There may have been a local connection to Sentry speakers. In 1980, I started with Kelly's who used to sell Pro Linear's and those were stocked pretty much in all the stores. New West was where I was but prior to that, the main store on Granville Street with several sound rooms, or maybe a previous location (Broadway?) had Sentry speakers on display or did have for a time, There were items at the large stores that did not appear in the outlying ones. I thought then that Sentry were likely from the same source as Pro Linear. The family which owned Kelly's had roots in furniture sales and manufacture so speakers were a natural.