The city commissioned DEKRA for immission measurements (where sound reaches residents) in Baiereck, not emission measurements at the turbines. Key measurement points: Brunnenstraße 5 and Büchenbronner Straße 6, with permanent systems at upper-floor height plus meteorological sensors.

Main DEKRA Findings (from the 12-page summary):

Night-time base levels (without penalties): 41–42 dB(A) at key points (e.g., Christmas 2025 example cited). The TA Lärm limit for general residential areas is 40 dB(A) at night — already exceeded on raw levels.

Tonality: Clear tonal components (Brummtone/ humming + swishing) at nearly all wind speeds, including low- load/weak wind conditions. Tonality penalties: +4 dB (partial load) to +5 dB (full load). This can push the assessed (Beurteilungspegel) up to ≤45 dB(A), or up to ≤50 dB(A) with additional factors.

The original TÜV sound propagation forecast (DIN ISO 9613-2 + interim methods) significantly underestimated real levels. DEKRA states the model inadequately represents conditions in this “mountain-valley-mountain” topography of the Nassachtal/Schurwald area. Standard distance-based attenuation does not fully apply.

This violates the operating permit, which prohibits perceptible tonality.

TA Lärm Tonality Penalties (Zuschlag für Ton- und Informationshaltigkeit)

TA Lärm (Technische Anleitung zum Schutz gegen Lärm) is Germany’s key administrative guideline under the Federal Immission Control Act (BImSchG) for assessing and limiting noise from industrial, commercial, and similar installations (including wind turbines). It defines how to calculate the rating level (Beurteilungspegel, Lr) that is then compared to area-specific immission limits (e.g., 40 dB(A) at night in general residential areas).

Tonal noises (distinct hums, whines, swishes, or prominent single frequencies) are more annoying and disturbing than broadband noise at the same overall level. The human ear notices them more easily, which increases perceived disturbance, especially at night or in quiet environments. TA Lärm therefore adds a penalty (Zuschlag KT) to the measured or predicted equivalent continuous sound level (LAeq) when tonality is present.

How the Penalty Works

The penalty is added when calculating the rating level (Lr):

Lr = LAeq + KT (tonality) + KI (impulsiveness, if applicable) + other adjustments

• KT values: 0 dB, 3 dB, or 6 dB, depending on how distinct/perceptible the tone(s) are.
  • 0 dB: No audible tonality.
  • 3 dB: Tones or informational content are perceptible/audible.
  • 6 dB: Tones or informational content are clearly/distinctly audible (prominent).

The exact value is determined either:

• Subjectively by a qualified expert listening to the noise (common in practice).
• Objectively via measurement according to procedures like the (older) DIN 45681 draft, which analyzes the frequency spectrum for prominent tones above the masking noise level.

Penalties apply per relevant sub-period (e.g., during specific wind conditions or operating states) and are added only when the tonal components are present in the assessed immissions.

Relevance to the Königseiche Wind Park Case

In the DEKRA measurements:

• Tonal components (brummtöne/humming + swishing) were identified across a wide range of operating conditions.
• Penalties of +4 to +5 dB were applied (likely based on the degree of prominence; some interpretations or combined factors can lead to values between the standard 3/6 dB steps in detailed assessments).
• This pushed the assessed night-time rating level well above the 40 dB(A) limit (e.g., from a base of 41–42 dB(A) to 45+ dB(A)).

The operating permit explicitly prohibited perceptible tonality, so any positive KT makes compliance harder or impossible without operational restrictions.

Previous Remediation Efforts (Acknowledged by the City)

• Turbines operational since December 2024.
• Gearbox replacement (August 2025) after earlier complaints.
• Temporary shutdowns, vibration dampers, and power curtailment above 9 m/s.
• Earlier (spring 2026) shorter measurement suggested tonality mainly at higher winds → leading to partial curtailment.
• None fully resolved resident complaints.

Mayor Matthias Wittlinger emphasized constructive cooperation and praised residents for remaining factual. The city has forwarded the DEKRA summary to the Landratsamt Göppingen (approving authority) for decision-making. A full detailed report is still pending.

Landratsamt Göppingen and Operator Response

• The authority considers the original immission prognosis “shaken” (“als erschüttert an”).
• As an interim measure, it proposes night-time shutdown of the two Nordex N149 turbines until final clarification.
• The operator (Uhl Windkraft) has already voluntarily suspended night operations (reported ~19 June 2026) “for transparency,” while questioning DEKRA’s background noise filtering and arguing the levels are overstated and not compliant with norms. The authority does not currently share this view but awaits the full report.

Current Status (as of ~20 June 2026):

Night operations are suspended (at least voluntarily). The Landratsamt is evaluating formal measures based on the DEKRA data. No final binding decision yet; the full DEKRA report will be key.

This situation illustrates real-world challenges with post-construction compliance for wind projects in complex terrain — model vs. reality gap, tonal noise persistence despite retrofits, and balancing energy goals with local livability.

This incident is a concrete example of post-approval compliance problems for wind energy in populated or topographically complex areas.

It underscores tensions between energy transition targets, permitting processes relying on models, and actual resident impacts.

Long-term, it may strengthen calls for more rigorous, site-specific immission monitoring in similar locations rather than relying solely on forecasts.