Sound quality acquires new weight (5)
I believe the answer is:
tonne
'weight' is the definition.
(I've seen this before)
'sound quality acquires new' is the wordplay.
'sound quality' becomes 'tone' (I've seen this before).
'acquires' means one lot of letters goes inside another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'tone' going around 'n' is 'TONNE'.
(Other definitions for tonne that I've seen before include "One thousand kilograms" , "Great weight" , "A thousand kilogrammes" , "Mass" , "Heavyweight" .)