There are a lot of things going on, and here's a small list.

• Great Plains Audio Community Meeting - Saturday, November 8th, starting at 2:00pm. This will be held at Mark Margiotta's house, and directions and a proper announcement are at the link.

• Comparitive study for T/S measurement techniques - Dr. Akhilesh Bajaj and I did a series of measurements in order to compare various techniques. We have the data points; Now all I have to do is to compile them. We measured using both the sealed box method and the added mass method, and we gathered data using a calibrated oscilloscope and two handheld DVM's. So the results can be averaged to give greater confidence in the data; Data can also be compared to get an idea of the relative strengths and weaknesses of each method and measuring device.

  Actually, this was done to obtain T/S specs for some Stephens drivers that Akhilesh plans to build single-driver systems around. Poor guy had to sit with me while I did everything three times just to get the datasets to do comparisons by. We "killed two birds with one stone" - Akhilesh wanted assistance finding T/S parameters for his drivers, and I had been planning to do this comparitive study, so we decided to do them together. But these drivers were produced earlier than the 50's, so I'd like to do the same thing with a pair of Eminence and/or JBL drivers sometime. That would allow us to compare a handful of datasets we've measured with those provided by a trusted manufacturer. What do you say, Akhilesh? Up for another measurement session sometime? Anyway, I'll publish this data as soon as I have time to compile it.

• Qms virtual circuit calculator - Chris Richmond wrote an excellent little applet that calculates the virtual circuit components that represent Qms. Sorry, Chris, I just blew your anonymity on that deal. But I think it's pretty neat and I'll probably use your program instead of doing 'em by the seat of the pants. Hopefully Chris will have time to post it in the next few days.

Midrange horns - I'm working on midrange horns that will be added as standard options in the π product line. They're along the lines of what Jeremy and I discussed yesterday. Actually, I'm pressed for time and I haven't been working on the designs so much as I have a set of requirements that I plan to solve for. Many times over the years, I've used a direct radiating midrange driver with a horn loaded tweeter and a cornerhorn loaded woofer; This configuration lends itself to passive crossover solutions that must deliver flat response performance over the entire bandwidth. But horn-loaded midrange systems have always been popular in prosound use where active crossovers are commonplace. The designs I have in mind will be ideally suited for high-end home sound systems or live sound. Should have something by the first of the year.

• Top Secret - A bunch of other stuff is going on too, and I'd rather allude to it than say. But read between the lines every chance you get; There's fun stuff going on behind the scenes, ready to spill over in the next few months.

It looks to me like 2004 is going to be an exciting year.

I'm interested to know what you are going to do for the midrange horns. Are they going to be larger drivers like ~10-12" or smaller ones like the Alpha 6's in my midrange horns? Is it going to be a horn which people will have to construct or one that you can buy?

Adrian

About the midrange horn, I'm planning to load with the JBL 2012 or Delta 10. Something for the Alpha 6 or JBL 2115 is sweet too, but I'm working on something a little larger.

Larry Acklin

The math is pretty easy with a calculator if you don't have perl
available to you. If you are stuck on Windows, check with
www.activestate.com. If you are on linux or other Unix, perl
should already be there. There's a version in BASIC from Wayne
at the bottom.

Here's how it runs:

Usage: ./mech_res.pl Zmax Fs Qms

./mech_res.pl 100 32 10.4

! mechanical reactance (32 Hz, Qms: 10.4)
C5: 9 0 517.4uF
L5: 9 0 47.8mH
R5: 9 0 104.0

And here's all the code and comments:

#!/usr/bin/perl -w

# Copyright (c) 2003 Chris E. Richmond All rights reserved

# This program is free software; you can readily redistribute it
# and/or modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 1, or
# at your option) any later version. You can receive a copy of this
# license by writing Free Software Foundation, Inc., 675 Mass Ave.,
# Cambridge, MA 02139, USA

#===============================================================================================
# Create mechanical parameters for Spice model for woofers.
# Input: Zmax and Fs, output equivilant L, C, and R, where their
# values are defined thusly:
#
# About making a virtual circuit that models mechanical resonance, the idea is to find
# parallel L,C and R that acts as the mechanical resonator does. R will be set by Zmax,
# so that one is easy. Then, the values of C and L will be the same at resonance, and
# since Q is the ratio of reactive impedance to resistive impedance, you will find a the
# value of inductor and capacitor with reactances equal to Zmax / Qms at Fr. Wayne Parham
#
# C5
# ----||-------------
# | R5 |
# --------\/\/\/------------
# | |
# ----((((((((-------
# L5
#===============================================================================================

if ( @ARGV != 3 ) {
die "\n Usage: $0 Zmax Fs Qms\n\n";
}

$Zmax = $ARGV[0];
$Fs = $ARGV[1];
$Qms = $ARGV[2];

$Pi = 3.141; # constant

$Q_ratio = $Zmax/$Qms;

$L = ($Q_ratio / (2 * $Pi * $Fs)) * 1000;

$C = 1000000 * ( 1 / ( 2 * $Pi * $Q_ratio * $Fs ));

#! mechanical reactance (40Hz, Q=6.56)
# C5 9 0 400uF
# L5 9 0 40mH
# R5 9 0 65.6

print "\n! mechanical reactance ($Fs Hz, Qms: $Qms)\n";
printf( " C5: � � %6.1fuF\n",9,0,$C);
printf( " L5: � � %6.1fmH\n",9,0,$L);
printf( " R5: � � %6.1f\n",9,0,($Qms*10));
print "\n\n";

__END__

And here's one in BASIC:

==============================================================
10 input "Zmax"; R
20 input "Fs"; F
30 input "Qms"; Q
40 Pi = 3.1415926535
50 Z = R/Q
60 L = (Z / (2 * Pi * F)) * 1000
70 C = (1 / (2 * Pi * Z * F)) * 1000000
80 print "Reactance = " reactance
90 print "Capacitor is " C " uF."
100 print "Inductor is " L " mH."
110 print "Resistor is " R " ohms."

==============================================================

! mechanical reactance (32 Hz, Qms: 10.4)
C5: 9 0 517.4uF
L5: 9 0 47.8mH
R5: 9 0 104.0

And the code and comments:


#!/usr/intel/bin/perl -w

# Copyright (c) 2003 Chris E. Richmond All rights reserved

# This program is free software; you can readily redistribute it
# and/or modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 1, or
# at your option) any later version. You can receive a copy of this
# license by writing Free Software Foundation, Inc., 675 Mass Ave.,
# Cambridge, MA 02139, USA

#===============================================================================================
# Create mechanical parameters for Spice model for woofers.
# Input: Zmax and Fs, output equivilant L, C, and R, where their
# values are defined thusly:
#
# About making a virtual circuit that models mechanical resonance, the idea is to find
# parallel L,C and R that acts as the mechanical resonator does. R will be set by Zmax,
# so that one is easy. Then, the values of C and L will be the same at resonance, and
# since Q is the ratio of reactive impedance to resistive impedance, you will find a the
# value of inductor and capacitor with reactances equal to Zmax / Qms at Fr. Wayne Parham
#
# C5
# ----||-------------
# | R5 |
# --------\/\/\/------------
# | |
# ----((((((((-------
# L5
#===============================================================================================

if ( @ARGV != 3 ) {
die "\n Usage: $0 Zmax Fs Qms\n\n";
}

$Zmax = $ARGV[0];
$Fs = $ARGV[1];
$Qms = $ARGV[2];

$Pi = 3.141; # constant

$Q_ratio = $Zmax/$Qms;

$L = ($Q_ratio / (2 * $Pi * $Fs)) * 1000;

$C = 1000000 * ( 1 / ( 2 * $Pi * $Q_ratio * $Fs ));

#! mechanical reactance (40Hz, Q=6.56)
# C5 9 0 400uF
# L5 9 0 40mH
# R5 9 0 65.6

print "\n! mechanical reactance ($Fs Hz, Qms: $Qms)\n";
printf( " C5: � � %6.1fuF\n",9,0,$C);
printf( " L5: � � %6.1fmH\n",9,0,$L);
printf( " R5: � � %6.1f\n",9,0,($Qms*10));
print "\n\n";
__END__


BASIC version:

==============================================================
10 input "Zmax"; R
20 input "Fs"; F
30 input "Qms"; Q
40 Pi = 3.1415926535
50 Z = R/Q
60 L = (Z / (2 * Pi * F)) * 1000
70 C = (1 / (2 * Pi * Z * F)) * 1000000
80 print "Reactance = " reactance
90 print "Capacitor is " C " uF."
100 print "Inductor is " L " mH."
110 print "Resistor is " R " ohms."

==============================================================

He and I used to have a tongue-in-cheek British/American rivalry. I always liked his participation, but I think he probably got sick of the yo-yo's on Audio Asylum.

Do you ever visit with him anymore?

Larry Acklin