My setup is the popular Modem -> Ooma -> Router; since day 1, I never thought I had any voice quality issues or setup problems.
Because when I ran these tests:
I got decent numbers.
Once in a while, especially evenings and weekend afternoons, I would see some dramatic degradations in my test results.
Instead of the normal 16 Mbps/2 Mbps, I'd see 2 or 3Mbps/1 Mbps or even lower. The VoIP tests would reflect some terrible jitter into the high teens and beyond and show Upload Quality of Service drop to the low teens.
I just thought the damx cable company was having issues keeping up with neighborhood demand and never thought 2wice about looking into my setup further because in the mornings or very late at night, things would go back to normal.
Besides, even when the tests were showing some terrible results, my phone conversations were fine on both ends with very slight noticeable dip in voice quality.
This evening, I got some horrible results again so I decided to pay http://setup.ooma.com/ a visit.
Went to Network, selected "Use Built in Modem Port MAC Address" instead of "Automatic" and clicked on update.
Then powered down everything and brought devices back up one at a time: modem, ooma, then router.
Voilà!!!! That improved my bad numbers dramatically! Even during the height of internet use in the neighborhood, my cable modem was putting out some awesome numbers. Of course, the voice quality went back to "outstanding" as well.
Conclusion: even if you think your setup's performance is great, go do this "Use Built in Modem Port MAC Address instead of Automatic." You'll thank yourself.