Unlike most portable speakers that can only connect through Bluetooth or an external 3.5mm auxiliary jack, the Z515 also includes a wireless 2.4GHz USB dongle for your laptop that can play wirelessly from around 50 feet away. This way, you don't have to deal with switching between Bluetooth on your computer and the same profile on your phone. Creative doesn't include a wireless transmitter with the D100, but instead sells a Bluetooth adapter separately for $40, which explains the $50 price break.
Like most Bluetooth speakers, connecting the Z515 via Bluetooth is simply a matter of holding down the two volume buttons for a couple seconds to put it in pairing mode, then connecting to the speaker on your music player. The process took us less than two minutes before we were blasting music out of our Apple iPhone 4, but you can use it with any player that supports the A2DP standard.
Sound quality from a Bluetooth-connected device will always come up short compared with a 3.5mm cable connection, but we're impressed with the Z515's ability to pump out myriad genres with zero distortion or fuzzy noise even at the highest volume--plus, the speaker gets fairly loud. The dual 2-inch drivers provide fairly balanced sound, but the lack of the bass tells us that the Z515 is better suited for a dinner party or a medium-size get-together--house parties need not apply; not to say that the Creative D100 is much better, but its 3-inch drivers are able to produce a better thump for hip-hop and techno songs. On the other hand, we were able to replicate the Creative's low-end on the Logitech Z515 by simply setting our iPhone EQ to "Bass Booster. It's not the most audiophilic solution, but it works.
Lastly, Logitech rates the rechargeable internal battery to 10 hours of continuous play using Bluetooth, but in the future we'd prefer the option to use alkaline batteries or even a USB-powered solution in the chance that a power outlet isn't around. Nevertheless, 10 hours should be more than enough to keep the party going well into the night.