Loudspeaker Measurements

Measurements were performed using the Sample Champion program developed by Paolo Guidorzi of Purebits.  The program is a Maximum Length Sequence (MLS) program that can generate an impulse response from this pseudorandom signal.  The Fast Fourier Transformation is applied to the impulse response to generate the system frequency response.  The operating principle is the same as that of the well known MLSSA program.

I received speakers with the sequential serial numbers: VY1307 and VY1308.  I have used these serial numbers to identify each test measurement taken.

Test samples were taken using 16 bit resolution with a 48 kHz sampling frequency.  Fast Fourier Transformations were performed at 64K allowing for a frequency resolution of .73 Hz, which is more refined than even 1/24th octave resolution at the lowest octave; the A0 key on the piano has a fundamental frequency of 27.5 Hz.  Quasianechoic response was compiled using a Blackman-Harris, half right window based on crossover frequencies provided in the owner's manual.  All measurements were taken with the phase response jumpers set to the center position unless noted otherwise.

Figure 1: Impule response of unit 1307.

The first figure is the normalized impulse response captured from unit 1307.  A theoretical impulse response should appear as a single pulse up from zero and back for a single driver.  This is a composite response for a three-way speaker system, and while the multiple drivers each have their own peak, a speaker with well damped behavior should have its dynamic response die out with few additional oscillations.

Figure 2: Freqeuency response of unit 1307 on axis and 30 degrees of axis.

The second figure is of the frequency response for 1307 for on axis (green trace) and 30 degrees off axis (red trace).  Initial lobbing of the response begins between 1000 and 2000 Hz, near the crossover frequency for the tweeter array.

Figure 3: Comparison of units 1307 and 1308.

I also compared frequency response for the two units, 1307 (green trace) and 1308 (red trace), shown in the third figure.  Response variations between the two units are typically within +-2 dB over the quoted frequency response except for a bump centered near 2300 Hz in the response of 1308.

Figure 4: Cumulative spectral decay of unit 1307.

The next figure shows the cumulative spectral decay based on the impulse response shown in figure 1 windowed over 4 milliseconds for quasianechoic response.  The plot shows decay over a 60 dB range for frequencies in the midrange and treble regions.

Figure 5: In room response of units 1307 and 1308.

The final plot is of in room response.  Unit 1307 (green trace) was measured from the left stereo position while 1308 (red trace) was measured for the right stereo position.  Both speakers were measured with their phase response jumpers adjusted to the corresponding left and right positions.