I read reviews of the UR20 over at Dan's Data and Amazon.com. Seems that the sound quality of the UR20 is not bad at all for the price. Most people like them. Better than the stock UR21, for sure, but have not seen an actual review comparing the 20 and 21.My UR21 mod could also work for the UR20, except Dan suggests that the UR20 earcups may be permanently sealed, so they may not be modifiable. The UR20 has a couple of other plus factors: longer cord (8 feet vs the 4 feet on the UR21), flexible headband, and higher sensitivity. The official list price for the UR20 is $25. HeadRoom sells it for $20.
Koss sells one other cheap closed headphone: the UR18 for $20. This model is slightly more efficient than the UR21 w/a 92dB/mW sensitivity rating, but the frequency response appears to be skewed for more bass at the expense of the treble. The UR18 has a bandwidth of 25-15kHz, where the UR20's spec is 40-20kHz.
The UR18 and UR21 may use the same transducers, and the different specs are due to the enclosures. I can't tell from the pics whether the UR18 can be modified.
posted 11-18-2006 12:41 PM CST (US) 
