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ALMA - Winter Symposium

ALMA

General Information

Dates: January 6th + 7th, 2018
Location: South Point Hotel & Casino, Las Vegas, Nevada, USA

Paper: Fast Measurement Under Simulated Free Field Conditions (Wolfgang Klippel)

Evaluating the loudspeaker performance requires a measurement of the sound pressure output in the far field of the source under free field condition. If the available test room does not fulfil this condition, it is common practice to generate a simulated free field response by separating the direct sound from the room reflection based on windowing and holographic processing. This paper presents a new technique that performs a filtering of the measured sound pressure signal with a complex compensation function prior to common time and frequency analysis. The influence of room, nearfield and positioning error is compensated in the measured frequency response and nonlinear distortion characteristics. Different methods are presented for generating the compensation function based on a reference response measured under anechoic conditions and a test response measured under in-situ conditions. Benefits and particularities are demonstrated by practical measurements using different kinds of test signals.

Workshop: Green Speaker Design Reproduction with Maximum Efficiency (Wolfgang Klippel)

Besides horn-loaded compression loudspeakers, most direct radiating loudspeakers convert only a fraction of the electrical energy into sound. The low efficiency generates not only a heat problem but also shortens the battery lifetime in portable applications. There is a greater need to increase the output while reducing the electrical power consumptions. This workshop discusses the physical limitations and the practical design of passive transducers, where efficiency is one of the most important design goals. This approach requires adaptive control based on digital signal processing to cope with nonlinearities and other time varying properties inherent in efficient transducers. The amalgamation of passive transducer design, digital signal processing and system integration requires reliable loudspeaker models and meaningful characteristics in order to simplify the communication and to evaluate the product. This new paradigm is illustrated with woofers used in automotive and professional applications and with micro-speakers used in personal sound equipment.

Workshop: Learning from Production (Robert Werner)

In many cases, production testing is a necessary burden required to make sure that the audio product fulfills the specification sheet data and that no defective units are shipped to the customer. At the same time it is necessary to ensure that the yield rate is as close to 100% as possible to be profitable and save resources. Modern production test systems provide fast and reliable means for automatic quality control of audio systems at the end of the line or for incoming goods inspection, based on objective parameters. Limits are defined to make a simple Pass/Fail decision or to assign different quality grades. At this stage the task of production testing usually ends. The resulting data is mostly omitted or only stored for traceability purpose. Nowadays, where “big data” plays an important role even in our everyday life, this is a waste of opportunities although the full complexity of the term may sound intimidating. At the same time normal process control strategies are not always suitable for the specifics of loudspeakers. This workshop discusses how you can exploit the production test data of your audio product, both on and off the production line. It addresses topics like optimal limit definition based on long term statistics, selecting “golden units”, using smart algorithms (cluster analysis) for root cause analysis (“golden defects”) and automatic on-line classification, handling rare error patterns, reducing data complexity, closing the QC-R&D loop, control rules and trend analysis for early rejects detection and smart process control.

Paper: Why Testing Voice Coil Position in Production Line and How? (Robert Werner)

The performance of loudspeakers at high levels is limited by nonlinear and thermal mechanisms related to motor and suspension as well as geometric constraints. Such transducer characteristics reduce the acoustical output, affect the speaker system alignment, cause unstable behavior and create audible nonlinear distortions such as intermodulation and harmonic distortion. In the R&D process, it is important to understand the whole complexity and effect of nonlinear transducer characteristics for optimal design with respect to the target application and quality. In production this matter is less complex, but still crucial. Most parameters can be considered as consistent because they are defined by transducer design (e.g. motor geometry). However, basic characteristics such as voice coil position and suspension properties may vary significantly during production and as a consequence, seriously degrade the large signal performance of the delivered product. Testing nonlinear symptoms, such as total harmonic distortion and applying simple pass/fail limits may prevent shipping bad units, but it is not sufficient for diagnostics and early defect detection. For example, it does not indicate whether the distortion is caused by the motor or the suspension and how it can be fixed (direction and quantity of coil offset). This paper discusses which large signal transducer parameters are important in production, how they are measured and how they can be used for root cause analysis and process control in order to maximize yield. Interfacing large signal parameter testing in R&D and QC is addressed as well. 

Meetings

For meetings during or after the show please contact Jasmin.