Have you ever looked at something and thought you were only getting part of the story? Many previous articles have discussed amplifier distortion at length but haven’t delved into how power output levels and frequency affect distortion measurements. If you’re looking for the best amplifier for your car audio system, especially for midrange drivers and tweeters, this information should be crucial to your purchasing decision.

Amplifier Distortion Specifications

If you’re browsing a car audio amplifier manufacturer’s website, you’ll see a single specification that’s intended to quantify the amount of distortion an amplifier adds to the audio signal. The CTA-2006-C standard requires that the total harmonic distortion and noise added to the audio signal be specified at an output level that is 50% of the maximum rated output for the amplifier. Of course, that power rating needs to comply with the CTA-2006-C standard as well.

Measuring Amplifier Distortion

When an amplifier is being tested for distortion, the technician or engineer will typically look at the harmonic information and noise added to a single test tone.

In the measurement above, you can see the test signal at 1 kHz at a level of 2.0 volts. The second harmonic (labelled with the pink 3) is at a level of -77.10 dBV, or 83.15 dB below the 6.03 dBV (2.00V) test signal. The third-order harmonic (labelled with the pink 1) is louder at an absolute level of -68.18 dBV and a relative level of -74.23 dB. You can see the pattern of even and odd harmonics continue well past 20 kHz. It’s worth noting that this is a good Class AB amplifier and not a poorly designed, inexpensive unit.

Sadly, this single specification is quite incomplete in terms of telling the whole story. Audio measurement and analyzer devices like those from Audio Precision and QuantAsylum can generate distortion graphs across a range of power output levels and frequencies. So let’s characterize this amplifier in terms of the amount of distortion it adds to an audio signal based on the amount of power it produces.

Before we dive into analyzing the data, we should explain that the horizontal X-axis scale is in decibel volts, known as dBV. This way of looking at voltage represents the amplifier output level using a decibel scale with 1 volt as 0 dB. Thus, the equation to convert dBV to a voltage is 10 ^ (dBV/20).

The output level of 6.03 dBV, where we measured %THD+N in the first chart, would be 2.00 volts. At the low level, distortion is at 0.075%. At an output level of 22.6 dBV, you can see that the distortion increased. This level is the point where the amplifier started to run into clipping. Maximum power output measurements are specified at the output level that corresponds to a THD+N of 1%. For this amplifier, that would be about 24 dBV, or 63 watts into a 4-ohm load.

At the other end of the scale, you can see that distortion increases as output power decreases. This performance is very typical for a Class-AB amplifier. At very low levels, the harmonic distortion content is buried in the noise created by the amp, which for this unit is at about -105 dBV. Crossover distortion at very low volume levels plays a significant role in adding unwanted information to the audio signal. As the output level increases, the audio signal passes through the transition between the positive and negative output devices at a steeper slope, reducing the time the signal spends in this transition region. As such, distortion decreases relative to the output level.

The CTA-2006 THD+N specification for this amplifier would be 0.02% at the output level of 21 dBV (-3 dB from the maximum power output level). This information doesn’t do a good job of describing how well the amp performs in a real-world application since most of the time, we’re only using a fraction of the power available to drive a speaker. For example, if we have a midrange speaker or a tweeter in a three-way system, we may only need 1/10 to 1/20 of the power a midbass speaker would need, or even less than a subwoofer. Played at high volume levels, a tweeter rarely needs more than a few watts.

So far, in all the TestDriveReview product evaluations we’ve published, the distortion has been specified at the same level as the signal-to-noise ratio. This would be at an output level of 1 watt in a 4-ohm load or 2.00 volts. From now on, we’ll include the Power versus THD+N graphs as shown above so readers can see the entire picture of how the amplifier behaves.

Distortion Versus Frequency Response

Another characteristic often overlooked is the amount of distortion an amplifier adds relative to different frequencies. We ran another test on this amplifier to characterize this. We used an output level of 1.95 volts (very close to our 2.00-volt number) and measured distortion at frequencies from 20 Hz to 20 kHz.

While the numbers don’t vary as much compared to output level changes, you can see that there’s more distortion added at higher frequencies compared to midrange levels.

In an upcoming article, we’ll start all over with a new set of measurements with the three amplifiers we used in the What Do Better Amplifiers Sound Like article a few years ago. We’ll throw in a Class-D amp or two to round out the mix, so you’ll have a benchmark from which to compare solutions.

In the meantime, if you’re interested in purchasing an amplifier for your car or truck, drop by your local specialty mobile enhancement retailer today and ask them about a high-performance solution that will make your music sound 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.

Not too long ago, we looked at the physics surrounding car audio tweeter directivity and why tweeters must be pointed toward the listening position. If you haven’t read that article, it established a foundation for understanding the need to aim midrange speakers. If you’ve seen people using towels, laser pointers or modelling clay to test the right location to mount a midrange speaker, you’ll want to share this article with them.

Car Audio Midrange Speaker Directivity

As we’ve discussed, below a particular frequency, all speakers produce sound in the same way that a candle or lantern illuminates a room or the sun lights up the planets that circle it. The energy disperses everywhere – forward, backward, upward, downward, left and right. To be crystal clear, backward refers to creating sound behind the speaker, behind the magnet and the enclosure.

Above the frequency with a wavelength equal to the circumference of the speaker, the output of any driver starts to become more directional. We can use the light source analogy again to explain this. The dispersion pattern becomes more like a floodlight, and as frequencies increase, it becomes more like a flashlight. By the time the playback frequencies’ wavelength is five times the circumference of the driver, we can consider the output to be fully directional.

Evaluating Midrange Speaker Directivity

In a similar fashion to the previous article, we’ll perform a test with a small midrange speaker. This audiophile-grade 2.5-inch driver is typically mounted in a door or the dash or in a small pod on an A-pillar. If we measure the driver, it has an effective cone diameter of about 5.8 centimeters or 2.28 inches. The effective circumference of the cone is 18.21 centimeters or 7.17 inches. The frequency with a wavelength equal to 7.17 inches is 1,883 Hz. Let’s see how this value correlates with our on- and off-axis measurements of this speaker.

We set the speaker up in our test enclosure and took a series of frequency response measurements. We started with the microphone at a distance of 1 meter (3.28 feet) directly on-axis with the driver, then at 12-degree increments to the side.

We predicted that the response of our compact midrange driver would remain relatively consistent up to almost 1,900 Hz based on our calculations. However, we can see that aside from some reflections off the test enclosure, the output from 670 to 900 Hz is in a fairly tight range of about 4 to 6 decibels. Above this frequency, the measurements spread apart, though output remains very usable to 3 kHz.

It should come as no surprise that the company that designed this driver also designed the tweeter for the system to be used with a high-pass crossover frequency of 3 kHz. This sort of “total system component” design consideration is what separates the experts from the inexperienced brands.

What About Aiming Speakers with Lasers and Towels?

As we mentioned at the beginning of the article, we’ve seen many people use lasers to aim midrange speakers at a specific position in the vehicle. We like this practice in terms of ensuring that the left and right speaker installations look symmetrical. However, from a performance standpoint, it’s a waste of time.

What about listening tests with the speakers wrapped in a towel? If aiming them with a laser offers no benefit, then tilting them up or down, in or out by 20 or 30 degrees, won’t either. The chart above proves that. What about those who claim to hear a difference as the speaker moves? Indeed, what you hear at the listening position might change slightly. Maybe by 4 or 6 decibels. These small changes can deliver the effect of moving the perceived center of the soundstage left or right and change the perceived frequency response. With that said, for the test to be valid, the midrange driver needs to be used with a tweeter so that the high-frequency information isn’t relevant.

Second, an equalizer will need to be set for each tested position to ensure that both drivers’ arrival time, output level and frequency response are identical. This is how the system will be used once the installation is complete. Once in this state, the differences a few degrees make on the midrange installation become irrelevant.

What About Midrange Drivers used Without a Tweeter?

Another group of audio enthusiasts purport that using a midrange driver without a tweeter is the way to go, as you don’t have to deal with a crossover. The speakers used in these installations are often called wideband drivers, implying that they cover a wider range of frequencies and offer extended high-frequency performance. When installed in a dash-mounted location at the base of a windshield, these installations can sound quite good. However, when aimed directly at the listening position, the system becomes extremely sensitive to the listener’s position.

The directivity we’ve demonstrated means that the speaker creates a very narrow beam of high-frequency information. If you move your head even an inch, what you hear can change dramatically. Moving your head around to find a sweet spot is a waste of time and energy when you can add a tweeter to the system design and eliminate this silliness. As for avoiding crossovers, if your installer knows how to configure a digital signal processor properly, this isn’t an issue.

The Final Word on Aiming Midrange Speakers

Short of pointing them into the floor, the effort put into aiming midrange speakers in a car audio system is a waste of time. If all the drivers in the system are used up to a frequency with a wavelength that’s well more than twice the driver circumference, then only the tweeters need to be aimed.

Drop by your local specialty mobile enhancement retailer today to find out about the midrange and tweeter upgrades that are available to make your car audio system sound unforgettable. When it comes time to discuss the installation, feel free to refer to this article.

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.

It seems like everything to do with car audio installations has something to do with managing voltages. For starters, your electrical system needs to produce enough voltage to keep your radio and amplifier going. And amplifiers need to increase the voltage to drive speakers. When adding an amplifier to a factory-installed audio system, your installer will need to measure the voltage that the radio or amp produces. Chances are, they’ll need to use a line output converter to reduce that voltage so it’s compatible with a new amplifier. Let’s look at how these converters work and some of the options they include to make upgrading your car audio system easier.

What Is a Line Output Converter?

These simple integration devices go by several names. They’re sometimes called high-to-low or hi-lo converters, speaker input adapters or line level converters. Their task, however, is relatively simple. They take an audio signal intended to drive a speaker and lower the voltage so that it can be connected to the RCA preamp input on an amplifier or signal processor.

Most amplifiers want to see a maximum input voltage of 4 to 6 volts. Beyond the rated maximum input voltage, the signal can overdrive the input circuitry and cause clipping and distortion. Yes, you can clip the input to an amplifier with too much voltage.

Even a modest car radio can produce about 6.5 volts (peak to peak) output on the speaker wires. A small amplifier rated at 45 watts can deliver 13.4 volts. A subwoofer amplifier integrated into a factory-installed audio system could easily produce more than 30 volts.

How Do Line Level Converters Work?

There are two common types of converters on the market. The least expensive incorporates small audio transformers to reduce the voltage. The input winding on the transformer might have two or three times as many turns as the output, lowering the voltage by 50 or 60%. These devices are often passive in that they don’t require a power and ground connection to function.

The second and most popular converter adds circuitry to provide a low-impedance output to the new amplifier. These devices require a power, accessory and ground connection to function. They can also serve as a line driver to increase the output voltage relative to the input. If you have a modest source unit that can only provide 1.5 or 2 volts of output on the preamp, adding a line driver to bump that voltage to 4 or 5 volts will let your installer turn down the sensitivity control on your amplifiers to improve the signal-to-noise ratio of your audio system.

What To Look for When Shopping for a Line Output Converter

If you’re in the market for a quality line output converter, you’ll want to know how much voltage it can accept on the speaker-level inputs and how much it can increase or decrease that signal, and you’ll need to know the output impedance on the preamp side. Most good-quality converters can accept up to 40 volts on the inputs and have an output impedance of no more than 200 ohms, though lower is better.

You’ll also want to check the frequency response of the device. Entry-level transformer-based converters may not pass deep bass or high-frequency audio information as well as the active units. Accordingly, a frequency response spec of at least 10 Hz to 40 kHz with a tolerance of 1 dB is a good benchmark.

Since these are audio signal processors, noise and distortion specifications are also worth checking. A total harmonic distortion (THD) spec of no more than 0.05% is good and noise should be quieter than 110 dB.

Remote Turn-On Detection Features

One of the most common features of a line output converter is providing an amplifier turn-on output signal. Let’s say you’re having a subwoofer amplifier added to a factory-installed sound system. There likely won’t be an easily accessible wire that goes to 12V when the radio turns on. Many output converters have several ways to detect when the radio is on and produce this trigger. First, they can monitor the speaker wires for voltage. Once it detects an audio signal, it turns itself on and generates the remote output. The drawback of this option is that the unit might be fooled into turning on when a car door is closed. If the vehicle is relatively airtight, closing a door or the trunk can momentarily pressurize the interior, causing the speakers to move. When that happens, they produce a voltage and sometimes this tricks the converter.

The second way these devices can trigger an output is to monitor the input connects for a DC voltage on the speaker wires. For example, most radios use a speaker output device configuration called BTL, or bridge-tied load. There will be a few volts on the speaker wires when the radio turns on. The converter will sense this voltage and activate the output. If the source in your vehicle works this way, this is the best option for your installer to use.

Bonus Line Output Converter Features

Many line output converters come with additional features. One of the most common is a remote level control. If you’re having a subwoofer added and want to adjust its volume relative to the rest of the system, this is a great option.

Another popular feature is an equalizer. Your installer may find that the lowest audio frequencies from the factory source are attenuated. Adding a little boost to that missing information is a great way to deliver bass with good extension and impact.

Many of the better processors include speaker load simulators. Most Class-D amplifiers used in factory audio systems need to see a speaker connected to their outputs to function. As such, if your installer is adding an amplifier to drive those speakers, a relatively low-impedance load needs to be added to the speaker wires.

Channels and Signal Summing

The last topic we should discuss is understanding how many channels are needed for the line output converter. As we mentioned, typically, these are used when adding a subwoofer amplifier to a factory-installed source unit. That doesn’t mean that they aren’t also common for adding an amp to drive front and rear speakers. Many branded audio systems (like Bose, JBL, Fender, Infinity, Lexicon, Mark Levinson and B&O) that come with new cars and trucks are easily upgraded using multi-channel line output converter interfaces. Your installer can feed the output of the converter to a digital signal processor and new amplifiers, speakers and subwoofers.

Many multi-channel line output converters can sum signals together from multiple inputs. These days, using this feature is a risky proposition unless your installer has confirmed that the audio signals are in phase at the crossover frequency. For example, let’s say the front speakers in your car include a woofer in the door and a small midrange speaker in the dash (what many call a middler). If there is signal delay applied to the woofer, summing the signals together in a line output converter can result in the audio signal having an unusable frequency response. The summing circuits on these devices work perfectly, but the signals coming from a factory amplifier may not be compatible. So everything has to be tested. We’ll talk about signal summing processors in another article soon.

If you plan to have an amplifier added to a factory-installed audio system, chances are you’ll need a line output converter. It’s even more likely that you’ll need one that can provide a remote turn-on signal for that new amp. Drop by your local specialty mobile enhancement retailer to find out about the solutions that are compatible with your vehicle to deliver great sound.

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 seems to be some misunderstanding about the relationship between subwoofer mounting depth requirements and performance relative to enclosure volume. We constantly see enthusiasts talk about having a 10-inch shallow sub mounted under a car or truck seat. Their expectation is full-size subwoofer performance without the need for a large enclosure. Let’s do a few simulations to see if they have any hope of getting the bass they want.

What Is ‘Great Bass’?

In our opinion, the purpose of a subwoofer is to extend the low-frequency output of an audio system such that the entire audio spectrum is covered. Unless they are massive (which causes other problems), the speakers in your doors or dash won’t play much below 50 Hz at high volume levels. The addition of a dedicated subwoofer with a dedicated amplifier can easily play to 20 or 25 Hz and relieves the smaller speakers of the task of playing these frequencies. As a result, the smaller speakers will sound better, and the subwoofer will give you the impact you expect from your audio system.

When quantifying bass performance, we talk about output capability and extension. Quantifying these characteristics is tricky, as the numbers depend on the vehicle into which the products are installed. Instead, we’ll use simulations from the BassBox Pro software to give you an idea of how different subwoofers perform in compact enclosure volumes. While not absolute in terms of in-car performance, the relative differences will be demonstrated clearly.

Sample 1 – Rockford Fosgate Subwoofers

Rockford Fosgate has dozens of differently sized subwoofers in their product line. Their solutions range from affordable entry-level products in the Prime Series to competition-grade Superwoofers in the Power Series. For this comparison, let’s look at a Punch P3 shallow 10-inch subwoofer and compare it to a full-depth version at the same feature level. The two subs will be the shallow-mount P3SD2-10 and the full-depth P3D2-10.

Because space is usually at a premium for shallow subwoofer installations, let’s take a look at how each of these subwoofers performs in a compact sealed enclosure with a net internal volume of 0.5 cubic foot. If you want to picture that enclosure, it might have a width of 13.5 inches, a depth of 5 inches and will need to be 22 inches long if constructed from ¾-inch-thick material (as it should be).

It would be easy to think that the shallow sub plays louder, as the peak output is 109.7 dB at 106.7 Hz compared to 109 dB at 75 Hz for the big driver. However, in almost every application, your subwoofers will be used with a low-pass filter that’s set somewhere around 60-70 Hz. As such, it’s the system efficiency below 70 Hz that will determine how much bass the sub produces for a given power level.

The P3D2-10 simulation predicts 103.2 dB of output at 40 Hz and 101.8 dB from the shallow sub at the same depth. In this case, the big woofer will be louder for a given enclosure size.

Sample 2 – JL Audio Subwoofers

Another company with a great selection of full-depth and shallow subwoofers is JL Audio. Let’s look at the big 10W3v3-4 to the shallow 10TW4-D8 driver. The big sub needs at least 5.93 inches of mounting depth, while the shallow TW3 driver requires only 3.25 inches. Let’s look at both of these drivers in a half-cubic-foot enclosure and see which is louder.

Here we see that both subwoofers are very similar below our crossover frequency. The big W3 sub is producing 102.9 dB at 40 Hz, and the shallow TW3 driver offers 102.6. In our opinion, that’s pretty much the same.

Sample 3 – Kicker Subwoofers

Let’s run these calculations one more time with a pair of Kicker subwoofers. This time, we’ll compare the 10-inch square dual-4-ohm L7R sub to its shallow-mount L7T brother. Both drivers are rated for 500 watts maximum power handling. The L7R requires 6.125 inches of mounting depth, while the L7T needs only 3.75 inches.

Just as with the JL subwoofers, the output of the shallow subwoofer is very similar to that of the big sub when driven with 300 watts of power. The L7R’s predicted output is 103.7 dB at 40 Hz, with the thinner L7T is calculated to produce 104.3 dB. You might be able to hear the difference, but not likely.

Are Shallow Subs the Same as Deep Subwoofers?

As one of our readers asked on Facebook, “So, the benefit is only shallow mounting depth, not a change in enclosure requirements?” He is right. The physics that govern output and low-frequency extension don’t change with a shallow subwoofer. Their benefit is minimized mounting depth, not magical deep-bass from microscopic enclosures. Your installer can create unique low-profile enclosures with a shallow sub, letting them mount them in spaces where a full-size sub doesn’t fit.

One thing to keep in mind is that shallow subwoofers may not have as much cone excursion capability as their full-sized brethren. The Kicker L7R has an Xmax spec of 13.9 millimeters, where the L7R is only 9.2 mm. The full-depth Rockford Fosgate P3D2-10 has an Xmax of 15.2 millimeters versus 8.4 mm for the shallow P3SD2-10. The chosen JL Audio subwoofers are the exception here. The TW3 has a rated Xmax of 15.2 millimeters, where the W3v3 sub is 14.0 mm. Both are good numbers, so it’s not a concern.

Do Shallow Subs Work in Small Enclosure?

The answer to this is that every subwoofer needs a certain amount of air volume behind the cone to perform. Subwoofers with shallow designs don’t produce more deep bass from a small enclosure. We’ve heard both deep and shallow subs in 0.2- and 0.3-cubic-foot enclosures. They sound terrible. Our take-away from this series of simulations is a recommendation to resist asking the local specialist mobile retailer you are working with to design and fabricate an enclosure that doesn’t provide the subwoofers you’ve chosen with adequate space. You’ll likely find that you’ll get more deep bass by using fewer subs in a properly designed system.

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 you’ve been a reader of BestCarAudio.com, you know we’ve published a lot of articles about distortion. We include detailed measurements of harmonic and intermodulation distortion in our Test Drive Reviews to help show you the quality and performance differences between products. In this article, we’ll make a series of speaker distortion measurements using our new Clio audio analysis hardware to explain why investing in the best quality speakers you can afford is crucially important.

An Overview on Distortion

Before we start talking about distortion, we ask that you forget about amplifier clipping. That’s not what we’re talking about here. Yes, clipping IS the addition of significant amounts of unwanted information to an audio signal. With that said, clipping should only happen when an audio system isn’t designed or operated correctly.

The distortion we are discussing happens in low, mid and high volume levels and comes from every component in the audio signal path. Source components in an audio system add a small amount of distortion. Quality amplifiers shouldn’t add much unwanted information when operated in their linear range. On the other hand, speakers can easily add a lot of distortion.

Any time information is added to the original recording, that’s distortion. It could be hiss from an improperly configured processor or harmonics from a poorly designed amplifier. Have a look at this article (https://www.bestcaraudio.com/what-do-better-car-audio-amplifiers-sound-like/) that discusses the performance differences between low-, medium- and high-quality car audio amplifiers to get a feeling for just what they add to an audio signal.

Let’s look at a theoretical example of distortion before we dive into measuring any speakers. Imagine that we’ve created a single-frequency test tone to evaluate the distortion characteristics of audio equipment.

The graph above shows a spike at 1 kHz. There’s nothing else of significance in the display.

Next, we might play the above recording of a 1 kHz tone through a medium-quality source unit. Though it can be subtle, every audio component will add a number of harmonics to the signal. The output of our head unit might look like the graph below.

The graph above shows the same 1 kHz tone, but harmonics have been added to the signal at 2, 3, 4 and 5 kilohertz. The loudest harmonic, measured at 80 dB below the original signal, would represent a signal distortion of 0.010%.

The source unit has added information to the audio signal that wasn’t in the original recording. For example, the small spike at 2 kHz is second-order harmonic, the spike at 3 kHz is third-order, and so on. The relative level of the even and odd harmonics can give the audio component a harsh sound or make it sound unintentionally warm. Either way, the sound has changed from the original recording, and that’s not what we want any audio device to do.

Passing that slightly distorted audio signal into an amplifier will have the same effect. It will create multiples of any and every frequency that passes through it. So, it will add more unwanted information at 1, 2, 3 and 4 kilohertz, along with harmonics of each of those frequencies as they were present in the signal going into the amp. Below about -110 dB, you aren’t going to hear that information. We’ll get into another deep discussion of intermodulation distortion as we prepare to evaluate speaker configurations.

Let’s Test a Car Audio Speaker

It’s easy to create a low-quality speaker. Guess at a cone mass, pair that with some random voice coils, spiders and surrounds, then glue them together, plop those parts in existing baskets and put a label on the box. If you think there are speakers on the market that aren’t created this way, you’re wrong.

A good speaker is typically designed backward, from a target performance objective. For example, the aim could be a smooth response through a particular range of frequencies, enhanced low-frequency extension or maximum output efficiency. Most often, a group of these characteristics are combined during the development phase. Once the guidelines have been established, an engineer can model different components in simulation software. Once a plan is in place, parts can be developed to hit target mass, dimensional, compliance and electrical characteristics.

The companies with a wealth of knowledge in designing and testing speakers have a foundation for what works in each application. As such, hitting a target performance goal is more efficient and the results more accurate. Some companies use test equipment that combines acoustic measurements with laser-based cone movement measurements to evaluate samples and adjust or fine-tune the design. Hardware like this is available from Clio and Klippel.

No matter how hard the engineer tries, designing and producing moving coil loudspeakers is challenging. A little too much or too little glue can change performance. A misalignment of the vertical height of the coil to the cone and spider can result in non-linear performance. It’s easy to get this all wrong, and as such, it’s difficult to produce speaker products that are consistent in offering excellent performance.

Let’s Measure Speaker Distortion

We will start this evaluation of speaker distortion by testing a 6.5-inch coaxial speaker that was introduced to the car audio market in 2004. I knew from the first time I heard it that there was something odd with the design. First, there’s a sharpness in the upper midrange that’s quite unpleasant. The second reason I chose this driver is that it has the tweeter mounted right at the base of the woofer cone. (Why this is important will be revealed in an upcoming article.)

Let’s set the speaker up in my 2.2-cubic-foot test enclosure and measure the driver’s frequency response at a drive level of 1 volt and the microphone at 0.5 meter. The results are in the graph below. Ignore what’s happening below 30 Hz – those are room reflections.

The measurement above tells us a few things. First, there’s a nasty dip of 10 dB at 5 kHz and a second dip that extends from 6.5 to 7.4 kHz. Second, it also has a LOT of energy in the top end, rising steadily from 2 kHz to be almost 10 dB louder than the midrange level. Even if these measurements don’t correlate directly to what might be found in an anechoic chamber, they give us a clear idea about what’s going on with the speaker design.

Let’s Look at Distortion

The Clio measurement system can measure total harmonic distortion and precisely quantify second- and third-order harmonic content. So let’s sweep this speaker again at the same drive level and look at the distortion output. Once again, please ignore the bass information below 30 Hz.

The red trace is the measured frequency response of the speaker that we saw previously. The blue trace is the level of unwanted second-order harmonic distortion. The green trace is the level of third-order harmonic distortion. Finally, the violet trace is the sum of all the distortion content produced by this speaker.

To clarify these measurements, when the speaker is fed a signal at 200 Hz and reproduces that tone at an output level of 85 dB, it will also produce output at 400 Hz at a level of 42 dB and 800 Hz at 34 dB. The 400 and 800 Hz sounds were NOT in the original recording. These characteristics repeat for every audible frequency. So tones at 201 Hz have 402 and 804 Hz harmonics added, 202 Hz tones have 404 and 808 Hz harmonics, and so on across the entire frequency spectrum.

We can see that below 500 Hz, distortion increases quickly as frequency decreases. This phenomenon becomes clearly apparent at about 125 Hz where the total distortion jumps to 21 dB below the primary signal. That’s equivalent to about 10% THD. From 500 to 1 kHz, the distortion level is fairly constant at around 45 to 50 dB below the fundamental signal. That works out to between 0.3 and 0.5% THD.

The type of distortion that is added changes based on frequency as well. Below 500 Hz, the distortion is primarily the second-order blue trace. This kind of distortion is usually because of variances in suspension compliance and magnetic field linearity. Above 500 Hz, the distortion becomes primarily third-order, which can be attributed to changes in inductance. Above 1 kHz, distortion is usually based on cone and surround resonances. When we refer to changes in a characteristic, we are talking about variations in cone position and drive level.

The Tip of the Iceberg in Speaker Distortion

As mentioned, this is a preliminary introduction to speaker distortion. We’ll follow up with additional tests on speakers over the next few months to help explain the differences between low-quality and premium solutions. In the meantime, if you’re shopping for speakers, let your ears do the math for you. Drop by your local specialty mobile enhancement retailer to audition the upgrade solutions available 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.