The Jensen M-1131 Intrarange Equalizer is a necessary component in accomplishing a Jensen Imperial sound. The M-1131 provides a 4db scoop between 1k-2k frequencies of the RP-201 midrange driver without affecting the other frequencies. It smooths the sound greatly. Please see before and after graph. It is a very hard to come by part and there is no published data for it. I spent hundreds of dollars on test equipment and many hours dissembling a M-1131. I was able to figure out the exact circuit. I have built a pair of M-1131 equalizers using high quality components. I’m using an air core inductor, 50 watt resistor and premium grade capacitor. These are much better than the original because the original capacitor had doubled in capacitance. The original also used a lower grade capacitor and lower wattage resistor. These come with a 2 screw terminal just like the original. You will love the smoothness and clarity these will bring to your RP-201 driver. I can also build a complete Imperial circuit A61, A402, M1131 or build them separately. I will answer any questions. I will ship internationally for .