Speaker and Microphone Measurements: Eliminate Reflections While Testing

Acoustic reflections in rooms, in the form of reverberation, contribute significantly to the characteristic of sound. In acoustic measurements for quality testing of loudspeakers and microphones, however, these reflections can produce inaccurate results and should therefore be excluded as far as possible. The measurement results must be reproducible and not significantly influenced by the room acoustics. In this article, NTi Audio explains how to remove reverberation from the measurement results.

An article detailing the vast experience in this field by one of the leading designers and manufacturers of measurement microphones, PCB Piezotronics. The article looks at the frequency response of a measurement microphone, general acoustic calibration, and the benefits and challenges of free-field calibration, and pressure calibration, among other approaches. The article was originally published in Voice Coil, September 2017.

This article describes a spreadsheet program for designing low-voltage power supplies using common IC three-terminal regulators. The spreadsheets are in standard Excel format, and should work in just about any spreadsheet program. Each file has two main pages: one for use with common variable-output regulator chips, the other for fixed-output devices. This article was published in audioXpress, March 2010.

Do you know what the crossover filters are doing to the response of the loudspeaker system? Some of you might have measured the frequency response of the loudspeaker system to determine what’s happening through the crossover region. However, most designers only look at the loudspeaker’s on-axis response. It’s equally important, or perhaps more important, to know what’s happening off-axis. Let’s see how loudspeaker modeling can be used to help with this. This article was originally published in Voice Coil, August 2017.

In this article, Dan Knighten (Applications Engineer, Listen) provides valuable perspectives on how to deal with the challenges of measuring devices that connect directly to Apple’s Lightning port or USB-C, or work wirelessly, using Bluetooth. In all cases, these headphones present unique challenges to measurement because they cannot be directly connected to traditional test and measurement systems. This article was originally published in Voice Coil, July 2017.

Is the solid part of a loudspeaker motor just a magnet or is there more to it? Simulation tools have helped to create effective and powerful magnet constructions, which make it easy to build a prototype based on calculations and experience. The next obvious step is measuring and listening to the assembled speaker. However, more conclusions can be drawn by analyzing the individual parts further. This article was originally published in Voice Coil, May 2017.

Loudspeaker modeling files are most often used with acoustical modeling programs such as EASE, Focus, CATT-Acoustic, and others to help determine how well the loudspeakers cover the audience areas and how much “spill” there is on the room’s surfaces. It is important to have accurate data about the characteristics of the loudspeakers that are used in the models. In this article, we will detail some of the requirements to help assure good measurement data for use with loudspeaker modeling. This article was originally published in Voice Coil, April 2017.

Following his original 2008 essay on sound pressure level (SPL) meters, in this article for audioXpress published in March 2015, Ethan Winer considers some practical applications for a basic SPL meter, such as calibrating loudspeaker levels and measuring room acoustics, using a simple Galaxy Audio CM-130 SPL Meter as an example. He then moves on to a more sophisticated model, the NTi Audio XL2.

This Voice Coil Spotlight by Marian Liebig (Klippel GmbH), discusses the specific challenges of Testing Mobile Devices such as Bluetooth headphones, smartphones, and tablets. Those devices have become part of people’s daily lives but increasingly pose important new challenges in terms of quality assurance, where defect symptoms need to be detected sensitively and quickly while measured under tough acoustical conditions.

Michael Kiwanuka’s article “Current Feedback and Voltage Feedback Fallacies” (audioXpress June 2017) elicited comments from Walt Jung, with supporting signatures from a number of well-known designers, to which Kiwanuka responded. Since some editing errors have crept into the article, we decided to make available a complete correct version of the article, together with the mentioned comments and exchange.