This is a video review on the AKG K240 Studio semi-open headphones. These might be the industry standard for semi-open headphones and VERY affordable, too.
AKG Pro Audio K240 STUDIO Over-Ear, Semi-Open, Professional Studio Headphones : Everything Else
AKG K612 Pro Reference Studio Headphones have an open-back, over-ear design and feature neodymium magnet drivers. Their self-adjusting leather headband and velour ear cups are designed to provide comfort while in use.
AKG - K612 Pro Reference Studio Headphones
Review: AKG K240 Studio Headphones
AKG K240 Studio Headphone Review - Sonarworks Blog
AKG K240 MKII Semi-open Pro Studio Headphones Reviews
AKG K240 Review
AKG Pro Audio K240 STUDIO Over-Ear, Semi-Open, Professional Studio Headphones : Everything Else
AKG K240 MKII Semi-open Pro Studio Headphones Reviews
AKG K240 Review - Analysis After Years of Use
AKG K240 Studio Review – A Truly Unique Specimen - Home Studio Basics
Enrich Your AKG (AKG K240 MKII with Beyerdynamic EDT-990V)
AKG K240 Studio Headphone Review - Sonarworks Blog