Fire hoods are required to comply with UK Building Regulations. They are necessary to maintain the fire resistance of ceilings and delay the spread of fire. They must be fitted to any in-ceiling speaker installed below a habitable space or in an area of escape.
Fire & Acoustic hoods are made with sound deadening materials to help reduce sound transfer to other rooms, in addition to providing a fire barrier. This type of hood is recommended in most situations, but especially when installing speakers below a bedroom for example.
Other benefits of fire hoods include improving the performance of open-backed speakers. Installing speakers in a very enclosed space (eg. one full of insulation) or a very open space (eg. a large open roof void) can reduce bass performance. Open-backed speakers will perform at their best when enclosed in a specific volume of air, and this can be achieved by installing fire/acoustic hoods. Fire hoods also prevent insulation and other debris from falling onto the back of the speaker and drive unit which can affect performance.