We’ve talked at length about how car audio line output converters work and have even compared a few to see which sound best. We skipped over a discussion on whether a car audio amplifier upgrade needs a line-output converter. Let’s dive in!

What Does a Line Output Converter Do?

A high-quality line output converter serves three purposes. First and foremost, it can reduce the voltage from a radio or amplifier output to something acceptable on the preamp input of an amplifier. Second, it converts a bridge-tied load (BTL) signal to a single-ended signal that works with all amplifiers. Thirdly, it can provide a remote turn-on signal to activate an amplifier when you turn on a factory radio.

Most car audio amplifiers can only accept up to 5 or 6 volts on their preamp inputs. This voltage is equivalent to the output of an amplifier that produces a maximum of 9 watts of power into a 4-ohm load. Since most car radios can produce at least 20 watts, equivalent to just under 9 volts of signal, we need circuitry to reduce that level and not over-drive the input stage on the amplifier.

All car radios we’ve tested use the bridge-tied load speaker output configuration. This speaker driving method allows a radio to provide more power than a single-ended design without needing a dedicated switching power supply. If you’ve asked a technician to install an inexpensive or poorly designed amplifier, it will likely need a single-ended signal.

If you have a factory-installed radio in your car, truck or SUV, the chances of a wire going live only when the radio is on is quite unlikely. You’ll need a way to tell the new amplifier when it’s time to wake up and get to work. A good-quality line output converter can do that.

Modern Amplifier Features – Automatic Turn-On Circuits

If you look at most high-quality amplifiers on the market, you’ll see they include some sort of remote turn-on detection circuitry. Some of these circuits monitor the input connections on the amplifier for a presence of an audio signal. This is usually called a signal-detect turn-on circuit. Others look for the 55 to 6 volts of DC offset found on the output of BTL amplifiers as would be used in a car radio. These circuits are called DC offset or BTL detection solutions.

Car Audio Amplifier Differential Inputs

Decades ago, car audio amplifiers used the same single-ended RCA input circuitry as a home stereo receiver. Reputable car audio equipment manufacturers realized that switching to balanced differential circuitry inputs dramatically reduced the chances of ground loops that could cause unwanted engine noise in an audio system. This balanced input circuitry also helps eliminate any unwanted noise that the interconnect cables might have picked up as they run through the vehicle.

We’ve written a few detailed articles on the importance of balanced differential inputs and how to test an amplifier to make sure it has this feature. Don’t bother with amplifiers that don’t use differential inputs. You’re only asking for headaches and noise.

Too Much Preamp Voltage

It’s not often you hear the phrase “too much voltage” in the context of car audio discussions. With that said, if you feed too much signal to the RCA inputs on an amplifier, both the input and output can add huge amounts of distortion to your audio system. This distortion is called clipping.

Designing a car audio system upgrade requires an understanding of how the factory-installed audio system works. Your installer might need to take frequency response and amplitude measurements before recommending products. Some factory-installed subwoofer amplifiers can produce just shy of 40 volts of signal.

If you’re shopping for an amplifier to add to a factory-installed radio or amplifier, choose one that can accept a wide range of voltages. Some amplifiers have dedicated speaker-level input terminals. Others have a switch that attenuates the signal on the RCA jacks. Some DSP-equipped amplifiers have digitally selected input voltage ranges.

Questions To Ask When Purchasing Audio Upgrades

If you want to add an amplifier to your car audio system, you’ll want to ask the product specialist you’re working with some questions. Aside from everything we’ve suggested in our Buyers Guides, you need to know what accessories they plan to use for the installation. If they say you need a line output converter, ask what it would cost to move up to an amplifier that can accept the full signal from the source unit and turn itself on and off automatically without any adapters. The chances are good that the higher-quality amplifier won’t just simplify the installation but will likely sound better. If they insist a line-output converter is still required, ask why.

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 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.