High Power Test PortThe suspension mechanically loosens with hard use (break-in)
The suspension loosens due to environmental conditions (temperature)
The suspension will self heat due to mechanical energy loss (drive level)
Measuring and quantifying Thiele-Small and box tuning data at higher power levels is a
major step in designing higher quality speakers. The Woofer Tester Pro enables designers to see
these effects at a fraction of the traditional cost. The high power impedance and phase test port
extends the Woofer Tester 2's small signal milli-amp level tests to the multi-ampere Xmax level
where many drivers begin to distort and fail. The graphs below illustrate the effect that drive level has
on the base Thiele-Small parameters.
Idrive vs. Fs
Idrive vs. Vas
Click image to enlarge
Idrive vs. Qts
Idrive vs. BL
Thiele-Small Testing from Microwatts to 200 Watts
With the unparalleled accuracy of the WTPro, driver characteristics can be measured over a
range that extends from microwatts to over 200 Watts.
A careful examination of the AC and DC results will often show that the suspension mechanical spring constant (inverse of compliance) significantly decreases as the AC test signal level increases. This effect is much larger than the static changes seen in the DC offset test. Cms (suspension compliance) is strongly dependent on break-in and drive level. The underlying mechanism is a function of how the molecular bonds respond to these conditions:
The Woofer Tester Pro supports MLS, Step, Noise, Chirp, Continuous Sine and Pulsed Sine modes
for accurate as well as fast testing. High precision measurements are crucial for modeling and the
Continuous Sine mode provides the best signal to noise ratio. With the WTPro, results are as
accurate as .02%. Continuous Sine mode is best used for close microphone response or within an
SnapTS™, our fast test mode, is a great way to analyze speakers as they come off the production line. Just enable any real-time impedance testing mode. The DC analysis module also uses SnapTS™ technology to find mechanical offset information.
Advanced Thiele-Small Simulator & Box Analyzer
The advanced Thiele-Small simulator in the Woofer Tester Pro supports all box types - Vented,
Sealed, Band Pass and Passive Radiator. Using Frequency Dependent Inductance modeling, results
are improved over the traditional, flat or simple Le models. The simulator calculates Response, Impedance,
Phase, Velocity & Xmm of all Radiators.
The Box Simulator calculates box, port and stuffing losses and measures response, impedance, phase,
velocity & Xmm. The advanced features in the analyzer allow you to account for room or
car pressurization effects as well as vent resonances otherwise known as pipe organ effects.
Driver compression effects can be selected from the Test Environment, AC compression measurement table, or a
manufacturer's data sheet.
The Woofer Tester Pro introduces a new way to conduct box alignment that takes the guesswork out of using Fsb, Ha and Alpha values... only to find that the finished box doesn't produce the expected response! Our new method automatically aligns the simulator to the measured in-box impedance data finding the effective box size, tuning and losses. In addition, this same methodology can be turned around to refine your driver parameters if they have shifted due to drive level, temperature, break-in or box and driver interaction.
As shown in the two graphs below, the simulated and actual results match closely and produce
superior results to any traditional method using Fsb, Ha and Alpha (those are provided as well). Auto alignment works for both sealed and vented boxes, even when the driver and box interaction has shifted the initial design parameters.
32 Dual Buffers for Testing and Overlays
The large number of dual data buffers available enables you to construct intricate graphics overlays and setup complex testing scenarios. Each data buffer stores two data points; hence the name 'dual buffer'. The data points stored can either be Impedance, Phase, Response, Displacement or Velocity and are indicated in the Info column of the Overlay setup control (pictured below).
All data buffers are controlled from the Overlay setup control. To write to any buffer, simply select it from the list. With an additional click, name it as you wish. Then, select the checkbox on the left to display the data in the Overlay window. Easy!
Response and phase offsets as well as phase wrapping and polarity are also set here. You can either manually enter them or use the offset calculator, which automatically finds the difference between the desired and measured value for you!
In-Air Acoustic Response
The WTPro measures in-air acoustic response with any signal type. MLS, Noise, Impulse and Chirp real-time modes
allow you to easily position speakers perfectly in a room simply by moving the
test microphone and speakers around the room while watching the response on the screen!
Real-time response can also be converted to show the system impulse response. This reveals room reflections, which can be analyzed and rejected in the time gate window. Waterfall plots of Cumulative Spectral Decay (CSD) progressive FFT and Room Decay (similar to RT60) allow you to further analyze the characteristics of the room. If reflections are not a problem, because you have an anechoic chamber, or are using a close mike, very high noise rejection is possible by using a Sine sweep.
Interactive Crossover Design™ (ICD)
The Interactive Crossover Designer in the WTPRo software greatly speeds up crossover design time
by simulating crossover designs without actually having to build them! Designs
are entered via an ICD circuit file, which is then converted into filtered left and right test signals. When these test
signals are connected to your drivers, the db and phase accurate response is revealed. This even includes an optional inline tweeter protection circuit. Another huge advantage is that ICD is a real-time process. This means you can move the speaker or microphone and continue measuring! The graph below shows the results, accurate to fractions of a dB:
To find the optimal crossoverpoint, the ICD also measures Acoustic Distance to <.1mm and finds Delta
Phase at the crossover frequency. Decide on crossover topology based on Driver Delay and Phase.
Amplitude of both Channels
Delta Phase at XO frequency
ICD filter overlay, Left-Right Pan
Crossovers are affected by voice coil alignment. The ICD control window includes a time delay option to test these effects without having to physically move the drivers.
Harmonic, Inter-Modulation & SINAD Distortion Measurement
The WTPro includes various distortion measurements: 1st through 6th Harmonics on a relative or
absolute level vs. frequency, inter-modulation distortion as well as Signal to Noise and Distortion
Ratio (SINAD). SINAD can be viewed as Signal Relative To Drive Signal, Oscilloscope or Lissajoux.
Tweeter Response & Harmonics 1-6 on Absolute Scale SINAD at 1 kHz Shown as Lissajoux Pattern
AC & DC Thiele-Small Model Compression
The Woofer Tester Pro can also measure T/S models while stepping through DC bias or AC drive levels. DC offset testing reveals suspension and motor mechanical offsets, while AC drive levels provide compression modeling information. The XY plot tool compares any parameter pair.
Thiele-Small Parameters vs. DC Bias
Cms versus Xmm Displacement BL versus Xmm Displacement
Thiele-Small Parameters vs. AC Drive Level
These graphs show how TS parameters change with drive level. In addition to the XY parameter comparison, these AC test points can be imported into the simulator.
Vas (Liters) versus AC Current Drive
BL versus Xmm Displacement
Crossover Component & Cable Measurement
The WTPro's large dynamic range and utmost precision allows it to measure impedance and phase continuously from 1 to 20 kHz with 5 digit typical accuracy when used at full scale. With the low power port covering a range up to
3 mA and 4 Amps for the high power, a huge dynamic range is possible.
The low power port supports 100 pF - 1000 uF, 100 nH - 10 H and 10 milliohm - 100 kohm RLC measurement range, but it easily measures speaker cables as well.
Change in Inductance of 36" Leads Open/Closed 10 ohm cal resistor: 1 milli-ohm/div, 1-20 kHz