It should go without saying that a car stereo system designed around multiple amplifier channels and a DSP is the easiest way to get great sound in your vehicle. The technician working on your vehicle has complete control over the output level, sound arrival time and the frequency response of each speaker in the system. The result should be a sound system that is as optimized as possible – assuming the calibration process is executed properly. There are still many misunderstandings about what a DSP can and can’t do. This article will provide a few things to listen for to help you determine whether your DSP has been adjusted properly.

What Is a DSP?

What is a digital signal processor? Though we have covered the topic extensively, we’ll offer a quick “too long; didn’t read” for those new to our magazine. A DSP is a computer chip optimized to perform many calculations quickly and repeatedly on a sequence of digital samples. These samples are typically a digital representation of an analog signal. In the case of our car audio systems, the analog signals are the left and right channels of the audio recording. DSPs are common in other applications, including video processing and radio frequency transmission analysis. Modern recording studios and live venues use DSP-based mixing consoles.

How Is a DSP Used in Car Audio Systems?

In car audio applications, a DSP serves many purposes. A DSP can combine signals from multiple sources, adjust levels, apply equalization and frequency filtering, and add delay to a signal. In short, it helps the technician connect to a factory-installed stereo, optimize the signal to each speaker and compensate for your vehicle’s acoustics.

If your car stereo uses an aftermarket head unit, your installer will likely connect a DSP directly to the radio’s preamp outputs using RCA cables. Suppose you have a vehicle that uses a digital interface between a factory-installed head unit and an amplifier like A2B, MOST, AVB or a SP/DIF connection. In that case, you may have an interface that feeds a digital signal to your DSP over a fiber-optic cable. Finally, many audio system upgrades require recombining signals from multiple factory-installed amplifier channels and removing any processing to create a full-bandwidth signal. A high-quality DSP can help with this.

After the audio signal is in the DSP, the first order of business is to route that signal to the appropriate output channels. You don’t want the left-channel signal from the radio going to the right-side tweeter. Also, you’ll likely want the signals from both the left and right channels going to the subwoofer signal. All reputable DSPs have a signal-routing mixer to perform these tasks.

Next, the technician configuring the system must filter the signals to each speaker. You don’t want bass information going to a tweeter or midrange information to a subwoofer. A properly trained technician knows which high- and low-pass crossovers to apply to the speakers in your vehicle based on their design, directivity characteristics and the speakers that are operating in adjacent frequency ranges.

The last step is for the technician to use a calibrated microphone system and measure each speaker’s acoustic output at the listening position. Using that information, they can adjust the equalizer to smooth out any peaks or dips caused by reflections in the vehicle. Finally, the output level of each speaker is adjusted to ensure that the transition from one driver to another is smooth.

Auditioning Overall Tonal Balance

While a DSP often seems like some mystical black box of audio voodoo, they are quite simple devices. Yet they do have an extensive list of functions and require training and a thorough understanding of the laws of physics to implement properly. A DSP is effectively mandatory if your goal is realism and accuracy from a car audio upgrade. That brings us to the question, how would a consumer know whether the DSP in their car or truck is adjusted properly?

The first thing to listen for is a smooth frequency response. There shouldn’t be emphasis or deficiencies in any frequency range. For example, if the letters S and T seem overly prominent, the equalizer bands around 3 and 5 kHz might need adjustment. If voices are boomy or chesty, there might be too much output around 200 Hz. The bottom line is that if every genre of music doesn’t sound right, then the DSP needs more adjustment.

An idea offered by long-time car audio competitor Harry Kimura is to listen to a well-engineered piano recording. The lowest note on a piano has a fundamental frequency of 27.5 hertz. That’s well below what an audio system without a subwoofer can reproduce with any authority. The highest note has a fundamental frequency of 4.186 kHz. It’s crucial to remember that each note includes several octaves’ worth of harmonics to give the instrument its “sound.” There’s still important audio information beyond 12 kHz from this 4.186 kHz note. If someone plays a scale from the highest to the lowest notes, each should be reproduced by your car audio system with the same volume or intensity. If something is too loud or quiet, the DSP’s equalizer needs adjustment.

What about the Bass?

We can confidently tell you that a car audio system that plays the bottom two octaves of a piano at the same level as middle C won’t be much fun on the road. It might be super-accurate, but the bass will be drowned out when competing with wind, road and exhaust noise. The subwoofer in your car audio system should be 8 to 12 dB louder than the midrange for the system to be enjoyable while in motion. If you’re a basshead, fill your boots!

The Source of Sound

The second criterion to listen for is staging and imaging. Imaging refers to the ability of an audio system to render the sound of specific instruments accurately on a virtual soundstage. Think of yourself listening to a live acoustic music performance. A four-piece jazz band with a drummer, pianist, upright bass player and lead singer would be a perfect example. No matter where you sit in the audience, the sound source from their instruments is easy to detect. You’d know if the lead singer walked across the stage while performing, even if you didn’t see them.

In your car audio system, you should be able to pick out the specific instruments in a well-recorded track. If the singer and drummer were in the center of the stage, they should sound like they are in the center of the dash or windshield. If the bassist is on the left, then the sound should come from in front of the steering wheel. If the piano was on the right side of the stage, it should sound like it’s coming from the airbag on the right side of the dash.

Here’s a good example of what you should hear if the system has a solid soundstage and good imaging. “Listen to Money for Nothing” by Dire Straits. At 1:12 into the track, Pick Withers’ drums pan from the far right to the center. Each drum appears to have a dedicated microphone, and their signals are panned to fill the soundstage. As he hits different drums, the sound source should move. The system isn’t configured correctly if the drums are a big blurry mess.

How Do You Want Your System to Sound?

The above description assumes you wanted your car audio system calibrated as though you were in the audience. The other option is to have the system configured as though you were on stage with the performance. In this scenario, the sound in your car would be more like what you’d hear when wearing headphones. The vocals and drums might be in the middle of your head. The bassist would be to your left, and the piano to the right. Some call this a “club” sound, where music comes from around you. The product specialist you’re working with to design your mobile audio system should ask you about your listening preferences during the client qualification process.

A car audio system with high-quality amplifiers and an excellent DSP will offer better focus for each instrument. We call this better imaging. We’ve heard many factory-installed audio systems where the center-stage vocals came from a space the size of a large pizza. The best aftermarket systems we’ve listened to reproduced that same track from a point in space the size of a tennis ball. It’s not just equipment that achieves this goal. The technician adjusting the DSP needs to know what to look for and what to ignore in the acoustic measurements to get this right.

What Can’t a DSP Fix?

There are some product and installation issues that a DSP can’t resolve. If you’ve chosen speakers with resonance and distortion issues, the DSP can’t remove that harmonic information added to your music. If you find the high-frequency response harsh or fatiguing, you are probably hearing harmonic distortion from your speakers. The only solution is to switch to better-designed speakers that include distortion-reducing designs and technologies.

The same goes for sloppy midbass. If a rim hit on a tom drum sounds like a thud or bump rather than a sharp crack, you may have a speaker or amplifier distortion problem. Audio components (primarily amplifiers and speakers) with high levels of intermodulation distortion typically cause muddiness or unwanted warmth in the lower midrange frequency range. No amount of DSP adjustment can fix this.

Learning About High-Quality Audio Systems and Accurate DSP Adjustment

This article kicks off a series on how to listen to audio systems and components from a technical perspective. We’ve noticed that many consumers think certain products “sound really good” when they are, at best, mediocre. We hope that educating everyone about what to listen for when auditioning speakers and listening to demo vehicles will help people purchase solutions that offer the best performance possible for their investment. As you learn what high-quality car audio upgrades sound like, use that information when working with a local specialty mobile enhancement retailer to pick the best upgrades possible.
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.