Alpine PLV-7 Subwoofer - Design Of The Times

When I first heard that Alpine Electronics was introducing a new line of amplified subwoofers I had to ask myself, "Does the world need one more over-priced, underpowered, over-dressed, blam-thud-bloom box?" Notice that I didn't say "boom box." That's because most all-in-one bass systems just don't deliver. At least not to my taste. Despite the reputation of the manufacturer, I was "under-whelmed" when first approached with this review.

Shortly after receiving the unit, I learned that the Alpine PLV-7 subwoofer system was designed specifically for use in an SUV, station wagon, minivan or similarly styled vehicles. Being a real-truck guy, I assumed I'd get out of testing this bloom box after all! Then I got a call from my CA&E boss saying that Alpine offered to lend us one of their SUVs for a week. "Hmm. An Alpine vehicle for a week."

As soon as I started my research I knew that the PLV-7 would be very different from anything in the category. Peering through the acrylic window of what appears to be a bandpass enclosure, all I could make out was some silver tube-like structure with three openings and no subwoofer in sight. Obviously, the PLV-7 is far from a run-of-the-mill-powered sub system. This thing is special, made up of a number of new and interesting concepts and technologies.

For this particular project, Alpine looked outside their corporate walls to a couple of highly regarded companies for components and design technology to execute the PLV-7. The confounding silver tube sitting behind the enclosure's acrylic panel is actually the sub; or rather, a revolutionary Linear Array Transducer (LAT) from the Tymphany Corporation. To make this unit work to Alpine's specs, Whise Automotive was contracted to aid in the design of an innovative enclosure called Ultra Reflex.

Tymphany' LAT is a dramatic departure from the conventional cone subwoofer. Your typical subwoofer displaces air across a single cone, but the Alpine LAT displaces air using a linear array of multiple smaller cones. It uses six cones lined up in a cylindrical shape, and a motor on each end. To create a balanced drive design one motor drives half of the cones, while the other motor drives the other half in opposition. Sound radiates through multiple flow ports along the side of the housing of the LAT. The entire woofer assembly measures just 7" in diameter by 18" long, allowing it to go into much shallower and narrower boxes than conventional drivers. Tymphany claims that it is the equivalent cone area of two 12" subwoofers and has a frequency range of 20 to 200Hz while using 30 percent less space (the outside dimensions of the enclosure are 23.2" x 13.3" x 13.2"). And after listening to it, I think they may be right.

Whise Automotive is an Australian company with extensive experience in a wide range of acoustics and system design. Their sister company, Precision Audio, has patented a process called Parametric Acoustic Modeling (PAM), which Whise has employed in creating their patent pending Ultra Reflex enclosure alignment. The Alpine PLV-7 Senior Engineer, Jason Kemmerer, was involved in working with Whise to perform extensive computer simulations to finalize the PLV-7's unique Ultra Reflex enclosure design. The computer simulations were used to show where internal pressures and flows within the enclosure were not optimal, and it allowed them to tune those patterns within the enclosure to improve impact response, lower distortion and extend the lowest frequency limits of the enclosure. And it does go low and get loud! If you flip ahead a little, you will see that the maximum output of this system was amazingly high at 134.4dB.

The final piece to this design trifecta is a 500-watt Alpine PDX amplifier. This is no fabricated power number, it represents real, hardcore, hi-tech RMS watts. Its basic architecture is the same as the standard high-speed switching PDX amps, but the PLV-7 also utilizes patented techniques for intelligent power processing and feedback control of the subwoofer cone - enabling tight control, high efficiency and low EMI not found in other switching amplifiers. Because it works directly with the LAT, it is able to maintain high control of the output response while maintaining good efficiency; the latter helps make for a smaller overall package.

InstallationThe PLV-7 comes ready to install in just about any system you would want to add it to. It's complete with traditional stereo RCA, low-level inputs and speaker-level balanced inputs. Having both types of inputs allows you to add the PLV-7 to your high-end aftermarket head unit or factory system. The input selector switch and "Auto ON" signal detection circuit help make the PLV-7 more installer friendly. With the remote bass level control knob, the Polarity (Phase) switch, its variable crossover (LPF 50Hz - 200 Hz @ 24dB/oct) and the Bass EQ, the PLV-7 is easily tuned to perform at it best.

I mentioned earlier that Alpine offered up an SUV for the test session. The vehicle, an Acura MDX, had a very competent system in it - done by Transonic in Upland, CA. It featured all Alpine products starting with the CDA-7995 head unit and an MRV-T420 amplifier running the front SPX-F17m 2-way component speakers in the doors. We ditched the normal subwoofer and amp in favor of the PLV-7 and its 500 watts in the rear cargo area.

Mounting the PLV-7 was very straightforward. Supplied mounting plates screw into the bottom of the enclosure before it's placed into the cargo area of your SUV. You will need to pull in a minimum of an 8-gauge power and ground wire for the 12-volt supply. In this installation we used the RCA inputs. We mounted the remote bass knob; set the crossover, polarity and level; and were ready to rock 'n' roll.

Interview:Jason KemmererManager/Senior Engineer, Product Planning Division,Alpine Electronics of America, Inc.

CA&E: The Alpine PLV subwoofer systems use a Tymphany Linear Array Transducer. Could you give us a brief description of a LAT and how it works?Jason Kemmerer: The LAT is significantly different from traditional loudspeaker construction in that it uses multiple smaller diaphragms in a "push-push" configuration through a series of rod connections to opposing motor structures. The primary advantage is the ability to squeeze an enormous amount of cone area into a small footprint with minimal depth, but also the inherent cancellation of vibration and distortion. This sounds easy enough, but actually making it work and deliver the performance was extremely complicated. Not only did it require extraordinary new materials and adhesives with massive amounts of tooling, but also a completely different approach to assembly and testing.

While the LAT subwoofer is certainly unique, what inspired you to make use of it in an Alpine product?Having already been acquainted with several of the engineers involved with the LAT through previous projects and contacts, I was fortunate to see it at the very early stages of concept and prototype. Although it was a bit difficult to imagine how it could actually be manufactured cost-effectively at the time, or if it was even possible to reach the kind of performance and durability levels necessary, I was very interested in the concept and saw huge potential. Sharing mutual interest and zeal for innovation, Tymphany likewise believed that Alpine could make excellent use of the technology in a customized platform. While Alpine has been advancing subwoofer design through development of new motor structures, suspensions, thermal management, materials, etc., it is mostly a matter of fine-tuning and pushing the limits of the traditional loudspeaker. This was something totally new with a unique set of challenges. Working closely with the engineers at Tymphany, we were able to optimize the design for this first practical application, specifically tailoring it to suit our design goals for the PLV/PLT systems and in-vehicle performance.

What challenges were involved in making the LAT work in the relatively compact listening environment of a car or SUV?Probably the biggest challenge was to manage the extreme volume displacement in a comparably tiny enclosure, while also achieving wide bandwidth and high output. Those things don't usually go together without some other major compromise. We get the inherent advantage of acoustic lift of lower frequencies in the vehicle, but the trick was to keep the size down and get it to couple to the cabin without major response problems. Achieving up-front bass is one of the holy grails for most car audio fanatics, so it was also paramount to optimize the design to a point to where the distortion was extremely low. While low bass should be non-directional, it's often the distortion of most systems that draws attention and gives away its position in the rear to the listener.

Why was the decision made to use Whise Automotive in the design of the enclosure over standard loudspeaker enclosure programs?How does the PLV-7 enclosure differ from standard designs? Actually, there were several major reasons, but primarily because Whise could offer something no one else could, a truly predictive computer modeling technique for very complex systems and a unique approach to enclosure design. Simply throwing driver parameters into a typical box program and hoping everything would work out is not the way we do things anyway, but the LAT was an altogether different animal. Having a lot of cone area in a small footprint would quickly become meaningless if the enclosure ended up being huge. In order to push the limits of small enclosure size while also striving for excellent transient response, low distortion and high SPL, it was clear that we needed to try something entirely different.

Utilizing Whise's Ultra Reflex alignment as a starting point, we set out to optimize the LAT's performance in what would eventually be nearly half of a traditional enclosure size for a driver of its relative parameters. This necessitated effectively driving down the system resonance with a front-loading chamber, while also dramatically cutting out distortion with an effective acoustic lowpass. The Ultra Reflex alignment could be considered to be an over-tuned bandpass, but with the distinct differences of having wide bandwidth, minimal group delay and a rising response. This poses some significant challenges to achieving an optimally flat response, requiring a lot of power and control where it counts (both motor structure and amplifier) as well as careful management of system resonances and velocities. PAM was used extensively to calculate the optimum changes in cross-sectional area as well as position and size of stubs (dead end chambers). In total, everything in loudspeaker or enclosure design is a series of tradeoffs, but achieving a balance that actually sounds great vs. looking good on paper is where the black art comes in ... we built a lot of prototypes.

The amplifiers in the PLV systems are quite unique. Could you explain to us some of the technologies integrated into the amp and how they benefit the overall system?Based upon our PDX amplifier platform, the system's amp is an intentionally band-limited variation, coupled with a stout regulated power supply and application-specific front end. Besides its inherent high efficiency, the PDX platform provides particular advantages for use in the PLV/PLT as part of a closed system. Since the load characteristics are already known, extensive use of advanced feedback techniques could be employed for amazing control, as well as optimizing efficient power delivery. System performance could be further enhanced through integrated signal shaping tailored to the application. Additionally, with the chassis as an integrated part of the total design and predetermined connections between driver and amp, radiated noise could be well controlled through intelligent patterning, filtration and shielding.

From an acoustical point of view, what was the most difficult aspect of the PLV designs? Bringing three distinct areas of new technology together into one coherent system at the same time was not easy. Since the LAT technology was still in the early stages when the project began, it was difficult to foresee the final construction and alignment until quite late in the game. We couldn't finalize the enclosure design until there were reasonably complete drivers and amplifiers to work with. To complicate things further, mid-stream changes to the LAT, amplifier and enclosure were all necessary for a variety of reasons, but tooling had to be locked down to maintain the schedule. Having multiple elements in a constant state of flux throughout the development made it particularly difficult to determine which was having the most effect on the final acoustic behavior and performance. When everything is interdependent, the key to success was to quickly narrow things down and then decide what to modify most effectively and efficiently.

ListeningInnovation is great, but how does the technology pay off? The PLV-7 didn't disappoint. It sounded pretty damned amazing, as a matter of fact. I listened to a lot of music with the Alpine PLV-7. I mean, it wasn't my vehicle, so I spent a great number of hours driving, listening and enjoying the ride.

JazzDiana KrallLove ScenesThe first impression I got from the PLV-7 was its impressive impact response. The stand-up string bass on Diana Krall's Love Scenes album was tight and punchy. The detail in the note shifts and string oscillation was brilliant. String plucks and the kick drum were taut and fast; and, when you cracked up the volume, shook your pant leg and shirt.Score: 8.5/10

Folk RockTracy Chapman"Heaven's Here On Earth"All of what I heard with Diana Krall was confirmed when I listened to Tracy Chapman's "Heaven's Here On Earth." The bass guitar, toms and the bass drum delivered tight, accurate reproduction of each musical phrase. The imaging of the bass was absolutely up front. There was no hint of the PLV-7 being mounted in the rear of the vehicle. The upper bass frequencies had no suggestion of blooming or a lack of control.Score: 7.5/10

Rap, Pop & R&BWith rap, pop and R&B, the PLV-7 pounded out massive bass. This is no dainty SQ sub. I began to think about the possibilities of using two or four of these things to wake up an entire city block. The PLV-7 can move from a drum machine bass line to acoustic bass without any problems. I played Eminem, Usher and Will Smith. Regardless of whether the bass line went up or down, the PLV-7 did not give up or cry out. Pretty amazing stuff.Score: 7/10

ClassicalTelarc's Schubert"Symphony No.9"Now for the most impressive part of the PLV-7 performance: My longtime mentor and friend Rob Green and I were both extremely impressed with how accurately the PLV-7 reproduced the lower frequency information on Telarc's 20-bit recording of Schubert's "Symphony No.9" and Sheffield Labs Improvisation drum tracks album. The huge Telarc bass drum was appropriately loose and floppy, while the tympani and Jim Keltners drum kit were tight and forceful. This was the area where I, as well as Rob, were the most impressed, hearing just how faithfully the Alpine PLV-7 was able to recreate the original sound of the recording.Score: 9/10

RockLenny KravitzLennyWhile playing "Believe in Me," the fifth track on the Lenny album, the PLV-7 stayed tight and had good articulation. The multi-layered bass-lines maintained distinct from one another. The bass drum and bass guitar overlap throughout the song and are plainly definable. The PLV-7 again reproduced these instruments with excellent impact and note delineation.Score: 8/10

ConclusionAlpine should be very proud of their achievement with the PLV-7. Their partnership with Whise Automotive and Tymphany Corp. has resulted in capturing lightning in a bottle... or would that be in an Ultra Reflex? Either way, this is an uncommon product that offers extremely low distortion and tremendously high output. It's a subwoofer system that's a must on your shopping list if you're a serious music lover or even if you're into the boom. The PLV-7 works for audio fanatics across the music spectrum. It's one of the rare combinations that can deliver it all.

Ratings: Average performance is equal to 1/2 total points possible.

Max SPL 134.4 dBSPL in car measurement at 2.83 volts, 1 meter with Bruel & Kjaer Type 2231 Level Meter set to; Un-weighted, SPL, and Fast.