[sammed92]

Hello head-fi,
 
I own Sennhieser HD558, and I freaking love them. But I recently laid my eyes upon Frequency v/s Impedance curve of my headphones and they're quiet the way i did not expect. All other headphones in comparison (AT M50x, Grado SR60 and Sony MDR-XB700) have pretty much flat  Frequency v/s Impedance curve, where as HD 558 has a bell like curve peaking all the way up 
to ~270 Ohms at about 100hz.
 
I really don't understand this. Packaging of the headphone specifies 50 Ohm impedence but at some frequency it is reaching ~270 Ohms. Does this imply that i need a source good enough to drive ~300 ohm headphone to get best out of my HD558??
 

 

[mindbomb]

Specifically, it means you need low output impedance on your amp. Most phones and small amps already have this.

 

[sammed92]

  Specifically, it means you need low output impedance on your amp. Most phones and small amps already have this.

I know that 50 Ohms is quiet low but it's the spike i'm concerned about..

 

[Head Injury]

  I know that 50 Ohms is quiet low but it's the spike i'm concerned about..

It only matters when you take into account output impedance. You don't automatically need a "good" amp just because of impedance, this is a very misleading misconception. Impedance is only part of the equation.
 
The high impedance at ~100 Hz means the HD558 gets less power per volt at that frequency (in case you're curious, W = V^2 / R, R being impedance in ohms). This is true all the time, regardless of the amp. The driver sensitivity must already be tuned so that the high impedance frequencies have more volume at the same power, otherwise they'd be much quieter and this would be obvious on the frequency response graphs.
 
So the Sennheiser engineers have already balanced the sound to fit the impedance curve of their design. You don't have to worry about that. In fact, this is probably part of the reason Sennheiser publishes their sensitivity as dB/V instead of the more common dB/mW. Their high end open headphones all have a curve like this, and voltage is roughly the same regardless of impedance.
 
When you do have to worry is with an amp that has a high output impedance. This will divide the voltage between the amp and the headphone. The amp will deliver less voltage, especially at low impedances. So, ironically, with a high output impedance the high impedance frequencies will receive relatively more voltage and sound louder than the rest. This effect is mostly small, though, unless you're using balanced armature IEMs with complex crossovers. 10 dB output impedance is pretty common and might boost midbass volume slightly, but nothing major. Avoid anything higher than that, and lower is always better.

 

[sammed92]

That makes sense...Thanks a bunch!!!

 

[Lumos]

It means that HD558 driver is not accurately damped and you will hear some resonances.
see more here: http://www.innerfidelity.com/content/comparison-beyerdynamic-dt-880-32-ohm-dt-880-250-ohm-and-dt-880-600-ohm-headphones
 
http://www.innerfidelity.com/content/how-headphone-dynamic-drivers-work

 

[new reformation]

Are you sure that the impedance bumps are defects in Sennheiser design?  If you examine the complete line of premium high-impedance headphones (HD600,HD650,HD700, and HD800) they ALL contain a curved impedance signature that elevates mid-bass and the highest treble.  As different as the design characteristics are between these models, especially the ring-radiator driver of the HD800's, I am convinced that this is a purposeful design for use with higher output impedance amps.  If you look at the amp that Sennheiser made especially for the HD800, guess what you will find?  It has a relatively high output impedance compared to what those who think getting as close to 0 ohms as you can is the goal.  Additionally, amps that have high output impedance like the Bottlehead Crack are known for being incredible with Senn headphones. 
 
 
My main point is that I don't believe that this design is an engineering fault.

 

[mindbomb]

That output impedance isn't high relative to the impedance of those headphones. In this case, we are talking about a low impedance 558.

 

[Lumos]

  Are you sure that the impedance bumps are defects in Sennheiser design?  If you examine the complete line of premium high-impedance headphones (HD600,HD650,HD700, and HD800) they ALL contain a curved impedance signature that elevates mid-bass and the highest treble.  As different as the design characteristics are between these models, especially the ring-radiator driver of the HD800's, I am convinced that this is a purposeful design for use with higher output impedance amps.  If you look at the amp that Sennheiser made especially for the HD800, guess what you will find?  It has a relatively high output impedance compared to what those who think getting as close to 0 ohms as you can is the goal.  Additionally, amps that have high output impedance like the Bottlehead Crack are known for being incredible with Senn headphones. 
 
 
My main point is that I don't believe that this design is an engineering fault.

Yes absolutely sure, I have listened and owned all of them besides HD800 and I can tell you all of them have bass distortion problem. Including HD700. there are people who like this effect because it reminds old days and tube amps and there are some songs which are nice to listen with these. For the same reason I sold all Senns and keeping AKG Beyerdinamic audio-technica and etc.
visit innerfidelity links and check out phase response and non linear harmonic distortion all these senns.
 
cheers

 

[new reformation]

MANY factors must be accounted for in this discussion and this probably isn't the place for it. For example, what is the threshold of hearing distortion and what order is the distortion that is there?  A headphone like the HE500's has a fair bit of distortion, yet has been hailed as competitive with the true flagship headphones!  I have the HD650's and I really don't notice a bass distortion problem.  Something like the Bottlehead Crack has a output impedance over 100ohms so the damping factor is definitely impacting the sound.  I have indeed checked out innerfidelity extensively and find it interesting that Tyll wholeheartedly recommends the HD600/HD650 line with an OTL amp like the Crack or one of the Woo amps.  Now, I am not saying that he is right simply because he is a figurehead in the industry, but it is worth noting his impressions as an expert. I'm not going to argue that the Sennheiser line has the best bass in the world, but I really don't want someone to read your post and write off the brand as a whole because of some subjective, yet very emphatically stated opinions.
 
For the OP:  You could maybe try out an amp like the Fiio E9k that has little bit higher output impedance and see what it does for the sound.  Not saying you're going to like it, but it's worth a listen right?