Geoff Hill's Tetrahedral Test System & Loudspeaker Design

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Geoff Hill


Small Signal Model


Compliance, Volume & Frequency missing


Calculating the Voice Coil missing


Magnetic Flux Field Density


Theoretical Bl(x)


Acoustic Field Simulation


HOLMImpulse


I am in the process of writing a book on Loudspeaker Design

This page shows the current Aim of this Book along with various illustrations taken from the book, if you would like to be entered into a draw for the book (when it is published!), please enter your details into the contact form.

I am, and have always been, fascinated by Loudspeakers and amplifiers and how together they can reproduce music. How they do what they do, how to predict and to measure them has been a driving force with me for as long as I can remember.

Aim of this Book

My aim with this book is to concentrate on practical aspects of loudspeaker design, simulation & measurement and not the theory.

Ultimately the performance of any finished loudspeaker is dominated by the qualities or problems of the underlying driver(s). This is the case whether the drivers are being used in any of the following:

Ear-buds, Headphones, Computers or Tablets
Telephones and Mobiles
Radios / TVs / Cinemas, Hi-Fi or Home Cinema Systems
Musical Instruments, Public Address or Concerts and Festivals

All of these need one or more of the following:

-Micro speakers
-Full range drivers
-Tweeters, Mid-range drivers
-Compression drivers
-Bass drivers
-SubWoofers

This is quite a list and our society today would be almost unrecognisable without the capacity to reproduce sound and music. Whether that is advantageous or not I will leave others to debate. The fact is that loudspeakers have been around in their current form for nearly 80-90 years and the vast majority are based upon the moving coil loudspeaker. Most (but not all) designs trace their roots back to the Kellogg and Rice 1925 patent.

This book starts from where a decision has been made to use a moving coil loudspeaker and for one or more of the categories above . . .

DSP can correct some problems, but these are strictly limited.

So where does this book come in?

I wish to help and assist those people who are interested in the art of loudspeaker driver design. I have spent the best part of 40 years working on designs ranging from an 8mm microspeaker used in a mobile phone, tweeters through to subwoofer 18" Bass drivers and almost everything in-between.

How will I help you?

I will take you through the design process as I see it, building from initial concept to initial specification(s) and theoretical modelling, then onto detailed design, test and measurement passing statistical analysis on through to the final product.

How will I do this?

I will do this using a combination of open source, free and low cost software and modern computing techniques

Why this book and why now?

Although loudspeakers have been around for 80 or 90 years, only recently in the past 20 years have the modern analytical tools and computing power been readily available. Arguably it is only in the last decade that the tools have started to trickle down to the point that an individual can have access to both the knowledge and software - especially with the growth in OpenSource, Free and Low cost software, to do this.

This step change in the availability of knowledge and capability is unprecedented, and is the subject of progress in many fields from computing and software. Think of the changes Linux has wrought through 3D printing.

My target audience includes: Those people who are just interested in the loudspeaker design, as well as students and engineers who design the products we use and abuse unthinkingly 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 many others. There are many excellent reference books on acoustic theory, from Rayleigh, Morse, Beranek, Kinsley & Frey and many others. Unfortunately most of this has been from a purely theoretical background and many people have been and are put off from further exploration because of this and the "Academic" approach this implies. Much has been written about fitting or matching drivers to cabinets as well as crossover’s and system integration and this tends to be more accessible.

In my studies over the years, however, I became aware that there were relatively few books about the actual process of designing loudspeaker drivers, taking the reader through the whole process required before finally integrating these parts to produce whole systems. It has only been within the last decade that the tools have started to trickle down to the point that an individual can have access to both the knowledge and software, that is required for consistent high performance loudspeaker drive units.

The use of measurement hardware and software is not essential here but may help you understand what is happening more clearly, as is having access to the web and the use of a personal computer.

I will limit my explanations to those required to understand techniques - I make no apologies if these explanations are non standard ones, they are however ones that I find useful in understanding various techniques rather than providing theoretically exact explanations. I think and hope that there may be some demand for this approach. I will give specific worked examples of actually using various tools to design products.

I should say at this point to those who already understand or are conversant with the art of loudspeaker design this book may not be for you. Even so I hope that even for those with reasonable knowledge of Loudspeaker Design that it will demonstrate one or two techniques, hardware or software that you were not aware of.

I will try to be open and honest in my approach, especially when discussing potential alternatives. As so often it is balancing one thing off against another to best effect where the art of loudspeaker design gets most interesting.

As much, if not all, of this book will involve using equipment or software for these tasks, doubtless some people will say that it is the job of the software and hardware suppliers to provide the instructions for their products. Here I both agree and disagree; if we were talking about software and products designed and sold for a specific task; I agree that it is their job to explain their products. But with open source, free or low cost software this is neither possible nor practical so there is a gap which I hope to try to partially fill.

In any case I feel that the multidisciplinary nature of loudspeakers means that it is not the job of any of the "tool makers" to explain the process of loudspeaker design itself. There is an argument that the colleges and universities should do so but generally loudspeaker design is only a very small section of say even an MSC course in acoustics, let alone a qualification in physics or another subject, so inevitably only a small portion of the course will be devoted to it.

The result of these pressures mean that realistically most research is undertaken by companies with at best the results being published, inevitably these companies need to maintain a competitive advantage and so (it could be argued) that it is not in their interest to reveal how and why they do things that are actually essential to understanding loudspeaker design.

The obvious exception to this is where companies publish by way of a patent whereby in return for making information publicly available they are granted exclusive right to use these patented ideas for a period of time.

I believe this conflict of interest (which happens to a greater or lesser extent in all industries) is at the heart of why people are nowadays disengaged from the process of designing and making things. I fully accept that most people are not interested in how things work or how to design things; however as you are reading this, it probably does not apply to you.

Specifically it also means that it is difficult for someone new to loudspeaker design to get started, so this book is an attempt to demonstrate some of the techniques in use in modern loudspeaker design.

As this book will focus on these aspects I must state that although I have taken great care in the preparation of this book and its contents neither I nor the publishers can accept any responsibility for errors in this book, or an any losses or damage however caused by using the knowledge in this book for your own purposes. The risk is and will remain yours alone.

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