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KOSS PRO 4AA Review (Headphone)

amirm

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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:

KOSS Pro 4AA Review Headphone.jpg


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:

KOSS Pro 4AA Measurements Frequency Response Headphone.png


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:

KOSS Pro 4AA Measurements relative to target Frequency Response Headphone.png


Distortion however was extremely low:

KOSS Pro 4AA Measurements Distortion Response Headphone.png


KOSS Pro 4AA Measurements THD Distortion Response Headphone.png


Then again we have a ton of boosting to do.

Group delay is clean and not revealing of much:

KOSS Pro 4AA Measurements Group Delay Response Headphone.png


Sensitivity matches the average of all headphones tested so far:
Most efficient headphone review.png


Impedance is high and somewhat variable:

KOSS Pro 4AA Measurements Impedance Response Headphone.png


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:

KOSS Pro 4AA Equalization Response Headphone.png


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:

1632872256406.png


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.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Robin L

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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.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
That's the thing about Stereophile, it really has changed. Note that's a review of the Pro 4AAA, another, albeit similar, beast. However, if 1963 is the date of the original post at Stereophile, it must have been for the Pro 4A, the first in the series. They were about as good as it got back in its day, which isn't saying much.
Had a pair a couple of times, uncomfortable, shrieky. But I remember more bass, those earpads are messed up one way or another. The originals had liquid of some sort in the [rubber?] earpads, made for a tight seal.
 
Last edited:

sarumbear

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He bought it for $10, send it to Koss, they send back a new one!

Is that due to the lifetime warranty???
 

sweetchaos

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To import this PEQ profile into 'Equalizer APO', use:
Preamp: -11.1 dB
Filter 1: ON LS Fc 61 Hz Gain 6.3 dB Q 1.0
Filter 2: ON LS Fc 108 Hz Gain 4.2 dB Q 1.0
Filter 3: ON PK Fc 1000 Hz Gain 4.0 dB Q 2.0
Filter 4: ON PK Fc 2500 Hz Gain -3.0 dB Q 4.0
Filter 5: ON HS Fc 3000 Hz Gain 6.0 dB Q 1.0
Otherwise, see my PEQ guide.
..................................................................................................................
For those who don't have PEQ-capable app, and want to use GEQs instead:
See my GEQ guide for 10-band, 31-band, and 127-band GEQ profiles.
 
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snaimpally

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He bought it for $10, send it to Koss, they send back a new one!

Is that due to the lifetime warranty???

Correct.

The Koss PortaPros are much more comfortable and have good bass output for an open (non-sealed) headphone.
 

Labjr

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I worked for David Clark Company in 80's. They make the green headphones you see a lot of helicopter pilots wearing. They look similar to these. I supplied the old ladies on piecework with the parts to assemble them. They seemed to be very high quality but I don't imagine they would sound good for hi-fi.
 

GXAlan

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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.

J Gordon Holt had a different approach for sure.

"Decades ago, I grew accustomed to reviewing speakers that sounded bad because they really were bad, and calling crap crap was just a part of my job. But Genelec's 1031A speakers are not crap; they are superb for the purpose for which they were intended—close-range listening. My problem with them in the context of this review is that they are being marketed for applications—far-field and multi-channel listening—for which they were not designed and are ill-suited."

"I could not recommend the MG2.5/R for any listener who wants ballsy impact and lots of dynamic range; it isn't that kind of loudspeaker, and I don't believe it was intended to be. The 2.5 is more for the introspective kind of listener who craves suaveness and subtlety and the utmost in soundstage reproduction, and there are few systems at any price that can surpass it in those areas.

Any un-auditioned purchases should be made only with a clearly spelled-out stipulation that, if you can't get the 2.5s to work decently in your own listening room, you can get a full refund on your purchase price. (A credit will not do, as the dealer you buy from may not carry any other loudspeakers you'll like better.) It is more than likely that the 2.5s can be made to work very well in any given room, but not every room has the option of removable Tube Traps; the fact is that the 2.5s can sound really mediocre if the room and/or their placement in it is unsatisfactory."

I feel as if those conclusions provide useful information, are appropriately critical and still provide the context of the strengths of the product.
 

sarumbear

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Retired in the late ’80s, Koss swiftly returned the Pro4AA headphones to its product lineup due to overwhelming popular demand.


They said: You asked for it sunny! :p
 

beagleman

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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?
 

sarumbear

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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?
I think your memory is wrong. I had the same memory as I owned one in the 70s. I heard them again a few years ago and dear me, they sounded worst than AM on an old kitchen radio!
 

theshakomaster

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I sent these in - thanks Amir! The pair I sent in to KOSS were definitely vintage and I was hoping for a repair but instead they replaced with the newer model. The vintage pair wasn’t as stiff and had better pads than these. But I got what I got and I thought it was remarkable that they sent me a new pair at all considering I wasn’t the first owner and that these were discontinued for a period of time. These only had about 30 minutes of listening on them so they are essentially brand new.
 
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I worked for David Clark Company in 80's. They make the green headphones you see a lot of helicopter pilots wearing. They look similar to these. I supplied the old ladies on piecework with the parts to assemble them. They seemed to be very high quality but I don't imagine they would sound good for hi-fi.
I had always wondered who made the green headphones commonly used by helicopter pilots, and when search engines first became available, I tried and failed to find the answer. When someone gave it to me, I put it in a database, so I would not lose it.
 

musicforcities

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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.

----------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
It’s nice to know Koss still honors its lifetime warranty policy!

I noticed stereophile also said they were comfortable and attractive. Egads. If that doesn’t make one question their “subjective judgement” not sure what can.

But props Amirm for keeping the old school vibe going this week.

Has a koss porta pro ever been measured here? It has such a strong following but for me the high freq are pretty rolled off. Though I’ll admit I have a treble tooth (I enjoy the dt880 and old accustat 1+1 electrostatic speakers, measurement gods help me).
 
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_thelaughingman

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Correct.

The Koss PortaPros are much more comfortable and have good bass output for an open (non-sealed) headphone.
My PortaPro’ I bought a few months ago blew me away with the bass and tonality. They definitely out perform my HD560s and He400se for bass kick.
 

digicidal

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I think your memory is wrong. I had the same memory as I owned one in the 70s. I heard them again a few years ago and dear me, they sounded worst than AM on an old kitchen radio!
Isn't the brain's ability to seamlessly revise history amazing (and quite problematic especially in a legal sense)? I remember how huge and beautiful I found my first 17" CRT monitor... now I'd cry if forced to even browse a webpage on one. I thought the Panasonic quad setup I listened to when I was a child to be incredible as well... sadly I no longer have that setup to hear how truly horrible it undoubtedly was! ;)
 

Helicopter

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Thanks Amir. Nice to see a Koss product, and for my own sake, I prefer to see the current production model measured. I have several Koss headphones for special applications like cycling.

I sent these in - thanks Amir! The pair I sent in to KOSS were definitely vintage and I was hoping for a repair but instead they replaced with the newer model. The vintage pair wasn’t as stiff and had better pads than these. But I got what I got and I thought it was remarkable that they sent me a new pair at all considering I wasn’t the first owner and that these were discontinued for a period of time. These only had about 30 minutes of listening on them so they are essentially brand new.
Thanks for sending them. I had the same thing with a Leatherman Wave multitool I got from my mom as a young man and a blade snapped. I sent them in more than 20 years into the 25 year warranty and was disapointed to get a brand new imported tool back. Oh well. Still great service.
 

Labjr

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I had always wondered who made the green headphones commonly used by helicopter pilots, and when search engines first became available, I tried and failed to find the answer. When someone gave it to me, I put it in a database, so I would not lose it.
Yep. If you see the DC logo, they were made in Worcester, MA USA. They were used by Airforce pilots too. And still may be.

David Clark Co. also made the first Anti-G suits for the Airforce and space suits for NASA Gemini Program.
 
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Aperiodic

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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.
 
Last edited:

musicforcities

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My PortaPro’ I bought a few months ago blew me away with the bass and tonality. They definitely out perform my HD560s and He400se for bass kick.
Relative to portability and size they are impressive I suppose. I just have the same sense when I listen to them as when I am listening to some Bose table top speaker: an impressive amount of sound and bass relative to size and non/fatiguing to listen to in the background, but wildly inaccurate. The even cheaper Koss with ear hooks seem far cleaner. But getting proper fit can be tricky. Fortunately they snap into the porta pro band. Mix and match!

You can also wack a larger diameter foam pad on them. Makes them much more comfortable.
 

musicforcities

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I sent these in - thanks Amir! The pair I sent in to KOSS were definitely vintage and I was hoping for a repair but instead they replaced with the newer model. The vintage pair wasn’t as stiff and had better pads than these. But I got what I got and I thought it was remarkable that they sent me a new pair at all considering I wasn’t the first owner and that these were discontinued for a period of time. These only had about 30 minutes of listening on them so they are essentially brand new.
I bet you can get aftermarket cushions that will fit them. Cushion mods…oh boy is that an endless online forum pit of opinion….
 
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