KOSS PRO 4AA Review (Headphone)

[theshakomaster]

I bet you can get aftermarket cushions that will fit them. Cushion mods…oh boy is that an endless online forum pit of opinion….

Maybe these are great pads, they just need 700 hours of break-in! :-D

 

[fieldcar]

I kind of always expected this, so I never bought them. I was tempted though.

Zeos kept hinting at something new for the hifi crowd from Koss. He said "in the coming weeks" about 2 months ago. I wonder what they are cooking up. I think I've seen teasers for full sized open backs. I hope they come out soon.

 

[KxDx]

Had a pair many years ago. Weighed a ton and the gel-filled earpads, while providing good isolation, turned each ear into it's own little steam room. Don't recall them being bass-deficient (in fact, Koss was what the bassheads bought) but since I always wanted to take them off after 2-3 minutes, my recollections may not be reliable.

Same opinion here. I owned a pair from late 1990’s to around 2005 when I bought Senn HD600’s. Those Koss could play LOUD and the bass would pound.

I remember the upper midrange being a bit sharp, but otherwise I enjoyed them. They would cause some ear fatigue, but that’s because they were built like tanks.

 

[musicforcities]

Speaking of uncomfortable and stiff cans…Anyone have a vintage Beyerdynamic dt 100 or dt108 to send into Amir? They were ubiquitous in recording studios throughout the 70s to mid 80s. Preferably in white as worn by Barry Gibb below. Not that the white plastic sounds different, just because they match white suits and bell bottoms better.

Seriously, I would bee curious to know how the phones and other equipment used to record and mix classic recordings would measure. The results may be a “tragedy”

 

[musicforcities]

Maybe these are great pads, they just need 700 hours of break-in! :-

Lol. Maybe They are great for 10 hours, just after 700 hrs of break in and just before they start disintegrating…

Anyway, the cable needs at least 700 hours of break in as well to align the gluons. Or muons. Or bosons or bozos. . Or something. ;-)

 

[sam_adams]

Speaking of uncomfortable and stiff cans…

The AKG k140 series were probably the most uncomfortable headphones ever made. I think they may have been designed by Dr. Mengele himself.

I still have a pair.

 

[musicforcities]

Having owned these for years, I remember them having quite decent bass, and very good deep bass.....

In fact, I remember them sounding fairly good overall. Maybe my memory is wrong?

One thought, given their era , use, and high impedance I wonder if these were designed to be driven by high output impedance devices. My 600ohm beyer dt880s can be pretty anemic in bass but plug them into an integrated amp or receiver with 30-100ohm output impedance and they go deep. Of course those tend to have lots of power and voltage swing too because the headphone taps the speaker level outs. But the 600 ohm beyers seem to like high impedance output and that was common back in the day. Though the 880s go plenty deep on the Schiit heresy as well.

 

[musicforcities]

The AKG k140 series were probably the most uncomfortable headphones ever made. I think they may have been designed by Dr. Mengele himself.

I still have a pair.

So…much…brushed metal! Me like very nice.

Those looks like they may be supraural? Resting on top of your ears? I had a grado sr60 and those things killed my ears if I wore them over 20 min in spite of the foam pads. Urgh.

 

[Zensō]

Wow, that may be a record for the biggest bass boost yet on ASR!

 

[AndreaT]

The lack of bass (and treble) and the very uneven response shows that some progress was made in materials and design in the past 60 years or so. A headphone to avoid, IMO. Thank you Amir for the very precise testing.

 

[JDS]

This is a review and detailed measurements of the KOSS PRO 4AA headphone. It is on kind loan from a member. He bought it used for $10 but then sent it to KOSS and they sent him a new one. In researching it, I found a review (of a different revision) dating back to 1963 yet it is still on sale on Amazon for US $80!

The 4AA looks like an avionics headphone to me for some reason:

View attachment 156103

I found the cups very stiff and they became very uncomfortable after 15 minutes of listening.

Note: The measurements you are about to see are made using a standardized Gras 45C. Headphone measurements by definition are approximate and variable so don't be surprised if other measurements even if performed with the same fixtures as mine, differ in end results. Protocols vary such as headband pressure and averaging (which I don't do). As you will see, I confirm the approximate accuracy of the measurements using Equalization and listening tests. Ultimately headphone measurements are less exact than speakers mostly in bass and above a few kilohertz so keep that in mind as you read these tests. If you think you have an exact idea of a headphone performance, you are likely wrong!

Fitment on the fixture was VERY difficult. It would not fully surround the artificial ear, and I could not get it to fully seal no matter what I did. Slight movements and changes would vary the levels but in practice, I noticed frequency response did not substantially change. Still, be on notice that my confidence in measurements are not super high (although EQ settings verified that they were good enough for that purpose).

KOSS PRO 4AA Measurements
Let's start with our usual frequency response:

View attachment 156105

Ouch. That bass deficiency may be partly due to seal but still, we basically have no bass. There is some kind of resonance around 2.5 kHz and response then drops way off. In other words, this is as close to one-note headphone as we can get.

Relative response puts this in context relative to our target:

View attachment 156104

Distortion however was extremely low:

View attachment 156106

View attachment 156107

Then again we have a ton of boosting to do.

Group delay is clean and not revealing of much:

View attachment 156108

Sensitivity matches the average of all headphones tested so far:
View attachment 156109

Impedance is high and somewhat variable:

View attachment 156110

KOSS PRO/4AA Listening Tests and Equalization
Boy, does this thing sound flat and lacking in just about everything that makes music hi-fidelity. There is no bass or treble. I almost stopped there thinking it could not be salvaged with EQ. But I was wrong:

View attachment 156111

The transformation was dramatic. It was the classic toad turning into a prince! OK maybe that not far but you get the picture. There was even decent spatial effects now. Deep bass was pronounced but had a weird distortion about it. I took the levels down and it helped with that but then I thought bass was lacking with other tracks that were not bass heavy. After some back and forth, I left it as you see.

Conclusions
In researching this headphone, I ran into this Stereophile review for a slightly different version of it:

View attachment 156112

I don't think I have ever read such blunt and negative review in stereophile! Was this the norm back in 1991? If so, I wish that spirit was kept until today.

Anyway, I concur with it. Can't recommend the KOSS PRO 4AA.

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I had a pair of their cousins, the Phase 2, back in the 70s. Yeah, they were really uncomfortable, and sound quality was poor. And I remember them reeking of plastic and who knows what other noxious chemicals. But I used to wear them as hearing protectors during basement rehearsals of the rock band I briefly played in, so I guess I should thank them for my current hearing, such as it is.

 

[phoenixsong]

Ooh this is one of the iconic ancient ones! Thoroughly surprised by its distortion levels

 

[phoenixsong]

I wonder what kind of DACs/Amps it used to be paired with in the past

 

[phoenixdogfan]

Bought these in 1972. It was considered the SOTA dynamic headphone at the time. Don't remember too much about it except it was bass shy and could play at ear damaging levels. I only used it late at night to listen to music without disturbing my roomates (I was a college freshman at the time). Ultimately it fell apart. Don't think it was all that well made.

 

[phoenixdogfan]

I wonder what kind of DACs/Amps it used to be paired with in the past

The headphone out of your receiver.

 

[musicforcities]

I wonder what kind of DACs/Amps it used to be paired with in the past

Receivers and integrated amps very likely. Or pro equipment. All likely with relatively high output impedance as relative to today’s good SS headphone amps

 

[musicforcities]

Bought these in 1972. It was considered the SOTA dynamic headphone at the time. …. I only used it late at night to listen to music without disturbing my roomates (I was a college freshman at the time).

So here is the key question; how well did it play “dark side of the moon”?

 

[phoenixsong]

The headphone out of your receiver.

When I first started listening to earphones I tried the JVC HA-FX40 (one of if not the first carbon nanotube IEMs) out of the Yamaha A-S300's headphone out. It did sound rather bassy and a bit tube-like that way

 

[phoenixsong]

I wonder if pad aging has stiffened the interior foam? and is affecting fit and bass response

 

[amirm]

I wonder if pad aging has stiffened the interior foam? and is affecting fit and bass response

I think the owner said these are essentially new.