Sennheiser "impedance" marketing question

To get a good damping factor, you want the headphone impedance to be at least 8 times the amplifier output impedance. If it isn't, various problems occur, most often around the bass frequencies. Starting with 300 gives you better odds of achieving the correct damping factor than 50. (I used the word "odds", because many amplifier manufactures and reviewers don't provide this value.)

It's called a "nominal" impedance because that measurement is only taken at one point in the frequency spectrum. Just like a loudspeaker will have a nominal impedance of 8 ohm but will vary in relation to frequency. Usually manufacturers release the impedance measurement at 1kHz.

I'm going to say not necessarily.
Some headphones have a flat impedance in which case it would just be "impedance"

The difference is only technical and doesn't neceseraly affect sound quality because you cannot generalize. I will put it simple and understandable. I am not the most experienced person here (or most knowledgeable) but I can give you a good idea.

 

1. You definitely cannot say that low impedance headphones do a poor job at reproducing bass. Denon D7000 (32 ohms) for starters would disprove your point... and not to even mention planar magnetics with impedance from 38 to 50 ohms that have the best bass reproduction out of all headphones on the market. They are also some of the best headphones available. A lot of people would even argue that planar magnetic (or orthodynamic headphones, their synonym since they require insane amounts of power) headphones are the best headphones out there. 

 

2. The reason why (in your case) the HD598 and HD800 have different impedance is because they are meant for totally different things.. and it isn;t a "marketing trick". The HD598 which is an entry level headphone has a 50 ohm impedance mostly because of what it was meant to be used for.. like played from a laptop, a small music player (not portable), some basic studio use... etc (very much like the AKG K242 HD, 55 ohms). On the other hand the HD800 has a nominal impedance of 300 ohms because it is intended for high end audiophile listening from a variety of amplifiers and it also allowes to be used in studio.

3. Generally speaking studio cans and those intended for professional monitoring use have a higher impedance. The reason for this is basically because they put a smaller load on studio gear. They do require high voltage swings, but lesser current which is what studio gear has. 

 

4. What determines how easy a headphone is to drive..? Two factors basically: Impedance (ohms) and Sensitivity (dB/V). In some general terms (despite being slightly more complicated), a low impedance headphone has higher sensitivity and therefore it requires more current to be driven. This is done well by standard solid state amps.

 

A high impedance can is generally very dependant on large amounts of voltage. For voltage hungry cans, OTL amplifiers (tube amps) are perfect because they can swing insane amounts of voltage. 

 

There is also the type of headphone that has both low impedance and low sensitivity and needs very powerful amps to drive it. This is called an orthodynamic headphone and it has a different driver than a standard dynamic headphone. Some require up to several Watts of power.

 

5. Impedance vs Nominal Impedance:

 

 

As you can see here, 4 different headphones with differnent impedence vs frequency. You can notice, the Sennheiser HD700 has a rather strange looking curve. For this reason, it is stated that it has a "nominal impedance" of 150 ohms because it has the value of approx 150 at 1000 hz.

 

The other headphones have relatively straight lines therefore they are simply called impedance.

 

6 and final!  To answer your question directly: YES, there is a difference between the "low" and "high" impedance cans. However, it has nothing to do with quality, but more with the optimal way of driving it. A quality of a headphone is determined by other factors... such as the driver (transducer - magnet - diaphragm), the materials used and the way it affects resonance, the frequency response, etc..

 

Hope this helps

This isn't a spec you should/could compare - if there was a 300 ohm version of the HD 598 or a 50 ohm version of the HD 800 though, you could make such comparisons. But there are many other technical differences between these two - impedance here is not in any way a ranking of anything.


This is incorrect. Ignoring that damping factor is purely a machination of marketing and does not in anyway relate to performance, the higher Z spec on many cans is just the result of their specific driver's features. It doesn't really correlate to performance. Now in the case of many Sennheiser, Beyerdynamic, and so on headphones that are highly reactive - depending on the output Z and so on - you can get a shifted FR. If the impedance is fairly stable, this is less of a problem.


Impedance is frequency dependent - it's complex resistance. It cannot exist as a single point - a true impedance spec will be a graphic showing a range of frequencies with Z plotted along it. Nominal Z is meant to be a nominal representation of Z in order to make specs easier to read.


No, they would just be fairly stable or non-reactive.


+1.

The Denon headphones are 25 ohms, but yes, that is such an example. Orthodynamic is Yamaha's marketing term for planar magnetics. But yes, 100% agree that Z does not correlate to bass quality.

Not really. It's simply a specific of the driver - there are plenty of very high end audiophile headphones that have low Z (DX1000, D7000/D7100, RS1, GSK, PSK, ATH-W series, etc). Years ago there was (there still is, actually) an IEC specification that said amplifiers should target a 120Ohm Zout, as this will drive most all headphones properly (which is true), but that's very hard for portable players to accomplish. So very low Zout is not uncommon. A lot of headphones have accordingly moved towards the more sensitive and low Z side to match up with iPods fairly well - examples include the Beats Pro, T5p, and D7100. There isn't really any advantage for Z differences except when we're talking about portables with limited Vrms outputs (which is due to their batteries). For mains powered devices, it really doesn't matter - your receiver can drive anything from an A.00 to a T1 with relative ease.

Not true. They are usually older in design and higher Z was common - for a few reasons including noise rejection, targetting the 120Ohm spec, and simply part of the design characteristic. Power requirement is dictated by Ohm's Law and sensitivity values. Most studio equipment can provide enough power to destroy any headphones - high voltage or high current, doesn't matter. Again, it has mains power behind it.

Sensitivity and impedance are NOT inter-related in this manner. Low Z does not always correlate to high sensitivity. However impedance specifications can obfuscate sensitivity ratings (as can stating them in dB/V - dB/mW is more appropriate imho). The generalizations about solid state/tube are also inaccurate.

Also inaccurate. And "large" is very relative.

Not a single headphone in current production requires multiple watts of power. By a longshot.

Impedance is complex resistance in an AC system - nominal is the only way to represent it without a 2D graphic.
http://en.wikipedia.org/wiki/Electrical_impedance
http://en.wikipedia.org/wiki/Nominal_impedance

No.

I'd agree with this, but I'd say the "optimal way of driving it" thing is based more on various wives tales and myths than anything founded - tube vs SS doesn't really define that ability, it's just that many cheap OTL amps have poor current delivery and high Zsource and are therefore unstable with those loads (just like most cheap receivers can't handle 4 ohm speakers). With an OTC design, or a quality OTL, such considerations are generally irrelevant.

 

3. I was not exactly sure about this one. Thanks.

 

4. Again, I was not exactly sure if they are inter-related but that is not what I meant anyway. I meant to say that most of the headphones you gonna find have similar properties and all of the headphones that I have come across are either very dependant on voltage, or they are leaning on the current side.

 

I am not sure if you have come across Audeze or Hifiman. Planar magnetic headphones that needs huge amounts of power to be driven to their full potential (and to achieve a good tonal balance). For instance HE-6 can handle up to 8 watts because of its impedance 50 ohms and sensitivity of 83 dBs. My Lyr that can pump up to 6 watts/channel at 32 ohms struggles to power it!! 

 

5. Regarding impedances, I was simply trying to explain why the term nominal impedance was used sometimes... 

 

6. OTL vs SS.... I am aware that there are a lot of non-funded statements around head-fi, most of it defining the entire forum. However, I am not even that experienced to be able to judge this for myself, so I trusted other people on the forum when I made this statement. I guess ill have to figure it out for myself.

 

Thanks for the corrections, they were certainly welcome. I don't want to direct someone wrongly here.. its what has happened to me personally. I was merely conveying opinions of a lot of established head-fiers.

 

Most of the things I said however, have and do make sense, in either empirical or rational form...

This is more of a "wives tale" or "rule of thumb" though - all speakers need both (okay technically we can argue that an ESP uses "currentless drive" but there is actually some current (albeit VERY VERY little) going across them). It's dictated by Ohm's Law - so if you have two identical systems and all you change is Z, you will change how much voltage/current the system wants to "see" for equivalent output as a ratio. But the notion of a "voltage drive" or "current drive" headphone is un-true and an inaccurate over-simplification (again, outside of the realm of ESPs, which in a lot of ways you can (lazily) treat as voltage sink).

The HE-6 do not take up to 8W because of the Z spec or sensitivity - ribbons have generally higher power handling because there is no Xmax concern with the driver. Only thermal limits, which can be very high (they're high for dynamic drivers too - if you could load a few watts onto a Denon or Grado headphone without moving the cone, they'd probably survive quite a lot of input as well). The HE-6 needs around 20 mW to reach 90 dB (which is more than loud enough) - the Lyr can absolutely take your ears off powering that headphone, assuming the manufacturer's claimed power values are accurate (and there is no reason to believe they are, because all amp manufacturers lie). The whole notion of "driven to full potential" is a lot of fluff as well - quantify it and we'll talk. There's also the other side of the equation, where you have things like the LCD-2 that are very easily driven, and actually use less power than some Grados. So planar magnetic as a technology isn't really this big bad beastie, it's just HiFiMan's specific driver designs (and sensitivity doesn't really correlate to sound quality either, so it's not to disparage them).

The terms are used interchangably because marketing types and customers don't know what they're talking about. You should never see a spec stated as "impedance is 4 ohms" - NEVER. It cannot be. It's like saying I'm driving a car and it's doing 6 miles. It's a measureless value. Impedance ALWAYS has to be referenced to a frequency unless you're stating nominal, and nominal always should be identified as such. It's just bad practice when manufacturers/writers deviate from this. There's a Rane Note that covers this and a lot more, that you can see here: http://www.rane.com/note145.html

If you want to talk about a static resistance, in a DC system, you just say resistance. They're inter-related but different concepts. There is no "static impedance."

The big argument around OTL amplifiers is similar to claims about Damping Factor - in an empirical setting with no background in math or electronics the claims would make sense at face value. But if you dig a little deeper there's more explanation. Basically if you take an inexpensive OTL amp, Zsource will be something like 20-30 ohms (I think Schiit specs their OTL at like 35 ohms Zsource or thereabouts, too lazy to dig it up) which means that the amplifier is very poorly suited to drive something with a lower impedance than it's internal/output Z (so if you took like an A.00, which has a nominal impedance of 5 ohms), and it may even damage the amplifier (Bellari, for example, states on their OTL that no load shall be less than 16 ohms at any point or your warranty is void and the amplifier will likely be damaged - the load just wants too much current or does not provide enough resistance or otherwise puts the amplifier into an unstable place). With a very well designed OTL, that can deliver a lot of current has sufficiently low output Z, it becomes less of an issue. The other (or correct) way to deal with this, is with a transformer. This is how speaker amps do it. The problem is that cheap transformers will limit output bandwidth, power handling, etc, and good transformers are expensive as you want to increase current handling. An example of a good OTC amplifier in action is the Woo WA6 - it's basically load invariant from 8R-600R. A lot of SS amps can't even do that, and it's all because the amp section "sees" a constant loading from the transformer, and the transformer couples to whatever load you like.

With solid-state devices, current and voltage delivery are generally not an issue either way as long as you have good hardware. I have an amp on my desk that's entirely solid-state and will throw 2300Vrms all day - it's designed for driving ESP headphones. There's also plenty of integrated designs from TI, Maxim, National, etc that will do a few watts into 32R or 64R and have no issues with that, and can run down to 16R or 8R stable. Every modern amplifier on the market is solid-state, and there are plenty of designs from Accuphase, QSC, Parasound, etc that can nearly drive into a crossbar (which is RIDICULOUS) but just as readily drive into a line transformer (that's a few kiloohms) and maintain their composure. Quality really comes into play here, and unfortunately a lot of "dedicated headphone amplifiers" just lack that.

But if you didn't have any of that background, I can absolutely see where the claim would make sense - if you plug your RS-1 into a cheap OTL it will hum or buzz or maybe even blow up in your face, but the HD 600 will work just fine and there's no issue. But into a less-than-stellar solid-state device, like say the cheapo line-driver opamp on your Game Theater XP, the HD 600 will have rolled off bass and otherwise not behave themselves, but the RS-1 are going to work just fine. Damping Factor becomes inter-related here because of the same observation - but it's equally irrelevant as a "spec" (because it doesn't actually relate to anything tangible), and just seems to confuse the heck out of people (I "get" why it was created originally, but it doesn't seem to serve its intended goal).

 

LOL.

@obobskivich
You're right that a bad damping factor is less of a problem for some headphones. But 1) it's still a problem and 2) the question was about open high-end Sennheisers, which have wild phase/impedance graphs, making the amp impedance a big deal.

Here's the thing - there is no "bad damping factor" - it will always end up being some really small number once you actually do the math honestly and plot it. That's just math in action. The overall "DF" is going to be impossible to give you as a static value (because as I've said above - impedance is not static) - it will move along a 2D plot and once you factor the resistance of the cables and the voicecoil(s) into it, you always end up with a very small value (it's usually less than 10 in all cases). Damping factor has absolutely nothing to do with "control of the driver" (electrical damping is a pipedream unless you have an active servo in there - do you have an active servo in there?) - it's just a very bad way of trying to make Zsource into something consumers can latch onto and go "rah rah feel good" about - like megapixel ratings on cameras, or PMPO power values for speakers.

No. It isn't. Even if it actually panned out to something real or tangible (which it doesn't), the absolute only thing you could argue is that relatively high Zsource with a reactive load will result in a changed system FR. Which it does. With the HD 600 it means you gain a slight bump to the bottom-end centering around their ~100hz resonance spike and that only assumes the amplifier doesn't handle its business properly.

Damping factor is ENTIRELY a construction of modern marketing run amuck, and the gross inability of such marketing to properly explain or quantize Zout and its relevance because for probably 90% of the amplifiers out there, the values are so low that it does nothing to include it in specs. But when you can throw huge numbers on the board, people like that.

Now we're talking about phase? Which is completely unrelated, mind you, so what did you want to know? And do you mean acoustic phase or electrical phase? And where are you going with this one? (It should be interesting at least!)

The HD 580/600/650 are relatively reactive, but all it means is that with an amplifier with high-ish Zout will see some minor changes to the FR (it's usually less than a few dB which is more or less inconsequential).


No, it really isn't a "big deal" - it's a minor consideration that ultimately comes down to personal preference because there is never going to be an amplifier that gets to the "absolute HD 600 sound" unless Sennheiser has a Zout target in mind (which I have yet to see them out and out declare) - with Zout at 0 (which is impossible) and DF of inf you will hear one thing, and with Zout at inf (which is impossible) and DF of 0 you will hear another thing. Simple as that.

I also have an issue with the recent chart-warrior approach that insists we need Zsource at 0 ohms - for stable loads it really does not matter unless the amplifier is unstable driving into Znom that is lower than Zsource (which means OTL amps), and for reactive loads it becomes a purely preferential question (sadly only one headphone related manufacturer is honest enough to disclose this, but in the world of speakers and speaker amps, this is pretty well established).
Edited by obobskivich - 8/22/12 at 1:34am