I was browsing through the Grado website and had a look at their IEM's GR8, but was quite shocked to see that they need 120 Ohms of power to drive them. Which tells me that most MP3 players out there wont drive them, because I dont think there is an MP3 or even portable music player with Impedance of 120 Ohms to drive some thing like the GR8, unless you get a CMOY or seperate headphone amp.
But really isnt the purpose of an MP3 player and IEM's to do with portability.
I used to have a pair of the GR8s (the left side blew after a week of light use) and can attest that when used with an un-amped iPhone at half volume they sound clear and punchy.
When I first got the GR8s I was concerned with the impedance as well, so I plugged them into a Total AirHead amp; I soon realized that the amp wasn't necessary.
I know that this isn't a scientific reply. But if you are thinking about buying a pair, I wouldn't worry about being able to drive them with an iPod or anything similar. I constantly question whether I should buy them again, as I really liked the sound signature, but have been put-off by my aforementioned experience.
Ohm's aren't everything when determining how loud phones will be. As omega52 stated the sensitivity of 118db/1mw is an important factor. SPL (sound pressure level) as just as important as ohms.
Putting a tiny bit of science into the thread for anyone interested and just for fun . . .
Assume there are two earphones:
EP1 = 16 ohms, 101db/mw
ER2 = 120 ohms, 118db/mw
Ohms law: V = I * R
Power = V * I = I**2 *R = V**2 / R
If an amp can drive 1V rms, for example, and the EP1s impedance is 16 ohms (assumed constant across the frequency spectrum, which it is not), the drivers would dissipate 62.5 mW. If EP2s impedance is 120 ohms, the drivers would dissipate 8.3 mW.
A standard equation for db gives (Wikipedia) (I'm never sure when to pick this power equation or the amplitude equation where 10 is replaced by 20 when making this calculation. Any inputs?)
Ldb = 10 Log (P1/Preference)
where P1 = input power and Preference equals the power which gives the rated efficiency at 1mW input.
Doing a bit of algebra to get Preference for each phone and calculating the final value at full power:
EP1 should give a maximum loudness of 118 db for 1 volt drive
EP2 should give a maximum loudness of 127 db for 1 volt drive
So, for the assumptions made on driver efficiency and impedance, the lower impedance driver has a lower volume at 1V rms output.
If the efficiency of EP1 is increased, it can easily exceed the output power of the EP2, but then, 127 db is plenty loud, IMO.
My point here is that these are IEM's and not a pair of AKG's K702/701 or Senns HD800 where more Ohms or Imp is reqd to drive em. I mean even look at the other Grado's (the bigger brothers) I am sure even their Ohms isnt as high.
Originally Posted by Albinoni /img/forum/go_quote.gif My point here is that these are IEM's and not a pair of AKG's K702/701 or Senns HD800 where more Ohms or Imp is reqd to drive em. I mean even look at the other Grado's (the bigger brothers) I am sure even their Ohms isnt as high.
I think you still don't understand the terminology you are using. Understandable, if you haven't studied electronics or physics. Consequently, it is hard for me to understand the point you are trying to make. I guess that is why it appears that you are not comprehending the answers that your post has received. Bottom line is that the sensitivity spec for the product is what you should concern yourself with. The higher the dB/mw the louder the phones will sound. There is a point where the impedance plays a part, but in the cases you stated, it is not high enough to be a factor. My 600 ohm AKGs are a different story.
Cheers,
kev
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