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The Evangelical Pentecostal Church in Varna uses its hall for services with speech and live music, with a sound system. The hall is fairly new – about 1,630 m³ – but the sound in it “echoed”: speech was hard to understand and the music became blurred.
On 27.03.2023 we measured the hall together with its sound system at more than 20 points. The reverberation time was about 2.0–2.1 s at 500–1000 Hz, there was echo at some points, and speech intelligibility was low.
We built a 3D model of the hall and checked it against the measurement. The hall is used in three modes – rehearsals, about 40% and full occupancy – and we calculated each of them. We took the target values from the Austrian standard ÖNORM B 8115-3 for rehearsal and performance halls. Bulgaria has no mandatory limit for such a hall, so we use it as a reference.
We compared four options by cost and effect. For the chosen solution the model gives a reverberation time of about 1.0–1.1 s at 500–1000 Hz and speech intelligibility (STI) up to 0.70 – half the decay time measured.
We installed the final option:
By calculation, the minimum panel area was 120 m². The panels are our own production.
Result. On 02.08.2023 we measured the hall again at 17 points, in the same mode – empty hall. The reverberation time fell by about half and came within the target range of ÖNORM B 8115-3 from 100 Hz upwards:
| Frequency, Hz | 125 | 250 | 500 | 1000 | 2000 | 4000 |
|---|---|---|---|---|---|---|
| Before (27.03.2023), s | ≈ 1,8 | ≈ 1,8 | ≈ 2,0 | ≈ 2,1 | ≈ 1,9 | ≈ 1,6 |
| After (02.08.2023), s | 1,30 | 1,10 | 0,98 | 0,98 | 0,93 | 0,77 |
Values are averaged over all points, in octave bands. The measurement is an engineering assessment (REW, 1/3 octave), not an accredited report. “Before” was read from the graph in the project report, so it is rounded. The measured “after” matches the model’s prediction (about 1.0–1.1 s).
Similar problem? See Acoustics and Soundproofing for Public Buildings or contact us via the enquiry form.
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