miniDSP EARS User manual

miniDSP Ltd, Hong Kong / www.minidsp.com / Features and specifications subject to change without prior notice 1
MINIDSP EARS
HEADPHONE MEASUREMENT JIG
User Manual

miniDSP Ltd, Hong Kong / www.minidsp.com / Features and specifications subject to change without prior notice 2
Revision history
Revision
Description
Date
0.1
First draft
12 Sept 2017
0.2
Second draft
15 Sept 2017
0.5
Fifth draft
15 Dec 2017
0.7
Preliminary version, OK for public release
17 Dec 2017
1.0
First official version
20 Dec 2017
1.1
Added RAW and HEQ compensation, simplified SPL calibration
16 April 2018

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TABLE OF CONTENTS
Important Information.................................................................................................................................. 4
1Product Overview ................................................................................................................................... 6
2Getting Started with EARS ....................................................................................................................... 7
2.1 A note on measurement conditions...........................................................................................................................7
2.2 Check the EARS gain setting .......................................................................................................................................7
2.3 Download the calibration files ...................................................................................................................................8
2.4 Connect for measurement .........................................................................................................................................8
2.5 Check computer settings............................................................................................................................................9
2.6 Step-by-step: Room EQ Wizard ..................................................................................................................................9
2.6.1 Calculate SPL calibration target.........................................................................................................................9
2.6.2 Configure REW.................................................................................................................................................10
2.6.3 Measure the first channel................................................................................................................................12
2.6.4 Measure the other channel .............................................................................................................................13
2.6.5 Changing the calibration file............................................................................................................................14
2.6.6 Measuring at higher SPLs ................................................................................................................................14
3More about measurement .....................................................................................................................15
3.1 The frequency response graph.................................................................................................................................15
3.2 Other types of measurement ...................................................................................................................................16
3.3 More on headphone measurements .......................................................................................................................17
3.4 More on IEM measurements ...................................................................................................................................19
3.5 Effect of the amplifier (and DAC) .............................................................................................................................20
3.5.1 Amplifier frequency response .........................................................................................................................20
3.5.2 Output impedance...........................................................................................................................................20
3.5.3 What to do.......................................................................................................................................................20
4Calibration/compensation curves ...........................................................................................................21
4.1 Raw vs compensated response ................................................................................................................................21
4.2 Headphone EQ compensation (“HEQ”)....................................................................................................................22
4.3 IEM diffuse-field compensation (“IDF”) ...................................................................................................................22
4.4 Headphone measurement compensation (“HPN”)..................................................................................................23
4.5 Raw calibration with no compensation (“RAW”) .....................................................................................................23
5Further information ...............................................................................................................................24
5.1 Specifications............................................................................................................................................................24
5.2 Obtaining support ....................................................................................................................................................24

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IMPORTANT INFORMATION
Please read the following information before use. In case of any questions, please contact miniDSP via the
support portal at minidsp.desk.com.
DISCLAIMER/WARNING
miniDSP cannot be held responsible for any damage that may result from the improper use or incorrect
configuration of this product. Please read this manual carefully to ensure that you fully understand how to
operate and use this product, as incorrect use or use beyond the parameters and ways recommended in this
manual have the potential to cause damage to your audio system.
Please also note that many of the questions we receive at the technical support department are already
answered in this User Manual and in the online application notes on the miniDSP.com website. So please take
the time to carefully read this user manual and the online technical documentation. Thank you for your
understanding!
WARRANTY TERMS
miniDSP Ltd warrants this product to be free from defects in materials and workmanship for a period of one year
from the invoice date. Our warranty does not cover failure of the product due to incorrect connection or
installation, improper or undocumented use, unauthorized servicing, modification or alteration of the unit in any
way, or any usage outside of that recommended in this manual. If in doubt, contact miniDSP prior to use.

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FCC CLASS BSTATEMENT
This device complies with Part 15 of the FCC Rules. Operation is subject to the following two conditions:
•This device may not cause harmful interference.
•This device must accept any interference received, including interference that may cause undesired
operation.
Warning: This equipment has been tested and found to comply with the limits for a Class B digital device,
pursuant to Part 15 of the FCC Rules. These limits are designed to provide reasonable protection. This
equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance
with the instructions, may cause interference to radio communications. However, there is no guarantee that
interference will not occur in a particular installation. If this equipment does cause harmful interference to radio
or television reception, which can be determined by turning the equipment off and on, the user is encouraged to
try to correct the interference by one or more of the following measures:
•Reorient or relocate the receiving antenna.
•Increase the separation between the equipment and receiver.
•Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
•Consult the dealer or an experienced radio/TV technician for help.
Notice: Shielded interface cable must be used in order to comply with emission limits.
Notice: Changes or modification not expressly approved by the party responsible for compliance could void the
user’s authority to operate the equipment.
CE MARK STATEMENT
The MINIDSP EARS has passed the test performed according to European Standard EN 55022 Class B.
ANOTE ON THIS MANUAL
This User Manual is designed for reading in both print and on the computer. If printing the manual, please print
double-sided. The embedded page size is 8 ½” x 11”. Printing on A4 paper will result in a slightly reduced size.
For reading on the computer, we have included hyperlinked cross-references throughout the manual. In
addition, a table of contents is embedded in the PDF file. Displaying this table of contents will make navigation
easier.

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1PRODUCT OVERVIEW
Thank you for purchasing a miniDSP EARS headphone measurement system. miniDSP EARS is a measurement jig
for headphones and IEMs (in-ear monitors) that we've built using the same core technology as our extremely
popular UMIK-1 calibrated speaker and room measurement microphone.
EARS designed to be a useful and practical tool for headphone enthusiasts. It is ideal to:
1. Check that your headphones are operating correctly e.g. balance of left/right frequency response.
2. Take measurements that you can use as a basis for equalizing your headphones.
3. Observe the effect on frequency response of different earpads and eartips.
4. Measure the effect of modifications to the headphones.
5. Compare your headphone measurements with other EARS users.
Please note that EARS is not an industry-standard measurement head. Even expensive (i.e. tens of thousands of
dollars) heads can produce measurements that are different to each other. Our goal with the EARS is to produce
something that is affordable and fun to use!

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2GETTING STARTED WITH EARS
In a nutshell, you mount your headphones on the EARS jig (or put your IEMs in the “ear canal”) and run a
measurement sweep using your headphone amp and favorite measurement program. To get a useful
measurement, you will need to first load a suitable calibration/compensation file (which we provide) into the
measurement program.
2.1 ANOTE ON MEASUREMENT CONDITIONS
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.
2.2 CHECK THE EARS GAIN SETTING
There is a bank of DIP switches on the front of the EARS.
Switches 1 to 3 control the internal gain of the microphone amplifier, as shown in Table 1. (Switch 4 is not used.)
The default gain as shipped and as indicated in the diagram above is 18 dB. The remainder of this section
assumes that the default gain is used. If you change the analog gain setting and want to display correct SPL
values, you will also need to read Measuring at higher SPLs on page 14.
Table 1. Gain switch settings
Gain (dB)
SW1
SW2
SW3
0
Down
Down
Up
6
Down
Up
Down
12
Down
Up
Up
18
Up
Down
Down
24
Up
Down
Up
30
Up
Up
Down
36
Up
Up
Up

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2.3 DOWNLOAD THE CALIBRATION FILES
You will need two calibration files, one for the left channel and one for the right. You can download these files
from the EARS page on miniDSP.com by entering your EARS serial number.
You will also need to select a compensation (see Section 4 for more information). Table 2 lists the recommended
compensation curves for headphones and IEMs with the corresponding downloaded file names. (xxxyyyy in the
file name is the serial number of your EARS unit.)
Table 2. Naming of calibration files for EARS
Code
Type
Channel
File name
HEQ
Over-ear headphone
Left
L_HEQ_xxxyyyy.txt
HEQ
Over-ear headphone
Right
R_HEQ_xxxyyyy.txt
IDF
IEM diffuse field
Left
L_IDF_xxxyyyy.txt
IDF
IEM diffuse field
Right
R_IDF_xxxyyyy.txt
2.4 CONNECT FOR MEASUREMENT
Figure 1 shows a typical connection scheme for headphone measurement. The diagram shows a miniDSP HA-
DSP but you can use any other headphone amplifier. If your headphone amplifier doesn’t have a USB input, then
you will need to adjust accordingly i.e. by using a separate DAC and headphone amplifier. If your headphone
amp has DSP or EQ in it, make sure that it is completely disabled when running measurements.
Figure 1. Typical connection for headphone measurement

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2.5 CHECK COMPUTER SETTINGS
Some simple settings will need to be checked in your computer:
•The sample rate of your DAC is set to 48 kHz
•The input gain of the EARS is set to 0 dB. On the Mac, use Audio MIDI Setup. On Windows, use the
Sound control panel and open its Properties dialog. On the Levels tab, right-click to convert the display
to dB and adjust the slider so it reads 0.0 dB.
2.6 STEP-BY-STEP:ROOM EQ WIZARD
Room EQ Wizard (REW) is a free acoustic measurement program that runs on Windows, Mac and Linux. This
section provides step-by-step instructions with screenshots. Here is the documentation.
2.6.1 Calculate SPL calibration target
1) Work out your SPL calibration target. By default, this is −40 for headphones and −30 for IEMs.
a) Open one of your calibration files (e.g. by double-clicking on it). At the top, you will see two lines like
this:
"Sens Factor =-1.7dB, EARS Serial 8601001, compensation HEQ V1"
"Use this file on the LEFT channel. Your sensitive side is LEFT."
Write down the sensitivity factor (“Sens Factor”), and which channel is the “sensitive side.” In the
example above, the sensitivity factor is −1.7 and the sensitive side is the left.
b) Add the sensitivity factor to the SPL calibration target. For example, with sensitivity factor of −1.7, the
SPL calibration target is −41.7 for headphones and −31.7 for IEMs.
Note: the calculated SPL calibration target is valid only for REW, and only if the option “Full scale sine rms is 0
dBFS” is unchecked i.e. off:

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2.6.2 Configure REW
2) Start REW and open the Preferences window.
3) On the Soundcard tab, set the sample rate to 48 kHz. Select the headphone amplifier (or DAC) as the output
and the EARS as the input source. Choose the “sensitive” channel (Left in this example) for both output and
input, and set the Sweep Level to −20 dBFS.
4) On the Mic/Meter tab, click on Browse. Select the downloaded calibration file for the “sensitive” channel.
Make sure that the “Mic or Z weighted SPL meter” option is set.
5) On the View tab, ensure that the option “Full scale sine rms is 0 dBFS” is unchecked i.e. off.
6) Turn the volume on the headphone amplifier all the way down.