What speaker is commonly used for low-latency audio stimulation We need to purchase a new speaker for audio ERP study, so the sound should be played in lowest possible latency with lowest possible jitter. I have seen quite a few suggestion on the OS/driver/sound card part, but it seems that there is less information about how to choose the proper speaker. 

What is the common latency between the the time point when the sound card actually start sending out signal, and the time point when the speaker actually start vibrating? And are there any point that we should take care when choosing the speaker?
There is generally an intervening stage between the sound card and the speaker, the amplifier. From the output of the amplifier to the speaker, there is an electrical signal traveling at like 0.01C that then drive the speaker via an electromagnet. The transmission and transduction time is essentially zero. Further, you can safely ignore any jitter.

For powered speakers, or amplifiers, there are all sorts of models. Some might have some built in filtering that could introduce a delay, but it is probably negligible.