Sound of activity and energy, including a new kind (6)
I believe the answer is:
humane
'kind' is the definition.
(similar in meaning)
'sound of activity and energy including a new' is the wordplay.
'sound of activity' becomes 'hum' (eg the sound of a machine).
'and' means one lot of letters go next to another.
'energy' becomes 'e' (physics symbol as in E=mc2).
'including' indicates putting letters inside.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'hum'+'e'='hume'
'a'+'n'='an'
'hume' going around 'an' is 'HUMANE'.
(Other definitions for humane that I've seen before include "Merciful and considerate" , "Showing compassion for animals" , "Compassionate, benevolent" , "Kind-hearted and compassionate" , "Kindly and compassionate" .)