You’d think that something as simple as operating an on/off button or switch would deliver predictable results. These days, many electronic devices remain on and continue to draw small amounts of current, even when you think they’re off. Let’s look at how car radios work regarding their on/off status and how much current they draw.

Parasitic Current Draw Kills Batteries

This term should be very familiar to those adept at troubleshooting automotive and marine electrical systems. A parasitic draw is a circuit that consumes energy when you don’t want it to. The concept is similar to leaving the dome light in your car on overnight after searching for something that has tumbled into that abyss between the seat and the center console.

In reality, a parasitic draw consumes energy that’s unexpected or unwanted. You know that something evident like a dome light would kill a battery. If all the lights are off, but your battery is drawn flat in a day, you must address the problem.

Depending on the features included with your vehicle, even when it’s off, systems can draw upwards of 50 milliamps of current. If you have keyless entry, the receiver is awake and listening for a signal from your key fob. If you have a “smart trunk” system, there’s likely a second receiver in the back of the car listening for a signal from your key fob. All radios with clocks draw a tiny current to keep the clock running.

It’s Not Off; It Just Looks Off

Any device with a momentary on/off button has a tiny computer awake and waiting for the signal to spring to life. Your smartphone is a perfect example of this. The power button on the side or back sends a signal to the microcontroller and tells it to wake up. That microcontroller must draw a tiny bit of power from the battery to listen to the signal. This is one reason why devices with rechargeable batteries drain, even when “turned off.”

A desktop or laptop computer is another example. Not only can they be woken by tapping the power button on the case, but many can monitor a physical network port for a command that will bring the system to life. These commands are called Wake on Lan (WOL) and are great if you want to access a computer at home from a remote location.

Car Radios and Parasitic Draws

Getting to the point of the article, if your car radio doesn’t have a mechanical on/off switch like you might have found in a twin-shaft radio from the ’70s or early ’80s, it will draw a small amount of current from the battery when you turn it off. A better description of the state your radio is in after you press the power button is “sleep mode.” I measured the current consumption of a Sony XAV-AX7000 multimedia receiver in my lab. When on, but the volume turned down, it drew 776 milliamps of current. Pressing the power button to shut it off dropped the current draw to about 2 milliamps.

Two milliamps isn’t much current. With that said, your battery’s health isn’t good, and going on vacation or a business trip for a week will affect how much energy is left to start the vehicle. On the other hand, a remote car starter with a two-way remote can draw 15 to 20 milliamps of current. A dashcam might draw upwards of 400 milliamps when in parking mode, which could kill a weak battery overnight.

If you’ve ever looked at the wiring for a typical car or marine radio, you’ll know there are two “power” connections. A yellow wire typically needs to be connected to a constant power source. This wire is what feeds power to the microcontroller in the radio. A red wire should be connected to a switched power source. This wire is usually labeled as “accessory,” and the power source it is connected to should only be live when the ignition is in the accessory or on/run position. This wire typically only provides a signal to the microcontroller and doesn’t provide significant amounts of current to anything in the radio.

When no voltage is applied to the red wire, the radio “turns off.” Once again, this can be misleading because the yellow wire still provides a small amount of current to let the microcontroller monitor the red wire for a signal. We can consider this something akin to a “deep sleep” mode. Electronics manufacturers often refer to this measurement as the Dark Current.

The same Sony radio dropped its current draw to about 300 microamps when the power was removed from the red accessory wire. This current draw performs much better than radios from a few decades ago.

Car audio amplifiers, signal processors and integration interfaces also have small amounts of dark-current draw.

Marine Radios and Parasitic Draws

A little over a decade ago, Clarion introduced a marine radio solution with only two power wires: red and black. The radio was designed to include memory that would retain settings when power was removed from the unit. Items like station presets and equalizer and crossover settings would be retained when you turned on the boat. In a conventional marine radio with three power wires (constant, accessory and ground), radios would forget settings if you removed power from the yellow wire.

Parasitic draws are a concern in marine applications because most boats are only used on weekends. You roam around the lake or river for a few hours Saturday and Sunday, then tie the boat up at the dock for the week. That draw from the radio over the week would dramatically lower battery reserves, and the limited run time over the weekend wouldn’t recharge them fully. Boat batteries don’t last very long as they are often drained heavily and only partially recharged.

The solution is two-fold. If you plan on upgrading the radio in your boat, see if you can find a radio that uses a two-wire connection. One wire would be ground, and the other goes to the accessory or radio circuit. When you turn off the boat, no power is drawn from the battery.

Second, purchase a battery charger for your boat. It can be as simple as a Battery Tender Junior or a premium solution like the CTEK Multi US 7002. We’ve had phenomenal success with the latter; its recondition mode has restored the chemistry and capacity of batteries that less advanced changers and vehicle alternators couldn’t bring back to life. Whatever you decide to use, make sure it’s an intelligent unit that knows when the battery is full and switches to a float mode to prevent the battery from being overcharged.

You can also have a professional install a master battery switch in your boat. This switch makes disconnecting the battery easy if you’re going home from the cottage for the work week.

If your application uses Absorbed Glass Mat (AGM) or some Valve Released Lead Acid (VRLA) battery, your charger should have a specific charging mode for this type. These batteries rest at a slightly higher voltage than conventional lead-acid units. Sorry, we get a little geeky when talking about batteries. Regardless, proper maintenance is crucial to their longevity and reliability. Can you imagine the frustration of heading out on the lake for an afternoon of fun, only to be left stranded because the battery is too dead to restart the motor? What a mess!

Have Parasitic Power Draws Resolved Quickly

If you’ve run into a situation where the battery in your car, truck, boat, side-by-side or motorcycle constantly dies, you likely have a parasitic power draw. A local specialty mobile enhancement retailer can help troubleshoot the system with a current clamp or thermal imaging camera. Once they pinpoint the issue, they can repair or replace the misbehaving component, fix a wiring issue or devise a solution to ensure that your battery won’t die when you’re ready to head to work or school. It could be as simple as something wired incorrectly by an amateur or the incorrect selection of an aftermarket upgrade. Either way, you don’t want your car radio killing your battery.

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.

What is a custom car audio subwoofer enclosure? Does it need to be wrapped in leather or vinyl? Should it be made with fiberglass? Does it need acrylic windows? Is LED lighting a necessity? The short answer is no to all of these questions. Let’s delve into what makes a subwoofer enclosure custom and why it’s the best way to upgrade the bass in your car audio system.

Subwoofer Enclosure Volume Matters

How large does a subwoofer enclosure need to be? The answer to that depends on the subwoofers you want to use. Thinking that way puts the cart before the horse, though. The best way to design a subwoofer system is to tell the product specialist you’re working with how much space you’re willing to allocate to the enclosure. They can take a series of measurements, do some calculations and suggest a subwoofer or subwoofers to deliver the best performance based on the available air volume. No matter what the manufacturers tell you, cramming large subwoofers into small enclosures results in poor performance. You’ll get more deep bass from a single driver in an optimized enclosure than a bunch of larger drivers crammed into an undersized design.

Part of designating the space available for your subwoofer enclosure should include considerations about accessing storage or a spare tire. The last thing you want is to be stranded on the side of the road because part of your stereo has trapped a spare or blocked access to the vehicle battery. Before you tell the shop how much space they can use, look under the trunk floor to determine what you might need to get to. Make some notes so you can share that information with the shop.

Space Optimization Is Key

The number one factor that defines a custom subwoofer enclosure is that it optimizes the available space in the vehicle. Let’s say you want a vented enclosure with two 10-inch subwoofers. Most 10-inch subwoofers on the market work very well in about 1 cubic foot of air space. So, this enclosure would need a net volume of 2 cubic feet plus the displacement of the drivers and the vent. Let’s use a pair of ARC Audio X2 10D2V2 10-inch subwoofers for this simulation. With 1 cubic foot each, plus a 4-inch diameter round vent, the enclosure needs a net internal air volume of about 2.15 cubic feet.

The person designing the enclosure for these subwoofers should optimize it so that it intrudes into the cargo area of the trunk as little as possible. Therefore, it should use the full width and all the available height to make it as shallow as possible. If we have 40 inches of width and 15 inches of height, the enclosure would need to be 8.625 inches in depth. These measurements assume the enclosure is a rectangle with no angled rear panel. If we wanted the rear panel to have a 20-degree angle, the depth at the top would shrink to about 6 inches. That gives us two more inches of usable cargo space.

Both designs are custom enclosures if finished in a durable carpet that matches the cargo area. That’s it. Nothing fancy or exotic is required to make this a custom solution. The customization aspect is that the enclosure is optimized for your vehicle and uses the available space efficiently.

By contrast, if the shop has a pre-built enclosure that’s 34 inches wide and 13 inches tall, it would need to be 11.375 inches deep. Would it work? Yes. Would it sound the same? Yes. Might it save you money versus having an enclosure built specifically for your application? Maybe. Will you have the most space to fit your groceries, sports equipment, luggage or beer? No, not at all.

Here are a few examples of custom enclosures designed to deliver great bass while taking up as little space as possible.

More Custom Subwoofer Enclosure Options

Now, there is a next level of custom subwoofer enclosure beyond a square or slanted-back prism. You might have a significant amount of room inside a spare tire or behind a trim panel in the trunk that can be used for an enclosure. Once again, the choice of drivers for these applications depends on the available space. Just because you can physically fit a 12-inch subwoofer inside a spare tire enclosure doesn’t mean that’s the choice of driver that will produce the most low-frequency output or deliver the tightest bass. A single 10-inch subwoofer might play louder at lower frequencies. An 8-inch subwoofer in a vented design will likely be even louder. Once again, the shop you’re working with should calculate the available volume and suggest a subwoofer based on that information.

Vehicle-Specific Enclosures

Many companies offer off-the-shelf subwoofer enclosures designed for specific vehicles. These enclosures are typically optimized for a specific location in the vehicle and may use a combination of stack-fab or fiberglass construction. With the benefits of mass production, these custom enclosures can make adding an optimized bass solution more affordable than having a shop create a one-off solution. You’ll still need an expert to run all the wiring and configure and calibrate the electronics.

Net Audio in Wichita Falls, Texas, offers this 2019+ Ram 1500 Crew Cab bass reflex subwoofer solution.

Musicar in Portland, Oregon, offers a variety of BMW OE-Look subwoofer upgrades, including this enclosure for F32/F83 coupes with a Morel 10-inch subwoofer.

Audio Designs and Custom Graphics in Jacksonville, Florida, has a complete line of Phantom Fit enclosures, including this one for 2015-22 Mustangs.

MTI Acoustics in College Station, Texas, offers application-specific subwoofer enclosures like this one for Jeep Gladiators.

Upgrade Your Car Stereo with a Subwoofer System Today

As we’ve shown, there doesn’t need to be anything fancy or exotic about a custom subwoofer enclosure. The enclosure needs to be constructed to be specific to your needs. You can certainly go for something flashy if you want. However, we prefer to stick with a simple, well-constructed enclosure and opt for a subwoofer that includes technologies that make it more accurate and linear. No matter your goal, drop by a local specialty mobile enhancement retailer today to find out what they can build to deliver great bass in your car, truck or SUV.

Lead-In Image: Thanks to Perzan Auto Radio in Upper Darby, Pennsylvania, for the photo of this enclosure they constructed for a client’s 2023 Bentley Continental GT Azure. The enclosure features a pair of JL Audio 10W6v3 subwoofers and matching SGR-10W6v2/v3 grilles. The client can still access the space under the trunk floor without moving the enclosure.

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.

Once again, we approach a discussion of the laws of physics and how they affect the electrical systems in our cars and trucks. The enemy of all power transmission systems, be it the battery and alternator to the amplifier in your vehicle or the nuclear power station or hydroelectric dam across the state to your home, is resistance. I saw a power wire sizing chart earlier this week that had me rethink how car audio systems are wired, so I thought we’d take another look.

Ohm’s Law and Wasted Power

Ohm’s Law states that for every amp of current that flows through a resistance of 1 ohm, 1 volt is produced across that resistance. If we lower the current, less voltage is produced. If we reduce the resistance, less voltage is produced. We are typically limited to 14 volts from a fully functional alternator in our cars and trucks. If the wiring between the alternator and the amplifier has resistance (and it does), some of the voltage is wasted across the wire and doesn’t reach the amp. Most aftermarket amplifiers in car audio systems have loosely or completely unregulated power supplies. As such, the amplifiers can produce more power if fed more voltage. Conversely, if we starve them for voltage, the maximum power they can produce decreases.

Power Wiring and Voltage Loss

A member of the Motorsport Wiring Alliance Facebook Group posted the chart below. The folks at WireCare provided him with the chart in response to an inquiry about the conductor’s current carrying limits. What’s unique about this chart is that it considers conductor size based on temperature rather than voltage drop. Why is this important? When a conductor heats up, its resistance increases. The increased resistance produces more heat, which creates even more resistance. It’s easy to see that this can quickly result in a runaway situation.

Now, before we get into a discussion about why choosing the correct wire size is essential, let’s talk about Tefzel wire specifically. If you’re accustomed to the typical wiring used for car audio upgrades, Tefzel is entirely different. This type of wire uses an ethylene tetrafluoroethylene copolymer (ETFE) jacket that can withstand temperatures up to 150 degrees Celsius. The primary power wire most car audio folks use has a PVC jacket and is rated for around 105 degrees Celsius.

It’s worth noting that Tefzel is a brand of ETFE and not specifically a brand of wire. When referring to Tefzel wire, the name describes the type of jacket on the wire. Tefzel is a type of ETFE resin and is sold as a raw plastic material in pellet form. Tefzel is also used in heat-shrink tubing, valve linings and biomedical equipment. Tefzel is a Chemours Co. brand, just like Teflon, Viton and Freon.

Tefzel is the standard for aviation wiring and custom wire harnessing that you’d find on any professional-level race car. A key advantage to Tefzel is that the shielding is very thin and durable, which results in smaller-diameter wire bundles. Further, the ETFE jacket doesn’t contain chlorine, which produces a lot of smoke when it burns – a key consideration in aeronautics applications. The downside is that it’s expensive. But, as they say, you get what you pay for.

A secondary benefit of the thin jacket is the ability of the wire to dissipate heat quickly compared with a conductor with a thick jacket. Allowing heat to escape to the air around the wire helps keep the resistance down, which minimizes voltage losses and improves efficiency. However, if you look at the above chart, the ratings are not directly comparable to typical car audio wiring in dissipating heat.

Let Your Power Wire Be Free!

If you’re feeling particularly geeky, I recommend browsing NASA’s Re-Architecting the NASA Wire Derating Approach for Space Flight Applications document. In short, bunding many wires together can dramatically reduce their ampacity as heat generated in the conductor cannot escape the wire bundle easily. If you have a bunch of wires zip-tied together, they could present more resistance and consequently waste more energy than if each were out in the open with nothing touching them. From their research, a single 26 AWG conductor in free space could handle up to 4.7 amps of current and not exceed 200 degrees. When that same conductor was at the core of a bundle of 32 other wires, the maximum allowable current was 1.9 amps to reach a similar temperature. What’s the takeaway? Routing wiring away from heat sources will dramatically improve its current carrying performance.

This chart shows how the current handling capability of wiring decreases as more and more conductors are bundled together.

Power Wire and Heat Calculations

It’s common practice to consider all-copper 4 AWG power wire suitable to deliver up to 100 amps of current to an amplifier. Assuming the wire meets the ANSI/CTA-2015 Mobile Electronics Cabling Standard, 1 meter of 4 AWG should have no more than 0.88 milliohm of resistance. Assuming we usually need about 4.5 meters of wire to run from the battery to an amplifier in the trunk, we’d have a drop of 0.396 volt across the wire when 100 amps pass through it. Assuming the ground path has a similar resistance, that’s another 0.396-ish volt of drop. So we’ve lost about 0.8 volt from whatever the alternator produced.

I’ve measured dozens of copper-clad aluminum amp kits over the years. The best of those kits had a resistance of 1.43 milliohms per meter, and the worst I’ve tested had 3.37 milliohms per meter. So if we attempt to draw the same amount of current through those conductors, we have a voltage drop of 0.6435 and 1.517 volts, respectively. Add the drop of the return path, and you have a total of just over a volt and almost 2 volts for the dramatically undersized 4 gauge CCA wire.

The Tefzel wire chart describes an appropriate wire size for a given operating temperature range. In the case of their 4 AWG wire, their wire has an even lower resistance of 0.816 milliohm per meter. Drawing 100 amps through 4.5 meters of their wire results in a voltage drop of 0.367 volt. Honestly, that’s not worth the added cost. It’s also not the point of this discussion.

Tefzel rates the ampacity of their wire based on its operating temperature. According to their chart, 72 amps of current through Tefzel 4 AWG will raise the wire temperature by 35 degrees. Some simple math tells us that the wire dissipates 4.23 watts of energy per meter at that current level. For the maximum temperature to increase by only 10 degrees, they state that 40 amps is the maximum, which is 1.31 watts per meter. If we reverse the math, a 4 AWG car-audio-style all-copper power wire is only suitable for 38.55 amps of current to produce a temperature increase of 10 degrees. If we accept the 35-degree temperature increase, we max out at 69.35 amps. What about the CCA wire? The “good” CCA wire could pass 54.4 amps of current for the 35-degree rating, and the woefully undersized CCA is only good for 35.45 amps.

The issue with exceeding the ampacity rating of the wire is that it heats up. Pure copper has a temperature resistance coefficient of 0.00393. This means that for every increase in temperature of 1 degree Celsius, the resistance of the wire goes up by 0.393%.

As you can see, the effect of a conductor getting hot can dramatically increase its resistance. For example, at 100 degrees C, 4 AWG has more resistance than a conductor with an equivalent size to 5 AWG at 20 degrees.

Thankfully, we play music, not test tones, through our audio systems. Because of the dynamic nature of music, we get an averaging effect that dramatically reduces the power an amplifier needs to produce. Assuming you aren’t playing basshead music, it wouldn’t be unreasonable to consider that the average amplitude of a rock track would be about 12 dB, which equates to a 16x reduction in required power. In the context of our wire size discussion, if the maximum current your amp would draw is 100 amps, the average might be down to around 6.25 amps. Of course, there are a LOT of variables in that statement, but even if the average is 25 amps, you have a significant safety margin.

Don’t Starve Your Car Audio Amplifier

The first takeaway is that 2 AWG power wire needs to be much more prevalent in car audio applications. For example, a 1,500-watt amplifier that’s reasonably efficient would work well with 2 AWG wire.

Secondly, if you want your amplifier to produce all the power it claims, you must choose a high-quality power wire large enough for your application. The average power produced by an amplifier might be well below the maximum ratings, but that doesn’t mean you might still be limited when the peaks happen. Don’t skimp on power wire size or quality. A great way to add some reserve energy is to have the technician working on your car install a high-quality stiffening capacitor near the amplifier. Consult with a local specialty mobile enhancement retailer when choosing the correct power wire for the installation they’re performing.

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.