When Stereophile reviewer Michael Fremer writes “on electric bass… the M1200 is a monster”, he’s not alone. More and more emails daily come across my screen extolling the virtues of the M1200’s bass.
How can it be that one flat measuring power amplifier can sound remarkably more powerful in one area than another model of amplifier?
Flat is flat, right?
Not so fast. Let’s have a closer look at the M1200’s measurements. 10Hz – 20KHz – 0.5dB
A measurement of 10Hz – 20KHz – 0.5dB says a lot if you look closely (and know what you’re looking for). What’s first apparent is its ruler flat performance within the range of human hearing.
But a deeper look shows something else: the amp is down at 10Hz by only 1/2dB. This is important because it means that an octave higher the amp is perfectly flat. Ruler flat response within the audible band is critical for removing phase shift. Turns out the ear is very sensitive to phase shift and the way to keep the phase from shifting is to start any measurable roll off well below the limits of human hearing.
You see, most power amplifiers will have specs that are more like -3dB at 10Hz (-3dB is important because it’s believed that’s where the ear perceives a level change). Fine that the point we first perceive a level change is below the ear’s frequency limits but what’s not mentioned is the phase shift. To be -3dB at 10Hz means you’re 1/2dB down point is well up into the audible range of bass—and we get phase shift.
When phase shift happens in the audible frequency range it will convince the ear the bass sounds wimpy.
And one more point.
A monster amp like the M1200 not only has no phase shift in the audible bass regions, it also has the power and reserves to effortlessly deliver that phase free note without any change in character.
Measurements aren’t always clear and simple.
The story behind the measurements matter.