There is a trick which may help.
Filters on the results of table calculations are applied after all calculations have been evaluated. You can create a dummy table calculation which just returns the value of the field you want to filter on. That will limit the displayed rows to the ones selected in the filter, without affecting your calculations.
Say you want to filter on [Speaker], you would create a field called [Speaker_Filter] (say) like this:
LOOKUP( ATTR( [Speaker] ), 0)
That just looks up the value of [Speaker] in the current row. Put that on the filters shelf and it should do what you want.
Are you able to put together a simple mock-up of your workbook that you can share? I'm sure that approach can be made to do what you want - either I haven't understood how your original worksheet is structured or you haven't got the filter defined how I was trying to describe. Or maybe I'm just wrong! ;-)
Thanks very much Richard we could sort it out now.
We just created a Show/ Hide Calculation combined with a parameter.
Say: Parameter Displays a Speaker and if the Speaker matches the Display then show, else Hide
IF [Speaker] = [Display] then 'Show' else 'Hide' END
And Display: String - Speaker