Subjective
Story by: Mike Frost
The four subwoofers in this month's comparison were mounted in sealed MDF enclosures. The volume of each box was chosen to yield a Qts of around 0.8. It's important to have similar Q values in a comparison test of this type.
In-car frequency response curves were measured using LinearX Systems' pcRTA 1/3 octave real time analyzer. Pink noise was provided by an IASCA competition CD, and the woofers were running full-range with no crossover. All in-car tests were made in a Plymouth Grand Voyager minivan, with the speakers at the rear of the vehicle and the calibrated microphone in the drivers' seat at ear level.
A set of high-resolution measurements was also taken, both inside and outside the vehicle, with the LMS analyzer in order to generate a vehicle transfer function curve. Using the post-processing features in LMS, the measured curves were first smoothed to 1/3 octave. Then the in-car curves were divided by the free-field curves to derive four transfer function curves. These four curves were then averaged into a single curve to create the transfer function graph shown. This is the change introduced by the environment inside the car. Keep in mind that this transfer function would change if you decreased or increased the cone area of the woofer(s).
For the subjective sound quality scoring, the woofers were powered with an amp that produces 250 watts per channel into a 4-ohm load. The dual voice coil units were connected in stereo, and the single voice coil unit was connected to one channel with the left and right inputs summed. A 24 dB per octave crossover set to 100 Hz was utilized.
Source material for the testing included the following:
Tonal Balance:
Track 5 of the 1997 IASCA competition CD - "The Vikings"
Low Frequency Extension / Impact:
Track 2 of Radiohead's "Kid A" - "Kid A"
Clarity at Low / High Volume:
Track 14 of Tool's "Aenima" - "Aenema"
Overall Sound Quality:
Various tracks of Steely Dan's "Two Against Nature"
Crossfire BMF W12D
Engineering is all about making trade-offs. When you get just the right balance of all of the factors, you get a speaker like this. If I had to choose which of these four woofers to take with me to a desert island, it would be the W12D.
Hollywood Sound Labs XPRO12
If you play your music loud, and like to go heavy on the bass, this is the woofer for you. I felt a bit of overhang in this one, but it works great with very low synthesized tones. It has a sound that I like to refer to as "round."
Poweramper XP12D
For accuracy and tonal balance, you should consider this speaker. While it didn't do as well at higher levels as the others, it can't be beat for its ability to cover the lower spectrum evenly and smoothly. A great choice for those more concerned with reproduction of the original recording than with monster bass.
Soundstream SPL Mule
This speaker is, as the name implies, a workhorse in the SPL category. It loves to play low and loud. As with everything in life, you have to give a little here to gain a little there. In this case, you sacrifice a bit of accuracy for the ability to generate higher SPL. With a single voice coil and 0.25" Faston terminals for the speaker wires, quick-change operations will be easier in that monster SPL vehicle with 24 gazillion woofers.
For SPL and in-car sensitivity testing, an AC-powered amplifier was used to avoid the power fluctuations of a typical vehicle. The amplifier produces 500 watts per channel into 4 ohms. The DVC units were connected in stereo, while the SVC unit was connected to one output channel. In this case, the stimulus signal was a swept sine wave feeding both inputs of the amplifier. For the SPL tests, the acoustic energy was measured with pcRTA and the M52 high SPL microphone. A linear time averaging of 0.1 seconds was chosen, with the meter set to Peak Hold. For sensitivity testing, the LMS was used to take a sweep from 1 kHz to 10 Hz, and the data was then smoothed to 1/3 octave.
Conclusion
All of these speakers are great performers, with some having specific strengths and weaknesses. The Crossfire W12D wins hands down in the Overall Sound Quality category, and holds its own in the other scoring areas. The Soundstream SPL Mule is the loudest of the bunch, and takes the title of Best SPL Woofer in this shootout. Hollywood's XPRO12 has the best balance between high SPL and sound quality, and the Poweramper XP12D has the smoothest frequency response. You will have to choose the tool you want based on your preferences and application.
View the following reviews:
Objective by: Vance Dickason
Subjective by: Mike Frost