I recently picked up the Pioneer SW8 MK2 and the Martin Logan Dynamo 300. Since I've seen very few comparisons of these two budget subwoofers, I thought I'd post some thoughts.
First, let me say that this was a short and basic comparison where I put the subwoofers side by side and connected one high level and one RCA and then swapped the set-up and listened again. I listened to a variety of music via CD and DAC. Also, I only listen to music so theater use wasn't important to me. My room is about 12 by 20 with an partly open adjacent room about 10 by 12 and it has low carpet.
The two subwoofers are very similar physically. They are very close in size though the ML is a bit taller and wider. The black vinyl wood grain is similar though the Pioneer is clearly more like wood grain and the ML is more like a black cube. The pioneer has a blue light on the front and the ML has a red light on the back. The Pioneer has a bottom firing 8" woofer (coated paper I think) and a side port. The ML has a bottom firing 8" polypro woofer and a bottom firing port. The amp panel on each unit is almost identical. I would guess they came from the same factory although the Pioneer is stated at 50watts/100peak and the ML at 75/150 peak. I believe both are D class. The Pioneer has a hum (several individual reviews talk about this on some units) that is noticeable in a quiet room. The ML has a hum too, but it's much quieter.
At first listen one thing stood out: the Pioneer seemed to put out more bass at the same volume. After a few minutes of listening it became clear that the Pioneer had a little boost in its bass output. This makes sense because the measurements I've seen show a 40hz bump in the output. I couldn't find a measurement for the ML -- I'd love to see one. After some more listening that boost started to feel a bit artificial. I'm sure it would depend on the room and the speakers, but when I was able to listen side by side I found the ML to be less noticeable, but more even-keeled in the bass it added. I had both units crossed over about 70Hz and the volume at about 60%. On some tracks I prefered the Pioneer and the extra oomph; on most I prefered the ML. One other thing I noticed is that on a few tracks with heavy bass played loudly, the side firing port of the Pioneer created some port noise that was not present in the ML -- not sure if that was because of the flared design of the ML port or if it was due to the fact that it fires down.
In the end, I could be happy with either one though comparing them side by side my preference is for the ML. For the money they are both pretty amazing.
And, if you're wondering, I did play them both at the same time to see what that was like. They were side by side so not placed properly for two subwoofers. It was kind of fun, but probably too much bass for my ears. I suppose with better placement and a little reduced volume the two together could have sounded very nice.