[Tim D]

After getting the JMT amp and comparing and listening between different phones and jacks, I realize how it reminded me a lot of a Dekert article on speed:
http://www.decware.com/paper15.htm

I don't know a lot about impedance...but it seems that in good amp design a "good" amp is typically low impedance output so that its damping factor is greater, and in essence it comes off as having more "speed" or control.

Anyhow I wanted to see how the DT931's worked with the JMT amp and it did pretty well compared to other entry level low-impedance output amps I've tried, but honestly the DT931's are almost unlistenable with low impedance output "speedy" amps! Also whereas it used to be more subtle in noticing impedance related changes between different jacks, it is extremely apparent to me now after listening to the DT931's for awhile and I can now notice these differences in different headphones and jacks much easier as well.

Anyhow the DT931's I would describe as phones that definitely need a slow down, and one of the few phones I've heard that are like this. Through the JMT amp the DT931's seem too fast for its own good and without a doubt it sounds much better through my higher impedance output Audiosource Amp jack. My MS-1 on the otherhand seems supercharged through the JMT amp and absolutely love the greater speed and control of the JMT amp being muddy through the Audiosource jack. With Ety's it is up to preference and the music of wheter you want more speed/control or a slow down, I haven't honestly spent enough listening time but I think I prefer it with the JMT amp. Interestingly enough I never even noticed impedance changes with most other phones until the Beyers showed me just how much a difference it could make.

I think MOST headphones benefit from low impedance jacks and more speed/control. Most receiver/amp jacks are high impedance outputs. I want to pick up a better pair of Grado's after hearing how much the JMT amp just supercharges Grado's. It isn't necessarily correct to say that Grado's don't need dedicated headphone amps to sound good...at the very least you want low impedance jacks which rules out every receiver jack(Same goes for Senns even more IMO). DT931 on the otherhand is a headphone that might actually sound better out of a receiver jack than a high performance dedicated amp!

In fact I would describe the speed and control of the DT931 on the Audiosource to be on the level of the Grado's on the JMT amp. The DT931 being waay too fast on the JMT, and Grado's sluggish on the Audiosource.

Anyhow I now look at a lot of audio purchases with "speed" and impedance type relations in mind. Cables can be looked at in the same manner in altering "speed" perhaps through impedance as well i.e. silver cables probably have lower resistance giving a brighter more controlled and transparent sound, wheras the opposite being warmer, etc. I also wonder if there could be any DIY amps with completely adjustable impedance.

But like the Dekert article emphasizes, it is important to strike a balance in all components, and picking and choosing between audio components just isn't as easy as getting all "speedy" high performance this and that or you'll just crash and burn IMO.

We even know that Ety's have a very strong relation with impedance, but overall it still seems to be a mystery. It just seems like there is a little more to impedance, and maybe with enough knowledge we can make more informed choices in creating a more synergetic setup instead of one that is more "guesswork" to get the perfect speed/control we want.

 

[mbriant]

An "auto impedance matching circuit" would be a great headphone amp feature. One amp capable of perfect synergy with any headphone.

Like auto bias on a high end cassette deck.

 

[thomas]

I agree with you that different headphones need different output impedences... Grado's, with their low impedence, really need an amp with a low output impedece to get a decent damping factor. However, for high-Z cans like Sennheisers, I think a 120ohm output impedece would be better.

The frequency response varies depending on the impedence, and headphones are supposed to be designed to be used with amps with 120ohm output impedence. For Senns, even 120 ohms will give a decent damping factor, and have the right frequency response....

I disagree with many of the points on the site you posted...

According to the author, everything has to be matched based on speed... I think matching based on accuract/euphony is much more imporant.

input and output impedences obvioulsy must be matched, but i don't see any problem with using fast equipment throughout the signal path. Fast equipment should be more accurate, and it will give better accuracy and transparency than slow equipment. As for CD players, generally, all cd players are "fast", so they should work well with fast equipment. The reason that cheep Cd players sound bad is it has lots of distortion, not because it is "slow"... Good componants in the signal path reveal all of the distortion because they are accurate and neutral, not because they are "fast"... To fix the problem, i would use tube equipment to colour the sound and cover up the distortion, rather than trying to "slow down the cd player"....

I also disagree with his comments on spending 4X more on sources than speakers, and that the transport is more important than the DAC...

 

[joelongwood]

Quote:

I want to pick up a better pair of Grado's after hearing how much the JMT amp just supercharges Grado's.

Tim, thanks for the info. Now I understand a little better why I really love the JMT built amp. The music just seems to come alive with my Grados.....from the SR-100 to the HP-1, they all sound fantastic. The MG Head, Creek, and TA just kinda sit there.

 

[Joe Bloggs]

Sorry for waking up a dead thread, but I don't understand joelongwood's rationale here. The Creek and TA have low output impedances too don't they?

Or do they have 120ohm output?

(been searching for 'impedance matching' and came up with this)

 

[joelongwood]

Quote:

Originally posted by Joe Bloggs Sorry for waking up a dead thread, but I don't understand joelongwood's rationale here. The Creek and TA have low output impedances too don't they? Or do they have 120ohm output? (been searching for 'impedance matching' and came up with this)

Wow, this was awhile ago. Unfortunately, I don't understand my rationale either. I just know, to my ears, Grados sound much better with CHA47 amps than with the three amps mentioned above. Why? From a technical standpoint, I have no idea. Sorry.

 

[Joe Bloggs]

Hmm, just because the Creek was designed for driving low impedance phones (saw this while searching through google?) doesn't mean it has to be very good at it. Maybe the JMT is so good it beats the Creek even on its home turf.

(wow*(&^^??)

Tim's different reactions when pairing the Beyer DT931 and Senns with high and low-impedance amps offers some support for my current hypothesis on impedance matching:

There are 2 factors, (1)the method of damping used and (2)the phones' impedance.

1. The damping method determines the optimal ratio between the headphone amp output impedance, say o, and the headphone's impedance, say z. So call it the optimum o:z ratio.

Phones that use mechanical damping can take higher o:z ratios (ie. higher output impedance relative to phones' impedance) because they depend less on the amp for damping. (Do Beyers use mechanical damping? I'll assume yes if the opposite is not advertised, since this seems to be the more common form of damping)

Phones that use electromechanical damping (Sennheisers are advertised to use this) basically have little damping built into the drivers themselves and must have a low o:z ratio with the amp to be damped properly.

2. The phones' impedance is the z in the optimum o:z ratio, and thus transforms the ratio into hard numbers for o, the optimum output impedance of the amp.

You can put phones into 4 categories based on the combinations of these 2 factors...

a) Low optimum o:z ratio, low z--phones that depend on electromechanical damping *and* themselves having a low impedance? Sounds like a nightmare scenario... *must* use amps with 0 ohm output impedance...

b) High optimum o:z ratio, low z--this, I suppose, is the better option for low impedance phones. Since you can depend on almost nothing but 0 ohm outputs for proper electromechanical damping for low z phones, these phones would probably have to take damping into their own hands and use mechanical damping, thus increasing their tolerance for amps with non-zero output impedance. But since there seems to be no low-impedance phones that can tolerate a really high impedance output, it would seem that this tolerance only goes so far...

c) Low optimum o:z ratio, high z--presumably the category that Senn headphones are in. Their use of electromechanical damping means a low optimum o:z ratio, and thus they should not tolerate high output impedances much better than category (b) headphones. The confirmation for this prediction is only partial: more than one person thinks that the Senn 580/600 are ***** with the EMP, but Kelly (and others) seem to think that it is terrific with the RKV. Question is: just how much is the output impedance of the RKV??

d) High optimum o:z ratio, high z--if the Beyer DT931 uses electromechanical damping, it would belong to this category. The high o:z ratio and high z would translate into a high optimum output impedance for the amp used. I.e. if o is too low the phone may actually be overdamped, or 'too fast for its own good', as Tim put it.

What do you think, fellow Head-Fiers? Is anyone actually reading this at all?

 

[Duncan]

Wow Joe!!

This is heavy stuff... ZERO ohm headphone outs... now, excuse my naivety, but if the minimum figure for headphone impedance is 16 ohms, and speakers can go down to TWO ohms... does that mean that this headphone amp can drive speakers better than headphones?

 

[Joe Bloggs]

I don't understand what you're saying...

Impedance matching does not simply mean choosing to have the _same_ impedance for the amp output and the headphone / speaker impedance...

Exactly *what* it means is what I'm trying to discuss here--getting a good estimate for the optimum o:z ratio *range* for different phones and speakers would take us a long way to finding the answer.

Say if the optimum o:z ratio for a certain class of phones is 0, then 0 ohm outputs would be ideal for them, regardless of the headphones' own impedance...

OTOH if another class of phones / speakers has an optimum o:z ratio close to 1, then for these phones you *would* want to 'match impedance' on the most (seemingly) naive interpretation of having o = z, i.e. 16 ohm outputs for 16 ohm headphones, 2 ohm outputs for 2 ohm drivers...

Do you get my point now?

*Now* go back and read my last post and see if you understand what I'm talking about with the damping method affecting optimum o:z ratio, etc.

Joe

 

[Joe Bloggs]

This comparison between the DT990, DT831, DT931 and HD600 that I dredged up from the depths of HeadWize is another case where the DT931 was found to sound better with a 120ohm headphone out (on the Corda) than a 0 ohm output.

http://headwize.powerpill.org/ubb/sh...ance¦matching¦

Well, *something* is definitely going on here--the DT931 has slightly lower impedance than the HD600 (200-something ohms vs 300) but the DT931 was better paired to the 120ohm output whereas the 600 sounds better on the 0 ohm output by general consensus.

Based on this limited data, it would seem that the 600 has an optimum o:z ratio of 0 whilst the optimum o:z ratio for the DT931 is something closer to 0.5...

Whether this is because of the mechanical / electromechanical damping issue or just because the DT931 was tuned for the frequency response of a 120ohm output is another matter...

Ahh... confounding factors... always a barrier to straightforward scientific investigation

 

[Audio-Me]

Does anyone else think all this is nonsense?

 

[Joe Bloggs]

Quote:

Does anyone else think all this is nonsense?

How is that so, A&M?

I direct your attention to the part in bold. I don't really want to quote this again, but it illustrates my point so well--

Quote:

We discussed the high impedance value of the HD600 and I was told that Sennheiser prefers a high impedance for their premium models because these sound better. There are two methods to dampen/control the movements of the driver membranes. First you can use mechanical damping (by the air behind the membrane and by the suspension) and secondly you can use electromechanical damping (dissipation of the electrical energy that is generated by the coil if it moves freely in the magnetic field). Sennheiser prefers electromechanical damping as this one stays linear at higher sound pressures. However, for proper electromechanical damping the ratio of the output impedance of the headphone jack and the impedance of the driver should be as small as possible. Therefore driver impedance is rather high and therefore the HD600 sounds best at an output impedance near zero Ohm (Note that the international standard for headphone jacks gives 120 Ohm!).

So
using electromechanical damping -> 'the ratio of the output impedance of the headphone jack and the impedance of the driver should be as small as possible' -> 'the o:z ratio (see my definition) should be as small as possible (i.e. ideal = 0!)'

One would suppose that this does not apply if the phone in question does not use electromechanical damping--which means that the o:z ratio does *not* need to be as small as possible. Now, let's assume that for any phone there exists an optimal o:z ratio. Either this ratio is determined by random, arbitrary factors, or there is a way to determine at least a range for this ratio using available facts about the headphone. All I'm doing here is proposing a hypothesis for predicting the range of optimal o:z ratio and hence the range optimal output impedance for different headphones!

 

[Audio-Me]

So which "freak scientist" told you that little story? Or did you make it up? Have you actually heard what difference this technical mumbo jumbo has on the sound? I'll believe my ears, not a bunch of words or numbers thank you very much.

 

[Tim D]

Damnit stop keeping this old thread on life support!

Btw, I have since found that you can have plenty of speed, transient control, and detail without it corresponding to brightness or analytical sound anyways.

As for impedance outputs, yah it makes a difference IMO, but nothing I can easily sum up in a mathmatical formula after hearing different phones with different impedance outputs, etc. And the differences are definitely more subtle than any overt EQing I'm sure. Btw the only difference between 4S and 4P is output resistors, which is essentially the output impedance and damping criteria again. It just boils down to what works...no one can really say that either Beyers or Ety's sound uncontrolled even though they like higher output impedance. In fact the ER4S is supposedly more accurate because of its higher impedance. Anyways let this thread die...thanks.

 

[gaineso]

According to what I got from Jam Meier's post about his visit to Sennheiser, The HD600's are designed to use the lowest possible output impedance to improve the damping factor.

Maybe I didn't read it right. Maybe the good Dr. Meier will give us a little more information.