SR XR えてぃ
http://clarityfidelity.blogspot.jp/2016/09/etymotic-research-er4sr-iem.html
http://clarityfidelity.blogspot.jp/2016/10/etymotic-research-er4xr-iem.html
http://clarityfidelity.blogspot.jp/2015/08/etymotic-research-er-4s-iem.html
https://lh3.googleusercontent.com/-c4sAZLaBqeg/V82cOi4-t_I/AAAAAAAAEo4/BXDcZH8XQgc/s1600/Etymotic%252520Research%252520ER4SR%252520-%252520raw.png
Square Wave
30 Hz 300 Hz
https://lh3.googleusercontent.com/-j711zPFLMTM/V82cegWpxTI/AAAAAAAAEpM/lXNgMk3Lwtc/s1600/Etymotic%252520Research%252520ER4SR%252520-%25252030hz.png
https://lh3.googleusercontent.com/-CG_qh3U1TTo/V82ce1wW2OI/AAAAAAAAEpQ/tpuTCOazZrI/s1600/Etymotic%252520Research%252520ER4SR%252520-%252520300hz.png