SOULNOTE Kato’s Design Philosophy Part 11.

SOULNOTE Chief designer Kato continues his essay series with the topic Chassis resonance and damping and how they affect sound. 

Chassis Resonance

In this issue, we will discuss the “resonance” of the chassis, which, along with damping, has a negative impact on the sound.
Every object has its own vibration. Therefore, if you strike an object, it will make a unique sound. This is inevitable, but if the sharpness of the natural vibration, or the strength of resonance (Q value), is high, a strong and long-lasting sound like “kahn” or “keening” will be produced. This affects the sound and makes it sound habitual. Therefore, strong resonance should be avoided.
Similar to chassis, the sound of an electrical component can be predicted by the sound it makes when it is struck. For example, a film capacitor that makes a sharp and sharp sound when tapped also has a harsh sound quality. We feel that physical characteristics have a stronger influence on sound quality than electrical characteristics. 

The guitar does not sound when the strings are slackened.

To suppress strong resonance, damping materials such as rubber are generally used. This will certainly suppress resonance, but at the same time, the sound will be damped and ruined. In other words, damping degrades the sound more than resonance. This will be discussed in more detail later.
Now, there is a simple way to reduce the intensity of resonance while avoiding damping. Loosen the structure. By doing so, the overall strength of the chassis is reduced, and the strength of the resonance is reduced. Loosening the structure also has the advantage of not transmitting the resonance of one member to another. It is easy to understand that the strength of resonance is reduced by imagining a guitar with relaxed strings. 

SOULNOTE’s unfastened top cover

In the previous issue, I mentioned that as soon as the top cover is secured tightly with screws, the sound is ruined. We discussed air damping as the cause of this problem. Another possible cause is that the resonance of the entire chassis becomes stronger. This is because fixing the top cover creates a monocoque structure and increases the strength of the entire chassis. If tightening the top cover not only makes the chassis less open but also makes the sound harder, this is the cause.
SOULNOTE’s unfixed top cover is an idea to prevent air damping, suppress the strength of the resonance of the entire chassis, and prevent the resonance of the top cover from propagating to the chassis. 
Also, total aluminum CHASSIS looks gorgeous but is prone to strong resonance.SOULNOTE’s chassis is made of an optimal combination of aluminum and steel plates. The strength of the joints is also kept to a minimum to control resonance.
Even so, the chassis still vibrates. It receives sound pressure and vibration from the power transformer. It is very important not to transmit this to the printed circuit board. This is because most of the electrical components are mounted on the printed circuit board and vibrate together with the printed circuit board. 
However, it should not be floated by rubber, etc., because it will be affected by damping.
In SOULNOTE, the printed circuit board is supported at three points and not fixed. It is not fixed but only placed on three pillars without stress, in order not to transmit the vibration of the chassis to the PCB and to avoid the strong resonance of the PCB itself.
Also, the terminals are not fixed to isolate the vibration of the connecting cables. Furthermore, the damping effect of the chassis due to the weight of the connecting cable is also reduced.

Resonance and damping

Both are problems that should be avoided, but they have different effects on sound. Resonance is primarily a frequency-axis problem, while the damping is a time-axis problem. In other words, resonance creates peaks at certain frequencies but has little effect on velocity on the time axis. On the other hand, damping is a delay on the time axis that blurs the sound. I think the emphasis in audio up to now has been on suppressing resonance. However, I consider damping to be just as much or more problematic. This is because I believe that human hearing is highly sensitive to the time axis. This is why SOULNOTE’s design philosophy is completely different from that of other companies.
In my next entry, I will write about the criteria for sound quality in product development. This is the most important story that relates to everything I have said so far. When I develop SOULNOTE products, I listen and judge everything. However, I do not create any sound. I will write about the meaning of this.