In 1949, the same year that Hutchins began her study as a luthier, Helen Rice introduced her to Frederick A. Saunders (1875-1963), [FN13] a retired Harvard physicist who had been conducting research on violin acoustics since the early 1930s. Best known for the Russell-Saunders coupling (a principle of atomic spectroscopy), Saunders had been chair of the physics department at Harvard, a fellow of the National Academy of Sciences, and one-time president of the Acoustical Society of America. An amateur violinist and violist, he tried her viola and said that he would look forward to seeing her next one. At that point, Hutchins insists, she had no intention of making another. After speaking with Saunders and reading some of his articles, Hutchins realized how she could help him:[FN 14]

...the only thing he'd ever been able to do was to work with musicians who came with the instruments as they were. He didn't dare change anything except to maybe take a little bit of wax and put a penny, or a little bit of weight on the bridge...

What Hutchins offered was to build instruments on which Saunders could make actual changes, like the position and size of the f-holes or height of the ribs. Evidence of this joint work is found in the many surviving letters from Saunders to Hutchins.[FN 15] In early 1950 Hutchins offered to make a viola (Sus 3)[FN 16] with several tops for experimental reasons, but Saunders wrote back on February 14, 1950, saying that it seemed like a lot of work and reviewing the problems that Felix Savart (1791-1841)--a leading violin researcher--had found in testing tops.[FN 17] Hutchins, however, pushed ahead with her plans to make experimental instruments, and by September 22, 1950 Saunders was writing her with advice on how to make instruments with flat tops, discussing ways to save tune on the purfling, and the physics involved. Hutchins made three flat-top violas (Sus 11, 12, 13) on which they performed more than 200 experiments, and her catalog of instruments lists three more experimental violas made during the time of her work with Saunders (Sus 3, 7, 17). The experiments performed on the flat-top violas included changing the shape and location of the f- holes, manipulation of the purfling and bass bar (placed on the outside of the instruments for ease of moving), study of the air and wood modes in the vibration of the instruments, trying out different heights of ribs, among many other tests. Their overall conclusion was that early makers, either through careful trial and error or by accident, "...evolved a system that produced practically optimal relationships in violin construction".[FN 18] For many instruments made by Hutchins, experimental and finished, Saunders plotted loudness curves, playing notes to their breaking point and recording decibel output to find out how powerful the instrument is in various ranges.[FN 19] Hutchins credits Saunders with showing her how to run effective experiments.

Saunders and Hutchins occasionally met at his house and laboratory in South Hadley, Massachusetts for their experiments, often when the Hutchins family was headed to or from New Hampshire in the summer. However, much of their joint work involved correspondence and shipping instruments back and forth. Sometimes several letters from Saunders to Hutchins survive from a single month; for example in the summer of 1958, Saunders wrote on July 12, 13, 17, 18, 25, and 29. Hutchins wrote Saunders postcards crammed full of material, causing the physicist to remark on December 6,1962, "You do write rich and juicy postcards."[FN 20] This correspondence allows one to follow the joint work of Hutchins and Saunders, and to note some of the milestones in her career.

By 1951 Hutchins was sending Saunders instruments for testing. In a letter from April 1, 1951 Saunders acknowledges receipt of Sus 2 and 3, noting that he will show Sus 2, Hutchins's first copy of a 17 1/4 inch Gaspar da Salo viola, to Louise Rood. Saunders frequently showed Hutchins's violas to Rood, who also showed them to her students. Sonya Monosoff, one of Rood's students at Smith and today a noted violinist, wrote Hutchins on February 9, 1953 asking about the price of Sus 8 and saying that Saunders had brought one of the flat-top violas, Sus 11, to Rood's studio.[FN 21] On February 20, 1953 Saunders asked Hutchins what Berger thought of her most recent work, offering his own assessment on March 9: "More congratulations over #15, and your first pupil! What is the feminine of Stradivari? He had pupils and great fame; you will too!"[FN 22] This traffic in instruments between Montclair and South Hadley was sometimes heavy: on July 20, 1953 Saunders expressed his fondness for Sus 18 and had Sus 15 as well, and four days later noted that he had finished testing 11 and 18, and asked for Sus 8 and 14. Many such passages are found in the letters, including news of showing Sus 26 to a student in January 1963, the year of his death. References to instruments as late as Sus 36 are found in the letters. In his laboratory notebooks it is clear that Saunders took careful notes on each of the instruments that Hutchins sent him, leaving space for notes on instruments through Sus 52.[FN 23] Hutchins and Saunders also exchanged photographic strips made by Alvin S. Hopping of Lake Hopatcong, New Jersey, who had developed a method of photographing the output of an oscilloscope measuring the motion of a violin plate.

The joint work of Hutchins and Saunders, and contributions of Hopping's photographic strips, resulted in several joint publications concerning the most important work to emerge from this collaboration, and Hutchins's first important discovery: a method to measure tap-tone frequencies electronically in free violin plates.[FN 24] Luthiers have long tapped the tops and backs of violins during the final thinning and graduating process, holding the piece near one end and tapping at various points with a knuckle. The abilities to compare the necessary tap-tones between the top and back of an instrument properly and removing wood in the correct amounts and places are crucial to the making of a good violin. Through the tests of Hutchins, Saunders, and Hopping it was found that the so-called "tap-tone" of the luthier could be measured by clamping a free top or back plate at a node in the upper half and by vibrating it electronically, measure the response of the wood with an oscilloscope or soundlevel meter. Tests on a number of instruments tended to confirm the research of Savart, who found that the best violins had a tap-tone on the top plate one semitone higher than the back. (In later research Hutchins proved that the best instruments result when both plates have the same tap-tone.[FN 25]) Growing out of similar research was Hutchins's discovery of an electronic method of plate tuning in which Chladni patterns were formed by vibrating a plate covered horizontally with powder or small aluminum flakes over a speaker at specific frequencies, a process which told the luthier where to remove wood and how much to remove. As a result, of 200 violins made by this Chladni pattern method over a period of 20 years by Hutchins and her students, it was found that violins with the best tone and playing qualities result when three modes in the top free plate (Modes #1, #2, and #5) were each an octave apart (analogous to the harmonic series) and the upper two modes (#2 and #5, but not Mode #1) in the back at displayed similar frequencies.[FN 26]

It was during this period that Hutchins learned much about the physics of the violin and acoustics. Saunders's reference to the important work of Felix Savart in a letter has already been noted, and he gave her other advice as well. In a letter of August 14, 1956, Saunders informed Hutchins that the violist Lionel Tertis (1876-l975) was coming to the United States, and that Hutchins could meet him and show him her violas through Mary Fairchild, a Tertis pupil. Tertis was pushing a viola model of his own, which Saunders considered inferior to Hutchins's instruments. Hutchins recalls the visit, which took place on October 19,1956, and reports it ended rapidly when she told him what she thought of his viola model. On November 2, 1956 Saunders reacted to this news, suggesting that Hutchins make an instrument according to Tertis's specifications to find out what was wrong with it, which she did. Saunders also demonstrates that he was not shy about showing her instruments to visiting artists, suggesting opportunities with the Stanley Quartet in 1953 and the Juilliard Quartet in 1957 (violist Rafael Hillyer had already seen Hutchins's instruments). He also mentions her successes with other violists, like Eugene Lehner of the Boston Symphony Orchestra, who purchased Sus 41, and David Mankovitz of the Kroll Quartet, who bought Sus 34.[FN 27] In late 1960 Saunders encouraged Hutchins's plan to set up an electronics laboratory of her own for testing instruments, and gave extensive advice on what she needed. In a letter of October 31, 1959 Saunders acknowledged that their relationship had gone full circle, reporting that he had been asked about his association with the work of Carleen Hutchins, and offering (with tongue in cheek) her all of the credit and abuse for their work in the future! By the early 1960s Saunders was beginning to offer some of his guest lecture opportunities to Hutchins, famous in her own right after her first Scientific American article (1962). In his final letter of May 28, 1963, Saunders reported that his pulse rate was down to 34 and his muscles were failing to work properly, but he continued to write about technical matters. Soon thereafter Saunders died, but not before their joint violin research had entered a new period with other collaborators like John C. Schelleng, discussed below.