On calibrating home made speakers by ear using SennheiserHD-580 open back headphones as reference

At your risk. This is how it is currently done on Pleiades lab. In real time under real room listening environment. A good CD such as Guilty - Steisand, Gibb is on Sony CD Walkman. Its line out is connected to class A Pleides 2N3053 power amplifier feeding speaker to be acousticaly calibrated. Phones out is connected to excellent neutral Sennheiser HD580 headphones. Volume is adjusted so that headphones, or speaker sounds equally loud so that the listener's brain is on the same equal loudness curve (Fletcher-Munson curves). Say a Philips 8in woofer is placd on a 21cm by 29cm by 48cm Pioneer CS-353 box (actually this box may be small). If it is directly connected to amplifier it sounds mid and midhigh heavy. If a 1.07mH inductor is placed in series the midhigh heaviness is gone and the bass can now be clear. Say then a paper cone tweeter is connected by a series 2.2uF capacitor. We get the treble but it sounds a bit strange. Pressing pause on CD Walkmann, the power is disconected from power amp and the headphones are worn. Now Barbara Streisand voice sounds much more warm with less high frequency heaviness on the song A Woman in Love. Goinjg back to speaker mode, a variable series resistor is connected in series with capacitor and tweeter to control amount of high frequency content until Barbara sounds as equal as possible to Barbara on the reference headphones HD-580. When her voice sounds right the resistance can be measured to be say 20 ohms in this particular case. By still comparing speaker and headphones in turn it is found that there is still a mid high heaviness. Capacitor is now changed to 0.5uf which makes sencs as the high series resistance increases the time constant which is RC ie resistance times capacitance. Now it sound much closer to reference headphones and there is a smile in your face as you look at the blue sky. But there is still some midbass heaviness. It is decided to increase the woofer series connecetd inductance by inserting a screwdriver inside the bobbin core of said inductor. Now it sounds almost perfect and you laugh. The inductor is later measured on an impedance bridge to be 1.7mH. Same tactic can be used to remove midhigh heaviness from fullrange speakers, the capacitor usually is not needed but the inductor and a resistor in parallel with it is needed, see next post. So the most expensive apparatous is used to full advantage, your ears and your brain.