The desirable characteristics of a crossover system are easy to state but not so easy to achieve in practice. There is a general consensus that there are five principal requirements that apply to all crossovers, be they active or passive, and that they should be ranked in order of importance thus:
- Adequate flatness of summed amplitude/frequency response on-axis
- Sufficiently steep roll-off slopes between the output bands
- Acceptable polar response
- Acceptable phase response
- Acceptable group delay behaviour
To some extent the amount of space devoted in this book to each requirement is dependent on their relative importance as set out in this list.