What does SPT do?

SPT [Stable Phase Technology]® measures the speaker and enclosure, and then removes the effects of the system to improve the sound reproduction of the audio device.

Our artefact-free, audiophile-grade algorithms correct the time and phase distortions, not just the frequency. By applying the tailor-measured algorithm, we can perform near-perfect linear phase cross-overs, and improve sonic perception.

speaker cone chrome blur speaker cone blur speaker cone
Phase distortion is like a bad lens: smearing frequencies (colours). The sound image is also blurred by crossover and speaker alignment. With SPT enabled, the sound is ‘sharper’, ‘deeper’, and ‘brighter’.

Sontia SPT [Stable Phase Technology]

  • a wide ’3D-like’ listening area (side-to-side & front-to-back)
  • a clear, natural, life-like sound
  • higher perceived listening volumes for the same amp rating
  • improved spatial content separation & speech clarity
  • smoother, deep, extended bass
  • an immersive, non-tiring listening experience

Sontia SPT speaker optimization

Sontia’s SPT speaker optimisation system pre-corrects the inherent and precise characteristics of a particular combination of speaker drivers, cabinet and mounting combination. It measures the many types of distortions that the particular arrangement has imparted onto sample signals, and then performs a complex ‘pre-correction’ to cancel out these distortions and characteristics. In the process, the signal undergoes audiophile-quality processing in the time/phase-domain (including convolution) as well as the frequency-domain. Sontia’s SPT phase optimisation allows the drive unit to work to its full potential and exploits the maximum amount of bandwidth that the speaker can produce.

Phase performance comparison:
phase performance comparison

Increased frequency performance
frequency performance

Sontia SPT speaker excursion control

Sontia SPT undertakes advanced spectral volume and speaker driver excursion control to minimise the ringing and resonance of the speaker. In a conventional speaker, signals are not only distorted as a result of the inherent physics of electro-mechanical loudspeakers, but the speaker cone will resonate and continue to move after the original sound signal has stopped. Sontia’s optimisation accounts for this before it happens and pre-corrects the signal such that the output closely matches the desired signal shape.

spt reducing distortion

Original output from speaker

spt reducing distortion-withSPT

Sontia SPT reducing distortion

Excursion control also prevents damage to the speaker. Sontia’s processor knows the limits of the speakers in the system and monitors the signal, volume setting and requirements of the amplifier and drivers. This does not use the dynamic range compression/EQ, commonly found in other systems, and avoids the problem of the tonality of the sound constantly varying as the user is listening. When Sontia’s excursion control is used along with phase and frequency correction in the cross-over, amplifiers and acoustic enclosure, the output becomes much closer to the ideal ‘dirac’ impulse response:
Impulse response before and after sontia

Sontia SPT cross-over

Loudspeaker cross-over circuitry has typically suffered from a number of problems and characteristics that have a detrimental effect on sound reproduction. These include:

  • poor division of frequencies between the various speaker drivers, which leads to distortion, amplifier loading issues and reduced maximum sound levels
  • cancellation/phasing effects between sounds emanating from each speaker driver
  • poor matching of speaker phase and time-domain response so that the subsequent output from the speaker is not in phase-linear, even if the crossover circuitry itself is aiming to operate with linear phase
  • damaging pre- and post-ringing (in linear-phase crossovers)
  • ‘lobbing’ and ‘beaming’ effects from a non-uniform speaker radiation pattern
  • signal transient smearing

Sontia’s SPT Cross-over performs better than standard linear-phase, and conventional, crossover circuits, because it measures the output phase and time-domain response of the actual speaker driver units not by simply operating on the signals being fed into the driver. Therefore, Sontia SPT optimises the crossover to achieve fully corrected, true, stable linear phase from the speaker output, not just the inputs to the speaker drivers. This cannot be achieved by considering the crossover circuitry in isolation and without knowing the effects of the actual speakers driver on the sound—including the destructive interference between drivers connected to the crossover circuit.

Standard crossovers can achieve 6–24dB/octave of filtering and conventional linear-phase crossovers can achieve 12–24dB/octave; Sontia SPT crossovers typically use 48–192dB/octave.


For more information or to arrange an SPT demonstration please contact us