(Last Updated On: October 14, 2020)

A guide to set up and take measurements of headphone frequency response using the miniDSP EARS.

Eyes on the EARS.
Eyes on the EARS.
This guide is intended to provide the specific setup and settings that Headphonesty reviewers use to perform headphone measurements using the miniDSP EARS. If you own an EARS device and would like to relate your test results to ours, please follow this guide to ensure that the results are comparable.

There are two inescapably good reasons for using the miniDSP EARS test rig to measure headphones. Namely, its low price and ease of use. It’s a mere fraction of the cost of a professional measurement rig, and the ready availability and beginner friendliness of the EARS mean that its user base of headphone enthusiasts will continue to grow.

The miniDSP EARS includes very good instructions and documentation for beginners. It works well with the free and generally well-regarded Room Equalization Wizard (REW) software. It works on Windows, Apple OS, and Linux without installing drivers. Win. Win. Win.

In order for EARS measurements to have value, we do need to be realistic about our expectations and to openly discuss and identify any limitations. The measurements are only useful (and comparable) if we expressly state conditions, equipment, settings, and standards used. This will be discussed more fully in a companion article regarding the miniDSP EARS.

The goals are to:

  • As closely as possible replicate the same measuring conditions between multiple reviewers and across multiple headphones.
  • To be transparent in methodology.
  • To maximize consistency across all measurements regardless of location or operator.

The process will be broken up into three parts:

  1. Physical setup: this section will cover the environment and setup of the EARS device itself.
  2. REW software setup: this section will focus on ensuring consistent settings and results in the Room EQ Wizard software.
  3. Performing measurements: where the rubber meets the road (or the velour meets the silicone ear, so to speak).
Diagram of a typical EARS setup. (From the EARS User Manual)
Diagram of a typical EARS setup. (From the EARS User Manual)

Quick Links

Click on the links to jump to the relevant section.

Physical Setup

Work Space

First, let’s discuss the room in which measurements will be done. Ideally, this room should be SILENT and must not be interrupted during measurements. This is to ensure that no exterior sounds leak into the measurements. This means no background videos or music while performing measurements.

Turn off audible cell phone notifications. Move away from (or better yet, shut off) devices like fans, air conditioners, or refrigerators. Remove anything possible that may make noise.

The EARS itself should be firmly supported on a solid base. My measurements are done on my small writing desk in a corner of my basement. Admittedly the soundproof foot-thick concrete walls around me are marred by windows, but they remain closed during testing time.

My humble writing and measuring desk.
My humble writing and measuring desk.

“Measurements should be performed under good conditions. While the sweep technique used by modern acoustic measurement programs is quite robust, external noise can still corrupt a measurement. Be aware of external noise sources such as computer fans, air conditioning, traffic noise, aircraft and so on. If necessary, choose a location or time of day for measurement that minimizes noise.

Low frequencies in particular are susceptible to external noise. Even if you cannot hear (or are not aware of) external noise sources, they can still show up in your measurements. If you are not getting consistent measurements at low frequency, external noise is the most likely reason.

Try and keep the space around the EARS clear of other objects, and keep both sides similar. For example, don’t position the EARS so one channel is next to a wall and the other is facing into the room.” – EARS User Manual

EARS Unit Adjustments

I have found it unnecessary to adjust the height of the EARS unit from how it arrived – the screws remain in the fourth hole from the top and the second hole from the bottom. Full-sized headphones easily adjust to fit this size.

The back of the EARS unit.
The back of the EARS unit.

The internal microphone gain DIP switches (located on the front of the unit) should be left in their default (18 dB) positions as well: 1 up, 2 down, 3 down, 4 down.

The default 1 UP setting yields 18 dB of internal microphone gain. And yes, it does say H.E.A.R.S. rather than EARS.
The default 1 UP setting yields 18 dB of internal microphone gain. And yes, it does say H.E.A.R.S. rather than EARS.
I use the included USB cable for the connection between my computer and the EARS device.

DAC and Amplifier Requirements

In order to make a measurement, you must use a stand-alone, high-quality DAC and amplifier to generate tones and to calibrate the miniDSP EARS. I’m using an iFi iDSD Nano connected via USB to an older 2012 MacBook Pro. The Nano is a basic, but clean and reasonably competent device that will power most headphones properly.

My trusty, old, well-loved, and much used iFi iDSD Nano, now serving as the DAC and headphone amplifier for EARS measurements.
My trusty, old, well-loved, and much used iFi iDSD Nano, now serving as the DAC and headphone amplifier for EARS measurements.
The DAC and amplifier are not included with the miniDSP EARS (nor is a computer) and the user must provide their own to complete measurements. Users must use the same device for all their measurements and ideally a similar device to other users to compare measurements. Do not use the typically noisy and underpowered headphone jack in the computer itself.

I would suggest using an amplifier with a hardware volume control. The process requires calibrating the output for every pair of headphones measured. This must be done by adjusting the volume to a set output level, which requires more or less amplification depending on the sensitivity and impedance of the headphones being measured. An external knob simplifies the process and allows for some fine-tuning.

Computer Setup

Two things must be set on your computer before proceeding with measurements. Firstly, the sample rate of the DAC must be set to 48 kHz. This is the rate that the EARS is expecting. Secondly, the input gain of the EARS must be set to 0 dB.

Set the Format: to 48,000 Hz in the Midi Audio Setup app in Apple OS.
Set the Format: to 48,000 Hz in the Midi Audio Setup app in Apple OS.

Both the Sample Rate and input gain are modified in the MIDI Audio Setup app in Apple OS and in the Sound Control Panel Properties – Levels tab in Windows.

Adjust the EARS to 0dB gain in the Midi Audio Setup app in Apple OS.
Adjust the EARS to 0dB gain in the Midi Audio Setup app in Apple OS.

REW Software Setup

Room EQ Wizard Software

The fantastic and free Room EQ Wizard (REW) software is the heart of the measurement process. I selected version 5.15 of REW to best match the current EARS documentation. The 5.15 version is available for download from here.

In general, follow the recommended settings for REW in the miniDSP EARS instructions. This document isn’t intended as a replacement for the included instructions, rather as a summary companion.

Determine SPL Calibration Target

The top of all the calibration files shows the Sens Factor and Sensitive Side for your particular EARS.
The top of all the calibration files shows the Sens Factor and Sensitive Side for your particular EARS.

Write down the Sensitivity Factor (Sens Factor) and Sensitive Channel (sensitive side) of your specific EARS device. This information is found at the top of the calibration files. For example, my EARS sensitivity factor and sensitive channel are:

  • -1.1 RIGHT
All the calibration files must be downloaded and saved from the miniDSP EARS website (Unique Calibration File Download section) by entering the serial number for your EARS.

Use the sensitivity factor to determine the SPL Calibration Targets for headphones and IEMs. For headphones, this is -40 + sensitivity factor. For IEMs, this is -30 + sensitivity factor. For example, the SPL Calibration Targets for my ears are:

  • Headphones: (-40 + -1.1 =) -41.1
  • IEMs: -31.1

These values will be used on the REW SPL Meter window.

REW Preferences

Press the Preferences button on the REW toolbar.

The Soundcard tab in REW Preferences.
The Soundcard tab in REW Preferences.

In the Soundcard tab in REW Preferences, set the following:

  • Sample Rate: 48 kHz
  • Output Device: Your DAC/Amp
  • Input Device: E.A.R.S Gain 18 dB
  • Output: Default Output – Choose your Sensitive Channel (for my EARS this is RIGHT)
  • Input: Default Input – Choose your Sensitive Channel (for my EARS this is RIGHT)
  • Sweep Level: -20 dBFS

Mic/Meter Tab

The Mic/Meter tab in REW Preferences.
The Mic/Meter tab in REW Preferences.
  • Mic or Z weighted SPL meter: selected
  • Calibration File: Select the downloaded calibration file for your EARS. Select L or R (left or right) depending on the channel being measured.
  • IEMs: IDF (for my EARS this is: R_IDF_8602316.txt)
  • Headphones: HPN (for my EARS this is: R_HPN_8602316.txt)

To keep things organized, I saved the calibration files in the folder format:

  • miniDSP EARS Files/Calibration Files – 860-2316/HPN Headphone Measurement Compensation/
  • miniDSP EARS Files/Calibration Files – 860-2316/IDF IEM Diffuse-Field Compensation/

Calibration Files

miniDSP provides 4 different types of calibration files for the EARS. One is RAW (minimal compensation), one is for IEM measurement (IDF), and there are two for headphones (HEC and HPN).

For simplicity’s sake, we will perform measurements using the IDF files for IEMs and the HPN files for headphones. The appropriate file must be loaded into REW before running a measurement.

There are Left (L) and Right (R) files for each compensation.
The HPN and IDF calibration files.
The HPN and IDF calibration files.

The calibration files serve three purposes:

1. Correct the frequency response between the individual (left and right) microphone capsules.

2. Correct for any SPL sensitivity difference between the left and right capsules.

3. To apply a compensation so that the produced measurement is more easily and usefully interpreted.

The calibration files provide compensation for the particular characteristics of the measurement rig, and there are ongoing debates and discussions as to what is the ‘right’ compensation to use. All measurement devices typically use some type of compensation.

“The EARS is not an IEEE-standard ear simulator (those are very expensive). So, its compensations need to be different from those used with expensive measurement rigs (or published in research papers).” – EARS User Manual

The four different calibration files types are:

1. IDFIEM Diffuse Field Compensation – Based on the Etymotic ER4SR.

2. HPH – Headphone Measurement Compensation – Intended as a basis for headphone measurements.

3. HEQ – Headphone EQ Compensation – Intended as a basis for subsequent headphone EQ changes.

4. RAW – The raw measured response calibrated for the microphone capsules.

Although miniDSP suggests using the HEC compensation rather than the HPN, I find the HPN results to be more comparable to other respected publications such as Inner Fidelity.

View Tab

  • Full scale sine rms is 0 dBFS: unchecked (off).

SPL Calibration

Each time a new pair of headphones (or IEMs) are being measured, the sound pressure level (SPL) must be calibrated.

The REW Generator and SPL Meter windows. Calibration is being done for a pair of headphones to match the target of -41.1.
The REW Generator and SPL Meter windows. Calibration is being done for a pair of headphones to match the target of -41.1.

REW Generator Window

  1. Press the Generator button on the REW toolbar.
    • Output: Sine Wave
    • RMS Level dBFS: -20.0
    • Frequency: 300 Hz
  2. Press the green PLAY button to start.

REW SPL Meter Window

  1. Press the SPL button on the REW toolbar.
  2. Press the lower right red button to power on the meter. Slowly increase the volume on your headphone amplifier until the dBFS meter in the center reads the SPL Calibration Target you determined in the first step. The SPL Calibration Targets for my ears are:
    • Headphones: -41.1
    • IEMs: -31.1
. It may not be possible to get the dBFS meter to stop exactly on your SPL Calibration Target, so just get it as close as you can.
Set Headphones to 84 and IEMs to 94 on the SPL Calibration window.
Set Headphones to 84 and IEMs to 94 on the SPL Calibration window.
  1. Press the Calibrate button. Adjust the SPL figure in the box to:
    • IEMs: 94
    • Headphones: 84
  2. Press the Finished button.
The SPL calibration has been completed. Ready to take some measurements!
The SPL calibration has been completed. Ready to take some measurements!

Performing Measurements

  1. Press the Measurement button in the REW toolbar.
    • Start Freq: 20
    • End Freq: 20,000
    • Level: -20.0
    • Output: Default Output: Right
  2. Press the Start Measuring button.

The measurement process only takes a few seconds to complete. The first frequency response graph will be displayed.

Making a measurement.
Making a measurement.

Repositioning the headphones and running a minimum of 5 measurements per channel is necessary to identify and remove abnormal or outlier measurements. 5 valid measurements can then be averaged for a relatively accurate side measurement (left or right graph).

These 10 valid measurements can be averaged for a relatively accurate L+R graph.

Measuring the Other Channel

Preferences Window

Soundcard Tab
  • Output: Default Output: SELECT THE OTHER CHANNEL
  • Input: Default Input: SELECT THE OTHER CHANNEL
Mic/Meter Tab
  • File: SELECT APPROPRIATE CALIBRATION FILE FOR THE OTHER CHANNEL

Frequency Response Graph

This is where the measurement results are displayed. It’s the most common and useful graph we have to compare how the headphones sound. Start by setting several defaults for all measurements:

  • Use the Limits button to set the graph to display 20-20,000 Hz on the x-axis and 50-100 dB on the y-axis.
  • Select the All SPL tab above the graph.
  • After each measurement, from the Graph dropdown menu select: Apply 1/12 smoothing. This smooths the line using 1/12 octave smoothing.

After smoothing, save each measurement in the format:

  • HEADPHONE NAME – SIDE MEASUREMENT NUMBER. For example: “HD650 L1.mdat
The SPL graph is displayed after taking a measurement. Set the appropriate axis values and 1/12 octave smoothing.
The SPL graph is displayed after taking a measurement. Set the appropriate axis values and 1/12 octave smoothing.

Physically reposition the headphone on the EARS measurement rig. This may be done by entirely removing the headphones and placing them on again, or by rotating or sliding the headphones around on the EARS. Try to position them naturally over the silicone ears while maintaining a good seal with the ear pads.

Perform another measurement as outlined above. Discard any erroneous measurement that is clearly incorrect. Repeat until you have created 5 valid measurements for each side.

The impact of a bad seal between the headphone earpads and the EARS is seen in the pink line. Bass and treble response are significantly curtailed and out of line with the better (green and blue) headphone position measurements.
The impact of a bad seal between the headphone earpads and the EARS is seen in the pink line. Bass and treble response are significantly curtailed and out of line with the better (green and blue) headphone position measurements.
The most obvious measurement issue is created when there is a lack of seal between the earpads (or IEM ear tips) and the EARS. The bass response will be severely curtailed and will drop off significantly.

Press the Average the Responses button at the bottom of the graph to create an average of all the measurements currently displayed in the All SPL tab. You can Open or Close measurements as appropriate to finally save a file as:

  • HEADPHONE NAME – Avg – SIDE. For example: “HD650 Avg L.mdat

The Capture button at the top is used to create a picture of the graph that can be used to post online.

  • Image Width: 2000
  • Include Title: checked
  • Include Legend: checked
  • JPEG image: checked
  • Type any additional text here: Title of Graph. For example: “HD650 – Headphonesty”

Summary of Settings and Best Practices

  • Measurements must be completed in a silent room.
  • The user must provide a decent DAC and headphone amplifier able to properly power the headphones being measured. This device should be the same for all headphones being measured.
  • Use a single version of REW software. I use v5.15 so that it matches the version in the miniDSP instructions.
  • Use the sensitivity factor in a calibration file to determine the specific SPL Calibration Target for your EARS and the Sensitive Channel. Headphones: -40 + sensitivity factor. IEMs: -30 + sensitivity factor. Write these down.
  • Use the SPL Calibration Target to configure REW using the Generator window and SPL Meter for each pair of headphones or IEMs measured. Calibrate to 84 for headphones and 94 for IEMs.
  • Sample Rate: 48 kHz
  • Sweep Level: -20 dBFS
  • Gain Setting: 18 dB
  • Measurement Start: 20 Hz End: 20000 Hz
  • Use the Calibrated HPN (L or R) files provided by miniDSP for the particular EARS rig (based on serial number) for measuring Headphones.
  • Use the Calibrated IDF (L or R) files provided by miniDSP for the particular EARS rig (based on serial number) for measuring IEMs.
  • Default graph settings: Frequency: 20 Hz – 20 kHz. SPL Range: 50-100 dB. Octave Smoothing: 1/12
  • Repositioning the headphones and running a minimum of 5 measurements per channel is necessary to identify and remove abnormal or outlier measurements. 5 valid measurements can then be averaged for a relatively accurate side measurement (left or right side graph).

Conclusion

As an additional resource, I have posted a couple of videos of the above process to YouTube.

Videos:

  1. Part 1: I confirm all the necessary settings and measure the right channel of the Sennheiser HD518. Five measurements are completed and averaged.
  2. Part 2: I measure the left channel and average all the results.

While not perfect, the miniDSP can be a useful tool in comparing the relative performance of headphones and IEMs. The crucial step is to ensure that these measurements are being done as consistently as possible across all headphones being measured and across all miniDSP EARS users.