01-25-2010 03:07 PM
saratoga wrote:But my simple point, no need to call a person or his comment stupid ... (And the poster, by the way, explains and stands by his comments, as he notes above.) Life is so much more civil without.
01-25-2010 03:12 PM
We can do without the personal attacks. Everyone has the right to their own opinion and there are constructive ways to disagree without name calling. Please keep it civil.
01-25-2010 03:19 PM
Of course, but I didn't call anyone stupid. I said his argument is stupid because its already been disproved earlier. Theres a very big difference between saying "thats a stupid argument for the following well established reasons . . ." and "you're stupid".
That said I did call him "clueless" but honestly if you argue about impedance without actually knowing what it is, I think thats less an insult that an observation of fact
01-25-2010 03:30 PM - edited 01-25-2010 04:07 PM
"You've confusing impedance with sensitivity. With lower sensitivity headphones, you might need an amp. With lower sensitivity headphones you might need to turn the volume up more. Going from 16 ohm to 32 ohm drops the volume 3dB. Thats nothing! The threshold of detectability is usually around 1 dB for most people. But that doesn't mean lower impedance works better. It doesn't as I've shown above. It just means that if you get headphones that need an amp, you might need to get an amp. But you can still easily drive higher impedance headphones provided you pick ones with suitable sensitivity such that an amp isn't needed. And in fact doing so will give you slightly better performance then going with very low impedance headphones."
It isn't just about the impedance of the headphones though.
Impedance total= output impedance of player * headphone impedance/(output impedance of player + headphone impedance) The greatest amount of power is transfered when the headphone impedance matches the output impedance of the player.
Higher impedance headphones also tend to have a lower sensitivity.
Message Edited by JK98 on 01-25-2010 07:07 PM
01-25-2010 03:46 PM
Sometimes, those distinctions can be missed ... Just better, it sees to me, to explain the underlying rationale. as you had done. But the point's been made--thanks. And now, back to our regularly-scheduled programming.
01-25-2010 04:18 PM
For mp3 players the output impedance is pretty small, so really only the headphone impedance matters. Most people tend to ignore it, although over at ABI we discussed this in detail a while back.
Actually, for an mp3 player the way we talk about impedance you should be using the Thévenin model, not the Norton model (although your formula would work for other types of amplifiers, which is why i'm guessing it came up when you googled amplifiers). The Norton model won't work so well because you can't measure the short circuit current (the DAC will cut you off to prevent you from damaging it).
Using the proper model, the impedance is actually calculated like so:
Impedance total= output impedance of player + headphone impedance
On ABI I calculated the output impedance of the Clip using dfkt's measurements. Its about 1.6 ohms, quite small compared to the 16-64 ohms typically used in headphones, and so you can safely ignore it.
This is a common misconception. Its actually completely wrong for these amplifiers, which is why the output impedance of the CLip is 1.6ohms and not 16 ohms
Instead you maximize power transfer by having the smallest possible output resistance. Ideally it would be zero, in which case the clip would transfer 100% of its power to the headphones. Instead, with headphones at 16 ohms it transfers 91% of its power to the load. Conversely, if it had 16 ohms output, and 16 ohm headphones, just 50% of its power would be transferred. Not very good at all!
Interestingly, efficiency actually increases for larger impedance headphones. For 32 ohm headphones, over 95% of the output power goes into the headphones (and at 64 ohms, nearly 98% goes)!
01-25-2010 05:42 PM
Heyyyy! That's a derogatory term now and so not PC (No, not computer, but politically correct). These people have 'special needs', they're not (what it says). Even the Prez had to back-pedal & apologize for his remark about how he bowled as if he were in the Special Olympics. He got flamed big-time.
I think Carlos Mencia says it best . .
01-25-2010 08:03 PM
Let's see, we started with...
And we end up with...
Such good sport! I think that Fuze is sounding better by the minute. As you can see, my favorite companion is the e200 with Macally soft leather phones.