In the previous audio-visual guide, we mentioned that the design purpose of the “speaker port” is to reduce the “low-frequency standing wave” formed inside the speaker box. It makes the sound that the speakers can produce more realistic and natural. When we actually use the speaker, the “phase port of the speaker” cannot naturally play its due role, but we need to perform a series of correct operations and meet certain objective conditions before we can experience its function. practical effect.

Dear HIFI enthusiasts and friends, if the back of the speaker in your home is designed with an inverted hole, you might as well try this. Play a piece of music with a strong rhythm and a lot of bass, and then put your hand next to the port to feel what it feels like. Can you clearly feel the air shock wave ejected from the port along with the rhythm of the music?

There should be a certain distance between the phase port of the speaker and the back wall

The airflow ejected from the phase-inverted hole can be simply regarded as the sound waves generated inside the speaker squeezing each other, and then ejected from the phase-inverted hole. However, when they are ejected from the port, they don’t stop moving. The opposite of the phase port is the wall, and when the sound wave touches the wall, it will be reflected back. Let’s imagine if the speaker is placed close to the wall. The phase-inverting hole will be directly next to the wall, and the sound waves ejected from the phase-inverting hole will be reflected by the wall and re-enter the box of the speaker. In this way, the phase port did not play its due role, and the sound waves that could have been smoothly discharged from the speaker cabinet were forcibly pushed back.

All we have to do is to keep the sound waves ejected from the port from returning to the inside of the speaker box as much as possible. To do this, the correct approach is that we need to place the back of the speaker box at a distance from the wall. In this way, the intensity of the sound wave ejected from the phase-inverting hole reflected by the back wall will be greatly reduced, and the probability of the sound wave returning to the phase-inverting hole will also be reduced accordingly.

The size of the port hole of the speaker is different, and the reserved distance is also different

The size of the speaker port is generally designed to be larger with the increase of the maximum sound pressure level that the speaker can produce. In other words, speakers with larger port sizes generally have greater power requirements. The sonic energy ejected from the phase port is also more powerful. The requirements for speaker placement are also higher.

As for how far away from the rear wall it needs to be placed, different speakers are different. Adjust accordingly for the maximum sound pressure level your speakers are capable of producing. A relatively common reference value can be given here. Generally speaking, the larger-sized floor-standing speakers used in the home must be at least 10 cm away from the wall to correctly play the role of the speaker port. In some cases, it needs to be farther away from the wall, and the ideal value may be more than 15 cm. The small bookshelf box should be at least 6 cm away from the back wall.

Therefore, we need to place the speaker in a reasonable position so that the “speaker port” can play its due role.

The material used for the wall facing the port

Since our ultimate goal is to reduce the sound wave energy ejected from the phase port and be reflected by the back wall again, we need to adjust the distance between the speaker and the back wall. We can also adjust the material of the entire wall surface.

In most modern home environments, the walls of the living room and bedroom are generally painted with latex paint. How to reduce the reflection intensity of the wall surface to the sound wave without making a big fuss has become an intermediate topic we want to discuss.

Generally speaking, we first do the basic decoration of the house, and then consider doing some acoustic treatment on the wall. The formed latex paint wall itself is very flat and relatively smooth. Such a wall has a relatively strong ability to reflect sound waves. In other words, if no additional treatment is done, from a theoretical point of view, such a wall cannot be well matched with the phase port of the speaker.

To transform such a wall, we can make changes from the following two points:

1. Reduce the hardness of the wall surface

2. Reduce the flatness of the wall surface

Let’s look at the first point first. To reduce the hardness of the wall surface, we can achieve it by pasting sound-absorbing cotton materials on the original latex paint wall. The choice of sound-absorbing cotton does not have to be very expensive. As long as the surface of the wall can be softened, we can achieve our goal of reducing the intensity of sound wave reflection.

Our modifications to the surface of the wall do more than just cater to the speaker’s port, allowing it to function positively. We also want to reduce damage to the original surface of the wall. Therefore, the adhesive quality of the sound insulation cotton we choose must pass the test. If you need to tear off the sound insulation cotton in the future, the high-quality adhesive will not remain on the latex paint wall, and the process of tearing off the sound insulation cotton will become easier.

Once the wall is covered with sound-proof cotton, its hardness will be greatly reduced. The ability to reflect sound waves is reduced accordingly, and the sound waves ejected from the speaker port will be partially absorbed by the soft sound insulation cotton instead of being reflected back. This achieves our goal of reducing standing waves.

The second treatment direction of the wall is to reduce the flatness of the wall. In fact, after the sound-proof cotton is pasted on the wall, its flatness has decreased to a certain extent. To further reduce the flatness of the wall, we need a more professional acoustic design.

Professional acoustic design requires a relatively “big” renovation of the wall, which is usually planned during the pre-decoration of the house. Later stages are more difficult to achieve. We do not recommend ordinary HIFI enthusiasts to do such professional wall acoustic treatment.

But we can briefly introduce how professional acoustic wall treatment is done. In the professional world of acoustics, this type of wall treatment is known as creating a “bass trap.” The main method is to create a concave-convex effect on the original flat wall surface. The higher the degree of concave-convex wall surface, the stronger the ability to absorb the low-frequency sound waves ejected from the speaker port. If the room is large enough, the “bass trap” can be made very deep, and the ability of the back wall to reflect sound waves will be infinitely close to zero. In this way, the standing waves generated in the room will be greatly weakened. HIFI enthusiasts can maximize their listening experience to music.

How about it? After the above introduction, do you have a comprehensive understanding of the use of the speaker port? The small speaker port also contains profound knowledge! Therefore, when HIFI enthusiasts buy expensive speaker equipment, they must not forget that the placement of the speakers and the space for placing the speakers are also a factor that will make a big difference to the listening experience.