Speaker Impedance Rating

Impedance is something we’ll see or hear about Impedance while utilizing speakers, whether it’s on the specs sheet or printed as several ohms on the back of the speaker. To completely know how speakers function, we must first understand the seemingly strange parameter of speaker impedance.

What does speaker impedance refer to? The electrical impedance (AC resistance) experienced by the audio signal at the input of the loudspeaker driver is measured in ohms. Impedance is essential for matching speakers and amplifiers since it impacts how much power a speaker draws from an amplifier.

The implications of speaker impedance on speaker performance, how to match an amplifier and speaker properly, and the distinctions between typical nominal speaker impedance values will all be covered in-depth in this article.

General description of impedance

When a voltage is supplied to a circuit, electrical impedance measures the opposition/resistance to an alternating current. Impedance, like electrical resistance, is measured in ohms and can even be considered a form of “AC resistance” in an AC circuit. In an AC circuit, impedance is defined as the sum of DC resistance and any reactance. The obstacle to the passage of electric current is known as resistance.

Reactance is the resistance of a circuit element to current flow caused by its inductance or capacitance. In the context of audio, it’s easier to conceive of impedance as AC resistance. However, in this essay, we’ll go through the whole impedance of speakers.

There are frequency and phase components because impedance acts on AC circuits rather than DC circuits. Speaker impedance fluctuates over the audible range of frequencies, as we’ll see momentarily, hence a nominal figure is commonly used to indicate the impedance.

Read: A Complete Guide To Home Theater System

Source & Load Impedance

The source of an audio signal is the device that produces it, and the load is the equipment that receives the signal at its input. 

A loudspeaker serves as the load, while the amplifier is the source when coupled to a power amplifier. For best signal transmission from the source to the load, the load impedance should be magnitudes greater than the source impedance, as we’ll see in the next section.

Power Matching Vs. Voltage Bridging

We desire optimal signal/voltage transmission rather than power transfer. By connecting a speaker to an amplifier. We want as much of the amplifier’s amplified signal to drive the speaker. It’s fine if the power transmission isn’t perfect (speakers are notoriously inefficient anyway).

This leads to a discussion about power matching vs. voltage bridging. When looking for appropriate equipment, we’re usually faced with “matching an amplifier and loudspeaker,” which might be perplexing. However, power matching for maximum power transmission is not a problem. 

Rather, we desire optimum voltage transfer, known as voltage bridging in technical terms. It’s desirable to have the speaker’s impedance be significantly greater than the associated amplifier’s real output impedance. It boosts signal efficiency and transfer.

Read: Home Theater Wiring Tips

Speaker Impedance & Power Demands

Returning to maximum power transmission for a minute, we may say that lower speaker impedances require more power. Lower impedance speakers are more difficult to drive. They put additional strain on the amplifier, necessitating higher powerful amplifiers to drive them effectively.

When “matching” speakers and amplifiers, this is crucial information. It’s worth noting that speaker impedance parameters are usually reported as nominal or “average” values (more on this later).

However, amplifier output impedance characteristics are usually reported as rated values. This implies that the amp’s “impedance rating” indicates which speaker impedance ratings it will be able to drive adequately. It doesn’t truly give us the amplifier’s true output impedance.

Damping Factor

It’s necessary to discuss the damping factor before wrapping up our source and load impedance discussion. Damping factor (DF) is the ratio of nominal loudspeaker impedance to total source impedance that drives the loudspeaker in technical terms. This comprises the amplifier (source) and speaker cable impedances.

DF = ZL / ZS

High DFs indicates that the amplifier has more control over the moving driver of the speaker. Another advantage of having a high speaker input impedance compared to the amplifier output impedance is this.

The quick responsiveness of the amplifier-speaker interaction improves with a greater damping factor. When the audio signal ceases, it also permits the amplifier to damp (slow down and stop the speaker from moving).

Lower damping factors result in less amplifier control, which might result in a “loose” speaker sound. This is especially true at low frequencies. High speaker (load) impedance is essential for signal transmission, system efficiency, and speaker control!

As a matter of thumb, a damping factor of ten or more is ideal. In other words, a speaker with a 10x or higher input impedance than the amplifier’s output impedance is preferable. This is true in most systems.

Read: What Need to Know About DTS Sound

Active Vs. Passive Loudspeakers

Let’s talk about active and passive loudspeakers before further our quest to understand speaker impedance. Passive loudspeakers do not require electricity and do not have built-in amplifiers. Instead, they rely on external amplifiers to give them powerful enough signals to drive them adequately. Passive speaker inputs expect speaker-level signals.

We’ve been talking about passive loudspeakers up to this essay.

On the other hand, active loudspeakers contain built-in amplifiers and must be powered to operate. Line, instrument, and even mic inputs can all be found on active loudspeakers. Their built-in amplifiers will increase these low-level impulses to a level where the speaker drivers can be driven appropriately.

Remember that the information about voltage bridging and damping factors described above applies to active speakers. However, unlike passive loudspeakers, this everything takes place inside the speaker rather than between the speaker and a separate power amplifier.

So what about the inputs of active speakers?

As we’ve seen, active speakers’ inputs may be configured to receive a variety of various signal formats. Different load impedances are required for different signal types.

Mic inputs are generally intended to take mic level signals and have impedances ranging from 1 KΩ to 10 kΩ. Line inputs are intended to take line-level signals and have impedances ranging from 10 KΩ to 50 kΩ. Instrument inputs are less tightly controlled, with impedances ranging from 47 kΩ to 10 MΩ

As a result, unlike a passive loudspeaker, the impedance specifications of an active loudspeaker will not be in the range of 1Ω to 16Ω. Rather, they will be in the above ranges depending on the inputs accessible in the active loudspeaker, they will be in the above ranges.

Read: Equalizer Settings for Clear Voice on TV

Impedance Of Speaker Level Vs. Line Level

Why does line level operate better with lower impedance than speaker level? Though there are several reasons for this (including standards and history), the major cause is electrical current. Impedance refers to the resistance to electrical current. Lower impedance indicates greater current, whereas higher impedance means less.

Too much electrical current can be extremely damaging to sensitive electronics, necessitating the use of more robust components. This raises the price of audio equipment significantly.

For example, passive speaker crossovers, which deal with speaker level (high current) signals, are more durable than active speaker crossovers, which deal with line level (low current) signals and are less durable but more precise.

The nominal line level is used for audio recording, processing, mixing, storage, and playback. Due to the low-current nature of line-level, electronics (including analog-to-digital and digital-to-analog converters) are more simply (and cost-effectively) built.

A speaker’s job is to oscillate back and forth to convert audio impulses into audible noises. Its motor (which consists of a voice coil and a magnetic structure) converts electrical energy from speaker signals into mechanical wave energy (sound waves).

The speaker transducer requires more current due to its relatively robust nature. One approach to do this is to reduce the impedance. It’s also worth noting that speaker voltage is often greater than line voltage. Because of the higher current, the speaker wire is thicker (lower gauge) than the standard audio (line level or mic level) cable.

Speaker Impedance Specifications

The speaker impedance specification in the manufacturer’s datasheet usually refers to the speaker’s nominal impedance. The ideal impedance values are usually expressed as 2, 4, 6, 8, 12, or 16 ohms. 

The IEC (International Electrotechnical Commission) regulation for rated speaker impedance is as follows: across the stated frequency range of the speaker, the minimum impedance should not fall below 80% of the nominal (rated) impedance.

For example:

4 Ω speakers must have a least impedance of 3.2Ω.

8 Ω speakers must have a least impedance of 6.4Ω.

The speaker’s designated frequency range is between the -10 dB low and high points over its average (0 dB) sensitivity.

Manufacturers use the rated impedance values of speakers (and accompanying power amplifiers) to express clearly (or ambiguously) what their devices are built to handle. The user must then follow the “guidelines” stated in the amplifier and loudspeaker specs sheets to get the best results and avoid damaging their equipment. The primary takeaway is that there’s more to learn about speaker impedance.

Higher currents are associated with lower impedances. Higher currents cause the amplifier and speaker to dissipate more heat. Power amplifier manufacturers indicate the lowest load impedance (the connected speaker(slowest )’s safe impedance value). So we know that impedance ratings stated by the manufacturer are usually nominal.

Actual Speaker Impedance

Is it possible to obtain information on a speaker’s true impedance ratings over its whole frequency response?

Unfortunately, most manufacturers do not provide their speakers’ impedance graphs. Third-party testers, fortunately, measure and publish impedance graphs for various loudspeakers. Of course, speakers with many drivers are quite difficult to comprehend in terms of impedance. The following part will concentrate on improving our grasp of real speaker impedance.

Understanding Phase & Impedance

The speaker’s phase is positive when the driver resonance is “pushing” the electrical audio signal up towards resonance. The speaker’s phase is negative when the driver resonance is “pulling” the electrical audio signal down to resonance.

At resonance frequencies (where impedance peaks), the phase is essentially 0°, halfway through a flip. The phase angle controls whether the current waveform will lead or lag the voltage waveform in a reactive circuit. Reactance is a key component of overall impedance and describes an AC circuit’s resistance to changes in electrical current when a voltage is applied.

The current in inductive circuits lags behind the voltage, resulting in a positive phase angle. The current will always lead to the voltage in capacitive circuits, resulting in a negative phase angle. The phase angle will alternate since speakers have both inductive and capacitive qualities.

Even though phase angles are fundamental to speaker design, they reveal more about the role of the amplifier than they do about the speaker. The amplifier will dissipate twice much power at a phase angle of 45° as at a phase angle of 0°.

Speaker Driver’s Impedance Design

A conductive voice coil is linked to a moving diaphragm of a speaker driver. A magnetic construction suspends the voice coil inside a gap. A shifting magnetic field is created when electrical audio impulses flow through the coil, causing the coil (and diaphragm) to oscillate.

The diaphragm should move in the same waveform as the audio source to generate sound representing the audio signal without distortion. The crucial aspect is that speakers feature conductive voice coils, which have electrical impedance by nature.

Resistance to Speaker Drivers

The voice coil has a continuous DC resistive element (and speaker driver as a whole). This electrical resistance is constant across all frequencies and is frequently at or just below the speaker driver’s minimum impedance value.

That’s the less difficult part. The back EMF and reactance of the speaker driver are the most interesting parts of the frequency-dependent impedance of the loudspeaker driver.

Impedance Increase The Back EMF of the Resonance Frequency

The fundamental resonance frequency of the speaker driver is (Fs). This is the natural frequency for the speaker driver to vibrate at. Making the driver vibrate at its resonance frequency is simple; resonating at other frequencies is more complicated. 

The driver will vibrate at its resonance frequency by tapping the speaker diaphragm. Like a tuning fork, exposing a loudspeaker driver to a sound wave at its resonant frequencies causes it to vibrate.

There is a spike in impedance at this resonance frequency. This can appear to be paradoxical. The driver travels with the least physical resistance at its Fs, but its electrical current impedance increases dramatically.

Back EMF can help to explain this:

Placing a voltage across the voice coil causes the coil to move due to the induced magnetic field. This is how speakers function like transducers in the end.

Likewise, the inverse is true. A voltage is induced across the voice coil when moved inside a magnetic field. This voltage is opposed to the voltage required to move the coil. Back electromotive force is the term for this. Back EMF, in other words, opposes the passage of energy through the voice coil of a speaker (just like impedance).

The speaker driver will try to vibrate freely at the resonance frequency, causing an increase in back EMF and, as a result, an increase in impedance. The Fs of a moving-coil speaker driver are usually between 20 and 600 Hz, causing a spike in the impedance of the speaker driver.

One of the several Thiele-Small factors that make up a substantial amount of a speaker driver’s specs is the fundamental resonance frequency (Fs). Another TSP called Zmax (“impedance at resonance” or “maximum impedance”) measures the impedance at the Fs.

It’s vital to remember that many speakers contain numerous drivers, each with its resonance. This might result in many spikes in the speaker’s total impedance. These peaks are often damped or adjusted in the speaker design to generate a smoother impedance profile.

Impedance Rise at High Frequency Because of Inductive Reaction

The property of an AC circuit (such as a voice coil in a speaker driver) that opposes current change is known as inductive reactance.

In that it is measured in ohms, reactance is comparable to resistance. The definitions differ: reactance opposes the change in the electrical current, whereas resistance opposes the current itself. The total impedance of a speaker driver is made up of both reactance and resistance.

As previously stated, audio signals range from 20 Hz (or less) to 20,000 Hz (or above). The hertz values represent cycles per second. Higher frequency signals change direction more times per second than lower frequency signals, as we know. As a result, the reactance of a voice coil resists higher frequencies more than lower frequencies.

The Effect Of The Number Of Speaker Drivers On Impedance

We’ve just gone through the differences inside a single driver. Consider the possibility of several drivers in a single speaker device. Most loudspeakers have at least two drivers (a woofer and a tweeter), and many have more. As we may guess, each driver will impact the speaker’s total impedance.

This might result in many peaks in total impedance that correspond to each driver’s resonance frequency. To reduce spikes in total impedance, tweeters are frequently constructed with little Fs impedance peaks (either naturally or damped/tuned).

Crossovers are used to direct certain frequency bands to the drivers that can reproduce them the best. As a result, the rise in high-frequency impedance caused by inductive reactance is most likely related to the tweeter (as no high frequencies will be sent to the midrange speakers or woofers).

The Speaker Enclosure and Its Impedance Effect

Loudspeaker units are almost typically integrated into enclosures.

A speaker enclosure enhances a speaker’s performance by successfully eliminating out-of-phase sound waves from the speaker driver. This increases phase coherence and results in a more powerful/loud output. Each enclosure has its resonance, which comes in various forms and sizes (s).

The impedance of the total speaker unit is affected by the resonance(s) of a speaker enclosure, just as it is by the resonance of the speaker driver. The driver will oscillate more readily at the enclosure’s resonance frequency, causing more back EMF in the voice coil. As previously stated, this increases the speaker unit’s impedance.

The enclosure resonance is usually lower than the driver resonance, although not always. The enclosure and driver resonances cause impedance peaks corresponding to their resonant frequencies.

Wiring Multiple Speakers vs. Wiring A Single Speaker

We’ve only discussed the impedance of a single speaker and the load impedance between that speaker and its attached amplifier so far in this article. Several stereo amplifiers with multiple channels can connect to numerous speakers on the market. These separate channels serve as several single connections between the amplifier and a speaker. in most cases

In this part, I’d like to discuss how to connect numerous speakers to a single amplifier channel and the load impedance that results. Multiple speakers can be connected to a single amplifier channel using one of two methods:

  • In series: speakers linked in series have a single conductive route. The same current passes through all of the speakers, but the voltage across them is reduced (due to the impedance of the speaker).
  • In parallel: Speakers linked are connected over numerous pathways, dividing the current while maintaining the same voltage across all speakers.

Parallel wiring is recommended when connecting two (or more) speakers with an impedance of 8Ω or greater, parallel wiring is recommended. And when connecting two (or more) speakers with impedance ratings under 8Ω, series wiring should be utilized. This is because we must consider the overall load impedance of the circuit when connecting numerous speakers to a single amplifier channel.

Let’s make things easier by dealing with speaker resistance rather than complex impedance. This isn’t strictly right, but it makes comprehension straightforward.

FAQ

What is the function of audio power amplifiers?

The audio power amplifier’s job is to convert line-level signals from audio players to speaker-level signals at its output (to drive speakers). It accomplishes this by using energy from the power grid to power the vacuum tube or transistor-based amplification circuit.

Microphone preamps and headphone amps are not the same as power amplifiers. Check out my posts What Is A Microphone Preamplifier & Why Does A Mic Need One? for more information on these other amplifiers. 

What is a decent speaker’s wattage?

The power output of the amplifier driving the speaker determines the speaker’s optimum wattage (power handling rating). “Large speakers” should be paired with “big amps,” while “small speakers” should be paired with “small amps.” Poor signal output, distortion, and even blow-out can occur when mismatched speakers and amplifiers.

With so many loudspeakers on the market, deciding which one(s) is appropriate for your application can be difficult. As a result, I’ve put together My New Microphone’s Complete Loudspeaker Buyer’s Guide. Look it through to see if it can assist you in deciding on your next speaker purchase.

Conclusion

This article will go through the effects of speaker impedance on speaker performance, how to correctly match an amplifier and speaker, and the differences between typical nominal speaker impedance values. Understanding speaker impedance is crucial if you want to hear every note without distortion or interference from other speakers.

Speaker impedance is a measurement of a speaker’s capacity to handle power and should be considered before purchasing. Have you ever wondered why certain speakers have a 4-ohm rating while others have an eight or 16-ohm rating? We hope this article will explain how speaker impedance works and what it implies for your audio system if that’s the case.