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  1. Home
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  3. Test Bench 2.1

Test Bench 2.1  
Changelog

 0
By Nicholas LimUpdated Mar 12, 2026 at 11:34 am

See the previous 2.0 changelog.

Headphone Test Bench 2.1 rebalances the Harmonic Distortion test and removes the Group Delay test. We've also added the JM-1 HRTF (for IEMs) to our Graph Tool.

What's Changed?

Test Group Description
Group Delay Completely removed from the review and methodology
Harmonic Distortion Rebalanced scoring without modifying the test
Audio Reproduction Accuracy Redistributed weight resulting from Group Delay removal
Sound Profile/Raw FR Graph Added JM-1 HRTF (IEMs)

Why Are We Making These Changes?

In our previous test bench, we noted that both Harmonic Distortion and Group Delay are difficult to hear and, as a result, were given a lower weight in usages like Audio Reproduction Accuracy. However, after further research and observation during testing, we concluded that we had previously overestimated the effects of both metrics on practical listening.

Group Delay

As we tested more products on Headphones Test Bench 2.0, we noticed that headphones (that reproduce audio with high fidelity) had their Audio Reproduction Accuracy weighed down by comparatively low Group Delay. Despite these low scores, we didn't identify any audible issues typically associated with poor group delay after an in-depth subjective assessment of several headphones, casting doubt on the test's ability to meaningfully reflect an impact on the end user.

Test Designer Pierre's Notes: Most headphone acoustic engineers conclude that headphones are essentially minimal-phase devices, meaning any deviation in phase would result in a corresponding deviation in magnitude at these frequencies. In other words, group delay errors were already reflected in our frequency response measurements, making the test and its associated score redundant. This measurement is also quite sensitive to actual delays in the digital pipeline. Since our measurements are an average of many passes, our methodology introduced variations that resulted from the overlay of responses that weren't consistent from one pass to the next; the result was a worse picture when calculated in aggregate compared to on an individual basis.

The Group Delay measurements for the Audeze MM-500, scoring 5.7/10.
The measured Group Delay issues on Test Bench 2.0 on the Audeze MM-500 aren't audible, but resulted in a Group Delay score of 5.7, which brought down the headphones' Audio Reproduction Accuracy score to 7.1.

hARMONIC dISTORTION

Our literature review and our own investigation on distortion, in partnership with Dr. Sean Olive, found that in practical listening at normal levels, distortion is largely inaudible and "even when measurements predict subtle differences, those differences are extremely difficult to detect." As a result, we've modified the Harmonic Distortion scoring to be much more lenient, with most products scoring exceptionally well to better reflect perception rather than performance differences that may not be observable. Still, we've opted to continue measuring (and scoring) THD, since some enthusiasts chase the lowest possible Harmonic Distortion. Because perception is a moving target and varies between individuals, we can't definitively say when most people will notice Harmonic Distortion, but we're confident that you won't notice anything as long as the score is green (above 7.4).

Audio Reproduction Accuracy

Because of the removal of Group Delay and lower significance of Harmonic Distortion, we rebalanced Audio Reproduction Accuracy with weighting distributed to other components that make up the score (Peaks/Dips and Stereo Mismatch):

Test Bench 2.0 Test Bench 2.1
An image of the Score Component breakdown for Audio Reproduction Accuracy for Test Bench 2.0.
An image of Score Component breakdown for Audio Reproduction Accuracy for Test Bench 2.1.

Sound Profile/Raw FR Graph

We've added the JM-1 HRTF for in-ear monitors (IEMs) to both the Sound Profile and Raw FR Graph Tool. JM-1, developed by Joel Merrifield, is a modified HRTF that combines the ear canal response portion of the B&K 5128 HRTF and the population-average pinna effects from Hammershøi and Møller's Determination of Noise Immission From Sound Sources Close to the Ears. Though JM-1 isn't a target in itself, portions of the community prefer the JM-1 HRTF over the B&K 5128 HRTF as a baseline for preference curve development and HRTF compensation due to its closer resemblance to how the average human will experience in-ears.

Test Designer Pierre's Notes: This work by Merrifield, adjusting for the B&K 5128's ear gain in IEM measurements that don't reflect the general population, is valuable. Beyond our publication, some manufacturers use these findings in the tuning of IEMs (MOONDROP x Crinacle DUSK [USB]). In addition, other reviewers derive IEM target responses using the JM-1 HRTF as a baseline by applying tilt to the curve or bass elevation based on Harman's research. Being able to compensate measurements to this curve is helpful for our readers, especially since it brings some comparability with other publications that have adopted compensated measurements as their primary visualization (Headphones.com). To avoid confusion, our Graph Tool now displays only in-ear-specific curves when viewing in-ear headphones, so you won't see JM-1 or Harman IEM as options if you're researching over-ears.

The MOONDROP Blessing 3 frequency response compensated using the JM-1 HRTF.
In the Graph Tool, you can visualize sound profile measurements compensated to a chosen HRTF. In this example, the MOONDROP Blessing 3 are normalized to the JM-1 HRTF.

Let Us Know What You Think!

We're always improving our testing and methodologies, so if you have any feedback, questions, or suggestions, please leave a comment below or email us.

50 Headphones Updated So Far

We are retesting popular models first. So far, the test results for the following models have been converted to the new testing methodology. However, the text might be inconsistent with the new results.

103 Headphones Planned To Be Updated

We are also planning to retest the following products over the course of the next few weeks:

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