ACI Sub test CD Owners manual
Adjusting ACI Subs Using the ACI Test CD
1. By Ear: Use the test tones, (most people prefer the sinewaves), to try to
achieve the smoothest system response. Note, you will find very different
results by just moving your head. This is because of the very strong effects
that room modes have on low frequencies.
2. Using the Radio Shack SPL meter and Excel spreadsheet: This
method is relatively easy, inexpensive, and quite accurate. You must have
Excel on your computer to be able to load and use the spreadsheet. It can
be rather time consuming compared to methods four or five.
3. Using the Radio Shack SPL meter and hand plotted graphs: Very
similar to #2 but you'll have to do a little math when hand plotting.
4. Using a test system such as ETF, CLIO or MLSSA: If you have this type of equipment
you can run the measurements quickly and accurately. Usually the most expensive option.
Most of these instruments are extremely powerful and can have a relatively steep learning
curve. Separate measurement microphone and possibly microphone pre-amp will also be
required.
5. Using a RTA (Real Time Analyzer): This is probably the fastest method as you can see the
results of your adjustments on-screen, in real time. RTAs used to be quite expensive.
Computers with soundcards have drastically changed that! An excellent RTA can be found
at: www.trueaudio.com. Separate measurement microphone and possibly a microphone
pre-amp will also be required.
The Steps
1. We provide both sine waves and warble tones. Many people prefer sine waves for listening
tests and warble tones for using the SPL meter.
2. Insert the test disc in your CD player. Position the SPL meter at head height in the primary
listening position. The meter should be aimed toward the speakers. A camera tripod can be
used as the SPL meter has ΒΌ -20" threaded insert on the bottom.
3. Set the SPL meter to "C" weighting, and response to slow.
4. Start with the system volume turned down. Play a 60Hz warble tone and adjust the
subwoofer volume to read 70dB on the SPL meter.
5. Download the "Subwoofer One" MS Excel worksheet*. Go to:
http://www.audioc.com/library1/testcd/testcd.htm
6. Play the warble to tracks, read the measurements, and record in the spreadsheet. The
spreadsheet will make the calculations and show you a graph.
7. Using the graph, you can now use the controls on your sub or experiment with placement to
get the smoothest possible response.
* If you don't have Excel, you can print the other PDF Subwoofer Worksheet out and do manual
calculations. Your steps will be the same as above. However, for steps five and six you will
need to manually plot your graph. Be sure to add or subtract the required correction for the
meter.
Using Alternate Measurement Systems
All Rights, Audio Concepts, Inc. 2003
ACI Subs Worksheet #Two
Some of you may own or have access to a RTA such as the 1/3 octave unit manufactured by
Audio Control. This type of unit will allow you to quickly see the changes as you make
adjustments. The disadvantage is that 1/3 octave resolution is rather marginal. We have found
1/6 octave to be ideal for optimizing systems. These types of analyzers are available as
software based systems using your computer sound card. Another excellent option is the ETF
system, which takes quick, high-resolution measurements of not only frequency, but time as
well.
Software based analyzers are inexpensive, (in some cases free), and very powerful. That power
comes with a price. The learning curve to setup and use some of these programs can be rather
steep. Other factors to keep in mind; 1) Most of the software programs have certain
requirements for the computer hardware and the soundcard used. 2) Separate measurement
microphone and possibly microphone pre-amp will be required for any software based RTA or
Analyzer.
Additional Resources:
ETF: www.etfacoustic.com
Trueaudio: www.etfacoustic.com
Subwoofers.org: www.subwoofers.org
2
ACI 901 South 4th Street
La Crosse, WI 54601
Manual Plotting For Those Without Excel www.audioc.com
sales@audioc.com
Frequency Response
80
78
76
74
72
70
SPL
68
66
64
62
60
20
22.52527.5
30
35
40
45
50
55
60
Frequency
65
70
75
80
90
100
110
125
140
160
200
Frequency 20 22.5 25 27.5 30 35 40 45 50 55 60 65 70 75 80 90 100 110 125 140 160 200
Measured SPL
Add 6.2 5.4 4.4 3.7 3.4 2.5 2 1.7 1.3 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.25 0.2 0.15 0.1 0
Actual SPL
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