Slam Poetry Stage Acoustics Calculator

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Slam Poetry Stage Acoustics Calculator

Calculate key acoustic parameters for slam poetry venues: reverberation time (RT60), speech transmission index estimate, critical distance, and recommended sound pressure level. Optimized for spoken word clarity.

Room Length (m)

Room Width (m)

Room Height (m)

Average Surface Absorption Coefficient (α, 0–1)

Typical: bare concrete 0.02, carpet+soft seats 0.35, acoustic panels 0.70

Audience Size (persons)

Each person adds ~0.5 m² of absorption (seated, clothed)

Performer Sound Power Level (dB re 1 pW)

Unamplified spoken voice ≈ 65–75 dB; amplified ≈ 85–100 dB

Source Directivity Factor (Q)

Omnidirectional = 1; human voice forward = 2; directional mic = 4–6

Calculate Acoustics

Results will appear here.

function slaCalc() { const L = parseFloat(document.getElementById('sla-length').value); const W = parseFloat(document.getElementById('sla-width').value); const H = parseFloat(document.getElementById('sla-height').value); const alpha = parseFloat(document.getElementById('sla-absorption').value); const audience = parseFloat(document.getElementById('sla-audience').value); const Lw = parseFloat(document.getElementById('sla-source-power').value); const Q = parseFloat(document.getElementById('sla-directivity').value);

// --- Validation --- const errors = []; if (isNaN(L) || L 200) errors.push("Room Length must be between 2 and 200 m."); if (isNaN(W) || W 200) errors.push("Room Width must be between 2 and 200 m."); if (isNaN(H) || H 30) errors.push("Room Height must be between 1.5 and 30 m."); if (isNaN(alpha) || alpha 1.0) errors.push("Absorption coefficient must be between 0.01 and 1.0."); if (isNaN(audience) || audience 5000) errors.push("Audience size must be between 1 and 5000."); if (isNaN(Lw) || Lw 120) errors.push("Sound Power Level must be between 40 and 120 dB."); if (isNaN(Q) || Q 10) errors.push("Directivity Factor must be between 1 and 10.");

if (errors.length > 0) { document.getElementById('sla-result').innerHTML = 'Input Errors:' + errors.map(e => '').join('') + ''; return; }

// --- Room geometry --- const volume = L * W * H; // m³ const S_floor = L * W; const S_ceiling = L * W; const S_walls = 2 * (L + W) * H; const S_total = S_floor + S_ceiling + S_walls; // m²

// --- Sabine absorption --- // Audience absorption: each person ≈ 0.5 m² equivalent absorption area (Sabine units) const A_room = alpha * S_total; // m² (Sabine) const A_audience = audience * 0.5; // m² (Sabine) const A_total = A_room + A_audience; // m² (Sabine)

// Effective average absorption coefficient with audience const alpha_eff = A_total / S_total;

// --- RT60 — Sabine formula --- // RT60 = 0.161 * V / A (seconds) const RT60_sabine = (0.161 * volume) / A_total;

// --- RT60 — Eyring formula (more accurate for higher absorption) --- // RT60 = 0.161 * V / (-S * ln(1 - alpha_eff)) const RT60_eyring = (0.161 * volume) / (-S_total * Math.log(1 - Math.min(alpha_eff, 0.9999)));

// --- Critical Distance --- // Dc = 0.057 * sqrt(Q * V / RT60) (metres) const Dc = 0.057 * Math.sqrt((Q * volume) / RT60_eyring);

// --- Room Constant --- // R = S * alpha_eff / (1 - alpha_eff) const R = (S_total * alpha_eff) / (1 - alpha_eff);

// --- Sound Pressure Level at listener distance r --- // Using combined direct + reverberant field: // Lp = Lw + 10log10( Q/(4pi*r²) + 4/R ) // We evaluate at r = Dc (critical distance) and r = 1m (near field) const r_near = 1.0; // 1 m from performer const r_mid = Dc; // at critical distance const r_far = Math.max(Dc * 2, 3); // beyond critical distance

function Lp(r) { const direct_term = Q / (4 * Math.PI * r * r); const reverb_term = 4 / R; return Lw + 10 * Math.log10(direct_term + reverb_term); }

const Lp_near = Lp(r_near); const Lp_mid = Lp(r_mid); const Lp_far = Lp(r_far);

// --- Speech Clarity C50 estimate --- // C50 ≈ 10 * log10( (1 - e^(-6.908 * 0.05 / RT60)) / (e^(-6.908 * 0.05 / RT60)) ) // Simplified Moorer approximation: C50 ≈ 10log10(e^(6.9080.05/RT60) - 1) // More practical: C50 ≈ 10log10( (0.04/RT60) * e^(0.04 * 13.816 / RT60) / (1 - e^(-0.04 * 13.816 / RT60)) ) // The standard relation: C50 (dB) ≈ 10log10( (1/RT60) * 7.22 ) — Barron's approximation // Accurate form: C50 = 10log10( (e^(13.8160.05/RT60) - 1) ) [Beranek] const exponent = 13.816 * 0.05 / RT60_eyring; const C50 = 10 * Math.log10(Math.exp(exponent) - 1);

// --- STI estimate from RT60 (Houtgast & Steeneken approximation) --- // STI ≈ 1 - 0.17 * log(1 + (RT60/0.5)^2.5) — simplified empirical fit // More standard: for speech, STI degrades with RT60; rough estimate: // STI_approx = 1 / (1 + (RT60 / 0.65)^1.5) — empirical for typical SNR const STI_approx = Math.min(1.0, 1 / (1 + Math.pow(RT60_eyring / 0.65, 1.5)));

function stiRating(sti) { if (sti >= 0.75) return "Excellent"; if (sti >= 0.60) return "Good"; if (sti >= 0.45) return "Fair"; if (sti >= 0.30) return "Poor"; return "Bad"; }

function rt60Rating(rt) { if (rt >= 0.3 && rt 0.7 && rt 1.0) return "❌ Too reverberant — speech clarity will suffer"; return "⚠️ Very dry — may sound unnatural"; }

function c50Rating(c) { if (c >= 0) return "✅ Good clarity (C50 ≥ 0 dB recommended for speech)"; if (c >= -3) return "⚠️ Marginal clarity"; return "❌ Poor clarity — too much late reverberation"; }

// --- Format output --- const res = document.getElementById('sla-result'); res.innerHTML = ` ### Acoustic Analysis Results

ParameterValueAssessment

Room Volume ${volume.toFixed(1)} m³ ${volume

Total Surface Area ${S_total.toFixed(1)} m² —

Total Absorption (A) ${A_total.toFixed(1)} m² Sabine Room: ${A_room.toFixed(1)} + Audience: ${A_audience.toFixed(1)}

Effective α (with audience) ${alpha_eff.toFixed(3)} —

RT60 — Sabine ${RT60_sabine.toFixed(2)} s ${rt60Rating(RT60_sabine)}

RT60 — Eyring ${RT60_eyring.toFixed(2)} s ${rt60Rating(RT60_eyring)}

Critical Distance (Dc) ${Dc.toFixed(2)} m Listeners within ${Dc.toFixed(1)} m hear mostly direct sound

Speech Clarity C50 ${C50.toFixed(1)} dB ${c50Rating(C50)}

STI Estimate ${STI_approx.toFixed(2)} ${stiRating(STI_approx)} (${(STI_approx * 100).toFixed(0)}%)

Lp at 1 m (near stage) ${Lp_near.toFixed(1)} dB SPL ${Lp_near > 85 ? "⚠️ Loud — check performer comfort" : "✅ Comfortable"}

Lp at Dc (${r_mid.toFixed(1)} m) ${Lp_mid.toFixed(1)} dB SPL Direct = Reverberant field here

Lp at ${r_far.toFixed(1)} m (far field) ${Lp_far.toFixed(1)} dB SPL ${Lp_far >= 65 ? "✅ Intelligible" : "❌ Too quiet — amplification needed"}

Recommendation:
${RT60_eyring = 0 && STI_approx >= 0.60
? "✅ This venue is well-suited for slam poetry. Speech clarity is good."
RT60_eyring > 1.0
? "❌ Reverberation is too high. Add " + Math.ceil((A_total * (RT60_eyring / 0.6 - 1))).toFixed(0) + " m² of additional absorption (panels, curtains, carpet) to reach RT60 ≈ 0.5–0.7 s."
"⚠️ Moderate adjustments recommended. Target RT60 = 0.4–0.7 s and C50 ≥ 0 dB for optimal spoken word intelligibility."}

`; }

#### Formulas Used

Room Volume: V = L × W × H

Total Surface Area: S = 2(LW + LH + WH)

Total Absorption (Sabine units): A = α·S + Naudience·0.5  [m² Sabine]

RT60 — Sabine: RT60 = 0.161·V / A

RT60 — Eyring: RT60 = 0.161·V / (−S·ln(1−αeff))  [more accurate for α > 0.2]

Critical Distance: Dc = 0.057·√(Q·V / RT60)  [m]

Room Constant: R = S·αeff / (1−αeff)

Sound Pressure Level: Lp = LW + 10·log₁₀(Q/(4πr²) + 4/R)  [dB SPL]

Speech Clarity C50: C50 = 10·log₁₀(e13.816·0.05/RT60 − 1)  [dB]  (Beranek)

STI Estimate: STI ≈ 1 / (1 + (RT60/0.65)1.5)  [empirical, assumes adequate SNR]

#### Assumptions & References

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