Line out vs headphone out quality

Besides Arny's correct answer, I wouldn't be surprised if some devices use the same output for headphone and line outputs.

I am and was 100% familiar with the the dock and its 30 pin connector. I'll stick to my story, including the part you apparently didn't read where I already mentioned the impedance difference.

One of the lesser-known lessons of audio is that there are approximately an infinite number of ways to get the same perceived sound quality, so the fact that there is a volume control in one path, that the voltage is different, that the impedances are different and that the circuitry is different need not matter to sound quality if both are well-engineered, which they are.

If you need the higher voltage, or if there is a problem with continuing  to use the volume control on the iPhone even if you just set it to max, then of course get the dock. But the use of the dock would be your preference, not because it improves potential sound quality.  Evertyhing doesn't matter, just the important stuff.

One day I ran into a market survey of current DACs, and it ran to over 400 distinct makes and models.  What's ironic is that I've measured over 100 of them, and done DBTs on a few dozen of the ones that looked marginal enough to be interesting.

Interesting factoid - one of the first DACs to reach the consumer market (in 1983), the DAC that centerpieced one of the first CD players sold the Sony CDP 101, can with the right program material be coaxed into having a discernible audible signature.  Of course, with more typical program material, its random guessing for everybody listening.

This DAC (like the Dyna Stereo 120 power amp before it) has a reputation among audiophiles that claim to have listened to it of being utterly horrible sounding. The bad sound has even been ascribed to jitter, which is a performance area where it is actually close to being SOTA. These "audio eggspurts" are just guessing, not actually listening. 



A general rule is that the distortion of a power amp goes up as the load impedance goes down. In the case of a portable digital player, the actual in-use headphone jack's load runs from something like 15 ohms (some headphones) to 10,000 ohms (a standard high line level input) to 100,000 ohms or more (tubed gear and some SS gear designed to be more compatible with tubed gear).  


In every case I know of, the distortion with the headphone loads (which run up to a couple of 100 ohms) are always measurably higher than what one measures with the loads that are appreciably greater. Usually, things are as good as they get around 10,000 ohms and up.  One of the hallmarks of a good headphone jack on a portable digital player is that it can drive low efficiency and low impedance headphones to the European legal limit SPL with inaudible distortion.  iPhones can do this since the first model, and have only gotten better or stayed the same since then. [/quote]

(1) Help with technical problems.

(2) Reinforcement

One of the well-known forums dealing with headphones even has called itself the "I'm OK, you're OK" forum.



IEMs can go either way, but done right they are the least difficult way to obtain true deep bass.



Any such limitation in the bass is an audiophile myth. Wavelengths are far more important at high frequencies.  However, a large diameter driver  can and often will be a pretty good high frequency reproducer, except that it will be as directional as all get out.



Because of the small, sealed space that has to be presurized to make real bass. there is very little need to fake anything.



One of the problems with earphones and headphones is that the air volume they have to work with with while favorably small, strongly tends to be significantly acoustically different for everybody.

A person who knows what they are doing, custom fitting them to each individual, can do well.



There is a big difficulty that lies in the fact that everybody's ears are different and highly personalized, especially from the standpoint of earphones and headphones.

Some of that gets factored out of the equation by the fact that our brains naturally adapt what we hear to be somewhat similar.

Hi philietes,

You wrote "It seems impossible for a 7mm driver to produce such long wavelengths". arnyk answered this this a myth. I'm sure the reason for this is the misunderstanding of "wavelength".

Very simply, wavelength = velocity / frequency. Think of the wavelength in linear terms, emerging from the driver front surface. The wavefront will move away from the driver at the velocity of sound through air (1130 f/s). It does not matter how small the driver diameter is, what maters is how slow or fast the driver can move back and forth. So a 7mm driver can reproduce a low frequency easily as long as it can vibrate slowly enough. The basic principle has nothing to do with the size of the driver.

Cheers,
Rock