We see a lot of questions like “My car audio amp can produce 800 watts; how much power does each of my subs get?” If you aren’t versed in the calculation basics of Ohm’s law, the answer might not be intuitive. Let’s dive into the math and logic that will let us calculate how the power from an amplifier is distributed through multiple speakers or subwoofers.

How Much Power Does an Amplifier Produce?

Without going off about the unimportance of power production versus amplifier quality, we should discuss what determines how much power an amplifier can produce. Most car audio amps use a switching power supply that is designed to chop up and boost the 12 to 14 volts from the battery and alternator, then regulate it to fixed DC voltages that drive the output devices in the amplifier. We refer to these as rail voltages, and they determine the maximum voltage available to the speaker terminals and, ultimately, the speakers or subwoofers.

If we use the example of an amplifier with +30- and -30-volt rails, we have a maximum theoretical voltage of 60 volts that we can apply to the speaker. Ignoring some losses through the output devices themselves, this amp could provide 900 watts into a 4-ohm load. The formula to calculate power given voltage and resistance is P = V^2/R.

Unless the amplifier uses a stiffly regulated power supply design, the rail voltages are typically a fixed multiple of the supply voltage. We’ll ignore some losses and say 30 volts is 2.08 times the supply voltage of 14.4 volts. If the supply voltage drops to 12 volts, our rail voltage would then drop to 25 volts, and we’d only have 50 volts we could use to drive a subwoofer. Our maximum theoretical power is now only 625 watts. This example highlights the importance of ensuring that the most possible voltage is delivered to your amplifier and why you should never skimp on power wiring.

How Amplifier Power Is Divided into Multiple Subwoofers

Our example so far has discussed a single 4-ohm load. What if we have two 8-ohm subwoofers wired together to the amp? How much power can it produce? The answer depends on how the subwoofers are wired. If the subwoofers are wired in parallel to get a net load impedance of 4 ohms, then the amp would produce 900 watts – the same as with a single 4-ohm load. Because both loads are identical, that 900 watts of output is shared evenly between the drivers, with 450 watts going to each.

Now, what happens if we decide to wire the subwoofers in series? An 8-ohm subwoofer wired in series with another 8-ohm subwoofer gives us a net load impedance of 16 ohms. Our amplifier can only produce 156.25 watts into a 16-ohm load. As both subwoofers have the same impedance, the power to each sub is divided evenly, with each receiving 78.125 watts. It’s very unlikely that we would want to run an amplifier at 16 ohms, even though it might be quite efficient.

The amount of power an amplifier produces depends on the maximum unclipped voltage it can produce on the speaker outputs, the impedance of the speakers connected to the amp, and how much current the amplifier can supply to the speakers. Why is current a consideration? What if we connect a 2-ohm subwoofer to our example amplifier? Theoretically, the amp should be able to provide 1,250 watts. In order for this to happen, the amplifier needs to be able to supply 25 amps to the load. That formula is I = P ÷ V, where I is current in amps, P is power in watts and V is voltage. For a well-designed, high-power amplifier, 25 amps isn’t an unreasonable amount of current.

What happens if we connect a 1-ohm load to our amp? The theoretical power jumps to 2,500 watts, and the amplifier would need to be able to supply 50 amps of current to the load. If you’ve looked at amplifier specifications where an amplifier’s power output capabilities don’t roughly double as the load impedance is divided by two, it’s likely because the amp can’t provide the required current into the lower impedances.

Why the Confusion about Amp Power Ratings?

Over the decades, we’ve been taught to think that amplifiers double their power when the load impedance is cut in half. An amp that produces 300 watts into 4 ohms should produce 600 watts into 2 ohms and 1,200 watts into a 1-ohm load. The massive “cheater” amps that were popular in the 1980s and ’90s were often rated similarly to this. However, things have changed significantly.

Let’s look at an example of a modern high-quality subwoofer amplifier like the Rockford Fosgate T500-1bdCP. This amp is rated to produce 300 watts into a 4-ohm load, 500 watts into a 2-ohm load and 500 watts into a 1-ohm load. We can tell from the 4-ohm rating that the amp likely has rail voltages of roughly plus and minus 17.5 volts. Knowing how Rockford Fosgate under-rates their products, the rails are likely running at 19 volts, and that amp would produce roughly 360-ish watts into a 4-ohm load. Nevertheless, let’s stick with the 17.5-volt rails for this discussion. Running a 2-ohm load should then produce just over 600 watts. It’s clear that current delivery into the lower impedance is the limiting factor if the amp is rated for 500 watts. Our math says the amp is limited to about 17.5 amps of current into the speaker load. That’s why the amp doesn’t produce more power into a 1-ohm load.

Current-Limited Amplifier Design Considerations

Why would a manufacturer of high-quality audio products make a design decision to limit how much current one of their amplifiers can produce? The first consideration is heat management. We’ve tested many Rockford Fosgate amplifiers in the past few years. Their high-mass heatsink designs typically allow their amplifiers to run at maximum output continuously for at least 30 minutes if not more.

While 30 minutes doesn’t seem like a long time, for car audio amplifiers, that’s an amazing performance. We’ve seen compact amplifiers from supposedly reputable brands that overheated and shut down in less than three minutes at their maximum undistorted output. Some Brazilian amplifiers we’ve tested shut down in less than two minutes at full power. Reliability is as important as audio quality – you don’t want your music to stop playing because a poorly designed amplifier overheats.

The second reason for the limited-current design is that the output when driving a 4-ohm load is higher. In a classic design that is closer to doubling its power, the amp would only make 125 watts into 4 ohms if it made 500 watts when driving a 1-ohm load. Amp design is much like speaker design in that you have to trade one performance factor for another. As such, it’s not really a “current limited” design; it’s just optimized in a different way than the car audio industry is used to.

Guidelines for Amplifier Power Distribution

Here’s the takeaway in terms of figuring out how much power each subwoofer or speaker connected to an amp will receive. First, determine what your net load will be to the amp. Our article about “Ohms and Loads” can help you with that. Next, look at the amplifier’s published specifications to determine how much power the amp should make. If the specifications aren’t compliant with the CTA-2006-D standard, be wary of their accuracy. Finally, divide the expected power from the amp evenly among the subwoofers connected to the amp.

The above comes with a caveat: All the speakers or subwoofers must have the same impedance. We strongly recommend not mixing and matching drivers with different impedances on the same amplifier channels.

A single 4-ohm subwoofer on our T500-1bdCP would receive 300 watts. A pair of 8-ohm subs wired to a 4-ohm load would result in the amp producing 300 watts, and each driver would get 150 watts of power. If we run a single 2-ohm sub on the amp, it would get 500 watts. If we ran two 4-ohm subs wired in parallel, the amp would produce 500 watts, and each subwoofer would get 250 watts of power. A single 1-ohm sub would get 500 watts. A pair of 2-ohm subwoofers wired in parallel would get 250 watts each. Four 4-ohm subs wired in parallel would result in the amp producing 500 watts, and each sub would get 125 watts.

One last word of advice: Loading your amplifier down to lower impedances in hopes of it making more power will dramatically reduce its efficiency and likely shorten its lifespan.

Upgrade Your Vehicle with a Subwoofer System Today!

We’ll circle back to the beginning of this article to remind everyone that power production has no correlation to audio system quality. You could have a 2,500-watt amplifier, but a better-designed 1,000-watt amplifier might sound better and produce bass that is more accurate.

If you have several subwoofers and want help choosing a great-sounding amp for them, drop by a local specialty mobile enhancement retailer and find out about the solutions they have available. They can explain the options for wiring the subwoofers you have or suggest solutions that will offer amazing performance.

Lead-In image credit: Thanks to Bing from Simplicity in Sound in Milpitas, California, for providing the photo of the four Sony Mobile ES XS-W104ES subwoofers.

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.

Before about 2000, upgrading a factory-installed car audio system was pretty easy. You could start with a new set of speakers and a subwoofer and have something quite enjoyable. In the last few decades, automakers, or more specifically, the companies that supply their audio system components, have learned how to maximize the performance of the inexpensive speakers they use. While this makes the audio systems sound better, the same processes they use can result in a speaker upgrade making your stereo system sound awful. We look at why this happens and how a professional installer can work around it.

Sound Quality = Smooth Frequency Response

Shopping for new speakers can be challenging. Listening to the same music at the same volume level on different options is nearly impossible. High-quality speakers all have one thing in common: flat frequency response. You don’t want to be listening to Lorde or Billie Eilish and have their voices sound hissy and harsh rather than smooth and natural. When voices sound like real voices, a key reason is a smooth frequency response.

Here’s an example of the importance of frequency response. Imagine you have two identical vehicles. One has a set of absolutely top-of-the-line component speakers installed in the doors. A high-quality amplifier provides power to the speakers, and an equally high-quality radio serves as the system audio source. A second identical vehicle has the same amp and radio but uses moderately priced speakers and includes a carefully calibrated digital signal processor between the radio and the amp. Aside from the potential improvement in the accuracy of the soundstage and how the system images, the digital signal processor offers equalization that compensates for reflections and resonances in the vehicle to deliver fairly smooth frequency response. The system with the DSP will sound more realistic and will be more enjoyable.

The companies like Harman, Bose, Panasonic and Sony that provide speakers, amplifiers and radios to car manufacturers understand the importance of smooth frequency response. This factor is key to their ability to deliver good sound with low- to medium-quality speakers. One tactic they use to provide a good listening experience is installing small midrange speakers – instead of a tweeter – on the dash, in the A-pillars or at the top of the door. The equalizer in the radio or amplifier is then adjusted so that these small speakers deliver good high-frequency performance. One of the first times we ran across this was in the second-generation Dodge Intrepid and its sister vehicles. The amplifier in those vehicles had surprisingly impressive processing capabilities, even for its late-’90s vintage. This audio system design technique is now popular in many makes and models of vehicles.

If you’re curious why they use a small midrange rather than just a tweeter, check out this article.

When Speaker Upgrades Go Awry

Here’s a scenario we hear of quite often: A client buys a set of coaxial speakers and installs them in the dash of their pickup truck. The speakers are connected to the factory-installed amplifier. In theory, this should be a nice upgrade, right? The new speakers have far too much high-frequency output because the signal from the factory amp has been equalized for a speaker without a tweeter. The result is a system that sounds overly sibilant. If you’re lucky, you might be able to tame the screechiness by turning down the treble control on the radio. In most cases, though, the result still isn’t ideal.

As you can see from the above measurements, the boosted high-frequency phenomenon is far from isolated. These professionals have the tools and training required to measure the frequency response of the signals coming from the radio or amplifier so they can design an upgrade solution that will sound good.

How To Deal with Boosted High-Frequency Response

So, if you want to upgrade your car audio system, what do you do? First, visit a local specialty mobile enhancement retailer that can make these frequency response measurements. Once they confirm whether your audio system has this high-frequency boost, they can suggest a speaker solution that will offer the performance you want.

If there’s a lot of equalization in the signal, the next step will be to select an amplifier with a built-in digital signal processor or a separate amplifier and DSP. Modifying the signal’s frequency response to the speakers is the only way to ensure that they sound correct.

The DSP will help tame much more than aggressive high-frequency output. The equalization process will resolve inconsistencies in the midrange frequencies, unruly resonance in the midbass and peaky response from a subwoofer. The output of each speaker in the system can be adjusted for amplitude and arrival time so that the system will recreate an accurate soundstage with good imaging.

There are a few vehicle platforms where an experienced technician can adjust the equalization presets in the factory audio system. This is a reasonable in-between solution. It could reduce the high-frequency boost but won’t result in audio system performance that matches the inclusion of a properly adjusted DSP.

Another option is to replace the factory-installed radio and amplifier with an aftermarket solution. This upgrade will eliminate any high-frequency boost, but you will have a system with performances similar to the situation we discussed.

However, if you choose a radio like the Sony XAV-9000ES or XAV-9500ES with its built-in eight-band parametric equalizer, your installer can fine-tune the system for the new speakers. There may be other radios with dedicated equalizers for each output channel. However, an EQ that affects all the speakers in the system won’t yield the same results.

Choose an Expert to Help Upgrade Your Car Audio System

One last tidbit of information before we send you off: The technician working on your vehicle will need to test the speaker outputs for the presence of all-pass filters before deciding whether to apply time correction to the new system. Without this information, you may have uneven midrange performance and a severe lack of midbass.

As you can see, upgrading a modern car audio system isn’t all that easy. And not all car audio shops around the country have kept up with the technologies vehicle manufacturers are using to optimize the audio solutions they deliver. If you want your car stereo to sound better, do your research to find a shop with the tools, training and products to deliver on your goals. Finding that shop might take some time and legwork, but if you want your car audio speaker upgrade to sound great, it’s time well spent.

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.

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.