Pacific Northwest AES Section Blog

Bob Smith: 
(PNW Section Committee, Physio Control, BS Studios)

The topic of impedance comes up in many audio-related discussions and it's safe to say that unless you are an EE, there is a high degree of misunderstanding of this important topic, something worthy of more than just tribal knowledge.

Early on you're told to match impedances; i.e., the source impedance and load impedance must be equal. It seems easy enough to grasp. Then suddenly you're told that the load impedance needs to bridge the source impedance. What's with that? With video and RF, you find that impedance matching does matter... and even the cable has an impedance parameter. If your brain hasn't locked up yet, there is the matter of acoustical impedance.

It's all enough to give you impedance on the brain!

To match or not to match... That is Z question!

Our March meeting covers Impedance in both the acoustic and audio (electrical) contexts.

• Steve Macatee will provide a brief introduction and definition to set the stage for the four main presenters.
• Dennis Noson will extend the definition of impedance – a dynamic (vs. static) parameter of pressure waves in the air – to explore how this concept helps in understanding audio system speakers, singer's voices, and acoustic instruments. Using beautiful slides, colorful graphs, and bit of handwaving, the dynamism of radiated sound will be revealed, whether transduced by audio or radiated by tubes and plates – from organ pipes and piano soundboards (not that soundboard), right up to Amar Bose's presumably ideal one-eighth of a pulsing sphere.
• Colin Isler from Rane will cover the Impedance of Audio Interfaces.
• Our own Dana Olson will show some plots of impedance curves — perhaps even measure one actively live to show the process and to hear it sweep. Then he'll talk about what these curves mean, how they are used and what effect a 4 ohm vs 8 ohm speaker has on amplifier performance.
• Mark Rogers will point out the pitfalls in the wiring of distributed speakers, whether wired in series or in parallel or in 25/70 V systems. Problems can manifest themselves not only as large losses, but also as frequency response anomalies that will be different at each speaker.