Let me explain again about the difference in sound based on the selection of wood or metal for the backplate of the rear housing, as I have mentioned several times before.
The materials for the backplate are very diverse, and wood varies from piece to piece. Therefore, instead of individually discussing each piece of wood, I believe it’s easier to understand how the sound changes based on the hardness and density of the material.
To begin with, it’s important to understand the basic role of the rear housing.
Role of the Rear Housing:
The housing of earphones is divided into front and rear by the dynamic driver.
This time, I will explain about the rear housing behind the driver.
The interior of the rear housing plays a role similar to a spring, moving the diaphragm by the air inside the housing, and by compressing and rebounding the air inside the rear housing due to the movement of the diaphragm, it affects the degree of movement of the diaphragm.
I often liken the rear housing to instruments like drums or percussion. The diaphragm is like the drum head, and the drum shell (body) is like the side walls of the rear housing, while the bottom is akin to the backplate.
Now, what kind of changes in movement would occur in the diaphragm depending on whether the rear housing material is “hard,” “soft,” “high density,” or “low density”?
Hard Material:
If the rear housing material is hard, the material of the housing does not deform due to the pressure of the air inside the rear housing when the diaphragm moves, so the air rebounds quickly and sharply.
As a result, the diaphragm moves quickly and finely. This kind of diaphragm movement makes it easier to produce tight, high-resolution, clear sounds with a fast attack and precise contours.
Soft Material:
If the rear housing material is soft, the material of the housing is easily deformed by the pressure of the air inside the rear housing when the diaphragm moves, so the air rebounds slowly and gently.
Consequently, the diaphragm moves slowly and broadly. This kind of diaphragm movement tends to produce thicker sounds, particularly enriching the mid to low range. However, compared to hard materials, the contours of the sound might be less sharp, giving a slightly softer impression.
High Density:
If the rear housing material has high density, it strongly rebounds against the pressure of the air inside the rear housing when the diaphragm moves. This means that the spring of the air inside the rear housing becomes stronger.
Therefore, the diaphragm moves strongly and broadly. This kind of diaphragm movement tends to increase the sound pressure, resulting in powerful sounds. However, it also tends to produce more pronounced attacks and peaks.
Low Density:
If the density inside the rear housing is low, some of the pressure of the air inside the rear housing is absorbed by the material when the diaphragm moves, reducing the air rebound. This means that the spring of the air inside the rear housing becomes weaker.
Therefore, the diaphragm moves gently and slightly. This kind of diaphragm movement makes it easier to produce soft and gentle sounds. As a result, the sound pressure is restrained, especially the bass tends to be more subdued.
Comparative List of Wood Hardness and Density:
Taking these into account, let’s look at the list of woods commonly used in 634EARS, which are rated for hardness and density on a scale of 1 to 10.
*These figures are known at this time and may change in the future.
Until now, I have used the criterion of “specific gravity,” but now I use the criterion of “density” because it is not the same as actual density.
These values are actually quantified based on my own experience and feel of cutting and shaving wood.
In addition, the “Dry” and “Oil” items are described for wood that is particularly dry or oily.
A-E group similar items based on hardness.
F is a special wood (material).
The table is designed to give you an idea of the hardness and density of the wood and how it will sound in comparison to other woods.
Please note:
While the list quantifies the hardness and density of the wood and makes it easier to grasp the sound image, there are some points to consider.
The differences in sound due to hardness and density are only applicable when compared to “other woods.”
For example, using Snakewood, which has a hardness of 10, does not necessarily mean that it will exhibit the characteristic sound of hard woods (high resolution, clear, sharp, tight).
It means that compared to woods with hardness ranging from 7 to 9, such as Cocobolo, it will have a sound characteristic of harder woods.
Therefore, the sound tendency of the wood alone cannot be clearly understood since it depends on the base earphones and individual perceptions. It can only be used as a guide to compare what kind of sound it will produce compared to other woods.
So, it’s not possible to answer the question, “What kind of sound does this wood produce?” Instead, it’s possible to answer questions like, “If this wood is used in a headphone called XYZ, how does it compare to Indian Rosewood in terms of sound?”
This was the most basic explanation, so next time, based on this, I would like to delve a little deeper into the explanation.
