Choosing Your Perfect Subwoofer System
One of the most exciting aspects of a car stereo is the subwoofer system. For many first time enthusiasts the lure of the deep bass and pounding rhythms is what initially draws them to car audio. But how do you know which system is right for you and your listening tastes? Do you need one 10" subwoofer or should you get two 15" subwoofers? What type of box should you get? Sealed, ported, bandpass, infinite baffle...the choices are numerous.
What Kind of Music Do You Listen To
One of the most important criteria in choosing your perfect subwoofer system is to know what type of music you listen to. If you mainly listen to country music then your subwoofer system will be vastly different then if you listen to hip hop. It will also guide the type of enclosure you will need for your system.
What Are Your System Goals
This is something you should do in the system planning phase. Do you want to be heard for three blocks or do you prefer lower listening levels? How much bass do you want? Do you want to shake the trim off your car or do you want a balanced sound? There is no right or wrong answer. It's all a matter of personal preference.
Enclosure Types
 |
| Infinite Baffle "Enclosure" |
The simplest enclosure type is an infinite baffle or free air system. Note: Free-AirT is a trademark of Stillwater Designs (Kicker) In this system the woofer has the front of its cone isolated from the back of its cone by mounting the woofer to the rear deck or on a board placed across the back of the rear seat.
Advantages of this design include simplicity, minimal occupation of space and lower cost due to not having to have a box type enclosure.
Disadvantages of this design are a larger power requirement, difficulty (sometimes extreme) in completely isolating the two sides of the cone from each other, and slightly less accurate sound reproduction.
 |
| Sealed Enclosure |
The simplest box type system is a sealed enclosure. Here a woofer is mounted in a completely sealed box that isolates the front and rear waves of the woofer.
Advantages of the sealed design include ease of assembly, more lenient box size requirements, excellent transient characteristics, high power handling, and a typically smaller enclosure.
Disadvantages are less efficiency (requires more amplifier power) than vented enclosures and less low bass as compared to a properly tuned vented enclosures above the port tuning frequency.
 |
| Ported (Vented) Enclosure |
Vented enclosures are similar to a sealed enclosure in design except that they add a “port” that is a certain length and a certain area around. This port, usually a length of PVC pipe, is tuned to a certain frequency by variation in the two parameters of area and length. By adding this port, the rear wave of the cone motion is used to reinforce the front wave. When done properly the subwoofer system becomes more efficient than a comparable sealed enclosure above the port's tuning frequency. However, below the port tuning frequency the woofer will become unstable and "unload" causing the woofer to oscillate violently, leading to premature woofer failure when driven with excessive power.
Advantages of this design are increased efficiency and a lower frequency extension above the port tuning frequency.
Disadvantages are a more complex design, a larger enclosure as compared to a sealed design, lower power handling, and slightly less transient accuracy.
 |
| Single Reflex Bandpass (4th order) Enclosure |
The most complex design of the common enclosures is a band pass system. The purpose of the band pass system is increased efficiency over a small range of frequencies. This design also helps filter out unwanted midbass and upper frequencies. There are variations on the band pass design known as orders. The simplest design is the single reflex (4th order) in which a woofer in a sealed enclosure fires into a vented enclosure.
 |
 |
| Dual Reflex Bandpass (6th order) Enclosure |
Series Tuned Dual Reflex Bandpass Enclosure |
There are also dual reflex designs (6th order) in which both enclosures are vented and series tuned designs in which the woofer and first vent fires into the second vented enclosure.
Advantages of this design are a high efficiency over a small range of frequencies and some filtering characteristics.
Disadvantages are decreased frequency response, less accurate reproduction, extreme complexity in design and assembly, larger enclosure size, greater woofer unloading and decreased power handling.
 |
| Isobaric Loading |
Another enclosure design that you may hear of is isobaric. Isobaric is not actually an enclosure type but a woofer loading method. Isobaric loading can be used in conjunction with any of the enclosure types, except perhaps infinite baffle. Isobaric loading consists of two woofers coupled together by a short enclosure which is only long enough to prevent the two woofers from striking one another. The woofers may be mounted face to face, back to back or front to back. It is important however to have the woofers firing in phase with one another. In order to accomplish this with the woofers firing front to front or back to back one of the woofers speaker leads must be reversed with respect to the other woofer.
Isobaric loading is usually used when space is at a minimum or a maximum number of woofers wish to be used in a certain volume of space. By isobarically loading the woofers, a box of only half the size of a one woofer box is needed. For example, if a 12" woofer requires a two cubic foot box, the same 12" woofer isobarically loaded only requires a one cubic foot box. The cost of this design, other than doubling the woofer cost, is a reduction in the subwoofer system efficiency by three decibels (if both woofers are given the same power as a single woofer), which is equivalent to halving the amplifier power. New, small box subwoofer designs have all but negated the need for isobaric loading in car audio and it has fallen out of popularity.
Advantages of this design are increased linearity in the speaker movement, lower space requirements, and increased power handling.
Disadvantages are increased cost, increased design and assembly complexity, and decreased efficiency.
So which is right for you? For the vast majority of consumers, especially do-it-yourselfers, the sealed box is the way to go. Simple to design and build, forgiving of less than optimal airspace and smaller enclosure requirements make them a good choice for almost any system.
Material and Coverings
Enclosures are most often built of MDF (medium density fiberboard) or particle board. I personally recommend using MDF as it is much stronger and doesn't chip like particle board. MDF should be available at most lumber yards and home improvement centers (Home Depot, Lowes, Eagle, etc.). Expect to pay between $15-20 for a 4'x8' sheet depending on thickness. The larger the enclosure and the more power it will see, the thicker the wood needs to be. Small enclosures may get away with 1/2" thickness but I would always use at least 5/8" or 3/4" stock. It's the most readily available and can be used for most enclosures.
There has been a surge in the popularity of enclosures based on fiberglass due to their strength and light weight. They can also be molded to the contours of your vehicle which maximizes available space. Creative installers can also design custom shapes and designs in the medium which can make for a real show stopping vehicle. You may want to find a competent installer to build a fiberglass subwoofer enclosure if weight is an issue for you. If you want to build your own fiberglass projects then I'd recommend looking at the fiberglass video available here.
Enclosures can be covered in box carpet which is similar to the material used to line most trunks. Many colors are available to match the color theme of your vehicle. Expect to pay about $5/yard. Popular coverings for fiberglass enclosures are carpet, vinyl and paint. Vinyl is more expensive then carpet but has a better look. Your enclosure will need to be finished to a smooth surface prior to application or imperfections will show through the vinyl. Paint is even more expensive and should only be attempted by a qualified person. The surface needs to be absolutely flawless or the imperfections will be seen in the painted finish. Even more so than in the vinyl wrapped enclosures. Expect $10+/yard for vinyl depending on the quality you use. Paint varies widely in the type used and the quality of the finish.
 |
Box Carpet Samples |
Size Matters
There's an old saying among hot rodders. "There's no replacement for displacement" meaning there's no substitute for an engine's cubic inches. The same is true for subwoofers except we're dealing with square inches of cone area rather than cubic inches of engine displacement. Subwoofers produce bass by moving large volumes of air. It makes sense then that a larger diameter speaker is going to be able to move more air than a smaller diameter speaker. This is why you will see the larger 15" woofers used in high powered boom cars. But just like a large engine needs more fuel, a large subwoofer needs more power. Expect to need the following as a minimum guideline to power subwoofers effectively.
Subwoofer Size |
Recommended Minimum Power |
8" |
50 watts |
10" |
75 watts |
12" |
100 watts |
15" |
150 watts |
18" |
250 watts |
How Much Space Do You Have
This is something that should be determined in the system planning. How much space do you have and how much of it are you willing to give up for your subwoofer system? Two 15's aren't going to fit in a Fiero no matter how hard you try. Know your vehicle's limitations and work around them by choosing the right enclosure type and subwoofer size. If you can't fit the size subwoofer you want then choose a smaller size and give it more power to help overcome the smaller cone area.
Location and Placement
 |
Subwoofers are large and their enclosures are even larger. So where are you going to put this thing? For most cars this is going to be the trunk. For hatchbacks it's going to be against the back seat or in the far corners of the hatch. Regular cab pickups will have to go behind the front seat while extended cab pickups can sometimes be fit under the rear seats such as in the JL Audio StealthBox pictured here. Minivans and SUVs can use the cargo area for a standard enclosure or a custom fit enclosure such as the StealthBox can often be used. Ask your dealer for available options. Also take into consideration where the best place in the vehicle to maximize the output of the subwoofer. This is covered in the chapter on cabin gain.
No matter what location you choose, make sure your enclosure is securely mounted. This is especially true for vehicles such as hatchbacks, SUVs, minivans and other vehicles where the subwoofer shares space with the occupants. If you were to get in a crash with an unsecured subwoofer the consequences could be fatal. While your forward motion might be stopped by your seatbelt and airbag the momentum of the subwoofer enclosure would continue forward, stopping only when it strikes a stationary object such as a passenger. With the weight of the enclosure and the speed of the vehicle this force could easily decapitate a human. Ensure you or your installer secures the subwoofer system to prevent this from happening.
Buy or Build
As with anything there are pros and cons to buying and building. Buying a pre-built enclosure is a no-brainer. Just write a check and walk out with an enclosure. But is it the right kind of enclosure for your woofer? If you buy an enclosure from a manufacturer with the subwoofer already installed then it might be. But be careful of the pre-built BYOW (bring your own woofer) enclosures. Woofers should not just be thrown into any enclosure that they'll fit into. This is especially true of the ported and bandpass enclosures. Serious sound problems can arise if a vented enclosure isn't made for a specific woofer. There's no guesstimating with these types.
Another problem with the pre-built enclosures is their one size fits all shape. They may not physically fit where they would give the most output. From my own test with enclosure placement I have found that some locations outperform other locations in the vehicle by as much as twelve decibels. That's the equivalent of increasing your amplifier power by a factor of SIXTEEN (100 watts to 1,600 watts)! So while you may save some money by choosing a generic enclosure you could be losing out on some serious output.
The option I prefer is to create a custom enclosure for the exact vehicle, woofer and sound desired. This gives me free reign over the entire design and let's me choose the best location for the enclosure. It also let's me choose the shape, enclosure covering and hardware that works with the cosmetics of the vehicle. No more dark gray carpeting in a light tan interior.
The cost is less than that of pre-built enclosure and you have the option of customizing the appearance. There's also a lot more satisfaction in doing it yourself too. Of course not everyone enjoys DIY projects but if you do it's a great way to spend an afternoon. Custom enclosure construction is covered in both the basic installation video and the advanced enclosure video.
Subwoofer Enclosure Software
If you would like to design your own subwoofer boxes then you'll want to use a software based design program. There are quite a few different enclosure design software programs out there. The prices range from free to $1,000+. For most designs that the novice box builder will attempt there are a few free ones I could recommend:
Blaubox - Blaubox has been around forever it seems. Provided by Blaupunkt, it's a DOS program and is very easy to use. It's free and definitely worth checking out.
WinISD - WinISD is made available by LinearTeam. It's a very highly rated, free program. Definitely worth checking out. The tone generator is a nice addition. It lets you hear what different frequencies sound like.
MacSpeakerz - For the Macintosh users without a PC emulator there is a program out called MacSpeakerz. I haven't used it personally but it's fairly popular. Provided by TrueAudio
Videos
Car Stereo Installation
Car Alarm Installation
Advanced Enclosures
Fiberglass Fabrication
Fiberglass Fabrication II
School's Out Special
Car Audio Background
What is Sound
Cabin Gain
Kick Panels
Ohm's Law
Electronic Components
Electrical System Upgrades
Car Audio Equipment Info
Car Audio Head Units
CD Changers and MP3
Car Audio Speakers
Choosing a Subwoofer
Car Audio Amplifiers
Signal Processors
Mobile Video
Satellite and Digital Radio
Wiring and Power
Power Capacitors
Security Systems
Exotic Components
Car Audio Planning and Buying
System Planning
What Fits Your Car
Budget Systems
Sample Systems
OEM Upgrades
Spotting Good Equipment
Equipment Reviews
Where to Buy New
Tips for Buying New
Get the Best Retail Deal
Free Installation
Common Scams
Avoiding Bait and Switch
Mail Fraud Laws
Where to Buy Used
Tips for Buying Used
More Than You Can Afford
Buying Wholesale
Selling Used Audio
Hidden Costs
Car Audio Installation
Choosing Installers
Installation Goodies
Installation Pictures
Installations You Can Do
Ten Car Audio Myths
Amplifier Installation
Capacitor Installation
Vehicle Wiring Diagrams
Noise Troubleshooting
Car Stereo Help
Become an Installer
Car Audio Care
Keeping Your Stereo Safe
Car Stereo Insurance
Making Your Stereo Last
Car Audio Warranties
Getting Free Repairs
Avoiding Noise Violations
Car Audio Safety
Car Audio Competitions
The Future of Car Audio
Equations
Contact
Terms of Use
Privacy Policy
