The HD250 Linear was Sennheiser highest-end closed offering in the late 80s / 90s. The Linear I was produced from 1987 to 1991, the II model following and discontinued in the mid 2000s.
It probably has similar drivers Sennheiser used on the HD540 / HD560, but with different damping and pads. Like the HD540, the HD250 is very light and comfortable. The Linear offers actual isolation, on par with good current passive closed headphones. With 300 Ohm and 94-96 dB/mW sensitivity, the HD250 II will not run loud from any portable device. They were mostly targeted for studio use.
○ Release : 1991
○ Current status : Discontinued
○ Type : Over-ear / Closed-back
○ Measured weight : 230g
○ Impedance : 300 Ohms
○ Sensitivity : ~94-96 dB/mW
○ Average used price : $80-200
The HD250 Linear II (with stock pleather pads, in rather decent condition) offers a slight V-shape sound signature. Bass is definitely elevated, and surprisingly so considering they are almost 30 years old – most headphones, open or closed, were bass shy or not bassy back then. Extension is pretty good, with nice rumble around 35-60hz, but lacks absolute low-end (below 30hz) a good planar can deliver.
Midrange is mostly fine, but in direct comparison with HD580 / 600, sounds a bit thin, and I suspect that is caused by a dip in the lower-mids. Bass is a bit boomy and detached from the midrange. Male voices lacks some body, while most instruments and female voices are less affected. Treble is not edgy but a bit sibilant and piercing around 8-10 khz. Less bothersome than a DT770 or DT990, but much more present than a HD600. Treble response is otherwise very good – especially its upper-treble extension.
The technicalities are quite good for an old closed headphone. Presentation and staging are wider than a good bunch of recent closed cans. They are okay at detail retrieval, but not quite as detailed as an HD600, especially in the midrange and treble.
The HD250 Linear, just like the Sony CD1700, are two proofs the closed market has not improved in quality, especially in the lower-end / middle-end offering. The Linear would still be considered as a decent value if sold in 2020 for $200 (but easier to drive). Unfortunately, the tonal balance is far from perfect, as the treble could annoy a lot of people. Additional pad swapping or modding could improve that. Original pads are not available anymore.
Elevated bass around 30-200hz. A bit of channel imbalance around 150-300hz (probably caused by different L/R seal). Red curve show a dip around 250hz that affects the midranbe body. Very nice from 300hz to 5khz, but the treble starts rising up a bit too much.