What are speakers, or loudspeakers, or even subwoofers? Before we DIY speakers, we need to understand what they are! They are electro-acoustic devices that convert electrical signal to sound or audio waves. It may just be the individual drivers alone, or the whole speaker itself with single or multiple drivers, crossover and the enclosure.
There are several types of speakers and drivers. Each one of them serves a different purpose. They cover different range of frequencies and their usage models vary. Human listening ranges from 20Hz to 20,000Hz. It is quite difficult to have a single driver covering the full audio frequency spectrum. The frequencies are usually divided and conquered by several drivers, namely tweeters, midrange and woofers. Usually, crossover is used to divide the frequencies into blocks to match the intended driver.
The number of frequency blocks divided by the crossover determines the number or ‘nth-way’ of the speakers. For example, if a it is using tweeter to produce high frequency and woofer to produce low frequency, that is a 2-way speaker. Sometimes several drivers are parallel to produce the desired impedance or SPL (sound pressure level) to match the usage.
Let’s briefly look into several commonly used terms so that readers can understand them when we go deeper into designing or using various types of drivers.
Note: frequency specified here is just a generalization; there might be drivers out there that fall out of the ranges.
- Super tweeter – produces the super / ultra high frequency, usually is from 20 kHz onwards.
- Tweeter – produces the high frequency, ranges from 1 kHz to 22 kHz or maybe more.
- Midrange driver – produces the middle range, ranges from ~80 Hz to 10 kHz.
- Wide range driver – handles larger frequency range than the midrange, ranges from 60 Hz to 15 kHz, and sometimes can be used as standalone as Public Address speaker or background music speaker.
- Full range – a system that handles the full spectrum of audible frequency from 20 Hz 20 kHz.
- Single full range driver – a driver produces the full spectrum of audible frequency from 20 Hz to 20 kHz.
- Coaxial – contains a tweeter and woofer in a single chassis to produce the full audible frequency band from 20 Hz to 20 kHz.
- Triaxial – contains a tweeter, midrange and woofer in a single chassis to produce the full audible frequency band from 20 Hz to 20 kHz.
- Woofer – produces the low frequency, ranges from 200 Hz and below.
- Subwoofer driver – a driver that produces the very low frequency, ranges from 20 Hz to 80 Hz.
- Subwoofer – a system that specifically produces only the very low frequency ranges from 20 Hz to 150 Hz.
- Multi-way – a system that uses multiple types of drivers to produce the full audible frequency range, usually a tweeter, midrange and a woofer for a 3-way system; or a tweeter and a woofer for a 2-way system.
- Electrostatic – it is a thin statically charged membrane driven with high voltage electric field to produce sound instead of a cone with conventional speaker drivers.
- Horn – this uses a shaped waveguide in front or behind the driver to direct the waveform (sound) to the mouth of the horn, from a high to low pressure condition to increase the directivity and sensitivity of the speaker.
- Open baffle – this refers to a speaker system with a flat panel / baffle to mount the speaker drivers instead of an enclosure.
This is generally how a driver is constructed of.
- Diaphragm – the cone where the movements will create the sound waves
- Basket – the frame to house all the components of a speaker driver
- Spider – a suspension system to keep the voice coil and cone in place in the basket
- Magnet – as is, and is use to interact with the magnetic field created by the voice coil to produce movements
- Voice coil – wire wound into a coil that interacts with the magnet when an electrical signal passes through to produce movements
- Speaker terminal – the terminal where the voice coil wires are soldered / fixed and it will be connected to the speaker wires to receive signal from the amplifier
- Dust cap – a dome mounted on the diaphragm to protect the inner part of the driver (voice coil and the air-gap) from debris and dusts.
Crossovers are usually used in multi-way speaker system. The crossover splits the audible frequency to different ranges for each driver. Each respective drivers only receive the power for their dedicated range and therefore it won’t be damaged and work outside of the tolerated frequency band. It also lowers the distortion too since the drivers work at their optimum range.
Crossover can be active or passive.
Active crossover is an electronic filter circuit that is placed in between the source and the amplifier where it divides the signal into different bands before sending it to the amplifier to be amplified. Each band needs to be amplified by individual amplifier.
Passive crossover is an electronic filter network placed in between the speakers and amplifier that uses passive components (resistors, inductors and capacitors) to permit only the intended frequency range to the speaker drivers. One amplifier is used to drive both the high and low frequency.
In summary, we’ve looked at this subject at a 10,000ft perspective, from the driver to the speaker as a whole. We shall go deeper into the design itself in other chapters. Stay tuned for more!
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