Recirculating and venting are the same thing. Did you ever see a WRX BOV? The flange is fucked up but its pretty much the same thing as a DSM. It'll recirculate the air into the atmosphere

 

yes, I realize that too.

Typically the ones made especially for venting have a horn or make a gay noise like the HKS (isn't that the tweet one).

 

ya the construction looks identical, the only thing is the flange is a wierd shape. it doesn't matter if its made for recirculating or not, if you leave it open it makes a 'whoosh' noise. not a 'psst psst' squawk like the hks/greddy. its more like a blitz whoosh. in the wrx, with it tucked down and the opening faced down, i can tell you that with the hood opened its very loud, but with the hood closed its barely audible. so positioning will be the difference unless you put a horn on it imo.

 

Here is my wrx blow off valve.



Like XDEep said, it has a "whoosh" sound. I like it