When Everything Is Done Right—But the Result Is Wrong
Sometimes in engineering and manufacturing, you can do everything exactly according to plan and still end up with the wrong result. And when that happens, it can be incredibly frustrating.
This happened to us years ago when we started producing a new series of one of our high-end Edition headphones.
For safety and consistency, we maintain detailed assembly documentation that specifies every step of the production process down to the smallest detail. Because of this, it is normally very unlikely that something goes wrong during assembly.
The Final Test: Measurement and Listening
After assembly, every headphone undergoes two final checks:
Frequency response measurement
Listening test
The tricky part about headphones is that excellent measurements do not always guarantee excellent sound.
That is why every headphone is tested with the same music and at the same volume level before cleaning and packaging. Only when it passes both the technical measurement and the listening test do we consider it ready to ship.
When the Problem Appeared
And this is where the drama began.
Every headphone in the batch was mechanically perfect.
All measurements were correct.
All units were assembled exactly according to the documentation.
Yet they all sounded terrible.
The sound lacked energy, felt muffled, and appeared flat and lifeless. Obviously, we could not deliver headphones like that.
The Investigation Begins
The first step was to compare two of the problematic units with a reference headphone from the original production run.
Both headphones were completely disassembled, and every sound-relevant component was inspected carefully.
But we found no differences at all.
This triggered what became a two-week detective story.
We replaced each component one by one:
drivers
cables
housings
damping materials
internal components
After each change, the headphone was reassembled and tested again.
Since a headphone contains far more than just three parts, this process took a very long time.
The Unexpected Culprit
Eventually, we discovered the source of the problem.
It was the ear pads.
At first glance, the pads appeared completely identical to the original ones. The dimensions, firmness, and mechanical properties were exactly the same.
So why did they sound different?
After persistent questioning, our long-time supplier finally revealed the answer.
Their foam supplier had changed the foam material because the original material was no longer available. The replacement foam had the same technical specifications, which is why we initially noticed nothing unusual.
However, there was one critical difference:
The air permeability of the foam was slightly different.
This tiny change in airflow completely altered the acoustic behavior of the headphone, ultimately destroying the sound signature.
My Perspective
We invest a great deal of effort to achieve excellent sound quality. And even today, there are cases where individual headphones are set aside because something about them bothers us.
Those units then receive what we jokingly call “acoustic special treatment” until they sound exactly as they should.
Fortunately, we have never experienced a situation quite like that one again.
But this story also illustrates something important:
Achieving great sound requires extreme attention to detail.
And that is one of the reasons why headphones from Ultrasone are sometimes a little more expensive than others. 🎧
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