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P-FILTER.DOC
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1990-05-31
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Documentation for the program P-FILTER.
P-FILTER is a design aid for loudspeaker crossover networks. The program
designs standard topology, 2 and 3 way, 2nd and 3rd order, All Pass
crossover networks based on the formulas of Robert M. Bullock. Crossover
schematics with parts values are displayed. A frequency response curve is
plotted for the complete system based on resistive loads. The design is
saved to a file for subsequent loading into the Loudspeaker Modeling Program
(LMP) described in this document.
System requirements: DOS 3.0+, 384K, 1 floppy, Herc, CGA, EGA, VGA monitor.
User requirements : familiarity with loudspeakers and crossovers; a burning
desire to build your own system.
Herc users must run their graphics program first.
Starting the program: type P-FILTER and press ENTER
TUTORIAL/EXAMPLE.........................................................
Select <C> to create a new model.
Enter the number of drivers (ways) in the system. Drivers in parallel are not
considered as separate drivers. So, for a 2 way system, enter 2. For a
3 way system, enter 3. Enter a 3 for this example.
For your convenience, you may enter a descriptive name for each of the
drivers. Driver #1 is treated by the program routines as the woofer.
Driver #2 is treated as the tweeter. Driver #3 is treated as the mid-range.
Indicate whether you wish to hook up the driver in out out of phase. For
this example, accept all the default N's for phase.
Choose the order of the network you wish to design. For this example, pick
2 for a second order network.
Enter 500 for the lower crossover frequency and 4000 for the higher.
Enter 8 for an 8 ohm woofer.
Enter 8 for an 8 ohm mid-range.
Enter 8 for an 8 ohm tweeter.
The crossover is now designed and you are returned to the menu.
Press V to view the schematic and parts list.
Note that the band pass filter has some gain. This means that for a system
with a woofer sensitivity of 90db, a mid-range sensitivity of 90db and a
tweeter sensitivity of 90db, the output from the mid-range driver, when
connected to the crossover, will be greater than the outputs from the woofer
and tweeter. The resistor Ra can be other than 0 ohms to absorb this excess
gain by appending the letter A to the mid-range impedance. If an Ra of >0
is used to absorb the excess gain, the band pass component values will be
different than they would be if Ra=0 because the load on the filter is
different. An L or T pad may be used to compensate for the gain without
affecting the component values.
Press M to go back to the menu.
Look at the response curve by selecting R.
Note the dips in the curve at 500 and 4000. 2nd order networks have a
180 degree phase shift at the crossover point. To correct for this, the
mid-range driver should be connected in reverse phase.
Press M to return to the menu and M again to modify the design. Cycle
through by pressing enter to accepts the defaults and input Y for the driver
#3 phase. Contine pressing enter until back at the menu. Now check the
response curve.
REGISTRATION.............................................................
1. Register P-FILTER only for $15. Upgrade contains 1st order filter, also.
2. Register P-FILTER and recieve the LOUDSPEAKER MODELING PROGRAM, as
described below, for $60.
3. Register P-FILTER, recieve the LOUDSPEAKER MODELING PROGRAM and the
Loudspeaker Design Cookbook for $70.
Send the registration fee to: SITTING DUCK SOFTWARE
PO Box 130
Veneta, OR 97487
(503) 935-3982
The LOUDSPEAKER MODELING PROGRAM (LMP)......................................
Similar in operation to P-FILTER, LMP will import the crossover design from
P-FILTER and allow you to add to add information relative to the various
drivers being used in the system. Information which may be added includes;
the low and high frequency cut-off's and Q's of each driver, relative
foreward/rearward offset of each driver, each driver's sensitivity, etc.
LMP plots a predictave frequency and phase response of the completed system.
Designed systems may be kept in a disc file for later loading.
For more information on loudspeaker system design, I suggest the Loudspeaker
Design Cookbook by Vance Dickason. This book is available from us for
$20, whether you register P-FILTER or not.
Armed with P-FILTER, LMP, Dickason's cookbook, some speaker catalogs and
a workshop, you are on the road to designing your own speaker system. Use
our newest program, The Listening Room, to find the best locations, in your
room, for the speakers and seating position. Proper setup of your listening
environment ensures freedom from standing wave and boundary effects
problems.