Over Four Years in the Making

Measuring Flex and Stiffness

Measuring carbon fiber flex and stiffness.

With this simple device we were able to measure the resistance to flex of a Violin quality spruce spline, compared to one made out of carbon fiber. By adding small weights we could compare the flex resistance of the two. Tests were done by creating carbon fiber spline build ups that had the same stiffness factor as the spruce. A Violin top was made with these parameters and bonded into a playable Violin body. Tonal qualities were then evaluated from this top when played.

Many plates were constructed and tested with higher and lower flex ratios. In this way we determined which stiffness factor made our Carbon fiber violins sound their best.

Measuring Flex Ratio

Measuring the flex ratio of carbon fiber

Measuring the flex ratio of carbon fiber

With this simple device we were able to measure the flex ratio of a panel of violin quality spruce. Flex resistance is greatest longitudinally in the direction with the grain . Flex resistance is much less across the grain. First we recorded the flex ratio of the spruce and then of a carbon fiber panel of the same dimension.

It is known that the lower the flex ratio in the order of 30:1 or lower, the better sounding the violin. By changing the carbon fiber weave direction you can alter the flex ratio, using uni-directional carbon fiber is the easiest way to accomplish this. Many violin plates were made and tested on fully functioning Violins and the results noted. It was very clear which flex ratio gave us the best tonal qualities.

Multiple test panels of our carbon fiber violin body

Tap Tone Testing

Fred Gayford doing a tap tone test on a carbon fiber violin body panel

This is another method of checking the Mode 5 frequency of a trimmed Violin plate that is ready to be permanently bonded to the Violin Body. At this point the Violin plate can still have the frequency lowered by careful sanding off material in specific areas. The Violin plate is held at a Node point, which is a point of the panel that does not move during vibration when tapped with a rubber hammer. The microphone picks up the tap tone which is analyzed in a software program that shows the M 5 as well as the whole spectrum of the plate’s oscillations.

This information for the top plate and the back plate is added to a file specific to the serial number of that particular Violin manufactured. This gives us a useful data base of information for future developments and improvements. The software used confirms the Mode 5 frequency of a Violin plate easier than the method below.

“Mode 5” Ringtone Frequency Tests

Measuring the sonic frequency of carbon fiber violin body panel

With this apparatus we show a carbon fiber Violin plate suspended and isolated above a loud speaker using foam blocks. The speaker is connected to an amplifier driven by a frequency generator. The violin plate is first sprinkled with fine glitter and then subjected to a high volume frequency. As we go up through the frequency range you can see how the particles vibrate wildly at the “Mode 5” for this particular violin plate and produces the classic “Chladni” pattern for Mode 5. It is well-known among Luthiers that a master violin from the golden age of Stradivarius has a Mode 5 of approximately 350-360 Hz.

It is possible to raise or lower this ring tone by adding material or removing material. For example a thicker plate will have a higher Mode 5 ring tone, while thinning the plate will lower the ring tone.

Many Carbon Fiber plates were made and tested with thicker and thinner construction. Each test plate had its M5 recorded and was then installed on a fully functioning violin. The tonal qualities were evaluated as the Violin was being played. The same process had to be done for the back plate as well.

Eventually the optimum plate frequencies were determined for our Carbon Fiber instruments. It is interesting and surprising to us that the most pleasing sounding instruments had a M5 frequencies that was not in step with what was required for a good sounding Wooden Violin.

Air Mode Frequency Tests

Measuring the air flow of our carbon fiber violin

With this test apparatus we are measuring the “air mode frequency” a common term used by Luthiers, also known as the “AO” frequency.

By carefully directing the air lance over one “F-Hole” at a precise airflow and angle the entire violin chamber is made to resonate at its natural frequency. It’s like blowing across a pop bottle neck where you hear the air chamber frequency. This strong resonance frequency is loud enough to be heard with the ear, which we then record with a microphone and sound processing software.

By varying the internal air volume of the Violin you can change the “ Air Mode Frequency.” To do this many Violins needed to be constructed, some with higher and some with lower rib heights. Which in affect increases or decreases the internal air volume of the Violin. The “AO” was recorded on each Violin and then played as a fully functioning Violin. The ultimate conclusion for these tests was reached by listening to the voice and character of each test Violin as it was played. Even though the old master Violins of Stradivarius usually had an “AO” of 280 Hz, we discovered that Carbon Fiber does not follow the same rules as Wood.
These tests have given us valuable information and shown us what the optimal “AO” is for our Carbon Fiber instruments.

Recording "Signature" modes

Measuring the signature frequency of our carbon fiber violin

Measuring the frequency of our carbon fiber violin

To do this the violin is suspended in the cradle as shown and then struck once at the top of the scroll.

Using the Audacity software program we can map the “signature modes” of each of our violins. The Audacity program has a spectral analysis function that plots all of the resonance frequencies generated by this impact. It is likened to the finger print of the violin. Each one will be slightly different.

A typical signature modes recording using the Audacity software program.

Another way to excite the entire Violin is to strike the bridge with a small hammer input and recording the frequency spectrum generated.

This will be useful in future acoustic developments, as each change for better or worse can be tracked with this program and compared with the best sounding instrument.

Comparative Sound Evaluation

Comparing the sound of our carbon fiber violins

Once a number of violins are completed they are placed in this holder where the final adjustments are made. We compare the tonal qualities of the newly completed violins, with a violin that is used as our standard. We check for balance, ease of play, wolf notes, etc.

Not until we are happy with the sound do we present the violin to a professional artist to give us their evaluation. If they are happy, we are happy! The instrument is now ready for its new home.