STAX SRS-2170 / SR-207 Earphone System Measurements The STAX SR-2170 system consists of an SR-207 headphone and SRM-252S amp. This is an electrostatic headphone system, which means that we cannot use a phono jack on a stereo or iPad to play music from these headphones. The cost of this system is about $700 (in the USA) if obtained grey market via eBay. STAX's distribution gets more and more horrific the farther we get from Japan. I am not sure if the Needle Doctor (USA) even carries STAX anymore since STAX is such a pain in the ass. But the nice thing is that the system includes an amp that does the job quite well. It's not like we have many available choices. Also, USA service for STAX is craptastic. Not only is service impersonal, but expensive. STAX USA tends to dick around with customers and try to decline service as much as possible, finding weak reasons to do so. In other words, they bend their backwards to make sure we are NOT taken care of. Personally, I think the guy running STAX service in the USA is lazy. Or maybe it was an idiot room position given to someone who was related to one of the STAX founders. I was quoted near $2000 for a driver repair on a SR-007. Fortunately, the lower end STAX seem to be more reliable, but it should be noted that more than half of of STAX gear I have purchased has failed. This includes an SR-009, SR-007 (dead drivers) and SRM-323 (rca jacks). I have heard of many SR-009 and two other SR-507 failures (my SR-507 did not experience any issues.) Here is a picture. The amp uses a 12VDC 0.5 from a watt wall wart. This was a Japanese spec, so a voltage converter was used to drop 120V to 100V. A 120VAC to 12VDC wall wart would be a more suitable solution. The SRS-2170 sounds super clean, with only a hard time reproducing sub and low bass before 50Hz or so. For most music, particularly of natural instruments, there shouldn't be a an issue. Bass tends toward a softish bouncy quality commonly heard with thinner diaphragm planars. Mid-bass (60Hz to 200Hz) is much clearer than almost any dynamic. Treble was fast, refined and exquisite. The MrSpeakers line of planar Ether speakers has this quality, but STAX presentation still wins out in terms of refinement, smoothness, naturalness. I actually prefer the treble of the SR-207 to that of the more expensive SR-507, which was tizzy. (SR-507 could be described as boom and tizz). The one thing that stood out and really bothered me was the midrange bump. The folks here who bitched about the midrange bumps of the Focal Elear or to a lesser extent the Utopia are going to hate this bump. It's so excessive that it's not even recording dependent. It permeates through all recordings. The bump has a side effect of slightly creating a dip in the lower mids / upper bass, result in a loss of body or on occasion a colder presentation. I attempted to get as good a seal as possible for the measurements below. I added a piece of non-leaky high density foam to better simulate how the funky earpads conform to the head. A weaker seal will increase amplitude of the bass peak and move the resonant frequency higher. We can get a pretty punchy fun sounding 90-100Hz emphasize if we wanted. STAX 207 Frequency Response (0db line = 100dbSPL) STAX 207 Distortion (at above levels) I re-measued the left driver several times to confirm the worse measuring sub to low bass distortion. Bass quality from 60Hz to near 160Hz is better than that of the HD650. We can easily hear this too. The sub bass roll-off is more sudden with the SR-207. STAX 207 CSDs Thanks to @Mikoss for this item. Loaner program?