Crack Headphone Specs

[cspirou]

Could anyone tell me what the impedance for the Crackheadphone is? I tried finding it on the product page but it wasn't there.

[Grainger49]

You are right. 

The Crackheadphone is intended for use with the Crack OTL amp.  It isn't intended to sound good with other amps.  So in the intended use its impedance is a moot point.

Just saying....

[cspirou]

I know that it is a specially designed product for the crack amp. But i would at least like to know a few performance specs. Even though I would love to have a frequency response curve of this combo I don't really expect that. But I don't think knowing the resulting impedance is an unusual thing to ask for since it's a common spec. I am just wondering if the impedance on the headphones are increased substantially or if they basically remain the same but the interplay with the Crack is done in a way that greatly enhances the sound you would get otherwise?

[mcandmar]

The base headphone is ~40ohms however there is a resistor installed in series to raise the impedance.

[Grainger49]

As for impedance, I had 10 weeks on just impedance getting an EE degree.  It is not a simple thing.  The number, magnitude, changes with every frequency as does the angle, reactance:

http://bottlehead.com/smf/index.php?topic=3873.msg35184#msg35184

[cspirou]

As for impedance, I had 10 weeks on just impedance getting an EE degree.  It is not a simple thing.  The number, magnitude, changes with every frequency as does the angle, reactance:

http://bottlehead.com/smf/index.php?topic=3873.msg35184#msg35184

I do know that impedance for inductive elements,Like headphones and speakers, is frequency dependent. However the simple number the manufacturer gives is good for a rough idea for what I can expect; i.e. a pair rated for 300 ohms is much higher in impedance than a pair rated at 50 ohms. I am not looking for an impedance/frequency curve but just want to know what the corresponding rating would be for the Crackheadphone.

I am really just trying to educate myself on what is needed in a headphone if you know the output impedance as well as other factors. I might not have an EE degree but I do have a Ph.D in physics so none of this is really foreign to me. I read that an important factor for amps is the damping factor which is the ratio between the output impedance and input impedance. Which to me would indicate that a headphone amp like the Crack would preform poorly due to a very low damping factor. However this might not be as important if the amp is a transconductance(current driven) amp. My line of questioning is somewhat related to this amp.

http://www.firstwatt.com/f1.html

It has an output impedance of 80 ohms which is far higher than the typical speaker. But it is a CURRENT driven amp and so the output voltages aren't as important. I read that tube amps are more current driven as opposed to voltage driven. So even though OTL amps may have a high output impedance, it is not that much of a factor for distortion because they are more current driven. So I am curious if the crackheadphone/crack amp pairing is similar to the F1 amp or if the impedance is much higher which gives the combo a good damping factor.

[Paul Birkeland]

Yes, there is some resistance installed in the Crack Headphones to make them compatible with the Crack.  The actual resistor value used is extremely dependent on the model of headphones themselves, so we are totally open to discussing the specifics, but not necessarily able to pinpoint what will work for a certain pair of headphones.

-PB

[Doc B.]

I see it as a tradeoff. Adding the resistance increases the output impedance of the amp as the headphones see it. Which lowers the damping factor. And which isn't much of a problem with the Monoprice headphone.  I also look at the setup from the amp's point of view, and the amp is also seeing a higher load with a resistance in series with the headphone impedance. I seem to have a hard time convincing anyone around here that that makes a difference. But I only have a bachelor's in physics. And we plead guilty to not measuring response. Ask Tyll Hertsens about measuring headphone frequency response - it's very difficult to come up with a measurement that relates to anything. I suppose would could run an impedance curve of the system. I'll ask Peebs to do that when he has some time.

With the added acoustical damping in the cups and the better cable I think the bass actually comes out cleaner and more dynamic than the stock headphones running on a lower output impedance amp like a S.E.X. amp. Everyone seems hung up on that resistor and pays little attention to all of that acoustical treatment.

[cspirou]

Yes, there is some resistance installed in the Crack Headphones to make them compatible with the Crack.  The actual resistor value used is extremely dependent on the model of headphones themselves, so we are totally open to discussing the specifics, but not necessarily able to pinpoint what will work for a certain pair of headphones.

-PB

Thanks for the information. I wasn't really looking for something exact but just really wanted to know if the Crackheadphone has an impedance greater then the 120 ohm output impedance of the Crack amp. Since I keep reading that the Crack amp is for high impedance headphones, I would assume that the Crackheadphone must also satisfy this requirement.

With regards to low impedance headphones in general and the Crack amp, does simply adding enough resistance to surpass 120 ohm make it sound 'better'? Note that I am not asking if it sounds great or really implying that you can just mod any pair of headphones to instantly work with the Crack. But I am trying to determine if this is a necessary condition and that any acoustic treatment is useless until the impedance mismatch is satisfied.

[Paul Birkeland]

With regards to low impedance headphones in general and the Crack amp, does simply adding enough resistance to surpass 120 ohm make it sound 'better'?

Yeah, that's the real crux of the issue.  There is probably a resistance for a given set of headphones that will make it sound better out of a Crack (and a lot worse out of most other headphone amps), but there will be other resistances that make things sound much worse.

[Doc B.]

Thanks for the information. I wasn't really looking for something exact but just really wanted to know if the Crackheadphone has an impedance greater then the 120 ohm output impedance of the Crack amp. Since I keep reading that the Crack amp is for high impedance headphones, I would assume that the Crackheadphone must also satisfy this requirement.

With regards to low impedance headphones in general and the Crack amp, does simply adding enough resistance to surpass 120 ohm make it sound 'better'? Note that I am not asking if it sounds great or really implying that you can just mod any pair of headphones to instantly work with the Crack. But I am trying to determine if this is a necessary condition and that any acoustic treatment is useless until the impedance mismatch is satisfied.

My impression with the Crackheadphone was that the upper bass got a little fat with the resistance added, but that the damping of the cup resonance actually cleaned up the upper bass and lower midrange enough that the overall result was cleaner bass with a better sense of dynamics. The stock cable with the damped cups sounds cleaner with a low impedance amp than the umdamped cups, but the tonal balance doesn't sound as good. But open back cans, or cans with wooden cups or simply different plastic could be completely different sounding to begin with. So it's hard to predict what the outcome would be in taking the same approach on a different phone.