In this issue, as a continuation of the previous “What is required for front housings,” I will discuss “Characteristics of different materials for front housings.
If you have not yet seen our last post, please see that first.
The topics of this issue are as follows
1) A variety of housing materials.
2) Materials commonly used in 634EARS.
3) Characteristics of each material.
4) Which material is suitable for the front housing?
5) Which material to choose as a front housing?
1) A variety of housing materials.
There are many different materials used as front housings.
There are many different types of materials, including metal, resin, wood, and ceramic, each of which has its own unique characteristics.
For example, there are various metals such as aluminum, stainless steel, brass, copper, titanium, magnesium, etc., as well as resins and wood, each of which again has many types.
2) Materials commonly used in 634EARS.
Since there are so many different types of materials, let’s start with the materials commonly used for front housings in 634EARS.
The materials used for front housings in 634EARS are mainly metal. In the past, wood and other materials were used in rare cases, but now they are mostly metal materials.
The four main materials used are aluminum, brass, stainless steel, and titanium. Some are plated or anodized as surface treatment.
Copper and magnesium alloys have been used for the front housing in the past, but I have not used them because they are difficult to handle and do not match the sound quality.
3) Characteristics of each material.
Aluminum)
Aluminum is characterized by its very light weight. It is particularly light compared to other metal materials due to its low density. Its specific gravity is only 1/3 that of iron, brass, and copper. In other words, it is a low-density material among metal materials.
Because of its low density, the speed of sound propagation (Young’s modulus/density), which is calculated from density and Young’s modulus, is high.
However, it is not suitable for the front housing of D-type drivers, which require vibration suppression, because it has low internal damping and does not absorb vibrations very well. Therefore, it is not suitable for the mounting portion of a D-type driver, where vibration must be suppressed.
However, the lightness of the sound due to its light specific gravity is an attractive feature of aluminum.
On the other hand, it is not good for low bass and heavy sound.
Stainless steel)
Stainless steel is characterized by its high specific gravity and high internal damping rate of vibration among metal materials.
Because of its high specific gravity, stainless steel is characterized by a heavy sound, the opposite of lightness, and produces a hard and strong sound.
In addition, the internal damping rate of vibration is higher than that of other metallic materials, making it an ideal material for “vibration suppression” required for driver installation parts.
However, this also means that stainless steel is inferior to aluminum in terms of “transmission of vibration without loss.
For these reasons, it can be said that stainless steel is suitable as a material for suppressing driver vibration and for producing a strong, hard sound with a sense of weight and presence.
Brass)
Brass is characterized by its high specific gravity. It has an even higher specific gravity than stainless steel.
Because of its high specific gravity (density), the speed of sound transmission (Young’s modulus/density) is even slower than that of stainless steel.
Therefore, the sound tends to be a little slower.
Whether this characteristic is considered an “easy listening sound” or a sound with a slow start-up, there is a big difference in taste for brass.
Titanium)
Titanium is about half the specific gravity of brass, lighter than stainless steel and heavier than aluminum. It is also a material with very low internal loss.
Therefore, among the four materials introduced here, titanium is the material with the fastest sound transmission speed and the least sound reduction.
In other words, it is not so desirable in terms of “vibration suppression,” but in terms of “transmission of vibration without loss,” it is considered a more suitable material than aluminum.
However, its specific gravity is lighter than that of stainless steel or brass, and the sound is rather light.
It is also more expensive than the other three metals, and its hardness and workability make it a very difficult material to handle.
There are quite a few differences in characteristics among the four types of metals.
There are many other types of materials besides these four, so let’s consider them as well in the next section.
4) Which material is suitable for the front housing?
Now that we know the characteristics of the four types of metal materials commonly used for 634EARS, we would like to consider what other materials are suitable for the front housing, including other materials.
To give you some examples of materials other than the four mentioned above, there are copper and magnesium alloys for metals, ceramic materials, wood, and resin materials for other materials.
Copper is difficult to handle because it rusts easily and its properties can change depending on how the surface is protected. Magnesium alloys are good for reducing vibration, but their sound attenuation rate is too high.
Ceramic and some types of wood are porous materials that allow sound to enter the material and attenuate the sound too much, and wood is not stable enough to be used as a front housing because of individual variability.
Also, wood is not strong enough to be processed thinly, so it has to be made thicker, which narrows the sound path (nozzle) and darkens the tone because of the thickness required.
Resin material is very easy to make and handle, but its specific gravity and internal loss are inferior to those of metal.
The ideal front housing material is one that has the right specific gravity, fast sound transmission, and low internal damping.
However, there is no one material that completely satisfies all of these factors, and in fact, every material has its own advantages and disadvantages.
5) Which material to choose as a front housing?
So what is the best of these materials to choose for the front housing?
Well…that is a very difficult question.
Ideally, you should choose the one that matches the characteristics of each material and the sound you are aiming for, depending on what kind of sound you want to make from the earphones.
However, there are also some materials introduced here that are considered to be acoustically good.
Among the materials introduced here, there is one that satisfies to some extent the following three requirements: moderate specific gravity, fast sound transmission speed, and low internal damping. It is titanium.
Titanium has low internal damping, transmits vibrations without loss, and transmits sound at a high speed. It is heavier than aluminum and lighter than stainless steel, although it is a little lighter in specific gravity.
However, specific gravity and low vibration damping are the only aspects of D-type drivers that are not so good in terms of vibration suppression.
Again, the separation is getting a little long and complicated, so I would like to focus on titanium in the next section.