Filter
Top Products
48 Handbook of Intercom Systems Engineering
In the late 1970’s, microprocessors became available and the first truly intelligent
intercom system, the McCurdy 9400, was delivered. This was the first system that used
data sent from the user stations as opposed to one wire per intercom key. As
microprocessor technology improved, the 9400 was replaced by the 9500 series. This
series was more dense, allowing a 50 X 50 system in 3RU. The technology was modern; a
very conventional square array of switches allowing any input(s) to be switched to any
output, but the implementation was somewhat limited by what is called the “square law”
problem.
Briefly, in traditional matrix technology, in communications, audio, and video routing
systems, the size (electrical and physical) of a matrix is related to the number of inputs and
outputs, or “ports”, in a mathematical “square law” relationship.
Figure 4.3
A Comparison 3x3 vs. 9x9 Matrices
If you examine Figure 4.3, you can see that the 3 x 3 matrix, which is needed to support a
three-user intercom system, has nine crosspoints. The 9 x 9 matrix, for nine users has 81
crosspoints, so by tripling the number of users, the size of the matrix has increased from 9
to 81 crosspoints or nine times. As nine is equal to the threefold increase in number of
ports squared, the term “square law” has come to represent the problem.
3 X 3 Matrix
with 3 (9) Crosspoints
2
1
2
3
XX
123
X
XXX
XXX
XXXXXXXXX
XXXXXXXXX
XXXXXXXXX
XXXXXXXXX
XXXXXXXXX
XXXXXXXXX
XXXXXXXXX
XXXXXXXXX
XXXXXXXXX
1
2
3
4
5
6
7
8
9
1234
5
6
7
89
9 X 9 Matrix
with 9 (81) Crosspoints
2