MASS with 15 watt rating. 8 ohms. May be used on 4, 8, and 16 ohm amplifiers. Includes MASS bypass, and line out. This is one of our most unique MASS units in that it has two power level controls, one for the bass-mid frequencies and one for the upper mids-treble frequencies. They may be adjusted independently for the best tone at all levels of attenuation. These controls affect the actual signal going to the speaker, not just a line out signal like in our other units. So, it is like having high level tone controls. The controls are very effective and the tonal combinations are virtually infinite. Because a MASS motor is employed, a more realistic interaction between the attenuator and the output circuit of the amp occurs. The attenuation is continuously adjustable from zero to over -50db using the attenuation controls. Like all Weber attenuators, setting the attenuation controls to minimum (maximum attenuation), allows the MicroMASS to be used as a dummy load for testing or for DI use.