The Art of Buying A Subwoofer

Everything you need to know before buying a subwoofer.

When deciding to upgrade your audio system, adding a subwoofer can produce massive results. Adding volume at sub frequencies is like adding a third dimension to your music. Whether you’re considering building a new audio system, or just adding one (or more) subwoofers to your factory system, this addition will give you the single, most significant sonic improvement. Simply adding even a little bass will make a HUGE improvement.

I’ll never forget my first experience listening to the heart-pumping sound of bass. I was listening to my friend’s newly-installed system (he had a couple of 12’s with a decent size amps), and it was literally shocking how R-E-A-L it sounded, how you could actually feel the music. I was completely amazed that you could actually feel the impact of the woofers. From that moment on, I’ve been a car audio fanatic.

But, choosing a subwoofer can be confusing. There are a few questions that you should ask yourself before actually running out and buying woofers.

What type of sound are you looking for?
There are two main camps in the sound world: Sound Quality (SQ) or Sound Pressure Level (SPL).

Sound Quality refers to just that — a very linear response that’s not boomy and is very controlled, especially when listening to complex software. An SQ System generally uses a smaller woofer and requires a smaller enclosure. A sealed enclosure would typically work best for this application.

SPL, on the other hand, is for you “Big Bass Lovers.” If you’re like me, and like a lot of impact with your music (extended bass response and 3 dB more efficient gain), then you’re probably looking for a ported enclosure.

Sealed enclosures are also known as “Acoustic Suspension” enclosures. When a speaker is placed in a sealed enclosure, the pressure becomes trapped in the box and restricts the cone movement, so the air inside the enclosure acts as a spring. The smaller the enclosure, the more pressure is exerted against the cone under movement. With a sealed enclosure of predetermined volume, we can also predict the cut-off frequency and Q* of the system.

Sealed enclosures will also forgive minor mistakes in design (up to 10 percent), without major effects on sonic performance.

The real advantage is that they just consume less space, not to mention they’re easier to design and construct. Choosing a sealed enclosure will give you clean and accurate bass with good low-end extension.

Ported enclosures are very similar to a sealed enclosure in construction, but feature an additional opening for an attached port. This allows the rear-radiated energy to be phase inverted (matched in time) and to become in phase with the energy from the front of the speaker cone, essentially doubling the effective cone area.

The main drawback with a ported enclosure is that the design and construction are not very forgiving of errors. Unlike a sealed box, you must determine a number of different parameters: the box volume, tuned frequency, port area, and port length. But, the advantage is huge — you’ll get more output with the same number and size of woofers.

However, with all of that extra output there’s always a trade off. More bass naturally means more space. Generally speaking, ported enclosures will be to be 30- to 40-percent larger than a sealed enclosure.

You’re probably thinking, can a ported enclosure sound as good a sealed enclosure? The answer is, yes, but it’s different in that it will have a slight peak around the tuning frequency (35 Hz) and roll off very quickly. Both types of enclosures have true supporters. What you use really boils down to your application and how they load in your vehicle.

How much space are you willing to give up?
Now, that you’ve determined your music tastes, you’ll need to decide which one of the enclosures will fit your needs and your vehicle. Let’s review: A) Sealed: Clean, accurate, with a smooth roll off and small to medium sized enclosure or B) Ported: Very efficient, extended output (plays loud), and requires a medium to large enclosure. The decision is yours, but keep in mind that weight and space are at premium in vehicles over the past few years, particularly with the tuner crowd and their traditionally smaller vehicles.

Before you make your purchase, it’s also a good idea to find out how much air space and what type of enclosure is required for your dream woofers. Most manufacturers will have both specifications for sealed and ported applications. This information can be found several ways: through your local dealer, via the Internet, or by calling the manufacturer’s technical department. When in doubt, ask your dealer to help you determine the best woofer(s) for your application.

How much money should you spend?
This can be somewhat subjective. Many believe that the more you spend, the more bass you’ll get. There definitely is some truth to that, but I found that a lot of people get hung up on specs that really don’t matter. For example, I wouldn’t buy a woofer strictly based on its peak power handling capability, or by trying to match an amplifier’s output power to a speaker input power.

Here are three key subwoofer specs to look for:

Fs: The frequency at which the woofer naturally likes to resonate (like a tuning fork). The lower the Fs, the lower the driver will play naturally.

X-MAX: The amount of voice coil windings that overhang the top plate of the magnet assembly. This shouldn’t be confused with excursion — they’re two different measurements that go hand-in-hand. In most applications, the larger the number the better. Think of it this way: Woofers behave like giant air pistons; the more the pistons move, the more SPL you’ll create.

BL: The “BL” product is a measurement of the force (power) generated by the speakers’ motor. The more “BL” product, the more control the woofer will have over the cone.

Does the installation matter?
Absolutely. In a home system installation, where the installation is essentially plug-and-play, installation accounts for a very small percentage of the sound quality and is pretty hard to screw it up. Most home receivers have everything built into one unit and the engineers have taken most of the guesswork out. There’s no level matching between components and definitely no subwoofer enclosure building. In a vehicle, it’s much different — the installation takes a lot more finesse and accounts for about 80 percent of the success of how the system will sound. This is why it’s so important to spend the time and money on how it’s put together.

In fact, the installation is more import than the product itself. Think of it this way: If you build a house with a poor foundation, the house will always have a poor foundation and will never be able to support the house. If you’re installing it yourself, or if you’re going to have your local shop put it in, do a little homework and it’ll go a long way. Make sure you calculate the correct volume for your enclosure and use good quality materials like MDF or Fiberglass.

Should you be concerned about safety?
Safety is one of the most overlooked things in car audio. I’m specifically talking about mounting subwoofer enclosures — they generally just don’t get mounted to the vehicle. Can you imagine getting into an accident and having a 75-pound box fly through your car? Recently, several people have been killed because of this unnecessary tragedy — it really is serious. My advice: bolt your bumps down...

If you follow these tips, you too can reap the rewards of Great Bass.