[Hutnicks]

Quote:

 
 
     
 
 
 
[size=12.727272033691406px] I don't see any differences between the  T20-40-50RP series except for the damping:[/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] 1. T50RP          =  Stiff black felt over the internal lower cup vents allows limited venting [/size]
[size=12.727272033691406px]                             A plastic cap seals the central headband screw compartment[/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] 2. T40RP mk II =   A rectangle of plastic seals the internal lower cup vents allows no venting[/size]
[size=12.727272033691406px]                             A plastic cap covers the central headband screw compartment but has a ~ 4 mm hole in the center[/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] 3. T20RP mk II =   A more "open" or porous plastic grid material over the internal lower cup vents allows for more venting than T50RP[/size]
[size=12.727272033691406px]                             No cap over the central headband screw compartment[/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] So, Damping/Resistance from greatest to least: T40RP mk II > T50RP > T20RP mk II[/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] Equivalent SQ and FR is possible from all three with a few simple modifications to compensate for different damping schemes/resistance from model to model. You could try these reversible additions to your preferred mod configuration:[/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] 1. For T40RP mk II + Cover the hole in the central headband screw compartment cap with tape [/size]
[size=12.727272033691406px]                                 Remove the plastic rectangle covering the internal lower cup vents[/size]
[size=12.727272033691406px]                                 Use rubber cement to secure a rectangle of craft felt over the lower internal cup vents.[/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] 2. For T20RP mk II + Cover the central headband screw compartment with tape[/size]
[size=12.727272033691406px] [size=12.727272033691406px]                                Cover the plastic mesh overlaying the internal cup vents with thin craft felt[/size][/size]
[size=12.727272033691406px]                                 [/size]
[size=12.727272033691406px]  [/size]
[size=12.727272033691406px] I wonder if the power rating (2 watts vs 3 watts) has to do with the differences in damping schemes/resistance of the 3 "different" models? But wait. T20/40RP mk II are rated at 2 watts. T20RP mk II has porous mesh over the vents and no cap vs T40RP mk II has sealed vents and a 4 mm hole in the cap vs T50RP has semi-porous felt over the vents and sealed caps. Could the cap configuration be partially responsible for the power ratings??[/size]
[size=12.727272033691406px]  [/size]

 
It would be interesting to get one of those drivers in a chamber (small box preferably MDF open at both ends) And progressively close each end to see how A) the freq response changes and B) what the power draw actually is.
 
I'm thinking that with the number variations in Freq and power rating maybe they should be call Entropic headphones rather than orthodynamics

 

[GREQ]

.

 

[Armaegis]

Quote:

 
It would be interesting to get one of those drivers in a chamber (small box preferably MDF open at both ends) And progressively close each end to see how A) the freq response changes and B) what the power draw actually is.
 
I'm thinking that with the number variations in Freq and power rating maybe they should be call Entropic headphones rather than orthodynamics

 
I think those power ratings are a listing of maximum possible power. The power draw of a headphone is governed by ohm's law. Damping schemes will not change how much power goes through the driver. The amount of sound you get per unit of power will change, but that is the sensitivity rating, not power rating. 

 

[Hutnicks]

Quote:

 
I think those power ratings are a listing of maximum possible power. The power draw of a headphone is governed by ohm's law. Damping schemes will not change how much power goes through the driver. The amount of sound you get per unit of power will change, but that is the sensitivity rating, not power rating. 

True enough.
 
However what seems to be implicit there is that the same driver (I think) is capable of dealing with different power rating. This would suggest that the actual impedence is affected by the acoustic characteristics of the enclosure surrounding the driver. This would make sense given the amount of tuning which is possible with these headphones.

 

[Armaegis]

Impedance should not be affected that much by damping, at least not to the extent that it would change the power rating.
 
I suspect that when the drivers are manufactured, they have various quality control tests and whichever ones pass above a certain threshold get a higher power rating, and those that don't get the lower one. 

 

[Planar_head]

It doesn't appear that way, according to Tyll's measurements on Innerfidelity.
However, there is an inductive component to the impedance plots at frequencies above ~20kHz.
Also, there appears to be some driver impedance variability; varying about +-10 ohms from 50 ohms.
Quote:

True enough.
 
However what seems to be implicit there is that the same driver (I think) is capable of dealing with different power rating. This would suggest that the actual impedence is affected by the acoustic characteristics of the enclosure surrounding the driver. This would make sense given the amount of tuning which is possible with these headphones.

---
On another note, I've purchased a pair of Fostex T40RP mk2's and found there was a strange clicking sound from the left side. When I opened them to mod the headphones, I noted that the attachment point of the wires to the diaphragm was moving around and creating that clicking sound. I taped it down and it no longer makes any noise. Hopefully that helps someone.

 

[Hutnicks]

Quote:

Impedance should not be affected that much by damping, at least not to the extent that it would change the power rating.
 
I suspect that when the drivers are manufactured, they have various quality control tests and whichever ones pass above a certain threshold get a higher power rating, and those that don't get the lower one. 

 
Quote:

It doesn't appear that way, according to Tyll's measurements on Innerfidelity.
However, there is an inductive component to the impedance plots at frequencies above ~20kHz.
Also, there appears to be some driver impedance variability; varying about +-10 ohms from 50 ohms.

---
On another note, I've purchased a pair of Fostex T40RP mk2's and found there was a strange clicking sound from the left side. When I opened them to mod the headphones, I noted that the attachment point of the wires to the diaphragm was moving around and creating that clicking sound. I taped it down and it no longer makes any noise. Hopefully that helps someone.

The manufacturing qc idea sounds plausible. Lets hope the Interviewers from the Stax thread get over to Fostex and give them a ....grilling
 
I am still suspicious that there is an acoustic feedback component at play here. For lack of a better term "air loading " the driver seems to be of more significance here than one would expect.I would be extremely curious to see these tested in vacuum and see what the measurements come out as.
 
Do the Denon's that use the Fostex drivers use the same units as the RP series?
 
BTW Planar, your avatar makes my brain hurt

 

[Armaegis]

Quote:

I am still suspicious that there is an acoustic feedback component at play here. For lack of a better term "air loading " the driver seems to be of more significance here than one would expect.I would be extremely curious to see these tested in vacuum and see what the measurements come out as.
 
Do the Denon's that use the Fostex drivers use the same units as the RP series?
 
 

Theoretically, the atmosphere does have a role in the damping of a driver in terms of viscosity, resonant frequency, etc. But the pressure differences inside a cup... I don't think they'd be quite high enough to make any sort of appreciable difference.
 
The Denons do not use planar magnetic drivers.

 

[Hutnicks]

Quote:

Theoretically, the atmosphere does have a role in the damping of a driver in terms of viscosity, resonant frequency, etc. But the pressure differences inside a cup... I don't think they'd be quite high enough to make any sort of appreciable difference.
 
The Denons do not use planar magnetic drivers.

I thought one of the Denon's was using Fosgate's, maybe i am confused with another brand.
 
The stats posted on those phones would suggest that the atmosphere in the cup does in fact have an influence here. Curiosity, has anyone ever plugged one of these puppys into a mic jack and seen what they record like?

 

[MuZo2]

My pair of  Yamaha HP3(like new with original packaging) arrived today. Just a quick listen and wow in stock form they are better than Fostex T50RP. They are certainly bass heavy as some of you have reported here. 

 

[MuZo2]

More from Yamaha HP-3 sound. 
Bass- Its tight and extends deep, both quantity and quality wise they are very good for such small cans from 1970. Mid bass is present slightly which makes the mids warm.
Mids- Mids are warm and are bit laid back.
Highs- I think the highs are bit rolled off, I would have liked bit more sparkle.
Soundstage seems closed which is quiet understandable.
Overall they are quiet impressive, clarity and resolution ,didnt expect this from cans which were made in 1970. I think they can compete very well with modern dynamic headphones in the range of 200$.
I will try to make some comparative measurements during weekend.

 

[vid]

Quote:

Soundstage seems closed which is quiet understandable.

 
Based on my experience with the HP-50, what keeps them from actually being competitive against modern mid-fi cans - and some other cans for that matter - is their lack of soundstage. The sound is accurate but lacks authority.

 

[MuZo2]

SFI driver has frequency response from 5KHz to 20KHz is this because of diaphragm or because of magnet or spacers?

 

[GREQ]

Quote:

SFI driver has frequency response from 5KHz to 20KHz is this because of diaphragm or because of magnet or spacers?

SFI's might be rated so, but to my ears, they have a similar bass to Grados. It's quiet, punchy - but its absolutely there. 
The specifications don't always tell the whole truth. 
Plus with certain damping strategies and small pleather earpads, SFI's can get REALLY boomy mid/low bass (if that's what you like).

 

[vid]

^ You'd think the ortho thread the last place a lover of boomy bass would be. (But then again, might be the most obvious place, too.)