A very high damping factor=Overdamping headphones?
Oct 19, 2017 at 3:23 PM Post #31 of 239
From your calculations the 650 is already critically damped? I think I just like a mellow, bass heavy sound then. Seems less obtrusive and more relaxing on mediocre recordings to me with some series R. I stop noticing the headphones and relax. How did you extract the lumped elements from the impedance curve?

I just use a high NFB output buffer and switchable series R. I built my amp with 10-20-43-78-110-230 Ohms.
 
Oct 19, 2017 at 3:52 PM Post #32 of 239
I'm puzzled by your f0 for the HD650. The innerfidelity plots put both resonances at about 90 Hz. Both impedance plots are very similar, with the HD650 having very slightly better damping. Am I missing something?

Incidentally, there is a page about HF resonances in the electrical curves at https://diyaudioheaven.wordpress.com/tutorials/how-to-interpret-graphs/impedance/

The results are for a hypothetical headphone though!
 
Oct 19, 2017 at 8:41 PM Post #33 of 239
Mechanical damping reduces sensitivity. Especially in these days of "mobile audio" sensitivity is a selling point. That's why damping is done so much electrically. I wouldn't call it a cheap fix. On the mechanical side electric damping looks the same as mechanical, the diaphragm can't tell them apart.

There are not "resistors" inside headphones to dictate the impedance level. The electric resistance comes from the resistance of voice coil + the inverse of mechanical resitance on electric side. Larger mechanical resistance means smaller electric resistance and vice versa. Beyerdynamic has the 32 Ω version for portable devices which can't produce much voltage or power while the 600 Ω version is pure home audio to be driven form powerful amps. 600 Ω has much better electric damping, because even larger output impedance is small compared to the impedance of the phones and therefor the damping ratio remains large enough.

How about a headphone with changeable impedance? At home the higher impedance is used and then you have lower level for portable devices. It could be done with double voicecoil. In low impedance mode the voice coils are in paraller and in high impedance mode in series. For example: 70 Ω voice coils. In paraller mode the impedance is 35 Ω and in series 140 Ω. What if the phones had two cables, longer for home use and shorter for outdoor use? Special connectors + different wiring would produce the impedance modes. What if the phones would change from open to close for outdoor use: Closed mode: 35 Ω, open mode 140 Ω ? The voice coils could be even different, one 34 Ω and the other 566 Ω to have 32 Ω and 600 Ω impedance modes. The challenge of course is to have great sound on both modes.

The diaphragm can't tell them apart if you are only looking at sensitivity. To that extent, mechanical and electrical damping can both function to reduce efficiency. Electrical resistance is cheaper to engineer, and requires little to no research to implement. Mechanical damping, on the other hand, is more cost intensive. But increasing electrical resistance won't reduce resonance or distortion in the mechanical parts, it only reduces the chance of incurring it. The DT880 is a good example. The 32ohm version has more distortion than the 600ohm version, but both pairs measure similarly, and have that 10khz peak. So even though Beyer increased the electrical resistance of one model over the other, it doesn't cover up all the mechanical flaws of the headphone. With the 600ohm model, however, you are less likely to experience those flaws just due to the massive resistance and less chance of FR shift. And, of course, as long as you have enough power to drive them, damping ratio is not a concern at 600ohm either, so it makes amp matching a breeze. Increasing electrical damping can be helpful, but it won't fix problems in the transducer/housing, only mask them, hence why I called it a band aid.

There are pictures floating around of opened DT880 ear cups with resistors inside. I'm pretty sure that is the only difference between models. Beyer should have made a headphone with variable resistance more multi purpose. Sounds like a good idea to me. I suppose interchangeable cables would be a good place to house the adapters.
 
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Oct 20, 2017 at 2:38 AM Post #34 of 239
71dB I think you are saying that the HD650 is underdamped at primary resonance mechanically, and is pretty much critically damped with zero amplifier output impedance, i.e. by means of voicecoil resistance alone. Therefore it cannot be moved into the overdamped regime by too low an amplifier output impedance (unless the impedance is negative!). This makes sense to me, but I'm not sure I agree with your lumped parameters if they give a Z0 of well under 100Hz. This is simply the LC resonant peak, isn't it?
 
Oct 20, 2017 at 2:40 AM Post #35 of 239
The 880 600 Ohm has a diode at the driver, not a resistor. Don't ask me why though. I do wonder why?

Beyer states that the high impedance cans have "lighter wire" and can theoretically react "faster".
Not sure how that works, because using lighter wire means one needs more?



 
Oct 20, 2017 at 7:05 AM Post #36 of 239
From your calculations the 650 is already critically damped?

Overdamped just a little little bit. The damping ratio without electric damping is 1.014 > 1. I didn't expect this since HD 600 is underdamped (0.634).

I think I just like a mellow, bass heavy sound then. Seems less obtrusive and more relaxing on mediocre recordings to me with some series R. I stop noticing the headphones and relax.

Ok. Do you use cross-feed?

How did you extract the lumped elements from the impedance curve?

Step 1: Got the impedance curve from headphone.com
Step 2: Collected the impedance values at 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 500, 1000, 2000, 5000, 10000 and 20000 Hz.
Step 3: In LibreOffice Calc ("Excel") I copied a calculation tab for HD 600 and replaced the impedance values.
Step 4: Iterated the component values so that the calculated impedance curve matches with the measured one.

calc tab.png

Sorry about some of it being in Finnish. This is just to calculate things, not intended to be published to the world. The orange curve is measured and black simulated. Iteration of component values is pretty fast. Rc is basically the minimum value of the curve, R+Rc = maximum value. Lc is easy to get so that the rise at the high frequencies is right. Fo is easy to get and finally L and C dictate the width of the impedance bump around Fo. C is calculated from L using Fo, so actually only L is iterated.

I just use a high NFB output buffer and switchable series R. I built my amp with 10-20-43-78-110-230 Ohms.

Ok. NFB = 10 Ω and then you have 0, 10, 33, 68, 100 and 220 Ω resistors selected with a 2 x 6 rotary switch.

I'm puzzled by your f0 for the HD650. The innerfidelity plots put both resonances at about 90 Hz. Both impedance plots are very similar, with the HD650 having very slightly better damping. Am I missing something?

Maybe the unit innerfidelity measured is very different from the one headphone.com measured? If you list me the impedance values at the frequency point of step 2 above, I can calculate the "alternative facts" for you :wink:

Incidentally, there is a page about HF resonances in the electrical curves at https://diyaudioheaven.wordpress.com/tutorials/how-to-interpret-graphs/impedance/

The results are for a hypothetical headphone though!

Yeah, the high frequency spikes are some high frequency resonances according to this. The membranes aren't perfect.
 
Oct 20, 2017 at 7:20 AM Post #37 of 239
71dB I think you are saying that the HD650 is underdamped at primary resonance mechanically, and is pretty much critically damped with zero amplifier output impedance, i.e. by means of voicecoil resistance alone. Therefore it cannot be moved into the overdamped regime by too low an amplifier output impedance (unless the impedance is negative!). This makes sense to me, but I'm not sure I agree with your lumped parameters if they give a Z0 of well under 100Hz. This is simply the LC resonant peak, isn't it?

No. Minimum damping ratio 1.014 and maximum 1.558. So, overdamped always. If headphone.com has faulty data then my data is faulty too, because my calculations are based on their data. Your disagreement is with them, not me. You can't demonstrate faults in my calculations from given data, can you? Yes, my 67 Hz is the resonance frequency of L and C (diaphragm suspension and mass)

600 and 650.png
 
Oct 20, 2017 at 7:38 AM Post #38 of 239
here is my hd650 with the peak value marked. this is with the headphone on my head.
osef53135135.jpg
in free air the impedance peaks closer to 100hz.
 
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Oct 20, 2017 at 7:40 AM Post #39 of 239
The 880 600 Ohm has a diode at the driver, not a resistor. Don't ask me why though. I do wonder why?

Actually 2 diodes. Voltage protection.

Beyer states that the high impedance cans have "lighter wire" and can theoretically react "faster".
Not sure how that works, because using lighter wire means one needs more?

Never believe when someone say something is "faster" in audio. They are selling stuff to people who know next to nothing.

Lighter (thinner) wire means higher impedance per length and more protection against power, hence the diodes.
 
Oct 20, 2017 at 7:44 AM Post #40 of 239
here is my hd650 with the peak value marked. this is with the headphone on my head.

in free air the impedance peaks closer to 100hz.

Very different from what's on headphone.com. Your HD 650 is close to HD 600.
 
Oct 20, 2017 at 8:06 AM Post #41 of 239
castleofargh's HD 650:

fo = 92 Hz
Rc = 310 Ω
Lc = 1.4 mH
L = 400 mH
R = 140 Ω
C = 7.5 µF

Minimum damping ratio 0.826. Critical damping with 355 Ω output impedance. Maximum damping ratio 1.199.

Not going to calculate these for EVERY unit in the world. It seems everyone is different.
 
Oct 20, 2017 at 8:52 AM Post #42 of 239
Actually 2 diodes. Voltage protection.



Never believe when someone say something is "faster" in audio. They are selling stuff to people who know next to nothing.

Lighter (thinner) wire means higher impedance per length and more protection against power, hence the diodes.

Interesting. Thank you for the information!

What I am not understanding is how a diode in parallel with the driver will protect? How does it work with AC? Do you have a link for me that is worth reading?

(edit: Wait - 2 diodes per driver?)
(edit: What fault must occur that the diodes "work"? )
 
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Oct 20, 2017 at 9:03 AM Post #43 of 239
71dB Thanks for the work put into iteration of parameters. I believe the Q and therefore damping is a function of the L, C and R of the parallel circuit. The LC alone would be totally undamped. The total series R (coil plus z out) is effectively an extra parallel resistance component in the LCR circuit that brings the overall damping up. The series L is ineffective at frequencies at or near primary resonance. Is you 355 Ohms with or without the coil R?, i.e. do we need 45 Ohms or 355 Ohms amplifier output R for critical damping?

Your second '650 model seems better and the initial plot you worked from questionable. I have no reason to doubt your results, I just wondered how you did it. I was going to send you my own 650s to measure and resolve into lumped parameters:smile_phones:

I would have thought that electromotive force on the voice coil was current-governed if the magnetic assembly stays the same. Therefore the acceleration of the coil assembly relative to the magnet would be greater for a given current with lighter wire if everything else stays the same. Lower moving mass. But then the resonant frequency would go up all other things being equal.

Zeners or avalanche protectors back to back is a good idea with thin wire phones or windings not that well secured to the former.
 
Oct 20, 2017 at 9:08 AM Post #44 of 239
ev1wt The diodes would be zeners or avalanche breakdown types connected across the winding. They are arranged conduct when the applied voltage (whether positive or negative) exceeds a certain amount beyond which the wires might burn out or the magnetic force on the voice coil become excessive leading to mechanical damage.
 
Oct 20, 2017 at 9:19 AM Post #45 of 239
ev1wt The diodes would be zeners or avalanche breakdown types connected across the winding. They are arranged to conduct when the applied voltage (whether positive or negative) exceeds a certain amount beyond which the wires might burn out or the magnetic force on the voice coil become excessive leading to mechanical damage.

Am googling for "implement transient voltage protection"? Is that the correct term?
 

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