Contents of the PERFECT.DOC file
* PERFECT BOX *
Loudspeaker Enclosure Simulation
Neville Thiele - Richard Small Model
January 1, 1990
Warren A. Merkel
2851 Newcomb Ct.
Orlando, FL 32826
Program registration is required.
See final page of this document for details.
***** PERFECT BOX ***** Version 4.5 ******
* Program and documentation written by *
* Warren A. Merkel *
PERFECT BOX is a Computer Aided Design (CAD) program for the
simulation of loudspeaker performance. PERFECT BOX is a very
powerful tool for the amateur or professional speaker builder.
Loudspeaker design is a balance of compromises involving
enclosure size, low frequency cutoff, and transient response.
This program will allow you to model the loudspeaker-enclosure
combination entirely on your PC. With proper use, you can be
assured of the best (lowest in frequency) bass response in the
smallest enclosure. You can then build the enclosure with full
confidence that the final result will not become the new dog
house for Fido, but an accurate, natural sounding system.
PERFECT BOX does not deal with midrange or tweeter drivers. It
only considers the low frequency driver in a multi-way system (or
the only driver in a full-range system.) Since enclosure
alignments, such as box size, box type, and box frequency (now on
referred to as Alignments), effect the woofer response, PERFECT
BOX models systems covering low frequencies from 10 to 200 Hertz.
The mathematical model will hold for higher frequencies, but I
have optimized the program for the most useful range.
PERFECT BOX requires certain parameters that uniquely define the
driver's characteristics. Some of these parameters have been
coined as the Thiele/Small (or T/S) parameters. If you are new
to loudspeaker design, it isn't important that you understand
what each value represents, only that you are able to obtain
these values from the driver manufacturer, or measure them
yourself (the preferred method.)
Free air resonance (Fs) Hertz
Q Mechanical (Qms)
Q Total (Qts)
Volume Equivalent Compliance(Vas) Ft^3
D.C. Voice Coil Resistance (Re) Ohms
Peak Cone Displacement (Xmax) Inch
Effective Piston Diameter Inch
Thermal Power (P) Watts, RMS
PERFECT BOX allows you to store these driver parameters in a data
file ("BOXDATA4"). This file can store characteristics for
thousands of different drivers. A few sample drivers have been
included so that you can experiment with PERFECT BOX. These
samples represent "real life" units which are currently available
at this time.
PERFECT BOX uses a classical high-pass filter model to simulate a
loudspeaker mounted in an enclosure. The order of a loudspeaker
system represents the same characteristic roll off as that of an
electrical filter. The roll off rate (or slope) is:
roll off rate = (6 * system order) dB/frequency octave
or roll off rate = (20 * system order) dB/frequency decade.
PERFECT BOX can simulate both infinite baffle (sealed box), and
vented (ported) systems. Each of these systems have a natural
order in which they resemble an electrical high pass circuit.
For infinite baffle, order=2, or that is to say that they are of
2nd order. And for vented systems, order=4. It seems that each
kind of enclosure has pros and cons associated with them.
In general, both systems, if properly aligned, perform with the
same low frequency response. In practice, an infinite baffle
system is easier to build, and possibly has better transient
response. The vented system offers slightly higher efficiency
(2.9 dB), and good cone dampening near the vent frequency (but
less below Fb.) My preference is for 4th and 6th order systems.
The sixth order system involves the use of a 4th order system
tuned slightly lower than the 4th order ideal, and an 2nd order
active equalizer circuit in the amplifier path.
***SYSTEM CUTOFF FREQUENCY***
This is the frequency at which the system amplitude response is
exactly 3.0 dB less than at a mid-band reference frequency (where
response is basically flat at 0 dB.) This is a standard point of
interest that can be used to compare with another system's low
frequency response data. This point on the frequency plot
represents the "half-power" amplitude, as compared to the
amplitude at a mid-band reference frequency.
***OTHER SYSTEM ORDERS***
As you are probably aware, a Graphic Equalizer can make a
tremendous effect on the way your speaker system sounds. The
bad news is that an equalizer (EQ) usually doesn't have a control
exactly centered on the proper frequency to properly extend low
frequency cutoff, and thus will typically make matters worst.
PERFECT BOX can incorporate the effects of either a 1st or
2nd order, ACTIVE EQ (that you must build) into the loudspeaker
model. The affects of which are easily depicted in the PB Graphic
This mini EQ consists of a simple active high-pass filter, having
a low turn-over (cutoff) frequency (typically 20-60 Hz), which
actually has a slight boost (peak) in its amplitude response
above its cutoff frequency. If the amount of boost and cutoff
frequency are suitably chosen, the total system response
typically is extended a half-octave or more, while
providing infrasonic (rumble) filtering to boot. In
2nd-order EQ's, the boost is controlled by the "D" parameter
(D=1/filter Q, for you filter buffs.) Typical values of
"D" range from 0.3 to 1.414, giving most to least amount of
amplitude boost. A "D" of 0.52 gives approximately 6 dB of
boost, a typical starting value. The EQ frequency and the
"D" factor should be juggled for the flattest, most extended low
frequency response. Use the "EQ2.EXE" program to calculate
components to implement the 2nd order EQ.
A word of caution. Using large amounts of boost may tax small
power amplifiers (less than 50 Watts,RMS) beyond their
limits. A properly designed 3, 3.5, 5, or 6th order system will
not over tax your amplifier unless you listen to music either :
1. at extremely high SPL levels,
2. with heavy (double fortissimo) organ pedal notes, or
3. use other signal modification equipment such as an
extremely low-end boosted Graphic Equalizer
(quite stupid!), or Sub-Sonic Synthesizer (Harmonizer.)
The EQ can be inserted into the signal path of your system at
either a "Preamp-out/Amp-in" loop, or "tape monitor" connection.
A simple design for a 2nd order EQ is provided with PERFECT BOX.
Type EQ2 at the DOS prompt to execute this option. You must
have (at least) a CGA graphics card in order to run EQ2 because
the electrical schematic is drawn on the screen after all of the
circuit values are calculated.
IV. RUNNING PERFECT BOX - PROGRAM EXECUTION:
If you have an IBM, Epson or HP LaserJet compatible printer,
you can print the graphic plots generated by PERFECT BOX. Perfect
Box 4.5 has built-in support for Graphic printing for these
printers in CGA and EGA modes. You no longer have to use
the DOS GRAPHICS.COM or PERFGRAF.COM included with previous
releases of Perfect Box. You might have to set your printer
switches to DEFEAT "automatic" Linefeed [LF] after a Carriage
Return [CR], (see your printer manual.)
I have included a simple batch file called GO.BAT,
which will execute Perfect Box for you. You may change this
batch file to suit your particular needs. The actual program
file is BOX4_5.EXE. You will not have to change the program
file name until you receive a future upgrade of PERFECT BOX.
Insert the PERFECT BOX program disk into your default disk
drive, and type GO . You should see the PERFECT BOX
opening screen. Take the time to read this screen and remember
that many, many hundreds of hours of effort have been put into
this program. If you use this program more than five times, you
must be understanding the purpose so don't forget your obligation
to this author!
If you see an error message stating "Bad Command or
Filename", check to see if you are in the same directory as the
PERFECT BOX files. After about 5 seconds, you may press RETURN
If all is well, you should see the following screen.
PERFECT BOX - Version 4.5 Current Time:
Drivers on file : 1573
(B) Browse the database Boxdata path : G:\perfect\
(L) Load a driver by # Graphics mode : EGA
(S) Store New Driver data
(E) Edit the database Quick Mode
(B) Boxdata Reports Utility
(C) Change Boxdata path
(P) Sort/Pack Boxdata file
(A) Append new records
REGISTERED TO: (W) Write defaults
Trial copy. (D) DOS Shell
Your name or (Q) Quit to DOS
company name should
be listed here.
Use PgUp - PgDn - Home - End - - - = Select - or HotKey
Each of the menu choices may be executed by either pressing the
"key letter" or by using the cursor arrow keys to highlight the
choice and then pressing RETURN. If you have a mouse, you can
choose by clicking the left button on any of the options
(B) Browse. This option will allow you to view the drivers
currently in the BOXDATA file. You can move through the list
using the arrow, Home, End, Page Up, and Page Down Keys. The end
key takes you to the bottom of the list, and Home will return you
to the first listing. Use these keys to point the "flashing
arrows" at your driver choice. If you have sorted your Boxdata
file using the Sort/Pack option, you can press any of the Alpha
keys (A-Z) to jump to that corresponding Manufacturer name. If
you have a mouse installed, you can move the highlight arrows
straight to the driver of interest with the left button. The
right button will load the currently selected line.
Browse-Choose the driver with the arrow keys and press RETURN.
106 PR 38 XM 150 POLYDAX 15",PRO,MONITOR,96dB
107 PR 38 XT 150 POLYDAX 15",PRO,FOAM EDGE,MONITOR
108 PR 38 XT 250 POLYDAX 15",PRO,99dB
109 PR 38 XT 350 POLYDAX 15",PRO,HI-POWER,100dB
110 TA-305 FSW PRECISION DUAL V.C. SUBWOOFER
111 TA-305F PRECISION OMEGA
112 TD-125F PRECISION ALPHA
113 TD-255F PRECISION EPSILON
114 TD-255F-SW PRECISION 10",Alum Dual VC,90.7dB
115 TO-205F PRECISION INFINITE BAFFLE 8"
(** Only ten drivers are listed here for clarity. **)
=Quit - =Edit - =Load defaults.