Uncertainty and repeatability in frequency response measurements

Frequency response measurements are commonly used to characterize modal behavior and predict tonal qualities of musical instruments. In the case of violin family instruments, the response can be measured as bridge admittance (sometimes called mobility), which is the frequency domain ratio of the velocity of one side of the bridge to an impulsive force applied at the opposite side. As with any measurement, it is important to characterize and minimize the uncertainty of an instrument's frequency response. This is especially true for studies that investigate subtle changes in the frequency response of a single instrument due to structural adjustments (e.g., bridge material or sound post location) or environmental conditions (e.g., humidity, age or playing time). This presentation will demonstrate a method for measuring violin bridge admittance using a laser vibrometer and small impact hammer, with a focus on how the measurement is sensitive to details of the experimental setup. Methods of quantifying the variability in frequency response will be discussed along with example applications.