WT3 Setup and Calibration

Introduction

Today’s loudspeaker DIYer is fortunate in having quite a few choices to select from when it comes time to choosing the measurement tool (or tools) needed to achieve a successful project outcome. Critical to the project’s design process is being able to accurately assess the Thiele/Small driver parameters of the various mid-range, woofer and subwoofer drivers being considered. (Tweeters are typically handled differently, though accurate tweeter impedance & amplitude response data are just as essential to the design process as it is for all other drivers used in the system).

If the budget doesn’t leave room for the pricier measurement tools out there or you’d simply rather spend more on the hardware you pack your cabinets with than on the gear you measure it all with, then Dayton Audio’s WT3 Woofer Tester may be the perfect choice for the job. Its inexpensive, easy to install and use and the accuracy of the data produced can rival that of measurement tools costing 10x as much or more!

First Impressions

Everything comes packed in a smallish box and the kit includes the hardware, a hardcopy, single page quick-start quide, the installation CD and a calibration resistor.

The front page of quick-start guide contains all the information needed to get the software & hardware installed, the system calibrated and also includes basic measurement instructions. The back page of the guide contains extra information for those who’d like to use the WT3 system on PCs running Microsoft Vista.

Setup

The software installation doesn’t run automatically (as is typical these days) off of an autorun file: there isn’t one to be found on the CD and the installation won’t start automatically when you pop the CD in the drive. Rather, you have to manually hunt for the setup.exe file and run the installation from that. (Partially in response to this review Dayton Audio will be adding an Autorun.inf file to the WT3 distribution CD so that installation will begin automatically when the CD is inserted). As well,the limited Help Topics section mentioned at the top of this review are currently being expanded to better cover impedance measurements of resistors, inductors, closed and vented boxes.

Once installed, however, everything needed to run the WT3 system is in place, including the USB Audio Codec.

Overall, the installation of the WT3 compared to that of other commonly available products was quick and easy. The fact that the system is USB-based makes connection quite convenient as well. Overall, once installed, the convenience and ease-of-use of the product in practice is outstanding.

Calibration & Measurement

Once the software is installed, the application is up & running and the WT3 probe is plugged into a USB port everything is in place to finally begin measurement. Two things you’ll notice right away when you do connect the probe to a USB port: a blue LED on the probe lights up and the USB Audio Codec takes over. The blue LED is a minor but nice feature that lets you know the probe is active.

You’ll know the USB audio Codec is active because when it takes control, the PC focuses solely on the WT3 probe to the exclusion of all other audio process, which means you won’t be able, for example, to play music through your PC’s sound card while making measurements using the WT3.

Once the probe is plugged in, the manual recommends a 90-second wait time before you begin measurement. According to the manual, this wait is essential to allow the probe’s circuitry to stabilize. This required start up wait-time is a good time to set the Windows mixer Master Out and Wave levels to max as, once again, recommended by the manual. Setting levels anything above 50% is worth experimenting with; anything below 10% produces noisy, essentially useless data. For this review all measurements were made with Master & Wave levels set at 100%.

If you need to keep track of your Windows mixer settings for different audio-related items, use something like Quickmix to keep track of those settings. Quickmix uses templates you create to keep track of mixer settings for different applications/requirements. So, for example, if you’re using your sound card to make dB SPL measurements using software that requires mixer settings be the same whenever the software is running, you can set up QuickMix to remember those settings. You can then build a second template to take care of the settings WT3 needs to see and recall them, via QuickMix, whenever you need them. It’s a great way to go if you regularly need to recall different mixer settings for different applications.

At any rate, once the probe is plugged in, the software up & running and the appropriate levels set in the mixer, its time to calibrate. Calibration of the WT3 involves both calibrating out the impedance of the probe leads as well as calibrating the system to the supplied 1 kΩ, 1% resistor. If you have a way of accurately measuring the value of the calibration resistor, then by all means do so and use that value when you run the Impedance Calibration utility. In the case of the calibration resistor supplied with this review sample, the actual value measured was .9976 kΩ. (Note: the measured value of the calibration resistor should only be used if the meter’s accuracy is BETTER than 1% (the resistor’s rating).

Both calibrations are easy enough and each takes just a few seconds to run. Click on Impedance Analyzer…, then Test Leads Calibration…, connect the WT3’s alligator clips together and run the calibration. Once that’s done, connect the supplied 1 kΩ calibration resistor to the alligator clips. Click on Impedance Analyzer… again, then Impedance Calibration … You’ll then be presented with a screen that asks for the value of the calibration resistor. Enter that value and click OK, the system calibrates itself and you are now ready to begin actual measurement.

Running both calibrations prior to actual measurement is essential to ensuring the measurement data you’ll be generating is as accurate as possible.