Yes. How's that coming. Lots of interest.
One year or so later, is this still a hot topic? I'm a DIYer and have been using TDA for about 6 months and I like to write so let me jump in.
TDA, from Acoustics Power Labs, provides a new way of looking at the responses of speakers in rooms. Its Intuitive 3D Display of sound level vs arrival time and frequency spotlights speaker and room anomalies.
An impulse response shows energy arrival over time; TDA shows both the amplitude and the spectrum of that arriving energy over time. It is useful in both the design and fine tuning of the speakers themselves, especially their crossovers, and in integrating those speakers into rooms. TDA is the analysis step on a ladder of tools from APL that provide increasingly more powerful equalization solutions for adapting speakers to listening spaces.
TDA uses a sine sweep to obtain an impulse response that can be viewed by use of the IR and Log IR buttons on its control panel. The calculated impulse response contains non-linear distortion information that can also be displayed. Distortion can also be seen as a series of spikes before the main peak of the IR in the log IR view. Third party tool IRs can also be imported and viewed.
The obtained IR is then processed by TDA at 126 frequencies, 12 log spaced points per octave to create its unique 3D display - a 3-dimensional map of normalized sound pressure plotted with delay and frequency along the X and Y axes and SPL encoded in both color and on the Z axis. Boundary effects, room modes, timing alignment issues with multi-way speakers, and frequency response aberrations are easily recognized in this presentation. This 3D map is a very good tool for quickly evaluating a new speaker in a familiar space or a familiar speaker in a new room or position.
TDA also provides conventional frequency, delay, and phase response graphs. TDA attempts to separate the direct response from reflections based on time of arrival and succeeds in doing so down into the modal zone to an extent limited by room modes, near reflections and the increased difficulty of precisely determining the time of arrival of low frequencies. This time selectivity enables us to see both the direct response, otherwise viewable only as an anechoic or quasi-anechoic measurement, and the effect of the room. It’s not a coincidence that the human ear has the same/similar ability to separate direct sound from reflections and the same/similar limitations.
TDA’s frequency response graph, the AFR, shows this separated direct response while its 3D display allows you to judge the extent to which it stands above room and boundary effects. Where it is reflection free, it is minimum phase and thus can guide equalization; other products from APL use multiple AFRs taken at multiple positions to do just that.
The review will continue in additional posts. Meanwhile, you can follow this link to the APL websitehttp://aplaudio.com/conc2/products/tda/