The staff here at BestCarAudio.com look at dozens of installation photos each day and continue to see tweeters that aren’t installed in a way that will maximize the listening experience. Our goal is to help consumers get the best performance possible from their car audio system upgrades, so we’re going to perform two tests to demonstrate the importance of understanding speaker dispersion patterns. This information is vital to optimizing the angle at which tweeters are installed in a car audio system.

Let’s Talk About Speaker Directivity, Again

The term directivity describes where the sound created by a speaker goes. For the purposes of this article, we are going to talk specifically about tweeters. (We’ll follow up soon with another article about midrange speakers and woofers.) A clear understanding of these concepts for all speaker sizes is crucial to proper car audio system design and installation.

As a caveat, we want to make it clear that directivity occurs with every type of speaker from every company at every price point. Inexpensive speakers are no different from those that cost thousands of dollars. For this test, we used a 1.5-inch audiophile-grade automotive tweeter. We choose this driver because we know it has a flat response and minimal distortion.

When we talk about speaker directivity, we need to compare the circumference of a speaker to a wavelength of sound. Wavelength is calculated by dividing the speed of sound (343 meters per second) by frequency. As an example, a 1 kHz tone has a wavelength of 34.3 centimeters or about 13.5 inches. A 40 hertz tone is 8.575 meters or 337.6 inches. The length of the pipes in a church organ is calculated using this wavelength information. The same holds for wind instruments like trombones or trumpets.

For speakers playing low frequencies relative to their circumference (and proportionately, their diameter), energy radiates forward, backward, sideways, up and down. You can think of this in the same way that light radiates from a candle. Candles aren’t brighter to the side or above. The light created by a candle is a point source that radiates outward and evenly in all directions.

At extremely high frequencies, sound radiates from the speaker similarly to light from a flashlight. If you are off to the side of a narrow-beam flashlight, you won’t be illuminated. For speakers, the same thing happens. Off to the side of a speaker, high-frequency information can be attenuated by 24 decibels or more compared to being directly in front of the speaker.

Speaker Diameter Affects Directivity

The directivity characteristics of a speaker depend on the size of the speaker cone or diaphragm. Keep in mind that the advertised “size” of a woofer or midrange doesn’t describe the diameter or circumference of the actual speaker cone. For example, a 6.5-inch speaker doesn’t have a cone with a diameter of 6.5 inches. It’s usually closer to five.

For our 1.5-inch tweeter, the diaphragm has a circumference of roughly 4.712 inches, which is the wavelength of 2.865 kHz tone. Each speaker has a unitless value known as ka. The ka value is the driver’s circumference divided by wavelength. Directivity can be described as multiples of ka. For our tweeter, ka is equal to 4.712 kHz; ka = 0.5 is 1.43 kHz; ka = 2 would be 5.7 kHz; and ka = 5 would be 14.3 kHz. Above a frequency where ka = 1, the speaker becomes increasingly directional. Below this frequency, sound radiates evenly in all directions — even behind the speaker.

The graphs above represent a generalization of how the output of a speaker changes as you move off-axis from being directly in front of the driver. As can be seen in ka values of 1 or less, you would hear almost as much of that frequency when standing behind a speaker as you would being directly in front of it. By the time ka = 3, you don’t hear anywhere near as much to the speaker’s side, and it only gets worse as frequency increases.

Directivity Testing

We set the tweeter up on a pedestal and took a series of measurements at 12-degree increments. The graph below shows how the tweeter output decreases at high frequencies as the listing angle increases.

The red trace represents being directly in front of the speaker. Frequency response is within 5 dB from 1.5 kHz to above 20 kHz. Since we don’t have an anechoic chamber and are using windowed FFT measurements, these are adequately accurate results for this article.

The blue line has the microphone positioned 12 degrees to the side and directly on-center. At a meter, that’s a distance of only 20.9 centimeters or roughly 8.2 inches to the side. There are some minor changes in response up to 15 kHz of about 1 dB. At 20 kHz, the output has decreased by about five dB.

The dark green trace now has the microphone located 24 degrees off-axis. Overall output is down another dB or two between 3kHz and 15kHz, but the output at 20 kHz is down 13 dB. As we move farther and farther to the tweeter side, the output decreases more and more.

Think back to the math we did to calculate that ka = 1 frequency of 2.865 kHz. All the frequency response measurements are nearly identical at that frequency and below, and they start to separate more and more at multiples of that frequency. It’s almost like the math works!

Option 2 – The Tweeter Bounce

It’s not always physically easy to position a tweeter so it aims equally at the driver and passenger. One option in these instances is to install the tweeter near the base of the windshield and point it upward. The sound from the tweeter will bounce off the glass and radiate into the listening area.

While this sounds ideal, there are drawbacks. In this configuration, you effectively have two sound sources with different path lengths. This difference in path lengths will cause a certain amount of constructive and destructive interference called comb filtering.

The graph below shows the response of our audiophile tweeter at zero degrees in red, at 48 degrees in blue and measurement at 90 degrees off-axis in green. The fourth measurement is still at 90 degrees, but we have added a large piece of glass in front of the tweeter and angled it at 45 degrees. This last trace is in gray and shows us the measured response off of the glass.

Bouncing the tweeter output off our windshield analog, the response above 4 kHz is as good as if the tweeter were installed on-axis directly with the listening. But, unfortunately, everything comes with a price. We now have a dip of about 8 dB at 2.7 kHz. Yes, we could fix that with an equalizer, but that would require driving the tweeter with more than six times as much power around that frequency range. We could raise the crossover point to 3.5 kHz, but now we might have frequency response problems with the high-frequency information from the midrange speaker.

The Takeaway on Aiming Tweeters

If you want to hear all the music your stereo reproduces, then it would be ideal to be within plus or minus 15 degrees of on-axis with the tweeters in your car audio system. Any effort you might have put into reproducing the highest audio frequencies with better amplifiers or high-resolution audio players is lost if you are beyond that angle. You can also explore how your system behaves with the tweeters in the corners of the dash. You’ll sacrifice a bit of stage width and may have to deal with some frequency response issues at lower frequencies than sail panel locations, but it might require less fabrication.

We’d never argue that installers and technicians have different tuning and installation methods. With that said, and in spite of their best efforts, they can’t change the laws of physics. Choosing a tweeter location that has both of the tweeters pointed at the middle of the car between the driver and passenger’s head will ensure both can enjoy extended frequency response with good symmetry from both sides of the vehicle. Drop by your local specialty mobile enhancement retailer today to discuss how they can aim the tweeters in your car or truck for the best performance.

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 do-it-yourself installers have taken a liking to our discussion about wiring multiple subwoofers to a single amplifier. The popularity makes sense, since many car audio enthusiasts aren’t familiar with series and parallel wiring. A question came up on Facebook a few weeks ago asking if it was better to wire a pair of dual voice coil subwoofers in series with their coils in parallel or vice versa. We thought it might be fun to turn that question into yet another experiment and dive deep into the options of series-parallel wiring.

Wiring Dual Voice Coil Subwoofers

Unless your installer has access to some very low impedance subwoofers, most installations will see the subwoofers you have purchased wired in parallel. For example, say you’ve chosen a pair of 10-inch subs with dual 4-ohm coils. In that case, your installer could wire all four coils in parallel to present a 1-ohm load to a monoblock subwoofer amplifier. What if you’re after a solution that will offer the best sound quality possible, and you’ve chosen a two-channel Class-AB amp to power your subwoofers? In most cases, these amplifiers want to see a 4-ohm load when bridged. It’s not difficult to wire a pair of dual 4-ohm subwoofers to present this load, but there are a couple of options.

Series the Coils’ Woofers on Each Driver, Parallel the Subwoofers

Your installer’s first option is to wire the voice coils on each subwoofer in series. For our dual 4-ohm subwoofers, this wiring configuration would add the voice coil impedance on each driver to produce a nominal 8-ohm load. Next, your installer would wire each subwoofer in parallel with your amplifier to create a 4-ohm load.

Parallel Each Woofer’s Coils, Series the Subwoofers

The second option is to wire the voice coils on each subwoofer in parallel, then wire the two subwoofers in series with each other to the amp. Each subwoofer would have a net impedance of 2 ohms, and wiring those loads in series would present our amplifier with a 4-ohm load.

However, our subwoofers aren’t resistors. We talked about the reactive characteristics of speakers and subwoofers not long ago in this article. Since we’re dealing with inductance and capacitance along with the resistance of the voice coil, is there a chance that the two wiring options present different results in terms of performance? Let’s see what happens!

Let’s Do a Test!

We have a pair of 10-inch subwoofers that we’ve meant to install into the sound system in our office. Yes, we need the ability to reproduce 25 Hz with authority while watching Cleetus McFarland, AvE, Project Farm and bigclivedotcom on YouTube. OK, maybe we don’t NEED it, but we want it. As we described in our examples above, the subwoofers have dual 4-ohm voice coils, so they’ll be perfect candidates for our experiment.

First, we measured the Thiele/Small parameters of one subwoofer using our new Clio Pocket 1 portable measuring system. Next, we measured the sub with its voice coils wired in series and then again with the coils wired in parallel to generate the data below.

Not surprisingly, the mechanical characteristics like resonance frequency (Fs) and compliance (Vas) didn’t change. As we expected, the electrical measurements like DC resistance, electrical Q, and inductance (at 1 kHz) did change.

Electromechanical Series-Parallel Wiring Results

Next, we wired the subwoofers together in the configurations we showed in the two diagrams at the beginning of the article and repeated the measurements to see what, if anything, had changed.

We’ll start by saying that the differences are minimal. The reality is, the system will work just fine wired either way. With that said, there are signs that wiring the coils on each sub in series and wiring the subwoofers in parallel is slightly beneficial.

If you look at the chart above, the DC resistance of the C-S W-P configuration is a little lower, as is the driver’s total Q (Qts). A lower Q-factor can mean less resonance at Fs and a more accurate bass response.

Sometimes an experiment yields earth-shattering results. Other times, the outcome is subtler or less controversial. Most professional installers wire coils in series and those subwoofers in parallel. If you need a hand choosing suitable subwoofers for your car audio system or help in wiring them, drop by your local specialty mobile enhancement retailer today.

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.

We were recently at an event that was hosting a mobile audio system SPL competition. If you aren’t familiar with this sort of thing, it’s a contest to see who has the loudest stereo. We aren’t talking about cranking the dial on the factory radio. Instead, some of these folks build steel and concrete reinforced subwoofer enclosures and feed tens of thousands of watts to their subwoofers.

As you can imagine, delivering that much power requires significant electrical system upgrades. Many of these creations have multiple alternators and huge banks of batteries. If you’ve upgraded your car or truck with an amplifier that can produce hundreds of watts to your speakers, there’s a wiring upgrade called the Big Three that can improve the efficiency of your electrical system. Let’s look at what this upgrade is and why it’s a great starting point for a high-power car audio system.

How Automotive Charging Systems Work

The first thing you need to know about delivering power to your amplifier is that most of the energy will come from your alternator, not the battery. The battery is there to start the car. Once a vehicle is started, the alternator, which is mechanically driven by the engine, provides power to replenish the battery for the next start. The alternator also runs the computers, ignition system, fans and lights in your vehicle. Once you’ve started the vehicle, you could remove the battery and everything would, under normal conditions, operate just fine.

This scenario changes if you add a high-power amplifier to your vehicle. Say you have a 1,000-watt amplifier and you want to deliver that full amount of power to a few high-power subwoofers. At 13.8 volts, most amplifiers of this type will consume about 100 amps of current. If you have the engine running, headlights on and a climate control system in operation, your car or truck may be using 30 or 40 amps of current to power those systems. If the alternator is only rated to produce 80 amps, there certainly won’t be 100 amps left for your stereo.

The additional current the amplifier wants will come from the battery, albeit at a lower voltage. You will likely find that an amplifier rated for 1,000 watts at 14.4 volts can only produce about 800 watts at 12 volts without clipping the output signal and adding significant distortion.

How To Make the Most of Your Alternator

The first step in optimizing the electrical system in a car or truck is to reduce waste. In this case, waste is the power converted to heat because of resistance in cables and connections. First, have a look at your alternator and battery. How large are the wires running to and from them? Unless you have a big truck with a high-output alternator, chances are that the wiring is 4 or maybe even as small as 6-AWG.

Please make no mistake about it, the company that built your car or truck deliberately chose the smallest, lightest and least expensive wire that would allow the vehicle to function reliably. They had no intention of providing conductors that could handle two to three times what the alternator was rated for.

The Wiring Upgrades that Make the Difference

The Big Three upgrade involves adding to or replacing the existing conductors with larger, high-quality wires. The upgrades in the Big Three are:

• The run from the alternator chassis to the negative terminal of the battery.
• The run from the output of the alternator to the positive terminal of the battery.
• The ground connection from the negative terminal of the battery to the chassis of the vehicle.

Depending on your vehicle, there may be other wires that can be upgraded at the same time. For example, if there is a main power distribution box under the hood, running new wire to it can help provide more voltage to the factory-installed electrical and electronic components in your vehicle.

Another upgrade you may want to make at the same time is replacing the battery terminals. Some factory-installed terminals are notoriously flimsy. If you’re demanding significant current from the battery, then optimizing each component along the way only makes sense.

Is the Big Three Enough?

In 2012, we wrote an article about upgrading the stock electrical system wiring in modern cars and trucks. Even though it was a decade ago, new vehicles at the time were being constructed out of materials like QuietSteel and aluminum, and some companies had started using adhesives instead of spot welds to bond unibody panels together. All of these advances in vehicle assembly work against our desire to deliver large amounts of current to an amplifier, especially when we want to use the body as the ground return path.

Power delivery from the positive terminal of the alternator is as important as the ground connection to the chassis and battery. If the current can’t flow through both, you are wasting energy by transforming it into heat. Upgrading and adding grounds with the Big Three is a start. If you are serious about optimizing your electrical system, then you’ll want to add a ground wire from the battery or alternator directly to your amplifier. Back in 2012, we called this the Big Four.

Full disclosure: This wasn’t our idea. The first we heard of running a dedicated ground wire was when we were checking out Precision Power’s fleet of Chevrolet Suburban demo vehicles back in the ’90s. The topic came up again when Ford introduced QuietSteel in the F-150 vehicles, and companies were having problems with amplifiers failing because of low voltages. As a solution, JL Audio suggested adding what they called a parallel ground. This wire would connect to a conventional ground point in the rear of the vehicle and run to the battery’s negative terminal or the alternator. A benefit of the parallel ground is that it offers less resistance than a dedicated ground wire or using the chassis. As a result, current can flow through both paths, reducing the voltage drop and improving system performance.

Optimize Your Vehicle Electrical System

If you’ve purchased a high-power amplifier for your vehicle, talk to your local specialty mobile enhancement retailer about upgrading all the wiring in the electrical system. Implementing an upgrade like the Big Three or, better yet, the Big Four will allow the amplifier to produce more power and allow the system to play louder with improved reliability and efficiency.

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.