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1988-06-16
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***** PERFECT.DOC ***** (v 3.0)
I. INTRODUCTION:
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. You are 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
refered 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.
II. REQUIREMENTS:
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
(more accurate.)
PARAMETER UNITS
Free air resonance (Fs) Hertz
Q Electrical (Qes)
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
NOTE: Qts=(Qes*Qms)/(Qes+Qms)
PERFECT BOX allows you to store these driver parameters in a
data file ("BOXDATA"). This file can store characteristics for up
to 998 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.
-1-
III. DEFINITIONS:
SYSTEM ORDER: 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/octave
or
roll off rate=(20 * system order) dB/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.
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 represents the "half-power" amplitude, as compared to the
amplitude at the mid-band reference frequency.
OTHER ORDERS: As you are problably 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 into the loudspeaker model. 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 freq. 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,
typical starting value. The EQ frequency and the "D" factor
should be juggled for the flatest, most extended low frequency
response.
-2-
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 organ pedal
notes, or 3. use other signal modification equipment such as an
extremely low-end boosted Graphic Equalizer (Stupid), or Sub-Sonic
Synthesizer (Harmonizer.)
The EQ can be inserted into the signal path of your system at
either a "Pre-amp 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
a graphics mode in order to run EQ2 because the electrical
skematic is drawn on the screen after all the circuit values are
calculated. You may execute a screen dump (PrtSc) for a hardcopy
(as with all screens in PERFECT BOX.)
IV. RUNNING PERFECT BOX:
PROGRAM EXECUTION: Before you start PERFECT BOX, you must
execute your DOS command GRAPHICS.COM. This command sets aside
memory for doing graphic dumps of your CRT to your graphics
printer. I have created a simple batch file called GO.BAT, which
will do this for you. Of course you must have either GRAPHICS.COM
on the program disk or in the current DOS path. The actual
program file is BOX3_0.EXE.
1. Insert the PERFECT BOX program disk into your default
disk drive, and type GO <Return>. You should see the PERFECT BOX
opening screen. After about 5 seconds, you may press RETURN to
continue. Note: All questions requiring operator input that have
default values will have those values prompted between
parenthesis. Just press RETURN for the default.
2. At this point, you need to choose either ;
1. for Automatic Parameter Entry or,
2. for Manual Parameter Entry.
If you choose 1., you can LIST, LOAD, STORE, EDIT or PRINT
driver parameters from the BOXDATA database file. Option 2. will
ask you to enter each driver parameter and box characteristic, one
at a time. This choice is good if you only want to run a driver
through PERFECT BOX once, with out saving the parameters. Since
you can store up to 998 different drivers in the data file, I
rarely use this option!
3. Choose "Automatic", and then choose "1. LIST current
Drivers in database. You should see a list of drivers with a
record number for each. You may choose a particular driver from
this list by entering the record number, and then press RETURN.
4. Or, choose "LOAD a Driver by Record Number," and enter
the record number you had memorized in the "LIST" step above. You
will be prompted if this is the right driver. A "N" will take you
back to "Enter Driver record number."
-3-
5. At this point, PERFECT BOX will calculate the "Ideal Box"
volume, the port frequency for that ideal box volume, and the
cutoff frequency (-3dB point.) The ideal box volume is the
smallest enclosure that provides the flatest, deepest low
frequency response. The cutoff point will give you a general idea
of how low the driver will perform in any box design (best case.)
The port frequency (box frequency) must be set as calculated to
obtain the cutoff predicted.
6. Now you must choose the system order. If the driver Qts
is 0.5 or greater, I would try infinite baffle (order=2) systems
first, otherwise, use order=4, with the ideal box size and
frequency. Save the other order options for later. PERFECT BOX
will also recommend an order to you.
7. Enter the box volume in cubic feet. I suggest that you
use the ideal box size and box frequency (for 4th order up) as a
starting point. Then, on the next pass, change one of the box
alignments and check how the response was affected.
8. PERFECT BOX will now calculate : 1. Amplitude, 2.
Maximum Power, and 3. Maximum Sound Pressure Level, at each
frequency cycle between 10 and 200 Hertz. Then an Output Menu
will be presented.
Option 1. will plot the classical Bode (pronounced BO
DEE; or Frequency Response) plot.
Option 2, SPL & Power vs. Frequency, will give you an
picture of the system driven at maximum power. This plot gives
the Sound Pressure Level (in dB) and the input power required to
reach the excursion limit (Xmax) of the driver.
Option 3. will list on the screen, all calculated data,
between the frequency limits of your choice.
Option 4. prints option 3. on your printer with the same
limit choice.
Option 5. produces on your printer, a worksheet which
gives you a handy reference table to use as you change the
different alignments about your system. Each block can be filled
from data printed on the bode plot option. I suggest that you do
this option first (only if you have a printer on line.)
Option 6. allows you to save your current design
parameters to the BOXDATA file for future use. This becomes very
handy if you want to keep track of your best designs for each
driver. If you are loading previously saved values, the default
values of the next iteration are taken from the BOXDATA file. You
must go to the CHANGE menu, and choose "Change ALL Parameters," to
complete the process.
Option 7. toggles you between EGA and CGA modes. If you
are using EGA and want to use the Print Screen function, you have
to switch to CGA (Yuk!, I know), for the Graphics dump to work.
Option 8. (or RETURN) will take you to the Change Menu.
At this point you may choose what parameter to change in an
attempt to optimize the frequency plot, or what ever else you are
trying to acheive. If you are currently working on a 2nd or 4th
order system, the "Change EQUALIZER Frequency or D." choice will
not be allowed. Thus if you want to change to an "equalized"
order, you may do use the "Change ALL Parameters. option first.
Remember that the previous value for each prompt in the CHANGE
menu will be the default value (just press RETURN.)
-4-
After you are satisfied with the current design parameters,
choose "NO CHANGES" in the Change Menu. PERFECT BOX will now
calculate the port lengths required to tune the box to the
frequency last chosen. A column for two identical length ports is
given also. Dual ports are useful when the box volume is large or
the MACH speed is too large for a single port. The MACH number is
the percent of the speed of sound that will occur at the largest
port output. Stay away from large (speed> 0.2) port MACH speeds
as they will cause unmusical whistle noises from the port. Also,
ports that are longer than the box depth, can be curved inside the
enclosure with PVC swept elbows.
V. DESIGN HINTS:
If the ideal box volume is too large to be realistically
built, PERFECT BOX will allow you to see just how the loudspeaker
performance will suffer, as you down size box volume. It is this
iterative design process that PERFECT BOX is designed for. By
changing either box volume, port frequency, or in EQ cases, EQ
frequency and boost, a "perfect" frequency curve can be obtained.
At this point you can tell how good a driver really is because
sometimes another driver will out perform others in half the
enclosure volume!
The port frequency is set by the area and length of the port.
PERFECT BOX will calculate the port for you, but the length is
typically 10-15% off, so add an inch to the calculated value, and
measure the box frequency for yourself (or have a technician do
it.) The system will not perform as calculated if you miss the
port frequency by as little as 1 Hz. Also, after you have reached
a final box size, increase the box volume by as much as required
to account for volume used by the drivers, bracing, and crossover
network.
To find box diminsions from the box volume, take the volume
in cubic feet, multiply by 1728 cubic in/ft^3, to get in^3. Then
take the cube root (or raise it to the 0.3333334 th power.) Now
this number is the width in inches. Multiply the width by 1.62
for the height, and multiply the width by 0.62 for the depth.
volume (ft^3) * 1728 = volume (in^3)
width (in.) = (volume (in^3))^0.3333334
height (in.) = width * 1.62
depth (in.) = width * 0.62
NOTE: All diminsions are internal, not external!
This will give the box a "typical speaker look" and also set
the diminsions up for minimum internal reflections. PERFECT BOX
calculates these diminsions for you and prints them in the port
length table.
-5-
VI. REFERENCES:
This document and the program PERFECT BOX are only tools for
the speaker designer. One must know how to use these tools
properly before judging the usefulness of PERFECT BOX. I suggest
that you read any of the following publications on the finer art
of speaker building.
SPEAKER BUILDER MAGAZINE (6 times a year)
Edward T. Dell, Jr., Publisher
PO Box 494
Peterborough, NH 03458
"The Loudspeaker Design Cookbook"
by Vance Dickason
Distributed by:
Old Colony Sound Lab
PO Box 243
Peterborough, NH 03458-0243
"How to Design, Build, & Test Complete
Speaker Systems"
by David B. Weems
Library of Congress # TK9968.W43
Published by:
TAB Books
Blue Ridge Summit, PA 17214
No. 1064
VII. VERSION 2.3 ADDITIONS:
The latest version of PERFECT BOX, v2.3, adds the following
options to the previous versions.
1. The ability to change the path to the boxdata file.
This allows you to have multiple boxdata files, each in separate
subdirectory, or disk. The current path is now displayed at the
opening menu. The default DOS path is the initial drive path.
2. The ability to save the current alignment (box volume,
box frequency, order, EQ frequency, and D,) to the BOXDATA file.
This allows you to save your favorite box alignment for each
driver. You may also load previously saved parameters for a
starting point on a new design.
3. Dual driver systems are now handled. You may now choose
from three different configurations in series or parallel:
Standard --Drivers side-by-side, sharing the same box.
Push-Pull--Same box, mounted back-to-back or
front-to-front, wired out of phase.
Isobaric (constant pressure) systems--Drivers close-coupled
by a small air-tight tunnel.
See "The Loudspeaker Design Cookbook" for more information on
these variations in system design.
-6-
4. A BOXDATA file print option which makes a complete
hardcopy of the current BOXDATA file drivers, including all
parameters, or Ideal Box values.
5. Maximum SPL and minimum power values above 20 Hz. are
denoted on the Excursion limit plot, for quick reference. Also
these values are helpful when designing dual-driver or very heavy
power rated systems.
6. One of the prompts in the LOAD driver sequence has been
deleted to speed up the process of parameter loading.
7. A DOS Shell is provided to allow non-resident DOS
commands to be executed without leaving the PERFECT BOX program.
Typical uses would be to : view disk directories, disk space,
format disks or execute any new PERFECT BOX utilities (currently
the BSORT.BAT and ADDATA.EXE progams.)
See the PERFECT1.DOC for more details on new additions.
VIII. ERRATA:
Your support helps! PERFECT BOX is supported by you, the
user. Without user support, Shareware can not continue to exist!
Use this program, give a copy of PERFECT BOX to your friends (the
BBS Archive file is the best way to make sure all the PERFECT BOX
files are present.) Above all, don't forget your part in the
deal! If you are using PERFECT BOX on a trial basis, that's fine.
If you are using PERFECT BOX in your business, that's great! Just
don't forget the concepts under which shareware functions.
PERFECT BOX is under constant scrutany for improvement. If
you have any ideas for new features/functions, or problems in
program operation, send them to me at AUSTIN ACOUSTICS. Your
suggestion could be included in the next revision of PERFECT BOX,
of which you will recieve the first copy!
By registering your copy with me, you will be notified of
major PERFECT BOX revisions, and new BOXDATA file parameters. I
will update your present version, and append any BOXDATA
parameters I have recieved from others to your disk. Please send
a COPY of your PERFECT BOX program disk (5.25" or 3.5") in a U.S.
Post Office approved disk envelope (or safe equivalent,)
and $40 (check or money order)
to cover registration and return postage ($52 for Overnight
Express Return.)
Please note that a registered user will not have to see the
annoying "Please Register" boxes that are sprinkled throughout the
program. But this doesn't mean that the un-registered copy is
"crippled" in any way, because it isn't. All PERFECT BOX
functions are available on the un-registered program.
Please make checks payable to:
WARREN MERKEL
9874 LANCEWOOD STREET
ORLANDO, FL 32817-4251
*** End of Document ***
-7-
