Tyll Hertsens

Got the electrical shit working on my CB360 rebuild. (Hmm..can I embed videos here?)

In the mean time, congrats Naaman. And this ... you have no idea. Enjoy!

Hey, you be careful with your partying and whatnot, ya hear?

Boy, that's pretty cool. It's the republican version of Andy Worhal's 15 minutes of fame you know.

Decided to get my own personal membership in the EAS and their library. $234! Ran a search for "Headphones" in their papers, returned 1828 hits. Two out of three are pretty relevant to my interests. I'll have crapper reading for the next 6 years!

The problem there is that you'd have to do research related. I think what's needed is headphone stuff for the hobby. Differences between grado pads, changes in amp output imp, j$ pads, etc. Amp measurements, too. Generous guy, I doubt many are as generous. (Though I 've donated here personally.) Sorry, getting off topic here. Back in my box.

Indeed. But how to finance it? Would you pay a membership? How much?

Our policy is the we don't ever distribute the actual data from our measurements, but I do feel the same desire to see some more meaningful information extracted from our data and available on the web. It'll just take time.

Yupper. That article I pointed to makes that point. It is more complicated though, because it's really the phase angle (amount that voltage leads or lags current) that makes the headphone a difficult load to drive. Simple sine wave sweeps is one thing, but instantaneous changes in random signals relative to the current nature of the signal can set up very complex relationships that deliver a whole different set of problems. It's why a lot of analysis is done with impulse responses, MLS sequences, and transient measurements. It is friggen complicated; I don't really know shit about it, but I read quite a bit lately. The funny thing is you'll still get camps of differing opinion publishing AES papers. Who the fuck knows WTF to believe sometimes. From what I've been reading today, the first hump (around 100Hz) is the mechanical resonance of the driver --- the pendulum effect, so to speak, of the diaphragm. It's mildly inductive before the peak, at the peak it's purely resistive, and then is capacitive after the peak. Tradition says that the characteristic impedance of the cans is the floor after the first peak, so the T1 indeed shows 600 Ohms. Then gently rising slope starting at 1 kHz is the ever increasing electrical inductance of the voice coil itself. My guess is the little glitch you see around 8kHz has to do with acoustic frequency shaping. I'm coming to the conclusion that you want a low response between 1-2kHz to keep things from sounding harsh, and then you want a bump somewhere between 5-8kHz to bring out air and imaging. But that's kind of a guess on my part; none the less the glitch is either an acoustic tweak, or some kind of mechanical resonance in the headphone.

Yeah, I've asked about that before; I can't make it hit the priority list high enough though. C'est la vie.

Nah, I'm just being my normal, old school, objective self; placebo effect be damned, the humming bean is an exquisite sensor, we may not really know what's in our head and what's not, but we hear stuff. Gotta get some files from another computer ..... .... here you go: http://putts.smugmug.com/HeadRoom/On-Line-Content/t1-impedance/805803381_RNtX3-O.jpg[ATTACH=CONFIG]2785[/ATTACH]

FWIW this was a pretty okay article about headphones and impedance.

No need, you're right, it doesn't matter much with a high impedance driver. The hub bub about matching the 120 Ohm thing isn't important, and it's especially not important when you just over power the problem with a good amp. The current drive thing is really cool though ... been reading some AES papers.

That's the coolest part of your damn good post. Current amplifiers have been around for a long time. I've often wondered why they aren't used in audio, and I'm not surprised the great Nelson Pass has played around with them. They were used in the scanning coil amplifiers when I used to work on scanning electron microscopes because they make nice linear sweeps because the electron deflection was directly related to the magnetic field stength which was directly related to the magnetic coil current. The problem is that a speaker is not quite like that because the inertia of the whole floppy mess is much more reactive then a nice lightweight electron beam. I'd have to look into it, but I would guess that the load reactance on a current drive amp would create the need for much higher voltage swings on the amp which makes it impractical except in tweaky applications.

Gotta agree that it's getting better, but I'd still bet people plug T1s and HD 800s more into pre-amp headphone jacks than dedicated headphone amps. Maybe I'm wrong; I'd love to see the numbers. In any case, if more people are using dedicated amps the argument is all the stronger for low-Z amps. I'll admit to being close to the edge of my knowledge here, so I'm not really sure, but I think they're two different things and lower output impedance will always drive the cans more accurately. I'll try to do some research on that.

Lemme try again: Designers make sure the headphone have enough damping to work reasonably well with 120 Ohm output impedance. If the headphones happen to be driven by an amp with a lower output impedance you will get better fidelity because the driver movement will more closely match the output signal of the amp. If you put a Porche engine in a VW it will perform better even though the bug was designed for the smaller engine. A) Again, if the manufacturers don't tell you what the specified output impedance is there's no way to test at the designed spec. 2] Assuming we're talking about the goal of fidelity reproduction, all else being equal, the lower the output impedance the more fidelity it will have. I'll reiterate, they use 120 Ohms because they know they'll be plugged into crap amps, not because they can make it sound better with 120 Ohm impedance in.

Since the damping is significantly acoustic or voice coil resistance related, you can't very easily make an undamped headphone with a damping adaptor. In other words you can put 120 Ohms in series with the amp output if you want, but the only thing it's really doing is making the amp worse. I tend to doubt the 'amp market' is big enough to have much effect. It's more about making the headphones sound good on crappy headphone jacks that still make up the majority of applications. Though, I will admit, it's getting bigger and better all the time.

Think of the headphone like a spring. Push it and let go and ... BOING ... it resonates. Not good for sound quality. There are two ways to approach driving the spring: Put a shock absorber or some other resistive element in the spring to stop it from vibrating when you drive it. This would be like manufacturers building in acoustic damping features. Or drive it with an amp so strong that it doen't even feel the 'boing' of the spring; it just drive the spring with authority. This is like the amp with a low output impedance. Now, if MFRs make headphone like in case 1., and you hook up a very low impedance amp, the amp just drives through the acoustic damping and remains authoritative. But it would have done a marginally better job of making good sound if all the acoustic damping got out of the way. But if MFRs build headphones for low impedance amps that don't have any damping, and then you hooked it up to a 120 Ohm output impedance amp, the spring would be spronging away to beat the band ... literally. Despite what the hobbysts may think, most people still have never even heard of a headphone amp, and will be plugging into the nearest headphone jack in blissful ignorance of the fact that it's likely an op-amp with a little series resistance for protection. So, for the most part, they just have to build headphones with internal damping. NOTE: the 120 Ohm spec comes from a simple guess at what a typical headphone jack might be. There's not other technical reason that 120 Ohms is some good or special number useful to headphone performance. The answer here is complex; suffice it to say OTL amps are valued by the particular character (coloration) they create, and there is a lot of interaction between amp and speaker in this case. Not knocking it at all, but they are not technically designed to be neutral power amps. A power amp --- literally by definition --- changes a high impedance line voltage signal into a low impedance power signal. It certainly provides voltage gain (although not much in the case of headphones), but mostly a power amp provides power gain, and that, in large measure, is indicated by a dramatic lowering of line impedance. Bottom line, all else being equal, you can almost always improve headphone performance by lowering output impedance (increasing damping factor).

The problem is we're talking about a headphone that aspires to be in the "World's Best" category. One would think that the typical amp in that intended usage is a very high quality one --- which means it should have a low output impedance. That's true. A headphone designed for use on a low output impedance/high damping factor amp could rely on the amp to do the damping. Headphones that are designed for 120 Ohms have to provide their own essentially passive acoustical damping. That means you are going to get various phase artifacts as the acoustic damping poles and zeros fight with the various resonances in order to get best performance without the help of a low output impedance amp. If the cans were designed with the idea of a low output impedance amp which will provide the damping, headphone designers wouldn't have to play a bunch of acoustic games to damp the driver which essentially introduces reactive impedance schmutz. But! Here's the worst part, IMHO, no manufacturer I've found EVER represents the specified output impedance in thier specs, so you really don't have any idea what amp impedance the cans are designed for. For example here's the beyer T1 specs: Technical Specifications Transducer typeDynamic Operating principlesemi-open ConnectorGold vaporized stereo jack plug 6.35 mm Weight without cable350 g Frequency response5 - 50,000 Hz Nominal impedance acc. to IEC 60268-7600Ω Nominal SPL acc. to IEC 60268-7102 dB Nominal THD acc. to IEC 60268-7< 0.05% Power handling capacity acc. to IEC 60268-7300 mW Sound coupling to the earCircumaural Average pressure on ear acc. to IEC 60268-72.8 N Cable length3 m / double-sided balanced cable (6-core) They go to great lengths to tell us that they are using the IEC spec, but they don't tell us what impedance is being used. So, if you want better headphones in the future, we ought to be complaining about manufacturers limiting the performance of their product by designing around 120 Ohms, and encouraging them to go ahead and build 0 Ohm headphones.

That's exactly the kind of thing I'd like to fill my life with for the next 20 years. Deadly serious.

FWIW the old IEC headphone measurement spec required using a 120 Ohm output impedance amp. The spec is now changed and says that manufacturers can specify a particular output impedance at which to measure the cans. Beyer was a proponant of the 120 Ohm spec and I wouldn't be surprised if they are still designing their headphones around it. Personally I think it's stupid for high-end cans to be designed with a 120 Ohm output in mind.

tkam's join date was 2-21 Blow out the candles and let's open a bottle.

Sigh. Oh well ... I will work for this hobby again one day.

Oh great, you wish a guy happy birthday and he shows you all the good grog he got to drink. Oh well, happy birthday anyway Stephan.