There are some points to consider when choosing a headset. The "acoustic principle", one of the technical details we see while classifying the headphones, expresses the capsule design and acoustic character of the headphones. Before classifying the earphones according to their capsule designs, let's explain what the acoustic principle means.

What is the Acoustic Principle?
We define headphones as 'transducers' just like speakers and microphones. Headphones are devices that convert the sound signal into acoustic energy and therefore into sound. For this reason, the most important detail we expect in good headphones is the acoustic design of the headphones. We can say that there is a very serious acoustic engineering in well-designed quality headphones. In other words, it is not possible to get results by simply placing a driver in a round or oval shaped capsule. For this reason, it is necessary to design the capsule of the earphone well acoustically for a quality sensation.

To better understand the acoustic principle, we can compare the headphone capsule to a room. The acoustic character of the room where we listen to music affects our sensation. So the better the acoustics, the better our sensation will be. The same is true for headphones. The size and structure of the ear capsule, its internal acoustic arrangement and the material used are the most important factors affecting the sensation.

According to the acoustic principle, we classify capsule designs in 3 main groups:

  1. Close Back
  2. Semi-Open Back
  3. Open Back

It is possible to find these capsule designs in the around-the-ear, on-ear and in-ear models. At this point, it is necessary to choose according to our usage area and expectations.

First of all, let's give examples by explaining these capsule designs.

1) Close Back
These are designs in which the headphone capsule is completely closed, there is no opening on the outer side of the capsule, and has high insulation. It is preferred in studio recordings, outdoor location sound recordings or when we want to listen to music without being affected by external noise.

2) Semi-Open Back
These are headphones with designs that we can call a transition form between closed and open design. Although we cannot see the driver from the outside of the headset, they are models that allow sound output through the grilles on the back of the capsule. While giving the wide stage feel of the open earphone, they can also reflect the dark tone of the closed design headphones. It is weak in blocking outdoor noise.

3) Open Back
These are models in which the back of the capsule is designed completely open and the driver can be seen from the outside. The main reason why the capsules are made open as acoustic design is to prevent unnecessary resonances by expelling the power accumulated in the capsule, especially at high volumes, and to increase the sense of stage and dimension. Depending on the capsule width, design and the material used, they are the models that offer the most realistic sensation that can be obtained with a headset. Generally, high-end Hi-fi headphones are designed as models with open and wide capsule structure, high impedance and can be driven with professional amplifiers. On the other hand, there are many headphones with open capsule design in models that appeal to the end consumer.

It is possible to find an open capsule design in in-ear models as well as in around-the-ear and on-ear models. [video]

The Effect of Acoustic Principle on Sensation
While explaining the effect of the acoustic principle on the sensation, it will be useful to explain one by one according to the above designs and to mention the effect of the material used.

Sensation in Closed Designs: Although it varies depending on the design and material, we can say that the headphones with closed design have a dark, bodied and narrow-stage sensation. Here, it is useful to consider the inner volume of the ear capsule and especially the material structure. For example; Ear cushions…

Another factor that has an important effect on the sensation as well as the capsule structure in the headphones is the structure and material of the ear cushions ... While designing ear cushions, materials such as standard sponge and memory foam (Memory Foam) are preferred. In particular, the ear cushions, which we call memory sponge and use the materials that return to their old shape when crushed and released, take the shape of the ear contour, both grip the ear better and provide high insulation because it wraps around the ear without gaps. The other material that supports this is the coating materials on this sponge.

Real leather, artificial leather, synthetic material and fabric derivatives (velvet, microfiber) are preferred as the covering material on the sponge for the ear cushions. Since the acoustic characters and sound permeability of all these materials are different, the sensation is also affected. Since the ear cushion designs, in which the memory sponge is covered with genuine leather material, prevents the sound input as well as the sound output, the feeling of closure increases and a sound character that is considered to be 'dark', 'dark' or 'covered' emerges in the audiophile world. This accumulation and the vacuum effect created inside makes the bass frequencies sound stronger and more bodily.

Wear a leather ear cushion on one of the same two headphones and a fabric ear cushion on the other… Although everything is the same, only the ear cushions, so you will notice how the sensation changes when the acoustic design changes. You will observe that the leather one plays darker and with a body, while the fabric one plays a little softer and "spacious". It is possible to observe the change of the sound character of the earphone by changing the material and the internal volume of the earphone. Such changes are made consciously by many music lovers who are interested in the earphones and this is called "modification". In this way, the headphones can be personalized according to taste.

Sensation in Semi-Open and Open Designs: Although their insulation is not good, they are models that give better results in terms of sound input-output in a closed environment, unlike closed models, they are more detailed, spacious and have a wide-stage sensation. Depending on the capsule volume and material, they offer a more reference listening. As I mentioned above, as the acoustic balance in the capsule is provided better, unwanted resonances are also prevented. This helps to achieve a more realistic, voluminous feel and a wider stereo image. All details regarding the material and ear cushions also apply to the open capsule headphones. Especially in studio work, if the mixing process needs to be continued with headphones, open capsule models surrounding the ear will be useful.
To sum up; While the headphones are designed acoustically, criteria such as the capsule structure, the type of material used, the compatibility of the inner volume of the capsule with the driver's diameter are taken into consideration.

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