Helmet workmanship screw nuts, comfortable, powerful (hp of about 9 cm) and light enough as it dates from about 1970. was originally assembled into 8 ohms, the importer (perhaps Lem?) added impedance transformers for use pro (revox example, TANDBERG Uher). Competing brands in the impedance 600 ohms + and used mainly micro capsules (whose noise level is much lower +).
other pro headphones with microphone also exists for TV reporters "Zitrone" but one in isolation from outside noise and pushing the price + + much higher. since I have had many major brand headphones which have all passed away, while this one is indestructible. "Price is the only quality is" ideal for output magneto REVOX I would buy it without reservation for this use