Which Enclosure Is Best For Speaker?

ByScarlett Evans

Speaker enclosures play a critical role in the performance of loudspeakers. The enclosure helps control the vibrations produced by the driver and can optimize the frequency response. Selecting the right enclosure for a speaker driver is essential to achieve the desired sound reproduction. The enclosure interacts with the driver’s acoustic properties and together they behave as a system.

There are several main types of speaker enclosures, each with their own advantages and disadvantages. The most common types include sealed, ported, passive radiator, transmission line, horn loaded, infinite baffle, and bandpass. The enclosure can significantly impact sound quality, efficiency, bass response, power handling, and directivity. This article provides an overview of the major enclosure types and key factors in selecting the optimal enclosure design for a given speaker driver and application.

Sealed Enclosure

A sealed enclosure is a fully enclosed speaker box with no ports or openings. This creates an airtight environment inside the enclosure. Some key pros and cons of sealed enclosures include:

Pros:

Cons:

  • Typically requires more amplifier power compared to ported enclosures
  • Less efficient than ported designs
  • Lower maximum sound pressure level (SPL) output
  • Can require large enclosure size for low frequency extension

Ported Enclosure

different types of speaker enclosures such as sealed, ported, passive radiator, etc. have various pros and cons to consider when selecting the optimal design.

A ported or bass reflex enclosure uses a port or vent to enhance bass response. The port is tuned to resonate at a specific frequency, boosting low frequency output. Ported enclosures can provide louder and deeper bass compared to sealed enclosures, but have some drawbacks.

Some pros of ported enclosures include:

  • Increased low frequency output and bass extension below the port tuning frequency
  • Greater efficiency and louder bass compared to a sealed box of the same size
  • The port provides damping control improving transient response

Some cons of ported enclosures include:

  • The speaker has reduced damping and control below the port tuning frequency which can increase distortion
  • Careful box and port design is required to prevent port noise
  • The bass response has peaks and dips and is not as flat as a sealed enclosure

Overall, ported boxes can provide louder, deeper bass at the expense of some control and flat response compared to sealed enclosures. Careful design is required to optimize the performance and prevent issues like port noise. As one expert states, “A ported box can sound very boomy at higher frequencies as well, and have their own issues, but they are ‘flat’ in response” (source). The choice between ported vs sealed often comes down to the desired balance of efficiency vs damping and transient response.

Passive Radiator

A passive radiator is a type of speaker enclosure that utilizes a passive driver to enhance low frequencies. The passive radiator is not powered directly, instead relying on the movement of air inside the enclosure to produce sound. Here’s how passive radiators work:

A passive radiator looks similar to a regular speaker driver, with a cone, surround, and basket. However, it does not contain a voice coil or magnet. Instead, the passive radiator resonates at a specific frequency based on its mass and the enclosure volume.

As the active driver moves back and forth rapidly inside the enclosure, it compresses and rarifies the air. This fluctuating pressure causes the passive radiator to vibrate at the same frequency as its resonant frequency. The movement of the passive radiator cone in turn creates low frequency sound waves.

The combination of the active driver and resonant passive radiator allows the system to reproduce lower frequencies than a sealed enclosure of the same volume. Passive radiators essentially act as a supplement to the active driver at the rolloff frequency.

The resonant frequency of the passive radiator is determined by its mass, the compliance of its suspension, and the interior volume of the enclosure. Adjusting these parameters allows tuning the passive radiator to augment the low end response at a desired frequency.

Overall, passive radiators provide increased low frequency output compared to a sealed box, while avoiding the complexity of a ported design. The passive nature prevents the potential for port noise found in some ported enclosures.

Transmission Line

A transmission line enclosure utilizes a long tunnel or pathway for sound waves to travel through inside the speaker cabinet before exiting the port. This tunnel is designed to be around 1/4 the wavelength of the lowest frequency the speaker will produce (1). The length and cross-sectional area of the transmission line are carefully tuned to provide an impedance-matching environment for the speaker driver. This allows the driver to couple efficiently with the air mass in the line. The resulting bass response is very accurate and clean.

Transmission line enclosures have some key advantages compared to other designs:

  • Excellent low frequency response due to the long pathway enhancing driver/port tuning.
  • Minimal distortion since the driver is unloaded gradually along the line’s length.
  • Good transient response as the enclosure doesn’t store much energy.
  • Tunable design parameters like line length and shape to optimize performance.

The downsides of transmission line enclosures include their large size, complexity to construct properly, and sensitivity to internal damping. Overall, transmission line designs deliver superb bass accuracy and definition for critical listening applications (2).

Horn Loaded

Horn loaded speaker enclosures are designed to control the dispersion of sound waves produced by the driver. The horn acts as an acoustic transformer, gradually expanding the area that the sound waves emanate from. This allows the speaker to efficiently transfer acoustic energy into the air.

Horn loaded enclosures work by coupling the driver diaphragm to a horn shaped flare. The small throat opening of the horn is attached to the driver. As sound waves emerge from the driver into the horn, they progressively expand. This expansion controls the dispersion pattern, while also increasing the acoustic loading on the diaphragm. The horn effectively transforms the high acoustic impedance at the driver into a lower impedance at the horn opening. This improves the overall driver efficiency across its operating bandwidth.

Properly designed horn enclosures can significantly increase a driver’s sensitivity and power handling capabilities. The controlled dispersion can also improve sound coverage in some applications. The primary downsides are increased size and limited low frequency response compared to other enclosure types. Horn loaded designs are often used for high frequency drivers in professional sound reinforcement and theater applications.

Infinite Baffle

An infinite baffle enclosure is essentially a giant sealed enclosure with one open side where the speaker driver is mounted. The speaker driver is mounted in a wall or baffle that separates the front sound waves from the back sound waves. The open backside allows the rear sound waves to dissipate into a much larger space, essentially making the enclosure “infinite” in size and volume.

In an infinite baffle, the front sound waves are isolated from the rear sound waves emanating from the back of the speaker driver. This prevents the normal cancellation that occurs from the colliding front and rear sound waves in a typical sealed enclosure. The result is improved bass response down to the speaker’s free-air resonance frequency.

According to Kicker (https://www.kicker.com/app/misc/support/tech/tech_papers/docs/InfiniteBaffleGuidelines.pdf), infinite baffle enclosures work best with subwoofers that have a low free-air resonance and low Qts ratings. The larger the baffle and space behind it, the better the bass performance. Infinite baffles can provide great bass extension in home theater and car audio applications when properly implemented.

Bandpass

A bandpass enclosure uses a combination of ported and sealed enclosures to create a passband in which the subwoofer plays. The speaker fires into a smaller sealed chamber, which is connected via a port to a larger external chamber. This port between the two chambers acts as a low-pass filter, only allowing lower bass frequencies through while blocking out higher frequencies.

The design provides increased efficiency within the passband, allowing the subwoofer to play louder compared to a standard sealed box. However, because it blocks out higher frequencies, the frequency response is more limited compared to other enclosures. Bandpass boxes also tend to be larger due to requiring two chambers.

Bandpass enclosures can provide very high output at certain low frequencies, making them common for car audio applications focused on hard-hitting bass. However, their limited frequency response makes them less ideal for music applications. Proper design is crucial to achieve optimal performance based on the driver and desired frequency range.[1]

Comparison

When choosing the best enclosure for a speaker, it’s important to compare the pros and cons of each type:

Sealed enclosures provide good low frequency response and power handling while having a smaller size. However, they may lack bass extension compared to other designs. Ported enclosures can extend the low frequency response but require more space and can have issues with port noise. Passive radiators act like a port but avoid port turbulence issues – though they also need more space. Transmission lines provide excellent frequency response but are complex and require very large enclosures. Horn loaded enclosures are highly efficient but can suffer from distortion and limited frequency response. Infinite baffle mounts the driver in a wall so no enclosure is needed, but performance depends on the characteristics of the wall. Bandpass enclosures isolate a fixed frequency range but have limited applications.

Overall, the ideal enclosure depends on the specific speaker, desired frequency response, available space, distortion tolerance and other factors. Sealed boxes offer the simplest and most flexible design while ported and passive radiator enclosures provide extended bass if properly designed. Horns and transmission lines can optimize efficiency and frequency response but require more design expertise. Carefully evaluating the tradeoffs allows selecting the best enclosure for a given speaker setup.

Conclusion

In summary, there is no single “best” enclosure for all speakers and purposes. The optimal enclosure depends on the specific driver properties, intended frequency response, output level desired, and physical environment limitations. However, some general guidelines can be made:

Sealed boxes offer good low frequency extension and minimal distortion, making them a common choice for accurate audio reproduction in home theaters or studios. Ported boxes can provide greater bass output from smaller enclosures but require more design effort to optimize the port tuning. Passive radiators act as tuned ports but avoid port turbulence noise. Transmission lines offer excellent bass precision but are large. Horns provide extremely high sensitivity but have limited low frequency response. Infinite baffles have very wide dispersion but limited low end. Bandpass boxes isolate a specific frequency range.

For typical home hi-fi use, a properly-designed sealed or ported box offers the best balance of small size, good bass extension, low distortion, and simpler construction. Transmission lines and horns tend to be impractical for most home settings. Carefully modelling the system requirements and driver parameters using available enclosure design software helps ensure the best real-world results.

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