Have you ever listened to music that sounds dull through certain speakers? Well, that’s probably because those speakers lack a crucial component which is responsible for bringing more clarity and brightness into your music. If you are looking for a more “crisp-sounding” music listening experience, then ask yourself this – What is a Tweeter?
Audiophiles and music enthusiasts are usually aware of how this important speaker component affects the overall sound quality. However, the average consumer might not be aware of what they are missing out on. Hence, in today’s article, we will look into the inner workings of a tweeter, and how it affects our listening. Lets start learning shall we?
The Tweeter – A Must Have?
Also known as “treble speaker”, the tweeter is a type of loudspeaker (usually dome or horn-type) that is specially designed to efficiently reproduce the high frequencies in an audio signal, usually from around 2,000 Hz to 20,000 Hz (which is the upper limit of the human hearing range). Some specialty tweeters can even deliver high frequencies up to 100 kHz.
Most tweeters are electrodynamic drivers, consisting of a voice coil suspended within a magnetic field. When current flows through the voice coil, a varying magnetic field is created, which works against the fixed magnetic field of a magnet (surrounding the suspended coil). This makes the voice coil and the diaphragm attached to it, to move back and forth, thus producing sound.
Designing a tweeter does come with challenges such as: ensuring sufficient damping to stop the dome’s vibration quickly when the signal ends, providing high output for the low end of its frequency range, ensuring there’s no contact with the magnet assembly, keeping the dome centered while its moving, and providing adequate power handling with minimal addition of mass.
Here are the topics that we’ll be looking into:
- Tweeter types
- Various applications
- Frequency range
There are several types of tweeter drivers available in the market. All of them have unique characteristics that you should consider, before making a decision to buy a new speaker. For this article, I will only cover three of the most common ones.
These tweeters are probably one of the more common ones found on cheaper sound systems. They have the same design as woofers but are optimized for higher frequencies. These optimizations include:
- a very small and light cone to allow rapid movements.
- cone materials are picked based on stiffness (e.g., ceramic cones in one manufacturer’s line), or good damping properties (e.g., paper, silk or coated fabric) or both.
- a “spider” (speaker suspension) that is stiffer than the ones used for other drivers, since less flexibility is needed for high frequency reproduction.
- smaller voice coils (usually 3/4 inch) made with light and thin wires (helps the tweeter cone move rapidly).
Cone tweeters exhibit a narrow dispersion characteristic. Due to this, many believed that it compliments cone midrange and woofer speakers, producing excellent stereo imaging. However, the narrow dispersion of cone tweeters only creates a small “sweet spot”. Hence, speakers with cone tweeters can only offer the best stereo imaging when placed in the corners of a room.
During the 70s and 80s, cone tweeters started to become less popular, due to the introduction of higher quality audiophile discs and the advent of the CD. Cone tweeters rarely reproduce frequencies above 15 kHz, thus, audiophiles felt that they are unable to produce the “airiness” that dome tweeters and other types of tweeters are capable of creating.
A dome tweeter driver consists of a voice coil that is attached to a dome (usually made of woven fabric, thin metal or other suitable material), which is then attached (using a low-compliance suspension) to the magnet or the top plate. Unlike cone tweeters, dome tweeters do not have a frame or basket, but instead uses a simple front plate attached to the magnet assembly.
Dome tweeters are categorized by their voice coil diameter, and range from 19 mm (0.75 in), through 38 mm (1.5 in). The overwhelming majority of dome tweeters presently used in hi-fi speakers are 25 mm (1 in) in diameter.
(Picture on the right: 1-Magnet, 2-Voice coil, 3-Dome, 4-Suspension)
These tweeters uses a very thin diaphragm (often made of aluminum, or some type of metalized plastic film) that supports a planar coil typically made by deposition of aluminium vapor. The diaphragm is then suspended in a powerful magnetic field (usually produced by neodymium magnets). This design is actually very similar to the design of ribbon microphones.
The ribbon itself (diaphragm) is made of very lightweight material, allowing very high acceleration and extended high frequency response. Ribbon tweeters are very directional, with a very wide horizontal sound dispersion and a very tight vertical sound dispersion. They can easily be stacked vertically, to create a high frequency line array that produces high sound pressure levels at much longer distances as compared to other tweeters.
Tweeters used in live concert systems and instrument amplifiers are generally similar to high fidelity tweeters, but are called “high frequency drivers” instead. Their mountings are built to be more durable (for rugged handling), and the drivers may be mounted to horn structures to allow higher sound levels and better control of the sound dispersion.
The voice coils in these tweeters are also more robust (as compared to high fidelity tweeters) in order to withstand the higher power levels typically present in live sound reinforcement systems. Take note that high frequency drivers in PA horns are often called “compression drivers” due to the mode of acoustic coupling between the driver diaphragm and the horn throat.
Most tweeters are engineered to efficiently produce frequencies as high as 20 kHz (upper limit of the human hearing range). Some can even reproduce frequencies up to 100 kHz, which is useful for psychoacoustic testing, extended-range digital audio such as Super Audio CD, biologists researching on animal response to sounds, and also for ambient sound systems in zoos.
That’s all I have for you folks today. I hope you now understand the significance of tweeters in the world of audio. So does your home stereo have quality tweeters? Or maybe you just don’t need them?
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