SIZE MATTERS, BUT SO DOES COMFORT | #019

What is good, and what is bad comfort? Just as we don't have a consensus on what a cool, soft, relaxing, smooth sofa, actually is, we don't have a consensus on what airy light and comfy headphones actually are. Here is how we go about it.

There are quite a few researches done about head sizes in the 50s and 60s with Telco companies and Stanford university. To sum it up. The average guys' head width or breadth is about 15 centimeters.

And this is Frank - he's our average guy. The way we measure force is using Newton meter. When the headphone moves a little bit is, where the force is kind of counteracting, we can measure it. And it's roughly about 3.5 Nm with our headphones on this average Frank over here.

As your head size increases, gets bigger, the more force is required, or the more (clamping) force is actually present. The funny thing is - the force is not a linear thing. It's logarithmic - the bigger the head size, the more clamping force you're going to have. But the clamping force is not exactly the pressure on your head, because the pressure comes down to how big the pads are, and the touching surface between the headphone and your head. The bigger the coupling surface is, the less pressure is actually present to your head.

The clamping force affects the sound. As mentioned before - your head size will affect the clamping force, so it's all very much connected. And when it comes to measuring devices, for example, the 45CC is actually one of very few, if not the only one on the market that you can get, which is not based solely on Telco standards from the 40s, 50s, and 60s, but it also incorporates the feedback from other companies doing measurements in headphones for the last few decades.

It's actually one of the most accurate when it comes to adjusting it for correct head sizes. If we take a look at the specification used the bitragion diameter, which is the diameter or the space between these two little bones you have in front of your ears, is set to 14.3 centimeters, which is exactly the same as Kemar manikin.

DIFFERENT HEAD SIZE - DIFFERENT FREQUENCY RESPONSE

We've measured something with the Kemar manikin standard on, and then we've expanded to a really, really big head.

We've might exaggerated a little bit, but it has obviously shown us how the frequency response changed with it.

For the second test run, the width was extended to the maximum of the GRAS 45CC ability to still perform valid measurements, which is 17 centimeters. As you can see, the differences on the higher spectrum are quite obvious.

Empirical proof, clamping force changes with the head size. With it, you basically change the acoustic impedance inside the cup, because the volume changes in there and that will affect the final frequency response.

STRAPING MECHANISM FOR BETTER COMFORT

Clamping force is one of the two forces, that are actually keeping headphones on your head. In our case, we use a strapping mechanism from day one. One of the main benefits of this kind of design is related to comfort. First of all, it's self adjusting, so you can move it, give it to another recording artists in the studio very easily without adjusting and all this noise that other headphones usually make.

That's one benefit, and the most important part is the pressure on your head. With this design, the weight distribution is spread across a large area on your head. It actually minimizes, the side effect of pressuring your head on a single point, which is, having headaches. Traditional headbands rely on the foam to provide comfort, and have a predefined curve based on statistics of average head size and shape. In case your head is not in the median, you can experience uneven pressure across the headband touch points.

So this is the reason we've designed, used, and are gonna keep the strap on the new model, the S4R 2021.

EAR PADS - THE HEART OF COMFORT AND SOUND

In everyday communication with our customers I see how little our users understand the impact of ear pads on the sound. The majority considers ear pads a comfort feature and assigns the sound to the speaker. In reality, it’s both factors that contribute to the final frequency response, but If I was given a challenge to tune headphones either using ear pads or speakers, I’d go with the ear pads.

That said, the challenge to hit the right balance between comfort, size and sound when making and tuning ear pads is more than obvious.

I’d say it’s worth considering these four features:
1. Effect on the overall sound
2. Softness and feel on your head
3. Sound insulation properties
4. Heat dispersion

I’ll show you how two different ear pads change the acoustic impedance of the exact same headphones and makes them sound very different.

For example, these are our S4X headphones with original pads. We've changed the pads and repeated the measurements with the same settings.

The acoustic impedance changes a lot - dramatically actually, with the volume of the cavity. So for example, the previous ear pads on the older model, or on the S4R 2018, they are a bit shallower, which means there's less air in there.

As you can see, there is a massive difference in the mids section. A totally different headphones by changing ear pads and nothing else.

I’d advise changing your ear pads twice a year if you’re a daily user. Why? To keep the sonics and reliability in check.

Now here's the question. How to keep nicely balanced sound, and at the same time, make them comfortable? Soft pads will feel more comfortable and will seal nicely, but will also be more prone to deformation by the clamping force, hence changing the response quite a lot.

SOUND INSULATION

To get a really good seal using poly leather pads is usually the way to go. To demonstrate the insulation of fully poly leather pads vs hybrids that we use on S4X model, we've done a very simplified test. We've played 600Hz sine wave from a phone, in this noisy environment.

If I play 600Hz sine I can read the SPL at the ERP position of our RA 0039 coupler. Changing the pads results in a different reading. So again, it’s a balancing act between insulation, comfort and sound.

As you can see, a massive difference from over 70dB, to 66dB. So 4 or 5 dB change in acoustic isolation, just by changing the ear pads. That's the game we play - how to have a minimal sound leakage in and out at the same time, keeping the comfort.

HEAT DISPERSION

The final aspect of ear pads is their heat dispersion properties. We do not have professional tools to measure it properly. In a simplified test, this is how a hybrid ear pads versus poly leather ear pads concentrate heat around your ears.

Wearing one ear pads with a probe under the ear pads for 15 minutes, doing the measurements, changing the ear pads again for another 15 minutes, do the measurements again.

And here is how well they actually disperse heat.

The first measurement stopped at 33 degrees Celsius, the second measurement stopped at 34 degrees Celsius, again after almost 15 minutes, and nothing changed pretty much.

The sensitivity of the measurement device is big, which means that the temperature inside was quite constant in both scenarios with both ear pads. The second ear pads are a bit hotter, which is kind of logical  due to polyethylene material. The S4X ear pads are more airy, meaning less temperature is actually caught in there.

This is of great importance for prolonged use, when having just a portion of your head with higher temperature can result in headaches. Combining this with a bad headband design, you can easily have a pair of headphones that are not suitable for professional use.

ERGONOMICS AND THE CABLE ANGLE

Cable is probably the most overlooked part of comfort in headphones. In the past few months, we've reached out to you guys, asking you about the cable angle and we dived more and more into behavioral science. So basically how are you using our headphones, in what kind of scenarios, and what do you do when you use them?

For example, our headphones are often used behind a (mixing) desk when an engineer looks at the screen and back down to the faders and even further down, below the desk to some outboard gear.

In both these positions, the cable is pulling the headphones out of it’s perfect position (together with gravity) and affecting sound reproduction plus, the comfort and user experience.

When a recording artist, for example Frank would be playing a guitar, he would be looking down to the pedal board, maybe on the fret, and the cable would go either over the strings - so pulling forward or behind his back, pulling backwards.

If we change the angle position of the cable plug, this changes the game. The side benefit is that our headphones are symmetrical and the new model will also stay symmetrical. Meaning - you can flip them around, you can change the cable left to right and have the cable coming to the headphones over your back. So, if that would be the case at an angle - there is a lot less strain on the cable. And this change will be implemented in the 2021 model.

That’s how OLLO goes about comfort for the new S4R 2021 model. If there’s something we have missed. Feel free to give us your feedback or ideas at the S4R 2021 landing page, where we regularly publish updates on the process.

Thank you all, for being a part of this!

Rok Gulič