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Headphone Measurements: Part One, Prolog. - Page 2

post #16 of 40
12/5/07 at 7:58pm
Quote:
Originally Posted by thrice View Post
So while the FR indicate that they ought to sound almost the same, wouldn't the impedance graph suggest otherwise and add to the story.
I don't understand. If higher impedance means that it takes more power to produce that frequency, then the higher impedance of the 650's below 200 Hz would mean less bass output from the 650's at those frequencies as compared to the 600's, wouldn't it? (all other things being equal).
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post #17 of 40
12/5/07 at 8:00pm

What's "Phase Angle"?

Can someone please explain "phase angle" to me, and can someone also explain how phase angle relates to whether or not a headphone or speaker is "hard to drive"?
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post #18 of 40
12/5/07 at 9:01pm
Thread Starter 
Quote:
Originally Posted by pbarach View Post
Can someone please explain "phase angle" to me, and can someone also explain how phase angle relates to whether or not a headphone or speaker is "hard to drive"?
Oh my! In 16 pages or less? But you bring up a very good point, and it might be possible to make some measurements of that as well. The best resource that's easy to get your hands on is a recent article in the July 2007 issue of Stereophile by Kieth Howard.

Once we're past the basics in thread two, please bring this subject up again. It is a bit of a difficult set of concepts to grasp.
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post #19 of 40
12/5/07 at 9:59pm
Quote:
Originally Posted by Tyll Hertsens View Post
Oh my! In 16 pages or less? But you bring up a very good point, and it might be possible to make some measurements of that as well. The best resource that's easy to get your hands on is a recent article in the July 2007 issue of Stereophile by Kieth Howard.

Once we're past the basics in thread two, please bring this subject up again. It is a bit of a difficult set of concepts to grasp.
Tyll: I found the article you had in mind (and it's also on the Stereophile website at Stereophile: Heavy Load: How Loudspeakers Torture Amplifiers). However, the article uses the term "phase angle" without defining it. I recall reading the article last summer and saying, "Huh??" For example, this bit: "Fig.4 makes the point that impedance phase angle is a critical factor when assessing, from the amplifier's point of view, how severe a load a loudspeaker is. But even if modulus vs frequency and phase vs frequency graphs are both plotted, we still don't get a clear picture of this, because what matters is the interplay of modulus and phase angle."
Clearly written, but I think you have to know what he's talking about before you can understand what he's saying, and nobody is letting me into the club.
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post #20 of 40
12/6/07 at 1:29pm
Thread Starter 
Let me try to make a very simple (read vitually useless) analogy.

A speaker has resonances. Let's say a speaker has only one resonant freq. And now lets imagine that speaker is a swing with a kid on it, and the natural resonance is the periodicity of the swing as it goes back and forth. The amp is the dad pushing the kid on the swing.

Now imagine you're pushing the kid. When the kid comes towards you and reaches to top of the arch, you start to push. You are actually pushing slightly ahead of the natural swinging motion. Your pushes are slightly ahead in phase relative to the phase of the natural swinging motion of the kid. In this case the amp is happy as a clam because it's staying ahead of the kid and has something nice and solid to push against.

Now imagine that you've pushed the kid very high and that (magically, because a swing won't do this) the frequency/periodicity of the swing increases, so the kid is swinging higher and faster. You, the dad, have the same strength and power as before, and the kid weight the same. But now, you have to push faster, and it's very hard to get a lot of energy into the kid because he's going by so fast. And, at some point, you won't be able to keep up and you'll push with all yur might, but the kid will be by you and you be pushing thin air .... and you'll fall flat on your face.

So, when an amp drives a speaker with a complex signal, there are sometimes moments when the amp is "pushing thin air", in other words, it looks, momentarily, to the amp like it's driving a dead short. Or worse, like less than a dead short.

Imagine our kid on a swing again, going like crazy. And that you're having to push this very fast moving swing, and your hands are tied to it. Try to push it when it's going fast and it will just suck you along. Well, an amp is soidly connected to the speaker, and when the speaker is getting ahead of the amp momentarily in phase angle, the amp is not only dumping current as hard as it can but current is getting sucked out of amp. Amp not likey.
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post #21 of 40
12/6/07 at 6:19pm
Quote:
Originally Posted by thrice View Post
No they sound different to me. I hear deeper and more quantity of bass with the HD650 and while the graph may not represent the difference as dramatically, it's there.
Variations in perceived bass level have a lot to do with the quality of the acoustic seal between the headphones' pads and the contours of the wearer's face. It is one of the reasons why it is difficult to correlate measurements made on a dummy head with one's own experience. This is something that we will need to examine in more detail in Part 3.
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post #22 of 40
12/6/07 at 6:57pm
Quote:
Originally Posted by Tyll Hertsens View Post
Let me try to make a very simple (read vitually useless) analogy.....Amp not likey.
Thanks for this explanation! It's a very clear image and I understand what this situation would do to an amp. What I don't understand is how phase angle is measured and how it relates to impedance measurements, but you might not want to get into that much depth at this point. I will, however, stay tuned...
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post #23 of 40
12/6/07 at 8:53pm
This may help. Have a look at section 2.1 on Phase Angle Vs. Transistor Dissipation
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post #24 of 40
12/6/07 at 9:19pm
I made a chart up that got lost in the big outage where I showed several headphones and comparing their impedance curves. I still have it on my hard drive though. Some had curves that had very little change while others (HD650 and G1K) had changes greater than 50%. This has to suggest that some headphones are harder to drive than others. Amps with very stiff power supplies would respond much better to the difficult loads I would think such as the SP amps. Other amps power supplies that are not as stiff would be able to handle the easier loads without the over head of the stiffer power supply I would think.

Is there any way to qualify this?
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post #25 of 40
12/7/07 at 12:31am
Quote:
Originally Posted by 4Tw0 View Post
This may help. Have a look at section 2.1 on Phase Angle Vs. Transistor Dissipation
Yes, it helped quite a lot. And there are lots of other interesting, well-written articles on that site, too. Thanks!
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post #26 of 40
12/7/07 at 2:38am
lots of background on dynamic driver measurement/distortion at Klippel's site

Klippel GmbH - Home Page

getting a headphone designer to comment on generalities common to dynamic headphones and what differs from Klippel's loudspeaker info would be nice
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post #27 of 40
12/7/07 at 10:19am
Thread Starter 
Quote:
Originally Posted by jcx View Post
getting a headphone designer to comment on generalities common to dynamic headphones and what differs from Klippel's loudspeaker info would be nice
Hey now! There's an idea. Most times the real experts at Sennheiser, AKG, Shure, etc, are too busy to participate in open forum, but I might just be able to get a few to monitor this thread over time and make pointed and clarifying comments. I'll work on it.

I do have permission to quote up to 2000 words from Jens Blauert's "Spacial Hearing" I can't reproduct any illustrations, though, so any of you who are very interested might want to get the book before we get to part three.
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post #28 of 40
12/7/07 at 2:10pm
I'm not sure where this fits in with the whole thread quintology, but I think listing what test equipment you're using to measure the FR, etc., and why you're using those particular pieces of gear would be helpful and good for education's sake. What I'd imagine that means is explaining what make and model of the microphone you're using, the make and model of the imitation head, what's driving the headphones, how each gear affects the overall measurement, so on and so forth. Much like every scientific experiment I've done since grade 9 (I'm in second year Electrical Engineering, so no more Science labs for me! Woohoo!), every featured review in the forums, Stereophile, wherever, the read needs to know what the test equipment is, as everyone's HD650 will measure differently because of the different setups. The discrepancy between HD650, HD600 experiences for thrice and Tyll could be explained by difference in gear. All in all, that is a long-winded way of saying, "Please (and thank you), list your gear."
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post #29 of 40
12/7/07 at 3:34pm
Thread Starter 
Quote:
Originally Posted by joneeboi View Post
I'm not sure where this fits in with the whole thread quintology, but I think listing what test equipment you're using to measure the FR, etc., and why you're using those particular pieces of gear would be helpful and good for education's sake.
Yeah, great idea. I'll try to remember---actually I think it will come up naturally---to hit that in section three. If I space it, remind me.

edit -- and this kind of chatter is just perfect for this thread; please keep your questions coming.
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post #30 of 40
12/8/07 at 6:01pm
Quote:
Originally Posted by Tyll Hertsens View Post
Just to get things started, I'll post some clicks to download some XL spreadsheets that have all the measurement data the we collected on our first pass at looking what might be done. We've picke three traditional cans, and three IEMs to look at: AKG K701, Senn HD650, Beyer DT880 (new), Ety ER4S, Shure SE310, Shure SE530.

OK folks, the floor is yours. What do you want to learn? What is the relevance of measurements to you? What measurements might be relevant for a wide base of users? Stray related comments?
Could it be possible to get data measurements for other headphones? I am especially interested in the beyer dt990 2005 version. Thanks!
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