**UPDATE – 10/7/15**
One user reported that when he turned up the bass it seemed like all that did was turn the volume up. Since EQ commands aren’t sent to the Alexa app (at least, not as of this writing), I had to resort to a more hands-on testing approach.
I started with a song I know very well that has a strong bassline (Mondo ’77 by Looper), with the volume set very low. I placed my hand lightly on the side of the Echo cylinder so I’d be able to feel any vibration, and there was none. Then I issued the command, “Alexa, turn up the bass,” and both the bass and volume did go up, and I could feel vibration in my hand. However, after I used the remote to turn the volume back down to where it was at the start of the experiment, the Echo cylinder was still vibrating. Since I’d turned the volume back down to where it was before, when it wasn’t vibrating at all, I concluded this was a sign that the bass had been increased when I issued the command.