Dynamic Motor Analysis - DMA Optimized Motor
JL Audio's proprietary Dynamic Motor Analysis system is a powerful suite of FEA-based modeling systems, first developed by JL Audio in 1997 and refined over the years to scientifically address the issue of speaker motor linearity. This leads to vastly reduced distortion and faithfully reproduced transients... or put simply: tight, clean, articulate bass.
Since 1997, JL Audio has been at the forefront of Finite Element Analysis-based modeling of loudspeaker motors and suspensions. This research is aimed at decoding what we refer to as the "Loudspeaker Genome"... a project aimed at understanding the true behavior of loudspeakers under power and in motion. A major component of this integrated system is DMA (Dynamic Motor Analysis). Starting with the 15W3v3 and the W7 Subwoofers in the late 1990's and early 2000's, DMA has played an important role in the design of all JL Audio woofers sold today, including our component woofers.
DMA is a Finite Element Analysis (FEA)-based system, meaning that it takes a large, complex problem, breaks it down into small solution elements for analysis and then assembles the data to form an accurate, "big-picture" solution. DMA's breakthrough is that it actually considers the effects of power through the coil as well as coil/cone position within the framework of a time-domain analysis. This gives us a highly accurate model of a speaker's actual behavior under real power, something that the traditional Thiele-Small models or other low power measurements cannot do. Because DMA does not rely on a steady-state model, it is able to consider shifts in the circuit elements being analyzed. These modeling routines are intense, requiring hours to run for a whole speaker.
DMA is able to analyze the real effects of fluctuating power and excursion upon the magnetic circuit of the motor, specifically the dynamic variations of the "fixed" magnetic field. This delivers intensely valuable information compared to traditional modeling, which assumes that the "fixed" field produced in the air gap by the magnet and the motor plates is unchanging. DMA not only shows that this "fixed" field changes in reaction to the magnetic field created by current flowing through the voice coil, but it helps our engineers arrive at motor solutions that minimize this instability. Analyzing this behavior is critical to understanding the distortion mechanisms of a speaker motor and sheds light on the aspects of motor design that determine truly linear behavior:
- Linear motor force over the speaker's operational excursion range
- Consistent motor force with both positive and negative current through the coil
- Consistent motor force at varying applied power levels
Our ability to fully analyze these aspects of motor behavior allows our transducer engineers to make critical adjustments to motor designs that result in extremely linear, highly stable dynamic loudspeaker motor systems.
The payoff is reduced distortion, improved transient performance and stellar sound quality.
W-Cone (U.S. Patent #6,496,590)
The W-Cone is a unit-body cone assembly that delivers astonishing cone stiffness with minimal mass. The shape also provides superb torsional rigidity, which is critical to maintaining voice coil alignment at the suspension limits.
The more excursion and motor force a speaker has, the more important cone rigidity becomes. The acceleration forces are extreme, requiring the cone to withstand rapid changes in speed and direction without deformation. Deformation not only leads to distortion, but can also affect the speaker's mechanical integrity by allowing the voice coil to go out of alignment and rub on the top-plate and the pole-piece of the motor.
There are several approaches to enhancing cone rigidity. The obvious ones are using a thicker material and/or a stiffer material. In recent years, several manufacturers have used composite cone materials (Kevlar®, fiberglass, etc.) or metals (aluminum, magnesium, titanium alloys). The use of these exotic materials is typically accompanied by marketing claims that the material chosen has exceptional stiffness-to-mass characteristics. These are true statements, but can be misleading. While these materials have excellent stiffness-to-mass properties (compared to paper or poly), they are not lighter than paper or poly in practice. This means that their use accepts the compromise of added moving mass on the design. This leads to efficiency penalties and suspension complications (it's harder to keep a heavy mass aligned properly).
A simple poly cone diaphragm, while sufficient for lower power designs, would not remain rigid under the demands that the W7 design requires. Our engineering team knew that high levels of cone rigidity would be needed, but they focused on achieving rigidity without a huge weight penalty. This ultimately led to the design we call the W-Cone. The W-Cone assembly achieves its rigidity through architectural means, rather than through inherently stiff materials. The design addresses the stiffness issue by using two lightweight mineral-filled polypropylene skins, bonded together at the perimeter and the center of the assembly. The lower skin's cross-section is shaped like a 'W', hence the name, and provides incredible rigidity when bonded to the dished upper skin. The effect is not unlike the trusses of a bridge or the unit-body construction of a modern automobile. In addition to the overall rigidity benefit, the lower skin's shape distributes the force generated by the coil and motor more evenly than a typical diaphragm. The force is not only applied to the apex but also distributed to the perimeter of the outer diaphragm for more linear behavior. A further benefit of the W-Cone is that the upper skin (the one in contact with the listening environment), is isolated from the high air-pressure gradients of the enclosure, further reducing deformation (and distortion).
As a point of comparison, the W-Cone assembly of a 12W7 is 32% lighter than a typical aluminum-alloy 12-inch cone. If analyzed in terms of weight per square inch of piston area, the W7 cone-body weighs 1.24/sq.in., compared to 1.45g/sq.in. for an aluminum-alloy cone and 1.66g/sq.in. for a titanium-alloy cone.
So why polypropylene? As stated above, our patented W-Cone technology achieves all of the benefits of more exotic materials while better suiting the unique nature of the W7. Since the W7 surround is detachable, the moving system (including the diaphragm) is subject to mechanical stress unseen in conventional designs. Because the user can tug on the cone while manipulating the surround, the cone must be able to handle this without buckling or deforming. Paper, metal or brittle composite cones would not handle this well. Our two-skin unit-body cone design achieves outstanding axial and torsional stiffness to withstand all kinds of abuse, and will remain largely unaffected and unblemished.
Elevated Frame Cooling (U.S. Patent #6,219,431 & #6,229,902)
JL Audio's patented Elevated Frame Cooling design delivers cool air through slots directly above the top-plate to the voice coil of the speaker. This not only enhances power handling, but also sound quality by minimizing dynamic parameter shifts and power compression.
Many speakers employ venting techniques to enhance voice coil cooling. This is typically accomplished by having big holes in the sides of the frame just below the spider attachment shelf. While it provides a modest cooling benefit, this low-velocity air-flow does not blow directly or strongly on the voice coil.
Our patented design improves upon this cooling technique in a number of ways. By elevating the frame above the top-plate of the motor (via stand-offs integrated into the bottom of the frame) a narrow, high-velocity air-path is created between the bottom surface of the frame and the top surface of the top-plate. This air path leads directly to the voice coil and then turns upward into the spider air cavity. By utilizing the pumping action of the spider through this focused air path, a large volume of cool air hits the coil windings directly.
Another important benefit is that the upper surface of the top-plate (one of the speaker's hottest parts) is directly exposed to cooling air flow, whereas on a conventional design it is isolated from the air flow by the lower flange of the frame. The elevated frame technology greatly increases thermal power handling, reduces compression effects and does so without any additional parts.
Floating Cone Attach Method - FCAM™ (U.S. Patent #6,501,844)
This assembly technique, conceived by JL Audio, ensures proper surround geometry in the assembled speaker for better excursion control and dynamic voice coil alignment.
JL Audio's patented FCAM™ technology is an innovative method of bonding the surround/cone assembly to the voice coil former/spider assembly. This feature helps ensure concentricity of the surround, spider and voice coil without torquing the suspension to achieve it. This allows for the inevitable, slight variations in production part dimensions without having them negatively impact the integrity of the suspension and coil-centering at high excursions.
OverRoll™ Surround (U.S. Patent #5,687,247 & #5,949,898)
By utilizing space wasted in conventional speakers, this ground-breaking innovation controls the W7's massive excursion without sacrificing precious cone area.
One of the first things you notice about a W7 is that something is "missing"... the mounting flange. Of course, this is actually not the case. The mounting flange is simply hidden beneath the surround and is made accessible for mounting purposes by detaching the outer edge of the surround and moving the roll to the inside (a pretty neat little trick). Apart from the obvious benefits of amazing your friends as you pull the surround off your speaker, there is a serious technical issue that led us in this design direction: Effective Piston Area ("Sd"). This is essentially the speaker's "cylinder bore", to use an automotive engine analogy, and is calculated by measuring the diameter of the diaphragm including one-half of the surround roll-width. In other words, from the top-center of the surround on one side to top-center of the surround on the other side.
The displacement capability of a speaker is determined by this piston area times the speaker's excursion capability. Displacement of air is directly linked to output potential. Therefore, the more air a speaker can ultimately displace, the louder it can play. That being said, there is a big difference between piston area and excursion: piston area doesn't need power to make it happen. This means that by making a larger piston, you are directly improving displacement for a given amount of excursion and, therefore, making your speaker more efficient. This is not the only factor that governs efficiency, but it is a major one.
To make a speaker have more excursion capability not only requires a motor design that can deliver more stroke, but also requires a surround rugged enough to handle the demands of longer excursions and controlled enough to keep everything lined up properly. If the surround's roll-width is not adequately large, its behavior (compliance) is not linear over the useful stroke of the woofer and it is more likely to fatigue and fail. For this reason, speakers with longer excursion capability generally need larger surround rolls (we won't comment on the ones that use large rolls strictly for cosmetic effect).
The problem with big surrounds is that they begin to encroach on the effective piston area of the driver. For example, a typical 12-inch woofer with a medium-sized roll has an effective piston area of 81.52 square inches. Compare this to a fat-surround 12-inch woofer which has a piston area of 69.07 square inches (15.2 % less effective piston area than the medium-size roll.) To overcome this loss, the fat-surround woofer has to produce more excursion to displace the same air as the woofer with the medium surround (and will require more power to do so).
OverRoll™ technology neatly sidesteps this compromise by allowing us to make full use of the entire footprint of the speaker, placing the surround further to the outside than in a conventional woofer. This means that we can use a large roll for all its benefits without sacrificing cone area (in fact, the 12W7 has 1% more piston area than the medium-surround conventional woofer). By maximizing the effective piston/total footprint ratio, we can deliver more output for a given excursion and outside frame diameter. This means that the prodigious excursion advantage of the W7 can be put to full use enhancing output, rather than making up for lost piston area.
The technology also provides a geometry advantage on the outside edge of the surround roll, allowing for more linear operation. A further benefit is that the mounting holes are inherently sealed by the surround, resulting in an improved box seal.
Radially Cross-Drilled Pole-Piece (U.S. Patent #6,243,479)
This innovative venting system greatly enhances thermal dissipation and power handling by directing air flow onto the voice coil former, working in conjunction with the Elevated Frame cooling technology to effectively remove heat from the voice coil. This improves power handling and reduces power compression effects, leading to more linear performance.
This technology differs from a conventionally vented pole-piece in that the air flow is capped off at the top of the pole-piece and directed through machined holes on the outer wall of the pole-piece to the region directly behind the voice coil. The top portion of the pole-piece is smaller in outside diameter where the holes vent and helps create a high-volume, high-velocity airflow path between the inner-coil cavity and the ambient air of the enclosure.This helps remove super-heated air that is trapped between the coil former and pole-piece on a conventional design, leading to a dramatic improvement in cooling efficiency, especially at high excursions.
Engineered Lead-Wire System (U.S. Patent #7,356,157)
Carefully engineered lead-wire design and attachments ensure controlled, quiet lead-wire behavior under the most extreme excursion demands.
Managing the lead-wires on a long-excursion woofer is one of the trickier aspects of its mechanical design. To address this, many long-excursion woofers today rely on a simple solution that weaves the lead-wires into the spider (rear suspension) of the driver.
The biggest problem with this approach is that spider limiting behavior plays a hugely important role a woofer's performance. Lead-wires that are attached or woven into the spider material can alter the spider's "stretching" behavior. The tinsel wire naturally has less 'give' than the fabric material of the spider leading to asymmetrical spider behavior and non-uniform stress distribution around the spider circumference. The wire attachment points can also cause localized pulling and tearing forces at the spider's excursion limits. As such, longevity becomes a major concern and makes the woven-in design less than ideal for very long-excursion designs.
While a traditional 'flying lead' design does not compromise spider linearity or radial stability, it creates its own challenges on a long-excursion woofer. Managing the 'whipping' behavior of the wire and making sure it does not contact the cone or spider is one challenge. Another is ensuring that the leads do not short one another or the frame of the woofer.
To overcome these issues, JL Audio's engineered flying lead-wires work in conjunction with carefully engineered entry and exit support structures molded into the terminals and the voice coil collar. Some models also feature jacketed lead-wires to further reduce the likelihood of shorting and fatigue. The result is flawless high-excursion lead-wire behavior, with outstanding reliability and none of the compromises inherent to a woven-in lead wire system. Building woofers this way requires much more labor and parts complexity than the simpler woven-in approach, but the payoff is in reduced distortion, reduced mechanical noise and improved reliability.
Precision Built in U.S.A.
JL Audio's Miramar, Florida loudspeaker production facility is one of the most advanced in the world.
At a time when most audio products are built overseas, JL Audio’s commitment to in-house loudspeaker production continues to grow. All W7’s, W6’s, TW5’s, TW3's, W3v3’s and some of our ZR products. We also build our Marine Speaker Systems, Home Subwoofers, Stealthbox® products and the vast majority of our enclosed subwoofer systems in Florida.
To pull this off in a competitive world market, our production engineering team has created one of the world’s most advanced loudspeaker assembly facilities. This commitment to state-of-the-art technology allows our highly skilled workforce to efficiently build JL Audio products to extremely high quality standards.
While it is also feasible to build good quality products overseas (and we do build some of our products in Europe and Asia), it can be challenging when the product’s technology is innovative or complex. Since most of our premium loudspeakers incorporate proprietary, patented technologies requiring specific assembly techniques, we prefer that the people who design them have close access to the people manufacturing them.
- Continuous Power Handling (RMS) 750 W
- System Nominal Impedance 3 Ω
- Enclosure Type Sealed, rear-firing design
- Finish Black carpet / laminate
- Grille Included Aluminum Bar Grille
- External Width (W) 17.75 in / 451 mm
- External Height (H) 14.625 in / 371 mm
- External Depth (D1) 16.625 in / 422 mm
- External Top Surface Depth (D2) 11.50 in / 292 mm
- Net Weight 61.2 lb / 27.77 kg