1 Introduction
reference group
Updated 2005-01-26
This document gives a few examples how LspCAD 6 is used in a real situation. This document is meant to expand with more examples as time goes by. All the examples are available as project files in the examples folder.
2 An optimization example, a two way
crossover
In this example we have a simple two-way
crossover (Two way tutorial 1.lsp).
We see that L1 and C1 only affect the
response of the Bass unit. Open up the
advanced settings for L1.
Check the Optimize box and also the box
next to “Bass”.
We have now instructed the
optimizer that L1 should be
optimized when we start to
optimize the response of the Bass
unit. Do the same with C1. In a
similar way we see that C2 and L2
only affect the response of the
Treble unit. (Two way tutorial
2.lsp)
Open the Optimizer, we choose to
optimize the response of the Bass
unit, we therefore click on the box next to “Bass”, if we look at the schema we will see that the component text for L1 and C1 has become boldface.
Click on the Range tab and set the Include range to the
interval 100 to 6000Hz
target for the optimization, click on
the Target tab and then on the LP
tab, check the Enable box and set
Fc to 2000Hz and order to 2, also
set the alignment to Linkwitz.
With this we are ready to start our
optimization.
Click on the Start button and watch
the miracle happen. Optionally one
can turn up the step size to get a
faster convergence. When the stop
the optimization L1 and C1 are
roughly 0.160mH and 39uF and the
mean error is close to 0.01dB.
For some reason it is possible that
one did not like the result, the
remedy is simply to click on the
Undo button to get back to the state before the Start button was clicked.
optimize the response of the treble
unit for a 2nd order HP Linkwitz
alignment at 2000Hz, but instead
we test what the lock XO option can
do for us.
We check “Treble” in the optimize
tab, also wee set the target to flat,
and the range to 100 to 20000Hz
and the optimizer screen looks like
After a while we have a crossover with a flat system response and a crossover frequency locked at
2000Hz. (Two way tutorial 4.lsp)
3    A closed box… and a bass reflex
box
At first glance the modeling of various loudspeaker boxes might look overly complex, the intention is however that it should be possible to model other, more complex boxes than the standard closed, bass reflex and passive radiator boxes. This section describes how modeling of a closed box is performed in LspCAD, this example is then extended with a bass reflex port.
box
3.1 Closed
First of all we need a signal source and a Loudspeaker unit, pick this from the component tray, we also need to ground one of the speaker terminals (Closed tutorial 1.lsp).
In a closed box we have free air in
front of the speaker cone. This is
modeled as a Radiation element.
Pick a radiation element. This acts
a load of the front part of the cone.
Behind the code we have a box
and also a load from the air inside
the box. This is modeled with a Box
load and a Box component. After
the components are picked and
arranged a little on screen (don’t
use too little space) we have a
schema that looks something like
(Closed tutorial 2.lsp).
So far we have been in edit mode, now it is time to enter simulate mode. Said and done, we click on the Simulate tab.
In this mode we need to do a few extra things before we are in business.
The Radiation component needs to know a little about the
loudspeaker unit (such as Sd). For this to happen we click on the
Radiation component and a small configuration dialog appears.
Click on the dropdown list box below “Ref to…” and select
“Loudspeaker unit 1” (nothing else to select by the way). Once
you have done this you will see a typical 2nd order high pass
response of a closed box in the graph window.
We are getting close but we are not
quite there yet, recall that the Box load
component models the load behind the cone, for this to happen
the Box load component must also know a little about the
loudspeaker unit. Click of the Box load component and set the reference to “Loudspeaker unit 1” as
before.

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