solderdude
Grand Contributor
When I bought the K702 from the previous owner he asked me to also measure the 'bass port mod' but kind of forgot ... until today.
So I looked into this (as well as output resistance effects) on this headphone and updated my review.
Some info I will post here as well (to save you from combing the review).
Below the effect of sealing and opening the centre hole in the driver magnet (referred to as bass port mod).
As can be seen a substantial subbass extension is possible. One may wonder why AKG still puts on those damping stickers when they can increase bass so easily. Well the answer is you shouldn't remove that sticker and below is why.
Aside from the stock and 'port open' plot there is a 3rd plot in there showing distortion when used with EQ that mimics the bass extension of the 'port mod'. In fact that EQ lowers bass extension even more. EQ does not increase distortion. All is measured at 90dB SPL b.t.w.
So those contemplating doing the often 'hailed to be great sounding' bass port mod I would say ... don't .. just apply some EQ.
Another aspect is the output resistance which would change the damping factor and make the K702 sound boomy and muddy because the membrane would not be 'controlled' or 'gripped by the amplifier' any more.
Below the frequency response change from 0.2Ω, 10Ω, 32Ω and 120Ω (note the 2dB/div amplitude scale)
Hardly any changes. Even with 120Ω bass increase is around 0.4dB. Not inaudible (120Ω is a LOT) but not obvious either.
How about the ringing of the membrane itself. Is that difference in damping clearly visible in the CSD plot (note from 10Hz to 30kHz) ?
Group Delay is that changed in audible ways ?
Or distortion... does this change a lot when driven from 10Ω or 32Ω and what about 120Ω ?
Nah.. you are pretty safe driving the K702 (and similar AKG's) driving it from most amplifiers.
That said... the output resistance from many power amps/AVR's may well be far above 120Ω and may well become audible.
More measurements in the usual place.
And yes, I know... not an industry standard rig... FR is incorrect... the treble peaks aren't real.. not the correct acoustic impedance etc. etc.
My Measurements May Vary..
So I looked into this (as well as output resistance effects) on this headphone and updated my review.
Some info I will post here as well (to save you from combing the review).
Below the effect of sealing and opening the centre hole in the driver magnet (referred to as bass port mod).
As can be seen a substantial subbass extension is possible. One may wonder why AKG still puts on those damping stickers when they can increase bass so easily. Well the answer is you shouldn't remove that sticker and below is why.
Aside from the stock and 'port open' plot there is a 3rd plot in there showing distortion when used with EQ that mimics the bass extension of the 'port mod'. In fact that EQ lowers bass extension even more. EQ does not increase distortion. All is measured at 90dB SPL b.t.w.
So those contemplating doing the often 'hailed to be great sounding' bass port mod I would say ... don't .. just apply some EQ.
Another aspect is the output resistance which would change the damping factor and make the K702 sound boomy and muddy because the membrane would not be 'controlled' or 'gripped by the amplifier' any more.
Below the frequency response change from 0.2Ω, 10Ω, 32Ω and 120Ω (note the 2dB/div amplitude scale)
Hardly any changes. Even with 120Ω bass increase is around 0.4dB. Not inaudible (120Ω is a LOT) but not obvious either.
How about the ringing of the membrane itself. Is that difference in damping clearly visible in the CSD plot (note from 10Hz to 30kHz) ?
Group Delay is that changed in audible ways ?
Or distortion... does this change a lot when driven from 10Ω or 32Ω and what about 120Ω ?
Nah.. you are pretty safe driving the K702 (and similar AKG's) driving it from most amplifiers.
That said... the output resistance from many power amps/AVR's may well be far above 120Ω and may well become audible.
More measurements in the usual place.
And yes, I know... not an industry standard rig... FR is incorrect... the treble peaks aren't real.. not the correct acoustic impedance etc. etc.
My Measurements May Vary..
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