Objective
Story by: Vance Dickason Priced between $270-$300 these four woofers would have been considered moderate to high priced a mere five years ago; but given the fact that we now have 12" subs that cost in the vicinity of a kilobuck ($1000 to you non techy types), $300 doesn't seem so expensive. The subs submitted for the comparison test were the Crossfire BMF W12D, the Hollywood Sound Labs XPRO12, the Poweramper XP23D and the Soundstream SPL Mule.
While the prices were pretty close for all four subs, there are some specific differences between this group. First, three of these woofers, the Crossfire, HSL and Poweramper, were dual voice coil types while the Soundstream SPL Mule uses a single voice coil. All four woofers were primarily intended for sealed box use; however two of them, the Crossfire and HSL, can be mounted in a fairly small enclosure while the Poweramper and Soundstream subs required larger box volumes for the same level of damping.
Testing was carried out as on previous subwoofer tests. The LinearX LMS analyzer (using the new Windows software) was used along with the LinearX VIBox to produce separate voltage and current curves (also called admittance curves) in a limited frequency range from 10 Hz-10 kHz. These two curves were then divided (V/I=Z) to produce high-resolution impedance curves. This data was then imported into the LinearX LEAP software (a Windows version of LEAP is due out in a few months also). Once loaded into LEAP, box simulations were created at 2.83V, and at a voltage level high enough to produce cone excursion that was equal to the Xmax of the voice coil plus about 15%. This technique defines the linear operating envelope of the driver. While this may sound complicated, all it means is that this information answers the question of approximately how loud the woofer will get before it starts creating noticeable distortion.
Crossfire BMF W12D
Crossfire has been designing car audio loudspeakers for over five years. The model submitted for this comparison was the BMF W12D; that is one of three models in Crossfire's top-of-the-line BMF subwoofers lineup (I'm guessing B stands for "Bad", and MF, well, you can add that yourself). Like the other two woofers in the BMF series, the W12D is built on a silver painted caste aluminum frame. This is a well-conceived frame and is used by a number of different manufacturers, including Poweramper in their Model XP12D that is also included in this test. The most important part of a frame, besides holding the motor and cone assembly together, is to provide sufficient room for rearward travel of the spider so that it doesn't hit the rear of the frame on long excursions. In the case of the Crossfire W12D, the frame has a reasonable 23.8 mm (15/16") of available travel for the spider.
Powering the W12D are dual stacked ferrite magnets, joined to the frame using a shaped T-yoke (this includes a "bumpout" for longer rearward excursion) and front plate. Both T-yoke and front plate have a black emissive coating that enhances heat dissipation (black objects radiate heat more efficiently). A black rubber "boot" covers the twin stacked magnets and also enhances cooling via the same black body radiation effect. Other details for this motor system include a 13 mm extended pole that improves the symmetry of the magnetic fringe field on the top side of the motor and also helps guide the voice coil back into its channel on excessively long strokes that take the voice coil completely out of the gap area. The pole piece includes a 1.25" diameter vent to further enhance cooling.
This is a dual voice coil woofer and has two 2-layer voice coils wound on a 2.5" Apical former (this is a high temperature plastic type material designed for loudspeaker voice coils). The voice coil lead wires are terminated with two pairs of chrome-plated spring loaded push terminals located on opposite sides of the frame.
The W12D's cone assembly starts with a stiff mica filled polypropylene cone that has a 4" diameter hard poly dustcap with the usual silk-screened logo. For rear mounting the W12D has a closed-cell foam gasket. Connecting the outside diameter of the poly cone to the frame is a Nipol rubber surround that has a moderate 20 mm width and 12 mm height. A flat 6.75" diameter laminated cotton/Nomex linear type spider provides the remaining compliance for the W12D.
Lastly, the folks at Crossfire have posted a high SPL warning on the W12D carton (not visible until you open the box) and another warning message in their manual that encourages users to be smart and not endanger their heart or their hearing with long term exposure to high SPL. It's hard to enjoy music when you're deaf and your heart stops!
Hollywood Sound Labs XPRO12
HSL has been building car audio speakers since 1987 and besides producing their own brand of products, have also supplied woofers to a number of other well-known manufacturers. The company builds most of its own woofers and also has partnership ties with speaker factories in Taiwan and China (a majority of car speakers are produced in Asia, Brazil, India and the Philippines). HSL submitted their new XPRO12 for this review comparison.
Hollywood Sound Labs started the design of the latest entry into their eXcursion series of long stroke subwoofers, the XPRO12, with a new frame. One of the obvious problems with some of the ultra wide surround subwoofers is that while the wide surrounds provide longer mechanical excursion, the extra surround width also decrease the size of the cone for a given frame size. When the cone size goes down, it takes more excursion to produce the same amount of bass at a given frequency, so it's a "double edged sword" of sorts. HSL's answer to this dilemma was to use a slightly larger than standard 12" frame with a wider mounting flange that would accommodate a somewhat wider surround, but keep the cone diameter from having to be decreased. Painted with a black wrinkle finish, the new frame also provides 31.75 mm (1.25") of rearward travel for the spider. HSL also cast in a series of small fins near the motor area that should provide some cooling benefit.
Like all the woofers in this comparison, the HSL XPRO12 uses a dual stacked ferrite motor assembly along with their patented MAFOS shaped T-yoke with integrated "bumpout". Both the MAFOS T-yoke and front plate have the same black emissive coating for improved heat dissipation. Another interesting feature of the MAFOS T-yoke is that it is has a channel cut into the rear of the T-yoke that accommodates further rearward travel of the voice coil insuring that the unit will not mechanically bottom (the voice coil cannot move far enough to the rear of the motor assembly to actually come in contact with the backplate). The pole piece of the MAFOS assembly incorporates an 8 mm extended height above the front plate and a 7/8" diameter pole vent for cooling. Finishing off the motor assembly is a black rubber "boot" covering the dual stacked magnets.
Driving the cone assembly is a dual voice coil wound on a Kapton former (a high temperature plastic used for voice coils). Each of the two-layer coils is terminated to a pair of silver 5-way binding posts located on opposite sides of the frame.
HSL uses a composite Kevlar/pulp blend that produces a stiff paper type cone assembly that has a shiny black appearance. This includes a 5" diameter 3D-molded dustcap. Connecting the outside diameter of the cone to the frame is a foam surround that measures 27 mm wide and 15 mm high and is described by HSL as their patented DWS (Double Wide Surround) system. Again, their idea is to make the surround taller and the frame wider to get the required mechanical excursion without decreasing the cone diameter appreciably. Remaining compliance for this woofer is provided by a flat 6.5" diameter black treated polyester/cotton blend linear type spider. For increased travel on this frame, HSL mounts the spider on a high plastic riser.
Like Crossfire, HSL has a high SPL warning printed on their carton. I'm not certain that this acts so much as a warning than as a marketing tool. After all, if you're putting together a system that you hope will get realistically loud, choosing a woofer that has a warning against hearing damage ought to do the trick! Seriously, I'm glad more companies are starting to help increase user awareness of long-term hearing loss from excessively high SPLs.
Poweramper XP12D
Poweramper is a relatively new company; it began in the car audio OEM manufacturing business in 1993 and changed to doing its own product line in 1996. The company introduced its first series of car audio speaker products last year.
Poweramper's XP12S is built on a black painted cast aluminum frame. While I've seen this frame used by a number of woofer manufacturers (such as the Crossfire woofer in this comparison review), it is well designed and has a very reasonable 23.8 mm (15/16") of rearward travel available below the spider mounting flange.
Dual stacked ferrite magnets fitted to a forged and shaped T-yoke/bumpout assembly provides the "Horsepower" for the XP12D. Both T-yoke and front plate have a natural finish and are not coated or painted. Motor features include a 3/8" extended pole piece to increase the fringe field symmetry above the front plate, increase the cooling potential of the motor system and also as a guide to the voice coil on extremely long excursions. The pole piece also incorporates a 7/8" diameter pole vent for additional cooling of the voice coil assembly.
As with many of today's high powered subwoofers, Poweramper uses a high temperature Kapton voice coil former for the 2.5" diameter voice coil. The XP12D is a dual voice coil woofer and has two 2-layer voice coils wound onto the former that are terminated to gold plated 5-way binding posts located on opposite sides of the frame.
The cone assembly on the XP12D is rather different from the other products in this comparison. The largest difference is the use of a single piece magnesium cone that does not require a dustcap. Elimination of the dustcap is its primary advantage. Although most manufacturers have solved the problem, long throw woofers working into very small sealed enclosures produce very high pneumatic pressures on the dustcap that in some instances can cause the cap to separate from the cone. The single piece cone avoids this problem altogether. Being a metal cone, Poweramper was also able to anodize the cone a very attractive deep blue to which they added a white logo. This cone is actually more of a composite as it has a 6" diameter paper cone sleeve on the underside to provide additional stiffness. Connecting this cone to the frame is a very large foam surround that measures 40 mm wide and 32 mm high and also extends the connection point to below the frame mounting flange. A 6.75" flat double layer progressive spider made from a composite cotton material supplies the rest of the compliance for this woofer.
Soundstream SPL Mule
Soundstream Technologies has been in car audio since 1984, which makes it sort of an "old timer" among car audio companies. Last year Soundstream was acquired by Matt Coleman Enterprises which also owns Escort, Bel-tronics, Audio Product Incorporated and Clearlink Communications. The addition of Soundstream Technologies pushed the combined sales of this corporate group to over $100 million.
Introduced in 1998, the Soundstream SPL Mule series of car subwoofers has been field proven for going on three years. Unlike the other three woofers in this comparison, the SPL Mule is built on a silver painted heavy steel stamped frame as opposed to a cast aluminum frame. This frame was designed for long rearward excursion and has 38.1 mm between the spider mounting flange and the rear of the frame.
Soundstream employed a dual stacked ferrite magnet motor for the SPL Mule that incorporates a T-yoke backplate/pole assembly. Both T-yoke and front plate have a black emissive coating to increase cooling. Also unlike the other woofers in this comparison, the SPL does not use a rear "bumpout." However, Soundstream does use a very interesting device that takes the shape of an aluminum ring spacer between the frontplate and the frame that also lines the gap area. Not only does this unique device wick serious amounts of heat away from the motor area; it also functions as a shorting ring that lowers harmonic distortion (although mostly out of the normal subwoofer bandwidth). An aluminum pole extension also provides for efficient voice coil cooling as well as the usual function of increasing the motor fringe field symmetry and acting as a voice coil guide. For additional cooling, the "Mule" also has a 15/16" diameter pole vent.
The cone assembly of the SPL Mule includes a stiff coated paper cone that is further stiffened by a very large 7" diameter flat hard poly dustcap with the SPL Mule "kicking ass" logo. A moderate sized polyether foam surround (22 mm wide and 12 mm high) connects the cone to the frame with the remaining compliance provided by a 7" diameter cotton progressive type spider. For rear mounting, the SPL Mule has a laser cut MDF gasket with a foam surface.
While the rest of the woofers in this comparison all have dual voice coils, Soundstreams SPL Mule is a single voice coil woofer. The 2.5" diameter voice coil is wound on a special red Kapton/epoxy former. The voice coil leads are connected to standard push on terminals that can use either terminal lugs or be soldered (my choice).
Overview and Conclusion
In terms of objective performance it's a little hard to actually compare all four of these woofers. The Crossfire and Hollywood woofers work into rather small enclosures and produce very high SPL numbers, but also roll off fairly high at the low frequency end of the spectrum. The Poweramper and Soundstream woofers need bigger boxes and produce lower SPL numbers, but both yielded lower F3's. However, it's clear that all four of these woofers are capable of producing SPL levels with no noticeable distortion up to an incredibly loud minimum SPL of 110 dB. This means that with program material you could easily see 113-115 dB peaks and never notice any signs that the any of these woofers are nearing the limits of their performance. Years ago, I could tell people that when they hear distortion (when the music starts to sound fuzzy), they should lower the volume. With the cheap watts available today, clipping distortion is much less of a problem and with any one of the subs in this comparison; your ears will probably start distorting before the equipment, especially in installations with multiple subs.
Objective performance in woofers usually ends up being described in terms of trade-offs and this group is no exception. While each of the woofers represents a slightly different approach, all will achieve the desired objective goal of high SPL. Bear in mind as you look at the results (see "Objective Score Chart") based on the point system that a clear winner from the objective data is difficult to determine. All four products exhibited very good build quality and each has attributes and enhancements that ensure that, from the objective measurement point of view, they will each one do the job intended. However, none of this tells you anything about how they sound with music.
View the following reviews:
Objective by: Vance Dickason
Subjective by: Mike Frost