While Head-Fi was down for maintenance yesterday I took the time to catch up with a few websites I hadn't been to in a few weeks. I stopped by Stereophile where I noticed an article/review on the new and improved Grado SR60i headphones. At the bottom of the page, at the end of the review, I noticed a link titled "Exploding a Myth About Headphones". I thought I would bring it to everyone's attention and share with you what it stated.
Link to main review page --> http://stereophile.com/headphones/grado_sr60i_headphones/index.html
Link to "Exploding a Myth About Headphones" --> http://stereophile.com/headphones/grado_sr60i_headphones/index2.html
"So what is the source of the myth that high-impedance 'phones are harder for portables to drive? It probably has to do with the volume level attainable. Most amplifiers are designed to deliver a certain voltage at a certain volume-control setting—but volume depends on power as well as voltage. Ohm's Law says that power is inversely proportional to load resistance. All else being equal, a higher resistance means a lower volume at a given setting. If the impedance is too high, you may not get the volume you want.
But a headphone's sensitivity depends as well on things other than impedance. The Grado SR60is have a nominal impedance of 32 ohms; my Sennheiser HD650 'phones have a nominal impedance of 300 ohms. Conventional wisdom would have it that the lower-impedance Grados would be the better choice for a low-power portable device. Yet, at a given setting of the volume control, the Grados and Sennheisers deliver very similar volume levels. So which is the better match for a low-power portable device? Both have adequately high impedance, and both sound fine through my iPhone—but the Sennheiser, with its higher impedance, is theoretically the better choice, both because it draws less current from the battery-powered player and because variations in its frequency response will be less severe.—Jim Austin"
Seems as though we are going to all have to change up our recommendations for people with iPods.