Enclosure, box or cabinet: Whatever you want to call them, where you install your speaker or subwoofer is critically important to their resulting performance. In this article, we focus on the simplest and most forgiving of enclosures to design and construct – the acoustic suspension or sealed enclosure.

The Laws of Physics

There are a few characteristics to keep in mind about every speaker. The first is that as frequency decreases, cone excursion increases. In fact, to produce the same acoustic output, a speaker must move four times as far for every halving of frequency. As an example, if your subwoofer were moving 1 mm at 80 Hz, it would have to move 4 mm to produce the same output at 40 Hz. To produce the same output at 20 Hz, it would have to move 16 mm.

A speaker includes an element called a spider. The spider stores energy when the voice coil of a speaker moves the cone forward or rearward from its resting position. When the cone reaches the end of its travel and comes to a stop, the stored potential energy in the spider wants to be released. This stored energy pulls the cone in the opposite direction. Each transfer of energy includes some losses, and eventually, the cone comes to rest.

Think of the cone motion like a swing at the park. You exert a force on the swing to get it started, and it continues to swing back and forth with a decreasing amplitude until it comes to a stop. Thankfully, a speaker stops moving a lot faster than the swing at the park.

In a speaker, this transfer of energy from the cone to the spider and back is most efficient at a specific frequency. We call this the resonant frequency of the speaker. At the resonant frequency, there is a dramatic increase in impedance because the spider stores a great deal of energy. This energy storage causes the cone to want to continue to move. The movement of the voice coil moving through the magnetic field generates a voltage. This voltage generates a flow of current in the opposite direction to the current flowing from the amp. We represent this opposition to current flow as an increase in impedance.

We also have to consider that every speaker is limited in how far the cone can move. Once we exceed the excursion limitations of the speaker, bad things happen. The voice coil former can hit the back plate. The suspension components may be compromised and start to fail. As a by-product of the cone, dust cap, surround, spider and motor geometry, harmonic distortion also increases as excursion increases.

Our goal in designing any audio system should be to keep distortion as low as possible. Most of the distortion at low frequencies is resonance. These resonances decrease as we move above the resonant frequency of the speaker. The spider and the changing motor force, as the coil moves past the edge of the gap, are the biggest contributors to distortion.

Why Do We Need an Enclosure?

Let’s consider a few additional characteristics. The low-frequency roll-off of a speaker is a high-pass filter. The spider in the speaker is like a capacitor—a spring stores energy and so does a capacitor. The air inside the box is also a spring, and it is in parallel with the spider. The air spring and the spider work together at the same time to do the same thing. The combination of the air spring and the spider increases the high-pass filter frequency. Yes: Contrary to our efforts to produce as much low-frequency information as possible, an enclosure limits low-frequency reproduction.

If that is the case, why do we want to limit cone motion? Consider what we’ve said about how much excursion is required to reproduce low frequencies and about distortion. Limiting low-frequency output from our speaker is not an ideal goal, but limiting some of the really low frequencies to get the right amount of bass at higher frequencies is worthwhile.

There is a benefit to increasing the resonant frequency of the speaker and enclosure system. Let us say we have a subwoofer with a Q of 0.5 and it is our goal to have a total system Q of 0.707. We choose an enclosure air volume that increases the Q, which then increases the system output at the new resonant frequency. Yes, we sacrifice output at lower frequencies, but we gain output around the new system resonant frequency.

I Want More Bass!

Modern speaker designs continue to reduce distortion through computer simulation and modeling of material behavior. Qualified and properly equipped speaker designers can simulate spider, cone and surround behavior to analyze individual resonance and distortion behaviors. They also can model the interaction between the voice coil and the motor structure to predict changes in magnetic field strength and inductance that can further affect how a speaker will sound at moderate to high excursion levels.

These advancements have resulted in speakers that produce less distortion at higher excursion levels. This improvement in performance allows enclosure designers to build speaker systems that will play lower and louder.

Some basic principles govern low-frequency sound reproduction. Cone area is critical. An old article published by the Audio Engineering Society called “The Problem with Low-Frequency Reproduction,” by Saul J. White, included a graph that compared cone excursion vs. frequency vs. system output for a 12- and 15-inch loudspeaker. In the chart, it shows that a 15-inch driver cone only has to move half as much as a 12-inch driver to produce the same output.

To produce sound, we need to displace air. Displacement is calculated by the product of speaker cone area times the distance the cone can travel. In other words, bore times stroke. For the same displacement, more bore requires less stroke.

What is the punch line? If you want it louder, buy more speakers or subwoofers.

Driver Behavior in an Enclosure

The increase in the system Q caused by the addition of air stiffness in the enclosure can cause distortion if the Q is increased excessively. This increase in Q works against our desire for a low-distortion system. Making the enclosure too small increases the Q too much, and we wind up with a system that produces a great deal of output in a narrow frequency range. These undersized enclosures are often referred to as a “one-note-wonders.”

What causes this behavior? The one-note quality is a result of the increased energy storage and transference in the resonant system. The bass just keeps going and going – like our swing at the park.

Power Handling

In an acoustic suspension enclosure, cone excursion increases as frequency decreases. This increase in excursion continues down to the frequency at which the force of the spider and the box exceeds the force of the motor. At that point, the excursion level is limited, and we will not see the increase in excursion . The result: We protect the speaker from physical damage due to cone excursion beyond the design characteristics of the speaker.

Predicting the limits of cone excursion relative to frequency and power is relatively simple for a sealed enclosure. The volume of the enclosure is inversely proportional to the amount of power the speaker can handle when perceived from the standpoint of excursion. A small enclosure limits cone excursion a great deal at very low frequencies, but the system does not produce a lot of deep bass. A large enclosure allows the speaker to move further and produce more low-frequency output, but we cannot drive the speaker with as much power for fear of damaging it.

As we increase the volume of the subwoofer enclosure, the air inside has less “spring effect” on the subwoofer’s motion. This graph shows the increase in driver excursion as air volume increases in four different enclosures.

Acoustic Suspension Overview

An acoustic suspension speaker enclosure reduces bass output at a rate of -12 dB per octave below the resonant frequency. When you combine this roll-off with the cabin gain associated with most vehicles, you can get excellent and linear low-frequency extension well into the infrasonic region. Acoustic suspension enclosures are easy to calculate and to construct. They are very forgiving of minor errors in volume calculation.

Finally, it is worth remembering that acoustic suspension enclosures are not the lowest-distortion enclosure designs available.

When it comes time to design a subwoofer enclosure for your car or truck, visit your local mobile electronics retailer and discuss your requirements. They can help you choose a subwoofer and enclosure design that will give you a solid foundation on which to build your audio system.

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.

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When it comes to buying or upgrading a car audio system, there are hundreds of products to choose from and dozens of questions for you to ask the sales staff at your local car audio retailer. This article provides some basic guidelines to help make the process easier for you, and ensure you get the equipment and service that fulfills your goals.

1. What is your point?

Have you ever been driving while listening to music and thought to yourself, “That doesn’t sound right” or “This system doesn’t get loud enough”? Even worse, maybe you have headphones on – something that is illegal in many states and provinces. If there has even been a thought other than “I love my car stereo,” then you should make a visit to your local car audio retailer. Before you go, make sure you know why you are going. Is part of your system broken? Do you want a radio with a new feature? Do you want better sound quality? more overall volume? a little more bass? a lot more bass? Knowing what to ask for will help you arrive at the perfect audio solution quickly and efficiently.

If you have friends with aftermarket car audio systems, ask them if you can have a listen. Write down what you like about their systems and what you would do differently. If you enjoy your music loud, take some notes on a system that you think plays loudly enough – the make and model of speakers, amplifiers and subwoofers. If there was something you liked, like a pair of speakers or radio, write down the model numbers. Do the same for your existing system. If you provide clear goals, your retailer can narrow down upgrade suggestions accurately and efficiently.

A request from your retailer: Be honest about your goals and expectations. If you tell your dealer that you just want a small sub, but you like the sound of a pair of 12s in the back of your friend’s truck, you will end up being disappointed, and will likely push the system beyond its limits or to the point of failure. Ask for what you really want, and you will get something you will enjoy.

2. The Latest Thing

Over the past five years, the number of people who have chosen to add some form of Bluetooth hands-free solution to their vehicles has been considerable. If the solution has been a new head unit, then they also get USB for music playback from their phones or memory sticks. If there is something new that you want, let your retailer know. Some popular upgrades include a new source unit with CarPlay or Android Auto interfaces, cellphone voice dialing, SiriusXM satellite radio, a backup camera or parking sensor system, or a source unit with a Pandora Radio interface or support for high-resolution audio files like FLAC. Your local dealer would be happy to show you some of the features and products available to the mobile electronics industry.

3. Check it out

Once you have narrowed down your reason for visiting a retailer, you should have a plan to audition the product you have chosen. If it’s a radio, using it on a display board can often tell you almost everything you want to know. Make sure the user interface is easy to use and to understand. If it has Bluetooth, make sure your phone will pair with it and reconnect automatically every time you turn on the radio. If you are looking at a multimedia source unit, make sure you know how long it takes to start up when you start your car. This is important if you are adding a backup camera to the vehicle. Waiting for the radio to start so you can use the camera to back up is somewhat frustrating.

If you are after speakers or a subwoofer system, then auditioning those in a vehicle is a great idea. Once you have established how the products sound, you can listen to different speakers or subs on a display board in the store, and reference the difference from the product you listened to in the car.

4. What Flavor?

Do you need an audio system with everything from a single manufacturer? Absolutely not. While there is nothing wrong with having amps and speakers from the same company that makes your radio, different companies have different areas of expertise. The store you are dealing with carries certain brands for several reasons. Typically, a retailer chooses brands for their performance, reliability, and how easily the store owners can work with the manufacturer or supplier. When a store has a good relationship with a supplier, that often translates into better pricing and service on the products for the store, and subsequently for you.

Some consumers are skeptical about why a brand is suggested to them. That is not unreasonable, since many big box retailers are prone to pushing products that are profitable for them. Do your research and audition the products for yourself. If you like something different, then go with that. Just make sure your comparisons are “apples to apples” as best you can, and are based on fact, not reputation.

5. Trained Professionals

When it comes to handing over the keys to your car or truck, you want to know that the person working on the vehicle knows exactly what they are doing. There are programs like MECP (Mobile Electronics Certified Professional) and various local and regional government-run qualification standards that can help to quantify the skillset and knowledge of the person who will be working on your vehicle.

It is also worthwhile to ask to look at some of the work the shop has done. You want to ensure that everything is always neat and tidy when it comes to wire routing, and that products are mounted safely and securely. A neat and tidy installation area can be a good sign. You can often quantify the reliability of a shop by its clientele – if there are high-end cars around, then it probably has a good reputation.

6. Do It Yourself?

Over the years, do-it-yourself car audio installations have allowed people to learn a great deal about how their systems work. With the quality of factory systems improving day by day, the challenge of installing something “better” is becoming more and more difficult. Understanding polarity, phase, summing, equalization and time alignment is paramount to a successful installation. From a physical installation standpoint, working with aluminum chassis vehicles or ones with adhesive panel bonding and data communication buses poses unique challenges. Finally, even choosing a location to mount equipment has become more difficult. There are multiple computers scattered around modern vehicles, and any one of them could be a potential source of audio interference.

All of these are reasons not to do it yourself, but to turn to an established, reliable, knowledgeable shop.

7. Hook Me Up!

Modern vehicles offer many challenges when it comes to installing audio equipment. In many new vehicles, it is impossible to remove the factory radio because other vehicle functions are incorporated into it. In the case of these vehicles, you will want to make sure the shop you are working with has the tools and knowledge to test the factory audio equipment properly for signal connection points and deal with any integration challenges that come up. There are many products on the market designed to integrate with factory audio systems; ask your retailer which they use and why.

8. Stepping Higher

If you are looking for real performance from your audio system, your retailer may suggest several accessories that can improve that performance. Adding sound-deadening to your vehicle should be at the top of your list. Properly installed sound-deadening not only makes the vehicle quieter but can improve the performance of your speakers by preventing the sound coming from the rear of the speaker from canceling with the sound coming from the front. Bluetooth systems work better when the vehicle is quieter, and most sound-deadening materials also block heat, so your vehicle will be more comfortable. A moderately priced set of speakers installed with proper sound-deadening can sound better than an expensive set without deadening.

If the shop needs to create adapter rings for your speakers, what materials are they using? Ideally, you want something that will not be harmed by water – ABS plastic, HDPE plastic, or Lexan and plexiglass materials are great choices.

A higher-end installation may start to involve some cosmetic fabrication. Many shops are adept at creating trim and accent panels that can add unique style to your system and you vehicle. Materials like leather, vinyl, suede, transparent plastics and mesh are very commonly integrated into custom door, dash and trim panels. Shops should have some samples of their work on display so you can see what they offer.

9. Play Me a Tune

One of the most critical aspects of installing any car audio system is ensuring that each speaker is working in harmony with all the others in the vehicle. From the simplest check of balance and fader controls to ensuring that the acoustic polarity of your subwoofer is correct, each system deserves a good listen by your installer before it leaves the install bay.

As you delve deeper into the quest for realism and sonic perfection from your audio system, you will no doubt encounter Digital Signal Processing (DSP). There are several source units and amplifiers on the market with great DSP features, and the standalone processors are amazing. The key to the success of any of these systems starts with the design of the system and finishes with proper tuning. You will never get a great soundstage in front of you if your speakers are beside you. Auditioning a shop’s skills in tuning DSP systems can usually only be done in a vehicle, although a few shops have some dramatic displays in their showrooms. Have a listen to the demo vehicle.

10. After the Fact

Once your system is installed and tuned, the shop should give you a thorough walk-through of how it works, what adjustments you can make and what you should not touch. If you find that you don’t like some aspect of the system’s performance, then go back to the shop. Do not start turning dials and pushing buttons on your own – if the system was tuned properly and you start messing with it, you are more than likely to start to damage your equipment. This is a nice way of asking you not to turn up the gains on your amps.

Many shops offer lifetime installation warranties on products they install. Don’t get hung up if they don’t – it’s the philosophy of more and more shops to invest in making the installations they do so good that there is almost no chance of failure. Talk to your salesperson and understand their logic. In this case, the right answer is the one that works best for you.

Also, be sure to ask about the warranty on the products you are purchasing. Many car audio products have longer warranties when they are installed by an authorized dealer. Ask the shop what happens if something breaks. A few shops offer a direct exchange program; some send the product away for repair. Just make sure you understand how your shop of choice handles things before you make the purchase.

Buying Car Audio

The bottom line: Work with a competent retailer and you will end up with an audio system that sounds amazing and lasts for years and years. Great-sounding music can make a drive much more enjoyable.

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.

Installing mobile electronics in a vehicle is a balance of technical skill and creativity. From the seemingly simple task of connecting wires to the creation of a custom amp rack or subwoofer enclosure, each task requires the car audio installation technician to call upon many different skills. When it comes to installing audio gear in your car, many retailers offer packaged solutions at different performance levels for their clients – this is often called the Good, Better, Best approach. In this article, we look at a few examples where this approach is commonly applied and examine the benefits for each.

Door Speaker Installation

It sounds simple, doesn’t it? Take off the factory door panel, unscrew a speaker, connect the new one, then screw it in place. Finish up by putting the door panel back on. For the average mobile electronics retailer, this would just barely qualify for a “Good” installation. With the speakers connected and installed, the installer typically will have a listen to the system before putting it all together to confirm all the wiring is correct. If you require a speaker adapter, the shop may offer to supply one made from painted wood or crafted from HDPE or ABS plastic. Always take the plastic adapter. Wood will swell up when it gets wet.

For those looking for a “Better” installation, several companies offer speaker mounting baffle rings. These are foam rings that surround the speaker and seal the mounting surface to the back side of the door trim panel. This ring can help with the transfer of sound energy into the vehicle and is likely to reduce the chances of buzzes and rattles. Your installer may also place a sheet of damping material behind the speaker – 12×12-inch pieces are common. This material helps to damp the metal to which the speaker is mounted and ensure there is no gap between the speaker and the mounting surface.

In a “Best” quality installation, the installer will cover the entire surface of the door in a high-quality damping material. Sealing up the access holes in a door panel can dramatically improve the low-frequency response and overall efficiency of the speakers you are having installed. In fact, money spent on proper damping offers a bigger gain in performance than an equivalent upgrade in the quality of speakers.

Several companies offer composite damping solutions that combine damping with a layer of closed-cell foam. This type of damping material offers a further reduction in buzzes and rattles, and improvement in sound absorption.

You may opt to have damping material installed on the outside door skin while the trim panel is off. Damping the outer door skin will further reduce the transfer of outside noise into your vehicle, making your audio system easier to enjoy. If you are using a moderate- to high-power amplifier, you may also opt to have new speaker wires run into the doors.

Subwoofer Enclosure

One of the first upgrades you should do to your audio system is to add a subwoofer. Almost every factory audio system, even one that includes subs, sounds anemic and weak.

When it comes to the choice of subwoofer enclosure, the options are nearly limitless. The most basic of subwoofer enclosure solutions is to pick a pre-fabricated enclosure from a catalog, have your installer install the sub and plunk it in your vehicle. This solution doesn’t qualify for our standard of “Good”, but it works, and it’s better than not having a sub at all.

Choosing to have your retailer design an enclosure specifically for the subwoofer you have chosen and the exact space you require moves us up to the “Good” standard. The enclosure should be made of 3/4″ MDF and finished in a material that matches your vehicle. It should maximize the available room in your vehicle reasonably well.

The move to the Better level may take different directions, depending on your vehicle. Fiberglass or Stack-Fab enclosures can further maximize the available space in your vehicle. If constructed correctly, these enclosures can be more rigid thanks to additional bracing. This bracing results in better performance. At the “Better” level, your installer may choose to incorporate some cosmetic accents. Including a trim ring around the sub in an accent material is pretty common.

At the “Best” level, the enclosure design will be topnotch! Your installer may even choose to measure the Thiele-Small parameters of your subwoofer before starting work. The enclosure will be extremely rigid and well-reinforced internally.

Your installer may choose to line or stuff the enclosure with materials like Dacron or foam. Cosmetics will also take a leap forward at this level. Having the enclosure trimmed flush to the sides of the vehicle is a must to make it look like it came from the factory. Your installer may choose to use vinyl or leather on the visible parts of the enclosure to further improve the match with factory styling. A product or vehicle brand or logo may be incorporated into the design as well. At the Best level, anyone who sees the resulting creation should be immediately impressed.

Design and Cost

There is no limit to how creative your installer can get with the installation – it’s all governed by how much you want to spend. At the higher end, the installer may provide drawings or sketches of the finished product. You will probably have to pay for this design time. That said, many shops will credit some or all of that back to you as part of the final cost.

The top installers around the country charge upwards of $100 per hour for custom work or more. Their experience and creativity allows them to be very efficient in executing their ideas, and the work behind the scenes is often equally exemplary. Attention to detail for wiring, product mounting with Nutserts or stainless steel hardware, and proficiency in system design and tuning are all part of getting the Good, Better or Best value for your money.

Visit Your Local Specialist For Car Audio Installation

When it’s time to go shopping, drop by a few of your local mobile electronics specialist retailers. They would be happy to show you different options for your project.

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.