The text below is the result of an extended "conversation" with ChatGPT, based on my experience—along with significant help from the forum—diagnosing harshness and imaging issues in an aging pair of Martin Logan Ethos speakers. I’m particularly curious about the strength of the psychoacoustic explanations; everything else seems solid.
In aging pair of Martin Logan hybrid electrostatic speakers with passive crossovers for the panel and active analog low-pass filters for powered woofers—a listener reported increasing vocal harshness, grain, or instability. This is most, although not always, audible during dynamic vocal passages, where the fundamental (around 300–400 Hz) becomes more prominent than the harmonics. Phantom imaging may also become unstable or shift slightly in these moments. The effect completely disappears with a different model from the same manufacturer - older pair of Martin Logan Vista speakers, or with brand new KEF R5 Meta speakers in the same listening room with the same amplifier, etc.
Martin Logan hybrid speakers commonly cross over squarely in the vocal fundamental range. A likely cause of the perceived harshness is subtle phase or group delay misalignment between the woofer and panel, introduced over time by component drift—particularly in capacitors, op-amps, or power supply elements within the active crossover. Even small shifts in timing or polarity near crossover can disrupt driver integration enough to affect perceived coherence.
Standard REW sine sweep measurements may not reveal any obvious blending issues or destructive interference. The magnitude and phase traces may appear nominal, with no major dips or anomalies between drivers. However, the absence of visible flaws in these plots does not rule out perceptual degradation.
Sweep-based measurements operate at moderate, constant levels and may not expose level-dependent group delay or phase shift. Additionally, they reflect sound at a single point in space, whereas the auditory system processes information across time, both ears, and multiple spatial reflections. A mismatch of just a few degrees in phase—or a few milliseconds in group delay—especially in the 100–500 Hz range, can cause smearing and textural artifacts that resemble distortion.
These effects are particularly audible in systems with electrostatic panels due to their exceptional transient clarity. The ear’s sensitivity to midrange timing irregularities, combined with asymmetric hearing or tinnitus, can further exaggerate spatial or tonal inconsistencies—even if the measurements look balanced.
In summary, age-related drift in the active crossover path may introduce subtle phase or timing errors near the woofer–panel transition. While these errors may not be easily captured in traditional sweep measurements, they can cause vocal roughness and spatial instability that are perceptually significant. The issue lies not in nonlinear distortion per se, but in the breakdown of temporal coherence across the crossover—a domain where the ear is far more sensitive than standard measurements suggest.
In aging pair of Martin Logan hybrid electrostatic speakers with passive crossovers for the panel and active analog low-pass filters for powered woofers—a listener reported increasing vocal harshness, grain, or instability. This is most, although not always, audible during dynamic vocal passages, where the fundamental (around 300–400 Hz) becomes more prominent than the harmonics. Phantom imaging may also become unstable or shift slightly in these moments. The effect completely disappears with a different model from the same manufacturer - older pair of Martin Logan Vista speakers, or with brand new KEF R5 Meta speakers in the same listening room with the same amplifier, etc.
Martin Logan hybrid speakers commonly cross over squarely in the vocal fundamental range. A likely cause of the perceived harshness is subtle phase or group delay misalignment between the woofer and panel, introduced over time by component drift—particularly in capacitors, op-amps, or power supply elements within the active crossover. Even small shifts in timing or polarity near crossover can disrupt driver integration enough to affect perceived coherence.
Standard REW sine sweep measurements may not reveal any obvious blending issues or destructive interference. The magnitude and phase traces may appear nominal, with no major dips or anomalies between drivers. However, the absence of visible flaws in these plots does not rule out perceptual degradation.
Sweep-based measurements operate at moderate, constant levels and may not expose level-dependent group delay or phase shift. Additionally, they reflect sound at a single point in space, whereas the auditory system processes information across time, both ears, and multiple spatial reflections. A mismatch of just a few degrees in phase—or a few milliseconds in group delay—especially in the 100–500 Hz range, can cause smearing and textural artifacts that resemble distortion.
These effects are particularly audible in systems with electrostatic panels due to their exceptional transient clarity. The ear’s sensitivity to midrange timing irregularities, combined with asymmetric hearing or tinnitus, can further exaggerate spatial or tonal inconsistencies—even if the measurements look balanced.
In summary, age-related drift in the active crossover path may introduce subtle phase or timing errors near the woofer–panel transition. While these errors may not be easily captured in traditional sweep measurements, they can cause vocal roughness and spatial instability that are perceptually significant. The issue lies not in nonlinear distortion per se, but in the breakdown of temporal coherence across the crossover—a domain where the ear is far more sensitive than standard measurements suggest.
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