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.

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.

A while ago, we talked about why dashcam resolution is crucial to capturing details in the event of an accident or near-miss. The topic of dashcam image sensor resolution appears to have become a defining factor in the sales pitch from many brands. But is resolution the ultimate decision-maker when it comes to quality? Let’s take a look at some considerations.

Do You Need a 4K Dashcam?

Having a dashcam in your vehicle is important if you want to protect yourself from staged accidents, fraud or false accusations. Most basic cameras have image sensors that offer 1920×1080 resolution. That’s enough information to know whether a light was red or a car actually stopped at a stop sign. With solutions like these, you’re looking for general information about a situation.

What if there’s a hit-and-run accident, or you see someone driving dangerously and want to report it? In those cases, capturing identifying information about the vehicle and driver is paramount. Having a higher-resolution camera with a 2K 2560×1440-pixel or preferably a 4K 3840×2160-pixel image sensor dramatically increases your chance of being able to read a license plate and provide that information to the authorities.

Does a 4K Dashcam Guarantee You’ll Capture a License Plate?

We’ve seen several retailers and dashcam brands promoting 4K solutions as a guarantee that you’ll be able to see a license plate. Be wary of that type of statement. If a car passes perpendicular to you, the plate will likely only be visible for a few frames of video. The same applies if it’s coming toward you. Once the vehicle is close enough for the camera to make out the letters and numbers, it will pass by very quickly. Having a high-resolution camera increases your odds of seeing a tag, but nothing guarantees you’ll capture it.

What Other Features Affect Dashcam Image Quality?

If you’re shopping for the best camera solution, there are other considerations beyond camera resolution. For example, if you’re driving at night, then a camera with an image sensor that’s optimized for low-light levels will dramatically reduce noise in the image and help make objects clearer.

High Dynamic Range (HDR) processing is another feature that helps to brighten dark image areas and tone down parts that might be overexposed so that you can see details. In reality, this is contrast compression, but it makes a big difference when bright light sources like car headlights or the sun are in the image.

Camera Speed Matters!

If you want to increase your chances of capturing details, one essential feature to look for is a higher frame rate. If you look at how video is captured, it’s essentially a series of still images. When we play the pictures back in quick succession, we see the perception of moving objects. Most dash cameras record at a rate of 25 or 30 frames per second. This means there are 25 or 30 still images recorded for every second of the video. This framerate is very similar to what we see on broadcast television (29.97 frames per second).

If you want to capture those split-second moments when a license plate might be visible, look for a camera that offers 60 fps recording. These cameras take 60 images for every second of video they record, doubling your chances of seeing something crucial. Yes, it will use the storage on the memory card faster. However, storage space isn’t a concern unless you need to go back a check something from a few hours earlier. Plus, large-capacity micro-SD cards aren’t overly expensive.

Image Compression and Video Codecs

Another factor that affects image quality is the video compression settings. Most cameras store videos in MPEG format to make the files compatible with popular computers and smartphones. There are several different settings that the camera manufacturer can configure to determine how much information is stored and how much is discarded to reduce file size. Compared with uncompressed video files, the MPEG format can reduce file sizes by six to 26 times. Some cameras offer options to make global adjustments to compression settings. Again, we suggest using as little as possible to help capture details.

Another advancement in video compression came with the move from the H.264 compression standard to the newer, more efficient H.265 format. The H.265 format offers more video file compression while claiming the same image detail. People will argue the efficacy and fine details with any lossy compression format. Nevertheless, H.265 is worth looking for in your next camera purchase, though its ultimate performance depends on how the manufacturer configures the system.

Wi-Fi Connectivity

While it isn’t a feature specifically related to the image-capturing capabilities of the camera, Wi-Fi connectivity is also an important option. If your dashcam doesn’t have Wi-Fi, then you’ll need to remove the memory card and connect to a computer to view what it’s recorded. If you see something happen and want to share it with the police in short order, being able to connect your phone and download a file in a minute will let you show a video or send a screenshot right away.

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Pick the Right Dash Camera for Your Needs

Having any dashcam is better than none at all. With that said, the frustration of looking at a blurry or pixelated image when trying to extract information is frustrating. We’ve been there. Drop by your local specialty mobile enhancement retailer today to find out about the dashcams they have available with the options and performance features that will meet your expectations.

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.

If there’s a single marketing statement that makes my eye twitch, it’s one that claims a specific subwoofer will “work” in a small enclosure. Contrary to many marketing claims, enclosure volume is directly proportional to low-frequency extension and sound quality. Let’s look at the math and how these tiny enclosures ruin the performance of your subwoofer.

The Backstory on Enclosure Volumes and Subwoofer Size

Many years ago, I flew to Edmonton, Alberta, for a distributor trade show. A friend graciously picked a few of us up in his pickup truck at the airport. As we drove toward the venue, I asked if he’d blown the subwoofer in the system. It didn’t produce any deep bass and sounded sloppy. He said that it was brand-new. I asked what subwoofer it was and what enclosure it was in. He told me it was a very popular name-brand sub (yes, I’m concealing the brand) and that it was in a 0.25-cubic-foot sealed enclosure. I thanked him again for picking us up.

The Relationship between Subwoofer Size and Enclosure Volume

For this article’s purposes, we will focus this discussion on acoustic suspension (sealed) enclosures. From 2-inch midrange drivers to 19-inch monster SPL subwoofers, the relationship between the cone area, suspension compliance (softness) and the volume of air in an enclosure is critical in determining how low the speaker will play. The correlation is so constant that many companies have tweeters that behave differently based on the air volume behind the diaphragm.

As a generalization, we can say that a larger enclosure will produce more low-frequency output. Since the goal of adding a subwoofer is to improve low-frequency extension, limiting this characteristic by putting a large subwoofer in a small enclosure is counterproductive.

Considering how it will sound is an even more important factor in designing a high-performance subwoofer system. We can analyze the calculated Qtc value of a subwoofer system (driver and enclosure) to see how well the cone motion is damped. Many car audio enthusiasts fail to consider this part of an enclosure simulation. This oversight results in subwoofer systems that sound terrible and perform poorly – like the one in my friend’s pickup truck.

We get the following qualifications if we look at the description of different speaker Qtc values from Vance Dickason’s Loudspeaker Design Cookbook.

Do you want the subwoofer to stop immediately after the drive signal is removed (Qtc = 0.5), or would you like a bit more upper bass output at the expense of slightly degraded transient performance ( Qtc = 0.707)? Perhaps you want a great deal of output at higher frequencies while sacrificing low-frequency output and cone control (Qtc > 1.0)? While there are simple algebraic formulae to calculate these values based on a chosen subwoofer’s Thiele/Small parameters and the volume of the enclosure, we’ll use our tried and tested BassBox Pro software to generate the volume, F3 or Qtc for our sample subwoofer.

Let’s Model Some Subwoofer Enclosures

We’ll start with a typical high-performance 10-inch subwoofer. This driver has a free-air resonant frequency (Fs) of 29 hertz, an equivalent suspension compliance (Vas) of 35.4 liters and a Qts value of 0.501.

While I like extremely well-damped bass, most car audio enthusiasts want a bit of boom and warmth, so let’s start with a target Qtc of 0.707 for our subwoofer system.

For the above enclosure simulation, the software tells us the subwoofer needs to have a net air volume of 0.833 cubic feet. The resulting F3 frequency will be 45.95 Hz. This is typical of a reasonably sized sealed enclosure for a 10-inch car audio subwoofer.

The manufacturer recommends an enclosure with a net internal volume of 0.53 cubic foot. Let’s see what modeling the driver in this enclosure tells us.

The 0.53-cubic-foot enclosure results in a system Qtc of 0.806 and an F3 frequency of 48.86. To put the latter value into perspective, the system output at 30 Hz has been reduced by 1.7 dB. Quite simply, the smaller enclosure isn’t as efficient at low frequencies. This is still a very reasonable enclosure design and will provide good output and reasonable physical power handling for the driver.

Let’s switch to looking at specific enclosure volumes. What happens if we cram this sub into a 0.4-cubic-foot enclosure, as is common with many pickup truck under-seat solutions?

We now have a system Qtc value of 0.881 and an F3 frequency of 51.64 hertz. Bass output at 30 hertz is now down 3.2 dB from our original 0.833-cubic-foot enclosure. In real-world terms, we need twice as much for the sub to play as loudly as the same driver in a larger enclosure. More power means that your amplifier has to draw more current from the vehicle’s electrical system.

If you’re pondering the benefit of multiple subwoofers in a small enclosure vs. a single driver in an ideal enclosure, you’re starting to get the picture.

Let’s finish this by looking at what happens when our 10-inch sub is crammed into a 0.25-cubic-foot enclosure.

It isn’t hard to see that the sub doesn’t produce anywhere as much bass as it would from a properly sized enclosure. Specifically, the system Qtc is now at a very undesirable 1.034, and the F3 frequency is at 53.38 hertz. Output at 30 hertz is down by a whopping 6.2 dB compared to the original design. Our original 0.833-cubic-foot design only requires 70.4 watts to reach the same output level as this enclosure. Which do you think the amplifier and electrical system will prefer delivering?

What Does “Works in a Small Enclosure” Mean?

As we decrease the size of the enclosure, the air inside acts as a tighter spring and limits how much the woofer cone can move for a given amount of power. From a sound quality perspective, this tighter spring rings and resonates increasingly as enclosure volume decreases. Look at the increase in output around 90 to 100 Hz. This is caused by the woofer cone continuing to move (ring or resonate) once the input signal has been removed. This unwanted motion wasn’t part of the original audio signal and would be considered distortion. The subwoofer system will sound sloppy and is often described as a “one-note wonder.” In short, it should be avoided.

Let me put this into perspective for you in a different way. The graph below shows the output of a 6.5-inch midrange/midbass speaker mounted in the door of a car or truck. With no high-pass filter applied, it produces more bass (with the same power) at 40 hertz than the 10-inch subwoofer crammed into the small 0.25-cubic-foot enclosure. While a 6.5-inch speaker can’t handle 300 watts of power at 40 hertz, there are typically two in the vehicle. One hundred fifty watts is still a stretch, but I think you get the point. A subwoofer in a very small enclosure isn’t acting like a subwoofer – it’s more of a midbass speaker.

It’s not much of a stretch to say that stuffing subwoofers into microscopic enclosures is counterproductive. From a perspective of not failing, yes, they work. Do they sound good? No. Do they produce extended low-frequency output? No. Are these enclosures efficient? No. As such, do they make sense? No.

If you’re shopping for a subwoofer system for your vehicle, drop by a local specialty mobile enhancement retailer and work with them to choose a subwoofer system that will be efficient and offer excellent low-frequency extension. They should be able to show you computer simulations of how different drivers perform in an enclosure that works with the space you have available. If you want to hear those 35-hertz bass lines in your favorite music, proper subwoofer enclosure size and construction matter.

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.

Not too long ago, we took a look at how speaker-level line output converters worked. We discussed the difference between passive and active devices and explained what features to look for. If you have a vehicle with a premium factory-installed sound system, those interfaces might not be adequate to provide your amplifier with a signal that will sound good with new speakers. So let’s look at some of the intelligent car audio speaker-level interfaces available and why they’re the best choice to upgrade your stereo.

Factory-Installed Audio Systems are Complex

While modern factory-installed sound systems might not use the best speakers and are often limited in power delivery, the signal processing included in them can be pretty complex. Companies like Bose, Panasonic and Harman (the brand behind JBL, Infinity, Lexicon, Mark Levinson, Bang & Olufsen and Harman Kardon) know a LOT about optimizing their products to sound the best they can. So while an aftermarket system might sound better with larger subwoofers, better speakers and more powerful amplifiers, these companies and their technicians are masters when it comes to system configuration and calibration.

A prime example of the capabilities of these companies is the Mark Levinson system in the Lexus LS. There are 23 speakers, including four in the ceiling. The system has a state-of-the-art upmixer that takes a stereo audio track and creates left, center, right, left side, right side, left rear, right rear, front overhead and rear overhead channels. The signals going to each channel are unique, so the system reproduces audio as though you were in a live venue with the stage in front of the listening position. In addition, the system has 2,400 watts of power, so it gets good and loud.

Upgrading these audio systems is complicated. It requires careful planning and accurate measurement of the audio signals that will be used for the upgrades and testing of signal routing for different frequencies and audio sources. This isn’t something you’d want to undertake in your driveway.

Intelligent Line Output Converters

In a more conventional factory-installed audio system, upgrading is less involved but still complicated. Crossovers, equalization, all-pass filters and signal delays are expected on systems with door and dash speakers in the vehicle’s front. Thankfully, a few companies have created line-output converters with built-in digital signal processors that can undo these features and provide a reasonably wide bandwidth signal that’s phase-coherent – like you’d get from an aftermarket source unit.

When the technician upgrading your audio system completes the wiring, these processors require a calibration step. Most include an audio track to be played through the system while the software analyzes the audio signals being produced. Once the measurement step is done, they analyze the information and configure the digital signal processor to undo equalization and signal delays, and combine signals from multiple channels. Once complete, your installer can move on to configuring your new system.

What Happens if You Don’t Undo Signal Processing?

Some upgrade methods work from what the OEM audio system offers. In those instances, you’ll need a digital signal processor with dedicated inputs for each channel from the factory amp. In addition, the system will need to use similar drivers and stock locations. For example, suppose you want your installer to build new A-pillar pods or use speakers that operate in the frequency range where a crossover existed in the factory stereo. In that case, intelligent line-output converters (or a DSP with these features) are necessary.

Let’s look at a simple example of combining two audio signals where one has been delayed from the other by a few milliseconds. This would be akin to using an active line-output converter to combine door and dash speaker signals.

The graph above shows the frequency response of our original signals in red. I applied a 0.6-millisecond delay to one signal, then combined the two to produce the orange trace. As you can see, the frequency response is a disaster. That curve is what’s known as a comb filter, as it looks sort of like a comb you’d use to straighten your hair before work or school. Signal delays are just one of the reasons why it’s crucial for the installer working on your vehicle to understand what’s happening in the time domain and the frequency domain for each channel of your sound system.

Choose Your Upgrades Wisely

If you’ve read this and think, “I have no clue what they are talking about,” that’s 100% OK. This is where you need to choose a professional mobile enhancement retailer to help you upgrade your car audio system. You’ll want to ask them what test equipment they have to measure the frequency and phase response of the factory-installed audio system before you let them work on your vehicle.

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.