A design that was conceptually eye candy has developed into one of Harman-Kardon’s proudest engineering feats.
As with any mildly complex electronic device, some degree of cross-discipline engineering is required when designing a new product. Design and electrical engineers have to understand the needs of each other to make a product come to life. Harman-Kardon blankets the engineering process with a web of complex communication and understanding among design, protyping, software, electrical, and acoustic engineers, specifically when designing the famed GLA-55 speaker system. “They all work in parallel to meet the requirements of the product,” System and Acoustics Design Engineer at Harman-Kardon, Charles Sprinkle explains. “Acoustics are engaged very early to make sure we have a complimentary concept to an acoustic design.”
Cabinet Design
The initial idea for the GLA-55 was to create a speaker that looked as though it was cut out of crystal. Sprinkle explains that this would not only be outrageously expensive, but also that “glass is far from being acoustically ideal.” So, leaded crystal was out. “The encloser had to be rigid enough to not have sympathetic vibrations, and be able to be relatively durable.”
When dealing with plastic structures Harman-Kardon typically uses ABS or PC techniques, but this makes a crystal-like design nearly impossible. Additionally, the design needed to be thick for proper anti-vibration support as well as the proper aesthetic appearance. After serious inquiry the team chose PMMA acrylic, because of its optical characteristics and its ability to be polished after molding. The tricky part about the GLA-55, Sprinkle says, “You can’t use established rules of injection molding with a part like this.”
Conventional molding cycling time on a plastic part is usually between 65 and 70 seconds, but the GLA-55 required 18 minutes to allow the cooling of such a thick plastic part. After that part is pulled and cooled, it goes into an annealing oven for seven hours to remove the residual stresses. This annealing is required to be able to do the post-machining that is required to pull the 10 mm gate, that the GLA-55 requires, without cracking the part. The part is polished and then annealed for seven more hours to remove the stresses created by polishing that gate off. All in all, each individual speaker unit requires over 16 hours of manufacturing time before they are ready to be packaged.
This design of the GLA-55 presented such a challenge that the engineers were essentially inventing the process as they went along. That process was to overcome the consequences of having an injection molded part that was 12 mm thick in places. Challenges ranged from the seam between the two halves of the cabinet to the glue seal holding such a thick structure together. Holding a large, heavy structure together was troublesome by traditional means. Solutions to these problems helped make the design what it is, Sprinkle says, “The fasteners holding the two halves together really completes the overall eye-candy factor of this system.”
Electrical Design
When building a speaker, the most important components are the transducers. A unique and specific transducer was developed by Harman-Kardon for the GLA-55, and it is still used in many of their speaker systems. “It started with an extremely high linearity transducer and excursion that were already being used. Enhanced with a copper cap, the diaphragm, and tweaks in the motor structure the proper transducer emerged,” Sprinkle explains.
As with any other speaker, once the transducer was deemed fit the work went to prototype. Sprinkle says, “When we have a mechanical design that we can prototype as an enclosure, we will populate it with transducers, ports, and all the other good stuff.” This is so the team can start to develop system integration and tuning.
For tuning the system, Harman-Kardon uses double blind listening tests to take objective measurements with professionally trained, subjective opinions. Sprinkle explains, “We use 72 measurements for each transducer, measured at 10 degree increments in both horizontal and vertical planes to have an idea what the acoustic response is everywhere. We have modeling systems that can predict that total integration of performance as we implement crossovers and equalization.” Once a design is stable, the trained ears come into a specially designed listening room to get the human touch to the frequency response in a double blind test.
Acoustic Design
The Harman-Kardon Slip-Stream Port Tube demonstrates a unique fluid dynamics structure in the world of acoustic and design engineering.
Another design milestone Harman-Kardon achieved was the creation of their Slip-Stream Port Tube. This new port tube system allows the GLA-55 speaker to make quality noise in such a small package. The integration of the Slip-Stream port creates powerful sound with 16 mm of speaker linearity (a measurement usually reserved for much larger sub-woofers and guitar cabinets) with just a three-inch driver. High excursion with extremely high linearity and a stable force make this speaker fill a room without being distorted.
The distinctive curve to the Slip-Stream Port Tube is a truly unique design, Sprinkle explains, “Typically, long port tubes would be required to get such a sound, which would not be possible with conventional port design. A straight port tube at low output performs OK, but at moderate or high outputs it will start to make a lot of noise because of boundary layer separation, from a fluid dynamics stand point.” The flow of air separates from the walls of the port tube creating turbulence, and ending with distorted sound. The Slip-Stream “gradually speeds the airflow up on the way in, and on the way out, gradually slows it down. The Slip-Stream Port Tubes create a constant adverse pressure gradient.” With straight tubes, the flow separates at the inlet, but with the slip stream and constant adverse pressure, that separation is put off as long as possible. Also, it makes sure that when there is separation it happens at the same time rather than in bits and pieces. This creates a louder, more dynamic sound.
A design that was conceptually eye candy has developed into one of Harman-Kardon’s proudest engineering feats. “I’ve never seen anything like this,” says Sprinkle. Thriving on sophisticated appearances, the GLA-55 delivers a unique decoration with the quality sound that Harman-Kardon has come to be known for.
When asked about the challenges that keep him up at night as an engineer, Sprinkle explains, “With the challenges that continue to present themselves I still sleep very good at night. It’s a changing world. It is a constantly changing universe and everything is always different. Maybe the worst thing is the fact that the challenges are always changing, so the solutions that I find today, I may not be able to use tomorrow. I actually enjoy that though.” As Harman-Kardon continues to push the envelope of aesthetic design as well as sound quality, they are sure to keep engineers on their toes.
For more information, visit www.harmankardon.com.