ADV. The Model 3 BA4 uses the patented Quad (4) Balanced Armatures in a passive crossover configuration that accurately reproduces the entire frequency range of sound for maximum detail. This uncolored tuning invokes transparency and an intense sense of realism in the sound, making it an ideal instrument for guitarists, sound engineers, and composers.ADV. The Model 3 BA4 uses the patented Quad (4) Balanced Armatures in a passive crossover configuration that accurately reproduces the entire frequency range of sound for maximum detail. This uncolored tuning invokes transparency and an intense sense of realism in the sound, making it an ideal instrument for guitarists, sound engineers, and composers..PZA MORE SPECS