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.

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.

High-quality speakers and proper installation are crucial when upgrading your car’s audio system. The ease with which your installer can reliably integrate tweeters into your vehicle will determine a portion of the labor cost. Will the technician need to fabricate a mounting bracket? Will they need to create a little pod? Is there even enough hardware provided to ensure a reliable and safe installation? Let’s look at some tweeter installation hardware solutions.

Why Are Tweeters Important for Great Sound Quality?

Before discussing tweeter installation, we should review the importance of having dedicated tweeters in a car audio system. By definition, tweeters are relatively small speakers designed to play the highest audible frequencies. They vary from 0.5 to over 1.25 inches in size. The larger tweeters can typically play lower frequencies, making them ideal for two-way front speaker systems. However, a large diaphragm might have some resonance at extremely high frequencies.

Tweeters are made from a variety of materials. Textile domes like silk, metal domes like aluminum, titanium and beryllium and plastic materials like polyetherimide are among the most popular. While the metal versus textile performance discussions will go on forever, what’s more important is that the tweeter diaphragm doesn’t have resonance issues. Most companies add a damping material to the diaphragm to prevent this. The damping applies to both textile and metal designs.

Most tweeters in the car audio market use a dome-shaped diaphragm. However, some use a ring-radiator design, like the tweeters in the Rockford Fosgate T4652-S set. The concept of the ring tweeter is to eliminate the chance of resonance in the center of the dome. While it’s unwise to make blanket statements about one design over others, we were very impressed with the clarity of the T4 ring radiator tweeter.

Flush-Mount Tweeter Installation Options

There are four common options for tweeter installation. First, we have flush-mounting. In this type of installation, the tweeter and a grill are mounted in a panel, and the result is basically flush. This means the tweeter may only protrude a few millimeters or 0.25 inch. This type of installation requires that the panel be modified to accept the tweeter, which means a hole between 1 and 1.5 inches must be created.

The most basic reliable tweeter mounting method uses a U-shaped spring-steel bracket that bolts to the back of the tweeter assembly. The bracket must be spring steel to retain tension and hold the tweeter securely.

Some companies have created more complex installation solutions for flush-mount applications. For example, KICKER’s QS-Series speakers include a nut that threads onto the back of the tweeter to keep it pressed tightly against the mounting surface. The legs of the nut can be trimmed to work with mounting surfaces of different thicknesses.

Rockford Fosgate’s Dual Discrete Clamp mounting solution is one of the most elaborate mounting options we’ve seen. The DDC comprises two cast aluminum brackets sandwiched on either side of a mounting surface to hold the tweeter in place. Once the two clamps are secure, the tweeter locks into place, and a trim piece finishes the installation.

Surface Mounting Options

The second type of installation is to mount the tweeters on the surface of a dash or door panel. This is less invasive as there doesn’t need to be a huge hole cut. That said, holes for wiring or hardware might be required depending on the location. Many tweeters include surface-mounting solutions that position the tweeter parallel to the mounting or at an angle. Angled mounting solutions are helpful when mounting a tweeter off-axis to the listening position. Ideally, a tweeter should be within 15 to 20 degrees of being on-axis with the listener. Alternatively, the tweeter can point at the windshield, dispersing high-frequency information into the listening area.

Tweeter Pods

Another option for installing tweeters is to use pods included with the system. These pods are typically bullet-shaped and mount through a single hole. The design should have a way to conceal the wiring for a neat appearance. You will want to ensure that the pods can be directed at the listening position for maximum performance.

Original Equipment Locations

Most modern vehicles have tweeters integrated into the factory audio system. These are often behind small grilles in the A-pillars, the dash, the doors near the release handle, or the sail panels in the front corner. Often, the factory tweeters are quite small in diameter and overall size. As such, it can be tricky to replace them with aftermarket tweeters. Some companies offer tweeter designs specifically engineered to work in original equipment locations, eschewing grilles and other hardware.

The key to a successful installation in these locations is reliability. We’ll be very clear in stating that mounting with hot glue or butyl rubber is unsatisfactory. These materials can quickly melt when the vehicle interior gets hot in the summer, causing the tweeters to fall out of place. If there aren’t options for mechanical fastening solutions, an epoxy adhesive like 3M Scotch-Weld DP8005 designed to work with plastics is an acceptable alternative.

Custom Installations

Of course, a custom installation solution for your tweeters is always an option. You may want them to blend into the A-pillar, dash or door. You may want a technician to create a custom pod that puts the tweeters in a specific location or points them in a particular direction. You may wish for the installation to look unique. So long as the guidelines about tweeter directivity are heeded, you can have the technician construct almost anything.

The Importance of Proper Tweeter Installation

While a tweeter doesn’t seem like a large item, in the unfortunate event of an accident, the last thing you want is to get hit by a tweeter that’s come out of place. Yes, this is a bit extreme. However, true professionals put significant effort into ensuring that their upgrades to our cars and trucks are safe and reliable. Do you want a tweeter to fall into the door or an A-pillar because it was held in place with hot glue? Certainly not. When shopping for car audio speaker upgrades, drop by a local specialty mobile electronics retailer and ask them which component speaker systems they offer. Be sure to inquire about how they integrate the tweeters into client vehicles.

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 while back, we looked at how different subwoofer locations affected system performance in a Hyundai Santa Fe SUV. A client of ours asked if that information was relevant to a sedan. So, let’s take a cool little enclosure and see what happens when we try several different sedan subwoofer locations.

The Test Subject

Our goal in this experiment is to evaluate how the location of a subwoofer in a vehicle affects what we hear. We reached out to Lee Mattason at Burlington Radioactive in Burlington, Ontario. He let us use his 2001 Honda Accord for the test, lent us a subwoofer and provided room in the install bay to do the measurements. We’ve known Lee and his team for over 25 years, and he’s a class act.

We didn’t want the size of the subwoofer to affect the measurements, so the goal was to choose something very compact. Lee had a JL Audio CP108LG-W3v3 8-inch ported MicroSub enclosure in stock. This little monster measures 18.625 inches wide, 11 inches tall and only 5.125 inches deep. The enclosure uses a 8-inch 8W3v3-4 subwoofer. The sub is rated to handle 150 watts of power, and the enclosure’s build quality and finish are exemplary. Honestly, this is a subwoofer solution we’ve been curious about. Will it play low enough for this test? Let’s find out!

The Measurement Configuration

As we’ve seen with other subwoofer enclosure systems designed by manufacturers with extensive experience in the industry, they know how to get the most out of a system by taking advantage of the transfer function of a vehicle. Before doing a complete set of tests, we took a frequency response measurement to ensure that the little woofer was suitable for the application. We set up our Clio Pocket microphone in the front seat and powered the subwoofer with a home audio amplifier. The output level was set to produce a sine sweep referenced to 6.32 volts at 60 hertz. This works out to 10 watts of power into a 4-ohm load. Here’s the first measurement we made with the sub placed in the middle of the trunk.

Um, what? This incredible little subwoofer measures ruler-flat to 10 hertz in the car at an output level of about 100 dB SPL when driven with 10 watts of power. Knowing it can handle 150 watts of power, it can easily produce 110 dB SPL. This is another prime example of expertise in subwoofer enclosure design and an understanding of vehicle acoustics. Sometimes, what looks “right” in a computer simulation might not transfer to in-car performance. There’s no equalization or filtering applied to this. It’s just a signal from the Clio Pocket to a full-range amp. Kudos to JL Audio; this is a little masterpiece!

Measurement Consistency

The graph above shows the subwoofer enclosure frequency response from 10 hertz to 1 kilohertz. We noted that the information below 20 hertz varied significantly during our measurement process. There is a machine shop next door to Burlington Radioactive. Whatever equipment they were using affected this infrasonic range. Sometimes the response was flat; sometimes it had a 10 dB peak at 13 hertz. We know the latter isn’t possible based on our measurement configuration and process. As such, we will leave that data out of the subsequent measurements.

Sedan Subwoofer Location Testing Round 1: The Middle

We started the testing with the enclosure in several locations through the middle of the trunk and facing different directions. The graph above, and as shown in light green in the chart below, shows the subwoofer in the middle of the trunk, standing up on its long side with the subwoofer facing rearward. The medium green trace has the subwoofer facing toward the front of the vehicle. Finally, the dark green trace has the subwoofer lying down on its back, with the driver pointed upward toward the trunk lid.

This graph will serve as a giveaway for what we’ll measure as we continue the testing. The direction doesn’t matter significantly in terms of deep bass, from about 45 hertz and down. The output levels are within a few decibels of each other. What does change is the upper bass performance around the crossover frequency. We’ll leave it at that until the summary at the end.

Round 2: To the Back!

The next three tests will have the little subwoofer enclosure placed at the very rear of the vehicle by the taillights and trunk latch. Once again, we repeated the testing with the subwoofer facing forward toward the front of the vehicle, facing upward toward the trunk lid and facing rearward toward the taillights.

The results mimic what we saw with the enclosure in the middle of the trunk. From about 45 hertz and up, the output is consistent. In this test, the upper bass output changes significantly.

Round 3: Back of Trunk

The next test has the enclosure at the back of the trunk, right up against the rear seats. It’s a long and painful story, but we lost a measurement here, so there are only two. We saw the graph of the subwoofer facing forward in this location, and it wasn’t much different than these two. I know it’s frustrating. It is for us as well. The car isn’t available to repeat the test, or we’d be on it in a flash. Sorry.

These measurements have the light orange line with the sub against the seat back and the driver facing rearward. The darker line shows the sub’s output, with it lying on its back and facing upward.

The conclusion is that there isn’t much difference in output from the various measurements at this location, though up is better than backward. If we recall the measurement with the driver facing forward, it was better in mid-bass output than either. Down low, it was the same.

Round 4: Hide in the Corner

The last location we’ll measure is the right corner of the trunk. We stood the enclosure up on its long side. There are measurements with the driver facing inward toward the vehicle’s center and outward towards the fender. We also flipped the enclosure over so the vent would be facing forward toward the front of the car and at the taillights.

Once again, the direction changes didn’t affect this location’s upper or lower bass output. The last measurement, with the woofer facing the fender and the port directed towards the rear, would be the “best.” However, there is just a few dB SPL variance across all the measurements.

Conclusions on Sedan Subwoofer Locations

In terms of deep bass, below 40 hertz, it doesn’t matter where the enclosure is located. The graph below shows maybe 2 dB SPL of variance across all the tests.

What does change, as we indicated earlier, is mid-bass performance. When installers experiment with different locations, the process likely won’t significantly affect how much bass you hear. The difference is in the mid-bass. The best location is in the corner of the trunk, with the subwoofer pointed outward to the fender and the vent pointed rearward. In contrast, the worst location was with the subwoofer lying flat on the floor at the back of the trunk, with the woofer pointing upward. At 90 hertz, there is more than 20 dB SPL less output. The lack of midbass is typically perceived as the presence of more deep bass. These measurements show otherwise.

If you compete in SPL competitions, this data might not be transferable to that application. At high excursion levels, the vent in an enclosure can be affected by its proximity to nearby surfaces. Moving an enclosure forward or rearward by an inch can yield measurable changes. You’re looking for a peak in the response, not flatness or extension. Different rules altogether.

Yes, different vehicles might present slightly different results. However, our editor-in-chief did this test 21 years ago for another publication and found the same results. Given the variance, we’d ignore that green trace.

When upgrading your car audio system with a subwoofer, the corner of the trunk is an excellent choice. This location keeps the subwoofer out of the way when carrying cargo. It also allows access to the spare tire or a battery that might be stored under the floor. Of course, if you want to run a pair of 12-inch subwoofers, then the back of the trunk will be about the only option. Drop by a local specialty mobile electronics retailer today and ask about adding a subwoofer to your car stereo system. It’s easily one of the best upgrades you can make.

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’ve talked about how speaker power handling is tested and the importance of delivering accurate test data. In the context of car audio speakers, we’ve explained that the physical size of the voice coil is a crucial element in determining how much power a speaker can handle. In this article, we’ve put together a simple, practical demonstration to show the thermal limits of a speaker.

What Defines Speaker Power Handling

Before the demonstration, we should discuss the definition of “power handling” in the context of speakers and subwoofers. Power handling describes the amount of power from an amplifier that a speaker can handle without being permanently altered negatively. This negative effect could be thermal damage to the voice coil former, the speaker’s suspension, or physical damage from excessive excursion. For example, too much low-frequency information fed into a small midrange driver might cause the voice coil former to hit the T-yoke and cause permanent deformation.

Unlike test tones, music is very dynamic. In this context, dynamic refers to a varying average level of energy. For example, a quiet passage in a song with only a female artist singing might require only a watt of power from an amplifier. When the bass guitar and drums start playing, it might take 10 or 20 watts of power to reproduce those lower frequencies. A stick hitting a floor tom drum’s skin takes less energy than strumming the lowest note on a five-string bass. The guitar sound could last several seconds, whereas the drum strike might only be a half-second. Power over time is what builds up heat in a speaker voice coil.

Cooling Capacity Analogy

A good analogy here is a car engine. For example, a Honda Civic might have a single radiator 14 inches tall and 14 inches wide with a ½-inch thick core. Conversely, a Dodge Challenger Hellcat might have a radiator that’s 25 inches wide, 18 inches tall and 1.625 inches thick. The Honda has 98 cubic inches of cooling capacity, whereas the Dodge has about 772 inches.

We know that engines are about 20-40% efficient. So, the Honda Civic, making 150 horsepower, will waste about 50 horsepower as heat under maximum load. That’s 37.3 kilowatts of heat energy. The Big Dodge can produce 700 horsepower, and assuming a similar 33% efficiency (which is likely generous), it will produce 174 kilowatts of heat.

The purpose of a radiator is to transfer the unwanted heat produced by the engine to air. If we divide the heat produced by the engine by the cubic inches of radiator area, we get 380 watts/square inch for the Honda and 225 watts/square inch for the Dodge. Given the chance that the Challenger will likely be driven more aggressively, some extra cooling capacity is cheap insurance against overheating.

Speaker Efficiency

Unfortunately, moving coil loudspeakers are notoriously inefficient. A 6.5-inch woofer might convert 0.02% of the energy from an amplifier into sound. A mid-level 12-inch subwoofer might only convert 0.25%. So, when you feed 20 watts into the midrange driver, you get the equivalent of 4 milliwatts of sound energy in the air. The rest of that power from the amplifier is wasted as heat in the voice coil and, subsequently, the parts surrounding it.

If you stop and look at different speaker designs with increasing power handling capabilities, you’ll notice that the voice coil size increases. A larger voice coil winding has more surface area. As such, the assembly can absorb more heat before failing.

For example, the Rockford Fosgate P1650 6.5-inch Punch Series speaker is rated to handle 55 watts of power. It has a voice coil diameter of 1.0 inch. The woofers in the Power Series T1650-S component set are rated for 80 watts of power handling and use a 1.2-inch diameter voice coil. The Power T3652-S set is rated for 125 watts, and the woofers have 1.5-inch diameter voice coils. So far, it all seems to make sense. An increase in diameter from 1 to 1.2 inches for a given winding height means 20% more surface area. Going from 1.2 to 1.5 inches in diameter is 25% more area. Combine this with a voice coil winding that’s likely longer, and you have significantly more heat management capacity.

Subwoofer Voice Coils

Speaker voice coils usually have a single winding of copper around the former. Subwoofers, on the other hand, can have multiple layers. Many higher-power subwoofers have four-layer voice coils, so they might be over 3 millimeters instead of a millimeter thick. This increase in size, specifically mass, further increases power handling.

The choice of voice coil former material also affects power handling. For example, aluminum has a thermal conductivity of 210 W/m-K. This means aluminum can transfer 210 watts of heat per meter of material per degree Kelvin. Copper is even better at over 400 W/m-K. On the other hand, air is a terrible conductor of heat energy at about 0.0235 W/m-K. Aramid fibers like Kevlar are also bad, at 0.04 W/m-K. If a speaker designer wants to extract heat from the voice coil winding, they might use an aluminum former. They might use an aramid glass-fiber former if they want a material that won’t heat up. Balancing physical strength, mass and thermal conductivity are all crucial in designing a reliable, high-performance speaker or subwoofer.

Let’s Compare Voice Coil Power Handling

We’ve sourced three different voice coils for this little experiment. All have relatively short windings, measuring just under 10, 18 and 20 millimeters in height. The coils have outer diameters of 26.4, 52.7 and 76.9 millimeters. The two smallest voice coils are wrapped around aluminum formers, while the larger uses two aluminum collars connected by a glass fiber backing. One collar is behind the winding, and the other is on top to connect the cone and spider. All three have two-layer windings.

I carefully measured each coil’s impedance. The small coil is wound to a DC resistance of 6.37 ohms. The medium coil has a DC resistance of 7.07 ohms, and the smallest is 3.53 ohms. I created a spreadsheet to calculate how much voltage I should apply to each coil so that it dissipates a specific amount of power. I will start with thermal measurements with 5 watts of power, then increase to 10 watts and see how hot things get.

Speaker Voice Coil Thermal Test at 5 Watts of Power

Starting with the large voice coil, the chart below shows that the temperature rose quickly from room temperature to 125 degrees after 1 minute before settling at about 137 degrees. While that’s warm, there was no concern of damaging the voice coil winding.

The medium-sized voice coil got warmer faster. It reached 132 degrees in a minute, then tapered off to 147 degrees after three minutes.

The smallest voice coil got quite hot quite quickly. It was over 210 degrees in a minute and 288 degrees in three minutes. This isn’t enough to damage it, but that’s a reasonable amount of heat.

Speaker Voice Coil Thermal Test at 10 Watts of Power

Now, let’s repeat the test using only 10 watts of power. The large coil warmed up a bit faster, tapering off around 180 degrees. The medium-sized coil followed a similar pattern, tapering off at just over 190 degrees. The tiny voice coil temperature skyrocketed almost immediately to 300 degrees, then held around 362. This temperature is the absolute upper limit of what a voice coil can handle. Prolonged use at this level would result in damage.

Undoubtedly, you’ve seen the different power ratings for Continuous and Maximum or Music power on a speaker. Constant, steady-state tones similar to what we used for this test are very hard on speakers from a thermal perspective. If this were music with 10 dB of dynamic range, you could understand how it could handle high-power transients while cooling off during quiet moments.

Another Reason Voice Coil Temperature Matters

Before we started the testing, we measured the impedance of each voice coil. The image below shows the impedance and phase plot of the small coil.

There are a few things to learn from this measurement. First, the voice coil winding doesn’t have much inductance. The impedance only starts to increase above 1 kHz. Second, the nominal impedance is at about 3.5 ohms at lower frequencies.

After the 10-watt test, I repeated the impedance measurement. The results are below.

The impedance starts at 4.2 ohms and drops to 3.8 as the voice coil cools. With very little thermal mass, the temperature drops quickly during the measurement. While the difference between 4.2 and 3.5 doesn’t seem significant, it’s an increase of 20%.

Does this impedance increase matter? Well, amplifiers output voltage, not power. The amount of power they produce depends on the impedance of the load. If an amplifier produced 5 volts RMS, the speaker would get 7.14 watts of power when cold. Once hot, the current would decrease, and the speaker would only get 5.95 watts of power. That’s not huge, but it’s a difference of 0.79 dB SPL. Suppose your installer has agonized over dialing in a digital signal processor to deliver perfectly smooth sound. In that case, a speaker with a voice coil that heats up quickly will have less efficiency once warm, altering the balance of your audio system.

Heat Management in Car Audio Speakers Is Crucial

This experiment doesn’t consider the pole piece or top plate’s proximity to a speaker to help extract heat. It also doesn’t include any benefits from the voice coil and cone moving to create airflow. However, those features don’t significantly affect the heating or cooling rate between the voice coil sizes shown here.

If you’re looking for speakers or subwoofers that can handle the most power possible, larger voice coils can handle more heat. However, they do come with some drawbacks. We’ll look at those in another article soon. In the meantime, drop by a local specialty mobile enhancement retailer to audition speakers that will sound amazing in your car, boat, or motorcycle.

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.