce a specific end product. When it comes to efficiency, the trade-off is typically bass performance. Shopping for speakers based on their efficiency parameters might not yield the desired results. When it’s time to pick speakers for your car, truck, boat or motorcycle, drop by a local specialty mobile enhancement retailer and talk to them about your expectations for the system. You might find that a driver with a lower efficiency specification sounds much better than one with a higher number.

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.

We recently witnessed a discussion on social media in which someone said that two 16 AWG wires could do the same work as a single 8 AWG wire. Unfortunately, the American Wire Gauge standard for stranded conductors isn’t intuitive in helping determine how multiple conductors can pass current. So let’s get geeky and do the math on how much current different-sized or multiple conductors can handle. We know it’s not something that comes up daily, but it’s an interesting topic.

The American Wire Gauge Standard

The American Wire Gauge standard for describing the cross-sectional area of a conductor was created in 1857. Knowing the area of a conductor is crucial to picking the correct size wire for a specific current-carrying application. For example, a small wire, perhaps one with a diameter of 0.1 inch, won’t be able to handle 50 amps of current without going up in smoke.

The AWG standard has a direct diameter-area relationship between one size and the next. For example, the diameter of a 10 AWG wire is 1.1229322 times the diameter of an 11 AWG Wire. The exact ratio applies to any two adjacent wire sizes. As such, the ratio of wire size to diameter is logarithmic, as the size doesn’t increase linearly. The chart below plots the data.

Given that the relationship is logarithmic, it’s tough to determine an equivalency between conductors. For example, if you have an 1,800-watt amplifier installed, it will need more current carrying capacity than a single 4 AWG conductor can provide. Does it need a full 0 AWG conductor? Well, it can’t hurt. But would two 4 AWG wires work? That’s what we have set out to determine.

Metric Wire Sizes

Just so you’re aware, Europe and Asia use metric wire sizes. While they use metric for most things, Canada still uses the AWG standard. For example, a 4 AWG power wire is sold as a 25mm2 wire across the ocean. It should come as no surprise that calculating equivalent current carrying capacities using the metric system is very simple.

There seems to be a discrepancy, however. If you look up 4 AWG in the above chart, it has an area of 0.03286 square inch. That’s equivalent to 21.2 square millimeters. An area of 21.2 is a lot less than 25 square millimeters.

Let’s look at another size. Most charts specify that a 10 AWG is equivalent to a 6-square-millimeter conductor. However, the American Wire Gauge chart lists it as 5.26 square millimeters. Clearly, some averaging is done at some point in the process. Even when trying to be accurate, it seems someone has taken a lackadaisical approach to math.

Power Wire Current Carrying Equivalency

One accurate fact we have is a resistance measurement for the different AWG sizes of copper wiring. This specification is part of the American Wire Gauge standard. We can compare the resistance of differently sized wires regarding their current carrying capacity. We’ve created a chart that compares standard wire sizes from 20 to 0000 AWG to other sizes.

Using the chart is simple, though perhaps not intuitive at first. Let’s start with some simple observations. Any cell with the same wire size will have a number 1. This indicates that the resistance is equivalent, which, of course, makes sense.

Let’s say we have a 4 AWG conductor and want to know its resistance compared to a 2 AWG conductor. Start by looking across the top row for the 4 column, then look down at the row represented by the 2. We see a number of 0.625. This means a single 4 AWG wire can carry 62.5% of the current of a 2 AWG conductor for the same voltage drop.

We can compare them the other way by looking across the top for the 2 column and then comparing it to the 4 row. Here, we see the number 1.6. This means a 2 AWG conductor can carry 1.6 times as much current as the 4 AWG for the same voltage drop.

Multiple Conductor Evaluation

The table also gives us information on how much current multiple conductors might handle to be equivalent to something more significant. So, how many runs of 4 AWG are comparable to a single 0 AWG cable? Look across to the 0 column, then down to the 4 row. We see the number 2.514. This means we need 2.514 runs of 4 AWG to pass the same amount of current as a 0 AWG cable with the same voltage drop.

A better example would be comparing a 6 AWG cable to a 0 AWG. Here, the ratio is 3.971. So, effectively, you need four runs of 6 AWG to equal a single 0 AWG.

Now, let’s get back to what started this discussion. How many 16 AWG wires are required to be equal in current-carrying to a single 8 AWG wire? If we go to the 8 column and then down to the 16 row, we see the number 6.389. This means you need more than six runs of 16 gauge to pass the same current as a single 8 AWG conductor. Six would have more resistance, and seven would have less than the 8 AWG.

Voltage Drop Look-Up Table

While understanding how much current a single or multiple conductors can pass, we need a standard for an acceptable voltage drop. This is a bit complicated as it considers conductor size, current requirements and the length of the wire. The ANSI/CTA-2015 Mobile Electronics Cabling Standard uses a voltage drop of 0.25 volt. For an electrical system providing 14.4 volt, that’s a drop of 1.7% across a single run of wire. We’d likely see the same drop along the ground path.

Please refer back to our article about conductor ampacity (how much current a wire can handle) to determine what’s suitable for a specific application.

Not All Wire Is Created Equally

Before we close out, we should remind our readers that this chart only works for all-copper, full AWG-spec conductors. The resistance will be different if you are looking at a tinned wire. If the wire is copper-clad aluminum, the chart doesn’t apply. If the wire label says gauge instead of AWG, it’s likely not full AWG sizing.

Be wary of these shortcuts and differences. You are buying something unique. Though the tinned wire might be a much better choice for marine applications, tin has only 15% the conductivity of pure copper. You may want to go up a wire size in a marine application to ensure reliable power delivery.

Be Sure To Get The Right Size Wire For Your Car Audio System

Be sure to discuss with the product specialist or technician designing the audio system for your vehicle what size wire they’re using. Before the project starts, understand whether it’s a single run of wire or multiple. This handy chart and a basic understanding of electrical theory from high school will ensure that your audio system performs reliably. Or, at the very least, you won’t make a statement that two 16 AWG wires are the same as a single 8 AWG.

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.

We’re back with the second of four articles discussing the listening experience of truly high-end car audio systems. In our first article, we discussed the importance of accurate frequency response. This second article will discuss the soundstage, provide a definition for it and explain why it’s crucial to recreating a recording accurately.

What Is a Car Audio Soundstage?

We need to define what a soundstage is before we get into describing the intricacies of how to evaluate one. Essentially, we’re talking about where the sound comes from in a vehicle. In a poorly executed system, the music might appear to come from each speaker. This is likely because of a lack of level adjustment, improper signal delay settings in a signal processor or a difference in frequency response between one side of the vehicle and the other. Most basic car audio systems with a radio and one or two pair of speakers deliver sound that seems to come from the speaker closest to the listening position.

As a system’s quality improves, the attention to detail in configuring and calibrating the equipment should also improve. Proper calibration will yield the best performance possible from even the most modest audio products.

We’ll be clear in saying that finding a mobile electronics retailer that is experienced and proficient in designing, integrating, configuring and calibrating an audio system so that it delivers what we’re describing is no easy feat. Some retailers still think digital signal processors are magic black boxes filled with voodoo. If accuracy, realism and detail are the goals of your car audio system, you’ll have to visit many retailers and audition their demo vehicles to find one that can deliver the performance you want. Don’t trust statements. Listen to their work and judge for yourself.

Soundstage Options

Before describing what to listen for in the perfect audio system, we should clarify that listening preferences play a significant role in system design and calibration. The standard for the ideal audio system is to recreate what seems like a live performance in front of the listener. This applies to both home and car audio systems. Many car audio enthusiasts prefer to be immersed in the center of a listening experience. This would replicate a listener’s experience at a dance club or when wearing headphones. The music is all around them, and while there are well-defined left and right channels, it fills the listening space. There is no right or wrong in terms of a client’s preference.

Many car audio retailers fail to qualify their clients’ expectations in this regard. Do you want the music to sound like it’s coming from the front of the vehicle or from all around you? Harman International includes an option in some factory-installed sound systems that allows the listener to switch from an “in audience” to an “on stage” experience. While the concepts are similar, we’ll refer to that in-audience experience for this discussion.

Music Source

In an audio system that is designed, integrated, configured and calibrated perfectly, all the music should seem to come from a well-defined location in front of the seating position. In most cases, this can be described as the windshield, as though it had speakers built into it. Some genuinely magnificent systems can create a soundstage that extends beyond the physical limits of the vehicle. We’ve heard cars that present sounds that extend beyond the left and right speaker positions and others that made it sound like Neil Young was standing in front of headlights.

What’s key is that the sound source is coherent. If your music comes from the dash or windshield, all the music should come from that location. The midbass shouldn’t seem to come from the steering wheel or the footwells. The bass shouldn’t come from the back of the vehicle. Specific frequencies shouldn’t move up or down. Think of it like having a set of high-end, full-range speakers in front of the vehicle, positioned so the left speaker is aligned with the left A-pillar and the right speaker is aligned with the right A-pillar.

Delivering Amazing Audio Performance

The key to achieving the goal of delivering an accurate sound source starts with the system design. If all of the speakers are behind the listener, it will be impossible for the system to sound as though the music is coming from in front of them. This overly dramatic statement gets at the core of proper system design.

Next, the speaker selection must deliver smooth dispersion through the listening environment. Let’s say you have a set of 6.5-inch component woofers mounted in the doors and a set of 0.75-inch tweeters on the dash. In this case, the system will be sensitive to the listener’s location because the woofers must play to frequencies well beyond where it becomes directional. This is why higher-end speaker manufacturers offer large-diaphragm tweeters that can play to lower frequencies.

Managing directivity is only the first part of the component selection process. The second involves choosing products with features that minimize distortion. As we demonstrated in our series about speaker performance, some drivers add significant second- and third-harmonic distortion. If the door speakers are playing up to 2 kHz, the harmonics could extend to 6 kHz, resulting in the soundstage being pulled down to the footwell.

The same concern goes for subwoofers. Imagine a crossover frequency of 75 hertz. This means the second-order harmonic is 150 hertz, and the third is 225. If you choose a subwoofer without a low-distortion design, you might have issues creating a stable and coherent soundstage. Few car audio companies focus on linearity and distortion in their subwoofer products. Do your research and choose wisely.

Car Audio System Calibration

You will need a digital signal processor if you want a car audio system with a well-defined soundstage. A few source units from Sony include enough processing to handle proper configuration. Alternatively, you can choose an amplifier with a built-in DSP or a stand-alone DSP that will work with your existing amplifiers.

Three features in the DSP require proper calibration to align the output of all the speakers in the vehicle. Of course, this only works if all the speakers have dedicated amplifier channels assigned to dedicated channels on the processor. If you have a component set on a single channel with a passive crossover, the ability to fine-tune the system will be diminished. Ideally, the tweeters and the woofers need dedicated processing and amplification channels.

The technician calibrating the system needs to set delays, output levels and equalization properly for each channel. The delays and levels compensate for the different distances to each speaker in the vehicle. The equalization compensates for resonances and cancellations in the vehicle because of reflections off various surfaces. In this context, equalization isn’t intended to improve frequency response, though proper settings simultaneously handle staging and system tonality considerations.

Table for One, Sir?

We skipped over another consideration when creating a soundstage: Do you want the system optimized for the driver or for everyone in the vehicle? The latter is often referred to as a two-seat tune.

If you listen to an audio system configured for a single seat, the location and size of the soundstage, as perceived from the front passenger seat, often suffer. The resulting sensation can vary from being slightly compressed to sounding like all the music comes from the far-right speaker location. Creating a two-seat calibration is time-consuming and often doesn’t sound as coherent as a single-seat tune. However, if you always have someone in the vehicle with you and they care about how the music sounds, it’s worth requesting.

This request might involve using or adding a center-channel speaker. If the signal processor has dedicated center-channel processing, this can work well. However, be sure to ask whether the center-channel signal contains any information found in the left and right channels. If it does, the effect usually narrows the soundstage significantly. Very few processors have full up-mixing capabilities for a center-channel output.

Soundstage Problems – Bass in the Back

Here are a few common problems with the soundstage in car audio systems. The most prevalent issue is not getting the bass to mix with the front-stage speakers. Your system might have a good soundstage for midbass through high-frequency information, but the deeper bass seems to come from the trunk or cargo area.

This issue can sometimes be solved by better calibrating the crossovers and delays between the midbass drivers and the subwoofer. Sometimes, though, this is a distortion issue with the subwoofer(s); the only solution is to upgrade them.

Soundstage Height Issues

Another common problem is that different frequency ranges come from different heights. If the vehicle has a two-way speaker system and the tweeters can’t play low enough, the midrange and midbass sounds seem to come from the lower part of the dash, while the higher frequencies come from the windshield.

Improving this with a steep filter and a lower crossover frequency on a tweeter might be possible. However, the proper solution is a much larger tweeter, or better yet, switch to a three-way system that uses a midrange up high on the dash or in the A-pillars.

Compressed-Width Soundstage

You might also experience a soundstage that’s much narrower than the vehicle width or where one side doesn’t extend as far to the opposite side. This can make the stage seem unrealistic in relation to the vehicle boundaries. It’s akin to the band congregating on the left (or right) side of the stage but never spreading back out.

The solution to this issue could be complicated. It might be level or delay-related. It can also be a speaker placement issue, which makes it harder to resolve without revisiting the installation.

Drooping Soundstage

Though it’s less common now that kick-panel speaker locations are less popular, another possible soundstage issue is a rainbow or drooping stage. In this case, the center image might be in the middle of the windshield under the rearview mirror. However, the left and right extremes might drop into the kick-panel area. The solution is similar to the fix for frequency separation.

No Sense of Depth

This last issue is a mix between a soundstage issue and an imaging problem. Imaging refers to the placement accuracy and size of instruments on the soundstage. Does the singer’s voice sound like it’s the size of a pizza pan, or is it more like a tennis ball? Are all the instruments placed in accurate and precise locations on the soundstage? The issue we’ll discuss is a soundstage with no sense of depth. You might see why this is a staging and imaging issue.

Not all recordings contain a sense of depth or layering. If you listen to a purely electronic recording, you will likely hear a wall of sound unless they’ve done some fancy tricks with phase adjustments. If the recording is of a band, choir or orchestra, and stereo microphones are used to pick up the space in the hall, a good car audio system should be able to recreate this sensation. If your system doesn’t present any sense of depth, it’s usually an issue with the channels not being calibrated equally.

Experience Your Music Like Never Before

If your car audio system doesn’t have a solid soundstage, drop by a local specialty mobile electronics retailer today. Start by auditioning their demo vehicles to see whether they can create an experience you will enjoy. Bring along your favorite music and listen to a half-dozen tracks. Pay close attention to where the music is coming from. Everything should seem to come from the windshield. The bass, vocals, guitars, drums – all should be coherent and realistic. If the vehicle doesn’t deliver, don’t fret. Find another shop and audition their work. Even once you’ve found what you think is the perfect solution, it’s often a good idea to listen to as many vehicles as possible to get a reference for tonal balance, soundstage, imaging and dynamics. Imaging will be the next topic in this series. Stay tuned!

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 1980s, most car stereo shops had charts in the install bays that showed what size power wire should be used with different amplifiers. Some charts were based on current and cable length, while others suggested amplifier power ratings and lengths. In all cases, an essential piece of information was missing. Today, we’ll sort that out. Let’s consider why we need large power wires, what factors affect the current draw, and how to select the wiring that’s the right size for your car’s audio amplifier.

Low-Voltage Electrical Systems

Most cars, trucks, boats and motorcycles operate on a 12-volt electrical system. The battery should rest between 12.2 and 12.6 volts when the vehicle isn’t running. Depending on the application, we might see 13.4 to 14.6 volts when the alternator charges the battery. These voltages might be slightly higher if your vehicle uses an AGM battery.

Power is the product of voltage times current. So, if a load like an amplifier or light needs 100 watts from the 12-volt electrical system, it will draw 8.3 amps of current. If we want 1,200 watts, we need 100 amps of current. This is Ohm’s law at its most basic.

Now, if we had the 120 volts we find in our homes and offices, the current draw for 100 watts would only be 830 milliamps. A load of 1,200 watts would only draw 10 amps. The amplifier might have a 240-volt supply if this was a concert or sizeable public-address application. If so, it would only draw 415 milliamps of current at 100 watts and 5 amps at 1,200 watts.

Here’s the problem with large amounts of current flowing in electrical conductors. The formula to calculate power is Current squared times Resistance. If we have a conductor with 10 amps of current flowing and 0.005 ohm of resistance, a voltage drop of 50 millivolts will be present across the wire, and 0.5 watt of energy will be wasted as heat. If that current draw increased to 20 amps, the heat wasted in the wire jumps to 2 watts. At 50 amps, 12.5 watts of energy is wasted in the wire; at 100 amps, there is 50 watts. This is the equivalent resistance to 12 feet of all-copper, full-AWG spec 6 AWG wire. Think about how hot a 50-watt incandescent lightbulb gets after being on for only a few minutes.

Cable resistance is why electric utility companies transmit power across the country at levels like 345,000 volts. You can transmit massive amounts of power this way without incurring significant losses from cable resistance.

Amplifier Efficiency Is Crucial

The second item to remember is that no electrical or electronic device is 100% efficient. This means you put more power into the device than you get out. Car audio amplifiers vary dramatically in their efficiency. We’ve seen subwoofer amplifiers offering more than 92% efficiency and others less than 58%. The amplifier’s efficiency plays a massive role in determining how much power it will consume.

Let’s say, for example, the above amplifiers are both rated to produce 1,000 watts of power. The 92% efficient amp would draw about 87 amps of current from a 12.5-volt electrical system. The inefficient amp would draw a comparatively mind-boggling 138 amps to produce the same power. Statements about power cable requirements based on amplifier power ratings need to be scrutinized.

Music and Test Tones

It stands to reason that we want to size the wire in our car audio system for a worst-case scenario. We don’t want to waste energy when we max out the power production capabilities of the amplifiers. However, average power consumption is much lower. We’ve analyzed a good amount of modern music, and the average power level is around 7.5 dB below the peaks. This means that if we average the power requirements of our amplifiers over the length of a song, they produce less than 20% of their maximum power when set so the peaks reach clipping.

Turn the volume down one notch, and the current requirements will likely drop by half. It stands to reason that we could, theoretically, undersize the power wire significantly and not run into much trouble. We’ve seen dozens, if not hundreds, of large amplifiers installed with woefully undersized power wiring. Is this a “best practice”? Most assuredly not. However, it happens frequently, and most of these installations don’t run into issues. Is there a downside? Yes, the amplifier will likely never make its maximum power rating, so you’re limiting the performance of your audio system.

What Determines Acceptable Wire Size?

The answer to the question, “What wire size is right for my amplifier?” requires that we pick an acceptable amount of waste or loss. Specifically, how much voltage drop is acceptable across the length of the power wire? The ANSI/CTA-2031 standard for car audio power wiring suggests we select power wire based on a maximum voltage drop of 0.25 volt. Given that the resistance of all-copper, full AWG-spec wire has precise nominal and maximum resistance requirements, we can create a table that provides the maximum allowable current in varying lengths of commonly available wires.

The chart above outlines the maximum allowable current for a given wire size (on the vertical scale) and length (on the horizontal scale). For example, if we have 16 feet of 4 AWG wire, we want to keep the maximum current draw to 58.3 amps. Putting that number back into our amplifier efficiency means we can run an efficient 670-watt amplifier or a 423-watt low-efficiency amplifier without exceeding 0.25 volt of drop across the wire.

One common mistake is to think of the values in this chart as a target. They are a worst-case scenario. For example, if you need to provide 60 amps of current to an amplifier, then 16 feet of 4 AWG wire seems about right. What about the ground wire? It only needs to be 2 feet. Would we want 2 feet of 14 AWG wire? Most definitely not. The goal is to have as little resistance as possible in the power wire to and from the amplifier. Use the same wire for all power connections.

Wasted Energy in Wiring

Now, this isn’t the end of the discussion. We always want to know what happens at those extreme limits, right? The chart says we can draw 2,412 amps of current through 2 feet of 4/0 (0000) wire. That sounds like fun! Or does it?

We need to calculate how much power is wasted in the wire. Two thousand four hundred amps is a lot of current. Here’s a second chart that outlines how much power is wasted (as heat) per foot of the conductor.

The chart above shows how much heat is generated if we draw the maximum possible current to provide a 0.25-volt drop through conductors of different lengths. So, our 4/0 cable with 2,412 amps flowing through it will produce 301.6 watts of heat per foot. I don’t need to tell you that the jacket on the wire will melt off quickly. Our calculations show that a bare 4/0 wire heats at a rate of 121 degrees Celsius per minute when producing 301.6 watts. Most wiring is rated for only 105 degrees C. I’m sure you see the problem. Even if we’re way off on our calculations, managing or, more accurately, preventing heat in conductors is crucial in making sure that the wiring in a car’s audio system functions reliably.

Big Wire Is Expensive

While the math checks out, using 16 feet of 2/0 cable for a good ~1,200-watt amp is expensive, right? What if we allow for 0.5 volt of drop across our power wire? Yes, the maximum power out of the amplifier will decrease, and the wire will get hotter. However, it won’t hit our wallets quite as hard. Is the trade-off worth it?

Here are the same charts again with 0.5 volt allowed as the drop.

With the higher allowable voltage drop, the maximum current for a given wire size and length increases significantly. Our 4 AWG wire is supposedly acceptable for 116.5 amps of current or a really efficient 1,000-watt amplifier. The 2/0 cable can supposedly handle 186 amps of current. It would be a good choice for a similarly powerful low-efficiency amplifier.

Wire Size Reality Check

While charts and spreadsheet calculations are interesting, the reality is that there are practical thermal limits that can’t be exceeded. How exciting would 4,800 amps of current through a 4/0 conductor be in creating a fireworks show? The answer is fascinating.

The maximum current a conductor can handle continuously has a lot to do with the environment in which it is used. Under the hood of your car or truck, where it’s likely very hot, the hot wire will heat up even more as current flows through it. This has the effect of increasing resistance. More resistance for a given amount of current means even more voltage drop and more heat being generated.

To put constant current demands into perspective, electric arc furnaces like those used to create steel often use 40,000 to 60,000 amps of current. The conductors that pass this current are sized in the thousands of square millimeters. A 0 AWG cable is 53.5 square millimeters. The furnace cables are usually encased in liquid cooling systems to maintain the conductor temperature. Yes, liquid-cooled conductors.

What Wire Size Does My Car Audio Amplifier Need?

What wire size you need depends on how your audio system will be used, the music you play, and the efficiency of the amplifiers. Rock or heavy metal music is more likely to have dynamic bass information, while rap or EDM is much more likely to have lengthy low-frequency notes. The energy the subwoofer amp requires will differ significantly for these two applications.

If you want to get the most power from your amplifiers, targeting a maximum voltage drop across the longest length of wire of 0.25 volt is a good reference point. If you aren’t as concerned about power as the installation cost, then the 0.5-volt drop chart is an acceptable concession.

Remember that the charts above are based on full AWG-sized, all-copper conductors. If your installer intends to use tinned copper, you might need a one size larger wire. If the wire is undersized or constructed of copper-clad aluminum, it’s anyone’s guess how much current it can handle. Work with a specialty mobile electronics retailer to choose high-performance amplifiers and appropriately sized power wires to ensure that your car stereo sounds great and performs reliably.

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