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KOSS PRO 4AA Review (Headphone)

phoenixsong

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Great review Amir! I bet some of us always wondered how those ancient headphones would sound and measure like.

You measured a product from the Koss lineup, is there a chance you would do an evaluation of Koss ESP950/95X (massdrop)?
 

solderdude

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shrill HD414 Sennheisers (I still have a pair and the 2k impedance makes them useless unless fed straight from an amplifier).

hd414-fr.png


I remember the 4aa from the mid 70's and they didn't seem to lack bass at all back then

The 1970 Pro4AA started to drop off at 80Hz the measured newer types at 200Hz. almost 2.5 octave higher.
 

sergeauckland

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I remember the 4aa from the mid 70's and they didn't seem to lack bass at all back then. Incredibly heavy and uncomfortable though, but th emain alternatives we had were the DT100's which I found incredibly coloured sounding and the shrill HD414 Sennheisers (I still have a pair and the 2k impedance makes them useless unless fed straight from an amplifier).
The main benefit of the 2k impedance is that they could bridge a standard 600 ohm balanced line without loading it down. Very useful for signal tracing on jackfields.

S.
 

solderdude

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Beyers tend to have a peak in the treble, but this headphone seems to be the peak itself :p

Beyers peak at piercing 9kHz frequencies, this one at the shrill 3kHz range.
 

nyxnyxnyx

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My bad, I should have checked the Index. Thank you for the URL
 

Thomas_A

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My bad, I should have checked the Index. Thank you for the URL

With respect to the Koss ESP 950 (original), a measurement made in 2003 do not show the bass drop as with the Massdrop version, whatever the reason could be for that. It was quite well regarded in the listening tests at that time.
 
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tdockweiler

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Reminds me of one of the ugliest frequency graphs I ever saw, it was of the Koss MV1. It almost looks similar to this!

koss-mv1.png


It was the most muffled sounding headphone I ever heard.
Somehow it wasn't the worst overall Koss headphone. That goes to the ESP950 look-alike with a dynamic driver in it's shell.
Anyone remember the name? It sounded like a more tinny version of the Beyer DT-880, but with ALL bass chopped off.

By far the best Koss headphone is the Koss Pro DJ200 (or even 100).
That's the one you want to really measure.
The only problem is that it doesn't sound at it's best until you use M50 pads.
Those fit perfectly on it!

Tyll from Inner Fidelity measured the Tony Bennett version. Yes a former DJ headphone with his signature on it!
It's a more expensive version of the DJ100 with a case and removable cable.
Only the DJ200 is still available.
The original DJ100 could often be found on sale at Best Buy for $50 and it was a steal at the time!

It's my favorite headphone ever and i'd take it over my HD-650. Not even kidding.
It doesn't match the Harmon curve, but has probably ruler flat sub-bass or close.
Better bass than the M50 and SRH-840 for sure.
I actually think it sounded far better than the K371 too (which I found to be a bit overrated).
 

Ken1951

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I bought a pair of the original Pro4A when I bought my first HiFi in the Spring of 1971. Plugged them into the Kenwood 4140 of that purchase. If memory serves, they had gel filled pads, were heavy, and sweat inducing. Still they sounded amazing to my ears and I used them regularly in the dorm and at home for years.
 

Svperstar

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I picked up a pair of these at a local thrift store for $3 like 2 years ago. People on a headphone Discord got a kick out of them. I moved earlier this year and tossed them as I was trying to simplify before moving.

I can confirm they sound awful. No bass at all on even on bass test tracks.
 

musicforcities

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That’s a great review of those. I bought a pair. They went back to Drop. First the craptastic plastic amp did not work correctly out of the box, buzzing and low level on one channel. The replacement worked but sounded anemic. Not just bass but midrange was also thin. And many were complaining about the amp developing noise after a few months, or the diaphragm of phones themselves loosening and rattling/cracking/arching. Not worth the hassle.
 

PuX

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I don't think Koss has ever made a good product
 

Not Daijoubu

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Classic bass seal issues with Amir's rig. Yep, that 2.5khz peak is there, but I personally got a great seal with my Pro4AA bought back in 2020 for giggles. so good it isolates better than any other closed-back I have tried.

I think Amir's EQ decisions are perfectly fair for getting a signature closer to harman. The Pro4AA does roll off, but no more than a typical open back really.

I too cannot recommend them, even with EQ, since they are ridiculously uncomfortable. I liked mine a good amount though.
 

beagleman

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So we have some saying they sounded bad and some saying they sounded quite good. Maybe different versions over the years, but I know for sure, when I played "Speak to me" on dark side of the moon, they have PLENTY of deep bass......

Not sure why so much variance in how they are perceived....
 

Not Daijoubu

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So we have some saying they sounded bad and some saying they sounded quite good. Maybe different versions over the years, but I know for sure, when I played "Speak to me" on dark side of the moon, they have PLENTY of deep bass......

Not sure why so much variance in how they are perceived....
Probably seal is different for various people. I for one do not wear glasses, and have never had any perceivable seal issues with any headphone really.

Choice of music? - some stuff is really bass skewed, others may be mix/mastered relatively bass "anemic" or is too compressed to appreciate punchiness/texture/whatever that better production would aid with. who knows.

Also, different people like different amounts of bass, possibly relevant is some people may be less sensitive in hearing/feeling sub-bass since hearing does roll off steeply starting there, idk. Personally, I enjoy "lean" bass; stuff like the M40x, Air Pod Max, speakers that dig deeply into <60hz make me a bit nauseated really.

Of a different note, The drivers at least look different between vintage and current production Pro4AA. I opened mine up, and the back side was a bit different from photos of old Pro4AA I have seen. Pads - the vintage ones use gel filled (almost all are rock hard now) while the current pads are simply air cushions with some foam inside. I wanna guess sound is more or less the same, but at least in terms of physical build their are differences. The first version of the Pro4AA had very different drivers - much like the Pro4A the speaker magnets stuck out from the cups:
$_1.JPG
 

musicforcities

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So we have some saying they sounded bad and some saying they sounded quite good. Maybe different versions over the years, but I know for sure, when I played "Speak to me" on dark side of the moon, they have PLENTY of deep bass......

Not sure why so much variance in how they are perceived....
Hypothesis:

Head seal plus higher Amplifier output impedance (with power) = Happy Harmon fr curve (sorta)

Bad head seal and low power low impedance output = Bell’s palsy frowny face fr curve (no bass on one side, messy highs on the other)

Again, as per solderdude’s excellent info above, mmmthough the exact model number / variant seems to matter as some are designed for very specific things, like emphasizing vocal range for recording/mixing or maybe talking while in a helicopter etc.

I bet Amir and this forum has now spent more effort and thought on these cans than has been done since their design….
 
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Not Daijoubu

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Head seal plus higher Amplifier output impedance (with power) = Happy Harmon fr curve (sorta)

Bad head seal and low power low impedance output = Bell’s palsy frowny face fr curve (no bass on one side, messy highs on the other
The Pro4AA bass response does not change going from a Schiit Magni 3+ to a ~150 ohm output vintage stereo amp I have. Stuff like the Porta Pro or ATH-AD900x did get a bass boost on that same amp.

It's probably mostly seal dependent. with the Pro4AA. If you have a great seal and no way to really vent it, where does it all go? I wouldn't say it's close to being harman though, at the least it isn't as mid-bass emphasized as a lot of closedbacks i.e. DT770 or M40x if at all.

To add, these things are practically on ear because it compresses my ears right to the side of my heads, and my ears are not large at all. Shallow pads, vice-like clamp. I would wager it's hard to get a good seal with the Pro4AA because of the shallow pads, applicable to the rig and some people maybe.
 
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