The problem with your Audacity experiment is probably that the EQ filters just aren't steep and selective enough. (and using a single sine wave as input, which leaves the filters with nothing to filter) Try something like Pure Data and use three or more band-pass filters in parallel (not in series), creating a really steep contour. Try searching for formant filters, they are done as parallel band pass filters. Your source article gives you frequencies F1 and F2, but you need something that gives you F3 etc. And use band-pass filters in parallel, not Audacity's EQ curves.
I once tried this and I was able to do a semi-intelligible vocal synth with one oscillator (actually, more than one because there was noise as well) and a formant filter consisting of a bank of three filters set to the right frequencies. To switch between vowels, morph/slide the three filters to the next vowel's frequencies. IIRC, two filters was too few, there needs to be at least three filters to create recognizeable vowels. Some letters like W that are classified as consonants can be done by morphing the formant filters between vowels very quickly. Plosives like t, p, k are more difficult and I couldn't do those with the simple synth building blocks I tried, namely oscillators and filters.
Here's a Sound on Sound article on formant synthesis https://www.soundonsound.com/techniques/formant-synthesis
Edit. I didn't look at your audio example. Seeing user1079505's answer, I recalled what the oscillator was in my vocal synth. It was not a simple sine wave, but something more complex like a square wave that has many partial frequencies besides the fundamental - and I mixed in some noise to simulate breathiness. More noise = more breathiness. If you have only noise, then it sounds like whispering. Wind noise of air flowing through a pipe, filtered by a formant filter. But filters need there to be something to filter. If there's no frequency content at, say, 400 Hz, then what does a band-pass filter at 400 Hz let through? Nothing.