Deciding on which subwoofer you want to buy is becoming an increasingly difficult task. Not only is there a seemingly countless number of manufacturers to look at, each company has perhaps four, five lines of subwoofers to choose from. Moreover, there's a lot of marketing hype you need to decipher, to figure out what's valid or not. This process of doing a subwoofer comparison test has shown us more clearly the challenges faced by consumers in this segment of the car audio market. Some of the criteria we had that seemed legitimate enough at the start turned out not to be quite as significant (see below the point system we employed). Lost in our theories on what makes for a great subwoofer we failed to consider that most essential consideration: price. That is why we've started off this test with the "budget" woofers (Look for the next price group in an upcoming issue.) Because that's what readers want to know: what is the best speaker that they can afford. In the end, all of the above is an extended way to say that our readers will benefit from the process we went through to put this together. That being said, there are some general rules you can follow when choosing a subwoofer. Start by picking a speaker according to the music that you listen to the most. For instance you don't want a sound quality woofer if you listen to hip-hop or rap; or, you're not going to go for SPL if you listen to jazz or classical recordings all the time. If you want the loud drown-out sound of the boom flowing out of your vehicle, be sure to make a point of that as you talk to your retailer. The more specific you are with the salesperson, the better your chances of that retailer selling you the product you actually want, not the one that is going to make him the most profit. Always listen to the subwoofer you are about to purchase. And keep in mind that it doesn't mean the speaker you're buying is the best for you just because it's the most expensive or has flashy cosmetics.
Guidelines for Testing
Objective section
Enclosure size
Given the fact that we are discussing car audio, space is a large factor to consider. There are not many people who can honestly give an entire trunk of their vehicle for an enclosure. For that reason, it is only right that we award points for it. However, what those points mean to consumers with different kinds of applications is up to them to determine. The point system in this test is applied to an enclosure volume that equals a "Q" of 0.8. This same enclosure will be made use of throughout the majority of tests performed within this article. Given this, a maximum of 15 points may be awarded to each woofer per the enclosure volume recommended.
SPL ( in lab)
SPL is a term that most audio consumers are familiar with these days. The simple fact that a loud system draws attention generates interest in SPL. For those of you unfamiliar with the initials, this stands for Sound Pressure Level. This is the measurement of sound volume (acoustical energy). The in-lab measurements for SPL are actually LEAP Software generated outputs. These outputs are derived using the Theil/Small measurements as shown in the Data Comparison Chart. Even though they are not actual test numbers, we have come to respect the accuracy of the LEAP system. Top honors will take home five points and leave second a point behind.
SPL (in car)
Subwoofers can perform noticeably different in a vehicle than they do in the lab. As well, the same sub will also vary performance from one type of vehicle to the next. Our test vehicle was a minivan, a Plymouth Grand Voyager, so keep that in mind. In-car SPL measurements were taken at a two meter distance using a sine sweep starting at 1 KHz and falling to 10 Hz. The peak output is then taken from the data and referred to as the max SPL. Based on this peak amplitude, a maximum of ten points is given.
Xmax
Xmax is one of the most misconceived measurements in the industry. Yet, this is one of the easiest of the measurements to calculate. Xmax is simply how much the voice coil overhangs, top or bottom (these are normally the same), the top-plate of the motor structure when the speaker is at rest. This number by itself has no real useful meaning and really cannot be compared against other woofers. In many cases, subwoofers with shorter xmax can produce higher max SPL and greater dynamic range. So we'll just chalk this up to bonus points by doubling the length in inches.
Subjective section
Tonal balance
Take into consideration that a typical subwoofer has an expected useable frequency response of 20 Hz to 120 Hz. Obviously, this is what one expects from a woofer. But how smooth will the response be over the entire bandwidth? This is how we apply tonal balance. Tonal balance points are based on how flat the response of the subwoofer in its enclosure is over the given 20 Hz to 120 Hz frequency range. Maximum of 10 pts.
Low frequency extension
Most subwoofers can play down into the 10 to 30 Hz range, but how well, or should I say "loud" can they play it? Up to ten points can be awarded in this category in respect to how much earth shaking, low frequencies these subs can muster up.
Clarity at high volume
Given moderate volumes, distortion can rise quickly with subwoofers. And, with every subwoofer comes a new threshold for audible distortion. A maximum of ten points is achievable for clarity at high volumes. Each of the subs in this test was analyzed at the same volume level to note their abilities and will be subjectively awarded points based on the performance.
Clarity at low volume
Distortion may not be a factor when you listen for clarity at low levels, but low frequency response may suffer for various design reasons. Different design philosophies can vary the low volume frequency response in terms of attack and output levels. Upwards of ten points may be awarded subjectively to those whose clarity maintained a respectable balance as well as accurate dynamics.
Impact
Attack and decay. These are the primary aspects of impact; the time it takes for sound to build up or die down. This subjective measurement is based on quickness of both attack and decay with respect to the recording. However, this subjective test may not be of interest to you if large, boomy bass is what you desire. Take it for what it is, but the results will be based on the quickness and accuracy on a ten-point scale.
Overall sound quality
Take all of the other subjective measurements together -- viola! Sound quality! Okay, maybe it's not that easy, but the essentials are all there. For overall sound quality, all aspects of performance come to play as one. The result could be better or far worse than any one of the other subjective measurements. Given the importance of this listening test, it carries a lofty 50 points. Let's hope our contributing editors weren't out drinking the night before.
View the following reviews:
Objective by: Vance Dickason
Subjective by: Mike Frost