It would be interesting to hear how bad the audio actually was...
First experiment (science conference talks from YouTube): "We selected two conference talks (in physics and engineering) from YouTube and altered their acoustic features using iMovie software. The good audio quality version of each talk was created with an audio filter called “small room,” which reduces the echo and increases the clarity of the speaker; the poor audio quality version was created with an audio filter called “Large Room,” which does the opposite, increasing the echo and decreasing the clarity of the speaker."
The second experiment (NPR interviews) was again using iMovie and they describe it like this: "The good audio quality version of each talk was created with no audio filters so that participants heard the interview as it was originally recorded. The poor audio quality version was created with audio filters that made it sound as if the researcher had called in on a bad phone line."
Of course that still means bad audio may influence the effect of your presentation, but not in the way suggested in the linked article.
That's what bad audio does. Echo is one part of that, but audio that cuts out or has crackles has a similar effect.
I disagree that the approaches are invalid. Bad audio is bad audio, and it shows that people's perceptions do change when audio is good and clear.