Most domestic speakers (whether they are traditional box speakers or the latest ceiling speaker design) are made up of two drivers; a treble driver (tweeter) for producing high frequencies and a bass driver (woofer) for producing bass frequencies. The size of the bass driver will dictate how much bass will be produced. Larger bass drivers are less rigid due to their larger surface area so they are better able to flex and reproduce lower frequencies. Smaller speakers will be more rigid and will struggle to produce lower frequencies. In addition, larger speakers will be able to disperse sound over a wider area due to their ability to push larger sound waves through the air, which makes them ideal for larger rooms.
For rooms where sound quality is important, you need to ensure that enough bass will be produced, otherwise, there is a risk that the speakers will sound ‘tinny’. Smaller speakers can offer a perfectly acceptable sound quality in small or medium-sized rooms where sound quality is less important and where music tends to be listened to in the background. A bathroom, short hallway or lobby area are good examples. Alternatively, you could consider a single stereo speaker. These speakers incorporate full-sized bass drivers so you benefit from greater bass, but only one of them needs to be installed in order to produce stereo sound as they incorporate the components of two speakers in one ceiling speaker enclosure.
Where small speakers are the only option due to the physical or aesthetic limitations dictated by your project, you can improve the bass performance by introducing a subwoofer to your system. These very large bass drivers are designed to only produce bass, and come in the form of a ceiling speaker (often called bass augmentation speakers) such as the SpeakerCraft 8.2BAS, or free-standing units such as the Monitor Audio Radius 380 that can sit in the corner of the room, or in a fully integrated option that gets built into the wall such as the SpeakerCraft Cinema Sub 10. The big benefit of introducing a dedicated subwoofer is that the balance of high and low frequencies can be adjusted easily to create a perfect balance.
Other factors to consider when deciding what size ceiling speaker
In addition to considering the purpose of the system and the size of the room, there are other practicalities to keep in mind. If you are planning to install ceiling speakers or in-wall speakers, you will need to carefully measure the space available behind your ceiling or wall and the width between your joists or studs. Larger diameter speakers will often require deeper depths due to the cone of the larger bass driver extending further back. These all affect what size of ceiling speakers you will need.