Crashem with you talking watts maybe you can clear...this up for me,the higher the resistance the harder it is to drive headphones,maybe I'm wrong here but aren't speakers with less resistance say from 8 ohms to 4 ohms puts more strain on a power amp yet it's less resistance,then you have power as in watts,now Rob watts says the Hugo has a powerful amp section that can drive most if not all headphones but only has 1w,not sure with headphones but with speakers for example 86 db spl is harder to drive than 90 db spl but I thought that was ohms as in the resistance,I just don't get it at all,I know you Go by the rms for accurate power to match amp and speakers but I don't think it's that easy
I hope I explain this correctly and that I understand you question correctly. I am assuming you are asking why speakers put more strain on an amplifier when the nominal impedance of speakers are normally from 4-8ohms and headphones are usually much higher (for example, HD800 is 300, HE-6 is 50).
Let me steal this from someone else (http://www.activebass.com/a42--Understanding-Basic-Electricity-of-your-Amp-and-Speakers):
"First let me explain it in terms that everyone can understand. Think of your amplifier as a water faucet or hose bib on the outside of your house. You connect the garden hose to the faucet. This is the wire going to your speaker. You then connect the end of the hose to one of those spinning water sprinklers. This is your speaker. Now. The amount of water PRESSURE is the VOLTAGE. The amount of water FLOWING is the AMPERES. If you have one of those little spinning water sprinklers for the lawn it does not take much to make it move but if it is a heavy industrial sprinkler for a large field it takes more water pressure and flow to make it move. The pressure and the flow overcome the resistance and the RESISTANCE is the OHMS. The total amount of land getting water is work, and the WORK BEING DONE is the WATTS. Also, the size of the hose will effect the amount of flow so whenever you do wiring on your speakers be sure the wire size is large enough to handle the flow."
Given the above, you can see that OHMS by itself doesn't mean anything. Its the WATTS needed by a speaker/headphone at whatever OHMS is what dictates how hard your amplifier will need to work to drive a speaker/headphone. While headphones may have much higher Nominal Impedance (OHMS) than most speakers, it doesn't require anywhere near as many WATTS normally. You can compare WATTS needed by A speaker/headphone to B speaker/headphone by normalizing the ohms. So Speaker A wants 50 watts at 8 ohms and Headphone B is .5 watts at 64 ohms, would make Headphone B similar to 4 watts at 8 ohms. btw, when they say 50 watts required, they really mean watts RMS.
Statistics around efficiency (db SPL Vrms) or sensitivity (db SPL Wrms) are interchangeable with some calculation. These calculations were meant as a way to give you relative apple to apples comparison. However, it does not really help in determining if your amplifier will drive your speakers/headphones correctly beyond a brief guideline.
The danger is under-amping your speakers/headphones. Over-amping isn't as big a danger as long as you control volume correctly and don't blow out your speakers. Under-amping is the danger as not providing enough volts can cause the type of clipping that will cause permanent damage to your speakers/headphones. This is why I am scared to plug my B&W 805's into Hugo as B&W says it requires a minimum of 50 watts at 8 ohms and Hugo says it provides 1 watt at 8 ohms. Also, remember most of the numbers quoted are typically average and the variation is going to depend on the frequency being played.
