User Guide for the IMP1 Loudspeaker Impedance fixture.
Group delay is a property of a device or a system: a plot of the change in phase of the response as a function of frequency; it is the negative derivative (slope) of the phase-vs-frequency characteristic of a device. Constant group delay across the frequency band means that all portions of a wideband signal arrive simultaneously. A pure time delay, equal at all frequencies, gives a level straight-line plot of phase versus frequency. In an audio component, this plot may vary with frequency, and the component is said to produce group delay distortion. Group delay is of interest to audio engineers, particularly in the design and test of low-pass filters used in digital audio and in loudspeaker design areas. For instance, an anti-aliasing filter will typically have a phase response curve which slopes sharply down at high frequencies. This means that the high-frequency components will be delayed longer in their passage through the filter, resulting in a loss of precision in musical transients and a more diffuse stereo image. It is possible to correct the group delay distortion of such filters by using an all-pass network, but this is seldom done in practice.
This utility determines the signal polarity between the Analog Generator Outputs and the Analog Analyzer Inputs. A common error in manufacturing of loudspeaker systems is to connect voice coils with reversed polarity. Even when all drivers in a multi-way system are phased correctly with respect to one another, it is possible to have the interior wiring to the external connection terminals of the cabinet reversed. An individual driver reversed will cause a dip in frequency response near the crossover frequency to the adjacent driver, since the two speakers are then producing acoustical output of nearly identical amplitudes but out of phase. An entire system wired out-of-phase would presumably be undetectable in a monaural application, but unacceptable in stereo systems. With minor adjustments, this procedure can be run as a stand-alone test, or it can be incorporated into other test setups. The procedure can test a single path, or it can test stereo channels. Equipment required is DSP or Dual-Domain version of System One, System Two, or System Two Cascade, and a microphone if you are testing acoustic paths such as loudspeakers.
Describes how to generate Impedance versus Frequency swept data using System One. This is of particular interest to loudspeaker designers where the impedance response can provide very useful information on the performance of a speaker. Includes a BASIC program that does the calculations.
Plots of group delay versus frequency are useful in filter design and loudspeaker design applications. This Technote includes a BASIC program that will use a phase versus frequency plot as generated by System One to produce a group delay plot. The BASIC program can be run in a DOS shell within S1.exe.
A look at some of the important features needed in an acoustic audio analyzer, the problems you may encounter in non-ideal testing environment, the needs of good production line testing, and the range of measurements and results that should be produced.
A single sheet description of APx Electro-Acoustic software options, including Thiele-Small characterization, Rub & Buzz detection and Loudspeaker Production Test.
ATS-2 Loudspeaker Impedance files associated with KB article 105
This zip file contains an APx project file named "PT-Demo External Loopback.approjx" that illustrates many of the production test and automation features added in release v4.2 of the APx500 measurement software. The project file focuses on an electro-acoustic application, specifically loudspeaker test. The file also contains a 15-page presentation describing how to use the demonstration project.
This utility for APx analyzers allows you to make an impedance vs frequency sweep across a loudspeaker, and then see the graph and data results directly in ohms. Clicking Help in the utility will display the complete instructions, including a discussion of the theory behind it. It can utilize the built-in source resistor on APx analyzers to make impedance measurements.
NOTE: This utility is only compatible with APx500 Software v3.3 or earlier. For users with APx500 v3.4 or later, options APX-SW-SPK-RD and APX-SW-SPK-PT provide a range of acoustic measurements, with SPK-RD including Thiele-Small characterization. An impedance-only alternative is also available for download and is compatible with APx500 v3.4 and later – please see the APx Speaker Impedance Measurement Project. This project requires an external sense resistor and uses the constant voltage method.
This project measures loudspeaker impedance using the constant voltage method.
Complete instructions and explanation are in the KB article "Measuring Loudspeaker Impedance Using APx Derived Measurement Results".
An external sense resistor is required for this project. The "APx Speaker Impedance Measurement Utility," also available for download, can utilize the built-in source resistor in APx analyzers.
The APx500 CSD Utility is a Windows application for making a Cumulative Spectral Decay (CSD) plot, sometimes referred to as a waterfall plot, from the measured impulse response of a loudspeaker. The APx CSD utility also requires the SPK-RD software option to be installed on the connected APx audio analyzer. If you require a SPK-RD software option, please contact your Audio Precision sales representative.