What Are Ohms In Headphones? (Everything You Should Know)

What Are Ohms In Headphones? Every pair of headphones has an impedance rating in ohms. But what exactly do headphone ohm ratings imply?

Impedance tells us how much power your headphones need to achieve a reasonable listening volume.

Simply put, the higher the impedance of headphones, the higher the source voltage required. Knowing your best headphone' impedance allows you to determine which audio sources will work best with them.

Let's examine low-, mid-, and high-impedance headphones and see which use cases they're most suited for.

The Fundamentals of Headphone Impedance [Explained]

There are numerous terms to be mindful of while describing impedance. When seen as a basic electronic circuit, the impedance of the audio source is referred to as output (or source) impedance, and the impedance of the wireless headphones is referred to as load impedance.

Headphone impedance is commonly rated between 8 to 600 ohms, with 32 ohms becoming more prevalent.

The audio source impedance is normally very low, often less than 4 ohms and approaching 0 ohms in many circumstances, but it can be as high as 120 ohms or more in the case of specialized tube amplifiers, particularly output transformer-less (OTL) kinds.

Low-, Mid-, and High-Impedance Headphones

Low vs High Impedance Headphones Compared

Low Impedance Headphones: up to 32 ohms

Low impedance headphones work well with the headphone outputs on battery-powered consumer electronics such as smartphones, tablets, and laptop computers.

Because these headphones don't require much voltage to operate, they should be plenty loud with all of your small, portable gadgets. But be careful: plugging an 8-ohm pair of earbuds into a pro DJ mixer and turning it up to 11 will certainly blow them out. Even if you don't permanently destroy your headphones, you'll get bad-sounding clipping distortion.

Low impedance headphone does not imply poor quality. Audio-high-end Technica's ATH-IEX1 earphones, for example, have an impedance of only 5 ohms! The majority of in-ear headphones and professional IEM earphones have a low impedance. Sennheiser IE 400 PRO earphones, for example, are 16 ohms, while Shure SE215 earphones are 20 ohms.

Mid-impedance headphones: Between 32 and 100 ohms

You can't go wrong with headphones in this price range because they operate with a variety of devices. They'll really shine when paired with the headphone output on your DJ mixer, audio interface, or standalone headphone amplifier.

They'll also sound good when plugged into portable consumer devices like your smartphone, albeit they'll be notably quieter than low-impedance headphones.

Look for a sensitivity rating of at least 100 dB SPL per milliwatt if you want your mid-impedance headphones to be loud enough when driven by battery-powered devices. (For further information on sensitivity, see “What about headphone sensitivity?” below.)

Most over-ear headphones for casual use, popular DJ headphones, and studio workhorse headphones come within this category.

Pioneer DJ HDJ-X10 headphones, for example, have a resistance of 32 ohms, Audio-Technica ATH-M50x headphones have a resistance of 38 ohms, AKG K240 Studio headphones have a resistance of 55 ohms, Sony MDR-7506 headphones have a resistance of 63 ohms, and Sennheiser HD 280 PRO headphones have a resistance of 64 ohms.

High-impedance headphones: 100 ohms and up

These relatively high impedance headphones demand greater source voltage than a normal consumer device can give. Even at maximum volume, you won't hear anything if you connect a pair of 250-ohm headphones to your phone.

They'll likely need a standalone headphone amplifier or a high-quality audio interface with a dedicated headphone amp built in to be properly driven and provide a higher voltage to fully realize their potential.

High-end studio headphones for casual listening, as well as audiophile headphones, frequently fall into this category.

Neumann NDH 20 headphones, for example, have a resistance of 150 pro ohm, Beyerdynamic DT 990 PRO headphones have a resistance of 250 ohms, and Sennheiser HD 650 headphones have a resistance of 300 ohms.

The 8:1 Rule of Impedance Matching

Have you ever noticed how different the same pair of headphones may sound when plugged into different devices? This is due to the fact that each device's output has an impedance rating as well.

Most dynamic headphones operate best when the source impedance (the device's output impedance) is significantly lower than the load impedance (the nominal input impedance of your headphones).

Audiophiles propose the 8:1 rule of thumb for appropriate impedance matching, or impedance balancing: link your headphones into a source with an output impedance no greater than 1/8 your headphones' impedance. Plug your 80-ohm headphones, for example, into a source with an output impedance of 10-ohm headphones or less.

Why is the 8:1 rule important?

If the source output impedance is greater than 1/8 of the headphone impedance, you will hear the perceptible change in the frequency response. Highs, lows, and mids may be given more weight. Variations in frequency response can be modest to loud and are frequently surprising.

There's just one problem with this 8:1 rule: audio equipment manufacturers rarely publicize the output impedance of their products – and there's no standard!

Fortunately, several high-end dedicated headphone amplifier manufacturers do disclose their output impedance specifications. And because high-end headphone amps are likely to have extremely low (near-zero) output impedance, they'll be less than 1/8 the input impedance of any electrostatic headphones you plug into them.

The Rupert Neve Designs RNHP headphone amplifier, for example, has an output impedance of only 0.08 ohms. That means you'll never breach the 8:1 rule no matter what headphones you plug into it.

But what if you wish to listen to a device with a high output impedance — or one whose output impedance is unknown? You could follow the 8:1 rule and use your expensive high-impedance headphones, or you could simply accept that your low-impedance headphones may sound slightly different when plugged into different sources.

READ ALSO: How Did Headphones Change Over Time? (Find Out Its History!)

Source and Load Impedance

The load impedance of a set of headphones has a significant impact on the distortion performance of an amplifier. The operating voltage and current (or bias) of transistors or tubes in amplifiers are optimized by the designer for low impedance loads, high impedance loads, or a combination of the two.

When a low impedance load is connected to an amplifier that is optimized for high impedance, it not only reduces power but also increases distortion. Some amplifiers include several outputs or switches that enable them to adjust to different impedance loads while remaining optimally biased.

At impedance spikes — the frequencies with the highest impedance for a specific headphone – the ratio of output impedance to load impedance increases drastically. This can lead to poor driver control (damping) and possibly audible distortion at particular frequencies.

Many Sennheiser headphones, for example, have an excessive frequency spike of around 100Hz. The Sennheiser HD6xx line can demand high voltage (3-6V) at the spike, making it an unsuitable fit for many lower-powered mobile devices, but an excellent match for the Bottlehead Crack OTL tube amplifier characteristics (120 Ohm output impedance and high voltage).

Problems with High Source Impedance and Low Headphone Impedance

The combination of high source output impedance and low headphone impedance causes serious problems. This scenario produces increased harmonic distortion and noise, a poor damping factor, and bass roll-off, and is often found only at the extremes of OTL tube amplification.

1. The Damping Factor

The damping factor between a source and headphones refers to the source/capacity amplifiers to influence the movement of the driver after the audio transmission has ended.

Kinetic friction contributes to the oscillating motor coming to a halt after a signal is removed. However, the electrical circuit (between the source and the driver) is also important and is defined by the damping factor.

The damping factor, in a broader sense, is the amount of control the source/amplifier has on the driver.

The damping factor is simply the ratio of the load impedance to the source impedance.

To ensure that the driver is well-controlled inside the audio circuit, we want the damping factor to be between 2.5:1 and 8:1, or even higher in some cases.

The “rule of eights,” which prescribes an 8:1 damping ratio for optimal headphone results, is a good starting point.

This is due to two factors.

The first is that low-end clarity suffers substantially when damping levels are low. Low-frequency vibrations in the driving diaphragm must be relatively slow but significant.

If the audio signal has insufficient control over the movement of the diaphragm, it will impair the driver's ability to perform the low-frequency oscillations accurately (more so than higher frequencies).

As a result, the low-end is boomy and imprecise, with a weak transient response, which is undesirable in any headphones.

Impedance spikes affect moving-coil headphones. If the headphones have an impedance spike, a damping factor lower than the nominal impedance may cause issues.

The headphones may distort or alter frequency if the impedance matching is insufficient at the impedance peak.

2. Roll-Off Bass

Low damping factor can roll-off bass frequencies in headphone frequency response and reduce low-end clarity.

This affects roll-off below the resonant frequency when the damping factor is less than 2:1.

3. Dispersion

As previously stated, a well-matched source and headphones have an 8x load (headphone) impedance.

The 8:1 ratio circuit drives the headphone driver with less current than lower dampening ratios. Not overloading driver circuits and avoiding crosstalk in unbalanced stereo headphones reduces distortion.

Testing headphones with the desired sound source rather than a random sound source at a retailer is best. Source impedance may affect headphone quality.

MP3 players and smartphones have changed headphone requirements.

For amplifier use, high-end headphones had high impedance. Nowadays, headphones have 32 for adaptability and use with mobile audio devices.

The Relationship Between Headphone Impedance And Sensitivity

Headphone sensitivity is the relationship between the loudness of headphones and a certain power level. It is normally measured at a certain frequency (1 kHz) and power level of 1 mW.

Headphone sensitivity standards are typically between 90 dB SPL and 105 dB SPL, with certain outliers falling outside of this range.

Though there is no relationship between impedance and sensitivity in headphone design, there is a strong relationship between impedance matching settings and headphone volume.

Remember that sensitivity is simply the amount of sound pressure produced by a headset when a specific amount of electrical power is delivered to the headphone drivers.

Impedance differences at the source will undoubtedly influence the potential power transmission between the source and the headphones, affecting the loudness capabilities of the headphones. The sensitivity value, on the other hand, is fixed.

Changing the source impedance has no effect on the sensitivity rating of the headphones.

Final Thoughts on What are Ohms in Headphones

Let's take a moment to review everything we've learned about impedance. It's a complex subject, but it doesn't have to be perplexing.

Impedance (measured in Ohms) is classified into two types: headphone impedance and source impedance. Impedance matching between headphones and source is performed to ensure a proper balance of sound quality and volume. A match denotes ‘complementary' rather than ‘equal.'

A headphone with an impedance 2.5-8 times higher than the source impedance should produce satisfactory results. This optimum ratio is usually referred to as the ‘rule of eighths,' and it aids in good driver control (damping factor). Pairing a headphone with an impedance equal to or lower than the source will most likely result in unpredictable (bad) sound quality.

Sensitivity, which is a measurement of loudness at specific power input, is also a significant aspect of headphones (usually given as decibels per 1 mW).

Volume is influenced by both sensitivity and headphone impedance, but they are unrelated. The impedance and sensitivity of headphones vary widely, and both must be considered when selecting an appropriate amplifier.

Sensitive (100 dB+), low impedance (8-32 ohm) headphones will often pair effectively with a portable source (such as a phone) without the need for an amplifier. Less sensitive (less than 95 dB) and/or medium to high impedance (more than 50 ohm) headphones would often benefit from a higher powerful amplifier than a phone (or portable device) delivers in terms of sound quality and volume.

Because dynamic headphones change in impedance at different frequencies and do not have a flat response, headphone impedance ratings can be deceptive (the rating is for a single frequency). Planar dynamic drivers do not have this issue because their impedance is flat across all frequencies.

Higher impedance headphones necessitate more source voltage (which portable devices lack) while lower impedance headphones necessitate more source current (something OTL tube amplifiers are not good at providing).

While certain high impedance headphones are built to a higher standard (such as using thinner voice coil wires) and can produce lesser distortion, higher impedance does not always imply better sound quality.

FAQs About Ohms On Headphones