Why the bass reaches you

Outdoor stage → fifth-floor window · Frýdek-Místek · 7 August 2026

60.5 dB/ 63 Hzclearly audible indoors

indoors 47.5 dBair 0.09 dBbarrier 14.8 dB

63 Hz remains. 4 kHz disappears.

Plan view of the exact 1045.4 metre route from Nová Osmička to Beethovenova 1847

plan → section
exact route / 1045.4 m

SNová Osmička
298.28 m ASL

RBeethovenova 1847
5th floor

Beginning of the vertical terrain and building cross-section from stage to fifth-floor receiver

live trace continues
plan → section / terrain + barriers

The venue is 6.6 m higher, but that buys only 0.3 dB.

Your fifth floor buys 5.7 dB.

The frequency gap reaches 69.7 dB.

The path is almost open.

Bare terrain never blocks the route. The floodplain gives 700 m of clear propagation; only two apartment rows enter the sight line near the receiver.

Lidar hillshade plan view from Nová Osmička to Beethovenova 1847, including the rivers, buildings, wind, and propagation corridor — Plan trace · exact source, receiver, corridor, and downwind vectoropen full resolution ↗

Geometry ledger

distance: 1045.4 m
bearing: 209.89°
stage terrain: 298.28 m
receiver terrain: 291.68 m
receiver ear: 308.68 m
dominant barrier: 25.4 m

The dominant block is 91% of the way along the route. Receiver height therefore has roughly ten times the leverage of elevation at the source.

Cross-section of terrain, buildings, sight line, refracted ray, and 60 Hz and 4 kHz Fresnel zones — Vertical trace · the 60 Hz Fresnel zone dwarfs the two real obstaclesopen full resolution ↗

Four filters remove everything except the low end.

The source already favors bass. Air then removes another 23.4 dB at 4 kHz relative to 63 Hz. Buildings add 14.9 dB of frequency discrimination, and PA direction adds the final 7 dB.

24.4source spectrum

23.4atmospheric absorption

14.9barrier diffraction

7.0PA directivity

= 69.7 dB

Arriving sound level by octave band compared with ambient and hearing threshold, plus a loss waterfall — Frequency trace · modeled arrival, indoor margin, uncertainty, and loss ledgeropen full resolution ↗

The wind points almost exactly down the route.

At 22:00 it came from 32°. The back-azimuth to the stage is 29.9°: a two-degree miss. Wind shear bends sound downward all evening; a true temperature inversion appears only at 22:00.

wind: 1.3 m/s
path offset: 2°
ray radius: 9.9 km
modeled gain: +2–5 dB

Hourly vertical temperature profiles, effective sound-speed gradient, and downwind component — Atmospheric trace · wind shear dominates until the late inversion arrivesopen full resolution ↗

Inspect every metre of the route.

Zoom, pan, and click the interactive trace. The map carries the per-sample terrain and surface clearance used in the analysis.

Measured geometry. Modeled sound.

The route itself is unusually well constrained. The largest uncertainty is not the terrain or buildings—it is the unknown directionality of the concert PA.

itemstatuseffect

terrain + surface profilemeasured twiceagreement 0.001 m

dominant buildinglidar + OSM25.4 vs 25.5 m

atmospheric absorptionISO 9613-1matched independently

barrier diffractionfour methods10.7–20.8 dB at 63 Hz

PA directivityassumed±15 dB, largest uncertainty

absolute predictionmodeled±8–10 dB rms

Replace “the venue is higher” with:

I am high enough to see over the last row of blocks, and bass barely notices what is left.