Minibar - The Report
Here are some excerpts from a very comprehensive study of the Rainger FX Minibar, kindly forwarded to us by the author Alex Chipps from the Massachusetts Institute of Technology (MIT), May 15 2025
Studying Fluid Effects on Electric Guitar Audio Using Photoresistors and Conductivity
Functional Description and Requirements
The goal of this experimental project is to characterize the guitar’s output signal characteristics (i.e., the gain and frequency response) as a function of the conductive and optical properties of various fluids in the pedal.
| Fluid | Theoretical electrical conductivity | Electrical conductivity | Opacity |
|---|---|---|---|
| Saltwater | ~8.2 (5) | high | low |
| Red wine | 0.88 to 2.57 (6) | low | low |
| 99% IPA (iso.) | 1E-10 (7) | low | high |
| Soy sauce | ~42 (8) | high | high |
Results
Observing the time domain of the audio signals in Fig. 5, it is evident that the raw signal travelling through all fluids generally results in higher gain than the raw signal alone for the theoretical frequencies comprising the Californication riff. The red wine and IPA fluids yield the most distortion/clipping of the signal, which is expected since it is thought that the lower the electrical conductivity of the fluid, the greater the electrical resistivity, and the greater the gain [1]. The IPA was the least conductive of the liquids and thus had the greatest overall gain. Soy sauce was the most conductive of all the liquids, thus its effect on gain was lowest among all the fluids.
Various guitar riffs recommended for emulating with each tested fluid in the Minibar pedal…
| Fluid | Conductivity | Opacity | Type of Effect | Guitar Riff |
|---|---|---|---|---|
| Saltwater | High | Low | Mild O/D |
Pride and Joy – Stevie Ray Vaughan My Body – Volbeat Californication – Red Hot Chili Peppers |
| Red Wine | Low | Low | Mild ‘Bassy’ O/D |
Crazy Train – Ozzy Osbourne Sunshine of Your Love – Cream Rhiannon – Fleetwood Mac |
| 99% IPA | Low | High | High-Octane Fuzz |
Icky Thump – The White Stripes Teen Spirit – Nirvana Foxy Lady – Jimi Hendrix |
| Soy Sauce | High | High | ‘Bassy’ Fuzz |
Satisfaction – The Rolling Stones Money – Pink Floyd Purple Haze – Jimi Hendrix |
Value of Project
Guitarists now have a better understanding of the effects of electrical conductivity and opacity on their guitar signals through the Minibar pedal, as it is backed up with gain and frequency response data from this work. They may use my suggestions for choosing fluids to get the desired kinds of tones in a fun and interactive manner. I enjoyed learning how to interface my guitar with a DAW and using signal processing techniques, which will be beneficial for helping me record new music in the future.
Summary of Findings
This project characterized the gain and frequency response of a guitar signal traveling through various fluids in the Minibar Fluid Analyzer pedal. It was found that more opaque fluids yield signals with an emphasis on the lower frequencies, while more transparent fluids yield signals with an emphasis on the higher frequencies. In terms of gain, the more electrically conductive a fluid is, the lower the signal gain was.
Future Work
While this study did not use external sensors to directly measure the electrical and optical properties of the fluids in this analysis, I was able to characterize the gain and frequency response of an electrical guitar signal traveling through various fluids. However, it would be beneficial to correlate my findings with quantitative measurements of the fluid properties. Additionally, a larger subset of fluids could be experimented with, pairing them with various guitar melodies and chord progressions to find new kinds of tone combinations. Electrical conductivity of fluids is also dependent on temperature, so it could be interesting to study the temperature-dependent effects on the audio signal. Finally, sharing these results with the guitar community will help other musicians dial in specific tones in a fun manner with the Minibar pedal.
