2024-01-03: Batch measurements on Faital Pro 4FE32 drivers

Jonas Hammerer, Paul Gründorfer and Thomas Grill made an effort to measure the frequency response on samples of the 288 drivers we have from this Faital model.

The infrastructure used was the following:

• Audio interface: Native Instruments Komplete 6 @ 48 kHz, mic gains at 12h, output volume dial fully clockwise.
• Amplifier: d&B D6 @ Linear preset, -30 dB
• Microphone: Two Sennheiser MKH 8020

The space was our mdw Klangtheater, the loudspeaker and microphone position was at an elevation of 1.85m above the reflective floor. The other walls and ceiling were at a distance of > 5m, walls damped with curtains.

We conducted two measurements, open baffle and with enclosure, in parallel from the frontal direction (0°) and from 45° to the side, at a distance of 1 meter.

Excitation was with three different sources:

• Pink noise (Reaper JS Pink Noise generator plugin at 0dB)
• Exponential sine sweep (20-20kHz) at -3dB
• A dirac impulse (1 sample 0dB), not band limited

The Pink noise plugin is not perfect, but its frequency reponse is close to 1/f by ±1dB.

Open baffle (1x1m)

We sampled 8 pieces from our drivers and numbered them LS1 thru LS8.

Open baffle measurement on-axis (0°), excited by exponential sine sweep:

The time between the original sound and the first reflection equals approximately (1.85[m] * 2 - 1[m]) / 340[m/s] = ca. 0.008[s]. This can be seen in the Fourier transformation of the spectrum which is shows the impulse response (IR):

The dashed vertical line at 0.008[s] marks the position where we should cut the IR in order to reject effects from floor and wall reflections of the space. The peak right of this position shows the first reflection off the floor. Cutting and transforming back to the spectrum yields a smoother spectrum with lower resolution in the bass frequencies:

Open baffle measurement at 45° from the side, excited by exponential sine sweep, windowed at 0.008[s]:

Prototypical 3D-printed PLA enclosure (10x10x20 cm)

For both measurements, the same driver LS1 is used, in two different (almost identical) enclosures. The only real difference is that the cabling was in case of Enc1.1 fed through holes with foam, in case Enc1.2 connected through soldered banana connectors.

Enclosure measurement on-axis (0°), excited by exponential sine sweep:

This measurement again windowed at 0.008[s] as above:

Enclosure measurement on-axis (0°), excited by pink noise and windows at 0.008[s]:

There is a noticeable tilt of the curve (about 2-3dB lower at 200Hz in comparison to the sweeps). We are not sure about the reasons. Clearly, the SPL of the sweeps is much higher at isolated frequencies than with pink noise. There might also be effects of intermodulation of the frequency mix for pink noise.

Enclosure measurement at 45° from the side, excited by exponential sine sweep, windowed at 0.008[s]: