Online User’s Guide Revised: May 11, 2008 WT3 is produced by: Dayton Audio 725 Pleasant Valley Drive Springboro, Ohio 45066 USA http://www.daytonaudio.com Copyright © 2007-2008 by John L. Murphy, Andersonville, TN USA All Rights Reserved. No part of this publication may be reproduced without prior express written permission.
Minimum Requirements for the PC The minimum requirements to run WT3 are: • • • A PC with a processor running at no less than 500 MHz with 64 MB RAM One available USB port A display with resolution of at least 800 x 600 pixels WT3 runs under Microsoft Windows 98, Me, 2000, XP and VISTA operating systems.
Quick Start for the WT3 Woofer Tester *** VERY IMPORTANT SAFETY NOTE *** NEVER connect the test leads of the WT3 to a speaker that is connected to any other equipment or to an equipment ground! Severe damage could occur to the WT3 unit or to the other equipment. Only connect the WT3 to an unconnected loudspeaker. Naturally, you will want to test your first woofer as soon as you get your WT3. Here are step-by-step instructions to get you going quickly. 1) Install the WT3 software.
6) Select “Impedance Calibration4” under the “Impedance Analyzer” menu. The software will sweep the resistor and plot the results. The uncalibrated impedance is displayed and the calibration is complete. You should also calibrate the test leads at this time by selecting the appropriate command under the "Impedance Analyzer" menu and following the on-screen instructions. 7) Connect the alligator clips from the WT3 unit to the terminals of the driver under test.
9) Measure the driver's V(as). Once you have measured the driver's free air parameters the "Measure V(as)" button becomes enabled. Select one of the three methods to measure the V(as). Then press the “Measure V(as)” button to start the measurement procedure. The three V(as) measurement methods are: Test Box Method Added Mass Method Specified SPL Method 10) After measuring the driver you can: • • • • • Save the data to one of 20 project memories. Save your work to a WT3 test project file (file type .
Windows Vista - Additional Setup Requirements PLEASE NOTE: STEP 2 IS CRITICAL FOR WINDOWS VISTA USERS! 1. Go to the Windows Control Panel and open the “Sound” control panel. At the "Playback" tab make sure that "USB Audio Codec" is selected as the default sound system for playback. (the icon should appear with a green check mark as shown). If not, click on the "USB Audio Codec" and then click the "Set Default" button below. 2. Change to the "Recording" tab at the top of the Sound control panel.
3. Click OK to close the "Sound" control panel. Note that this setup must be performed once for each USB port with which the WT3 unit will be used. Also, when starting WT3, always click on the Speaker icon in the task bar and make sure the Windows Volume Control is set at maximum.
Introducing WT3 No other loudspeaker parameter measurement system is as fast or as easy to use as Dayton Audio’s WT3. WT3 employs powerful new DSP measurement techniques to provide highly accurate parameters in seconds.
The WT3 Toolbar The WT3 Toolbar provides easy access for many frequently used commands. Memory show and hide operations are especially convenient with the toolbar. Note that empty memories are grayed out until data is saved to them. Once they contain data they become enabled to switch between show and hide modes.
Using the WT3 Memories The WT3 software features 20 user memories for saving your detailed measurements along with much other user entered information about the driver. Each memory consists of the impedance and phase plots, the test setup information (test box volume, added mass etc.) along with the three pages of parameters, ,specifications and comments that are seen at the Driver Editor. When you save a WT3 file (type ".
View Menu: Clear Memory These commands erase the contents of the specified memory. • • From the keyboard, use Ctrl+Alt+1, Ctrl+Alt+2 etc. through Ctrl+Alt+0 to clear the contents of memories 1 through 10 Use Ctrl+Alt+Shift+1, 2 etc. through Ctrl+Alt+Shift+0 to clear the contents of memories 10 through 20 For example, to erase the response in Memory 5 you would press and hold the Ctrl and Alt keys and then press the 5 key.
Frequently Asked Questions about WT3 Q: Why do I have to wait 90 seconds for the WT3 hardware to warm up? A: The initial 90 second waiting period delay is required in order for the hardware power supplies to ramp up and stabilize. To perform precision measurements down to 1 Hz very wide low frequency bandwidth is required. Q: My WT3 was working fine but it seems to have stopped working correctly.
Removing WT3 from your Computer You can easily remove WT3 from your computer’s hard drive if needed. • • • • Go to the control panel and double click on the “Add/Remove Programs” icon When the Add/Remove dialog appears, locate WT3 in the list Select WT3 and then click on the Add/Remove button When you are asked “Are you sure you want to completely remove the selected application and all of its components?” select “Yes” WT3 will be removed from your computer.
File Menu The commands under the File menu are as follows: :ew (Ctrl+:) Clears all current data to create a new empty WT3 project file. Each project file holds up to 20 measurements in individual memories. The memories can be displayed or hidden by clicking the corresponding memory buttons on the toolbar. Open… (Ctrl+O) Opens a WT3 project file (.wt3) which you have previously saved to disc. Note that WT3 can be launched and a project .wt3 file opened from the desktop by double-clicking on the file icon.
Import Impedance Data… Opens a file dialog to select a .txt (or .zma) file containing data to be imported to the Workbench. Within the .txt file each data point must be on a single line in the format: “Frequency Impedance Phase” with the frequency, impedance and phase data separated by a tab or spaces. When the file is opened the data is imported to the WT3 Workbench, interpolated via a powerful cubic spline routine and then plotted on the screen. Note that imported phase data must be in degrees.
Recent Files... A list of recently used files is displayed for easy access. Exit (Ctrl+Q) Exits the application. The keyboard shortcut is very convenient.
Edit Menu The commands under the Edit menu are as follows: Undo (Ctrl+Z) Undo is not implemented Cut (Ctrl+X) Cut is implemented for various text fields. Text is cut and placed on the clipboard for pasting to another location if desired Copy (Ctrl+C) Copy is implemented for various text fields. Copied text is placed on the clipboard for pasting to another location Paste (Ctrl+V) Paste is implemented for various text fields.
Preferences This command opens the Preferences Dialog (shown below) where you can change various printing, measurement and display settings Plots can be switched between fine and bold lines separately for display and printing. You can select metric units separately for Volumes and other units. Auto Ranging is normally on but can be switched off for those occasions where you need a different fixed scale for repeat measurements. An initial "connect the driver" dialog can be enabled for production testing.
View Menu The commands under the View menu are as follows: Toolbar Select the Toolbar command to alternately hide or show the toolbar. Status Bar Select the Status Bar command to alternately hide or show the status bar at the bottom of the main page. The Status Bar displays information for menu items and buttons. The Status Bar also shows who's parameters are currently displayed.
From the keyboard, use Alt+1, Alt+2 etc. through Alt+0 to save to memories 1 through 10. Use Alt+Shift+1, 2 etc. through 0 to save to memories 10 through 20. For example, to save the current response to Memory 5 you would press and hold the Alt key and then press the 5 key. Note: The most recently measured impedance plot is said to reside on the WT3 “Workbench.” This measurement is overwritten each time the analyzer is run.
Impedance Analyzer Menu The Impedance Analyzer Menu contains commands for running measurements and for performing calibration of the test lead resistance and master calibration as follows: Measure Free Air Parameters This command causes WT3 to run an impedance sweep and then extract the driver's free air parameters. You can also use this command to measure resistor and inductor values.
Impedance Sweep Use this command to perform a simple impedance sweep without the extraction of any parameters. Driver parameters will be cleared to prevent any confusion. Impedance Calibration... When first installed, WT3 is calibrated to within about 2% for the impedance range under 100 Ohms. This is adequate for measuring driver parameters. For even finer calibration you can use this command to custom calibrate the system for your particular WT3 hardware unit.
Test Leads Calibration... When the software is first installed the default test lead impedance is 0.3 Ohms which is typical of the units. Use this command to refine the test lead calibration for your WT3 unit. Shown below is the test leads calibration dialog. Just short the test leads and click OK. The software will measure the test lead resistance and adjust the internal calibration. When you exit the application the new test lead calibration will be remembered for your next session.
Help Menu The commands under the Help menu are as follows: Help Topics The complete WT3 User’s Guide can be found under the Help menu > Help Topics. User Information Enter your personal information in this window. This is the information that will display at the Splash Screen and in the title block of your printed reports. About WT3 Displays the WT3 version number, copyright and user information.
Using WT3 to Measure a Woofer's Parameters The basic steps to measure a driver's parameters are as follows. Before starting, be sure the unit has been calibrated. • • • • • • • Start by connecting the WT3 hardware unit to a USB port on your PC. Next, launch the WT3 software. Make sure that the woofer is not connected to any other equipment and then connect the test leads of the WT3 unit to the terminals of the speaker under test. Raise the Windows volume control to maximum.
Using WT3 to Measure a Tweeter's Parameters A typical sealed back moving coil tweeter operates as a very small closed box system and therefore can be characterized by it's closed box resonance and Q, F(sc) and Q(tc). You can use WT3 to measure both of these parameters for tweeters as well as woofers and midranges.
Here is a typical result when measuring a tweeter: We can read the tweeter's resonance frequency, F(s) (or, more strictly F(sc)), directly from the impedance plot or note the value at the Measured Parameters F(s) field. Just as with a closed box, the system's Q(tc) is read from the Q(ts) field. Similarly for the electrical and mechanical Q's. The above tweeter is seen to have a resonance of 1.848 kHz and Q(tc) of .5067.
Using WT3 to Measure a Resistor Before starting, make sure the WT3 unit has been calibrated and has stabilized for at least 90 seconds. Measure the value of a resistor as follows: • • • • • • Launch the WT3 software and make sure the volume is set at maximum. Make sure that the resistor is not connected to any other equipment and then connect the test leads of the WT3 unit to the resistor under test. Click the "Measure Free-Air Parameters" button at the left side of the WT3 screen.
at 0 degrees except for a slight rise at the high frequency limit. Here the measured value of 9.998 Ohms is seen to closely match the resistor's specified value of 10 Ohms +/- 0.1%. At full playback volume the "noise" on the measurement is usually only one or two pixels as seen above. Higher noise levels can indicate that the test signal level was low and should be raised.
Using WT3 to Measure an Inductor Before starting, make sure the WT3 unit has been calibrated and has stabilized for at least 90 seconds. Measure the value of an inductor as follows: • • • • • • Launch the WT3 software and make sure the volume is set at maximum. Make sure that the inductor is not connected to any other equipment and then connect the test leads of the WT3 unit to the inductor under test. Click the "Measure Free-Air Parameters" button at the left side of the WT3 screen.
phase response (red) is seen to be near zero degrees at low frequencies and increases to 90 degrees at high frequencies as expected for the simple (R-L) test circuit. The measured value of 0.9893 mH is in good agreement with the inductor's nominal 1.0 mH rating. At 0.2422 Ohms the inductor's DC resistance is nicely low as required for use in a passive crossover. Note that WT3 can measure inductance at either 1kHz or 10 kHz based on the selection at the Preferences dialog.
Using WT3 to Evaluate a Closed Box Loudspeaker A closed box type of loudspeaker system is characterized by a resonance frequency F(sc), an electrical Q value Q(ec), a mechanical Q value Q(mc) and a total Q value Q(tc). Just as you can use WT3 to measure a driver's parameters you can also use WT3 to measure the corresponding parameters of a closed box loudspeaker system.
Here is a typical result when measuring a single full range driver in a closed box type enclosure: By inspecting the impedance plot we can determine that this is a closed box type of loudspeaker system from the presence of the single impedance peak in the low frequency range. From the impedance plot alone we can identify the closed box resonance frequency F(sc) = 95 Hz by reading the center frequency of the impedance peak from the frequency scale below.
Using WT3 to Evaluate a Vented Box Loudspeaker A vented box type of loudspeaker system can be characterized by it's equivalent closed box Q(tc) and the vented enclosure's Helmholtz tuning frequency F(b). You can use WT3 to measure both of these parameters for any vented box loudspeaker system. The frequency response of a vented box speaker is more complex than that of a closed box being equal to the frequency response of a fourth order highpass filter.
Here is a typical result when measuring a single full range driver in a vented box type enclosure:
In order to read the vent tuning frequency, F(b), more precisely we can adjust the frequency display limits to zoom in on the frequency range containing the two impedance peaks as shown below: At this screen we can determine that F(b), the tuning frequency of the vented box, is approximately 40 Hz by locating the impedance minimum between the two peaks and reading the frequency where the minimum occurs. The closely zoomed view makes it easier to read the frequency from the scale below.
Using WT3 to Evaluate a Complete Speaker System You can use WT3 to measure the impedance of complete multi-way loudspeaker systems. Based on this impedance curve we can tell a number of things about the system, such as whether the woofer uses a closed or vented enclosure. While a single peak in the low frequency range suggests a closed box, a single peak would also be seen for a driver operating as a dipole on a large baffle. Twin resonance peaks typically indicate a vented enclosure.
Here is a typical result when measuring a complete 2-way speaker system: We can see that this system employs a vented woofer system with the vented enclosure tuned to about 40 Hz. Even with a minimum impedance of just over 6 Ohms this would often be considered to be a nominal 8 Ohm loudspeaker system.
Using WT3 to Diagnose Loudspeaker Fault Conditions When carefully applied WT3 can be used to spot common problems with a speaker system. For example, the screen below shows two impedance measurements of the same two-way speaker system. The green (lower) plot shows the normal impedance response of this system. The purple (upper) plot shows the system with the tweeter in an open circuit fault condition.
In the screen below you see the same system as above but this time with a shorted tweeter. The green (upper) plot again shows the normal impedance response of this system. The yellow (lower) plot shows the system with a shorted tweeter. The system with the shorted tweeter appears to have a suspiciously low impedance above 4 kHz or so but when compared to the normal response (green) it is easy to see there is a problem.
Now let's examine similar fault conditions for the woofer. The screen below shows the same 2-way system as above with the green plot representing the normal system and the orange plot showing the system in a fault mode with an open circuit woofer. The system is seen to be unloaded (high impedance) over most of the woofer's frequency range.
Finally, here is a screen shot showing the same system with the woofer in a short circuit fault condition (lower blue trace). As we see in these examples often a system fault is most easily detected by comparing the suspect system to a known good system.
Using WT3 to Design a Zobel Network Zobel networks are used to control the impedance of a loudspeaker driver in the upper frequency range where voice coil inductance normally causes the impedance to rise with increasing frequency. Zobel networks are used to help crossovers do a better job of keeping the highs from passing to the woofer. A Zobel consists of a resistor and capacitor connected in series and attached between the terminals of the driver.
we can get it in the upper frequency range. Let's start with around 1 uF for the capacitor and see what we get for a new impedance response. The screen below shows the new impedance response in purple with the original (uncompensated) response in blue. Notice that the impedance has only been reduced above 5 kHz. This is because our capacitor value is too low. Let's increase the capacitor and see what happens.
Below is the impedance with the capacitor increased to 2 uF (blue trace). The original (uncompensated) impedance is shown in green. The 2 uF capacitor has flattened out the impedance so that it rises only slightly above 8 Ohms. Since it is easy to do let's continue to increase the capacitor value and see if we can get a further improvement. Ideally we would like the impedance to be as flat as possible...at least above the resonance peak.
The screen below shows the effect of increasing the capacitor to 3 uF (blue trace). The increase from 2 to 3 uF gave even further improvement as the impedance above resonance is now quite flat. Just to see what happens, let's increase the capacitor further to 5 uF.
Below we see the effect of increasing the capacitor to 5 uF in the lowest (blue) trace. It seems we have gone too far with the increase to 5 uF. The impedance in the 2 to 3 kHz range has been reduced to the DC resistance value and is now rising above the previous measurement with the 3 uF capacitor. This rise may be due to an interaction with the voice coil inductance. It looks like the 3 uF capacitor will be the best overall choice to tame the driver's high frequency impedance.
