When it comes to producing deep bass from a small enclosure, adding a passive radiator offers some significant performance benefits. If you aren’t familiar with this type of subwoofer enclosure, then you’ve come to the right place. We’ll look at how this design works, the benefits it offers and analyze potential drawbacks. Ready? Let’s dive in!

Common Subwoofer Enclosures

Traditionally, there are two popular types of subwoofer enclosures. The simplest to design and execute properly is an acoustic suspension design, better known as a sealed enclosure. In this configuration, the air inside the enclosure adds to the compliance of the cone assembly to control its motion at low frequencies. When designed with a low-to-modest system Q value (Qtc <0.75, for example), the roll-off response is typically in the 40-55 Hz range at a slope of -12 dB per octave.

The second type of enclosure you often see is called a bass reflex design. These are also known as ported or vented enclosures. In these designs, a vent is added to the enclosure that lowers the system’s resonant frequency. The vent has a specific surface area and length in order to change the resonant frequency of the system. As a gross generalization, bass reflex enclosures are 50% larger than their acoustic suspension brethren but offer extended low-frequency output. In car audio applications, this extended response improves overall system efficiency. The design of the vent is somewhat complicated in terms of balancing surface area and implementing an appropriate radius on the ends to prevent unwanted noise from high-velocity air movement. Below the tuning frequency, the output of this type of subwoofer enclosure design rolls off at -24 dB/octave.

Passive Radiator Subwoofer Enclosure Designs

Imagine if there were a way to get the efficiency of a bass reflex design with the enclosure volume of an acoustic suspension enclosure. The passive radiator is a nearly ideal solution. Imagine that a passive radiator is a subwoofer in which the voice coil and magnet assembly have been removed. A precise amount of weight must be added to the remaining assembly to produce a very low resonant frequency. The weight of the passive radiator cone assembly is roughly equivalent to the air mass that would fill the vent in a bass reflex design.

Let’s Model Some Subwoofer Enclosures

As they say, the best way to visualize something is through comparison. For this example, we will simulate the performance of a Rockford Fosgate Power Series T1D210 10-inch subwoofer in acoustic suspension, bass reflex and passive radiator enclosure designs.

Let’s start with the sealed enclosure design. For a good blend of low-frequency extension and cone control, we’ll target a system Q of 0.707. The software suggests that a net internal air volume of 0.53 cubic foot is ideal. This results in a system F3 of 51.06 Hz, which is typical and acceptable for this type of subwoofer enclosure.

Next, let’s look at extending the low-frequency efficiency of our sub by moving to a bass reflex enclosure design. We’ll double the enclosure volume to a net of 1.06 cubic feet and add a vent that’s tuned to 29 Hz. The vent in this example is tricky. Ideally, it should have a diameter of 4 inches, but the length would be 36 inches and difficult to fit inside the enclosure. We aren’t talking about the difficulty of constructing the enclosure in this article, so we’ll leave that in place for the simulation. The F3 frequency is a thoroughly enjoyable 26.1 Hz.

Last and certainly not least, let’s look at the passive radiator enclosure design. For this simulation, we’ll use a 10-inch radiator with a resonant frequency of 15 Hz, equivalent compliance of 60 liters and a Qms of 4.5. We’ll keep the enclosure volume at 0.53 cubic foot.

As you can see in the graph below, we pick up a tiny bit of efficiency above 55 Hz compared to the bass reflex enclosure. Our passive radiator design is much louder at all frequencies above 25 Hz compared to the acoustic suspension system. This design yields an F3 frequency of 35.6 Hz.

Advantages and Drawbacks of Passive Radiator Designs

A second benefit of the passive radiator (P-R) design is that there is no chance of noise from the radiator as compared to a vent. A vent with a small area may produce chuffing noises as the air resonates up and down through the column. Likewise, a hard edge on the inner and outer edges of a vent contributes to the chance of unwanted noise. The passive radiator moves forward and rearward like the subwoofer itself.

On the flip side, the roll-off of the P-R system is steeper than both the acoustic suspension and bass reflex designs at -30 dB/octave. This is because there is a null in the output where the radiator resonates. If we expand the vertical scale on our simulations in BassBox Pro, we can see this dip at 15 Hz. In short, a P-R design isn’t as good as at reproducing infrasonic information as a bass reflex or acoustic suspension system. Whether this response dip matters or not depends on your expectations and the music you listen to. If you like rock, pop and rap music, it likely won’t matter at all. If you listen to classical music with lots of low-frequency organ notes, it might not be ideal.

Companies like Audiomobile, Kicker and Earthquake offer passive radiators that specialty car audio retailers can use to increase the efficiency of your car audio system. They don’t have to be used with the same brand of a subwoofer, so mixing and matching might offer a great opportunity. Some of these companies offer very specific designs for their solutions, while others provide more information to allow your technician to create something special and unique. If space for bass in your car or truck is at a premium, having a passive radiator subwoofer enclosure built might be a great solution.

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.

When it comes to car audio systems, more is better, right? Enthusiasts want more bass, more output and more impact. When your favorite song comes on, turning the volume knob all the way up seems like the right thing to do. For car audio professionals, we need to balance keeping our clients happy with great-sounding audio that will play loudly and ensuring that the equipment we’ve installed functions reliably. Yes, you can turn up the gains on amplifier and it might play a little louder, but that might create a lot of distortion that results in damaged speakers and subwoofers.

A Primer in Over-Driving Car Audio Amplifiers

Every car audio amplifier on the market, save for those classics with built-in limiters, has the ability to produce significantly more power than it is rated for. The issue is, this extra power is riddled with massive levels of distortion that renders the signal unusable. Allow us to explain.

If you’re playing a sine wave through an amplifier and you increase the output level so that the peaks are just below the level at which the amp clips, lets assume you get the full rated power of the amplifier. In this theoretical example, let’s say that’s 72 watts. The output waveform might look something like what’s shown below.

If you increase the signal going into the amp, or turn up the sensitivity (gain) control, the amp will attempt to amplify the signal more. The issue is, there’s always a limit to how much power the amp can produce. That limit is determined by the amplifier rail voltage or the power supply’s ability to deliver current to the load. Let’s say we increase the gain a little bit so that we can play really quiet music loudly. When we play loud music, the output might look like the orange trace in the image below.

It’s important to know that the amplifier is producing more power when it starts to distort. Power is the area under the curve, to put it simply. The speaker may not play significantly louder as this extra power is delivered as harmonic content rather than more output at the fundamental frequency.

In a theoretically perfect amplifier, you can drive the outputs to a point that it produces twice its rated clean voltage. The waveform would look something like the red trace shown below.

How To Calculate Amplifier Power

When calculating power in a sine wave, we use the 0.707 of the peak value as the average voltage, or more accurately, the RMS voltage. The RMS level is the alternating current (AC) signal level that does the same amount of work as a direct current (DC) amplitude. For the green trace, this would be 0.707 x 24, which is 16.968 volts. To calculate power, you square the voltage and divide by the load impedance. For our simulation, that’s (16.968 x 16.968) ÷ 4, which works out to 72 watts.

A square wave, like the one shown in red, doesn’t use this 0.707 multiplier. The peak voltage of 24 volts is used without any scaling. When plugged into the power equation, we get (24 x 24) ÷ 4, which is 144 watts. Unsurprisingly, that’s twice as much as 72.

If we had a speaker with a real thermal maximum power handling of 75 watts connected to this amplifier, and we fed it with 144 watts of power, it would fail. This is why seemingly under-rated amplifiers are capable of damaging speakers. Amplifiers can and will produce more power when pushed to clipping.

As full transparency, modern Class-D amplifiers can’t fully double their power output capabilities. They are more likely to be able to produce 100 or 120 watts in a similar scenario. That’s still well more than our 75-watt speaker can handle.

The Purpose of Amplifier Gain Controls

The gain control on your car audio amplifier exists for two reasons: to allow it to produce its rated power when fed with a variety of source unit voltages, and second, to allow the installer working on your audio system to balance the output of multiple speakers in an actively filtered audio system.

If you have one pair of amplifier channels for your door speakers and another channel for a subwoofer, the relative level between the two needs to be adjusted so that the system sounds good. Many shops will use a standard target curve to which they calibrate the audio systems they install.

It’s clear to see from the above that you don’t need as much power for the midrange speakers as you might for the subwoofer.

Considering Sensitivity Controls and Equalization Settings

Let’s look at another important aspect of setting up amplifiers. In our example, we have a 72-watt amp that’s going to power a set of two-way component speakers in the front doors of a car. As happens in every automotive installation, there are frequencies that need to be attenuated with an equalizer in order for the audio system to hit the target. Let’s say that we needed to pull out 3 dB of output around 1 kHz, boost 400 Hz by 5 dB and cut 100 Hz by 6 dB. The response curve of our equalizer would look like the image below.

Many amateurs will pick a specific frequency at which to set the gains on the amplifier running the midrange speakers. While this process ignores the target curve, it can also run afoul of equalization settings. Let’s say someone chose 1 kHz in our theoretical system to set the midrange amp. Look at our EQ response curve. We’ve reduced 1 kHz by 3 dB relative to the rest of the signal. We’ve also boosted 400 Hz by 5 dB. If the amp is set to clip with the volume control at maximum using a 1 kHz test tone, frequencies around 400 Hz will be significantly distorted. In fact, to reach our output requirements at 400 Hz, we need around six times as much power as is required at 1 kHz. Imagine how much distortion would be added!

What’s Wrong with Having Too Much Gain on Your Car Audio Amp?

If the gain controls are turned up too much, a significant amount of unwanted hiss may be added to your audio system. Worse, if you don’t know what to listen for in terms of clipping or distortion, you can easily send too much power to your speakers or subwoofers and damage them. Balancing all the criteria we’ve talked about while ensuring that you can get the cleanest output from your stereo isn’t as easy at it would seem.

Before you start experimenting with oscilloscopes, distortion detectors and voltage charts, talk to a local specialty mobile enhancement retailer and consider having them set up your system so that it sounds great.

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.

Did you know that a difference of 20 watts of power between one car audio amplifier and another might be completely inaudible? That same 20-watt difference might mean having to keep your windows rolled up on the highway to hear your music. Let’s look at the physics of reproducing sound with moving-coil loudspeakers and why choosing an amplifier with a few watts more than another may be significant or irrelevant.

Car Audio Speakers and Amplifier Power

If you look at a typical higher-end 6.5-inch coaxial car audio speaker, you’ll find that it has an efficiency rating of 86 dB when driven with 1 watt of power and measured at a distance of 1 meter. If the reference is 2.83 V, then that’s 2 watts into a 4-ohm driver, and the efficiency number will be 3 dB higher at 89 dB. If it’s a 2-ohm driver with a 2.83V spec, then that’s 4 watts, and they will add another 3 dB. Aren’t specification games fun?

The first takeaway from this is that it takes a doubling of your amplifier’s power to increase a speaker’s output by 3 dB. At the same time, halving the power reduces the output by the same 3 dB. If you only need 80 dB of output, then our 86 dB efficient speaker will only need 0.25 watt of power to reach that level.

Scenario 1 – Deck Power and Door Speakers

Suppose you have a modest audio system that is made up of a typical aftermarket radio and a pair of equally typical door speakers. Most radios can produce about 20 watts of output per channel, and we’ll use our 89 dB example speakers (though now we have two of them, so the pair will produce 92 dB when each is powered with 1 watt). With 20 watts of power on tap, the system should produce just a smidge over 104 dB of output. Of course, this assumes that the speakers increase the output linearly for every doubling of power. At 20 watts, especially if they are reproducing bass frequencies, you are likely near their upper limit.

What if we switch the radio to a high-power unit like the Sony XAV-AX7000 that can produce 45 watts of power per channel? Now, assuming the speakers can handle the extra power, the system will produce about 107.5 dB of output. That extra 25 watts increases how loudly our music will play by 3.5 decibels. It doesn’t sound like a lot, but it would be audible.

Scenario 2 – Small Subwoofer Amplifier Versus Large

In our second example, let’s look at the higher power levels involved with driving a subwoofer. Say we have a Rockford Fosgate amplifier capable of producing 1,000 watts of power. Considering the transfer function of the typical vehicle interior, a pair of 10-inch subwoofers in a vented enclosure might have an efficiency of about 101 dB at 40 Hz when each is driven with 1 watt. When we increase the power to the subs to 500 watts each, the system should produce 128 decibels of output. That’s pretty darned loud! Keeping in mind that we need to double or half the power level to produce a change of 3 dB, what happens when we pick an amplifier that can produce 1,050 watts or that same increase of 25 watts to each subwoofer? Well, the system will play 0.21 decibel louder. While you might be able to measure that with a Term-Lab SPL system, it’s unlikely you can hear that small of an increase.

Looking at Power Specifications Using Decibel-Watts

While most of us are used to seeing the decibel unit used in the context of measuring volume levels, it can be applied to a variety of electrical applications. If you take a close look at the power measurements in any of the BestCarAudio.com Test Drive Reviews, you’ll see we list watts and a number called dBW, or decibel-watts. The unit dBW refers to decibels referenced to one watt of power. As such, if the amp produced 1 watt of power, it would be rated at 0 dBW, or no increase or decrease relative to 1 watt. If it made 8 watts, then it would be rated at 9 dBW. One hundred watts is 20 dBW, and 1,000 watts is 30 dBW.

Suppose your speakers or subwoofers can handle the power in terms of thermal capacity and cone excursion capability. In that case, you can add the dBW number to the 1-watt efficiency number of the speaker to estimate how loudly it will play. Of course, no midrange speaker is going to able to deal with 200 watts of power, and a subwoofer isn’t going to increase its output linearly when driven with 10,000 watts.

Backtracking for a moment, to provide some clarity, when we use an RTA or SPL meter to measure a sound source’s volume level, we measure dB SPL. Similar to the way that the decibel watt (dBW) references 1 watt of power, the dB SPL unit references 20 micropascals or, 0 dB. A sound level of 20 micropascals is considered the lowest hearing threshold of a young, healthy ear. Of course, if we can measure this pressure (20 micropascals), then 0 dB isn’t absolute silence or a vacuum. It’s just a reference level. In the same way, 0.25 watt is -6 dBW; it’s possible to have negative SPL numbers or a room that’s quieter than 0 dB. Microsoft built an anechoic test chamber that has a noise level of -20.35 dB SPL, or 20.35 decibels quieter than 0 dB. It’s said that the sound that air particles create from bumping into one another in a still room is -23 dB SPL.

When Watts Matter and When They Don’t

Let’s take all this information and put it into use. If you’re shopping for a new radio, then one that produces 45 watts is going to provide an audible improvement over one that produces only 20 watts. If you are shopping for an amplifier for your speakers, a 75-watt and a 100-watt amp will only increase output by just over 1 dB. If one subwoofer amplifier produces 25 watts more than one that makes 750 watts, the difference is only 0.14 dB. The best way to think of amplifiers is by ranking them as small, medium and large. A small stand-alone speaker amplifier would be 50 watts per channel. A large one would be 100-125 watts. A small sub amp would be 250-300 watts, a medium would be 600-800 watts, and a large would be 1,200-2,500 watts. Worrying about whether the amp makes 1,150 or 1,175 watts (a difference of 0.09 dBW) is a waste of time.

When it’s time to upgrade your car audio system with a new high-power radio or an amplifier, drop by your local specialty mobile enhancement retailer and ask to audition several options on the same set of speakers or subwoofers and the same source unit. This is the best way to determine which solution offers the least distortion and most accurate sound. Just a reminder, don’t get hung up on a few watts – that’s truly the least of your worries.

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.

No matter how hard he or she tries, the installer who’s calibrating your car audio system can’t use a digital signal processor to tune distortion out of your system. We aren’t talking about the harmonic distortion that happens when a signal overloads the processor or an amplifier’s input stage. Preventing clipping is a simple process and one that’s fundamental to completing an amplifier installation. Every part of the audio chain – from the source unit and processor to the amplifier, speakers and subwoofer — adds (hopefully) small amounts of unwanted high-frequency information from harmonic distortion and lower-frequency products from intermodulation distortion to the audio signal. While that seems like a mouthful, it’s time to take a look at the big picture and how product selection affects the performance of your audio system.

Defining a Goal for Your Car Stereo

You don’t need to be an audiophile or “audio snob” to appreciate the benefits of combining amazing products with proper system design, installation and calibration. The difference that clarity and output capability offered by well-designed speakers and proper installation deliver, as compared to low- to mid-quality speakers, is easily discernable by even the most amateur music enthusiasts.

Here’s the first step. Find a song you like. Choose something you’ve listened to many times and really enjoy. Now, play it on your smartphone with the phone sitting on your kitchen table. Turn it up fairly loud. Now connect your phone to a Bluetooth speaker like a JBL Charge 4 or something similar. Listen to that same track again, and more particularly, listen for the differences in the way it sounds. Chances are, you’re going to hear a lot more midbass and drums, and other bass instruments will now start to stand out in the mix.

If you have a good home audio or home theater system, listen again at a similar volume level. If that audio system has a subwoofer, chances are the bass information will have more low-frequency extension, and voices and other midrange instruments will sound clearer. If you don’t have a good home audio system, ask a friend if you can listen to it on their system. Now you have a basic idea of how better audio systems change the way your music sounds.

The last step is to head to a local specialty car audio retailer and ask to audition the song in one of their demo vehicles. If the audio system is designed, installed and calibrated properly, you should hear the music laid out in front of you in what’s called a soundstage. The car or truck’s dashboard should recreate the space where the performers in the recording were situated in the recording studio or on the stage. The balance of the bass to midbass, midrange and high-frequency information should be smooth, and nothing should stand out. It should sound as though you’re sitting at the console of the recording studio.

Let’s Talk about Audio Clarity

Clarity, as defined by the Oxford Dictionary, refers to “the quality of transparency or purity.” Think of a photograph for a second. If you take a photo with a kid’s Fisher-Price camera and the same image with a Sony α9 II with a prime FE 50 F1.2 GM lens, the difference in the detail and color accuracy will be readily apparent. This is why high-end cameras exist – to capture a scene or moment with improved clarity.

Look carefully at the two photos above. The sharpness in the leaves is gone in the lower photo. The detail in the water droplets and the texture in the rocks have been lost. The color balance and the exposure of the images are completely different. Once the accuracy of the original experience is gone, it can’t be restored.

When you’re listening to music, clarity works the same way. The balance between the instruments and performers in the recording was determined by the recording and mastering engineers. That mix was referenced to the monitor speakers and the system calibration in the studio control room. That’s as “accurate” as that song will ever get. Moreover, what each performer or instrument sounds like in the recording studio or on the stage isn’t the reference for accuracy. The front row center seat or the “sweet spot” in an auditorium isn’t the reference either. The recording engineer hears what each of the microphones picks up after they are all combined together and processed. If your audio system isn’t calibrated the same way, or your equipment adds moderate levels of distortion, you don’t hear the same sound. It might still be nice, but it isn’t technically accurate.

What Is Distortion?

Almost everyone who has even a passing interest in car audio equipment thinks that distortion only happens when you overload a component in the audio system. If you ask someone to “draw” distortion, they’ll draw a clipped sine wave. This is an extreme example but isn’t wrong.

In reality, every time we pass an audio signal through an electronic device, (hopefully) small amounts of harmonic and intermodulation distortion are added to the signal. If you were to compare the shape of the original and audio waveform and the signal going to your speakers on an oscilloscope, they’d look very similar to one another. The reality is, small amounts of unwanted information have been added to the experience. Second-, third-, fourth- and maybe fifth-order harmonics, along with the product of multiple sounds being played simultaneously, add themselves to your music.

It’s time for an example. I downloaded a recording of a triangle and imported it into Adobe Audition. I copied the signal from the left channel to the right to ensure that I was dealing with exactly the same content. Then I locked the left channel and applied the distortion processing built into Audition to only the right channel.

If you look closely at the lower spectrogram, you can see that there are more purple lines running horizontally between the 1,650 and 4,570 Hz fundamental frequencies. That’s added unwanted distortion. Let’s look at it another way.

In the image above, you can clearly see the original recording in green and the unwanted content at 1,244, 2,064, 2,891, 3,299, 6,223 and other higher frequencies that have been added in the blue trace. Those are sounds that weren’t in the original performance or recording. That’s distortion.

Can’t My Installer Tune Out Those Frequencies?

I’ve heard people say that adding a digital signal processor (DSP) to a car audio system is a good way to tune out distortion. Sadly, that’s not how they work. The main goal of the processor is to calibrate the output of each speaker in the system to compensate for frequency response issues caused by the vehicle environment.

In our example, we have two frequencies to deal with in the original recording. If this were the only piece of “music” played on the system, then your technician could EQ out the unwanted information. The problem is that different instruments cover different frequency ranges. If you fix the sound of this triangle, you ruin the sound of an electric guitar, piano or violin. The only way to get rid of it is to prevent your audio system from adding it.

Choose High-Performance Car Audio Equipment

You can read any of more than 30 articles on BestCarAudio.com that explain what to look for when shopping for or comparing source units, amplifiers, speakers, signal processors and subwoofers. For electronics, signal-to-noise ratio and Total Harmonic Distortion and Noise are the numbers to check out. Be sure the SNR is compliant with the CTA-2006-C standard, lest you be fooled by inflated peak-power ratings. Since no car audio companies publish distortion graphs for their speakers or subwoofers, you have to look for features like aluminum shorting rings, flat spiders and copper T-yoke caps, or motor designs like eXtreme BL Linearity (XBL^2) or an underhung voice coil design that reduces distortion. Keep in mind that the latter two include some drawbacks along with their benefits.

What’s perhaps the best experience of all is auditioning products under controlled conditions. You CAN hear the difference between good and great sounding head units, amplifiers and speakers. Before you rush out and buy a deal you saw online or guess at the quality of a product you’ve heard about from a friend, drop by a few local specialty mobile enhancement retailers and audition the components you intend to add to your car audio system. Ask them about the product features and designs that improve their performance. Then find out if they have the tools and training to integrate everything into your vehicle and calibrate the system properly with a DSP. It seems like a lot of work, and it is, but it’s worth every second when your music sounds amazing.

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.

Look at any of the top car audio subwoofer amplifier models available from specialty retailers. You’ll find that most include an option for a remote level control or bass boost function. Being able to fine-tune the output of your subwoofer system is great for those times when you want to rock out to an amazing song or calm things down so you can talk to a passenger easily. This article will look at how the subwoofer level controls on source units, digital signal processors and car audio subwoofer amplifiers work.

You Can’t Get More than Full Power

Before we dive into the different adjustment options, consider that the maximum output you’ll get from your subwoofer system depends on the excursion capability of the sub and the maximum power available from your amplifier. You can’t get more bass by increasing the signal to the amplifier when it’s already optimized to make maximum power at full volume. With that said, you can get to full power sooner and increase the amount of bass relative to the midrange and high-frequency speakers in the vehicle. Remember that you may need to limit how high you turn the volume control on the radio if this is how your system is configured.

Think of your subwoofer system like the engine in your car. Once you’ve put your foot to the floor and the engine is making as much power as it can, there’s no way to get more power without some significant modifications to the vehicle. If you want more bass than is being produced by your car audio system, return to the retailer that installed the system and talk to them. You may need more subwoofers, larger subwoofers, a different enclosure, a more powerful amplifier or some combination of these items.

Subwoofer Level Controls in Car Audio Source Units

Almost every source unit on the market with electronic crossovers also includes a subwoofer level control function. This control adjusts the level on the subwoofer preamp output RCAs relative to the level on the front and rear RCAs. These source units are configured to work two ways.

The first example we’ll look at is configured the same as the Sony XAV-AX7000 that the BestCarAudio.com team reviewed here. In the subwoofer adjustment menu, when the level is set to 0, the subwoofer output level is the same as that of the front and rear preamp outputs. If you increase the subwoofer level to 10, the output on the sub preamp output increases. This configuration results in you reaching the maximum output capability of the subwoofer preamp outputs with the volume control set to 38 instead of 49. Turning the volume up higher will produce distortion on the sub preamp output. You can also turn the output down to -10 if you find there is too much bass. Lowering the signal has no adverse effect on the outputs.

Other companies configure their subwoofer level controls on a scale of 0 to 10 or 0 to 20. Though the labeling varies from brand to brand and potentially model to model, setting the output level to its highest setting would result in the preamp output being maximized without distortion when the volume is maximized. This configuration prevents the outputs from distorting when the volume is cranked. In an ideal world, the radio’s sub output adjustment labeling would be something more akin to -10 to 0.

Level Controls in Digital Signal Processors

Just as with a source unit, there’s an upper limit to how much voltage can be produced on a digital signal processor’s output. If the DSP is built into an amplifier, maximum output is determined by the voltage and current capabilities and the impedance of the subwoofer(s) connected to the amp. If your system uses a stand-alone processor, then it can likely produce 5 or 8 volts of signal on the RCA output jacks. Most signal processors include a subwoofer level option that can be adjusted with one of their optional remote controls. As a key part of the system calibration process, the technician working on your audio system will need to ensure that the signal remains clean and undistorted when the volume is maximized.

A unique option that ARC Audio includes in its PS8, PSM and PS8 PRO series signal processors is a configurable level control. When the optional LR1 remote is added, your technician can configure which channels it affects and by how much. If you want the LR1 to act as a sub control, it can be assigned to adjust over a range of -20 to 0 dB and be configured to work with the outputs that feed the sub amplifier. The software configurability means that this remote could also serve as a master volume control for the entire system, as a center channel level control or rear-fill speaker level adjustment.

Issues with Adjusting Subwoofer Output Level

Some digital signal processors offer a bass EQ control aside from their graphic or parametric equalizer. These adjustments are more likely to be found in processors that are compatible with the Maestro AR to integrate directly with factory-installed source units. In most of these cases, the bass EQ is a shelf filter that adds a specific amount of boost below a configurable frequency.

There is a problem with adjusting bass output this way. Suppose your audio system is calibrated to a target response curve, and the crossovers are set properly. In that case, the point at which the subwoofer’s output crosses over with the midbass driver’s output should be at the -6 dB point to sum flat in terms of phase and frequency. If you turn the bass up, that crossover point changes. This mismatch can result in some bass frequencies sounding as though they are coming from the front of the vehicle and some from the back.

In reality, applying the shelf control shown earlier to both the subwoofer and the midbass drivers maintains this phase and amplitude relationship, so your audio system sounds its best.

Bass Boost Versus Subwoofer Level Control

Many subwoofer amplifiers include a bass boost control. These are typically a narrow-band equalizer circuit that’s centered around 45 or 50 Hz. Some entry amplifiers have a switch that adds 6 or 12 dB of boost at this frequency, while others have an adjustment potentiometer that allows for a variable amount of boost, usually up to 12 or 15 dB.

Fancier amplifiers add frequency and Q-factor adjustments to the boost level control to allow your installer to fine-tune the system further. Used gently, these adjustments can add some low-frequency emphasis to a sealed subwoofer enclosure to make it more fun.

While these boost circuits can make listening to your music a lot of fun, when used excessively they typically don’t result in smooth and natural sound. If you want your car audio system to reproduce a recording of a set of drums in a way that makes them sound real, lots of bass boost isn’t a great solution. If you want to rock out with your friends to some rap, dance or techno, it can be awesome!

For technicians setting up an amplifier that includes a remote bass boost or remote level control, he or she will need to ensure that the system can play without unwanted distortion with the volume on the radio maximized and the control turned all the way up. The crossover adjustments will need to be optimized for the system’s typical listening preferences to sound its best.

If you’re considering adding a subwoofer system to your vehicle, an upgrade we highly recommend, then drop by your local specialty mobile enhancement retailer today. They can design and install a solution that sounds great and delivers the performance you want. If you listen to many different kinds of music, be sure to ask them about including a remote subwoofer level control in the system design.

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.