A while back we published an article that discussed why aiming speakers in a properly designed car audio system was futile. As usual, we received a good deal of feedback about the piece. The comments ranged from the typical “that’s not how it works” to more scientific discussions about how even minor changes in placement had significant effects on imaging and soundstage position. So let’s dive deeper into this discussion to flesh out some of the finer details in speaker positioning.

Proper Audio System Design

The first thing we need to discuss is proper audio system design and component selection. To deliver the most realistic listening experience possible, you need to choose high-quality speakers. Speakers that add significant distortion will lack clarity and detail and render all other efforts futile. Forget the hype about anti-resonant baskets and fancy cones – the technologies that dramatically reduce distortion are motor upgrades like shorting rings and copper inductance-reducing caps.

Next, the speaker system needs to be designed and integrated into the vehicle in a way that ensures the even distribution of sound through the listening environment. This typically involves using a subwoofer, a set of woofers or midbass drivers, midrange speakers and tweeters. As our article on directivity explained, below a frequency where the effective circumference of the cone is equal to the sound wavelength, the sound is emitted evenly in all directions — as such, tilting a speaker up or down won’t change its perceived frequency. Keep this in mind, as we’ll circle back to it shortly.

Lastly, the speakers need to be chosen so that the high-frequency driver operating in the adjacent frequency range can play low enough to ensure that directivity doesn’t become an issue. Unfortunately, this statement confirms that using a two-way front stage with a 6.5-inch woofer is difficult, as most tweeters bundled in component sets can’t play low enough.

Speaker Placement Matters

When we talk about speaker placement for the front stage of our vehicles, the options are typically a stock location in the lower part of the front door, a location in the middle or upper portion of the door, the dash or in a custom pod on the A-pillar. It should come as no surprise that every location has a benefit and an equal number of drawbacks.

For midbass drivers used in a three-way front stage, the door location often works well. Some will go further with the installation and have custom mounting solutions created in the kick panels. If this driver is going to play up to 400 or 500 Hz, this “farther away” position can help with the perceived depth of the soundstage.

The same concept applies to midrange drivers. If they are installed in the doors, as would be found in many Porsches and BMWs, the soundstage can appear to span the car, but comes from a position that’s in line with the steering wheel. Mounting the speakers in pods on the A-pillars can move that soundstage deeper into the dash. Finally, speaker positions in the corners of the dash, right at the base of the windshield, are about as far away from the listening position as is possible and help to create a soundstage that seems to come from the rear edge of the hood. Some listeners don’t concern themselves with the sound source, while others weigh it heavily in their system design considerations.

The angle at which tweeters are aimed matters. Suppose you want to have any chance of hearing the highest of frequencies. In that case, tweeters need to be aimed toward the listening position or pointed up into the windshield so their output can reflect off the glass and “spray” into the vehicle interior. Tweeters mounted in sail panels can help to increase the perceived width of a soundstage – another consideration in where the music seems to come from.

What About Fine-Tuning Mounting Angles?

Much of the feedback on our article about speaker directivity was targeted at the fact that car audio system performance changed based on the angle at which the speakers were mounted. We don’t dispute this for one second. How a speaker performs in terms of directivity is a constant. How sounds reflect off of nearby surfaces plays a huge role in what we hear, even after setting signal delays and calibrating the system with an equalizer.

Let’s say you have a speaker mounted in an A-pillar, and it’s aimed directly across the vehicle. There will be immediate reflections off the windshield and, a moment later, off the side windows. Given their proximity to the speaker, these reflections may be almost as loud as the sound coming directly from the speaker cone. Another moment later, there may be a reflection off the roof and the dash. Vehicles are very complex and behave differently than a listening room or recording studio.

If we tilt the speaker in or out, up or down, we can change the path lengths from the edge of the speaker to the surfaces off of which the sound will reflect. Even a fraction of an inch will change how the sound these speakers produce interacts with these surfaces.

Let’s Look at An Example

Let’s say you have a Porsche 911 or Boxster with a midrange speaker location in the middle of the door. A number of 2.5- and 3-inch midrange drivers will perform excellently in that location. On the inside of the car, there is almost nothing near the speaker that will cause a significant reflection, other than the smooth surface of the door panel itself. In terms of delivering a predictable performance that won’t require significant equalization, this is as close to an ideal mounting location as is possible in a car or truck.

Is this the perfect location, though? What if you like the sound to appear to come from the windshield or dash of the vehicle, or even out on the hood? Will this speaker location offer that? It isn’t very likely. The soundstage is apt to seem very shallow. Tonally, the system may sound excellent, and the lack of nearby reflections should offer impressive clarity.

If we put those same speakers in small enclosures up on the dash, just as we described above, the sound will reflect off of every surface imaginable. We can make the system sound good with an equalizer, but the interaction of multiple reflections won’t deliver the same amount of clarity.

Balance the Benefits and Drawbacks

The goal of any speaker system design (i.e., the placement and configuration of the drivers in a listening application) requires balancing the benefits and drawbacks of each location. The specialty mobile enhancement retailer you are working with can help explain each location’s benefits and disadvantages. Together, you can choose a solution that will deliver the sonic performance and aesthetics you want from your upgrade.

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.

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.