Tuesday, March 8, 2016

Sound Transformer vs Infinity Qe - Bass Response Compared

The Infinity Qe loudspeaker is a very high quality transducer throughout the audio range.  I set up an experiment to compare the response of a pair of Qe speakers versus the Sound Transformer pair in the bass region from 32.7Hz (C1) to 220Hz (A3).  I used a FFT program running on the iPad Air to visualize the response at each musical note in the scale.  I tuned each note approximately with a SWTP function generator using the Fluke 87 in frequency counter mode.  Here is the plot.


Sound Transformer vs Infinity Qe - Bass Response Compared
Sound Transformer vs Infinity Qe - Bass Response Compared
The top trace in dark blue is the Sound Transformer fundamental response level in dB (relative) at each musical note.  The pink trace is the Sound Transformer second harmonic level.  The yellow and light blue traces are for the Infinity Qe speakers.  The Qe is relatively free of second harmonic distortion throughout the frequency range tested.  The Sound Transformer has significant second harmonic distortion below the cutoff frequency of 41.2 Hz (E1) but starts to clean up at around 49Hz (G1) and remains so all the way to 220Hz (A3).

Comparing the top dark blue trace of the Sound Transformer with the yellow trace of the Infinity Qe, you can see that both the horn and the Qe don't have much output below E1.  The Sound Transformer begins to put out a level 19dB higher than the Qe at G1.  The Qe doesn't start putting out until 73.42Hz (D2) where it is still 12dB quieter than the Sound Transformer.

Much of what we are seeing in the unevenness of the traces would appear to be due to "room effects" and the fact that the microphone is located at one point in the room so it does not really represent a collection of the total energy released into the room.

The second harmonic, being the octave, can be considered still "musical" even though it really was added by mechanical nonlinearity somewhere in the setup.  Also visible in the FFT response curves for both Sound Transformer and Infinity Qe are the higher harmonics.  It is perhaps a stretch to claim that the higher harmonics contribute to the "musicality" of a speaker.  However, acoustic musical instruments naturally emit the fundamental and harmonics and they are regarded as musical.

All of the above is "steady state" testing with a pure sine wave as input.  The Sound Transformer is "louder" than the Qe by about 20dB in the frequency range of interest.  This testing does not reflect the overall impression of the listener regarding actual music including the impact of transient information in a musical performance.  Based on listening testing so far, the Sound Transformer sounds much more alive and has a stronger impact than any other speaker I have compared it with.

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