I've never heard of a bullpen before, it sounds like a pretty horrific work environment.
A civilised, open plan engineering office should indeed be quiet. Not silent, but fairly quiet.
We did exactly the opposite to your method by the sounds of things - meeting rooms for 4 to 5 people, and one or two much larger rooms, were available around the edges of the floor to go and bounce ideas around or discuss things. The rest of the floor was quiet space but informal conversation was fine. It worked very well for us.
A civilised, open plan engineering office should indeed be quiet. Not silent, but fairly quiet.
We did exactly the opposite to your method by the sounds of things - meeting rooms for 4 to 5 people, and one or two much larger rooms, were available around the edges of the floor to go and bounce ideas around or discuss things. The rest of the floor was quiet space but informal conversation was fine. It worked very well for us.