The Smaller Advent Loudspeaker
"This was the smaller version of the Original Advent Loudspeaker. The bass response in this unit rolled off at a higher frequency than the bigger version, but that's the only major acoustic difference. The woofer of this unit is the one with the huge dust cap. I presume that this cap was so big because they needed to add mass to the woofer cone. This speaker was intended for bookshelf use, and only came in the Walnut vinyl veneer. This unit was even more power hungry that the original Advent Loudspeaker, so they made it a 4 Ω unit to draw more current from an amplifier at a reasonable volume control position."