It’s difficult to recommend just one
loudspeaker software program because of the varying nature of the drivers
parameters under different conditions and the level and ability of the
operator to input all the data required. If you put the same box details
into 5 different programs you would get 5 different plots that all look
slightly different. This is not due to some programs being more accurate,
but down to the better programs needing more details and taking more
parameters into account to come up with there output. The better programs
can also start to predict, and that’s all it is a prediction, what changes
will take place with higher levels of input power. All programs derive there
output from the drivers T/S parameters and these are measured at very small
signal levels, usually less than 1 watt, and so when you hook the cabinet up
to your 500 watt amp and start feeding it some real world power most of the
T/S parameters change considerably. The fs will rise due to voice coil
heating effects and so will the Re. Vas is also temperature and humidity
controlled and so even if the driver is not connected to an amp will change
from day to day quite significantly. All this makes it impossible to predict
what will happen accurately. The simple programs like Win ISD and Bass Box
Pro just take into account the most basic parameters needed to give an
output. They use a set of calculations derived by T/S to calculate what the
optimum box size should be and will also let you suggest the box size with
the program showing you what the plot would look like. They will also come
up with the recommended port sizes and port lengths. Again you can enter
your own port sizes and the program will work out the length needed and also
the air speed within the port to make sure you will not get port noises. Out
of the two Bass Box Pro is the better program, but Win ISD is free and
because both these programs take the same parameters into account the
resulting plots look quite similar. There will be one difference in the
output plot between the two programs and this is due to the internal box
lining. Win ISD does not take the box lining into account and so its output
is only a rough guide. Bass Box Pro does take the amount of lining into
account and you enter whether you have minimal, normal or maximum amounts of
lining or fill. It should also give this as percentages, so it would allow
you to enter 10% (minimal fill, just the rear wall lined), 50% (normal fill,
opposing walls lined), or 100% (maximum fill, all surfaces covered). This is
an important parameter for a program to take into account as the more fill
you use the bigger the chamber appears, which in turn effects the port
length. These two programs also allow you to use the golden ratio to derive
the optimum box shape. While this is a good feature as it stops you making
overly short and deep cabinets, they don’t take driver size into account. So
it might suggest you make the cabinet 400 mm wide when you driver is 450 mm
wide. But used as a rough guide it’s quite a good feature. While were on box
shape, don’t get overly concerned about making the optimum shape box. If a
box has the right and correct amount of fill and is braced well then the box
shape is a secondary thing. Its good if you can get the shape near to
optimum but fill and bracing will make a lot more difference to the result
than the shape of the cabinet. Try to avoid making a box with the exact
dimensions in height, width and depth as this could have a problem with
standing waves.
The next program up from Bass Box Pro and similar programs is something like
Leap. This does all the simpler programs do but tries to give a more
accurate result by attempting to calculate the effects of box losses, port
non-linearity and effects due to the coil heating up. You don’t have to
enter too many more parameters than you would have to for the simpler
programs, it’s just that the program has a better understanding of the real
world. You do need to have a good understanding of speaker design though to
be able to interpret the results. Leap also has a really good frequency
measurement section. So you can make frequency, dispersion, impedance and
other time related plots from the cabinets you have just built. All this
comes at a price though and if your not going to use the measurement side of
the program, which is the best part of the program, you might want to
consider something else. As mentioned Leap is very good at giving frequency
and time dependent plots, but if you already have a system for doing this
then it’s a lot to pay just to be able to calculate the optimum box size. I
would be tempted to use something like Bass Box Pro instead to come up with
the basic box size, port lengths and box shape and then tuning the cabinet
by ear using the measuring equipment you already have. Why make the best
prediction you can when you can actually measure the plot for real and then
alter things like the amount of box fill and port lengths until you hear or
see what you like. Its ok to make the best prediction you can about how a
cabinet will behave, but it is a prediction and like fortune telling I don’t
really buy into it. Leap might give you a realistic prediction, but it will
not tell you how the cabinet will sound, so you might as well use a simple
program and your ears.
One step up from Leap and probably as far as most mere mortals want to take
it are modeling programs. These try to make a prediction by taking all the
details you can throw at them and then using known mathematical models to
calculate the behavior. One such program I use is called Akabak. This is not
for the fainthearted, as it requires a level of knowledge from the person
inputting the data that can only be gained from a life’s time of experience.
So if you don’t think that you are going to give your life over to designing
speaker systems all day long then look elsewhere. It’s a full time job this
program, not a hobby. The set of parameters required are not like you find
in programs like Bass Box Pro or Leap, you don’t even have to start with a
speaker, you can define all the parameters of the voice coil and then go on
to model a suspension system and cone assembly around the voice coil to end
up with the definitive driver. You don’t enter values into defined boxes
either, most data is inputted using scripts. These scripts are complicated,
even for a single driver in a simple sealed box. Below is a simple script
from Akabak showing a driver with impedance compensation firing into a horn.
|
| Driver model with discrete
elements System
'Dis '|Voice coil iimpedance
'I1' Node=1=2
Z={ Z=Ree + j*w*Le; }
|Motor Gyrator
'G1' Node=2=0=3=4 Bl={Bl}
|Mechanical part Impedance
'I2' Node=3=5
Z={ Z=Rms + j*(w*Mms -
1/(w*Cms)) }
|Reverse diaphragm Coupler
'C1' Node=4=0=10 dD={dD|
Front diaphragm
Coupler
'C2' Node=5=0=300 dD={dD}
|Radiation Radiator
'R1' Def='C2'
Node=300
WEdge=20cm
HEdge=50cm
Def_Driver
'D1' Meas_DoNotModify
dD=35cm
tD1=-50mm |Concave dome
fp=800Hz |Mass reduction frequency fs=60Hz
Mms=58g
Qms=3.41
Qes=0.32 Re=5.58ohm
Le=85mH
Inspect/Network Impedance
|Impedance compensation
Capacitor
Node=1=0 C=20uF
Rs=5ohm
BassUnit
'B11' Def='D1' Node=1=0
x=0
y=-10cm z=0
HAngle=0 VAngle=0
WEdge=20cm
HEdge=50cm
Filter
'F1' fo=300Hz
{b0=1; a2=1; a1=1.414214; a0=1; }
|Diffraction of finite baffle
System 'Bass'
BassUnit
'B11' Def='D1' Node=1=0
x=0
y=-10cm z=0
HAngle=0 VAngle=0
WEdge=40cm
HEdge=50cm
Filter
'F1' fo=300Hz
{b0=1;
a2=1;
a1=1.414214; a0=1; |
System
'S1' Horn driver
Driver 'D11'
Def='D1' Node=1=0=20=0
Duct
'Du1' |sound path around the
voice coil Node=20=0
WD={pi*5e-2}
|Perimeter of magnet cap (formula parser)
HD=8mm |Width of magnet cap. Len=20cm
|Depth of duct.
|Begin of funnel with a duct. Duct
'Du2' Node=20=30
dD=10cm |duct diameter Len=10cm|duct len
Vf=1.8cm3
|The mid section of horn is
conical Waveguide 'W1'
Node=30=40
Conical dTh=10cm
|throat diameter
WMo=50cm
|mouth widthHMo=50cm
|mouth height
Len=20cm |funnel length Radiation part of horn exponential
Horn
'H1' Node=40
T=1
|simple exponential flare
WTh=20cm
HTh=10cm |throat width/height
WMo=50cm
HMo=20cm |mouth width/height
Len=50cm
Rw=50cm
Wc=20cm
|radiation cone (horizontal)
Rh=20cm
Hc=10cm
|" (vertical)
x=0
y=0 z=0
|radiation position of horn HAngle=0
VAngle=0
Generate measured loudspeaker
with menu point:
|
"Tools/Generate Def_MeasRadiator File"
|from the files:
|
"\Import\Horn.spl"
and|
"\Import\Horn.imp"
|Input voltage: Uin=2.83V
peak |Distance: r=1.m
|Cross section 10cm x 5cm |
| I did said it wasn’t
simple. You even have to manufacture your own horn from conical sections,
ducts and funnels. So there’s no easy asking what happens if use a certain
driver with a horn this long with a throat this big and a mouth this big. It
is actually quite simple to use, its just that it take a life time to know
what to enter. Akabak will also help you to design active or passive
crossovers, many of the other programs listed here will do the same but Akabak
allows you to insert any amount of filters anywhere into the chain and see
what result it has on the plot. You can also design 4 or 5 way systems on
Akabak, with each band having its own driver, cabinet and filter network.
So that’s about it for
speaker software. People often ask what program do I use. Well I use all of
the ones listed above. You get to know how the results of all the different
programs relate to how the product will sound when you build it. So for one
project I might use all the programs to see what might happen. It kind of
covers it from all angles then. If a friend of mine wants a simple sealed
enclosure for the back of his car then I would use Bass Box Pro as there’s
no point in looking into it any further. Bass Box Pro also has a nice feature
that gives you the response for the back of a car, as it is very different
form a cabinet in room response. If I’m asked to design a two way system
with a 12” driver and a 1” horn in a trapezoidal box for a company then I
would use Leap to derive the box volume and port sizes and then make the
cabinet and continually make modifications and do listening tests until I was
happy with the result. For horn cabs, be it bass or mid top designs I would
use Akabak. I would also use David Mc Beans excellent
Horn Response
program.
While it does not go into the depths that Akabak does it is really nice to use
and you are able to see very quickly if a design is worth continuing with
early on into the project. I like it for bass horns and it seems quite
accurate at predicting what will happen when you finally listen and measure
the design. Horn Response is a free program and I thank David very much for
his input into making this planet a better place to be in with people such as
himself giving so freely that which others would not. So as you can see there
is no one program that does it all, I even have other programs (one by JBL)
that fills the gaps that the other programs leave. I sometimes even resort to
using a hand calculator and paper in making a design and then checking it in
the software domain to see how accurate I was. I also use a 3D CAD modeling program to draw and plot the final plan of the design. All the plans on the
speakerplans site were drawn by hand on a technical drawing board. One of my
jobs in life is as a speaker and system designer, and so if I summit plans to
a big company I always use the 3D computer CAD program as they are expecting
it, I can also come up with a file that can be used by a CNC router for large
scale manufacture. But for the simple plans on the speakerpalns site I like to
resort to doing things by hand as I find it quite a relief from having to work
with computers all day.
So which program for who? If
you’re a novice then don’t Leap into Leap or Akabak. They will do your
head in and you will forget about speaker designing forever. Start off with
Win ISD, it’s free and will teach you most of the basics quickly. You will
need to know that if you make the rear chamber of a ported box bigger you can
then reduce the length of the port, or that if you make the port diameter
larger you will have to increase its length to achieve the same tuning
frequency. Things like this can be learnt in all the programs, with the
exception of Akabak, which assumes you know everything about speaker design.
Akabak is a bit like a mirror in that it doesn’t tell you anything more than
you know already, it just shows you what you do know and how to better to
apply it. So the basics can be learnt form Win ISD, but when you grow out of
that then Bass Box Pro should keep you happy for years. It will never really
push you as a designer but will give you the opportunity to design some good
sounding sealed, reflex, 4th and 6th order bandpass
enclosures and even passive radiators. It takes enough detail into account to
be able to construct a cabinet that will sound a lot like its plot suggests.
If you get bored by this program and want to take it further into the
scientific realm then get Leap. The ability to be able to make measurements is
one of its strongest features, but the fact it takes a lot more parameters
into account make it more suitable for the pro designer or very serious
hobbyist. And finally if you are a nutter and your every waking and sleeping
thought is about speaker designing then you should get Akabak. If you are not
mad before you use this program you will be afterwards, its just really good
that it makes you go mad in a way that wants to make other people on this
planet have a good time and enjoy themselves though being better able to hear
music reproduced more accurately.
To finalize I would not jump
into an advanced program like Leap without some kind of prior training. You
could gain your training in that program but it would be slower doing it in a
program that assumes you know what you are doing that in a simpler program
that is there to help you. I know you want to do the best job you can quickly,
but in the end of the day it’s all about having something to listen to.
Starting off on an easier program will enable you to have a working cabinet
that will sound really good in weeks.
To
do the same thing in Leap will take months and probably years. And then as you
might have missed something you should have already known, your end product
might be not as good as if you had designed it in a simpler program that made
sure you understood what you needed to know. If you seriously want to change
the world and come up with groundbreaking designs that have multiple patents
applied to them like many of the systems I design for Big Mouth Speaker
Systems then use Akabak. But be sure this is the direction you want your life
to go in, as there’s no turning back. |
|
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