Again, careful control of the sound is key if this is to be accomplished without feedback. Acoustic design of the worship space is fundamentally important to both of these concerns, and many churches are designed with no competent acoustic advice. Often, there is so much reverberation in a church that the praise band has turned to mush before the sound system is even turned on. Careful sound system design and enough money CAN provide good speech intelligibility in almost any space. An acoustic consultant is an expert who you hire to design your church's acoustics and your sound system.
Some consultants specialize in acoustics, while others specialize in sound system design.
Many of the larger firms have people who do both. A consultant needs a good technical education in his field, and a lot of experience designing sound systems for churches and performance spaces. Most have earned degrees in acoustics, physics, or engineering. The sound system consultant needs a solid understanding of both acoustics and electronics, as well as ongoing education to keep up with advances in the field. The acoustic consultant will help your architect develop the shape and layout of your worship space.