Beyond the features and design of a subwoofer, no single factor affects the performance of a subwoofer system more than car audio subwoofer enclosures and their design. There are several popular enclosure design options available, each with their own unique set of benefits and drawbacks. The most popular enclosures are an acoustic suspension (sealed) and bass reflex (vented or ported) designs. We will close this “Bang For Your Buck” subwoofer discussion with a quick look and bandpass style enclosures.
Acoustic Suspension Subwoofer Enclosures
Acoustic suspension subwoofer enclosures are quite simply a sealed cabinet that adds to the compliance of the subwoofer system. This added compliance acts as a high-pass filter and reduces bass output, but also serves to increase excursion-limited power handling. If you look at the graphs below, the yellow curve shows a high-quality 10-inch car audio subwoofer in a 1.2 cubic foot acoustic suspension enclosure. The red curve shows the frequency response of the same subwoofer in a 0.5 cubic foot enclosure.
As you can see, above 60Hz, the smaller enclosure is a little bit louder but remains within a decibel or two. Below 50Hz is where things start to vary more. The larger enclosure is 2.15 dB louder at 35Hz and 3.35 dB louder at 25 Hz. While it might not appear dramatic, 3dB is the equivalent of having twice as much power driving the subwoofer. However, this increase in efficiency comes with no thermal power handling penalty.
Speaking of power handling, we should look at the physical power handling limits of these subwoofers based on cone excursion. The subwoofer in question has an Xmax specification of 19 mm in each direction from its rest position. The graph below shows the predicted cone excursion of the subwoofer when driven with 500 watts (the maximum power for which it is rated).
Once again, above 60Hz, there is minimal difference in the excursion between the two drivers. Below that, the larger volume of air in the big enclosure has less effect on the stiffness of the subwoofer system. The result is the subwoofer moves farther for each watt of power. If you compare the excursion graph to the frequency response graph, the efficiency levels are directly correlated.
As a summary, sealed enclosures are the simplest to design and are the most forgiving of construction errors regarding net volume. In most cases, sealed enclosures are also the smallest, making them extremely popular.
Bass Reflex Subwoofer Enclosures
The second popular option for a subwoofer enclosure is a bass reflex design. In this enclosure, a vent is added to the enclosure and is tuned to resonate at a specific frequency to increase the output of the system. If we take our 1.2 cubic foot enclosure and add a vent that is tuned to 30 Hz, you can see in the red curve on the graph below that we pick up an astonishing 6.9 dB of output at 30 Hz.
Now, while most vented enclosures are larger than their sealed brethren, the benefit is often an increase in output that is potentially more than having two subs in a sealed design. In fact, this vented design is louder from 20 to 60Hz than three identical subs in an enclosure that is 50% larger (1.8 cubic feet).
Besides efficiency, there is a second benefit to a bass reflex enclosure design. Cone excursion is dramatically reduced through the majority of the operating range. The graph below shows the cone excursion vs. frequency response of the 1.2 cubic foot sealed (yellow) and vented (red) enclosures. The null (reduction in excursion) at 30 Hz is caused by the tuning of the vent. At this frequency, the majority of the output from the subwoofer system comes from the vent itself.
This reduction in cone excursion increases physical power handling and also reduces distortion – as long as you have designed and constructed the vent properly. Vents need to have a large enough area so that air velocity in the vent is kept to a minimum. The mouth of the vent also needs to have a large radius
As with anything, there are always drawbacks. There is very little cone motion control below the tuning frequency of a bass reflex enclosure. In this 1.2 cubic foot vented design, the driver will reach its 19mm excursion limit at 22Hz when driven with 500 watts of power. Below that frequency, the sub will move more than it’s rated for and distortion will increase dramatically. This excursion issue can be offset by implementing an infrasonic (high-pass) filter around 20 Hz to reduce the power sent to the driver. Many subwoofer amplifiers have infrasonic filters built-in. Most digital signal processors can do the same thing.
Bandpass Subwoofer Enclosure Designs
Bandpass enclosures are called that because they not only act as a high-pass filter but as a low-pass filter as well. A typical bandpass enclosure features two chambers. The woofer is mounted between these chambers. In a single-tuned enclosure (often referred to as a fourth-order bandpass or single- reflex bandpass), one of the chambers includes a vent from which all the sound is created. A benefit of this design is the ability to feed that vent through an opening in a rear parcel shelf or similar to ensure coupling with the interior of the vehicle.
The second bandpass enclosure design is a Double-tuned design where both the front and rear chambers are vented. In a Series-tuned bandpass enclosure, the large rear chamber vent feeds into the front chamber. In a parallel-tuned design, the vents from each chamber feed directly into the listening area. Double-tuned bandpass designs are often referred to a sixth-order or dual-reflex designs.
Depending on the type of bandpass enclosure you choose to construct, you may gain some significant excursion-based power handling, and some overall system efficiency through it’s operating range. The main drawback of a bandpass enclosure is its complex design and sensitivity to construction errors. Unlike a simple sealed enclosure, errors in speaker parameters and simulations can produce unpredictable and potentially unwanted results.
The second challenge posed by bandpass design lies in the lack of mid-bass they produce. The low-pass filter abruptly reduces (relatively) high-frequency output. This filtering effect can make it very difficult to achieve a smooth transition between the output of a subwoofer system and the midrange or mid-bass drivers in a system.
The third challenge of a bandpass enclosure is the physical size. Put simply, if you expect low-frequency performance similar to a typical bass-reflex design, the bandpass enclosure will be physically larger. With space at a premium in modern vehicles, this could be reason enough to avoid them.
Picking the Right Enclosure for Your Vehicle
In most systems, the choice of enclosure design will come down to the space available. If you are trying to minimize the impact of a subwoofer on the available storage space in your vehicle, a sealed enclosure may be the best choice. If you want increased efficiency, then consider a bass-reflex design. If you have a unique application that requires a bandpass design, then by all means, go for it. But be prepared to pay more for the required design, fabrication and testing time required to get these enclosures perfect.
A quick note on “basic” subwoofer systems. Over the years, we’ve seen a LOT of retailers offer “bass packages” that include a sub, amplifier, enclosure and often a wiring kit. In the majority of these packages, the retailer has paired an inexpensive sub with an inexpensive amp and a sealed subwoofer enclosure to minimize the total cost of the system. When you are limited in power and output capabilities, upgrading these packages to a bass reflex enclosure is a great investment. You will typically double the efficiency of the system and reduce the chances of damage to the driver caused by overpowering it.
When it’s time to pick a subwoofer enclosure for your vehicle, work with your local mobile enhancement retailer. They will help design a solution that will balance your performance and space expectations. It’s not a complicated process, but, having someone with experience will make it much easier and more predictable.
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.
No single upgrade to an audio system offers a larger improvement in sound quality than the addition of a 
In the simplest of terms, a subwoofer is a large speaker designed to play frequencies below 100 Hz at relatively high output levels. Subwoofers are most commonly available in 10- and 12-inch sizes, but 6.5-, 8-, 13.5- and 15-inch subs are also readily available.
Picking “enough” subwoofer depends on several factors. How loud is loud enough? How much space can you afford to give the subwoofer system? How powerful of an amplifier can your vehicle’s electrical system support? It can be difficult to choose the right sub based on these criteria, especially since different vehicles offer different amounts of cabin gain. Would a single 10-inch sub in a sealed enclosure in the back of a Honda Fit be a suitable solution in a Cadillac Escalade or short-cab Ford F-150?
The next step is to decide 
If you want something truly unique, then ask about including LED lighting in the enclosure. You can choose to have a Lexan or Plexiglas window added and illuminate the interior of the enclosure or add acrylic plastic accent pieces that light up. Upgrades at this level are often combined with enclosures finished with multiple materials – different colors of vinyl can provide amazing cosmetics.
The next step, beyond a simple wooden 
Companies like JL Audio, MTX and Kicker offer subwoofer systems designed for specific models of vehicles. These enclosures are designed to offer impressive performance while minimizing how much space they use. Some companies construct these enclosures from fiberglass in large molds, while others use thick plastics. In most cases, while these enclosures are visible once installed, they are available in materials that match the color of the vehicle interior. An application-specific enclosure is a great way to add amazing bass to a vehicle quickly and efficiently.
You’ll note that we haven’t discussed the specific features of subwoofers that differentiate one from another. This omission is quite deliberate because we will dedicate an entire article to that topic. In the meantime, it is worth discussing the difference between a conventional subwoofer and a shallow-mount design.
When it comes to designing 
Up until recently, most recording studios used a pair of high-quality 
There are lots of ways to describe the experience of having the music come from all around the vehicle, but the analogy of a nightclub or – as we old fogies like to call them – a disco might work best. The concept here is that the music will seem to come from all around you. Unlike a performance where you can point to the source of sound from each instrument, it envelops the listening space. In most of these systems, we still balance the system with dedicated left and right channels.
You may have noticed that we haven’t talked about a live performance that takes place in a concert hall or indoor venue. This has been quite deliberate.
Another option is to use a signal processor to create a sense of room size. In the 1990s and 2000s, lots of processors had presets for jazz, concert and club settings that added reverberation and delay to dedicated rear channel outputs. These technologies have evolved to more-advanced processing algorithms like Bose Panaray and Quantum Logic Surround from Harman. These systems can analyze the content of a stereo recording and extract information that should be reproduced by side and rear speakers to create an immersive listening experience. If your vehicle has one of these technologies, your 
Just as the invention of the transistor eliminated the need for vacuum tubes, advances in technology allow us to create new and unique entertainment solutions with more and more features. We thought it would be fun to take a quick look at a few important car audio technologies throughout history.
The first car 
Radio was truly the technology that drove car audio systems. The first radio broadcasts were weekly special events that included concerts in 1914 and daily news broadcasts in 1916. On May 20, 1920, XWA – the experimental station of the Canadian Marconi Co. – began regular broadcasts in Montreal. XWA claims status as the first commercial broadcaster in the world. These were all AM (amplitude modulation) stations. FM (frequency modulation) radio was patented in 1933, but it wasn’t until the late ’30s that FM broadcasts became popular. The broadcast of a stereo FM signal was first considered by the FCC in the late 1950s, and a standard was approved in 1961.
Reel-to-reel recording on magnetic tapes was popular in the 1940s but wasn’t suitable for use in mobile applications. The 8-track was preceded by the Stereo-Pak 4-track cartridge in 1962. The endless-loop cartridge could store both sides of a vinyl album. The 8-track, known originally as the Lear Jet Stereo 8 Track Cartridge, was launched by Bill Lear in 1963. In 1965, Ford offered factory and dealer-installed 8-track options on its Mustang and Thunderbird and on several high-end Lincoln vehicles.
Most people don’t realize that digital audio (known then as pulse code modulation) was invented in 1937 in Britain and was used in telecommunications. In the late ’60s, Denon pioneered commercial digital recording. The BBC used digital audio transmissions to link its broadcast center to its transmitter in 1972. Sony and Mitsubishi drove the consumer popularization of digital audio in the early ’80s and brought about acceptance by major record companies. The first compact disc was released in 1982 using the Red Book Compact Disc Digital Audio (CD-DA) standard that is still in use today. The first OEM-installed CD players were in the 1987 Lincoln Town Car.
The benefit of Class D amplifiers is their efficiency and low-to-moderate power levels. Class D amps use high-frequency pulse-width modulation waveforms to switch MOSFETs (metal-oxide-semiconductor field-effect transistors) on and off very quickly to amplify signals. Filter networks on the output of the circuits remove high-frequency noise so that only the audio signal is left to drive our speakers. Class D amplifiers allow manufacturers to produce much more powerful amplifiers that take up very little space. These amplifiers consume less current than their Class AB counterparts.
The Apple iPod was introduced in the fall of 2001. The original compact digital media players were only compatible with computers running the Apple Macintosh operating system and as such, sales were limited. In 2003, the iPod 3G was launched with a standard USB port instead of Firewire, making it compatible with Windows-based PCs as well. By June 2003, Apple had sold 1 million iPods.
Though incorrectly perceived as a hands-free and audio streaming technology, 
Since the very first car radios were built, people were concerned about them being a distraction. Turning the tuner knob to find a local station meant you weren’t focused on the road in front of you. In the late ’90s, we saw drivers with headsets and earpieces making phone calls while they drove. Adding a headset was a common purchase with a new phone. In the mid-2000s, Bluetooth communication replaced wired hands-free connections.
In our Bang for your Buck series, we talk about product features and component designs that offer increased value and performance. We’ve discussed source units and speakers, and now it’s time to take a deep look into amplifiers and what separates one amplifier from another.
For decades, manufacturers of high-end amplifiers have provided damping factory specifications. This number is a ratio of the output impedance of the amplifier to a specified load impedance. The story goes that an amplifier with a higher number would produce a tighter, more-controlled sound because the low impedance of the amp would short the back-EMF signal from the speaker.
Any electronic device creates unwanted noise when a signal passes through it. Even something as simple as a resistor creates a small amount of noise. In this example, it’s likely too small to be audible – but it’s there. In a complex circuit with gain (an increase in signal amplitude), creating unwanted noise is a common byproduct of questionable design.
The image above shows amazing performance from a very high-end solid-state home amplifier. As you can see, there is a little bit of 150 and 175 Hz content, but it is at almost -120 dB below the stimulus signal.
In this example, we can see the harmonics created in a high-end home audio Class D amplifier. A 100 Hz signal is present at a level of -85 dB and a 250 Hz signal is present at a level of -90 dB.
To really highlight the potential for unwanted behavior, we have included the spectral content of a high-end vacuum tube amplifier. You can see that there is spectral content at 100 Hz at a level of -42 dB, 150Hz content at -54 dB and 200 Hz content at -67 dB. This distortion would be audible during listening.
This graph shows the same Class D as in the discussion of harmonic distortion. It is easy to see that the test stimulae created a significant amount of information. The peak is at -78 dB, so it’s not a complete disaster.