What happens when a subwoofer is used with an oversized subwoofer enclosure? This article will look at the good, the bad and the ugly in terms of an improper match between the electromechanical characteristics of a subwoofer and the need for a proper enclosure.

Why Do Subwoofers Need an Enclosure?

If you’ve been following our series of articles on understanding subwoofer quality, then you’ll know that the purpose of a subwoofer enclosure is to act as a mechanical high-pass filter. That’s right: The enclosure limits how much low-frequency information a subwoofer produces. Why? Well, below about 250 or 300 Hz, a speaker cone has to move four times as much for every octave lower it plays. Put another way, if you have a subwoofer playing a 100-Hz tone and it’s moving 0.25 mm, it needs to move 1 mm to produce the same output at 50 Hz, and 4 mm to produce the same result at 25 Hz. It would theoretically have to move 16 mm to make the same output at 12.5 Hz.

Why is cone excursion a problem? Well, the suspension components (surround and spider), along with the length of the voice coil and thickness of the top plate, determine how far the cone can move linearly. Linearity is vital because distortion skyrockets when things get non-linear. Think of this like mechanical clipping. It can sound just as bad as an amplifier that’s clipping. In extreme cases, mechanical components of a speaker crash into each other, which can cause damage.

If you’ve ever analyzed the frequency content of popular music, you’ll know that most of it has very little audio information below 35 Hz. The chart below shows the frequency content of several songs. The trace in red is “Dance the Night” by Dua Lipa. The orange trace is “Industry Baby” by Lil Nas X feat. Jack Harlow. The yellow trace is “Paint the Town Red” by Doja Kat. “Slime You Out” by Drake is in green. “Clocks” by Coldplay is in blue. Finally, the violet trace is “I’m Shady” by Eminem. There is nothing below 35 Hz of significance in any of these tracks. That’s not to say that some music doesn’t contain significant amounts of deep bass and even infrasonic information – it’s just less common than you think.

If we can control how much the speaker cone moves at very low frequencies, we can apply a lot of power to a speaker around and above 35 Hz so it will play loudly while preventing the speaker from bottoming out. An infrasonic filter, often mistakenly called a subsonic filter, does the same thing. The electrical filter has one huge benefit: It eases the load on the amplifier, the vehicle’s electrical system and the thermal power handling requirements of the subwoofer.

A Quick Comparison of Acoustic Suspension and Bass Reflex Subwoofer Systems

Two popular types of subwoofer enclosures are used in car audio systems: acoustic suspension (sealed) and bass reflex (vented or ported) designs. An acoustic suspension enclosure is a simple sealed cabinet. The math that predicts the frequency response and excursion of the subwoofer is relatively simple, and the performance is predictable. Notably, there’s no significant change in performance if the volume of an acoustic suspension enclosure varies slightly from the specifications. A bass reflex enclosure is typically larger and includes a vent (or port) of a specific area and length to create a resonating system. At its resonant frequency, most of the sound from the enclosure comes from the vent, and the subwoofer cone moves very little. This is why using a large enough vent with proper radii on both ends is crucial.

The traces in the above image are very typical in terms of this comparison of sealed and vented enclosures. The red trace is the sealed enclosure with a net volume of 1.02 cubic feet. We can see that the low-frequency cone excursion plateaus below 50 Hz. Why? The compliance of the air inside the enclosure adds to the compliance of the subwoofer’s suspension to limit motion. In short, the suspension becomes stiffer.

The yellow trace represents a vented enclosure with a net volume of 1.79 cubic feet and a vent tuned to 40 Hz. Around 60 Hz, the cone excursion on the vented enclosure is slightly higher. This increase happens because the enclosure is larger. Around the tuning frequency of 40 Hz, the woofer cone barely moves. The graph below shows the velocity of the column of air in the vent at the same 400-watt drive level.

The yellow trace shows us that the vent’s air column moves the most at 40 Hz. This makes sense, as this small area produces most of the sound from the enclosure at this frequency.

How Acoustic Suspension Enclosure Volume Affects Response and Excursion

Let’s start looking at how changes in enclosure volume affect frequency response and cone excursion. Considering both of these criteria is crucial since the enclosure’s purpose is to prevent our subwoofer from bottoming out.

Let’s use a roughly 25% variance in enclosure volumes so that the differences in performance are clearly visible. All drivers can work within a range of volumes, so 10% either way just isn’t going to make a huge difference.

In the graph above, I’ve modeled the predicted response of a Rockford Fosgate Punch P2D2-12 subwoofer, which is in the BestCarAudio.com lab for an upcoming Test Drive Review. The red trace is our 1.02-cubic-foot enclosure that matches the acoustic suspension enclosure suggestion on the Rockford Fosgate website. The green trace is a 0.75-cubic-foot enclosure. As expected, using this enclosure reduces output below 65 Hz and increases the resonant peak up to around 80 Hz. Going the other way, we have a 1.25-cubic-foot enclosure in light green and a 1.5-cubic-foot enclosure in orange. The increase in low-frequency output below 65 Hz isn’t significant, which tells us the driver’s suspension plays a more substantial role in cone control.

Regarding outright “accuracy,” the larger enclosures have a lower total system Q. This value is called the Qtc. Lower Qtc values correlate to less resonance and, consequently, tighter sound. The 0.75-cubic-foot enclosure has a Qtc of 0.976, which is considered high. The “optimized” 1.02-cubic-foot enclosure has a Qtc of 0.881, which is still on the high side but gives us a good upper bass kick with some added efficiency. The 1.25- and 1.5-cubic-foot enclosures have Qtc values of 0.826 and 0.781. Many consider a Qtc of 0.707 to be the ideal Q-factor. In reality, it’s a good balance of efficiency and damping. The ideal Qtc is 0.5, but an enclosure with enough volume to produce that value can result in excursion issues. The Qts value of this subwoofer is 0.52, so it’s impossible to get a Qtc value lower than that.

Speaking of excursion, let’s look at a comparison of cone excursion versus frequency for our four sealed enclosures.

As expected, the larger enclosures allow the woofer cone to move more at lower frequencies. Fortunately, this subwoofer has an Xmax specification of 13.3 mm, so we don’t run into any issues at any frequency at this power level.

Let’s look at an extreme comparison of sealed enclosure volumes.

The graphs above show the 1.02-cubic-foot enclosure predicted response in red and the subwoofer’s response in a 3.0-cubic-foot enclosure in violet. Larger enclosures mean more output at lower frequencies. This massive enclosure produces 3.3 dB more output at 30 Hz. That’s not a huge gain, but it represents an increase similar to what you’d hear if you could provide the subwoofer with twice as much power.

We do run into a problem, though. At frequencies below 20 Hz, the driver will exceed its 13.3-millimeter Xmax specification. A nice shallow -6 dB/octave infrasonic filter set to 20 Hz would protect this driver from damage should your music contain audio below 20 Hz. Your installer would have to use a DSP to configure an infrasonic filter like this.

Bass Reflex Enclosure Volume Comparisons

Let’s look at bass reflex enclosures with the same Rockford Fosgate P2D2-12 driver. We’ll start with the 1.79-cubic-foot suggested enclosure as our reference, then go up and down by 25% while maintaining the same 40-hertz tuning frequency.

In the chart above, the yellow trace is our reference 1.79-cubic-foot enclosure tuned to 40 Hz. The green trace represents an enclosure volume of 1.35 cubic feet, the light green trace is 2.24 cubic feet, and the orange is 2.68 cubic feet. The results show that the system’s peak output frequency moves closer to the tuning frequency as volume increases. Let’s look at the vent air velocity graph to see if it corroborates this hypothesis.

The maximum vent air velocity frequency moves closer to 40 Hz as the enclosure volume increases. It’s worth noting that the 4-inch diameter vent isn’t suitable for the largest volume enclosure as the velocity exceeds 34.5 meters per second. The vent must be larger and subsequently longer to function correctly with this enclosure volume. Analyzing vent air velocity is another crucial part of subwoofer enclosure design.

It should be no surprise that the larger enclosures provide less control over woofer cone excursion. Fortunately, the high tuning frequency controls cone motion around 50 to 60 Hz. Below the tuning frequency, we need an infrasonic filter set to 27 Hz for the largest enclosure to keep things under control at this power level.

Effects of Tuning Frequency on Output and Cone Excursion

We put woofers in larger enclosures to get them to play louder at lower frequencies. Let’s look at what happens if we change the tuning frequency of our reference 1.79-cubic-foot enclosure.

The chart above shows our reference enclosure of 1.79 cubic feet tuned to 40 Hz in yellow. The green trace is the same volume tuned to 45 Hz. The light green trace shows the enclosures’ predicted response when tuned to 35 Hz. The orange trace represents a tuning frequency of 30 Hz. There are no surprises here as we trade upper bass output for more output at lower frequencies.

Once again, there are no surprises shown here. The dip in cone excursion aligns with the different tuning frequencies. We don’t have any excursion problems above the tuning, and an infrasonic filter will keep things safe at lower frequencies.

What happens if we combine smaller and larger enclosure volumes with different tuning frequencies? In this example, with the Rockford Fosgate subwoofer, things work out. But that’s not always the case.

In the graph above, the yellow trace is our 1.79-cubic-foot enclosure tuned to 40 Hz. The green trace is 1.35 cubic feet tuned to 45 Hz. The light green trace is 2.24 cubic feet tuned to 35 Hz. Finally, the orange trace is 2.68 cubic feet tuned to 30 Hz.

Knowing that larger enclosure volumes focus the subwoofer system output around the tuning frequency, we should be able to get even deeper bass if we combine a larger enclosure with deeper tuning. Sure enough, the graph above supports this. The 2.68-cubic-foot enclosure tuned to 30 Hz would rumble! Driver excursion limits are very similar to the previous simulations.

Now, can we go too far with variances in enclosure volumes? What if someone doesn’t understand balancing speaker protection with frequency response and constructs a massive enclosure with a very low tuning frequency? Let’s look at that.

The massive 6-cubic-foot enclosure shown above is tuned to 17 Hz and has an F3 frequency of 24.5 Hz. On paper, this looks like a great home theater subwoofer enclosure. However, looking at the excursion graph shows us we have a problem. At 26.5 Hz, the massive enclosure isn’t controlling cone excursion. We are within a millimeter of the driver exceeding its limits. Remember from our subwoofer quality comparisons that distortion increases with excursion. So this solution likely won’t sound all that great, even if it produces lots of output at low frequencies.

Lesser subwoofers used in moderately large enclosures often encounter excursion issues above the tuning frequency. This is common with drivers with very compliant suspensions.

Proper Enclosure Modelling is Crucial

We see people on the internet “designing” subwoofer enclosures with free software daily. We love that enthusiasts want to experiment and build their audio systems. However, the instructions for the software don’t include knowing how to interpret the data these software packages deliver. You’ll find many expert mobile enhancement retailers who know how to combine enclosure designs with digital signal processing and the natural transfer function of a vehicle to deliver impressively compact and efficient subwoofer enclosure solutions that sound phenomenal and operate reliably.

So what happens when you put a subwoofer in an oversized subwoofer enclosure? Well, you might get more deep bass. You might get more controlled bass. You might run into excursion-based power handling issues and damage the driver. Thankfully, subwoofers from top-tier brands like Rockford Fosgate have a balance of suspension design and excursion capability, making them very flexible and resistant to enclosure design and construction errors. If you want the bass in your vehicle to sound the best it can, drop by a local specialty mobile enhancement retailer and have them design a custom enclosure that maximizes the available space in your vehicle and ensures that the subwoofers you’ve chosen will work well with your amplifier.

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.

One thing common to every car audio subwoofer enclosure is that they need to connect to the subwoofer amplifier. Most subwoofer enclosures include a terminal cup or something similar to facilitate easy connection to the subwoofers. Let’s look at subwoofer enclosure speaker wire connection options.

Guess What? Ohm’s Law

If you’re serious about car audio, Ohm’s law should be tattooed on your body – or at least, you should understand it explicitly. Almost every electrical connection requires some consideration of voltage, current and resistance. Regarding subwoofer enclosure terminals, we’ve seen many discussions where the primary consideration was power. In reality, power isn’t the issue – current is.

Let’s say you have an 800-watt amplifier powering your subwoofer enclosure. If the subwoofers in the enclosure have a net nominal impedance of 4 ohms, the amplifier must flow 14.14 amps through the wires to the enclosure. In terms of appropriately sized wiring, if your installation uses 5 feet of 16 AWG wire, you’d waste 1% of the energy from the amp as losses in the wire itself. Eight watts isn’t much and isn’t anything to worry about. Jump to 12 AWG, and the losses are only 3.4 watts. It’s still not something you’re going to lose sleep over.

These days, most car audio amplifier manufacturers offer subwoofer amplifiers designed to produce power into lower impedance loads. Let’s say your amplifier delivers 800 watts into a 2-ohm load. The amp must provide 20 amps of current to make the same power. Losses in the wiring still aren’t a huge issue. Five feet of all-copper, full-sized 16 AWG wire would convert 17 of the 800 watts into heat. Jumping to 12 AWG drops that to 6.8 watts. Still not a mess.

Let’s say your subwoofer enclosure has a nominal impedance of 1 ohm, and your chosen amp can deliver 800 watts into this impedance. We are now talking about 28 amps of current flowing through the speaker wire. That 5-foot run of 16 AWG wire would waste 34.4 watts of energy. The issue is that the power is wasted as heat. Dissipating almost 35 watts of heat is challenging, and the wire will get warm. When conductors increase in temperature, their resistance increases. That’s a whole other can of worms! If your installer uses 12 AWG wire to connect your amp to your subwoofers, the losses are down around 13.6 watts – which is pretty safe.

A quick side note about low-impedance subwoofer loads: All but two or three of the hundreds of amplifiers I’ve tested increase the distortion they add to an audio signal when driving lower impedance loads. Every amplifier I’ve tested presents a significant reduction in amplifier efficiency caused by running subwoofers at lower impedances. If you care about sound quality in any way, you’ll find a nice two-channel amp and bridge it to run your subwoofers at a 4-ohm load.

Here’s a quick chart to show how much current is required to feed subwoofers with different power levels of amplifiers and 4-, 2-and 1-ohm loads.

Any time current flows through a connection, there is going to be some amount of resistance. When current flows through a resistor, be it resistance in a connection or an actual resistor component, heat is generated. The formula to calculate the power wasted in a resistor is P = R x I x I. As the current in the equation is squared (I x I), small increases in current flow result in significant increases in the amount of wasted power and heat created.

Subwoofer Enclosure Terminal Cups and Connections

If you visit a local specialty mobile enhancement retailer and look at the prefabricated subwoofer enclosures they offer, you’ll see a variety of terminal cup solutions. Some use large binding posts that accept bare wire up to 10 or even 8 AWG. Others use small spring-loaded terminals that might accept 14 AWG wire.

The first terminal we’ll look at is the basic spring-loaded terminal type. This terminal type will be the least ideal for conducting surface area between the speaker wire from your amplifier and the connections inside the amplifier. All the current has to pass through a thin piece of stamped steel. We see people sharing images of these terminals melting all the time.

The next step up in terminal cup quality is also spring-loaded but has significantly more surface area. These terminals pass the current through a stud rather than a piece of stamped steel.

A common drawback with this type of connection is that some are designed so the clamping portion doesn’t squeeze small-gauge wire well. If the speaker wire is flopping around loose, things will get hot when you pour on the power. If the springs have enough pressure, the right size wire is used and the wire is inserted properly, these should work better than the previous option.

The last terminal cups we’ll look at are called binding posts. These are similar to the previous cup in that the wire is inserted into a hole in the center stud. A nut threads down to secure the connection rather than a spring applying pressure to the wire.

The number one issue is whether or not the nuts are tightened correctly and if they stay tight. If anything were to loosen over time, you’d end up with a high-resistance connection, which will produce significant amounts of heat.

If your car audio system uses binding posts, it’s worth checking them frequently to make sure they’re tight.

Testing Subwoofer Terminal Cups

So, just how much current can a terminal cup handle? As you can imagine, this is an excellent idea for some testing. We rounded up a few cups and connected them to the power wire on an amplifier. With a shunt resistor in series, we can accurately measure current flow. We wired the terminal cups up one at a time and slowly increased the current flow until they produced significant amounts of heat. We’ll give them an approximate current rating based on being able to handle two minutes at a specific current level. You can use the chart above to determine the amount of power the cup can handle based on the impedance of your subwoofers.

Up first was the inexpensive spring-loaded cup. We started with 5 amps of current. Not much exciting happened, and the connection generated no heat. Things stayed pretty steady as we increased current. The voltage drop also increased reasonably steadily. By 15 amps of current, the connection to the wire was producing 100 degrees F of heat. Fifteen amps equals 225 watts with the subwoofers wired to a 1-ohm load. Things started to go south at 23 amps of current, or just over 500 watts when wired to 1-ohm. The connection increased in temperature faster. At 24 amps, I could smell something, and the connection was over 180 degrees. At 25 amps, the plastic spring block started to smoke, and the connector melted. The wire is now permanently attached to the cup.

The other terminal cup I had here in the lab was a threaded binding-post style. I hypothesized that the added surface area of the center post, combined with the nut on the back securing the tab in place, would help provide less resistance and, thus, more current carrying capacity.

Once again, things seemed fine with current levels up to about 6 amps, with no measurable heat at the connection. Six amps equals 36 watts of power to a 1-ohm load. As with the inexpensive spring-loaded block, resistance increased as the current flow increased. The connection reached 100.5 degrees with 18 amps of current, which is only slightly better than the first terminal. However, this is nowhere near the performance I expected. At 28 amps of current, or 784 watts into a 1-ohm load, the entire metal assembly had melted the plastic, and the terminal started drooping.

Let’s do some quick math on my measurements during the testing. First, I measured the voltage drop from the wire connected to the terminal (just beside the connector) to the terminal strip on the back of each terminal cup. The graph below shows the blue spring-loaded cup and the orange binding post.

I used my thermal imaging camera to measure the temperature of each connection at each current level.

If we want to extrapolate some current handling limits from the day, the spring-loaded cup is good for about 22 amps of current, and the binding post cup can handle about 25 amps. These are, of course, continuous current numbers. These correlate to 484 watts at 1 ohm, 968 watts at 2 ohms and 1,936 watts at 4 ohms for the spring-loaded cup. The binding post can theoretically handle 625 watts at 1 ohm, 1,250 at 2 ohms, and 2,500 at 4 ohms.

There are a few caveats to this test. These are continuous current measurements. If you’re listening to very dynamic music, you can likely use more power. However, things don’t take long to melt at the upper limits, so be cautious in choosing your subwoofer enclosure.

Another caveat is that we used 14 AWG all-copper wire. You may experience different performance levels with larger or smaller conductors.

The Best Way to Connect to a Subwoofer Enclosure

Doing this quick test also gave us the idea to test a few quick-connect styles as suitable solutions for delivering significant amounts of power to a subwoofer enclosure. You’ll have to watch for that article soon. In the meantime, we suggest choosing an enclosure that uses multiple terminals if you’re attempting to deliver significant power at low impedances. Your local specialty mobile enhancement retailer can then run multiple speaker wires back to the amplifier to improve efficiency and provide an audio system that is as reliable as possible. Better yet, forego any connector and ask them to run the speaker wires directly from the amp to the subwoofers and seal the wire where it enters the enclosure.

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 concept of how car audio amplifiers distribute power to multiple speakers connected to the same channel seems simple. A little math with Ohm’s law and looking at the amplifier’s specifications should tell the tale, right? Yes and no. Things get more complicated when crossovers are involved. Don’t fret; we’re here to make everything easy to understand. Let’s dive in!

What Determines How Much Power an Amplifier Produces?

The first thing we need to understand is how amplifiers produce power. In almost all cases, car audio amplifiers increase the voltage of the incoming signal by a specific amount. The amount of increase in amplitude is called gain. Engineers specify gain in decibels. Depending on the amplifier’s sensitivity control setting, the gain might be as low as 5 or 6 dB for a small amp or 40 dB for something significant.

More gain isn’t better. That can lead to more unwanted noise added to the signal. Every source unit and amplifier combination has an ideal gain configuration that produces maximum power with as little noise as possible. More commonly, the correct gain setting ensures that the speakers connected to the amp blend smoothly with the rest of the system.

As mentioned, amplifiers increase voltage. Feeding a 1-volt signal from your radio into an amplifier might increase that by 10 dB to 10 volts. That voltage goes to the speaker connected to the amplifier. If the speaker has a nominal impedance of 4 ohms, you can use Ohm’s law to calculate how much current will flow through the speaker. We can calculate current by dividing the output voltage by the load (speaker) resistance. In this configuration, 10 divided by four is 2.5 amps.

You can also calculate how much power the speaker gets. To calculate power with voltage and resistance values, square the voltage and then divide that by the resistance. In this example, 10 squared is 100. One hundred divided by four is 25. So, 10 volts applied to a 4-ohm speaker results in the speaker getting 25 watts of power. Another option is to multiply current by voltage to calculate power. In this example, we have 10 volts and 2.5 amps of current, which equals 25 watts.

With a lower impedance speaker, as you might find with a subwoofer configuration, the amplifier’s power production increases because more current flows through the voice coil. Interestingly, this happens without any adjustment in gain settings. Let’s run the same math with a 2-ohm speaker. The speaker will have 5 amps of current flowing through it (10 volts divided by 2 ohms) and will get 50 watts of power (10 squared divided by two).

We can change the impedance an amplifier sees in several ways. A single 4-ohm speaker will, of course, present a 4-ohm load. Two 4-ohm speakers wired in parallel present a 2-ohm load. Read this if you need a reminder about parallel wiring. You could wire two 2-ohm speakers in series to get a 4-ohm load. You could wire four 1-ohm speakers in series to get 4 ohms. There are some performance-related drawbacks to wiring speakers in series. Primarily, the inductance values add and can dramatically affect midrange performance. It’s best to avoid series wiring when possible.

How Passive Crossovers Affect Amplifier Power Production

So far, this has all been relatively simple. However, we’ve assumed that our speakers act as a fixed-value load of 4 or 2 ohms. The reality is that they aren’t. Because audio signals are alternating current waveforms, and our speakers have characteristics like resonance and inductance, the impedance the amplifier sees varies with frequency.

Impedance is the term used to describe the opposite of current flow in a circuit with alternating current. It’s similar in concept to resistance but much more complicated to calculate and manipulate, as phase is also an issue.

The graph below shows the impedance of a 6.5-inch component speaker set with different settings on the passive crossover network.

The first thing to notice from the graph above is the spike at just over 60 Hz. This spike represents the resonant frequency of the woofer in the speaker system. The impedance at the resonance peak is close to 16 ohms. The amplifier produces much less power at this frequency, but the speaker becomes more efficient. Resonance implies that a small amount of energy produces significantly more output. If the speaker is well-designed, which is the case with the Rockford Fosgate T3652S woofer, the frequency response around the resonant frequency will match that of the higher frequencies.

The other bump in the impedance graph is around the crossover point between the tweeter and woofer. This impedance rise likely results from underlapping the woofer and tweeter crossover points. Ultimately, the system measures well in this area. This impedance bump is of no concern so long as the amplifier you have chosen has excellent output voltage stability in terms of load impedance.

Passive Crossovers and Amplifier Power Production

Now, it’s time to introduce alternating current signals and passive crossovers.

The purpose of crossovers is to limit the frequency range where a speaker plays sound. A low-pass crossover allows a speaker to play up to a chosen frequency. To remember how they work, keep this in mind: A low-pass filter passes audio frequencies lower than the crossover point. Above that frequency, the speaker produces less sound as you move farther from the crossover point. We use low-pass crossovers on subwoofers as we don’t want them playing midbass or midrange frequencies. A low-pass crossover on a midrange driver attenuates output where the tweeter takes over.

The other type of crossover is called a high-pass. This type of filter blocks low-frequency sounds. We use high-pass crossovers on midrange drivers and tweeters. An infrasonic filter, often mistakenly called a subsonic filter, is also a high-pass filter. These filters work the same way in attenuating output as you move away from the crossover point. Here’s how to remember how high-pass filters work: A high-pass filter passes audio frequencies higher than the crossover point.

In both cases, crossovers are not a brick wall. They don’t stop all information above or below the crossover frequency. The rate at which the sound gets quieter is called the crossover slope. For this article, we’ll talk about simple first-order -6 dB/octave passive crossovers. In real-world applications, these filters aren’t steep enough (don’t attenuate fast enough) to provide adequate filtering. Nevertheless, they are perfect for explaining power distribution when we connect multiple speakers to an amplifier.

The response graph above is a screenshot from the ARC Audio ARC DNA DSP software suite’s Graph option. These high- and low-pass crossovers are set to 500 Hz to make them easy to see.

How Passive Crossover Components Reduce Speaker Output

To add crossovers to speakers, a technician will wire a non-polarized electrolytic or a mylar foil capacitor in series to create a high-pass filter. An inductor in series with a speaker creates a low-pass filter. It doesn’t matter if the capacitors or inductors are on the positive or negative lead to the speaker.

We aren’t going to go into the math of how capacitors and inductors act as crossovers in this article. We covered capacitors here and inductors here. Consider these articles prerequisites if you want a detailed understanding of how these devices function. In short, the caps and coils increase their impedance at and beyond the crossover point.

The graph below shows the impedance of a 4-ohm speaker wired in series with a capacitor and a second speaker wired in series with an inductor.

We chose the values for the capacitor and inductor in the graph so that the crossover point is at 500 Hz. At this frequency, the impedance of the passive filters is the same as the speaker impedance or 4 ohms. The result is that the amplifier “sees” an impedance of 8 ohms and produces half as much power as it would without the capacitor in the circuit.

This second graph shows the power the amplifier produces for each speaker network based on the load impedance. You can see that the amplifier delivers 12.5 watts into both at the crossover point of 500 Hz. If we sum the power into each speaker, the amplifier still produces 25 watts.

A properly designed passive crossover network performs two tasks: Primarily, it serves as an acoustic filter between two speakers. The most common application in car audio systems is attenuating the output of a midrange speaker or woofer where a tweeter starts playing. The same network would include a high-pass filter so the tweeter wouldn’t play low-frequency information. The second task is to prevent an amplifier from seeing the impedance of two speakers at once. Some companies don’t execute this second criterion well, resulting in upset amplifiers and difficulty with system design.

Amplifier Power Distribution Takeaways

The inspiration for this article on speaker power distribution stemmed from a discussion about how much power an amplifier produces when driving a midrange speaker and a tweeter. Many people mistakenly thought that since the woofer and the tweeter have a nominal impedance of 4 ohms, the amp would see them as a 2-ohm load. Without crossovers, this assumption would be correct. However, the tweeter wouldn’t last long without a crossover to protect it from being over-powered and over-driven.

If you aren’t sure how power will be distributed among the many speakers connected to your car audio system, drop by a local speciality mobile enhancement retailer. They can help design, install, configure and calibrate a sound system you’ll enjoy!

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.

What is a custom car audio subwoofer enclosure? Does it need to be wrapped in leather or vinyl? Should it be made with fiberglass? Does it need acrylic windows? Is LED lighting a necessity? The short answer is no to all of these questions. Let’s delve into what makes a subwoofer enclosure custom and why it’s the best way to upgrade the bass in your car audio system.

Subwoofer Enclosure Volume Matters

How large does a subwoofer enclosure need to be? The answer to that depends on the subwoofers you want to use. Thinking that way puts the cart before the horse, though. The best way to design a subwoofer system is to tell the product specialist you’re working with how much space you’re willing to allocate to the enclosure. They can take a series of measurements, do some calculations and suggest a subwoofer or subwoofers to deliver the best performance based on the available air volume. No matter what the manufacturers tell you, cramming large subwoofers into small enclosures results in poor performance. You’ll get more deep bass from a single driver in an optimized enclosure than a bunch of larger drivers crammed into an undersized design.

Part of designating the space available for your subwoofer enclosure should include considerations about accessing storage or a spare tire. The last thing you want is to be stranded on the side of the road because part of your stereo has trapped a spare or blocked access to the vehicle battery. Before you tell the shop how much space they can use, look under the trunk floor to determine what you might need to get to. Make some notes so you can share that information with the shop.

Space Optimization Is Key

The number one factor that defines a custom subwoofer enclosure is that it optimizes the available space in the vehicle. Let’s say you want a vented enclosure with two 10-inch subwoofers. Most 10-inch subwoofers on the market work very well in about 1 cubic foot of air space. So, this enclosure would need a net volume of 2 cubic feet plus the displacement of the drivers and the vent. Let’s use a pair of ARC Audio X2 10D2V2 10-inch subwoofers for this simulation. With 1 cubic foot each, plus a 4-inch diameter round vent, the enclosure needs a net internal air volume of about 2.15 cubic feet.

The person designing the enclosure for these subwoofers should optimize it so that it intrudes into the cargo area of the trunk as little as possible. Therefore, it should use the full width and all the available height to make it as shallow as possible. If we have 40 inches of width and 15 inches of height, the enclosure would need to be 8.625 inches in depth. These measurements assume the enclosure is a rectangle with no angled rear panel. If we wanted the rear panel to have a 20-degree angle, the depth at the top would shrink to about 6 inches. That gives us two more inches of usable cargo space.

Both designs are custom enclosures if finished in a durable carpet that matches the cargo area. That’s it. Nothing fancy or exotic is required to make this a custom solution. The customization aspect is that the enclosure is optimized for your vehicle and uses the available space efficiently.

By contrast, if the shop has a pre-built enclosure that’s 34 inches wide and 13 inches tall, it would need to be 11.375 inches deep. Would it work? Yes. Would it sound the same? Yes. Might it save you money versus having an enclosure built specifically for your application? Maybe. Will you have the most space to fit your groceries, sports equipment, luggage or beer? No, not at all.

Here are a few examples of custom enclosures designed to deliver great bass while taking up as little space as possible.

More Custom Subwoofer Enclosure Options

Now, there is a next level of custom subwoofer enclosure beyond a square or slanted-back prism. You might have a significant amount of room inside a spare tire or behind a trim panel in the trunk that can be used for an enclosure. Once again, the choice of drivers for these applications depends on the available space. Just because you can physically fit a 12-inch subwoofer inside a spare tire enclosure doesn’t mean that’s the choice of driver that will produce the most low-frequency output or deliver the tightest bass. A single 10-inch subwoofer might play louder at lower frequencies. An 8-inch subwoofer in a vented design will likely be even louder. Once again, the shop you’re working with should calculate the available volume and suggest a subwoofer based on that information.

Vehicle-Specific Enclosures

Many companies offer off-the-shelf subwoofer enclosures designed for specific vehicles. These enclosures are typically optimized for a specific location in the vehicle and may use a combination of stack-fab or fiberglass construction. With the benefits of mass production, these custom enclosures can make adding an optimized bass solution more affordable than having a shop create a one-off solution. You’ll still need an expert to run all the wiring and configure and calibrate the electronics.

Net Audio in Wichita Falls, Texas, offers this 2019+ Ram 1500 Crew Cab bass reflex subwoofer solution.

Musicar in Portland, Oregon, offers a variety of BMW OE-Look subwoofer upgrades, including this enclosure for F32/F83 coupes with a Morel 10-inch subwoofer.

Audio Designs and Custom Graphics in Jacksonville, Florida, has a complete line of Phantom Fit enclosures, including this one for 2015-22 Mustangs.

MTI Acoustics in College Station, Texas, offers application-specific subwoofer enclosures like this one for Jeep Gladiators.

Upgrade Your Car Stereo with a Subwoofer System Today

As we’ve shown, there doesn’t need to be anything fancy or exotic about a custom subwoofer enclosure. The enclosure needs to be constructed to be specific to your needs. You can certainly go for something flashy if you want. However, we prefer to stick with a simple, well-constructed enclosure and opt for a subwoofer that includes technologies that make it more accurate and linear. No matter your goal, drop by a local specialty mobile enhancement retailer today to find out what they can build to deliver great bass in your car, truck or SUV.

Lead-In Image: Thanks to Perzan Auto Radio in Upper Darby, Pennsylvania, for the photo of this enclosure they constructed for a client’s 2023 Bentley Continental GT Azure. The enclosure features a pair of JL Audio 10W6v3 subwoofers and matching SGR-10W6v2/v3 grilles. The client can still access the space under the trunk floor without moving the enclosure.

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.