Loudspeaker Modelling and Design

A Practical Introduction

Geoff Hill

• Publisher: Routledge
• Year: 2018
• ISBN:
  9781351116404
• Edition: 1
• Topic: Technologie et ingénierie
• Subtopic: Ingénierie de l'acoustique

In this book, Geoff Hill demonstrates modern software and hardware being applied to the processes behind loudspeaker design and modelling. Modern computing power has progressed to the point that such analyses are now practical for any interested individual or small company. Loudspeaker Modelling and Design: A Practical Introduction examines the process from initial concept through specifications and theoretical simulations and onto detailed design. It demonstrates the processes of design and specification, by using detailed simulations of a loudspeaker driver; sufficient to give re-assurance that a design is practical and will perform as expected.This book brings together many different strands of modelling from electro-magnetic through to mechanical and acoustic, without getting bogged down in theoretical discussions and arguments. This practice-based book shows the techniques used in designing modern loudspeakers and transducers.

PART I

Introduction

Preface to Second Edition

This second edition concentrates more deeply on the core of modelling loudspeaker transducers. To do this I have relaxed the use of open source software, including a mix of commercial products.

Included are Klippel, CLIO, PAFEC, and the Tetrahedral Test Chambers.

Klippel’s dB-Lab and Analyser were of course a crucial part of explaining many of the key concepts in the first edition. This second edition goes into more detail, with a tutorial that demonstrates dB-Lab alongside a small-signal parameter analysis using the LPM module.

Audiomatica’s CLIO Pocket shows what can be achieved with more modest hardware and software. I show examples of SPL versus frequency response and with respect to time, as this shows the decay behaviour.

Pafec appears via the PafLS front end and undertakes loudspeaker driver simulation of impedance as well as SPL at selectable angles, showing how a loudspeaker drive unit behaves off-axis.

I introduce Autodesk’s Fusion360, which directly builds a 3D model, produces drawings (including 2D examples), and conducts mechanical simulations.

The entire manuscript has had the benefit of Paul Messenger’s editorial eye for detail and years of writing, and I am deeply grateful for his time and work here. Nevertheless, any remaining mistakes are mine and mine alone. I am also deeply grateful to Lyn Nesbitt-Smith for a comprehensive index.

There is a greatly expanded glossary of terms, and a list of references after each main chapter, where these refer to individual books, articles, or patents, etc.

Most of the simulations and models have been revised, and many of the 3D models have been redrawn using Fusion360. An additional chapter, Linkwitz Transform, rounds off the subwoofer design.

This second edition greatly benefits from the care and attention of the entire team, who will be able to bring this to a wider audience.

One thing I would stress is that, as an engineer, things always change. How something was done a few years or decades ago will be different; however, the fundamentals remain constant.

Although the core remains the same, I believe there is a gap between theoretical knowledge as it is often taught and real engineering where such theoretical knowledge is translated into actual products.

This is especially true now, when so many loudspeakers use ‘off the shelf’ loudspeaker drive units.

One of the things I do is try to bridge that gap, and I am interested in helping others do so too.

So while there still is some theory in this book, I have tried to ensure you do not get bogged down in it: neither do you need to be an expert in computer modelling, mathematics, or measurements.

I hope the tutorials are self explanatory and complete in themselves. If you don’t understand the detailed theory or modelling, don’t worry: just pick and choose the bits you need at the time.

I would particularly like to thank readers of the first edition who have written directly to me; I have tried to incorporate your feedback in this second edition. Necessarily, this work is ongoing, and some of the comments will have to wait for subsequent editions.

I should like to acknowledge the support and assistance of all the authors and programmers of the software and hardware used in this edition.

Lastly I should like to repeat my request for feedback on this edition. You can contact me directly at [email protected].

Geoff Hill August 2018

Aim of This Book

0.1 Aim of This Book

The main aim of this book is to bring together the disparate strands that are required to design and specify current loudspeaker drive units, all in one place. We believe that this book is long overdue, so if you don’t want to study hundreds of papers and pick out the relevant nuggets, this book may well be for you.

The book brings together nearly 40 years’ experience of actually designing loudspeaker drivers and systems. It’s fully up to date and is backed up by the development of both systems and drive units. Our aim is to concentrate mainly on the practical aspects of loudspeaker design, simulation, and measurement, rather than the theory.

There is a little theory, but we have tried to keep this at a fairly basic algebraic level, by leaving all the complicated calculations to the individual programs themselves. A key idea is to take the reader through the whole process required to design and specify loudspeaker drivers and ultimately speaker systems.

The performance of any finished loudspeaker is dominated by the qualities or problems of the underlying driver(s).¹ So the specification and simulation of the drivers need to be understood before we can design and produce high quality loudspeakers.

Loudspeaker drivers are currently used in the following devices: ear-buds, headphones, computers/tablets, telephones and mobiles (including smartphones), radios, TVs, cinemas, hi-fi and home cinema systems, musical instruments, and public address systems for concerts and festivals.

All of these need one or more of the following units: micro speakers, full range drivers, tweeters, midrange and bass units, subwoofers, and compression drivers. It’s quite a list, and society today would be almost unrecognisable without the capability to reproduce sound and music.

The fact is that many loudspeakers have been around in their current form for nearly 100 years. The vast majority are based upon the moving-coil design, and most (but not all) can trace their roots back to the Rice & Kellogg [5] patents issued between 1924 and 1929.

This book will take the reader through the design process as we see it, building from the initial concept to its specification(s) and the theoretical modelling of the transducer itself. It will then continue to the detailed design, test, and measurements, plus the statistical analysis of the final product.

We will do this using open-source, free, and commercial software using modern computing techniques. Only in the past 20 years have the modern analytical tools and computing power become readily available, and it is only in the last decade that these tools have started to trickle down to the point that an individual can have access to both the knowledge and the software.

This step change in the availability of knowledge and capability is unprecedented, and it is the subject of progress in many fields in computing and software. Think of the changes Linux has wrought in mobile phones, through the Android and Apple MAC operating systems to 3D CAD and printing.

The target audience includes those people who are just interested in loudspeaker driver design as well as students and engineers who design the products we use on a daily basis.

Much has been written about the theoretical aspects of loudspeaker design, some of which has been published in journals such as the Audio Engineering Society, the Acoustical Society of America, the Institute of Acoustics, and others. There are also many excellent reference books on acoustic theory, from Rayleigh [4], Morse [3], Beranek [1], Kinsler & Frey [2], and many others. Unfortunately, most of this has been from a purely theoretical perspective, which has put off many people from further exploration because of the ‘academic’ approach this implies.

Sometimes it may be necessary to develop a loudspeaker fully from theory, but in practice much real design is based upon tried and tested developments, often made by relatively inexperienced engineers thrown into a task at short notice. How to approach the tasks then?

In reality, a lot of the real design work is (and perhaps always has been) done by relatively inexperienced engineers or technicians perhaps a year or two out of college or university. They may well have been taught the academic theory by their lecturers, but do they really need to start from scratch? We would say no. That is a very poor choice today and leaves many points unknown, simply because those who are teaching design have (often) never actually done it! Another case is where designers or engineers are experienced, but in a different area, and they have a need to understand how to design and mod...