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Upcoming Seminar:
"Loudspeaker
Measurement"
Lone Star Audio Fest
May 2-4, Dallas TX
Details
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Calculation of Response - A Division in the Frequency Domain
All Woofer Tester products simultaneously determine the 'measure' and 'reference' signals eliminating the need to pre-calculate
reference levels that are later subtracted to reveal a measurement. Our software performs this task in the frequency domain
on all signal types (continuous sine, pulsed sine, step and MLS) using a complex division. The result is that all tests are
performed in real-time yielding direct measurements of amplitude and phase. This methodology is used for all impedance and
response test modes and for all signal excitation types.
Selecting the Measurement and Reference Signals
The Setup Control Window can be brought up either as a Window menu option, or by clicking on the 'Select' button in the WT
Control window. The first tab in this window - 'Signal/Mode' - is where the signal to be measured, 'A', and the signal to
be used as reference, 'B', are selected. The type of test to be performed and test drive signal type are also selected here.
Additionally, if the microphones are being used, the gain can be adjusted here. Note, how it is possible to divide a number
of signals, some of which may not make any sense. An additional restriction is that 'left' and 'right' side signals cannot be
intermixed, since the final mix down into the codec is ultimately 2 channels. Here is a list of possible setups and what they do:
A B Signal Anal Mode Comment
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MikeL LineR Sine db(A/B) Swept response of Microphone(L) -> Buffer
MikeL LineR Impulse db(A/B) Fast response of Microphone(L) ->Buffer
MikeL LineR MLS db(A/B) Fast response of Microphone(L) ->Buffer
MikeR LineL Impulse db(A/B) Fast response of Microphone(R) ->Buffer
LoZP V LoZP A Sine LoZP Swept impedance and phase of WT2 low power port
LoZP V LoZP A Impulse LoZP Fast impedance and phase of WT2 low power port
HiZP V HiZP A Sine HiZP Swept impedance and phase of WTPro high power port
HiZP V HiZP A Impulse HiZP Fast impedance and phase of WTPro high power port
MikeR HiZP V Impulse db(A/B) Response of MikeR - AFTER amplifier
MikeR MikeL Impulse db(A/B) Room Mode Measurement (MikeL placed at excitation source)
etc...
Notes:
Open the Impulse/Waterfall Control Window to adjust the impulse time window. 'Fast' Impulse and MLS
impedance and phase
modes are not as accurate as Swept Sine ZP.
Signal Selection and Mode Control
Click Image to Enlarge
Compensation Button
Additional compensation can also be applied using the Compensation button. This button opens the Setup Control Window to the
Comp & Bufs tab. The upper half FFT compensation area can be used to set the FFT size, or if the current response mode has
settled, save that response as a zero reference. You can enable or delete compensation files here as well.
Trouble Shooting
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Problem: |
I don't understand the 'A' and 'B' Measurement and Reference Signals.
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Answer: |
The ratio or db(ratio) can be calculated between two signals. Internally these signals are grouped into 'left' and 'right' signals that come into a 4:1 mux switch selecting the line, microphone, LoZP and HiZP ports (HiZP for WTPro enabled). Additionally, response can be calculated against the internal math reference. The test signal appears at both line outputs. The "A - Measure" (input) channel can be a microphone or line input, as selected on the Setup menu. The "B - Reference" channel requires an external loop from line out to line in.
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Problem: |
I can't figure out what signals are being processed.
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Answer: |
The FFT/Oscilloscope window shows the left and right channel before processing. This is a great way to hunt down many things. Just be sure the TS control window is open as this window has the base audio conversion routines attached to it.
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Problem: |
The 'A' and 'B' selections do not always update but clicking on those settings a second time updates them.
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Answer: |
This is a graphics update problem and has been fixed in beta release 3.04b.
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