Expanded Calibration Guide - BLUE SKY SUB 15 UNIVERSAL Owner's Manual

1000-watt subwoofer with adaptive x-over

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Expanded Calibration

Guide

Instructions for electroacoustic calibration of a 2.1 audio system using

a SPL meter and Blue Sky's test files.

Before starting this procedure you will need to download BlueSkyTestFiles.zip

(an 18 MB zip file) by going to www.abluesky.com/calibration. To download

the test file, "Right Click" and select "Save Target As". The file will begin

downloading once a location has been selected.

Once downloaded, either burn the test files to a CD or import them into your

DAW and follow the instructions below.

ADDITIONAL REQUIRED ITEMS

2.1 Monitoring System

SPL Meter - such as the SPL meter sold by RadioShack

in the U.S.

BlueSkyTestFiles.zip Includes 4 files:

•

1000Hz SINEWAVE -20dBFS.wav – a 1kHz file recorded at -

20dBFS for electrical calibration

•

40-80Hz PINK NOISE -20dBFS.wav – a 40Hz to 80Hz bandwidth

limited pink-noise file recorded at -20dBFS

•

500-2.5kHz PINK NOISE -20dBFS.wav – a 500Hz to 2.5Hz

bandwidth limited pink-noise file recorded at 20dBFS

•

Pink Noise full bw -20dBFS.wav – a full-bandwidth pink-noise file

recorded at - 20dBFS

These test files are all mono files. Please make sure you hard assign

them to the left and then the right, not both channels at the same time.

If you are using a CD player use only one channel of the CD player.

THEORY

The purpose of calibration is to adjust the overall electroacoustics system gain

so that 0dBVU of electrical signal level equals a certain acoustic level at the

listening position. Since most recording media is now digital, the reference

electrical signal level is usually –20dBFS with 20dB of headroom. The reference

SPL level however can vary based on the delivery media and speaker type.

Please note that the bandwidth limited signals that have been provided, limit

many of the room interaction affects often associated with measuring SPL and

broadband pink noise.

All test signals are recorded at –20dBFS including the 1 kHz sine wave tone.

The sine wave tone is used to set the electrical output level throughout the

signal path, right up to the point you get to the speakers, while the various pink

noise signals are used for acoustic measurements and calibration.

The following procedure assumes you are calibrating the system to 85dBC

SPL.

Step 1

TURN OFF THE MONITORING SYSTEM (until step 4)

Step 2

Remove all eq and dynamics from the signal path and set all

controls to zero / unity gain. Play the 1kHz Sine Wave, hard assign

it to the left channel only, and adjust the output fader so the output

meter reads -20dBFS. If you are using an analog console, set the

output level to 0 VU. Then hard pan the signal to the right channel

output and repeat for the right channel. Once calibrated do not

move the output faders.

Step 3

Mute everything and make sure the 1kHz tone is OFF .

Step 4

Now that the system has been electrically calibrated

turn ON your 2.1 System (SUB 15 Universal + monitors).

Step 5

Assign the 500-2.5kHz pink noise signal to the left channel only.

Make sure there is nothing coming from the right channel (or any

other channels). Because this signal is bandwidth limited, you

don't have to worry about turning the sub off. There are two

methods of setting the levels.

A. If you have a master monitor level control, you can set the sat

gain control at reference and then adjust the monitor gain control

for 85 dBC. Then mark the monitor level as your reference position.

B. The other method is to set master monitor level to the position

you want as a reference level and then use the volume controls

to set 85 dBC. If you use this method you should mark the knob

position with a grease pencil so you can always go back to

reference level if the knob gets moved.

For either method:

SPL should be measured at the mix position, with the SPL meter

at arms length, with the microphone at seated ear height, angled

at approximately 45 degrees, and pointed at the center point

between the left and right speakers.

Once the left channel is set to 85dBC, repeat this step for the right

channel

Step 6

Feed 40-80Hz pink noise signal to the left channel only. Adjust the

subwoofer level control until the subwoofer reads 85dBC (slow)

at the mix position. The meter will bounce around a little, so you

will need to do a mental average (I tend to filter out the peaks in

my mind, so I don't set the sub too hot). The right channel should

measure about the same and no additional adjustments need to be

made.

Step 7

You can play the full-bandwidth pink noise, assigning it to the left

and then the right channel (not at the same time). You should

measure about 85dBc. It may be a little higher, because below

30Hz the room may have a little extra gain. No adjustments should

be made with Full Bandwidth pink noise, unless you have an RTA

(real time analyzer).

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Step 8

You are finished and the calibration process has been completed

– enjoy!

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A note about the LF EXTENSION and PHASE switches:

One of the SUB 15 Universal's unique features is a switchable

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low frequency response characteristic, of either 30Hz to 200Hz

+/-3dB or, in "extended LF mode", 20Hz to 200Hz +/-3dB

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(anechoic), marked 30Hz and 20Hz respectively. The extended

mode is ideal for large rooms that don't exhibit the room gain

phenomenon of smaller sealed spaces. The only way to be absolutely sure

of which setting is appropriate for your studio is to use an acoustic analyzer.

Using the 20Hz in a sealed space, such as a small to medium size studio, can

result in a rising LF response characteristic below 30Hz.

The PHASE setting on the SUB 15 Universal should typically be set to 0,

especially when the SUB 15 Universal is used with Blue Sky SATs. However,

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there may be times, depending on the speakers used with the SUB 15 Universal

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or because of certain acoustic conditions, that the phase setting needs to be

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set to 180, so as to get proper summation between SAT and SUB. The only way

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to be absolutely sure which setting is appropriate for your studio is to use an

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acoustic analyzer.

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Expanded Calibration Guide - BLUE SKY SUB 15 UNIVERSAL Owner's Manual

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