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Interactive Crossover Design (ICD)
Crossover designing is both easy and accurate with ICD. The real world results shown below attest to the amplitude and phase
matching that can be achieved. Keep in mind, the example data shown was taken with the circuit exactly as shown. This
demo was built from a salvaged 6.5" computer system woofer (the amp was blown in lightning hit) by adding a polycarbonate
tweeter. An external crossover was then added such that it could be easily bypassed. The components used were what was easily
at hand.
Additional accuracy improvements are possible when variables and secondary modeling elements are considered. For example,
volume and balance control channel-to-channel gain matching is often off by some amount creating a low to high frequency
response tilt. Another factor might be driver and port tuning characteristics that are known to change with drive level.
A high power WTPro generated ZMA file would therefore improve this simulation. This example is, however, more typical of
Woofer Tester 2 and Speaker Tester users. Additional modeling elements would include inductor, capacitor and cable effects
(see notes below). However, at some point, it is usually better to build, listen and then make changes!
Learn about ICD Files and Syntax
Simulated versus Actual Crossover Response
(2.5 dB/Division scale)
Click Image to Enlarge
Note:
This is the raw data with no attempt at frequency or time domain windowing or smoothing. To achieve this level of precision,
you do need to take into account variables like channel-to-channel gain tracking. Even a modest gain tracking error can
become large!
Demonstration System. ICD Simulation vs. Real Crossover
 
Frequency Defined Response Filter (FDR) and ICD Simulated Response
Click Images to Enlarge
Frequency Defined Response (FDR) Filter File
One feature of ICD (Interactive Crossover Designer) is the ability to define channel response soley based on a Frequency
Defined Response and phase file (extension *.FDR). FDR files are read into the ICD tool using the 'XO_FFT' command
superseding a previously defined circuit. That is, you dont have to comment out your previous circuit, just the XO_FFT
command. To make the overlays easier to follow the first figure shows the 'brick wall' amplitude response of the two drivers
in isolation. The second figure then shows both channels driven, including their phase at the 5 Khz abrupt crossover point.
Finally, the ICD defined responses are shown in an overlay. Advantages include:
-
An abrupt zero phase 'brick wall' filter can be defined at the desired crossover point yielding precise measurement of
the phase, and therefore the effective driver to driver distance at the crossover point.
- The phase difference and phase slopes are usefull starting points for working out a potential crossover topology.
That is, the lead and lag may lead the designer in the direction of a particular filter order. Or, this information
may lead to a different spacial consideration. That is, should the drivers be physically moved forward or backward
relative to each other.
-
Arbitrary response and phase can also be defined allowing broad assumptions to be made with regards to the best type of
crossover topology.
ICD Circuit for DEMO speaker shown above
The following ICD circuit includes an 'XO_FFT' statement that is in this case commented using the '*' operator. When this
line is active, the file "4KSHARP.FDR" is used to define a 'brick wall' filter seperating the response of the woofer and
tweeter (figure on left). When the XO_FFT statement is commented, the woofer, tweeter and combined response are as shown
on the right. Finally, a comparison is made (first figure in this article) comparing the accuracy of the ICD simulated
and actual response.
Note:
You can use the balance control of your amplifier to simulate simple volume padding.
File Contents of 'DEMO.CIR'
*******************************************************
* 2nd order high pass, 1st order low pass
*
* (1) 615uH (2)
* o----L1----+----------+
* | |
* | C1 | |
* === 6uF +-+/
* (3)| | |) DEMO_WO.ZMA
* | +-+\
* R1 4 | |
* (0) | |
* o----------+----------+
*
* (1) 3uF (4) 5ohm (5)
* o----||----+-------R2--+--------+
* C2 | | | |
* | | +-+/
* L2 R3 | |) DEMO_WO.ZMA
* | 274uH | 4ohm +-+\
* (0) | | | |
* o----------+-----------+--------+
*******************************************************
Vsig 1 0 AC 10
**************************
L1 1 22 615uH
RL1 22 2 0.1
C1 2 3 6uF
R1 3 0 4
XO_LEFT 2 0 "demo_wo.zma"
**************************
C2 1 4 3uF
L2 4 44 274uH
RL2 44 0 0.3
R2 4 5 5
R3 5 0 4
XO_RIGHT 5 0 "demo_tw.zma" 5
******************************
*XO_FFT "5ksharp.fdr" * go with FFT defined responses
File Contents of '5KSHARP.FDR'
****************************************************
* High and low pass first order filters
* Freq db_Left phase_Left db_Left phase_Left
****************************************************
1.000 -90.000 +90.000 0.000 +0.000
4990.000 -90.000 +90.000 0.000 +0.000
4995.000 -90.000 +90.000 -90.000 -90.000
5000.000 0.000 +0.000 -90.000 -90.000
9600.000 0.000 +0.000 -90.000 -90.000
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