When a spec states something as + or - 2db it means that a product (speakers in your case) will only increase or lose volume by the specified 2db between the lowest and highest frequency's stated. So in your case, between the very low frequency of 28hz and the very high frequency of 25khz the speakers will only add or subtract 2db from the music sent to them.
DB's or decibels is a measurement of volume or loudness. 1db is considered the smallest amount of change in loudness that humans can hear. However in practice 10db to most people sounds like twice as loud. So 6db would be half way.
If you have ever messed with something that has traditional bass and treble knobs, 6db would be the same as turning the knob about half way.
HTH.
DB's or decibels is a measurement of volume or loudness. 1db is considered the smallest amount of change in loudness that humans can hear. However in practice 10db to most people sounds like twice as loud. So 6db would be half way.
If you have ever messed with something that has traditional bass and treble knobs, 6db would be the same as turning the knob about half way.
HTH.