[Reprint] As an important part of the Bluetooth headset, who is more important, the codec, the manufacturer’s tuning, and the driver unit?

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Referring to the previous post, there is a big difference between the codec, the manufacturer’s tuning and the drive unit, which are the most important factors affecting the sound quality of the Bluetooth headset. For everyone who has different opinions on which part of the Bluetooth headset is more important, I will express my views.

First of all, the Bluetooth transmission intermediate device needs to be transcoded. Taking MP3 files and SBC as an example, the transcoding process is MP3->PCM->SBC->PCM. Each transcoding will lose details. The codec is the core part of the headset. There is a gap between the sound quality effects emitted by SBC, AAC and LDAC, LHDC in the process of encoding the signal from the mobile phone codec to the earphone receiving and then decoding it through the earphone codec. In the previous post, it was mentioned that SBC and AAC are Lossy sound quality output LDAC and LHDC are lossless sound quality output. And what codec is your headset? The codec in the mobile phone emits the transmission bit rate of the corresponding codec. For example, if you are the codec of SBC, what you transmit from the mobile phone is the transmission code rate of SBC. It is impossible that your headset is the transmission code rate of LDAC transmitted by SBC to you. So from the very beginning what codec you have in your headphones determines whether your sound quality is lossless or lossy.

Let’s talk about the drive unit that is second only to the codec. The drive unit of the earphone is the speaker used by the earphone to make sound. It is a simple speaker. It can make its own vibrating element (different unit vibrating elements) vibrate by receiving the analog signal of the sound source and be driven by electricity, vibrating the air and being vibrated. The air in the earphone generates pressure waves, thereby producing sound through the structure of the ear. Its principle is to convert electrical energy into sound energy. The common headphone drive unit is composed of three parts: magnet, drive coil (voice coil), and diaphragm. When an electrical signal passes through the magnet and drive coil, it causes the diaphragm to vibrate and produce sound. Generally speaking, the stronger the magnet, the better the acoustics.

Are bigger drive units better?

In the case of using the same drive unit technology, the generally larger size (diameter) drive unit is better in overall sound quality, or at least in terms of bass. But it’s more accurate to say that the “loudness” is better without a headphone amplifier. Larger diaphragms make for better bass, but larger drivers make it difficult for headphones to reproduce highs.

Usually in-ear headphone drivers are in the 8mm to 15mm diameter range, while headphone drivers are in the range of 20mm to 50mm in diameter.

The size of the driver does affect the output and frequency range of the headphone, but the technology type of the driver has a far greater impact on the sound quality than the size of the driver.

What are the different headphone unit technologies?

Each driver unit has its own specific way of creating sound, which explains the many different types of headphones that exist. Let’s take a look at the different types of headphone driver technology in the mainstream.

Balanced armature (moving iron)

Generally, everyone will hear the word moving iron unit in advertisements. Its scientific name is Balanced Armature Driver.

Among the common headphone drive units, the moving iron unit is the smallest, so it is usually used for in-ear headphones and hearing aids.

The name of this unit says it all: it has a magnetic armature on a pivot that rotates and moves between two magnets. When the armature is at the center of the magnetic field, the net force acting on it is zero. This is the balance point of the magnet armature. When current is fired at the coils around the armature, the resulting force will move the armature. When this happens, the diaphragm also moves and produces sound.

The working principle of the moving iron unit (original image: knowles corp)

Although a certain amount of force is required to keep the armature balanced, it is still a simple and effective technique. Some headphones use many armature drivers, such as 1MORE’s triple drivers. With multiple moving-iron units, each unit has a specific frequency range: one unit handles the fundamental frequency, while the others work with a specific frequency. Most in-ear monitor headphones come with 1-4 moving iron units.

Some well-known models of moving iron units

Moving iron units are highly efficient, produce amazing treble response, and are also the most expensive. Especially when the moving iron is compared with the moving coil unit, the cost of the moving iron earphone is very high.

Dynamic (moving coil)

The dynamic unit, scientific name DynamicDriver, is the “moving coil” that everyone encounters the most.

The moving coil compound is very common in the daily use of headphones, which is often referred to as “speaker type”. The unit is stationary, and the body is made of very durable, powerful neodymium magnets that generate a static magnetic field. A moving coil unit operates with current passing through the voice coil and moves in a back and forth manner. This part moves according to the signal it receives. The voice coil is attached to a thin membrane that amplifies all vibrations, which is what you hear from the headphones.

The working principle of the moving coil unit

Dynamic drivers are very affordable, which is why they are used in traditional, low-end headphones. The assembly is lightweight, very compact, and durable even when the headset is heavily used. Of course, dynamic drivers don’t produce the best sound, and sound quality can vary depending on the type of headphone material. It also features the best feedback sound possible without the need for an external amplifier. This is because the moving coil unit can be made very large, so it can have a larger diaphragm, which can provide strong bass and obtain a good sound pressure without consuming too much electrical power. Since the size can be made larger, and the contemporary people’s preference for heavy bass, it is often used in earmuffs/over-ear style headphones with heavy bass as a selling point.

Static (Capacitance)

Compared to ordinary moving coil units, electrostatic drive units operate using a different technology. An electrostatic cell works by placing an electrostatic charge on a very thin film between two pieces of metal. When the signal passes through the metal sheet, the film moves back and forth due to natural electrical motion attraction and repulsion. This is the same principle as the condenser microphone, but in the opposite way, one is to use this principle to collect sound waves and convert them into electrical signals, and the other is to use this principle to convert electrical signals into sound waves.

The very thin membrane or diaphragm does not store or retain energy and has zero tolerance, so it does not have the distortion commonly found in moving coil headphones and speakers. Therefore, the characteristics of electrostatic unit headphones are ultra-small distortion, delicate sound quality, transient response and detailed expression. This technology is very precise, but very sophisticated and difficult to develop, which is why electrostatic units are only commonly found in professional-grade audio equipment.

Electrostatic (capacitive) units are common in high-end headphones. These types of units are expensive and require a dedicated headphone amplifier. However, the headset is bulky and heavy, and has relatively high requirements for moisture resistance. This additional requirement increases the cost of using such headphones.

Planar Diaphragms (Planar Magnetic, Orthogonal, Flat)

Planar diaphragm unit, also known as plane magnetic unit, is the abbreviation of Planar magnetic drivers. It also has a name called “Orthogonal Unit”.

This technology was invented by Yamaha and was originally used in open-back over-ear headphones. Flat-diaphragm drivers work on the same principle as moving-coil drivers, also using magnetic fields to create sound. But the biggest difference from the moving coil unit is that it is not the voice coil that moves back and forth under the action of magnetic force, thereby driving the flat diaphragm to vibrate, but the diaphragm is directly moved by the magnetic field to produce different kinds of sounds.

With less “drive” error loss of the voice coil, the flat-diaphragm unit can create better, professional audio with no distortion, good bass response, and high transient response, and for this reason, it It is widely used in high-end headphones.

A flat diaphragm (transparent) with a thin conductive component (green) is suspended in the permanent magnetic field of magnets (orange) on both sides, and the film vibrates and makes sound due to the magnetic influence of the conductive part of the film.

Also, since the working principle is not a metal coil that drives the diaphragm, but a magnetic force that drives the diaphragm, the unit must use larger magnets or vibrate evenly by using multiple magnets. This adds to the overall weight and bulk of the headset, and also requires the use of an external amplifier to increase overall power and output.

Meanwhile, companies like Oppo have developed new flat-diaphragm-unit headphones to address some of these shortcomings. For example, Oppo’s PM 1 flagship headset that won the International HIFI Award is a lightweight, low-impedance flat-diaphragm unit headset, weighing only 395 grams.

Ring iron

This is a hybrid unit technology that has emerged in recent years. Strictly speaking, it can only be called a “drive solution” because it is a combination of a moving coil unit and a moving iron unit in the earplugs.

The advantage is that the advantages are complementary. The low frequency advantage of the moving coil unit and the high frequency advantage of the moving iron unit complement each other, and the performance is comprehensive and balanced.

The disadvantage is that it is very difficult to select the crossover point. In short, it is very difficult to combine two good sounds of low frequency and high frequency into a good sound. A well-tuned ring iron earphone often loses its price advantage.

Bone conduction (magnetostriction)

This is also a recently popular drive unit technology. The so-called magnetostriction means that the core of these earphone units is an electromagnetically driven telescopic working motor, which uses the telescopic work of the motor to generate vibration.

And these vibrations do not drive any mechanical or electronic sound-producing units, it drives the human organs. The mechanical movement of the unit vibrates the temporal bone and the mandible, and the conduction resonance of the fracture transmits the sound directly into the inner ear, bypassing the eardrum, and receiving the sound information directly from the auditory ossicles. That’s why people prefer what’s called a bone conduction drive unit, which is helpful if you need to keep your ears out of the way during exercise or water. Therefore, many sports headphones currently use this technology.

Sound induction paths for bone conduction (red line) and air conduction (blue line)

The bone conduction unit makes the sound clearer and louder, especially for those who need hearing assistance and those who need to work or move without their ears being obstructed. Of course, due to the “precision” problem of the vibration of skin and bones, the sound quality may not be as pure as ordinary headphones, and it is easy to leak sound.

As for training, both Samsung and Sony have strong training capabilities. After all, Sony’s Dafa is not a vain name. Samsung, AKG, is one of the well-known brands in the audio field and one of the world’s four largest headphone manufacturers. Samsung’s training ability is beyond doubt. Apple, as one of the top 500 companies in the world, Apple’s biggest strength is its banknote capability. The headphone tuning of Edifier is also quite good in China, especially the low-latency GT4, the flagship game of HECATE, 45ms can hardly feel the delay of GT4s Thunder version 15ms is a must. The only regret is that GT4s Thunder version is SBC

As for the rising stars such as oppovivo Xiaomi Black Shark, they will continue to work hard to catch up with Sony, Samsung and Apple as soon as possible.
Finally, I will make a summary. My opinion is that the codec is the core part of the headset and must be put in the first place. Your codec can’t transmit the SBC transmission code rate from the mobile phone. Originally, the sound received by Lin Junjie’s sound headset is stale. Lin Junjie’s voice, no matter how good your drive unit is, no matter how good the manufacturer’s tuning is, there is no way to restore his own voice. And everyone’s voice has its own unique characteristics and unique taste. This is how the manufacturer adjusts the drive unit. Well there is no way to make up for it. So my point of view is that the codec is the first, followed by the drive unit, and then the manufacturer’s tuning. Well, that’s the end of my point of view, and I hope you can add more.

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