[Tim D]

No actually I believe its just that 0-ohm jacks are just described to mean close to zero but not actually zero. And divide by zero is undefined. Its like how many 9's there are in the purity of copper before you really stop caring.

 

[Wodgy]

JefferyK has the formula right (Jan got it backwards).

The idea is precisely to have the ratio as high as possible. An infinite damping factor would be the ideal, but in the real world things don't work that way. No amplifier has an output impedance of exactly 0 ohms, but good amplifiers try to get as close as possible. For example, Bryston amplifiers typically have an output impedance less than 0.02 ohms, giving them a damping factor greater than 500 with conventional (8 ohm) speakers. Recent NAD amps claim to have a damping factor of 200 (but for what it's worth Stereophile's latest review of the C370 measures this closer to 50, still pretty good).

The higher the damping factor (or the lower the output impedance), the less influence the transducer's varying impedance has on the sound. Usually this translates audibly into tighter bass. Because Grados don't have a huge amount of very low bass, you don't really hear the bass differences as much, but try the 55 ohm AKG K240S or K271 with a high impedance jack and the effects are pretty striking. Low bass (e.g. organ music) does get noticeably boomier.

Because transducer impedance typically varies most dramatically at both ends of the frequency spectrum, you'll usually also hear changes in how the highs sound as you increase the output impedance of an amplifier.

In the 1950s, speakers were actually designed to sound best at a particular damping factor, and until the early 1960s many amp manufacturers included terminals where you could hook up a wire-wound resistor to customize the output impedance of the amp. Nowadays, however, transducers are almost always designed independently of amplifiers and a high damping factor is considered ideal.

The Grado RA-1 has an output impedance close to 0 ohms, so I suspect that Grados were designed in the conventional way (i.e. for as low an output impedance as possible). That doesn't mean that some people won't prefer the smoother sound of a higher output jack, but you're not hearing the Grados exactly as they were designed to sound. That's fine; you should trust your ears, not the science!

 

[JefferyK]

Quote:

Originally posted by Wodgy JefferyK has the formula right (Jan got it backwards). The idea is precisely to have the ratio as high as possible. An infinite damping factor would be the ideal, but in the real world things don't work that way. No amplifier has an output impedance of exactly 0 ohms, but good amplifiers try to get as close as possible. For example, Bryston amplifiers typically have an output impedance less than 0.02 ohms, giving them a damping factor greater than 500 with conventional (8 ohm) speakers. Recent NAD amps claim to have a damping factor of 200 (but for what it's worth Stereophile's latest review of the C370 measures this closer to 50, still pretty good). The higher the damping factor (or the lower the output impedance), the less influence the transducer's varying impedance has on the sound. Usually this translates audibly into tighter bass. Because Grados don't have a huge amount of very low bass, you don't really hear the bass differences as much, but try the 55 ohm AKG K240S or K271 with a high impedance jack and the effects are pretty striking. Low bass (e.g. organ music) does get noticeably boomier. Because transducer impedance typically varies most dramatically at both ends of the frequency spectrum, you'll usually also hear changes in how the highs sound as you increase the output impedance of an amplifier. In the 1950s, speakers were actually designed to sound best at a particular damping factor, and until the early 1960s many amp manufacturers included terminals where you could hook up a wire-wound resistor to customize the output impedance of the amp. Nowadays, however, transducers are almost always designed independently of amplifiers and a high damping factor is considered ideal. The Grado RA-1 has an output impedance close to 0 ohms, so I suspect that Grados were designed in the conventional way (i.e. for as low an output impedance as possible). That doesn't mean that some people won't prefer the smoother sound of a higher output jack, but you're not hearing the Grados exactly as they were designed to sound. That's fine; you should trust your ears, not the science!

Makes me wonder what I'm missing: I plug my Sennheiser HD-580s (300 ohms) into my NAD C320BEE headphone jack (220 ohms). And they sound fantastic, markedly clearer than my Grado SR-80s with no audible distortion at either end.

Jeffery

 

[Wodgy]

As long as the damping factor is greater than 1 (it is in your case with the Senns), you're not missing all that much, especially with headphones. The Grados do have a noticeably different sound out of the C320BEE than out of a lower impedance amp though (I've owned the SR-125, HD600, and the C320BEE in the past).

 

[JefferyK]

I agree: When I went from a 120 ohm jack to a 220 ohm jack, my SR-80s got pretty boomy.

Jeffery

 

[Steve999]

Thanks, now that's making a lot more sense to me, I really appreciate it.

Quote:

Originally posted by Wodgy JefferyK has the formula right (Jan got it backwards)... The idea is precisely to have the ratio as high as possible. An infinite damping factor would be the ideal, but in the real world things don't work that way. No amplifier has an output impedance of exactly 0 ohms, but good amplifiers try to get as close as possible.... The higher the damping factor (or the lower the output impedance), the less influence the transducer's varying impedance has on the sound... Because transducer impedance typically varies most dramatically at both ends of the frequency spectrum, you'll usually also hear changes in how the highs sound as you increase the output impedance of an amplifier.... That doesn't mean that some people won't prefer the smoother sound of a higher output jack...That's fine; you should trust your ears, not the science!

 

[wallijonn]

the confusion may be because there are actually two output impedances from an amp - the static output impedance and the output source impedance. they are not the same thing.

an amp with a zero output source impedance can still have a 120 ohm output impedance. this is because you are dealing with AC signals (sound) rather than DC signals. it's like saying that a zero source impedance amp is made to drive 8 ohm speakers. put a 2 ohm speaker on it and the transistors will fry because they cannot handle a near short and still deliver current and voltage.

on my Crown D60 amp, the output impedance is 15 milliohms in series with 3 microhenries. it cannot drive a 1 ohm speaker. it has .01 ohms Zo from DC to 200 Hz, .02 at 1 KHz, .16 at 10 KHz, and .3 at 20 KHz.

As far as damping factor, it is 800 from DC to 100 Hz. But the nominal output phase angle shifts from 0 degrees at 20 Hz to 80 degrees at 10 KHz.

huh? well, bass seems to radiate from everywhere. if it is just heard as coming from in front of you, the triangles would seem to come from the right (90 degrees). since the bass seems to come from everywhere, if you could phase shift it so that it comes from the left, then the triangle would seem to come from in front of you. this is a over simplification. phase shifting, as seen on an oscuilloscope would be on the z-axis, and therefore represents 3D spacial information. or what some can think of as soundstage depth and / or height (depending on the frequency).

now as far as damping factor - some say that it doesn't really matter with headphones, others seem to think that it does. it will all depend on what part of the sound spectrum is being listened to, and the resonance frequency of the driver. damping factor is applied across the whole spectrum, whereas point of resonance is strictly at one point (the AKG K501 being an exception).

if you are to "look" at an amp, you must take into consideration nominal phase response along with phase shift due to capacitance , resistance and inductance (reactance). one of the most important things to look at is the slew rate. the higher the slew rate the better because signals will tend not to blurr or mush. there will be no "over-ringing".

headphones are reactive devices, they contain coils which have inductance (millihenries) and resistance (milliohms), and as such the inductance interacting with the the capacitance of the cable will cause all sorts of phase shifts in an amp. beyond a certain range the amp will go from being capacitance driven to being inductance driven (or is it the other way around?). the point at where the shft is made may be discernable enough to make you think that the sound becomes recessed. or you just may perceive it as a collapsed soundstage. as it is, the higher the frequency, the less the channel separation which the amp can produce. which is why separate channels with separate power supplies are best. of course you'd have to work your way all the way back to the source, and I do not know of any CD or DVD player with twin beams working at the same frequency reading the same bit at the same time. it would be like playing two mono CDs at the same time (time sync) so that the sound is pristine. for all intents and purposes it cannot be done. but it can be engineered real close.

if you take a look at your typical opamp, you should see at least two resistors on it's output, with one possibily being used for feedback. these two resistances will "interfere" / "interact" with the output resistance seen (headphones).

as far as the headphone impedance being higher than the amp output impedance, this is so that there is not a "motor" generated. it's like the output impedance of your DVD player being 600 ohms, but the input impedance of the pre-amp or amp (next stage) being 5,000, 10,000 or 25,000 or 100,000 ohms. typically it sound be 10x. the next input stage is "loading" the previous stage. if it were otherwise the current flow would be from the amp to the dvd (or from the headphone to the amp). the amp would therefore burn up the dvd.

there is a "nominal" headphone output impedance, typically measured at 1 KHz. Other manufacturers will list what it is the lowest at at any frequency. they are just two different measurement standards.

i believe that most headphone amps just put a resistor in series with the output. as such it is increasing the resistance seen by the headphones (making them sound less bright), but they are also shifting the phase (even if it is so slight). Just "so slight" may be enough to shift a peak or a dip out of a certain range (make it less harsh). It all depends on where that dip or peak occurs. if it is a peak in the upper midrange, it could shift it out of the vocal range. if it is in the bass region it could become more or less boomy.

now, most replacement cables actually LOWER the capacitance. this lowering will also produce a phase shift. it should sound a little cleaner, with the bass a little tighter. this is because the overall reactance is reduced, and with it a phase shift occurs later or further up the sound spectrum. the "seen" signal is cleaner, there is less over-shoot because the amp is not fighting stored energy (capitance / capacitor effect). and just as there is capacitance from one channel to ground, there is also capacitance between the capacitances (or from one signal wire to another signal wire).

the reason why Grados sound the way they do is because they are basically electrosets or pizo tweeters. they are (I believe) built differently than regular coils over core bobbins. i think that they did a great engineering job.

so, it is not because of output impedance that a great amp sounds great - it is because of a high slew rate, the inherent sonic quality of the transistors / tubes / op amps, and because of the nominal phase shifting.

you have to try every amp with every headphone with every source and find one that is pleasing to you.

other than tubes, most of today's amps have less than 1 ohm nominal (source) output impedance. what decides if they sound good is the resistor network on the outputs. rather than just adding a 120 ohm resistor on the output resistor network, they should be reconfigured so that their interaction presents a different output impednace while still keeping the feedback within tolerance and the output voltage within acceptable levels.

just adding a resistor will cut down on brightness, and therefore the overall sound quality is "shifted" downward whereby it may sound boomy. the opposite is also true - put a low impedance headphone on a high output impedance and the sound could get really muddy or bright (no bass).

I'm sorry if this all sounds confusing. there are much better explanations in the amp section. just do a search for "impedance," "reactance," "resistance," or "inductance".

it's all in the engineering. different tubes, transistors and opamps sound different because they are made differently. in the case of tubes, it is the grid area and the gas content. in the case of opamps and transistors it is the gate and substrate materials. the purer the material, the more likely it will sound better.

 

[Steve999]

So, running a Senn HD580, a 300 ohm headphone, out of a traditional, industry-standard 120 ohm headphone jack, meets the traditional objective of a damping factor of greater than one, yes? And it's likely to present smoother highs than you'd get with a near-zero ohm amp? I think perhaps my 120 ohm meyer jack is taking down the mid and upper treble and therefore making the low treble (the HD580 weak point) sound relatively more prominent and balanced.

Am I too far off base? I'm learning as I'm going and trying to match up what I hear with what I'm learning in this thread.

Regardless of whether Jan was wrong in his analysis (edit: and if he was, it appears this was due to language issues), I feel the important thing is that he's done us Meyer-amp owners a major favor in supplying us with an industry-standard 120 ohm jack.

Quote:

Originally posted by Wodgy As long as the damping factor is greater than 1 (it is in your case with the Senns), you're not missing all that much, especially with headphones. The Grados do have a noticeably different sound out of the C320BEE than out of a lower impedance amp though (I've owned the SR-125, HD600, and the C320BEE in the past).

 

[Wodgy]

Jan wasn't wrong, he just got the ratio backwards, but I think it was more of a language issue (his native language is German). He gets it right on his web page that discusses this:
http://home.t-online.de/home/meier-audio/tipstricks.htm

If you visit his page, he has a graph showing how the HD600/580 frequency response changes with two different jack impedances. Notice that the lower impedance frequency response is more flat, whereas the higher impedance frequency response is rolled off in the highs. It's interesting to compare these graphs versus the 0-ohm measurements on the Headroom site (their frequency response graphs are taken with the Headroom Max, a 0-ohm impedance amp).

 

[Steve999]

Thanks! I've followed your suggestions.

Interesting, Jan was comparing a 150 ohm output amp to a 470 ohm output! The latter would violate the 1:1 ratio, and with the 150 ohm output amp it looked pretty flat, and this easily meets the 1:1 ratio objective (320/150); one can only presume that at the 120 ohm output it would be slightly flatter still. The 470 ohm out / HD580 curve looks unpleasant indeed, the bass looks exaggerated and the highs look quite rolled off. By contrast, at 0 ohms, by my ears, the mid and upper treble gets a little out of control (that is, exaggerated), and the Headroom graphs seem to bear this out. I feel this may cause the low treble dip to sound even more pronounced than it was intended to be. Now I think I am understanding things better.

Always willing to receive further corrections though.

Quote:

Originally posted by Wodgy Jan wasn't wrong, he just got the ratio backwards, but I think it was more of a language issue (his native language is German). He gets it right on his web page that discusses this: http://home.t-online.de/home/meier-audio/tipstricks.htm If you visit his page, he has a graph showing how the HD600/580 frequency response changes with two different jack impedances. Notice that the lower impedance frequency response is more flat, whereas the higher impedance frequency response is rolled off in the highs. It's interesting to compare these graphs versus the 0-ohm measurements on the Headroom site (their frequency response graphs are taken with the Headroom Max, a 0-ohm impedance amp).

 

[wallijonn]

Damping factor is determined by the guage of the wire the source resistance and the load resistance.

forgetting about the wire size, adding a 120 ohm resistor will increase the load resistance to 420 ohms. Your damping factor should then go up. up to a certain frequency. damping factor is usually "used" for the bass - to gain control of the voice coil so that it isn't slow nor fast - just right (no over travel nor under travel).

if you had a source resistance of 1 and a load impedance of 8, you'd get a damping factor of 8. if your source impedance is .1 and your load resistance is 8, you'd get a damping factor of 80. if your source resistance is 0.01, then you'd get a damping factor of 800 for 8 ohms.

now, let's say that your source resistance is 0.01 and your load resistance is 300, that's 300/0.01 = 30,000. add 120 ohms, and that would make it 420 ohms / 0.01 = 42,000. but that damping factor is usually good until about 200 Hertz. and it would only be good up to a certain length of a certain thickness of wire. the thicker the wire, the further you can go out. I think most headphones wires are about 22 guage. which means that they have to be up to a certain length before they start "losing" bass and therefore sounding "brighter".

Quote:

Originally posted by Steve999 I think perhaps my 120 ohm meyer jack is taking down the mid and upper treble and therefore making the low treble (the HD580 weak point) sound relatively more prominent and balanced.

That's right. I call it negative logic. You are taking away from the upper highs, which creates a tonal shift, making the lower highs sound "greater" IN RESPECT to what was. Basically you now have a slightly darker headphone. But what is now "bought out more" is what you are interested in hearing better.

So if you have overly bright sources, or bright music, and want to hear more bass or midrange, then adding the resisance AND turning up the volume will give you a different overal tonal quality which is more pleasing to you AT THAT VOLUME LEVEL.

But it has nothing to do with damping factor.

 

[wallijonn]

and to answer your question, to me, the HD600 sounds worse from a 120 ohm jack because I feel that the highs are muted already (even though it has a certain high frequency peak). overall the highs, to me, are not even.

but what do I know? i like the DT831, DT931 and the K501. My K501s now have better highs and lows after I swapped the cables. And the DT931 is less bright since I added (2) 100 ohm resistors. I feel that, to me, the DT831 has a slight recessed midrange. Of course it could just be soundstage.

 

[Steve999]

Yes, thanks walli, that's what I'm hearing, I'm smoothing out the treble by using a source output of 120 ohms and thus attenuating the mid and upper treble, which I feel to be sharp at 0 ohms on the HD580s ... Jan's graphs verify clearly that with the HD580s the changes that occur in the high frequencies really accellerate in the mid and upper treble, as opposed to the low treble, which changes more slowly as the sources impedence rises. So the smoothing effect is very real and is significant enough to be audible to most anyone. As I understand it now from what I have read in this thread, this is due to the changing impedence characteristics of the HD580s in the upper frequencies, and how they intereact with the source impedence. An explanation beyond that is probably more than I could understand.

Interesting, Jan states explicitly that high frequencies change more rapidly with varations in source impedence than do low frequencies.....that's defintely what I'm hearing.

I am also surmising that once you get below a 1/1 ratio of headphone impedence to source impedence (see Jan's 300/470 graph for the HD580s), the bass increases and treble decreases at a much more rapid rate; this seems to be why a ratio of at least 1:1 is recommended.

I appreciate your impressions, wallijohn. I can see how some might opt for the elevated mid and upper treble on the HD580s at 0 ohms to give them some energy, and I agree, no matter what, it's a stretch to call the treble of the HD580s "even." I suppose I'm just making it a little less uneven by driving them at 120 ohms.

Quote:

Originally posted by wallijonn That's right. I call it negative logic. You are taking away from the upper highs, which creates a tonal shift, making the lower highs sound "greater" IN RESPECT to what was. Basically you now have a slightly darker headphone. But what is now "bought out more" is what you are interested in hearing better. So if you have overly bright sources, or bright music, and want to hear more bass or midrange, then adding the resisance AND turning up the volume will give you a different overal tonal quality which is more pleasing to you AT THAT VOLUME LEVEL.

 

[jona]

Quote:
And the DT931 is less bright since I added (2) 100 ohm resistors. I feel that, to me, the DT831 has a slight recessed midrange. Of course it could just be soundstage.
________

wallijohn-

By chance, did you add the 2-100 Ohm resistors in a reversible fashion (i.e. so that you could remove them easily if you did not like the sound)? It seems from this discussion that we might be able to customize source impedance for each can, although it may not be worth the effort. I would love to experiment with these different resistance levels but I don't want to risk my cans (or amp).

Jon

 

[Steve999]

I'm looking at the specs on my equipment, learning as I go. I notice the headphone outputs on my modern receivers and components are 32 ohms, not 120 ohms, so maybe 32 ohms is the new de facto industry standard for a headphone output jack (rather than the traditional 120 ohm standard), and is a pretty good match for most modern headphones (as most modern headphones have an impedence greater than 32 ohms but less than 120 ohms)?

I also notice line outputs tend to measure 1 kilo-ohm or greater... this would seem to mean that running headphones straight from a line out (as opposed to running them from the headphone output jack) will result in an impedence mismatch, audibly reducing the treble and emphasizing the bass, true?

Thanks for all the feedback.