Did you know that a sound system’s quality is not just dependent on the speakers themselves? There are many factors that will affect the overall performance of a loudspeaker, but this is one of them that people often overlook. Hence, if you want to be an informed audio enthusiast, you need to find out what is a Speaker Enclosure!
This would be another one of those article where we will be discussing a major subject, which requires a lot of time to cover. But as always, I will try to provide you with “bite-sized” information that will cover enough of the basics, such as design components, enclosure types and also its applications. Sounds fun? Well, let’s start learning!
Enclosures – Really Important?
A loudspeaker enclosure (usually box-shaped) is where speaker drivers (such as woofers, tweeters etc.) and associated electronic components, such as crossover circuits and, in some cases, power amplifiers, are mounted.
There are a variety of enclosure designs ranging from simple, homemade DIY rectangular particleboard boxes to very complex, high-end, computer-designed hi-fi cabinets that consists of composite materials, internal baffles, horns, bass reflex ports and acoustic insulation.
Enclosure sizes can range from small “bookshelf” speaker cabinets with 4″ woofers and small tweeters integrated into home stereo systems for casual listening, to large heavy-duty subwoofers with multiple 18″ or even 21″ speakers mounted in huge enclosures that are integrated into sound reinforcement systems for stadium-size rock music concerts.
Here are the topics that we’ll be discussing:
- Primary role
- Enclosure types
A speaker enclosure prevents sound waves created by the back-facing surface of the diaphragm of a speaker driver, from interfering with sound waves produced by the front-facing surface. Any interaction between the forward- and rearward-generated sounds in the listening space, will distort the original audio signal because both of the sounds are out of phase with each other.
This is why a loudspeaker must always be installed into a cabinet of some sort, or at least mounted into a wall or ceiling. Furthermore, an unmounted speaker would cause unwanted echo and reverberation effects, as the sound waves would arrive at the listener’s ears at slightly different times. This is because sound waves naturally travel different paths through the listening space.
Enclosures are vital in controlling vibrations produced by the speaker driver frame and moving airmass within the enclosure, as well as managing the excess heat generated by driver voice coils and amplifiers (especially for woofers and subwoofers). At times, the base of an enclosure may be attached with a special “feet” to decouple the speaker from the floor.
For loudspeakers used in PA and sound reinforcement systems, their enclosures usually have added features for easy transportation and protection, such as carrying handles, metal corner protectors, and metal grilles to protect the speaker. Home or recording studio speakers usually do not have the same features, but they often have a cloth or mesh cover to protect the woofer and tweeter.
Just visit any Hi-Fi sound system boutique, and you will soon realise the wide variety of enclosure types being used. However, in order to keep this article short and sweet, we’ll just go through a few of the common ones:
- Sealed (closed)
- Bass reflex
- Transmission line
In a sealed or “closed” type, the air inside the enclosure acts as a spring, which will return the cone to the ‘zero’ position when there is no audio signal. The “effective volume” of a sealed-box loudspeaker can be significantly increased by using a filling of fibrous material, typically fiberglass, bonded acetate fiber (BAF) or long-fiber wool.
By using this method, the “effective volume” can be increased by up to 40%. This is primarily due to a reduction in the speed of sound propagation through the filler material as compared to air. However, the enclosure or driver must be designed to have a small leak. This allows internal and external pressures to equalise over time, to compensate for barometric pressure or altitude.
Also called “vented” (or ported) speakers, these enclosures are designed to include a vent or hole cut into the cabinet and a port tube affixed to the hole. This mainly helps to improve low-frequency output and increase efficiency, as well as reducing the enclosure’s size. The openings or vents actually transforms and transmit low-frequency energy from the rear of the speaker to the listener.
Just like sealed enclosures, they may be empty, or stuffed (rarely) with damping materials. The port can also be frequency-tuned by altering its cross-section and length. Bass reflex enclosures are very common, and produces a higher sound pressure level near the tuning frequency, as compared to a sealed enclosure of the same volume, though it has less low frequency extension.
An ideal transmission line enclosure would have an infinitely long line, stuffed with absorbent material in order to fully absorb the rear radiation of the driver, down to the lowest frequencies. Theoretically, having a closed or opened vent at the far end, would make no difference in performance.
The density of the stuffing material and amount used is critical, as too much stuffing will result in unwanted reflections due to back-pressure. On the other hand, insufficient stuffing will allow sound to pass through to the vent. Different stuffing materials with various densities are often used, changing as one material gets further away from the back of the driver’s diaphragm.
Transmission lines can be considered to be a “waveguide” in which the structure shifts the phase of the sound waves coming from driver’s rear by at least 90°, thus enhancing the driver’s resonant frequency. The inherent resonance (typically at 1/4 wavelength) can actually enhance the bass response in this type of enclosure, provided there is less absorbent stuffing.
You can find speaker enclosures being used in many audio appliances such as home stereo systems, home cinema systems, televisions, and boom boxes. Even car stereo systems incorporate small speaker enclosures in order to enhance its performance. They can also be found in sound reinforcement systems, movie theatre sound systems and professional recording studios.
That’s about all the information I have for today. Do you now understand the significance of speaker enclosures? Or maybe it doesn’t matter to you at all?
Let me know your thoughts down below, and share this article with your friends!