Tips, Techniques, Examples about my favorite musical instrument, the Twelve-String Guitar.

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Wednesday, January 31, 2007

Feeling the Whomp - III

My short life as a practical scientist seems to have come to an end. In the Pursuit of the Wily Whomp I posited that by finding the correct location for the stereo microphones the whomp would be phased out, or at least noticeably dropped in volume. But I could not find any location on the face or sides or neck of the LKSM-12 where opposite phase vibrations were picked up by the music microphones. However I did learn something new that might help microphone placement for individual guitars.

The closest I came to finding out of phase information was finding areas where the frequency was strongly doubled. Doctor Russell used an "accelerometer" to measure surface vibrations, perhaps some type of surface contact device like a piezo pickup. I'm using a microphone, and I think the volume of sound coming out of the sound hole swamps any sound from surface vibrations at the sound hole's resonant frequency (91 hertz).

The top wave form is from a microphone at the bottom (guitar in playing position) of the lower bout and the bottom wave form is over the upper bout next to the cutaway. I found similar results in other areas. The area over the high frets (> 14) just above the sound hole yielded the smoothest fundamentals, and the areas around the edges, close to the sides, yielded the most complex waveforms. No surprises there.

There was one pleasant surprise - touch! I could feel vibrations in unusual parts of the guitar while playing single courses. For example, the very top of the headstock strongly vibrated when playing an open 6th course. I could also feel the vibration at the back of the nut. Various parts of the neck vibrate as you hit the open courses. You can feel this by lightly touching the back of the neck with your palm. You can also feel the volume of air pumped by the sound hole; hold the back of a moistened finger over it while plucking the resonant note.

So I didn't catch the willy whomp yet, but I have some good information for trying some new mic positions. For instance, I'd like to beef up the impact of the 6th course and lower the whomp of the 5th course, so my first experiment might be to place a microphone in the neck area where I feel the 6th course resonance.

1 comment:

Inked said...

Well, your experiment did establish useful ideas

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