Dirac is mainly for resonance (narrow band) taming and not suitable for normal EQ. Accudio is good. But since the L1 already has a strong bass emphasis, boosting mids or treble just makes the imbalance worse – i.e. the freq. response becomes more ragged and the sound more harsh. To get a smoother sound and better mids and treble, reduce the bass instead.
Total harmonic distortion: True, headphones with lower actual total harmonic distortion (THD) will sound better than those with higher THD. But the quoted THD numbers -- "less than 1 percent" -- aren't helpful in predicting sound quality. Listen to recordings of simply recorded acoustic guitar to assess the distortion of one set of headphones versus another. Some will sound appreciably cleaner than others.
These early headphones used moving iron drivers,[7] with either single-ended or balanced armatures. The common single-ended type used voice coils wound around the poles of a permanent magnet, which were positioned close to a flexible steel diaphragm. The audio current through the coils varied the magnetic field of the magnet, exerting a varying force on the diaphragm, causing it to vibrate, creating sound waves. The requirement for high sensitivity meant that no damping was used, so the frequency response of the diaphragm had large peaks due to resonance, resulting in poor sound quality. These early models lacked padding, and were often uncomfortable to wear for long periods. Their impedance varied; headphones used in telegraph and telephone work had an impedance of 75 ohms. Those used with early wireless radio had more turns of finer wire to increase sensitivity. Impedance of 1000 to 2000 ohms was common, which suited both crystal sets and triode receivers. Some very sensitive headphones, such as those manufactured by Brandes around 1919, were commonly used for early radio work.

I have heard only the 8.35D, which are slightly dark (tilted toward the low end a little bit). But the 8.35D is very smooth and linear overall, excellent for many genres if not all. With the SRH840 you should expect a big hump in the upper bass – not ideal for monitoring. The KRK 8400 seems like the most accurate of all which is ideal for monitoring, but that’s based on a bunch of reviews, and not all of them agree 100 percent.

Headphones are available with high or low impedance (typically measured at 1 kHz). Low-impedance headphones are in the range 16 to 32 ohms and high-impedance headphones are about 100-600 ohms. As the impedance of a pair of headphones increases, more voltage (at a given current) is required to drive it, and the loudness of the headphones for a given voltage decreases. In recent years, impedance of newer headphones has generally decreased to accommodate lower voltages available on battery powered CMOS-based portable electronics. This has resulted in headphones that can be more efficiently driven by battery-powered electronics. Consequently, newer amplifiers are based on designs with relatively low output impedance.
Choosing the right headphones makes it possible for you to hear your music the way the artist who made it intended, with all the nuances from the right bass and treble levels so you can hear every drum beat and guitar strum. Not all headphones are ideal for everybody and are a matter of personal taste, comfort and style. Find the ideal pair of headphones to use with your mobile device, stereo or computer, available at our Every Day Low Prices, and get your groove on.