OLLO S4R broken or working as intended?

I recently bought a pair of OLLO S4Rs and I’m really happy with their build quality and sound. They are pretty similar to HD600s in sounding neutral.

After a few days of listening though I noticed a hissing noise in some songs.

I compared to my HD600s and DT880s and the hissing is only existing with the OLLO S4R. Other than the cable and the headphones themselves the setup is the exact same.

I contacted OLLO and they send me a new cable but the problem persisted.

After further contact with OLLO, the headphones were sent back for inspection. No flaw was found but OLLO agreed to send me a new pair anyway (were they broken but they did not want to admit it?). I’m curious if the new pair will have the same problem or the first pair was really broken.

Now more info about the flaw itself.

Every recording has a noise floor, the noise that every microphone picks up because a room can never be perfectly quiet and a microphone can never be perfectly shielded from electromagnetic fields. Of course better equipment is also helpful. Cheap microphones often have a lot of noise. Usually, the noise is too quiet to be heard in a recording but sometimes the recording is too quiet and the gain has to be increased during the mixing of the song which makes the noise audible.
A nice example of this is the soundtrack of the Mandalorian with the track “The Mandalorian” at 2:35 where the wind instrument goes quieter and the noise is easy to hear before the recording of the wind instrument is cut off.

Usually, these are hard to hear and for most songs, you don’t hear any noise at all but with my OLLO S4R, the noise gets exaggerated. Now you might say that they just happen to be louder at that frequency where the noise is located compared to the HD600s but the noise is not just louder but there is a new tone of noise added.

I also noticed this problem more occurring on the right speaker of the headphones. When swapping the cables from left to right and right to left the problem was still there but not as much. This also indicates to me that the speakers have a different frequency response or one of them is broken.

This is hard to explain so I made a video.
I took my condenser microphone and played a snippet of a song where the problem is really outstanding through the right speaker of the OLLO S4R and recorded it. In this snippet after around 3 seconds, a string instrument starts playing with some noise.
For comparison, I did the same with the HD600s. I ran the recording through a DAW with an EQ and amplified the frequency band where the noise is occurring for better comparison. Then I applied a solo band of that frequency to only listen to the noise. I also included the original snippet and a recording of the OLLO S4R without EQ.
This is not a comparison between HD600 and S4R for which sounds better overall. The S4Rs need a good seal to sound good which I can not do with my normal condenser microphone while the HD600s are much more forgiving in that regard. I made this video to compare the noise.

The S4Rs have much more noise and they add a very consistent frequency of noise. The noise existing in the original is rather random and spread out. In the video, you can see the noise by the S4Rs as the bump where the arrow points at. For me, this is noise that is added not just amplified. If it just was amplified it would look like the original just with a higher amplitude.
The HD600s look pretty much like the original.

At least this is what I think. Why does the hissing added by the S4R only happen in some songs? It is not constant and so far noise in the recording is the most consistent thing to trigger it.
The hissing appears in other songs too and is not unique to songs with noise in them. Most often it is a strings instrument where it is also audible.
Is it a certain frequency that triggers the noise?

And I’m not talking about bad recordings sounding a bit worse with the S4Rs. There are a handful of songs that became unbearable to listen to with my pair of S4Rs while I never noticed anything bad with HD600s or DT880s. I had a colleague listen to the headphones too and he hears the same thing.

I’m awaiting the replacement pair and hope that they do not have the same problem.

I’m curious what more experienced people think of this and what a possible explanation for this is.

Could it be the noise from your amp? HD600 and DT880 have a lot higher impedance than the Ollo

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This is most likely the problem. Sometimes I hear no noise, then I take something like the KBEAR TRI i3 or the iBasso SR2 and immediately hear the noise if the amp doesn’t have a low enough noise floor.

As far as I know, the headphone cannot produce hiss themselves, hiss always comes from the source/amp. The headphones can produce distortion if the driver is damaged, but hiss is noise (correct me if I’m wrong).

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I tried the OLLO S4R on my phone and my dirt-cheap earbuds on my amp. The earbuds on my amp have less noise than the OLLO S4R on my phone.

Also, I have a Schiit Magni and Heresy so I don’t think they produce such an error.

Do you know what impedance your earbuds have?

Magni Heresy may have noise if your Ollo is very sensitive. It’s not an error, but almost all amps have noise.

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The problem might have been compression of the dynamic range.

Maybe the Ollo S4R has a kind of poor dynamic range which would make the usually quiet noise floor of a recording more audible. And since it was mostly I the right channel, it might have been a malfunction causing this compression.

What ever the problem, hopefully the new pair doesn’t have it.

Sennheiser says 32 ohms for the Sennheiser MX 375. Which is the same as the OLLO S4R

What about sensitivity?

don’t know what you mean with that

Sensitivity is the measure of how loud headphone gets when fed with the same amount of power. Both sensitivity and impedance will determine how hard it is to drive a headphone, and how easy it can detect the noise in the amp. It might be the case that Ollo is more sensitive than the MX375 so it picks up the noise whilst MX375 doesn’t, despite having the same impedance

I could not find a source by Sennheiser for sensitivity but third-party sites say 122 dB/mW for the MX375.
OLLO lists the S4R as 1vrms@1Khz 30ohm

So the replacement headphones arrived and while they still have more noise than other headphones it is not as extreme as it was before.

As others have said it is probably because they have a higher sensitivity so noise that is present in recordings is easy to be heard (which is good I guess because that means you can hear more details than other headphones too)

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