1. How to Design and Specify
High Quality Loudspeakers
Geoff Hill
Loudspeaker Design made simple!

2. How to Design and Specify High
Quality Loudspeakers
Part I - Introduction
This starts with the Abstract here we give a brief overview of the book and the methodology
applied throughout it along with a description of the key programs and tools used to design
and specify loudspeakers.
Next is the Aim of this Book The aim of this book is to concentrate mainly on the practical aspects
of loudspeaker design, simulation, measurement and not the theory of moving coil loudspeak-
ers only. There is a little theory, I have tried to keep it at a fairly basic algebraic level. Leaving
all the really complicated calculations to the individual programs themselves.
In my studies over the years I became aware of relatively few books about the actual process of
designing loudspeaker drivers and loudspeaker systems, taking the reader through the whole
process required to design loudspeakers
This is closely followed by What this Book is Not about which highlights that this book is NOT
intended to supplant the theory or academic methods.
Then we discuss What tools and equipment focuses on which tools and techniques are now avail-
able for designing loudspeakers - this has changed significantly even over the past 10 or 20
years and many older tools and techniques are now effectively obsolete - however some some
like the Thiele-Small parameters have morphed into mainstream design and specifications but
are not always in the way originally intended originally. This chapter outlines key categories
of software and hardware that I consider as minimal requirements today in 2015/2016
Part II - Basic Theory
Chapter 1 - How Does a Loudspeaker Work? we describe the basic operation of a conventional
moving coil loudspeaker and we look at the Rice & Kellogg loudspeaker and patent, upon
which so many of our current loudspeaker designs are based.
Chapter 2 - Frequency Response we start here with a Water Wave in a bath before going on to
how we can produce a Sine wave, then how we calculate the overall level of a signal which
is constantly changing over time (R.M.S.) before we get to how we display and interpret a so
called Frequency Response
Chapter 3 - Resonance we describe what Resonance is, some of the effects it has on a loudspeaker
and how we can calculate it from a knowledge of mass and compliance
i

3. ii HOW TO DESIGN AND SPECIFY HIGH QUALITY LOUDSPEAKERS
Chapter 4 - Damping As we saw in the previous chapter that resonance is the tendency of a
system or thing to oscillate or to keep vibrating; more at some frequencies than others. Damp-
ing acts to control or stop this tendency. In this chapter we examine both electrical damping
as applied to the measurement of electrical Q and also acoustical damping and the effect that
a lack of it can have...
Chapter 5 - in Young’s Modulus we will look at Young’s Modulus which is the ratio of stress
(force per area) to strain (the ratio of new size to the original size). We will see how it can be
measured and find why it is so important to modern modelling techniques
Chapter 6 - Finite Element Analysis describes in very simple terms what Finite Element is about
and how it achieves the results it does - but does so stripped of the mathematics, it also dis-
cusses what is important in any model and how in the authors view it is essential to be mod-
elling the most important things or parts first.
Part III - Loudspeaker Models
Chapter 7 - Small Signal Model as the name implies these models are only concerned with the
behaviour when the loudspeaker is working at a low level, or in linear conditions; also these
models are only concerned about the low frequency region from D.C up until the loudspeaker
starts to depart from a mass controlled system; quite simply these models are NOT designed
to work at higher frequencies where the diaphragm affects the response.
Chapter 8 - in Polynomial Models although these are a relatively old techniques, never less
these relatively simple underlying equations can effectively model much of a real loudspeakers
actual frequency response - so we need to be aware of the factors involved.
Chapter 9 - in Thiele-Small we explore three of Neville Thiele’s key alignments that are com-
monly used and examine certain aspects of there performance, we then will then explore how
these are extended into the Electro-Mechanical Parameters that as a designer you can directly
manipulate
Chapter 10 - in Large Signal Domain and Model we discuss the Large Signal Domain and Model-
ling as these techniques help us to understand what happens when we use a loudspeaker with
real world signal levels, our previous analysis has all been in the Small Signal Domain. In the
Large Signal Domain and Model this breaks down so we need different techniques.
Part IV - The Design Process
Chapter 11 - in There Is A Job To Do - But exactly what? we get to the heart of both specification
and it’s relationship to design, and we start to consider loudspeaker design in it’s widest sense:
Taking the example of our Sub-woofer we begin to break it down to bite sized chunks
Chapter 12 - Common Questions outlines some of the more common questions that can be used
to further define answers that in themselves will give you the information needed to break a
loudspeaker design down into smaller component pieces, these can then be looked at either
individually or collectively to ensure we are aiming at the correct specification(s). We also
discuss the importance of having a Sanity check
Chapter 13 - in Specifying A Loudspeaker Driver we examine the core essential key underlying
system specifications and what other parameters need to be included taking into account the

4. iii
type of enclosure or system before considering the make up of individual drivers how they are
being operated.
Chapter 14 - in Project Planning and a Bill of Materials here I strongly recommend producing an
outline plan and how this differs from a project plan and discuss why this is important and
how this can be developed later. A simple example is shown which can then be used to form
the core of such a plan.
Chapter 15 - in Designing a Subwoofer we discuss some of the key project stages required to
transform our idea’s into an actual loudspeaker - the key one’s we will consider here are the
physical and mechanical aspects.
Part V - What’s really going on inside a Loudspeaker?
Chapter 16 - in Driver Design we develop the underlying electro-mechanical parameters, these
are drawn from an extension of the Thiele-Small parameters by using idea’s drawn from
Garner and Jackson’s Theoretical Bass Unit Design, from the underlying equations we can
then produce the detailed specifications that we will feed into a FEA model. We also discuss
the type of FEA model appropriate.
Chapter 17 - in Magnet before we get into the detail of design, we ask what is a magnet we
will look at magnetic flux lines and how we can concentrate these into useful fields we then
discuss various modelling techniques and then summarise some common magnetic materials
properties.
Chapter 18 - in Voice Coil we begin to look in detail at the Voice Coil - in certain respects it is the
heart of the motor unit and hence the loudspeaker. Get it wrong the whole loudspeaker will
not function as we desire! So we we look not only at the materials used for voice coils but also
some of the alternative methods for designing them so that they do meet our requirements and
specifications
Chapter 19 - in Bl(x) we saw previously that the Voice Coil is at the heart of a loudspeaker -
However Bl B for Flux Density (T) and l for length of wire (m) is how the voice coil translates the
electrical current into the force that moves the loudspeaker, we also discuss in this chapter this
changes with displacement(x) and Shove or B·l2
Re
Chapter 20 - in Le(x) In this chapter we review briefly Le the inductive and the semi-inductive
behaviour of a loudspeakers impedance characteristic, helping us to understand the mech-
anisms behind the roll off we saw earlier, we also extend this to the changes in this due to
displacement the Le(x) term
Chapter 21 - in Motor Unit If as is arguably the case the Voice Coil is the heart of a loudspeaker.
Then the Motor Unit is probably best described as the structure that holds everything together,
just as with the voice coil get it wrong and no amount of tweaking with a x-over later will
correct it but get it right first time and things will go easier. Here we develop a complete motor
unit from start to finish
Part VI - FEA, BEM and Integration
Chapter 22 - in Material Specifications we discuss the various types of material specifications,
what they describe as well as why they matter, we then reference sources of further information
about them

5. iv HOW TO DESIGN AND SPECIFY HIGH QUALITY LOUDSPEAKERS
Chapter 23 - in Mechanical Finite Element Analysis We briefly describe how FEA works in non
mathematical language. We then discuss what is significant in a model and what is not, what
is the level of appropriate complexity which we need to model and only then do we start to
build a model taking as inputs various parameters we worked out earlier.
Chapter 24 - in Cms(x) Cms is the name we give to the mechanical compliance, it is the ease
with which a loudspeaker’s moving parts are moved away from there nominal rest position.
However we are more interested in Cms(x) and it’s inverse Kms(x) as these describe how these
parameters change with displacement or movement (x)
Chapter 25 - in Suspension Here we decide the essential requirements that a suspension must
meet, we build an axis symmetric model of the proposed suspension and model it using a Non
Linear static model, exporting the force displacement results into a spreadsheet for visualisa-
tion.
Chapter 26 - in Mechanical Simulations In this chapter we will discuss how we will produce
mechanical simulations rather than acoustical simulations as, Our efficiency and coupling is
usually so low that such simplification will make little difference. Programs like ABEC can
directly accept such mechanical data or calculations to produce the acoustic results we need
later anyway. What we will do in this chapter is to go through the process of developing this
mechanical model.
Chapter 27 - in PafLS takes a very different approach to loudspeaker simulation; rather than
go into the detail of electromechanical simulation, it takes the key Thiele-Small and Electro-
Mechanical parameters as Inputs these are feed into a mechanical template that couples to the
simulation engine behind PAFEC, this avoids much design complexity at the cost of limiting
the otherwise infinite choices. However it directly gives us access to frequency response and
axial plots of the simulations.
Part VII - Mechanical Design
Chapter 28 - in Visual and Mechanical Design here we start to translate a design into a final
loudspeaker, phone, or completed system, going beyond the driver and how it works towards
the final result.
Chapter 29 - in Cabinet we discuss the cabinet or enclosure as this often forms a large part of
the mechanical structure - in the case of a mobile phone or a tablet it maybe core of the physical
structure. Within a completed loudspeaker system, the cabinet or enclosure is the single largest
item it certainly has a significant effect on the performance of the whole system.
Chapter 30 - in Chassis here we consider some of the requirements that a chassis needs to meet.
We can of course use the same or similar CAD tools for the chassis as we can for the rest of the
mechanical design. The first critical requirement is to support the motor unit, often this is the
heaviest part of the loudspeaker so this needs a combination of strength and accuracy in order
to function correctly.
Part VIII - Measuring a Loudspeaker
Chapter 31 - in Acoustical Measurements We start from why acoustical measurements are differ-
ent from electrical or electronic ones and how to make reliable, consistent and accurate Acoustic
Measurements . We look at conventional anechoic chambers and wedges before pinning down

6. v
the real underlying requirements for measuring loudspeakers. We consider the accurate meas-
urements of loudspeaker drive units together with mounting baffles and the numerous ways
this could go and often does go wrong.
Chapter 32 - in A Universal Loudspeaker Driver Test System we discuss the idea behind a univer-
sal loudspeaker driver test system, together with the rational behind AES’s X-223 project, what
the alternatives are and how we could verify and confirm performance. We then introduce the
Tetrahedral Test Chambers
Chapter 33 - in Tetrahedral Test Chamber - White Paper I present a copy of a White Paper doc-
umenting the performance of a SEAS H1207 Bass/Mid Driver as measured by an IEC Baffle
configured as ground plane and measurements conducted in a TTC350 and TTC750 test cham-
bers
Part IX - Appendices
Appendix A - in Glossary is where many of the terms used throughout the book have been
defined.
Appendix B - in References is where many of the references both physical Books in B.1. and
virtual links to websites in B.2. have been listed all the Websites and Links were working as of
November 2015
Appendix C - in the ABEC and VACS Tutorial on ABEC - Acoustic Boundary Element Calculator.
We build up an mechanical and acoustic model of our Sub-woofer, the acoustical output is then
graphed using VACS - Visualising Acoustics
Appendix D - in the FEMM Tutorial we build a detailed axis symmetric model of the magnetic
circuit of the Sub-Woofer Motor unit, from constructing the geometry, setting up the boundar-
ies assigning the materials to calculating the flux and looking for saturation to estimating the
voice coil inductance.
Appendix E - in the HeeksCAD Tutorial we use HeeksCAD to produce and render a rotated 3D
model of our Sub-woofer drive unit, we will do this from a core *.dxf file which could have
been produced by FEMM or a CAD package such as Draftsight. This is then followed by a
listing of links to the HeeksCAD Unofficial Tutorials on youtube
Appendix F - in the HOLMImpulse Tutorial we use HOLMImpulse to demonstrate the process
of measuring and calibrating a Tetrahedral Test Chamber, HOLMImpulse is a freeware pro-
gram for measuring the Impulse, Amplitude including THD+n, Harmonics and Phase versus
Frequency.
Appendix G - in the MecWay Tutorial we build a model of our subwoofer driver; entering
nodes and elements then assigning materials, loads and constraints. Ultimately developing
a dynamic model which enables us to visually see the physical bending behaviour of a loud-
speaker drive unit or parts of one such an analysis brings real understanding to the process of
design.
Appendix H - in the Microcap Tutorial Is a Spice simulation tool or more accurately a lumped
parameter modelling tool which we will use for modelling relatively simple electrical crossov-
ers and many of the loudspeaker models presented here were produced using MicroCap, the
full version is capable of much much more but that is outside the scope of this book!

7. vi HOW TO DESIGN AND SPECIFY HIGH QUALITY LOUDSPEAKERS
Appendix I - in the PafLS Tutorial we take a peek behind the curtain that PafLS very carefully
lays over PAFEC, now PAFEC is a very powerful FEA engine, but it is a bit frightening to me at
least! As there is just so much that you could do with it - at least inTheory but you almost need
to know everything before you start! In this appendix we go through using PafLS to model
and ultimately build our sub-woofer driver.
Appendix J - in SpeakerPro Tutorial we will use some of the tools designed and written originally
by Geoff to aid loudspeaker drive unit design and system design: Included are standalone
programs, modules, and spreadsheets: BandPASS, BOXCALC, SpeakerPRO, TheoreticalBl &
VCoils amongst others.
Appendix K - in Statistical Analysis of Loudspeakers is all about, well numbers so statistical ana-
lysis is just using these numbers to tell us more information about a design product or process.
So, the first thing is to gather and then record data. Fortunately, pretty well all modern soft-
ware is capable of gathering the data by default. In this appendix we will explore some simple
statistical analyses from such data.
Appendix L - in the WinISD Tutorial we go through the steps required to enter a loudspeakers
parameters into the program, and then to use it to simulate the amplitude, SPL, impedance and
many other response curves. It is also useful for its database of loudspeakers. It is primarily
designed for Subwoofer Box and Driver as well as basic X-Over work.
Appendix M is a brief Autobiography of the Author: I am and have always been fascinated
by Loudspeakers and Amplifiers and how together they can reproduce Music. How they do
what they do, and why is and has been a driving force for me as long as I can remember.

8. Geoff is an acknowledged expert in loudspeaker design and measurement,
you may well have listened to one of his designs without knowing it!
Geoff demonstrates free, open source and low cost software being applied
to High Quality Loudspeaker Driver Unit Design. Modern computing
power, software and hardware have progressed to the point that such
analyses are now practical for an interested individual or small company.
Geoff show’s the process from initial concept through, specifications and
theoretical simulations into detailed design. Then onto the final parts and
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 Acoustics, so that it can act as a
primer for those specifying loudspeakers, those interested in using them or
those people new to loudspeaker or transducer design.
This book shows some of the techniques used in designing modern
loudspeakers and transducers and does so without getting bogged down in
detailed theoretical discussions and arguments.
This is a practical book, based upon nearly 40 years of designing,
measuring and testing loudspeakers and transducers. These loudspeakers
have been used in Automotive, Consumer Electronics, Hi-Fi, Mobile
Phones, Musical Instruments and Public Address Systems.
For further information www.geoff-hill.com/
Tetrahedral Test Chambers www.hillacoustics.com/