Listed is a rare find Matrix 802 High Pass Alignment Filter manufactured by B & W (Bowers & Wilkins), in decent condition and great working order. For use with B&W Matrix 802 speakers. You can check online the specs ,the purpose and the sound benefits from this device, I did it myself and most of the professional explanation it's still a mystery to me, the filter is upgrading the sound especially in the bass frequency from 2nd to 6th "something"... Anyway, as a music lover for decades mostly with analog sound I can share with you my personal opinion on this one : when using the above mentioned speakers in open space or large rooms the sound has more body and substance with this filter, the change of sound (for better) is really obvious. But again, I'm just a music lover not a specialist so all I can tell is what I hear, if you want more technical details check yourself online. 

As you can see in the pictures power adapter and filter coming  together as a set, condition is good with light scratches here and there, nothing major , anyway it's gonna stay somewhere in the back between the the amplifier and the preamp, basically not visible. As a vintage item doesn't carry any warranty. More audio items coming soon as I"m trying to let go a lot of audio equipment collected over the years.