All dates until December 2017
The attachment of the membrane to the loudspeaker chassis via an outer surround enables the membrane to move flexibly and easily while being airtight and closed off from the loudspeaker enclosure. Many surrounds are made of foam rubber, which are extremely prone to deterioration over time, which radically affects bass performance.
Such damage to the outer connecting surround should be repaired immediately. It is best to repair both pairs at once thus avoiding having to send the second loudspeaker at a later date.