Speaker as microphone question...

I have built the shotgun microphone out of tubes.The maximum width of the bundled tubes is 6" across from the two most fartherest tubes.Can I use a speaker (6") instead of a microphone in order to cover all the tubes or is it still better to use a microphone but just mounted in a funnel?If in a funnel, won't the microphone be too far from the tubes as the speaker can be put right up against them by separating the tubes and speaker via a peice of foam.

-Ken

I think a microphone and funnel would be best because the speaker does not have the same sensitivity over the face of it. The funnel for concentrating sound has been used for many years.