[rhythmdevils]

Yeah, the internal damping foam.  I'll send you a pm...

 

[keanex]

Just received some Fostex T50RP and really am enjoying these. They sounded flat and boring out of the box, I've put about 10 hours of burn-in on them. I plan to review once I feel they're properly burned in.

 

[Armaegis]

My in-progress pictorial of the SFI/Sextett transplant: http://www.head-fi.org/t/569510/
credit to rhythmdevils for the name

 

[plin]

Quote:

Quote:

Originally Posted by GuyMe I've read this term "mechanical damping" thrown around usually to describe the YH1K, what does it mean? Like a car suspension made out of felt?

......
So now you see why I use the term mechanical damping. It's in contradistinction to electrodynamic damping, the kind you get with dynamic drivers and woofers. You increase electrodynamic damping by increasing magnet strength or decreasing the output impedance of the amp, neither of which affects isodynamic drivers.

 
 
I dig that post while searching this excellent thread about the effects of amplifier’s output impedance on orthos. I am trying to understand it, but frankly, I can't.
It seems to me, and please correct me if I am wrong here, that if there is a significant mechanical resonance in the ortho driver, then lowering amplifiers output resistance will help control the mechanical resonance. The effect is almost the same as controlling a floppy bass in dynamic drivers: the counter electromagnetic feedback (CEF - a current) generated by the moving of the conductor inside the magnetic flux is been shunt by the low output resistance of the amplifier. This is equivalent as placing a mechanical resistance to the movement of conductor.
But, and this is a great but, orthos have almost flat and entirely resistive impedance. If there were one strong mechanical resonance it should be apparent in the impedance curve, as it is on mechanical drivers, wouldn’t they?
At least in one ortho driver, the HiFiman HE-500, there is a strong apparent mechanical resonance arount 9KHz, as can be seen by Tyll Hertsen of InnerFidelity  measurements (both frequency and impulse response), with a peak of almost +10dB and Q around 5. But there is no corresponding alteration of impedance curve.

 
I am baffled, can someone please clarify to me what am I thinking wrong here? Any conductor movement inside a magnetic field should generate a CEF. This CEF should be apparent in impedance curve. Why there is none in HE-500’s case?
 
Thank you for your answers.  
 

 

[tyre]

Hmm. Not sure what to think about this one.
 
http://page11.auctions.yahoo.co.jp/jp/auction/n103344906
 

 

 
 

 

[Kabeer]

What about it? Its a T50v0
(and yes welcomeback!)
Quote:

Hmm. Not sure what to think about this one.
 
http://page11.auctions.yahoo.co.jp/jp/auction/n103344906
 

 

 
 

 

 

[dBel84]

Quote:

Hmm. Not sure what to think about this one.
 

Now there is a name I have not seen on HF for a while, welcome back
 
That amp looks equally intriguing  = voltage and current outputs ....
 
..dB
 

 

[tyre]

Thanks. Yeah, it's been a while. I just snagged a pair of Realistic Pro 30's on ebay, in addition to a used Stax system from a head-fier last week. It's a never-ending cycle...

Regarding the T50, I wasn't sure if it was expensive or cheap. The amp combo probably threw off the price though.

 

[4nradio]

If anyone's interested, I have a pair of Fostex T50rp drivers available for DIY use, along with a pair of JMoney version 3.0 pads (Denon type). Please check the For Sale: Cables, Speakers, Tweaks, etc. section for the two separate listings.
 
(Hope that's OK to mention here  :^)

 

[wualta]

Yes, welcome back! Hope you can hang around, since I seem to recall there were a few questions about, guess what, the T50v1 we wanted to ask you while you were gone..  ...though I believe a ninja tracked you down.
I know what to say about that T50v0 auction: worst auction photos ever. Tyre, they need your photo skills. I'm guessing you're going to hate the Pro 30s, but let us know how it goes with them when they arrive.
 
I honestly don't know how to explain the flat-impedance-means-resistive-means-unaffected-by-source-impedance-thing to plin [and welcome to you as well-- we surely don't have many Greeks] any better than I already have. If there's not enough flux density [I originally had "inductance" here, which is incorrect-- apologies!] to generate back EMF even when there's a big mechanical resonance, the amp's output has nothing to work on/against, bla bla bla. But I know plin isn't the only skeptic here, so does anyone have a better explanation? JazZ and setmenu nearly took over the thread in the first few posts discussing this, bringing in the example of the Magneplanar single-ended planar-magnetic loudspeaker. Anyone?
 
4nradio, since you asked: If it were my forum, I wouldn't mind an occasional offer to sell small quantities of stuff, as long as it was thread-appropriate stuff. But it's not up to me, and we've all seen forums where things like that get out of hand. Our moderator will have to make the final decision. But tell us, did you try to make a Thundertrouserslike headphone? what happened? UPDATE: He did, sort of. Not a TP-style transplant but a JVC one.

 

[Nevod]

Here: http://player.ru/showpost.php?p=787771&postcount=213 and here: http://player.ru/showpost.php?p=787855&postcount=216 are pics of modding Fostex T50RPs and their drivers. The forum is in Russian, so I'll write some main moments:
Headphones' backs are covered with thin leather and filled with synthepon. Earpads are lifted by 3mm.
Fronts of the drivers are milled out for more open area (seen on 1st pic).
Cavities between magnets and steel ridges on rear parts of drivers are filled with soft skin to reduce reflections. only two holes are left for tuning damping. Whole rear op the driver is damped by thick felt, except for one of the holes left uncovered - hole is punched in the felt. it is then covered by rigid plastic with a smaller hole. It can be further damped by scotch tape.
 
Aren't the Thunderpants using the same milled-out and de-reflected drivers? If not, perhaps that could be incorporated into them? 

 

[plin]

 
Quote:

I honestly don't know how to explain the flat-impedance-means-resistive-means-unaffected-by-source-impedance-thing to plin [and welcome to you as well-- we surely don't have many Greeks] any better than I already have. If there's not enough inductance to generate back EMF even when there's a big mechanical resonance, the amp's output has nothing to work on/against, bla bla bla. But I know plin isn't the only skeptic here, so does anyone have a better explanation? JazZ and setmenu nearly took over the thread in the first few posts discussing this, bringing in the example of the Magneplanar single-ended planar-magnetic loudspeaker. Anyone?

 
 
Thank you for your warm welcome.
 
As far as I understand it, there is no need for high inductance (there is no need for a high-number-of-turns coil). Even a straight conductor, when moved inside a magnetic field, does produce a current. And the process is quite reversible; say you play a 90dB 1KHz tone through a ortho driver. The amplifier produces a voltage that makes a current that passes through the driver and is then transformed to motion. If you, yourself, could produce with your own voice this 1KHz tone with a 90dB amplitude close to the ortho driver, then a similar voltage should be present, with no amplifier connected.
The above reversible sound/current transformation has been tested by me in a normal dynamic headphone (I haven’t got any orthos yet - but I am planning to 

 ) by plugging my headphone 1/8 plug to my laptops mic input. Speaking close to the headphones I could record my voice with impressive quality. The electromechanic transducer (i.e. the headphone driver) is reversible, it can transform an electric current to sound, but it can also transform a sound to an electric current, working as a microphone! You could  test it yourself if this is true to orthos also (I don’t see why not).
 
So if there is a motion in the driver other than the one strictly produced by the amplifier itself (like a resonance), this motion should produce a respective current that should be apparent as a significant change in impedance curve.

 

[Armaegis]

I'm curious about something from a design point of view: are the magnet holes (or in the case of the newer LCD2/Hifiman orthos, the arrangements of the grid) arranged in such a way to account/optimize for the accoustic diffraction pattern of the sound passing through them? or does the diffraction not matter at such a short distance for audio frequencies?

 

[wualta]

Quote:

 
...So if there is a motion in the driver other than the one strictly produced by the amplifier itself (like a resonance), this motion should produce a respective current that should be apparent as a significant change in impedance curve.

So, obviously, ortho headphones can't possibly behave the way they do. Yet, oblivious to theory, they nevertheless measurably.. ..do. The logical conclusion: the theory needs modification. I think the key word here is significant. 
 
But as I said, there are many on this thread who, like you, remain skeptical, and there are regular calls for stronger magnets to get more bass, etc. I invite those folks to provide an explanation that will satisfy plin.
 
 
Quote:

I'm curious about something from a design point of view: are the magnet holes (or in the case of the newer LCD2/Hifiman orthos, the arrangements of the grid) arranged in such a way to account/optimize for the accoustic diffraction pattern of the sound passing through them? or does the diffraction not matter at such a short distance for audio frequencies?

Sounds like a question for the Audeze boys, or those close enough to them to've overheard diffraction-chat. My opinion is that the bad effects of diffraction, ie, having many tiny separate sources of sound which then interfere with one another and create roughness in the response curve and lobing in the polar response-- all things we find in box-type speaker design-- occur in a headphone over such tiny distances that the effects are almost all beyond the range of hearing.
 
 

 

[Armaegis]

Quote:

Sounds like a question for the Audeze boys, or those close enough to them to've overheard diffraction-chat. My opinion is that the bad effects of diffraction, ie, having many tiny separate sources of sound which then interfere with one another and create roughness in the response curve and lobing in the polar response-- all things we find in box-type speaker design-- occur in a headphone over such tiny distances that the effects are almost all beyond the range of hearing.
 
 

I just ran some quick calculations and assuming I did them right and if we assume the holes are infinitely small point sources (that's kinda a big "if"), there shouldn't be any diffraction pattern that emerges; at least, nothing that will cause superposition or cancellation.
 
That said, I do still wonder about the backwave produced from the pressure waves bouncing off the magnet itself.
 
I suppose damping in front of the driver helps to mush those point sources back into a pseudo-planar wavefront.