What would be your first though when you hear the term “passive equalizer”? At first, probably you think about the airy high frequency components, the rich subs and the widely applicable cuts and boosts wich can be used alongside each other. These types of equalisers have been around since the early 50’s, the most famous Pultec EQP-1 from Pulse Techniques was the first one that provided simultaneously passive filter circuits alongside high quality line amplifiers. The downside of the EQP-1 was the lack of ability to carry out precision frequency isolation, but it was able to change any sound in its core. Many of the modern equalizers are based on the original EQP-1 in both structure and functions that could be limiting in a modern music environment and production.