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University of Massachusetts-Lowell - February 8, 2012

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Summary

This week we had an interactive presentation on audio test and measurement by industry expert Dan Foley from Audio Precision. Dan spent a good deal of time talking about how and why measurements are important, and how they are done/used in engineering. We also discussed how manufacturers collect and represent (or misrepresent) their data in product specifications. This included total harmonic distortion (THD) characteristics and how to analyze them, as well as ways manufacturers specifically try to hide or skew results that are less than ideal. Tolerance ratings on a given statistic are also important in discerning the accuracy of a given graph or statistic, although it is not always listed in the gear manuals.

Dan conducted some measurements of frequency response and distortion with an AP System two Cascade running on a laptop. He brought in several speakers to measure, so that we could compare and discuss the differences.

Dan also brought a new desktop monitoring system that he has been working on with Jim Tuomy and Frank Schiller. They have a start-up company called Auradyne that is building medium scale 3-way desktop speakers. These monitors employ a DSP based crossover system that allows for ideal frequency matching and timing between drivers. The cabinets themselves are bright red and have a series of steps in the front of the cabinet. These steps are used as acoustic reflectors that force the common table-bounce that causes problematic comb filtering to pass over the listeners head. Not only do they eliminate this problem, but they also have a hinged tweeter/mid driver section with an adjustable alignment grid that allows the listener to position their head directly between the speakers from left to right, as well as angle the tweeter to the correct elevation.

We spent some time trading off as listeners in the ideal monitoring position, and listening to different familiar mixes. Dan also added two subwoffers to the system, listening to each individually and having us move around the room to find the nodes in the standing waves. The first sub was a typical omnidirectional loudspeaker and we had no problem finding the location of the room modes. He then switched to a sub by Velodyne which has a cardioid pattern. This sub energized the room in a much more even way, making it difficult to find the modes, as the differential between a peak and null were far reduced. It was also astonishing to walk past the speakers (L, R, sub, all in a line) to the back side and hear almost no bass whatsoever.

Many thanks to Dan, Jim and Frank for their demonstrations, discussions, and lugging all the equipment up to our facility! We loved learning about measurement, and the new speakers sound fantastic!

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AES - Audio Engineering Society