Lab Notes Electroacoustics & Audio • Consulting • Design / Testing Volume 12, Issue 4 December 2019 © 2019 CJS Labs • Training

Inside this issue: ASA 178th Meeting—San Diego, CA th ASA 178 San Diego, CA 1 The 178th Meeting of the Acoustical Society of ANSI/ASA S1.42-2019 1 America was held 2-6 December 2019 at the IEC TC-29—Warsaw 1 historic Hotel del Coronado in San Diego, CA. The ASA Custom In-House Committee on Standards Training Services 1 met on Tuesday morning, 3 December. The meeting Improved Zobel Network 2 also featured numerous sessions and technical presentations. ASA will meet again 11-15 May 2020 in Chicago, IL. More information at: https://acousticalsociety.org/ Training Services asa-meetings/

CJS Labs offers customized in- house training. Our design experience, proven processes, and measurement expertise will make News and Upcoming Events your product development more efficient. Learn how to optimize ANSI/ASA S1.42-2019 IEC TC-29—Warsaw expected this spring. I will both your designs and test rou- also be giving a guest lec- tines. Having a thorough under- ANSI Working Group S1-24, IEC TC-29 will meet in War- ture at Gdańsk Polyteknik standing of fundamentals, cor- saw 23-27 March 2020 in the following week. rect terminology, and proper which I chair, has completed its revision of S1.42 Warsaw, Poland. Delegates techniques will also enable you Please contact us and let to make more informed decisions “Design Response of and accredited experts from us know how we can be of and communicate more effective- Weighting Networks for around the world will attend. ly with your customers and ven- service to you and your Acoustical Measurement”. I will head the US Delega- dors as well as within your own organization. organization. Understand why The draft has balloted and tion and participate in 4 certain failure modes are prob- passed and is awaiting final working group meetings: Happy Holidays! lematic, even if they are not ANSI approval. This new WG5 on Microphones; obvious or audible. Sample revision also includes a set WG13 on Hearing Aids; course outlines and details are Christopher J. Struck available on our website: WG21 on Ear simulators; of Matlab m-file scripts for http://www.cjs-labs.com/ designing analogue and and WG on Modular Instru- CEO & Chief training_seminars.html digital A-, B-, C-, D-, E, G- , mentation. I am also Con- Scientist and U-weighting filters. It venor of MT25, however, Contact us to schedule a training CJS Labs course for your organization. should appear in the ASA the revision of IEC 60263 Standards store in early was completed in October 2020. is awaiting translated and final CDV ballot, which is

57 States Street • San Francisco, CA 94114 - 1 4 0 1 • USA Tel: (415) 923 - 9 5 3 5 • E m a i l : c j s @ c j s - l a b s . c o m • U R L : http://www.cjs - l a b s . c o m /

CJS Labs is a consulting firm based in San Francisco, CA. We spe- CJS Labs cialize in audio and electroacoustics applications. With over 30 years of industry experience in engineering and technology man- “Sound Advice Spanning 3 Decades” agement, our areas of expertise include transducers, acoustics, system design, instrumentation, measurement and analysis tech- 57 States Street niques, hearing science, speech intelligibility, telephonometry, San Francisco, CA 94114-1401 USA and perceptual coding. We also offer project management, technology strategy, patent & IP evaluation, and training services Tel: +1 415 923-9535 E-mail: [email protected] Back issues of Lab Notes are available on our website at: Improved Zobel Network http://www.cjs-labs.com/ lab_notes_links.html

Passive crossover filter networks for multi-way loudspeakers cally limited when using this simplified compensation network. generally require a resistive termination for optimum perfor- An improved compensation network can be realized by using mance. The driver itself presents, at best, a semi-inductive load. the analogous circuit ‘dual’ of the L2/R2 model, assuming the Recall the inductive rise with frequency of the loudspeaker values for the driver impedance model are known. Recall that a electrical impedance. The L2/R2 impedance model depicted in circuit ‘dual’ replaces series impedances with shunt impedanc- Fig. 1 represents the electrical impedance as seen by the ampli- es and vice versa. Capacitors become inductors and inductors fier output: become capacitors. Resistors remain resistors. Applying these principles to the network of Fig. 1 results in the following net- R2 work:

RE L2 RZ1 +

Fig. 1 L2/R2 loudspeaker electrical impedance model.

The typical Zobel network used to make the driver impedance appear closer to an ideal resistive load is a simple series resis- RZ2 tor and capacitor shunted across the driver terminals. - CZ1

CZ2

Fig. 3 Improved Zobel compensation network realized as the circuit ‘dual’ of the L2/R2 impedance model.

The component values for this network are calculated as

Fig. 2 Typical Zobel impedance compensation network. , , , and

The component values are calculated as This represents a dramatic improvement to the basic 2- component Zobel network, and compensates for the non-ideal semi-inductive behaviour of the loudspeaker driver across the entire frequency band. The component values are easily found if the L2/R2 impedance model values are known. The cost, , , with however, is increased size, complexity, and component count.

The resistor value is approximate and may need to be adjusted Please contact us for more information. for more extreme voice coil impedances. The resistor should be power rated as shown to handle the current to the loudspeaker. The flatness of the compensated impedance magnitude is typi-

57 States Street • San Francisco, CA 94114 - 1 4 0 1 • USA Tel: (415) 923 - 9 5 3 5 • E m a i l : c j s @ c j s - l a b s . c o m • U R L : http://www.cjs - l a b s . c o m /