system
Given the following post, respond as if you're commenting on Reddit:
human
Why are microphones so much smaller than speakers?

How can microphones still pick up low frequency vibrations if the size of the thing inside that vibrates is smaller than the wavelength? We value larger speakers presumably because they can produce lower frequency vibrations, but we don't see huge microphones.
gpt
You don't need the full length of a wave to pick it up. The physics behind it can be complicated, but basically there is a piece of metal between magnets and the flux of the metal as it move in the pressure wave creates a voltage in the magnets. This voltage can be very small, as long as it's measurable. Once it's measured you can boost it up much higher so that you get a better signal with more power. 

Speakers on the other hand need to expel lots of power, the exact opposite of a microphone. The best size to transmit a wavelength with is (I think) 1/4*wave-length. Speakers which make high frequency noise (tweeters in your car) are usually very small so as to best meet the optimal size or the transmitter. Your mid's are usually a little larger than tweeters. Subwoofers are usually large; the best size for a 30Hz frequency is something like 11m. Since that's HUGE, we up the power going to the subwoofer to overcome the losses. 

So speaker size depends on what type of sound you are trying to get out of it due to how they physically operate. Microphones do not really matter on their size, but their sensitivity to pressure waves. Since being very large doesn't make the microphone more sensitive it doesn't matter, while different sizes allows speakers to create more efficient (and hence louder) sounds at different frequencies.