“Z” is the symbol for impedance. Acoustic impedance is measuring the resistance of a system to acoustic signal flow.
What is Impedance?
The term “impedance” is used to describe the resistance of a circuit or device to the flow of alternating current (AC).
It considers both resistance and reactance (the resistance to the flow of electrical current brought on by the material the circuit is made of) (the opposition caused by any energy storage elements in the circuit, such as capacitors or inductors).
Impedance is measured in ohms, which is the unit of electrical resistance in the International System of Units (SI).
What is impedance “in audio”?
Understanding the meaning of impedance, a term commonly used in the audio industry, is crucial. A sound‘s quality can be altered by adjusting the impedance and resistance of its medium. Therefore, it is helpful to have an understanding of the concept before attempting to make or listen to music.
Impedance and Cables
Cables have impedance too, called the characteristic impedance, which is due to capacitance between the wires and the braid, and inductance along the cable’s length.
The characteristic impedance of cables doesn’t increase significantly when cables are connected in series, except for extremely long cable lengths, making it possible to use passive digital patchbays in matched-impedance digital systems to connect equipment.
Impedance and Monitors (Speakers)
Passive monitors need to be amplified by an external source (amplifier) to work so the sound is affected by the transfer of electrical power.
Passive monitors typically have an impedance value of 4, 8, or 16 ohms. This value is used to determine the type of amplifier to use with the speaker. Vintage valve amplifiers are typically used with 16 ohms, ehile the new amplifiers are used with 4 ohms.Monitors / speakers can be challenging for amplifiers to drive, especially those with passive crossovers, as the impedance can vary greatly.
To ensure accurate sound delivery, amplifiers are designed to have a low output impedance, which allows the speaker’s impedance to be significantly higher. The impedance of the connecting cable can also impact the sound quality. Cheap cables can have a high resistance that can lead to energy being lost as heat and can interact with the crossover’s characteristics.
Impedance and Headphones
Like loudspeakers, headphones have an impedance that the amplifier that powers them has to deal with. Impedance affects how loud the headphones are, how strong the magnet is, and other parts of the design. The best way to choose headphones is to look at how sensitive they are. This is measured in decibels per milliwatt (dB/mW). The volume of what comes out of the headphones is also affected by the amplifier that drives them.
According to their impedance, headphones can be divided into three categories: portable, professional, and broadcast. Broadcast headphones have a relatively high impedance, usually between 1.5 and 2 k, to enable signal source monitoring without excessively loading it and resulting in a level drop. Professional headphones typically have an impedance between 150 and 600, with a lower impedance resulting in a louder sound. Low impedance portable headphones, typically 8-32Ω, to allow for more power using limited voltage from the battery.
It is becoming more popular to use high-quality professional-impedance headphones with portable equipment, but doing so might reduce the maximum volume and possibly prolong battery life. Many manufacturers provide different impedance options for their headphone models, so it is worth checking to see if the preferred model is appropriate for the intended application.
Impedance and Guitars
Signal loss happens when a signal is sent to an amplifier. The input impedance of the amplifier determines how much of a loss there is.
If you use passive guitar pickups with a low input impedance amplifier, the sound will be dark. It might be because tube amps typically have high input impedance that some guitarists favor tube amplifiers.
The effects of cable capacitance are amplified by high input impedance, which also preserves the pickup level and produces smooth tone control. With a low-impedance input, a cable that lowers highs when used with a high-impedance amp may have little to no effect.
However, noise and other electrical interference are more likely to be picked up by high-impedance inputs. The objective is to achieve a balance between an input impedance that is too low and too high.
Impedance and Audio Interfaces
The XLR microphone inputs on audio interfaces and the 1/4 inch line-level inputs designed for electronic equipment with high output levels are not appropriate for passive pickups in musical instruments. In order to get around this, the majority of audio interfaces have at least one 1/4-inch high-impedance (Hi-Z), Hi-Z instrument input. The goal of this input is to give the DAW the cleanest sound possible while maintaining the level and high frequencies of the guitar.
A direct box for guitar must be used if an audio interface does not have a high-impedance input. The direct box’s high-impedance input and low-impedance output are connected to the guitar and the audio interface, respectively.
It is not necessary for the instrument input of an audio interface to be an exact electrical replica of a typical amplifier input because it is designed for high-fidelity sound. Some audio interfaces include amp-like input circuitry to mimic a typical amp input. For instance, Radial Engineering provides direct boxes that can be inserted between the guitar and the interface input and have a “drag” control that simulates cable loading and lower impedances.