Let’s say that you are building a car audio system intended to produce as much bass as possible. In that case, you are going to need subwoofers capable of handling vast amounts of power. You’ll also need amplifiers capable of pushing those subwoofers to their limits. It’s not uncommon to see cars and trucks with more than 5,000 watts of power being sent to a single subwoofer. In these systems, it’s common to see a pair of amplifiers in what’s called a strapped configuration driving a single speaker. This article explains how the concept of strapping works to deliver massive amounts of voltage and current to your subs.

Strappable Car Audio Amplifiers

First and foremost, you’ll need to make sure that the subwoofer amplifiers you have chosen are capable of being strapped. Making this assumption without checking the owner’s manual can result in a lot of frustration. If you try to strap two amplifiers that aren’t designed for this application, you will damage one or both of them.

Second, don’t assume that a subwoofer amp model is strappable because it has a master/slave switch or an audio signal input and output separate from the standard RCA input connections. Those inputs and outputs may exist to make it easy to daisy-chain multiple amplifiers together, so only a single sensitivity control, crossover adjustment, infrasonic filter and remote bass boost setting works for several amplifiers.

Strapping a subwoofer amplifier involves using two identical amplifiers. The amps must have some sort of master/slave switch, and depending on their design, might also have a polarity or phase control switch. For our example, we’ll assume we are using a single voice coil high-performance subwoofer, just to keep things clear. In reality, as long as the load impedance doesn’t exceed the rated limits of the amplifier, you can wire up as many subwoofers as you want.

Wiring Two Amplifiers to One Subwoofer

Image Caption: A pair of Rockford Fosgate Power T2500-1bdcp amplifiers wired to a single T3S2-19 19-inch Superwoofer. Individually, these amplifiers can produce at least 2,500 watts of continuous power into a 1 ohm load.

The drawing above shows the positive and negative speaker wiring, along with the required jumper wire that runs between the two amplifiers for this pair of Rockford Fosgate amplifiers. Your installer must obtain the correct strapping information from the amplifier manufacturer for the models you have chosen. Unfortunately, that information is not universal or transferable.

Aside from the right speaker wiring, these particular amplifiers have to be connected using a bd-Sync cable and a set of RCA cables. The top amplifier is set to master mode. This amplifier will be responsible for gain adjustment, low-pass crossover filtering, infrasonic filter selection and the remote Punch EQ control function. When set to slave mode, the second amp takes the audio signal from the output of the preamp stage of the first amp and feeds it to the output stage of the second amplifier. This configuration bypasses all the adjustments on the second amplifier.

For this configuration to work, the polarity of the second amplifier has to be inverted relative to the first. On the Rockford Fosgate amplifiers, this is achieved by setting the phase switch to 180 degrees. With this setting engaged, if the audio signal from the positive terminal of the first amplifier is increasing in voltage, the same terminal on the second amplifier will be going more negative. The result is twice as much voltage being applied to the subwoofer as would be available with a single amp, up to the current delivery capacity of the amp design. In the case of these two amplifiers, that would be 5,000 watts of power into this 2 ohm load.

Load Impedance Matters

Just as when your installer bridges a stereo amplifier to a subwoofer, the minimum load impedance decreases compared to when speakers are connected to a single channel. For the Rockford Fosgate amps, the minimum load impedance is 1 ohm when each amp is run independently. However, when two amplifiers are strapped to a single subwoofer, the minimum load impedance is 2 ohms.

The minimum load impedance is cut by half because the power production attempts to quadruple. Allow us to explain.

If a single T2500-1bdcp can produce 2,500 watts of power into a 1 ohm load, the maximum current it can supply to the sub would be 50 amps, and the voltage would be 50 volts. Strapping the amplifier now presents the subwoofer with up to 100 volts across the terminals. If we apply 100 volts to a 1 ohm subwoofer, the power would be 10,000 watts, and the load would draw 100 amps of current. While impressively powerful, these amplifiers can’t supply that much current, so we need to double the impedance to cut the load current in half. Delivering 100 volts across a 2 ohm load results in 50 amps of current flowing through the subwoofer.

Things to Think about When Strapping Amplifiers

By the way, you will want your installer to run at least eight AWG power cables from the amps to the subwoofer. By way of an example, the voltage drop across 12 feet (6 feet for the positive lead and 6 feet for the negative) of eight-AWG copper wire that is passing 50 amps of current is 0.404 volts. So it wouldn’t be crazy to make two runs, or upgrade to six or four-AWG cable if it’s available to reduce that drop and deliver more power to your subwoofers.

Not to sound all preachy, but a potential of 100 volts is a very high voltage. The electrical outlet in the walls of our homes operates at 120 volts. We know it’s not safe to play with those circuits. Make sure your installer has secured all the electrical connections to your subwoofers properly. You don’t want a wire coming loose or shorting. You also don’t want anyone to be able to touch those terminals when music is playing. Quite simply, the results could be lethal.

If you plan on competing in a car audio competition where maximum output matters, then look into car audio amplifiers that are strappable. This configuration delivers more voltage to your subwoofers and will increase the efficiency of your system compared to using low-impedance subwoofers. A specialist mobile enhancement retailer near you can help you choose amplifiers that will deliver thousands of watts to your subs. Drop in today to find out what’s available.

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.

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.