T50RP mk3

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Published: Feb-7-2017, updated: Jan-02-2022

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NO SMOOTHING is applied to the shown plots. Most measurement sites have some smoothing applied which ‘irons flat’ sharp peaks and ‘wiggles’. I do not use smoothing because some info about sound quality is lost when plots are smoothed.

Aside from a small correction of the microphone itself also some correction in the lowest frequencies is applied to the plots to compensate for the perceived loss of bass when using headphones. This is described HERE in more detail.
A ‘horizontal‘ frequency response curve on the shown frequency response plots on this website thus indicates a perceived ‘flat’ tonal signature.

ALL measurements are made with a good SEAL on a flatbed measurement rig.
shape of your head, bone structure, pad size, pad ‘softness,  (compliance), hair or no hair and or wearing glasses may (drastically) change the frequency response of some headphones, so… your personal experience may differ substantially from these plots.

Frequency response (tonal balance) is the most sound-determining aspect of headphones. A horizontal line shows audible neutral response in the plots on this website. Deviations in different severities at different frequency bands have an effect on the sound character.
The bigger the deviation the stronger the effect.

Below an aid to help determining the sound character of headphones with relation to the frequency response.


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Fostex T50RP mk3


The Fostex T50RP mk3 is an improved version of the T50RP (mk2). The driver is differently constructed (damping) and there is a different colour scheme and headband.

The comfort is somewhat better and I like the orange accents. It comes with 2 cables. A short orange one with 2 angled 3.5mm TRS plugs (locking in the headphone) and a longer black cable with an angled locking 3.5mm plug on one end and a straight 6.3mm TRS plug on the other side.
Same problem as before though. Very poor contact of the 3.5mm angled plug. Plugging it in and out multiple times and twisting it didn’t really help. The electrical contact is poor and intermittent/scratchy in the orange cable. Got weird measurement results using this cable as well. The black one fared slightly better and at least measured consistently.
One really needs to clean and scrub the connectors.

The pads are of the same quality as the old ones. Not very comfortable.

The efficiency is a bit lower as well because the area between 100Hz and 400Hz is about 5dB lower in amplitude which for a large part determines how loud it is perceived.
Impedance is a bit lower (in this particular set) 45Ω.

The price has almost doubled… But because the comfort and sound-quality improved it has gained back some value.


Type: over ear (circum-aural), open
Usage: home, studio
Driver type: planar dynamic
Pads: replaceable, pleather (thick vinyl)
Collapsible: no
Headphone cup connector: 2x 3.5mm TRS angled, locking
Cable entry: dual sided.
Cable: 1.5m orange and 3m black straight cable with split, 2x 3.5mm angled to 6.3mm TRS jack
Inner Pad dimensions: depth = 11mm, height = 56mm, width = 40mm.
Driver size: 40x40mm (effective 32x32mm)
Nom. power rating: 3W (estimated)
Max. voltage: 12.5 Vrms (34Vpp)
Max. current: 240 mA
Max. S.P.L.:  130dB
Impedance: 45Ω (measured)
Efficiency: 94dB @ 1mW
Sensitivity: 107dB @ 1V
Weight: 335 g. (without cable)
Clamping force: medium-high
Accessories: 2 cables of different length.


Below the measurements of a stock T50RPmk3, Left, Right.


The sound also differs and is closer to neutral. Below the differences between the T50RP mkII and ‘new’ T50RP mk3 are easily seen.


The differences in frequency response are obvious. The elevated area between 100Hz and 400Hz which significantly coloured the bass and mids is now much flatter. The dip around 4kHz is 5-10dB smaller. The treble quality has improved. The subbass is the part that has to pay for this new damping scheme of the driver though.

A roll-off starting at 50Hz is quite audible. The mids are much more realistic now and have gained in clarity. Also the treble is of a higher quality.
Still there are 2 areas that are not so good. The subbass extension and treble extension.
The lack of treble extension results in cymbals not being realistic sounding and a lack of ‘air’ to the sound. It just isn’t realistic in the treble. Bass quality isn’t really great and feel the earlier version had better quality bass when it comes it impact and ‘dynamic’ sound.
The mk3 sounds ‘pinched-off’ and overly damped. No deep bass.

The L and R channels in the first frequency plot show there is a decent channel matching except below 100Hz.

The distortion plots of the Left and Right channel also showed a much more disturbing result.


Above the distortion measured for the right channel. Below the measured distortion for the left channel. The signal itself is around 90dB SPL @ 1kHz.


The difference is massive… probably have a dud here ? At 80dB SPL the distortion dropped from 20% to about 3% so something seems funny with the maximum swing it can reach.
So… I decided to BLAST the driver for an hour with VERY LOUD music with the bass turned up to insane levels.
After and hour the distortion was measured again. The R channel measured the same but the ‘faulty’ left channel improved between 100Hz and 500Hz. Burn-in ?


In any case the bass distortion below 100Hz did not improve at all.
I reckon I either have to send it back or void the warranty and loosen the driver membrane and or have a look around in there.
Lack of time forces me to tackle this one at a later date and do some modifications and create a Kameleon module for this model.

The CSD (Waterfall plot) is quite decent though. Left and Right superimposed.


This actually looks quite decent and well damped. The same as the mkII actually.

Below the Spectrum plot of the mk3, left channel.


This is actually quite good. It shows no worrying ringing and the bass doesn’t linger on too long either. Around 700Hz it could be slightly better though. Maybe some modifications can help here later on.

Instead of the squarewave and needle pulse plots a step-response plot is shown.
Again L(top) and R(bottom) differ where the earlier bass roll-off of the right channel is more obvious.



These step plots are a bit disappointing. The drop-off in the lows is quite visible.

The distortion issue in the Left channel had to be looked into. On the website it was suggested that it may be caused by leakage of the (crappy) TRS socket. Indeed the socket has a substantial opening into the world around it. Not only through the hole but also around the connector itself. The plug, however, seals that hole almost completely off.
The hole was sealed on the inside applying maleable eraser around it.
This did not make any noticeable difference in distortion and also not in frequency response. Sealed connector, stock.


Below some plots made during the investigation. Top left is the stock left channel. Top right is the stock right channel. As can be seen a substantial difference in distortion below 500Hz. Around 30Hz the left channel reaches almost 20% where the right channel reaches 2%. This was measured with 1kHz at around 90dB SPL. It looks like the driver has problems with larger amplitudes. To test this I remeasured at 80dB SPL (mid right plot). This showed the bass distortion is lowered to around 7%. I decided to give the driver hell and played an hour long extremely loud music with the bass dialed up a lot. As the driver can take a lot of power it was turned up till it started to distort. After an hour I remeasured again. The distortion around 30Hz was only slightly down but the peaks around 200Hz, 300Hz and 4ooHz had come down.


Based on the observations made I came to the conclusion that the driver cannot make larger swings and the membrane may be too tightly tensioned.
Fortunately the Fostex drivers can easily be taken apart. I loosened all the screws and as the membrane was sort of stuck on the chassis I pried it free. Tightened the screws again and remeasured (picture bottm right). On the bottom left above the stock left driver for an easier comparison. Sure enough the distortion at 30Hz had dropped to slightly over 2% and is around the same as the right driver. Driver fixed…
The frequency response altered somewhat though. stock versus fixed.
2dB more bass around 100Hz. The driver drops off a bit sooner as well though, maybe a seal issue ?


The sound did not change in any obvious way despite the distortion being much lower and the bass being slightly higher.

Next step is to add a little subbass and improve on the clarity and make the treble of better quality. This is done using a Kameleon filter. Below the stock T50RP (Right challel) and via the Kameleon.


The bass response is much improved (+ 10dB at 20Hz). A bit more ‘body’ is added given the area between 100Hz and 300Hz is raised by about 2dB. The dip around 3kHz is improved by 2.5dB. This doesn’t seem like it would be quite audible but it is. Clarity has improved noticeably. The treble ‘peak’ aound 9kHz is lowered a few dB as well. Treble extension has improved somewhat. The treble level is now more even between 4kHz and 18kHz which results in more ‘air’ and a more realsitic treble. Below L and R of the stock T50RP mk3 via Kameleon.


The frequency response is more linear now. Good bass response, good clarity and better quality treble. Below the CSD via the Kameleon (left and right superimposed)


The step response also improved somewhat but still shows subbass response is just slightly lacking.


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