In this issue of audio-visual strategy, let’s talk about a special design in the speaker. That is, there will be a large hollow hole on the back of many speakers. What is the purpose of this design that seems to be very inconsistent with the overall tall shape of the speaker? Why design such a “hole”? Now, we will reveal the answer to this mystery for you.

What kind of speaker has a hole in the back?

When we visit offline audio product physical stores, we may notice that some speaker products have a large, hollow “hole” on the back, and some speaker products even have more than two such holes on the back , while the back of some other speaker products is completely closed, without such a hole.

At this point, many people have such a question in their minds. Since not all products have such a “hole”. Does that mean that this “hole” design is not necessary? Due to the fact that the “hole” does not look very good, should we choose those speaker products that do not have this “hole”?

To answer this question. We first need to figure out what kind of speaker products will add this “hole” design. Not all speakers will have such a “hole” on the back. If we look for the rules in these speaker products, you will find that it is generally easier to see this “hole” on the back of a large-sized speaker, while a small-sized speaker does not necessarily have this “hole”. For example, this “hole” cannot be seen on some desktop two-channel mini speakers for PC computers. On the contrary, floor boxes and bookshelf boxes produced by regular manufacturers generally have such a “hole”.

And, if you continue to look for the rules in depth, you will find another phenomenon, that is, the size of this “hole” seems to become larger and more in number as the grade of speaker products increases.

Yes, the rules we have drawn above are all correct. Next, let’s thoroughly decipher the above phenomena and see what kind of “mystery” this “hole” contains.

First of all, the reason why such a “hole” is designed on the back of the speaker box is to reduce the “standing wave” generated inside the speaker box.

“Standing wave” concept

Here we need to introduce a new concept, that is “sound field standing wave”. As listeners of music or background sound, we must hope that the sound we hear is clearer and better, and the higher the degree of restoration, the better. However, limited by the technical limitations of playback equipment and various interferences in the listening environment, the sound we actually hear will deviate from the original real sound to some extent. Among them, “standing wave” is an important factor that interferes with our hearing of real sound. In this guide, we only briefly introduce the “standing wave”, and will give detailed introductions to HIFI enthusiasts in subsequent articles.

Among all the “sound field standing waves”, the most disturbing to our music listeners is the “low frequency standing wave”. This type of “standing wave” has the greatest impact on human hearing. Therefore, the standing wave concept that HIFI enthusiasts talk about generally refers to “low frequency standing wave”.

“Standing waves” exist not only in the room, but also inside the speaker box. Because all sound waves are diffused from the inside of the speaker, therefore, to eliminate the “standing wave”, the “standing wave” inside the speaker cabinet must first be eliminated.

The “hole” design on the back of the speaker is to eliminate the “standing wave” generated inside the speaker box.

Since this “hole” can play such a big role, why don’t some speakers have such a design on the back?

Speaking of this, you who are smart must have discovered that the design of this “hole” is likely to be related to the maximum sound pressure parameter of the speaker. To put it bluntly, it is related to the maximum volume that the speaker can emit.

Small-sized speakers generally produce a lower volume, and the amount of “standing waves” generated inside the speaker cabinet is also relatively small, which will not significantly affect the actual sense of hearing. Therefore, the manufacturer of the speaker does not design such a “hole” on the back of the speaker. Therefore, this also confirms the second law we have drawn before. It seems that the higher the grade of the speaker, the larger the hole on the back is designed, and the greater the number. In fact, it is because the higher the grade of the speaker, it The maximum sound pressure increase that can be emitted has also increased, resulting in the need for larger “holes” to reduce the generation of standing waves.

The exact name of this “hole” on the back of the speaker

The “hole” on the back of the speaker should be called “speaker inverter hole” accurately. We already know that the reason why such a “phase-inverting hole” is designed on the back of the speaker is to reduce the “standing wave” generated by low-frequency sound waves inside the speaker box. For the effect of reducing the standing wave, we can simply understand that if there is no such “speaker port”, the sound of the speaker will be very “dull” when it emits bass. feeling, and it will be obviously distorted. This is why all subwoofers must have a phase port design.

This kind of distortion is more obvious on speakers that can produce a higher sound pressure level. This is why in a multi-channel system, the surround box and the center box often do not have a “speaker port”. Because the surround box and the center box are usually not used to emit a huge amount of low-frequency sound waves, there is no need for a “phase port” design. The front box that needs to bear a large amount of bass output, especially the large front floor box, must have a “speaker port” design.

The photo above is of the back of a pair of large three-way, four-driver floorstanding speakers. From this photo, we can clearly see that the speaker of this model has two “phase-inverting holes” on the back, the upper one is larger and the lower one is slightly smaller.

If there is no “phase port” for a pair of floor-standing speakers like this, the original high-fidelity sound quality will be greatly reduced. Especially when the volume is increased to a certain level, the performance will be particularly bad. A set of high-end floor-standing speakers will become disorganized and obviously distorted because there is no “phase port”. It can be seen that the “phase-inverting hole” design of the speaker is a very particular idea to improve the sound quality of the speaker.

An experienced speaker equipment manufacturer with a long history will definitely realize the importance of correctly designing the “speaker port”. In the actual design, the manufacturer also needs to adjust the shape, material, orientation, quantity and other factors of the inverter hole accordingly, and invest a lot of audio testing work. Install such one or more phase-inverting holes on the backs of different speakers as accurately as possible, so that the sound effects of different speakers can be optimized.

It can be seen that the design of speakers is really an art of excellence. Designing a small “inverting hole” requires a lot of manpower and energy to do a lot of detailed work. No wonder, when every HIFI enthusiast goes home with their favorite “speaker”, they will sincerely express unconcealable joy in their hearts.