Let's put the message in a cell, say D16.

In a standard module insert the follow line:
Public OldVar As Variant

Insert the following event macro in the worksheet code area:

Private Sub Worksheet_Calculate()
If OldVar = Range("B15").Value Then Exit Sub
Range("B16").Speak
OldVar = Range("B15").Value
End Sub


Insert the following macro in the workbook code area:

Private Sub Workbook_Open()
OldVar = Sheets("Sheet1").Range("B15").Value
End Sub


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Gary''s Student - gsnu200817