Investigating if ultrasound is harming LPs

I actually studied the effect of ultrasonic cleaning of LPs in great detail back in the late 70s when I built my first ultrasonic cleaner. I used a combination of optical microscopy (Olympus Laboratory Microscope at about 10,000X) and Photoelectron Spectroscopy (HP 5950A Spectrometer) to analyze sacrificial test LP samples before and after various cleaning procedures. Photoelectron Spectroscopy is sensitive to the top 5 nanometers of the LP surface and can determine the chemical structure of the LP surface and the chemical composition of contaminants on the LP surface. These experiments were done on sacrificial records that had obvious contamination. All of these experiments were done in a clean room environment.

Regarding US cleaning time, my experiments demonstrated that longer than a few minutes in the ultrasonic bath had little beneficial effect on the overall cleaning process and the possibility of a detrimental effect. Most of the cleaning took place in the first few minutes in the bath. I did observe that extended time in the bath would leach plasticizers, stabilizers or other additives from the bulk of the LP and eventually pit the LP surface. Once the plasticizers or stabilizers are fully depleted, the LP surface would become brittle and micro-cracks start to form. So I tried to keep the time in the bath to a minimum. When I finally set up my ultrasonic cleaner, I typically had it set at about 2 RPM and a run time of about 6 to 9 mins. That corresponds to actual exposure times of ~ 2 to 3 minutes (~1/3 of the LP surface is in the bath at a given time). For my setup, between 1 to 3 RPM worked fine. The 6 min time was for my LPs purchased new which had no obvious contamination and the 9 min time was for previously owned LPs. An LP that was quite dirty might occasionally require some extra time. I used this ultrasonic cleaner for over 30 years with excellent results and never any issues with my LPs. Even new LPs exhibited a significant improvement in SQ after US cleaning. Typically once an LP is US cleaned, it will need no further US cleaning if handled properly.

Besides time in the US bath, the key to optimum US cleaning is the proper bath solution and choice of surfactant. The most common bath solution is distilled water or distilled water with a small percentage of isopropyl alcohol. There are many surfactants to choose from. Typically nonionic surfactants are preferred. For my US cleaner, I used an alcohol ethoxylate with the general structure R(OCH2CH2)nOH where R is the alkyl chain and (OCH2CH2)n is the ethylene oxide (EO) chain. I chose the lowest molecular weight that would be soluble in water at room temperature. For solubility in water at room temperature, alcohol ethoxylates should have an average alkyl (R) chain length of 12 C atoms or more and contain at least 5 ethylene oxide (EO) units. The lower molecular weight surfactants were less likely to leave residue on the LP surface and were easier to remove with a distilled water rinse after the US bath.

For reference, the alcohol ethoxylate I used is similar in structure to Tergitol which is a secondary alcohol ethoxylate. Triton-X 100 is an octylphenol ethoxylate which in this case contains a phenyl group as part of the hydrophobic tail.

The concentration of the surfactant is also critical for proper cleaning. It is important for optimum cleaning to have the surfactant concentration at or above the Critical Micelle Concentration (CMC) and the cleaning bath at the proper temperature for micelle formation. The CMC and bath temperature are surfactant dependent. A micelle is an aggregate of surfactant molecules in a liquid solution with their hydrophobic ends on the inside of the aggregate and their hydrophilic ends on the outside, so that hydrophobic residues can be emulsified inside these aggregates. Micelles only form when the concentration of surfactant is greater than the CMC, and the temperature of the system is sufficient for micelle formation. The importance of micelle formation is that the micelles can emulsify surface contaminants that would otherwise be insoluble in the cleaning bath. This allows for the hydrophobic contaminants to be removed from the surface. For my nonionic surfactant the ideal bath temperature for CMC formation was between 36 to 38 degrees C.

Pindac, If you can bear to read all the posts on this thread (and I don't blame you if you cannot bear it), I invite you to look for mine back up near the beginning, where I suggested that one proper way to make the assessment is to use test LPs with specific pure tones encoded on them or it, say 100Hz, 1000Hz, 10kHz (all 3 frequencies on the same surface of the same test LP).  Since we would expect HF to be affected by excessive US cleaning, ahead of any effect on lower frequencies, you could play the test LP tones into a storage oscilloscope, to measure both amplitude and accuracy of the frequencies produced, before vs after cleaning, using same cartridge, tonearm, TT..  Yes, this is an oversimplified desription of the experiment I would endorse; I do realize that the US parameters, perhaps the buffer, the temperature, and many other factors could affect the results, and proper controls would be needed.  But basically, any eroding of the signal voltage amplitude or alteration of frequency of the 10kHz band in comparison to the 100Hz or 1kHz bands encoded on the very same LP would be meaningful to the degree that the lower frequency bands would have been exposed to the exact same conditions as the HF bands on that test LP.

Your questionable scientific method aside, the proof is really in the pudding.  I've been using ultrasound for many, many years now (was an early convert to Audiodesk).  I always clean my LPs before playing.   On Sunday mornings, I almost always listen to one of the MFSL first Beatles albums.  I'd say "Help" and "Rubber Soul" have been ultrasonically washed well over 200 times (probably more).  And they still sound perfect.

In fact, writing this post had whet my appetite for Rubber Soul.  Later. all....

@lewm, The experiment you suggest is interesting but as I have observed and others every LP that I have cleaned with an US cleaner sounds better after cleaning. The majority of my LPs were purchased new and US cleaning improved the SQ on all of them. In some cases a slight improvement and in others a significant improvement. Primarily reduced background noise and elimination of clicks and pops, and improved detail and clarity. 

As i stated in mp post above, US cleaning only requires a couple of minutes of actual exposure and in that time frame I never observed any measurable degradation of the LP surface. Certainly degradation of the LP can occur with long US exposure. 

Then there is me, who doesn't even own a US RCM and does not even care if US can damage an LP.  But for the umpteenth time, the question put forth by the OP was about a METHOD to determine whether US RCMs can damage an LP.  Not per se whether US does in fact damage an LP.