For the difference in tone, it's hard to know, but it seems to be a consensus about birch and poplar souding different. Some say it should be more focused with birch, some that poplar gives a more woody tone, but apart doing 2 identical cabs, one in birch and the other in poplar, wich I won't do, it's hard to know what the difference is...
Different wood types and tone tends to be subjective, not objective. Subjective meaning a person or a number of persons opinion(s), not fact or measured, which is objective.
If you were talking about resonant things like say a guitar or a drum shell, then there is a lot of information around about the subjective opinions that people say or have, suggesting that differing wood type can display tonal changes.
Such comments may include descriptive words like warmer, smoother and so on, but they are subjective because they are warmer or smoother than ?????.
Certainly, in musical instruments, people want their instruments made of the timbers they prefer, based on reading, research and others opinions. Does that mean they are measurably different?
Not really, because there are simply to many variables to make apples to apples comparisons.
The same idea shouldn't extend itself to speaker cabs of any description though.
Speaker cabs, in the perfect world, should not resonate. That means they shouldn't add any "colour" to tone.
It is a fact though that different ply types have different weights or density, and some are easier to work with than others, because, for example, they tend to warp less.
So your choice of poplar as a cab building material should be about having a lighter in weight cab compared to a birch one, rather than tone.
However, a cab made of birch ply may be easier to build because it tends to warp less.
One thing is certain. A cab made of poplar ply will not take the knocks and bumps that a cab made of birch ply will. Poplar "bruises" and marks quite easily...
2 x DR 250 (melded array) with March 2012 plans.
4 x 20" BP102 T39's, 2 x 28" 3012lf loaded underway.
3 x WH8 with melded array.Bunter's Audio and Lighting
"like"s would be most appreciated...