The Loudspeaker Inverting Hole: How It Works and Functions

The Loudspeaker Inverting Hole: How It Works and Functions


The inverting hole the speaker a special design on the speaker cabinet to improve the bass response of the sound system. It is usually a tubular or cylindrical hole in the front panel or side of the speaker cabinet.

The Loudspeaker Inverting Hole: How It Works and Functions
The Loudspeaker Inverting Hole

What Is The Inverting Hole of The Speaker?
What is the hole in the back of speakers for?
When playing music, we will feel airflow coming out of it when we approach it. What is the function of it ?
Is it for ventilation, or is it simply for decoration?
If there are one or more air outlet holes on speaker boxes , it means that is a phase-inverted box, and this is a phase-inverted hole, which can expand the low frequency.

The inverting hole is a special design on the cabinet to improve the bass response of the sound system. It is usually a tubular or cylindrical hole in the front panel or side of the cabinet.
The function of the it is to combine with the audio drive unit (usually the woofer) inside to change the output mode of the bass. 
It is a key design element(also known as the inverted tube).
It is a part of the sound system, shaped like a hollow tube (plastic tube or metal tube), which can expand (enhance) low-frequency sound waves.
It is also known as an inverted tube, air hole, sound hole.

Please check the product with inverting holes, what they have in common is that they all have Slot Invert Holes on the back.
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Slot invert hole

What Are The Types of Invert Back Holes?
The invert hole of the speaker is a part of improving the performance and sound quality. 
Reflex invert holes come in different types and shapes to suit different types and design goals.
1. Bass Reflex Invert Hole
This is the most common type and is used to enhance bass output and extend low-frequency response. It is usually a round or rectangular opening located on the front panel or back of the speaker.

2. Slot Invert Hole
A slotted invert hole is a narrow slot, usually located on the front panel or bottom. They are used to limit wind noise while providing good bass.

3. Tapered Invert Hole 
The tapered invert hole shape tapers from one end to the other. This design better manages airflow, reducing eddy noise while maintaining bass performance.

4. Round Invert Hole
Circular invert holes are usually cylindrical or tubular and are also used to enhance low-frequency response. They can be more easily coordinated with the design and appearance of the sound box.

5. Passive Radiator
A passive radiator is a special invert hole that does not have a traditional diaphragm, but a passive element that resonates with the diaphragm. It is used to boost bass and can be very intricately designed to achieve specific acoustic goals.

6. Dual Invert Holes
Some speakers use two invert holes, located on the front and rear panels, to improve the uniformity of bass response.

Each type has its own unique acoustic impact and application scenarios, and audio manufacturers will choose the appropriate type according to the design goals and required acoustic characteristics. 
The design and location  have a significant impact on the performance and sound, so it is one of the key considerations in design.

The Cardboard Plastic Inverting Hole

What Are The Materials of The Speaker Invert Hole?
The primary material is usually chosen to optimize acoustic performance and durability. 
In addition to considering the cost, its material selection also needs to combine the material and design of box and use the best material.
ABS plastic is a common material, which has good mechanical properties, durability, and processability. ABS plastic is commonly used to make round and rectangular inverting holes.

2. MDF (Medium-Density Fiberboard)
MDF is a wood composite material with uniform density. It is an excellent damping resonance material and is often used in the cabinet and inverting hole of the speaker. 
It can be cut and machined to create various shapes and has excellent acoustic performance.

3. Metal
Some high-end speakers use metal for the invert hole, usually aluminum or steel. Metal vents can provide additional heat dissipation, but may introduce some vibration and resonance.

4. Rubber
In some cases, rubber can also be used to manufacture the sealing part of the invert hole to reduce air leakage and vibration transmission.

5. Cardboard
Cardboard material is often used in low price speakers.

6. Composite Material
Some premium products may use composite materials, such as fiber-reinforced plastic or composite wood, for greater performance and acoustical advantages.

Choosing a right material often depends on the audio design goals, cost and desired acoustic performance. 
Different materials have different acoustic properties, so audio manufacturers will choose the appropriate material according to product positioning and performance requirements.

How It Works: Why Is There A Hole In The Subwoofer Box?
The horn is generated by the vibration of the paper cone driven by the voice coil to repeatedly push the air. When the horn is working, it will generate sound waves before and after.
The working principle is based on the phase and interference principle of the acoustic wave. 
When the woofer inside the speaker vibrates, it creates sound waves that travel to the front panel of the speaker and out through the it.
This process involves two aspects:

1. Phase Inversion
It affects sound waves by introducing a phase reversal. 
When the sound waves pass through the hole, their phases are reversed, that is, the sound waves that were originally positive half cycles become negative half cycles, and vice versa. 
The effect of this phase reversal is especially pronounced for low-frequency sound waves.

2. Interference Effects
The phase-reversed sound waves interfere with the sound waves emanating from the woofer's front panel. 
Specifically, they add up in a specific way, depending on the wavelength and phase of the sound waves. 
This interference effect results in sound enhancement and attenuation within a certain frequency range.

In addition, when the speaker has an inverter hole, the air in the box communicates with the air outside the box. 
When the speaker vibrates, it will compress or expand the air inside, so that the air in the box will be discharged from the inverter hole. In other words, the air inside is driven out through the phase-inversion hole.

The inverting hole is equivalent to a second diaphragm that drives the air. 
This part of the energy is used to drive the internal air to vibrate, thereby widening the low-frequency range and sense of volume, and increasing the total output efficiency of it.

The ABS  Invert Hole

The Function of Invert Holes: Improve The Bass Response

It can significantly improve the bass response of the speaker. 
This is because it increases the output of bass frequencies and extends the frequency response of the bass. 
In loudspeaker design, engineers carefully calculate and select the diameter and length of the invert hole to ensure the desired phase reversal and interference effects at specific frequencies.

Applicability and Limitations
Reflex invert holes are not suitable for all types of audio systems. 
It is often used in enclosures designed as woofers since bass frequencies are more sensitive to phase inversion and interference effects. 
This design is less common for midrange and tweeter.

Also, the effect may vary from speaker to speaker, depending on the size, shape and material of the cabinet. 
Therefore, when designing a sound system, engineers need to carefully consider the use and parameter settings.

Invert Holes Is A Key Element In Design
As a key element in design, the invert hole remarkably improves the bass response through phase inversion and interference effects. 
It is a powerful tool for acoustic engineers to optimize the performance of sound systems.
However, to be fully effective, precise calculations and adjustments are required to obtain the desired sound characteristics within a specific frequency range.

Your Leading Supplier of invert Hole Design and speaker
Guangzhou AUSMAN Audio Co., Ltd is an audio design manufacturer integrating industry and trade in China. We focus on the R&D, manufacturing and exinvert hole of speakers for civilian use.
The speakers we supply include outdoor speakers, invert holeable trolley speakers, PA active speakers, floor-standing speakers (DJ Speaker), multimedia series and Sound Bar, etc.

AUSMAN may provide speaker design solutions (including inverting hole), and you can adopt OEM/ODM and other cooperation methods for production. 
Our production capacity (200,000 units/month) and mature R&D capabilities can serve as a strong backing for your brand expansion and sales.

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