This discussion has descended into a quagmire of pseudoscience. The test itself was as sample size of 1, and not statistically significant. And, if you really wanted to do it right, you would have a third party person play the bass lines, not knowing which one was alder and which was ash, so that both the performer and the listener would be blinded. That said, the one group that actually had an alder and an ash A:B comparison (the first group), was pretty easy to hear the difference between the two basses. Also, I want to commend Dan on taking the time to make sure that both basses were set up the same, etc., and he plays well, and the tracks are recorded well

.
I'm just disappointed that he had to pull the "trick" with the last 2 clips, as that puts his motives of the test into question.
This was more a test of psychology and preconditioning and test taking methods than a test of whether ash or alder sound different, due to the "trick" where the last 2 clips were the same, in spite of Dan stating that he recorded both clips with different basses.
I imagine people going through this thought process...
"The first 2 clips are obviously different. 1A sounds like ash, and 1B sounds like alder.
I can't hear much difference between 2A and 2B though.... hmm....but he SAID they were recorded on different basses....
the first 2 are obviously different, and 1A really sounds like ash...well, I'm sure 1A isn't alder so that rules out answer 1, so answer 2 must be it. The clips 2A and 2B sure sound similar, but he SAID they were recorded on different basses. I'm sure 1A is ash, so I guess 2A is ash too".
Now, had Dan said, "The following 2 groups could be a comparison of ash vs. alder, or they may be me playing the same bass. Let's see what you think. Are the clips different or not? If they are different, which one is ash and which is alder? If they are the same, is it ash or alder?"
That would have yielded more info about whether people can hear the difference between ash and alder, and I'm sure the results would have been different. Instead, it was more of a psychology test on preconceptions, and a test to see who can figure out that the test itself is rigged. Save it for the Psychology 101 class.
The discussion on wood densities is a stretch too. (Dan has nothing to do with this).
Ash is just as likely to be less dense than alder as it is to be more dense.
Alder: 26-42 lb/cf
Other tonewoods that fall in the same density range:
Ash: 40 - 53 lb/cf
Beech: 32-56 lb/cf
Hickory: 37-58 lb/cf
Mahogany: 31-53 lb/cf
Maple: 39-47 lb/cf
Oak: 37-46 lb/cf
Spruce: 25-44 lb/cf
Teak: 41-55 lb/cf
.
There is only a small overlap in the Ash and Alder density ranges. Without distribution density curves for the 2 wood density ranges, you cannot say that "Ash is just as likely to be less dense than alder as it is to be more dense". If you look at the density ranges you posted, the only way that could be true is if the distribution of alder density was skewed way to the right (more dense) and the distribution of ash density was skewed way to the left (less dense). I doubt that's the case.
When all is said and done, after taking neck construction, fingerboard choice, strings, pickups, preamp, amp, speakers, and finger technique into account, body wood has a small impact. To say that body wood has no impact, or a miniscule impact is foolish. Just listen to the clips 1A and 1B. I heard an obvious difference there...and that was listening through my iMac built-in speakers with my 2 year old son crawling on my lap trying to play with the keyboard while I listened. Before this test, I felt that body wood probably had a very small effect on tone, but after listening to clips 1A and 1B, I'm convinced that body wood CAN have a pretty obvious effect. Does it have the largest effect on tone? Nope.
Does it have a discernible effect on tone? Looks like it does.
At least in this sample of 1.
How does that affect me? It really doesn't because I base what I think about a bass on how it sounds (and looks). It would be a consideration if I were having a bass custom made, but I would still realize that there's no guarantee that an alder bass is going to sound "warm" and an ash bass is going to sound "snappier" but there's a good probability that this will be the case to some extent.