Why is it a external wastegate produces noise yet an internal ones doesn't?

I don't mean 'wastegate chatter'

I remember Christian doing a brilliant write up on this but can't bloody find it.

 

Would an external be heard if the dump pipe was fed back into the system rather than vented to atmo??

 

Ah right I see what you mean now.

Why does an explusion of air make such a noise tho?

 

what noise? its just the sound of an unsilenced exhaust at high rpm.

if you hear a external wastegate venting at low rpm you will see it just sounds like a POS.

its hard to tell, but a lot of the whistle from a turbo car is actually out the exhaust, so that again is part of the screamer noise, jus unsilenced.

BTW, external or internal wastegate, even if they plumbed back into the main system you can tell when the wastegate opens if your exhaust is loud enough.
on my cossie you could tell the exact time it hit full boost and the wastegate opened as the noise would get a lot louder as the turbine was no longer silencing it...

 

The external gate is not so much referring to the ease of abilty to vent gas without passing it down the system but more to the fact its not actually part of the turbo housing anymore. On some internal gated turbos you can vent to atmo by constructing a partition in the dowpipe that seperates waste gas inside the turbo housing.
Its all about gas flow disruption at exit point,as the internals(from factory) have both used and wasted gas trying to escape down the same tube it can case disruption in flow....which ideally you dont want,you want to gas the gas out as quick as possible....restriction free almost.
They so noise just because there alot of air trying to esacpe down a lmited size pipe...............like blowing through a straw or leaving an air line open on a compressor.

 

Ah right I see now guys cheers,