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SpeakerSim Demo
(c) 1988 dissidents
The Up Front Information
We would like to thank you for your interest in our
products. SpeakerSim is the outgrowth of our own search for a
good loudspeaker analysis tool. Actually, this demo shows off
the third generation of SpeakerSim. The first generation program
was produced in 1980 for a time sharing mini computer, while the
second generation appeared some 4-5 years later running on a
small 8 bit home computer. Neither program was released
commercially, rather, they were used for our design and
consulting work only. When the Amiga was introduced, it appeared
to be the perfect vehicle for the third generation of SpeakerSim.
SpeakerSim now boasts far more flexibility than was dreamed of
back at generation one. SpeakerSim offers a full Intuition
interface, color control, a variety of graphing modes, high
resolution display, and very fast calculation times. In fact, it
takes only a few seconds to produce plots that required several
minutes with generation two.
This instruction sheet assumes that you are familiar with
the operation of the Amiga personal computer. SpeakerSim uses a
relatively standard Intuition interface with pull-down menus,
requesters, gadgets and so forth. If you are not familiar with
these items, we recommend that you read the Amiga Users Manual
before running SpeakerSim. Some familiarity with AmigaDOS is
also helpful. Please note that when this manual says to 'select'
or 'click on' an item, move the mouse pointer over the object in
question and then depress and release the left mouse button.
This demo does just about everything that the real program does.
The exceptions are that this demo runs only in 640 x 200 mode
(640 x 400 version not available in demo), plotting is disabled,
and that you are stuck with a single driver and have no way of
calling in other loudspeakers for test purposes. Also, some of
the calculations have been altered, which slows down the plotting
times a bit. Finally, some of the 'saftey valves' and 'bullet
proofing' have been eliminated, so we suggest that you not try to
do anything that is out of the ordinary or just plain 'weird'.
Obviously, we had to 'sabotage' the demo to prevent its use in
serious design work!!
Amiga, Workbench, and Intuition are trademarks of Commodore-
Amiga, Inc.
'What's All This Then?'
SpeakerSim is a tool that will help you to design
loudspeaker systems. These systems can be used for a variety of
applications, including home Hi-Fi and professional sound
reinforcement. In order to successfully utilize this program,
you must be familiar with the concept of frequency response and
the practical limits and trade-offs of loudspeaker system design.
SpeakerSim's primary use is in modeling the lower half of
the audio spectrum. Technically, the program uses the
established Thiele-Small vented approach. Vented systems
(sometimes called ported systems) offer the advantages of simple
construction and smooth, extended frequency response. SpeakerSim
can also be used to model closed-box (AKA sealed or infinite
baffle) systems. Generally, the resulting graphs are accurate up
to several hundred Hertz. Above this, cone breakup modes
dominate the response curve. Since cone breakup usually occurs
at higher frequencies for smaller diameter drivers, midbass and
midrange drivers may also be modeled.
When first activated, SpeakerSim will simply show a blank
screen and its title bar. You should think of this surface as if
it were a very intelligent and dynamic sheet of graph paper. All
response plotting will take place here and you will have control
over a number of different parameters and graph types. You share
this surface with a number of small windows and requesters which
will pop up when SpeakerSim needs input from you. At the bottom
of the display is a status line containing relevant information
about the plot. By holding down the left mouse button, you can
determine the frequency/amplitude coordinates of whatever section
of the plot that you happen to be pointing.
Generally, there are two ways of using this program; either
in the design of an all-new system, or in the customization of an
existing system. In either case, you will be trying to produce
the smoothest, most extended response curve possible. SpeakerSim
allows you to alter the key parameters, Fb (tuning frequency) and
Vb (box volume). You may also note the effects of device
parameter variation by using the 'multi' graph mode. This mode
(actually two different modes) produces 14 frequency response
curves. One parameter of your choosing is altered from sweep to
sweep, allowing you to take construction tolerances into
consideration. It may also be used to speed the design process
in other ways. Once you achieve the response curve desired, you
may save it as an IFF picture, or dump the image directly to your
printer. SpeakerSim will also calculate the required vent
dimensions for you. SpeakerSim will multi-task with other
programs. You also have complete control over color, with 16 of
your choosing out of a palette of 4096.
Demo Lesson part 1
'So what's the basic idea here, eh?'
If you would like to see a few examples of SpeakerSim
graphs, examine the picture files with the Display utility. To
use Display, open the System drawer and click on the Display
icon. Now, while holding down the shift key, double click on the
desired Example icon. In a moment you will see the Example. To
stop Display, simply click in the upper left corner of the
screen.
When the program is started you will be greeted by a blank
screen and the title bar. To see an example of just how quickly
the program plots, hold down the mouse menu button and select
Do-It under the Do-It menu. You will be greeted with the
plotting requester. By default, a loudspeaker called 'Demo Unit'
is set to run. The other menu attributes default to 2D Normal
mode, Smooth shape, and Small Signal response type (You may wish
to verify this). Now, simply click on the 'Plot' button and
watch. The requester will disappear, semi-log paper will be
drawn with the appropriate scales, title and status bar, and the
plotting will start. Note that the title bar now says
'Graphing..' and that the pointer has turned into a 'Wait' sign.
The plot should only take a few seconds to complete, signified by
the return of the normal arrow type pointer.
You may now go back to Do-It, set new Fb and Vb values,
erase the screen and plot this new set-up. You may call Do-It as
many times in succession as you wish. To overlay graphs, just
skip the Erase step. You may also change any of the graph
attributes between plots, such as Mode, Shape, Multi-Parameter
(if applicable), and Response-Type. To find the coordinates of
any point on the graph, just hold down the left mouse button and
move the pointer to the desired location- the coordinates will
appear in the status bar, updated in real-time. Once you have
settled on a design worthy of remembering, you may select Print
from the Project Control menu for a hard copy, or you may select
Save IFF for a screen image file (standard IFF ILBM form). When
you are finished with the program, select Quit from the Project
Control menu, and answer 'Yes' when it asks for verification.
That's the basic idea behind using SpeakerSim. Now,
continue on to the next section for a more detailed, step-by-step
example.
Demo Lesson part 2
'I gotta know more, More, MORE !!!'
First, boot up your Amiga and start the SpeakerSimDemo
program. Don't alter any settings yet.
Let's plot a single small signal graph. For the attributes,
select Shape = Smooth, Mode = 2D Normal (Multi-Parameter will be
ignored), and Response-Type = Small Signal. Select Do-It and set
Fb and Vb to 'reasonable' values, like 40-60Hz and 2-6 cubic
feet. Note that, like Multi-Parameter, the Start and Stop
Factors will be ignored since we have chosen 2D Normal Mode.
(Either 2D Multi or 3D Multi must be chosen for these factors to
take effect, as you shall see). At this point, your screen
should be blank, so click on 'Plot'. In a few seconds, a nice,
flat curve should be drawn. Note that the status line now
contains the driver name and the chosen Fb and Vb values. Let's
examine this plot a little closer with the mouse. While holding
down the left mouse button, move the pointer around the screen.
You will notice that the Frequency (F) and Amplitude (dB)
coordinates in the status line are constantly tracking your mouse
position. Releasing the mouse button will "freeze" the readings.
At this point we would like to do an overlay, so it would be a
good idea if we switched pen colors. To do this, select Color
and click on one of the middle color boxes. To exit, select
either 'Okay' or 'Cancel'. To graph, select Do-It, type in new
value for Fb, and select 'Plot'. DO NOT SELECT ERASE. In a few
seconds a second plot will appear over the first.
You may now ask yourself "How tight is the manufacturers
quality control?". Let's examine how a +/-10% tolerance on
acoustic compliance (Vas) will effect the design. Select Mode =
2D Multi and Multi-Parameter = Vas. Select Do-It and set Start
Factor = .9 (10% down) and Stop Factor = 1.1 (10% up). Finally,
select 'Erase' and 'Plot'. A series of graphs is now drawn, each
one with a slightly different Vas. For a slightly different view
of the same subject, set Mode = 3D Multi, erase the screen and
re-plot. You will now see a third axis extending out from the
origin. This is the Multi-Paramter axis (in this case it
represents variations in Vas). Each curve is displaced at an
angle so that trends can be easily spotted. This displacement
'un-calibrates' the mouse cursor. In order to get a correct
reading for any curve, click on the appropriate color box from
the 14 that appear along the right edge of the screen. A small
arrow will point to the selected color. As you may have noticed,
Multi plots take awhile to generate. You can speed this process
considerably by setting Shape = Sketch (do this, erase, and
re-plot). Thm cost for this speed is a somewhat 'jaggy' shape.
You can also use Multi to run through designs quickly by
using Fb or Vb as the Multi-Parameter over wide ranges. Let's
say that a friend wants to use this driver in a 2 cubic foot box
that already exists. Where should you tune it? For this run,
set Mode = 2D or 3D Multi, Multi-Parameter = Fb, Start Factor =
.5 and Stop Factor = 2.0. Vb must be set to 2 cubic feet. For
Fb, try around 40 Hz, as this will produce a range of 20 Hz to 80
Hz, which should certainly show us the trend. Once these
variables are set, erase the screen, and plot. Note the
variation in shapes. Normally, you would find the flatest curve
and investigate further.
Once a satisfactory small signal response is produced, you
may wish to check the maximum acoustic output power. Set Mode =
2D Normal, and Response-Type = Max Power. Set Fb and Vb to the
desired values, erase, and plot. This curve represents the safe
operating area of the driver/enclosure. It is in essence, the
lesser of both the Thermal and Excursion Limits. As an exercise,
overlay the Thermal and Excursion Limit curves on the Maximum
Power curve and note which type dominates at given frequencies.
These curves can be useful for finding possible failure modes.
Note that the power graphs indicate signal strength in dBW. 0
dBW = 1 acoustic watt on these graphs. Designers of high output
monitors or PA systems should find this useful for minimum
acceptable output and direct/reverberant field calculations.
The only item left in the design cycle is to determine the
vent dimensions. To get these numbers, select 'Run Vent' from
the Project menu. The vent is calculated using the most recent
settings for Fb and Vb, (the drivers displacement volume also
plays a role in this).
When a given design is settled on, it would be wise to save
the result. You have two basic options; either save it as an IFF
picture (ILBM) file, or dump the screen image to your printer.
Saving an IFF pic takes far less time than doing a print dump.
To save the screen, select Save IFF from the Project menu. You
will now be greeted with the Save IFF file requester, which
allows you to scan your disks and directories to see what's
available. After finding an appropriate disk and/or directory,
type in a name for the graph. (Try something like FirstPic on
the RAM: disk.) When you've got the save name set, click on the
'Okay' button. A small requester will now appear with your
chosen name, and a place for an optional graph note for future
reference. This note will be saved in place of the screen's
title bar, and is particularly suited for use with the Display
utility. When you've finished typing, click on the 'Save'
button. Saving should only take a few moments. Now, if you pull
down the SpeakerSim screen and open the RAM disk on Workbench,
you will see your graph's icon, saved as FirstPic. If you try
saving another graph as FirstPic, the program will warn you that
a graph with that name already exists. The inverse of Save IFF
is Load IFF, which lets you call in old graphs to use for
comparisons, design starting points, etc. To try this, first
call up Do-It and erase the screen (exit via 'Cancel'). Select
Load IFF, and when the file requester appears, scan the RAM:
disk in order to see the available files. (Use the 'Next Disk'
button if required.) You should see the name of graph which was
just saved (FirstPic) as well as its icon (FirstPic.info). (If
it is not visible, scan though the names with the scroll bar and
arrows placed off to the right). By clicking on the graph name,
it will automatically be loaded into the 'Name:' box. At this
point, simply click on the 'Okay' button and a small requester
will appear with the chosen file name, and two loading choices.
If you click on 'Use Picture Colors', the graph will be loaded
with its own color map. By selecting 'Use Present Colors' the
picture's color map is ignored. (In our example both the picture
and present maps are the same, so it won't matter which one you
choose). If desired, you may load in any of the demo graphs, and
experiment with the Present/Picture choice.
For a direct hard copy, select 'Print' from the Project
menu. Two types of printing are supported; 'asynch' if memory
allows (which lets you continue doing other things), and 'synch'
(which forces you to wait until printing is completed before you
can do anything else with SpeakerSim). Generally, you will want
to say 'Yes' at the 'Remap background to white?' prompt in order
to minimize printer ribbon wear and tear.
The only thing left to do is to quit the program. Quit is
found at the bottom of the Project menu. Verification is asked
for. Answer 'Yeah' if it's really time to do something else. If
you find it difficult to do something else, you should answer 'No
Way', and continue to graph (but don't forget to let the dog
out).