Interesting observations of how a guitar vibrates
Its time to share some new data that I have learned in my quest to better understand the functionality of the guitar's mechanics. I purchased one of those vibrating gizmos from www.tonerite.com to see if it would make any real discernible improvement on my guitars "opening up". I had a shop mule test guitar, which had been setting in the corner for some time, because I was just not 100% pleased with the way it sounded. The guitar had a tight and compressed sound and since I had sprayed a sun-burst finish on the top I thought that I might have applied to much finish in the process. It was just an experimental spec guitar so there was no immediate pressure to improve upon its tone right away.
Recently, I played the guitar for about 15 minutes to get a general feel for the overall tone, volume and responsiveness of the guitar. The Tonerite was then wedged between the strings and slid down to rest against the bridge of the guitar. This was to allow the device to vibrate the strings and bridge much in the same way that the guitar would vibrate under normal playing conditions. However, it vibrates the bridge at [possibly] higher amplitude but only at one continuous frequency. After the Tonerite was attached, the guitar was banished back to its corner to let the little vibrator do its thing for 5 continuous days.
After 5 days of vibrating I took the guitar off its stand and noodled around on it. The guitar had a noticeable improvement everywhere from playing it 5 days prior. It sounded louder, seemed to have a wider and even dynamic range and the guitar responded to various string attacks. Before to Tonerite treatment, the top liked to be driven hard and was quite subdued to light finger style playing. I know my comments and “opinions” are purely subjective and immeasurable but the guitar has remarkably changed (for the better). It should also be noted that I have no vested interest in promoting this device and this is only a sample of one test guitar so we will see how it works its mojo on other guitars in the coming months.
The one astounding thing that I learned in the process is how and where the top vibrates as well as other components of the instrument. I have always been an opponent to quickly shoot down any claims that the top vibrates above the sound hole.
My proof test to refute that the top is basically dead above the sound hole is to tap on the bridge with your finger and then listen to the sound that the top makes. Now continue tapping all over the top and listen to the way the sound changes and how the sound dissipates as it nears the sound hole and especially above the upper transverse brace which is glued under the top above the sound hole. This area is extremely dead "sounding" when you tap on it with your finger. Keep in mind that my testing process consisted of finger tapping the top and NOT actually playing the guitar in question.
When the Tonerite is vibrating the strings and bridge you can lightly run your finger tips all over the guitar and quickly identify the nodes or the non vibrating areas of the instrument. You can also quickly feel which areas of the instrument are active and at higher or lower amplitudes as they are responding to the induced vibrations from the Tonerite device. The areas below the bridge, on both the top and back, had the highest amplitude of vibrating activity. As your finger tips approach the sound hole, just above the bridge, the top is dead, nada, hardly any vibration going on. This is contrary to what you hear when you tap the top in that area with your finger tips. You hear a slightly reduced sound by tapping on the area but the sound "suggests" that there is definitely some vibrating activity. The Tonerite quickly disproves this because hardly any vibrations can be felt.
I believe the Tonerite's method of exciting the top is closer to the actual way that the top is driven under real world playing conditions. Some builders, including me, have experimented with or heavily rely on Chladni pattern data. This is a method of driving the top using speaker and a variable frequency tone generator. The electronics generate an adjustable sound frequency which is outputted to a small hand held loud speaker. The speaker is held freehand above the bridge and the sound waves induce vibrations into that area of the top. Glitter, tea leaves, corn meal, salt or any dry, light weight, loose media is sprinkled over the top. The media settles on nodes (non vibrating areas) and this shows where the top is not vibrating. The media bounces off of the active vibrating areas and settles in the dead non vibrating areas of the top. Based on the “glitter patterns” the builder is able to loosen or move these nodes by adding or removing mass from the braces beneath the top.
This method has proven quite successful for many of us. However, in my opinion Chladni tuning does not accurately replicate the way the top is driven as close as the Tonerite does. For this reason alone perhaps there could be a LOT of learning potential for the builder using this device to tune tops. I know I am excited and plan to do more R&D work with it.
Now its time for me to eat some CROW. The Tonerite has proven to me that there is a considerable amount of vibration activity above the sound hole. It only takes one light touch of the fingertips to feel the amount of activity that is present in this area of the top. The neck shaft, fingerboard and peg head also are quite alive and radiate energy as well. Since the Tonerite is inducing continuous vibrations into the strings the upper bout activity [could very well be] some whiplash effect transferred back into the body by the neck itself. It would be interesting to be able to measure the actual frequency at which these areas of the top are vibrating. Perhaps the frequency spectrum would indicate if the upper area of the top was vibrating from the neck or from the bridge?
There is a slight amount of vibrations in the sides but it is hardly noticeable compared with the activity in the top, back and neck. The third predominate vibrating area is the back. The back feels like it is almost a mirror of the top’s vibrating surface. The waist area of the back has the lowest amplitude while the lower and upper bouts are very alive. This could also coincide with the fact that this test guitar is a brace-less “Hollow-back” design. I plan to continue experimentation on ladder and X braced bodies as well and will report my findings in the near future.
Stay tuned and God bless…