Mr. Wahl is a Fellow and Life Member of the AES, and has been principal applications engineer for Neumann and Sennheiser microphones in the USA for many years. He holds degrees in electrical engineering and economics, and from early youth has focused his interest on electronics and music. He has worked with Thomas Organ, UREI, JBL, Gotham Audio, and of course, Neumann and Sennheiser. He tours widely, holding Master Classes and lectures at many music conservatories, universities, audio engineering schools, and such audiences as NARAS and others. Mr. Wahl conducted a Master Class at the Art Institute of Seattle in conjunction with this lecture.

There was a slide-show playing as the audience arrived, and once the lecture began, Mr. Wahl surprised the group with a "pop-quiz" of sorts. He asked for someone in the audience to describe the music playing under the slide show. One audience member did a rather amazing job of identifying and describing the music, much to Mr. Wahl's delight. He used this opening to begin a description of the concept of critical listening, the practice of paying careful attention to sound and subjecting it to careful analysis so as to identify its components, allowing the listener to compare two sounds intelligently. It is this critical listening, Wahl suggests, that lies at the core of any ability to make subjective evaluations of microphones (or any other acoustical or electronic component in the sound chain). He pointed out the difference between objective evaluation, which must be made on the basis of hard data acquired in a controlled environment (i.e., an anechoic chamber), needing no human judgment to determine the outcome; and subjective evaluation, which is by definition an expression of human judgment of the difference between two sounds.

When making a subjective evaluation of a microphone, we are listening for three general categories affecting its sound:

1. Its tonal characteristic, represented by static properties such as capsule construction and detailed resolution of the fundamentals and harmonics of an instrument.
2. Its electronic performance, represented by electrical specifications such as signal-to-noise ratio and self noise.
3. Its acoustic behavior, represented by reactive properties such as its ability to capture room acoustics and accurately reproduce the frequency response from distant instruments.

He suggested that there were two requirements to successful subjective evaluation, first, the evaluator must understand the laws of physics, particularly as applied to acoustics. Second, the evaluator must find ways to reduce the number of variables being considered at one time. Suggestions for reducing the number of variables included using close microphone technique to reduce the impact of the acoustical environment, using a signal source that is particularly recognizable and appropriate (Wahl suggests piano), standardizing the setup between different trials, keep a careful record of all observations, simplify the signal chain for the evaluation, and use familiar (and consistent) playback systems and locations for all trials.

Mr. Wahl strongly suggested using a piano as a standard signal source for evaluation for a number of reasons, among those he specifically cited:

• Piano is instantly recognizable
• Pianos are usually abundantly available.
• Pianos have a wide frequency range.
• Similarly they have wide dynamic range.
• The quality of the source is easy to verify.
• Microphone setup is easy and easily repeatable.
• Pianos are relatively easy to play, even for non-musicians.
• The results are easy to analyze and to compare.

Mr. Wahl presented fascinating dynamic PowerPoint demonstrations of the musical output and mechanical noise output of various musical instruments, and used them to illustrate the appropriate locations to place microphones, and to discuss the appropriate microphone patterns to use on these instruments. As part of this discussion, he stressed that it was important to consider the room itself, both in terms of size and in terms of absorption characteristics of room surfaces, as a part of the total acoustical system that must be analyzed critically as a part of microphone selection and placement.

During the intermission door-prizes were awarded:

• Joe Waggoner with Sennheiser USA distributed Sennheiser tee shirts to:
  • Kevin Whitaker
  • Bagus Naryana
  • Jim Angerer
  • Kisha Kalahiki
  • Lindsay Smith
  • Andrew Lloyd
• and three Sennheiser polo shirts to:
  • Jerome Krug
  • Alex Cassat
  • Mark Rogers
• Fluke Corporation provided two digital multi-meters for door-prize gifts, presented to:
  • Erick Chapman
  • David Christensen
• David Christensen with the Art Institute of Seattle presented AIS coffee mugs to:
  • Nick Bild
  • Andy Boyd