[geoff]

On 31/12/2017 11:06 PM, Adrian Tuddenham wrote:
geoff wrote:

On 31/12/2017 2:45 AM, Adrian Tuddenham wrote:
[...]
I measured the frequency response of a pair of early-model AKG K-240
headphones some time ago and found they had a huge dip of about 20 dB in
the HF range. Both left and right transducers demonstrated this at
nearly the same frequency, so it appears to be an inherent property of
the design, not an individual faulty unit.


And nobody noticed this huge dip ? Maybe the transducers have had an
aging r=effect which is causing this now ?

I was quite surprised that nobody had noticed it. I heard it first on a
sweep tone and thought my ears were playing tricks, so I set up a
rough-and-ready test rig and confirmed it by measurement. Whatever was
causing it was almost identical on both earpieces.

Presumably both earpieces have been subject to the same usage, aging,
and storage conditions. SDo I wouldn't be surprised.

It would be interesting to test another pair from the same era and then
comare this with some of the later models, but I only have the one pair
that I bought secondhand. There is no way of knowing what conditions my
headphones were subjected to before I bought them; but it is difficult
to imagine a mechanism that could cause such a dip, let alone one that
would have been exacerbated by poor storage conditions.

I find it hard to imagine that professionals over several decades using
these headphones also hadn't noticed. Only JJ wouldn't be surprised.


I thought the manufacturer's data sheet or some of the independent
reviews might shed some light on this dip, but I was soon disabused of
such a quaint notion. There doesn't appear to be any sort of meaningful
specification for the performance of these headphones and the reviews on
the Web are utter bo**ocks; it doesn't look as though anyone has ever
bothered to check their frequency response.

I find that concept to be utter ******** ;- ) There *will* be a reason.

The AKG K-44 showed some minor wobbles in the frequency response curves
with a rise at the lowest and highest frequencies, but overall sounded a
lot better than the K-240.

To me K44s sound like they look. Cheap and plasticy. Haven't heard K52s.
Again, something is grossly wrong with the K240s.



My conclusioin is that, of the three models teated, the K-52 is the best
for flatness of response as long as it is properly positioned on the
listener's head. The K-44 isn't bad and the early-model K-240 is a
waste of time and money.


How about testing some more recent higher-end AKGs. And some actual
listening testing, because steady-state frequency response is only one
of many factors in sound quality. And arguably a minor one at that ...

I would be quite happy to do some simple frequency response tests if
someone is prepared to loan me suitable candidates. Perhaps more
elaborate dynamic testing would show up minor differences in the
performance of headphones that show apparently good static responses;
but when there are such gross errors in the basic properties, there
doesn't seem to be much point in going on to test for anything more
subtle.

Maybe pick up another pair of old K240s and compare ?

And another thought (though not necessarily specific to the particular
conundrum - what is the output load impedance specification of the sig gen ?

geoff