Few people in the car audio industry seem to grasp that speakers are typically the weakest link in audio systems, in terms of adding distortion to what we hear. Whether it’s a poor design with improper voice coil centering in the magnetic gap or poor magnetic or compliance linearity, speakers add significant amounts of unwanted information to what we hear. This article will take a deep dive into explaining how increased cone excursion affects distortion.

Understanding Car Audio Speaker Cone Excursion

Speaker cones move back and forth to excite air molecules and produce sound. They function in the same way that hitting the skin of a drum, blowing through a horn or vibrating the string of a guitar creates pressure waves in the air. If we apply more voltage to a speaker, the cone moves more. Reproducing low-frequency information requires that air molecules be displaced further, requiring more cone excursion (and more voltage) to produce bass frequencies. Larger instruments like an upright bass, concert grand piano and timpani also produce more low-frequency information than a banjo, spinet piano or bongo drum.

Unfortunately for speakers, the more their cones move forward and rearward, the more chances there are for the cone to not track the electrical signal perfectly. When this happens, unwanted harmonic information is added to the audio signal. We call this distortion. If the cone, dust cap or surround resonates, this also adds unwanted distortion. It’s not uncommon for speakers playing at moderate output levels to reach well over 1% distortion. This means that more than 1% of the sound they produce doesn’t follow the input signal accurately.

Measuring and Understanding Speaker Distortion

To help explain this concept, I took a popular 6.5-inch PA-style speaker that’s used in car audio systems and mounted it in my test enclosure. I set up my Clio Pocket with the microphone a few millimeters from the cone and performed a series of frequency response sweeps at different power levels. The Clio system can analyze the measurement and display second- and third-order harmonic information. Let’s look at the first measurement in detail.

The graph you see above shows three pieces of information. First, the red trace is the frequency response of the speaker. This trace tells us how much energy the speaker produces at different frequencies when fed with a chirp signal. The chirp signal is a sine wave sweep that starts at 20 Hz and ends at 40 kHz. I adjusted the output of the amplifier for this test such that it produced right at 1 volt of output, which is 0.25 watt into a 4-ohm load.

The perfect speaker (which doesn’t exist) would produce a perfectly flat frequency response from the lowest bass frequencies to the highest of high frequencies. This speaker was within about 5 dB of flat from 200 Hz to 3000 Hz. Remember, this measurement is with the microphone right at the cone, so the sound pressure level numbers on the left don’t directly correlate to what you’d hear in a car or truck unless you installed the speaker in your headrest. Uh, please don’t do that.

The blue trace is the second-order harmonic distortion trace. To explain what this information means, let’s look at a specific frequency, 200 Hz. The speaker is producing about 88 dB SPL of output at 200 Hz. This is called the fundamental frequency. The blue trace tells us that it’s also producing a second harmonic (which would be 400 Hz) at a level of 38 dB SPL. Again, the absolute numbers don’t matter, but we need to know that the distortion is 50 dB below the fundamental. That works out to 0.316% for the second-order harmonic.

The green trace is the level of the third-order harmonic, which for a 200 Hz signal is 600 Hz. We have an output of about 29 dB SPL, 59 dB below the fundamental and representing a distortion level of 0.112%.

I’ll reiterate and rephrase this to be precise: If you feed this speaker a 200 hertz signal at a level of 0.25 watt, it will also produce output at 400 hertz and 600 hertz (and many more multiples). This is how speaker distortion works, and it’s common to every speaker of every design, at every price point and from every manufacturer. Finally, better speakers add less distortion – that’s a key part of what makes them better. I deliberately chose this PA-style speaker because it has an extremely short voice coil, so it will be easy to push it into high levels of distortion at low frequencies with minimal power. The purpose is to quantify how distortion increases with cone excursion, not to “test” this speaker.

More Power Means More Distortion

For the next test, I increased the output of the amplifier to 2.83 volts, which works out to 2 watts of power. This added power should correlate to a 9 dB increase in output.

The first thing to notice is that the shape of the frequency response trace (red) didn’t change. Second, the speaker did increase its output by exactly 9 dB. You have to love the laws of physics! What matters in this measurement is that the harmonic distortion has increased significantly. The increase isn’t linear with the increase in output from the speaker. Looking at 200 Hz again, the first harmonic is now at a level of -44 dB relative to the fundamental, which is 0.631% THD. The third harmonic is at 50 dB below the fundamental, which is 0.316% THD.

Let’s double the power again to 4 watts and see what happens.

The fundamental has increased another 3 dB as expected. The first-order harmonic content at 200 Hz is at -42 dB relative to the fundamental, which is 0.794% THD. The third-order is 47 dB below the fundamental, which is 0.446%.

Let’s double the power again to 8 watts and repeat the measurements.

The fundamental is right at 103 dB SPL at 200 Hz, and the second harmonic is 40 dB lower at 63 dB SPL. This represents almost exactly 1% total harmonic distortion. The third harmonic is down 44 dB, which is 0.631% THD. We won’t get into the math here, but the total distortion caused by all harmonics wasn’t measured in this test, and you can’t add the numbers directly (e.g. 1.631%).

OK, let’s bump up the power again to 16 watts.

While we continue to focus on the 200 Hz calculations, look what’s happening to the third-order harmonic distortion down below 100 Hz – it’s getting louder very quickly and is actually catching up to the fundamental information. Nevertheless, at 200 Hz, the second-order harmonic output is at 37 dB below the fundamental, which is 1.412% distortion. The third-order distortion is at -40 dB relative to the fundamental, which is 1.0 % THD.

Hopefully, you’re starting to see a pattern. Let’s double the power again to 32 watts and see how the speaker behaves.

We picked up another 3 dB of output across the board. Our fundamental is at 108 dB at 200 Hz and the first harmonic is down only 34 dB, which is right at 1.995% THD. The third-order harmonic output is down 38 dB at 1.259% THD. If you’re getting the feeling the speaker would sound terrible attempting to reproduce audio information at 200 Hz at a drive level of 32 watts, you are right.

OK, one last time. Let’s double the power again to 64 watts and analyze the frequency response and harmonic content.

With the fundamental output at 111 dB at 200 Hz, we have 79 dB of output at the second harmonic of 400 Hz, which represents 2.511% THD. The third harmonic output at 600 Hz is at 76 dB, which is 35 dB below the fundamental, or 1.778% THD.

The chart above summarizes the increase in distortion relative to the increase in output. It’s easy to see how the second and third harmonics continue to get louder relative to the fundamental frequency.

Look at what’s happening down at 100 Hz and below. The third-order harmonic output is as loud or louder than the fundamental. When you feed this speaker 64 watts of power at 50 Hz, it produces 93 dB SPL of output (with the mic in this position) and 97 dB of output at 600 Hz. That’s audio information that wasn’t in the music. If you want to do the math, or, more accurately, if you’d like me to do the math, that’s 158% distortion.

What Have We Learned about Speaker Distortion?

There are two takeaways from this first look at car audio speaker distortion. First, the amount of distortion produced by a speaker increases as the cone excursion increases. We should already know from other articles that cone excursion increases at lower frequencies. Putting together these pieces of information tells us that we don’t want to push the smaller speakers in our vehicles to reproduce the bottom two or three octaves of the audible music range. Adding a subwoofer system with a dedicated amplifier and a speaker designed to reproduce low frequencies allows for more bass and can dramatically improve the clarity of the midrange speakers in your audio system.

Second, in general, 6.5-inch PA-style speakers aren’t good at reproducing audio below about 300 hertz. If you understand speaker enclosure design and have modeled this type of speaker using software like BassBox Pro, Leap or Term-Pro, you’ll know that most of these drivers have a -3 dB frequency in the 150 to 200 Hz range. So, pushing this type of speaker to produce audio information below 250 hertz is asking for trouble, or at the very least, lots of distortion.

Choose Your Car Audio Speakers Wisely

If you’re shopping for new speakers for your car or truck, drop by your local specialty mobile enhancement retailer and listen to the options they have available. Suppose you’re the type who likes to correlate features with performance. In that case, drivers that use aluminum or copper shorting rings, feature flat spiders or have a copper distortion-reducing cap on the pole piece are likely to add less distortion than models without.

Look for speakers with cone materials that balance mass with rigidity and damping characteristics – getting any of these wrong is a recipe for trouble. Finally, trust your ears. The speaker should sound smooth and natural with no emphasis anywhere in the frequency range, especially in the bass region. If they sound good on a display compared to the rest, they are a good choice for your car or truck.

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.

There’s no denying that pickup trucks are some of the most popular options for subwoofer system upgrades. Despite the creature comforts and luxury afforded by Lariat, Platinum, Longhorn and Denali trim levels, a high-performance subwoofer system can transform any of these vehicles from nice to all-out amazing. The issue is, there isn’t much space for subwoofers in these vehicles, and this means the options are limited for those who want some rumble. In previous articles, we’ve discussed the benefits and drawbacks of sealed versus vented enclosures. Unfortunately, we haven’t hammered this message home adequately based on the continued popularity of sealed enclosures with multiple subwoofers under the rear seats of pickups.

A Brief Tutorial on Subwoofer Enclosures

Subwoofers need to be used with enclosures for two reasons. First, the sound coming from the back of the speaker can’t mix with the sound coming front the front. If they combine, they cancel each other out, and you don’t get any bass. Try hooking up a subwoofer and feeding it 5 or 10 watts of power while holding it in your hand. It might make some noise, but it won’t make much bass. Separating the sound from the front and back is handled by the enclosure.

Second, and most important to this article, subwoofers require an enclosure to control how the cone moves at different frequencies. Without an enclosure, many subs would bottom out with as little as 10 or 20 watts of power.

When a speaker (of any size) is installed in an enclosure, the compliance of the volume of air in the chamber adds to the suspension’s compliance to act as a spring that limits cone movement. If the enclosure is tiny, the speaker and the air in the enclosure act like a very tight spring. If the enclosure is large, then the spring is much looser.

As you can see in the cone excursion versus frequency graph above, the smaller enclosures (red and yellow) limit how much the cone moves more than the larger enclosure (green and cyan).

In car audio subwoofer systems, designing a subwoofer enclosure requires balancing the size and quantity of subwoofers with the available space in the vehicle and the desired low-frequency output of the system. If a customer wants massive amounts of deep bass in a pickup truck, they’re going to have to give up storage or passenger space to make it happen. Let’s see what we can come up with to optimize low-frequency output without giving up the back seat or cutting out the back wall of the vehicle.

Bass in Pickup Trucks – Limited Space

The problem with designing subwoofer systems in pickup trucks is almost always space. First, there is rarely room for deep subwoofers. Thankfully, many modern shallow-mount subs offer impressive cone excursion capabilities, so the differences with their full-depth brethren are smaller than ever. With that said, there often isn’t much room for an enclosure. To reproduce deep bass frequencies, enclosures need relatively large volumes.

Let’s use an example of an extended cab Ford F-150. Many under-seat enclosures are available for this vehicle. The largest offer an internal air volume of around 1.5 cubic feet. How about we do several simulations to predict what size and combination of subwoofers will produce the low-frequency bass? Let’s start with a pair of 10-inch subwoofers in a sealed enclosure, since that seems to be the most popular solution.

The 10-inch subs have a nearly ideal Qtc of 0.692 and an F3 frequency of 48.62 hertz. This would be a perfect solution for someone who wanted to add a reasonable amount of bass to their factory-installed sound system.

Our goal is to get the most low-frequency output as possible from the available space. Can two twelves move more air than two 10-inch subwoofers? Let’s see!

If you like rock ’n’ roll, this might be an option. A pair of twelves in this enclosure gives us another 2.5 or 3 decibels of output at 50 hertz and above. Down at 30 hertz, they are no louder. The system Qtc is still acceptable at 0.804, and the F3 is 50.48 hertz. Still not bad.

Since there’s almost 50 inches of width under the seat, what about four 10-inch subwoofers?

We’ve picked up another decibel of output up high, but the Qtc is up to 0.844, and the F3 is 52.21 hertz. So, again, for rock music where there isn’t much deep bass, this might still work acceptably. But unfortunately, it won’t produce the rumble that many associate with a genuine subwoofer system.

Blow Your Mind, Port Your Box

If you’re looking for good output at low frequencies, then a vented enclosure design might be better. Yes, vented enclosures need more airspace per driver, but the efficiency benefits are impressive. How about a single 10-inch subwoofer in a ported enclosure?

From about 50 hertz and below, a single 10-inch driver in a vented 1.5-cubic-foot enclosure produces more output than a pair of tens, a pair of twelves or four tens. Since most subwoofer systems are crossed over at 70 or 80 hertz to blend into the midbass or midrange drivers in the vehicle smoothly, this is a killer option to add some serious rumble to your vehicle.

The 10-inch subwoofer in this example has a cone area of 53.87 square inches. A pair of 8-inch subwoofers might do well with an effective total cone area of 66.82 square inches.

Meh, nothing special. With that said, this might be a good option for trucks where the depth under the seat is very limited. You may have to cut back to one driver if there isn’t enough volume in the enclosure.

Last, let’s look at some of the 6.5-inch subwoofers that are available. Some of these little drivers have reasonable excursion capabilities. Maybe four of them would work well in this enclosure?

Four 6.5-inch subs don’t seem to offer anything of significance in terms of low-frequency performance compared to a single ten or a pair of eights.

What’s the Best Subwoofer System for Your Pickup Truck?

If you can find a robust subwoofer with good excursion capabilities and power handling, a single 10-inch in a well-constructed vented enclosure offers impressive efficiency and output. Keep in mind this is a comparison at 500 watts of power. If you feed 2000 watts of power to four tens, it will be louder than a single 10-inch subwoofer at low frequencies, but you’ll need an equalization or preferably a digital signal processor to tame the upper bass information that will produce. With that said, providing power to a 1500- or 2000-watt amplifier is very challenging, as would be finding a home for an amplifier of that size.

If you’re shopping for a subwoofer system upgrade for your truck, drop by your local specialty mobile enhancement retailer and ask them to provide some options in terms of enclosure simulations for the subwoofers they carry.

Lead-In Image: Thanks to MTi Acoustics for this Stage 3 Perfect-Fit enclosure photo.

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 subwoofer enclosures, the two most popular options are sealed or vented. As far as which design is best for your vehicle, let’s see if we can clear up some misconceptions and stereotypes. As often happens, some trade-offs accompany each decision. Consider this article the master reference for choosing the right subwoofer enclosure solution for your application.

Why Does a Subwoofer Need an Enclosure?

Let’s review a few key factors about subwoofers (and speakers in general). First and foremost, the primary purpose of a subwoofer enclosure is to prevent the sound that’s coming off the back of the speaker cone from mixing with the sound coming from the front. If these two mix, they cancel each other out almost perfectly. If you’ve ever held a subwoofer in your hand without an enclosure while it’s playing, you’ll know it doesn’t produce much sound.

Second, an enclosure acts as a mechanical high-pass filter that limits low-frequency output. Why do we need to limit bass from a subwoofer? As frequency decreases, cone excursion increases dramatically to produce an equivalent output. In fact, for every halving of frequency, cone excursion doubles.

The simulation above shows the predicted cone excursion (in millimeters) of an audiophile-grade 10-inch subwoofer without an enclosure. This is a great driver, and it has an Xmax specification of 19 mm. As such, at frequencies below 22 hertz, when driven with 500 watts of power, the distortion would skyrocket. If we increase the power to the subwoofer to 750 watts, that frequency increases to 28 hertz. At a drive level of 1,000 watts, the driver will reach its Xmax limit at 33 hertz.

Many subwoofers don’t have this much excursion capability, so we need to limit the distance the cone can move. We install the subwoofer in an enclosure so that the air in the enclosure combines with the suspension of the driver to limit cone motion. More specifically, we are adding the stiffness of the air spring in the enclosure to the stiffness of the subwoofer suspension (spider and surround) to make the net system stiffer. Here’s the predicted cone excursion of this driver in the manufacturer-recommend 0.6-cubic-foot enclosure.

This second graph shows that the driver’s excursion is limited to about 11.7 millimeters when driven with 500 watts. Excursion increases to only 16.5 millimeters at the lowest frequencies when fed 1,000 watts. In this enclosure, cone excursion is no longer an issue.

The trade-off for limited cone excursion is a decrease in output capability. The graph below shows the predicted frequency response of our subwoofer system in the infinite baffle simulation and the small sealed enclosure.

Below 47 hertz, the infinite baffle driver becomes more efficient. For example, at 25 Hz, it’s 3.6 dB louder in the infinite baffle.

Subwoofer Cone Excursion and Distortion

More output seems ideal, as long as we are below the Xmax limit, right? Well, yes and no. Every moving coil speaker produces more distortion as cone excursion increases. In addition, variations in suspension compliance (the inverse of stiffness) and magnetic field strength mean that the cone may not track the input signal accurately at high excursion levels. Given the above considerations, we want to limit cone excursion whenever possible. As such, more or larger diameter subwoofers in a system can improve sound quality, as long as each is in a correctly designed enclosure.

Let’s add the bass reflex (also known as ported or vented) enclosure to the mix. A vented enclosure is similar to our sealed enclosure, except it has a tube (or square, triangle or rectangle) with a specific length and area. The vent is a Helmholtz resonator. What’s that? Have you ever blown across the top of a bottle of pop (OK, soda) to hear it hum? That’s a Helmholtz resonator. The resonant frequency is lower if you drink some of the pop and blow again. This is because you’re exciting the air in the chamber, and it resonates at a specific frequency. Helmholtz resonators are used on the intact ducting and exhaust systems of cars to cancel out resonances in the system.

In a vented subwoofer enclosure, the vibration from the subwoofer cone causes the column of air in the vent to resonate. At a specific frequency, called the tuning frequency, the resonance in the vent is maximized. As a result, the vent now acts as the primary sound source for the enclosure, and output from the subwoofer cone itself is minimal. Here’s the cone excursion graph of our audiophile-grade 10-inch subwoofer in a 1-cubic-foot vented enclosure that has a vent tuned to resonate at 33 hertz.

We can see that cone excursion is dramatically increased around the tuning frequency of 33 hertz. It increases slightly at 60 hertz, but in this design, that’s inconsequential. What does matter is that the vent acts like a hole in the enclosure at low frequencies, and cone excursion increased dramatically below 27 hertz. If we want to maximize the output of the system, the use of an electronic infrasonic filter will be necessary at 25 hertz.

What’s the benefit of our vented enclosure, then? Here’s the predicted output graph.

As you can see, we gained an impressive 6.5 dB of output at 40 hertz for the same input power. We’d need to drive the sealed subwoofer with 2,235 watts to produce the same output. For many reasons, including the risk of fire, that won’t work.

Sealed vs. Vented – Enclosure Size

In the case of this example, the sealed enclosure has a net internal air volume of 0.6 cubic foot. Our vented enclosure is 1 cubic foot. Translated into dimensions, the outside dimensions of the sealed enclosure, constructed of ¾-inch MDF, would be (as an example) 12 by 12 by 11.75 inches. The vented enclosure would need to be 12 by 12 by 18.2 inches. That’s an increase in length of more than 50%. If you need a small enclosure to fit in a specific space, sealed might be your only option.

Sealed vs. Vented – Efficiency

Comparing the two enclosures above clarifies that the vented design is significantly louder at all frequencies above 18.5 hertz. So, if you’re looking for the most output from a system with a small amplifier, then a vented enclosure is the best choice. The vented enclosure is the best choice if you’re after the loudest system.

Sealed vs. Vented – Sound Quality

When it comes to outright sound quality, choosing your enclosure is more complicated. We’ll need to start by looking at what happens when we put these enclosures into a vehicle. The graph below shows two traces for each enclosure. The lower trace of each color is the free-field predicted response, and the second trace includes an approximation of the response of the system in a car or SUV. This in-car response information is based on data that Boston Acoustics included with one of their drivers in the BassBox Pro simulation software I use. I’ve seen in-car graphs from other sources that are similar, so this is adequate for our purposes.

As you can see, at low frequencies, based on the provided information, a significant amount of boost is added. It’s on the order of more than 20 dB SPL below 30 hertz. What looked like a smooth, flat response from the vented enclosure now has a prominent peak from 30 to 45 hertz. What looked like somewhat limited output from the sealed enclosure appears reasonably flat.

Here’s the answer to choosing sealed or vented for sound quality. If the system doesn’t have an equalizer to flatten the response, then a sealed enclosure would be better. If the system does have an equalizer, then choose a vented enclosure. Why choose the vented design when there is an EQ? Well, you can flatten the response and dramatically reduce the power required from your amplifier to hit a target response curve. More importantly, cone excursion will be decreased dramatically with the vented enclosure so that less distortion will be added to the sound produced by the subwoofer.

One quick note: For the last statement to be true, the vent in the enclosure needs to be designed and executed correctly. That’s a topic for an entirely different article.

Sealed vs. Vented – Infrasonic Performance

Many people really like deep bass. I’m not talking about 25 or 30 hertz; I mean 10 to 15 hertz bass. The kind that you don’t hear but feel in your back and behind. If that’s your cup of tea, then a sealed enclosure might be the better option for your car audio system.

Sealed vs. Vented – Limited Xmax Subwoofers

If you want to have an enclosure constructed for a subwoofer with limited excursion capability, you might want to consider the vented design. This might be an entry-level subwoofer with a short magnetic field or a shallow-mount subwoofer.

Sealed vs. Vented – Enclosure Construction Cost

This one will be up to the specialty mobile enhancement retailer you’re working with. The cost of constructing a vented enclosure is likely higher than for a sealed design. With that said, the performance benefits may offset this cost. You might want to read our article about choosing subwoofer sizes as a single 12 in a vented enclosure might outperform two 10-inch subs in a sealed enclosure. The net cost should be much less. Talk to the product specialist you’re working with and have them do some simulations with the drivers you have in mind.

Pick Your Priorities, Then Pick Your Enclosure

There you go – a whole slew of reasons why you might pick a sealed enclosure or a vented one for your car audio subwoofer. Depending on your application and expectations, there isn’t a clear winner. Make a list of what you want from a subwoofer, then cross-reference those criteria with the answers above. If you reach a stalemate, prioritize your criteria and repeat the process. Your local specialty mobile enhancement retailer should have no problem delivering a solution that will sound great based on that list.

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.

Ah, the oh-so-complex world of amplifier sensitivity control configuration. One would think that there would be a scientific process that would ensure that an amplifier could be set perfectly every time. But in reality, many criteria affect where a sensitivity control is adjusted. The topic of gain overlap pertains equally to source units as amplifiers. What is it? Why do we need it? Let’s find out.

Amplifier Sensitivity Settings

The purpose of the sensitivity (or gain) setting on an amplifier is to allow it to be matched with a variety of source options. For example, if you have a 100-watts-per-channel stereo amp and a radio that can produce 2 volts of output on the RCAs, the amplifier needs to have more signal gain than if the radio made 5 volts of output. However, the maximum undistorted power output remains at 100 watts no matter where the sensitivity control is configured.

A few things to think about as we dive deeper into this discussion. In 99% of cases, technicians use a 0 dB track at a specific frequency to set sensitivity controls. If the amplifier is powering a subwoofer or feeding a full-range signal to a speaker, this method should do a good job of preventing any clipping of the outputs. However, if the amp is used with a high-pass filter to power a set of midrange speakers, there’s an entirely different procedure to find an optimum setting.

Second, music isn’t always recorded at the loudest possible level. Modern music is close, though. Let’s look at a few tracks to get an idea of this concept.

First is the amplitude-based analysis of “Galway Girl” by Ed Sheeran.

As you can see, the song is recorded at a reasonably high volume and maintains a high average volume. Having a look at the statistics shows us that the maximum recording level is -0.09 dB, very close to the maximum possible level of 0 dB. The average level for the song is -9.65 dB, as shown below.

Let’s look at another track. This time we’ll analyze “Easy on me” by Adele.

Not surprisingly, this song doesn’t appear quite as loud – that is, until the drums come in at 1:27 into the song. You can see just how much her voice is compressed to the maximum level of -0.20 dB. The average level for this track is a little lower at -12.28 dB.

Let’s go back a few decades and see how music was recorded before the “loudness wars” resulted in produces and engineers boosting levels to make voices stand out on the radio. Here’s “Hungry Like the Wolf” by Duran Duran.

This track dramatically represents how the average loudness of modern songs has been boosted. You can see lots of black space below the 0 dB peak.

The peak level for this track remains high at 0 dB on the right channel, but now our average level is way down around -20 dB. In terms of how loud the song seems, this would be 8 to 10 dB lower than something modern.

Last and certainly not least, let’s look at “Brothers in Arms” by Dire Straits. It shouldn’t be news to anyone listening to this album that it has a low recording level. Or does it?

As you can see in the statistics below, the average RMS level of this track is way down around -24 dB. If you want this loud, you’ll need to turn up the volume a little more. Keep in mind, though, the maximum recording level is still high a -0.20 dB.

Introducing Gain Overlap

From a purely scientific standpoint, all of the recordings analyzed above have a very similar maximum recording level. As such, if your audio system is set up to just clip with the volume at full, it should be fine. However, in reality, we might want to be able to turn the volume up a little higher than full, so we can make quiet songs loud. This ability to turn the volume up higher is gain overlap.

Let’s say we want the average level of Duran Duran to be the same as Ed Sheeran; we need about 8 dB more gain in the system. That sounds simple enough, right? Your installer can increase the sensitivity control such that a lower input voltage will drive our 100-watt amplifier to produce full power.

All fine and dandy, right? What happens when our favorite modern song starts to play on the radio, and we crank the volume? Now we have 8 dB extra gain, and the amplifier is driving hard into clipping, adding tons of distortion. The music will sound terrible, and the additional high-frequency content (caused by clipping the outputs) can and likely will overpower the tweeters in the system and damage them.

Let’s take a look at a modern source unit. We have the Sony XAV-9500ES Mobile ES receiver set up on our test bench from its recent Test Drive Review. The built-in amplifier is configured with a typical amount of gain overlap. Playing a 0 dB test tone, the output of the amplifier reaches full power when the volume control is 44 out of 50. Add six more “notches” to make things good and loud. There is 6 dB of gain overlap in this particular radio on the built-in amplifier.

Use Your Power for Good, Not Evil

So, why design or configure an audio system so that you can easily push an amplifier to the point that it distorts? We’ve discussed the technical reason already: To play quiet audio sources at the maximum output level of the amplifier. Does having gain overlap built into a system mean you can potentially damage it? Yes. Absolutely 100%, yes. As such, this means that the system operator needs to take some responsibility for how loudly it’s played. Translated, that means you have to know when you’ve reached full volume in terms of the amplifier’s output capabilities. Your installer should be able to tell you what “full volume” is for normal modern recordings, just like the 44/50 on the Sony radio. Be honest with yourself; if you aren’t going to be able to curb your enthusiasm, ask the technician working on your installation not to include any overlap.

What if you ignore our suggestion and just crank the volume? How hard is your amp going to try to work? For example, a sensitivity setting with 6 dB of overlap would make the amp try to produce 400 watts of power if you maxed out the volume with a track recorded at 0 dB.

How To Avoid Distortion and Play Your Music Loudly

So, what’s needed to design an audio system where the amplifiers can’t distort? The short answer is money. If you want to feed 50 watts of power to your speakers, but have the system configured with 6 dB of gain overlap, then buy a 200-watts-per-channel amp. If you want to provide your subwoofers with 500 watts of power, choose a 2,000-watt amp. Financially, this doesn’t work, does it? A good 500-watt monoblock amp might cost $650. A 2,000-watt amp of the same caliber might cost $1,500-2,000.

Of course, while our wallets might not like the suggestion above, that’s not the only problem. The speakers in your car or truck won’t be capable of handling four times their rated power for very long. For example, if you have a subwoofer rated for 500 watts but feet it 2,000 watts for more than a few seconds, the voice coil is likely to be damaged. Likewise, the suspension components likely aren’t designed to provide the increase in excursion that 2,000 watts of power would command.

If you want your system to play at extreme volume levels, then you’ll want more speakers or subwoofers in the system. If a set of good quality 6.5-inch component speakers and a 10-inch sub aren’t loud enough, consider adding a second set of speakers and a second subwoofer. You can also double the system’s power, so each driver works equally hard. Pushing a low to moderately rated speaker beyond its capabilities will sound bad and likely damage it. Also, overdriven speakers shouldn’t be covered under the manufacturer’s warranty. That’s not a design or component failure; it’s abuse.

When you’re at a local specialty mobile enhancement retailer discussing your audio system, be honest about your expectations. If you can’t afford the system you want, wait until you can. Purchasing less than you’ll be happy with is a good way to damage the speakers or subwoofers.

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