Examples of two speaker bobbins with dual voice coils. In this animated diagram, you can see how a loudspeaker works. A stereo or amplifier drives the speaker with an electrical signal that alternates from positive to negative in the shape of the musical signal. This moves cone assembly that creates sound waves as the air moves rapidly. Speakers use alternating current AC that changes direction polarity just like sound waves in real life.
A speaker also referred to as a loudspeaker, a name from back in the day uses an alternating current AC electrical power signal and are driven by a stereo or amplifier. In a matter of speaking, speakers are just an electric motor of sorts: they are powered by an electrical signal and change it into a mechanical output: moving air to create musical sounds. Speaker impedance, measured in Ohms, is the total resistance to the flow of electric current through a speaker voice coil.
Unlike standard conductors, as the voice coil is tightly wound in a coil the makes this complicates things because it adds inductance. Inductance is different from resistance as it changes as the frequency changes and this is called inductive reactance. In other words, when the magnetic fields of the voice coil are created they oppose the flow of electrical current a bit. If you like fancy math, you can see here how speaker impedance is calculated. It is the geometric sum of the resistance in the voice copper wire winding and the resistance caused by its inductance at a given frequency.
Image showing how to measure speaker impedance with an Ohm meter. This measures only the direct current DC resistance of the wire in the voice coil, not the total impedance of it with music playing due to inductance. The practice began long ago when radios and speakers were first installed from the factory when cars were built.
In both cases these Ohm ratings became common for home and car speakers. While a subwoofer or mid range speaker needs to be used in a sealed structure tweeters do not. In some cases like for surround speakers they may be smaller than the front main speaker cabinet pair. An example of a typical speaker frequency response graph is shown here. Larger drivers can move more air, but the problem is that speakers become more directional as the frequencies they are reproducing go up.
This is known as beaming. As frequency increases, the associated wavelength decreases; speaker drivers usually start beaming at a frequency with a wavelength equal to the diameter of the radiating cone.
The simple solution is to use different sizes of drivers with each one tailored to reproducing a specific range of frequencies —different parts of the audible spectrum bass and treble, or bass, middle, treble. This concept works in tandem with a frequency dividing network in the speaker box called a crossover. A crossover delegates the right frequency range to each driver type: tweeters for the highs and woofers for the lows. A little base knowledge will help you understand why certain design decisions were made, how they influence the sound, and to help you identify snake oil salesmen.
Knowing how speakers work can also help you diagnose problems. And if this article has you interested to learn more, there are plenty of resources online where you can learn how to build them yourself from readily available parts. Check Price. Name: Subject: Message:. SoundGuys is reader supported. When you buy through links on our site we may earn an affiliate commission. Learn More.
How do speakers work? Remember that sound is mechanical waves energy, and audio is electrical energy. Our ears pick up the vibrations in the medium caused by sound waves and convert these vibrations into electrical impulses that our brains can understand. In other words, our ears are transducers. Microphones work similarly with diaphragms that move in reaction to the sound waves around them.
Their capsules cartridges, motors use this diaphragm movement to create electrical audio signals that represent the sound waves. Loudspeakers and headphones work in the opposite manner. Their transducer elements, known as drivers, are designed to receive audio signals and move their diaphragms to reproduce these audio waveforms as sound waves.
For a more detailed article on the differences and similarities between sound and audio, check out my article What Is The Difference Between Sound And Audio? Though there are certainly variations in the design of speaker drivers, the vast majority will be of the dynamic variety also known as moving-coil or electrodynamic.
To learn how each type of speaker driver works, check out my article What Are Speaker Drivers? How All Driver Types Work. The Dayton Audio RS link to check the price on Amazon is an example of a moving-coil speaker driver. So how does this seemingly complicated transducer with multiple components produce sound? The magnetic structure is made of the main magnet and several pole pieces. The pole pieces extend the magnetic poles of the main magnet and form a small ring-shaped cutaway just slightly larger than the voice coil.
This concentrates the magnetic field around the voice coil while still allowing it to move freely inwardly and outwardly. The surround and spider make of the suspension, limiting the movement of the voice coil and the diaphragm and dust cap to the inward-outward directions only.
Restricting lateral movement keeps the voice coil from hitting the magnet and causing issues. The voice coil has two electrical leads attached to it a positive and a negative and receives audio signals. Each terminal is connected to an end of the voice coil. Below is a picture of two terminals on a speaker driver photo taken from my quick and dirty experiment turning a loudspeaker into a microphone.
Note that we can also see the magnet, spider, basket, surround, diaphragm and dust cap in the picture. Remember our discussion on audio signals. These alternating currents flow through the terminals and the voice coil of the speaker driver. This alternating current causes an alternating magnetic field to be induced in and around the voice coil due to electromagnetic induction.
The ideal frequency response for a speaker is very flat. This means the speaker would be the same level at low frequency as it is in the mids or highs. The goal of a flat frequency response is to ensure that the people listening to your music experience it the way you intended it.
If your track is well mastered and sounds good on speakers with a flat response, you can be sure that it will sound its best on any playback system. Many speakers are not flat. Some do not have enough treble or enough bass, or they have peaks or dips in their frequency response where certain frequency ranges are over emphasized or hidden or masked.
If this happens some instruments may be louder or softer than you intended them to be and the mix you worked so hard on will not be properly represented. For high frequencies, speakers must move very quickly. For low frequencies, speakers must push a lot of air. This is why tweeters high-frequency drivers are typically small domes and woofers low frequency drivers are usually large cones. We hear 10 octaves 20hzkHz that is a very wide range for comparison, we can only see less than one octave of light.
Many speakers we use have limited frequency responses. For example: Try to hear the bass kick on your laptop speakers! No thump right?
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