Re: Beta 57a vs. Beta 58a for vocals
Hi Craig,
You're right that the the frequency response curve in your example is an accurate representation of the response on-axis, and gives valuable information about that single parameter. However, other less easily quantifiable parameters can make a different mic with the exact same on-axis frequency response curve sound completely different. I'll elaborate.
Harshness is a great example. A mic that people describe as smooth may show the same frequency response curve as another, but have a different diaphragm damping factor in the 2.5KHz to 6.3KHz range, altering the waveforms at those frequencies.
Resonances inside the microphone body and grille also drastically shape the sound, and are somewhat revealed by those very small bumps and valleys in a frequency response curve. Sound waves reflecting and refracting around the mechanical structures of the mic cause destructive interference effects that are far too subtle to appear on the curve, but can be perfectly audible.
Another way that on-axis frequency response curves can be misleading is when we fail to compare two microphones' off-axis frequency response curves along with their on-axis curves. I mean in addition to the polar pattern images like those I posted above. All of the signals entering the sides and back of the capsules significantly affect the overall sound of the mics, even when the sound source is primarily on-axis.
It all just goes to show that the very best instruments for analyzing a mic are located on either side of our heads. A graph will give us a rough sketch of the big picture, usually just enough to expose gross inadequacies or to help determine a mic's general suitability for a given source. The polar patterns shown above are a perfect example of that. But when we're splitting hairs about professional level equipment, our ears and brains (and those of our friends and colleagues) usually trump the test data.
