[Reticuli2]

If noise canceling designs have a built-in amp, are they designed to be used with a headphone jack or can they be used with an adjustable line-level? I assume a dedicated amp is not needed, but are there any known impedance considerations with feeding one line-level? Is the performance better? The same? Worse?  How does such a design even deal with potentially extremely large inputs from a headphone amp?  Do they have limiters?

 

[bedlam inside]

Hi,
Quote:

If noise canceling designs have a built-in amp, are they designed to be used with a headphone jack or can they be used with an adjustable line-level? I assume a dedicated amp is not needed, but are there any known impedance considerations with feeding one line-level? Is the performance better? The same? Worse?  How does such a design even deal with potentially extremely large inputs from a headphone amp?  Do they have limiters?

My Audio Technica Headphones allow the noise cancelling to turned off. With that they become good, purely passive headphones, I'd say middling sound quality, pleasant, nothing outstandingly great, but nothing really bad either. They do sound better that way too.

Turn the noise cancelling on and the sound becomes a lot louder, but also a bit more electronic sounding. Still in noisy places the result is absolutely brilliant, just running from a Smartphone! In the office I listen with an Amplifier and noise cancelling off...

Cheerio Rich

 

[Reticuli2]

When noise canceling is on (or on the models where they cannot be passive) is there an advantage to using line-level over a headphone jack or vice versa?

 

[obobskivich]

My understanding, based on the Bose ANC headphones, is that they just present a very high (like 40kohm) impedance to whatever they're plugged into. It means that from a headphone amp, they still won't "see" much power, and from more of a line type source they should also be able to derive a signal (because that kind of source is designed with such high impedance in mind, but doesn't output much current at all). I'm not sure if other ANC headphones follow this model or not. IME the Bose ANC headphones aren't very picky about amping - but I don't have a lot of experience with other ANC headphones (like the Klipsch or Koss models).

I know the QC15 has a limiter of sorts built into the removable cable; I don't remember if QC3 has the same, and I don't know much about the QC2. The Klipsch and Koss headphones do not have such a feature in their cable (the Koss have a volume control, but it isn't the same as the hi/lo limit on the Bose cable) - I don't know if something like it exists in the earcup or not. I know that even with the limiter set on the QC15, they still can get ear-splittingly loud, so it's certainly not clamping output to protect your hearing. The manual's explanation leads me to believe it's a pad to allow some range of motion on volume controls depending on the source device (so you don't have it turned all the way up, or have to keep it nearly all the way down).

 

[bedlam inside]

Hi,
 
Quote:

When noise canceling is on (or on the models where they cannot be passive) is there an advantage to using line-level over a headphone jack or vice versa?

I don't think you can break anything by just plugging the phones into the line out. So just try it. If it sounds pants you know it's not right.

Generally I think noise cancelling phones are designed to plug into headphone jacks.
 
Cheerio Rich

 

[skamp]

Just make sure to turn the volume WAY down before plugging the noise cancelling headphones. Contrary to normal headphones that would get somewhat quiet because of the very high output impedance, noise cancelling headphones will get very loud (even out of an iPod's LOD, which outputs a lot less voltage than a true line out).

 

[Reticuli2]

I already did it.  I know it doesn't harm anything.  I'm just wondering if there is an electrical/electronics reason to prefer one over the other.

 

[davidsh]

Well, line-out is probably better since you aren't double amping. But on the other hand, the amp inside the 'phones is probably not very good anyways.

 

[Reticuli2]

Yeah, but would something like drive, current swing/slew, and damping factor even come into play with an amp sending into an amp?  I have the ability to put a very hot line level input into the headphone and control the volume in the digital domain from the source without quality loss.  Assuming I compensate with said volume controls, would the NC headphones' batteries even last longer with an amp running into it?  I'm rather amazed these types of headphones can even run both a microphone and an in-built amp of some sort off of just two AAA batteries.  I'd rather have a 9V in each earcup.  Seems like a tiny amount of juice to feed an amp, being I'm used to using an O2 on AC.

 

[davidsh]

Dampening factor and the like will be eliminated. It's like asking if the output impedance of a DAC feeding an amp will alter the frequency response and dampening factor of the headphones. Most likely the input impedance of the built in amp in the 'phones is very high.
I don't know how you will get the longest battery life, but I'd expect you can't really do anything to the battery power consumation rate

 

[obobskivich]

Yeah, but would something like drive, current swing/slew, and damping factor even come into play with an amp sending into an amp?  I have the ability to put a very hot line level input into the headphone and control the volume in the digital domain from the source without quality loss.  Assuming I compensate with said volume controls, would the NC headphones' batteries even last longer with an amp running into it?  I'm rather amazed these types of headphones can even run both a microphone and an in-built amp of some sort off of just two AAA batteries.  I'd rather have a 9V in each earcup.  Seems like a tiny amount of juice to feed an amp, being I'm used to using an O2 on AC.

No need for a 9V (the AAA is giving you around the same capacity); and the Bose and Koss ANC 'phones use a single AAA (I've always found designs that need 2-3 batteries somewhat suspect). There's no quality loss there - it's properly mated to the drivers (which are likely low impedance/high sensitivity themselves, so voltage swing isn't much of a concern). Damping factor, as usual, is marketing run amock. Nothing to worry about (because you shouldn't worry about something that isn't).

I doubt you'd increase battery life substantially running them via line-out versus a headphone amp - maybe you'd increase the battery life on your portable, but it shouldn't matter much for the headphones themselves. As far as the O2 running on AC - that's all well and fine, but how much power is it actually using? Figure that you're probably only outputting a few mW - it's probably using less than 1W unless it's massively inefficient (like worse than 10% h34r. As far as fidelity/quality goes - yeah you are probably better off doing things with a preamp (assuming it isn't dropping bits to drop level). But I'm doubting there's much of anything being improved upon here beyond better channel matching and lower noise (and I know, those two aren't buzzword compliant explanations).

 

[Reticuli2]

[size=10pt]So it sounds like there's little to no possible improvement to running an amp prior to a NC headphone and the only possible consequences are either inconsequential or adverse if I do so. Since either way is equally convenient for me, I'll just run it straight into the line input until I hear otherwise when I have the opportunity. Thanks.[/size]

 

[obobskivich]

[SIZE=10pt][COLOR=000000]So it sounds like there's little to no possible improvement to running an amp prior to a NC headphone and the only possible consequences are either inconsequential or adverse if I do so. Since either way is equally convenient for me, I'll just run it straight into the line input until I hear otherwise when I have the opportunity. Thanks.[/COLOR][/SIZE]

Excepting channel balance or noise (your digital control preamp is very likely better than most pots), but if your amp doesn't have issues there, it should be pretty much consistent; yes.