{"id":100168,"date":"2026-02-15T20:22:05","date_gmt":"2026-02-15T20:22:05","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100168"},"modified":"2026-07-12T23:14:39","modified_gmt":"2026-07-12T23:14:39","slug":"noise-distance-attenuation","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/vi\/calculators\/noise-distance-attenuation\/","title":{"rendered":"Ideal Free-Field Point-Source SPL Transfer | Vibromera"},"content":{"rendered":"\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Ideal Free-Field Point-Source SPL Transfer Worksheet\",\"description\":\"Transfer one specified sound-pressure-level descriptor between two distances using ideal spherical geometrical spreading, with explicit applicability checks.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/noise-distance-attenuation\/\",\"applicationCategory\":\"EngineeringApplication\",\"operatingSystem\":\"Any\",\"offers\":{\"@type\":\"Offer\",\"price\":\"0\",\"priceCurrency\":\"EUR\"},\"creator\":{\"@type\":\"Organization\",\"name\":\"Vibromera\",\"url\":\"https:\/\/vibromera.eu\/\"},\"dateModified\":\"2026-07-13\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true}<\/script>\n\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[{\"@type\":\"Question\",\"name\":\"When is the 20 log10 distance relation valid?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"It is an ideal geometrical-spreading transfer for the same stable point-like source, the same sound-pressure-level descriptor and operating state, the same directivity sector, and two far-field receiver positions in a free field. It excludes reflections, barriers, ground effects, atmospheric absorption and meteorological effects.\"}},{\"@type\":\"Question\",\"name\":\"Is this an ISO 9613-2 calculation?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. ISO 9613-2:2024 is an outdoor engineering prediction method with octave-band source data and terms for geometrical divergence, atmospheric absorption, ground effect, reflections, screening and meteorology. This worksheet evaluates geometrical spreading only.\"}},{\"@type\":\"Question\",\"name\":\"Can dB and dBA be used interchangeably?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. The same fully identified acoustic descriptor, frequency weighting, time weighting or averaging interval, and source operating state must apply at both positions.\"}},{\"@type\":\"Question\",\"name\":\"Does a road or any line source always lose 3 dB per distance doubling?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. A fixed 3 dB rule is not a general model for roads or arbitrary extended sources. Source geometry, finite length, spectrum, ground, barriers and meteorology must be represented by a suitable validated method.\"}},{\"@type\":\"Question\",\"name\":\"Can this result establish a safe distance or regulatory compliance?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"No. It is not an exposure, dose, environmental-noise or compliance calculation. Those decisions require the applicable acoustic descriptor, measurement or a complete validated prediction, uncertainty and the governing requirements.\"}}]}<\/script>\n\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"BreadcrumbList\",\"itemListElement\":[{\"@type\":\"ListItem\",\"position\":1,\"name\":\"Home\",\"item\":\"https:\/\/vibromera.eu\/\"},{\"@type\":\"ListItem\",\"position\":2,\"name\":\"Calculators\",\"item\":\"https:\/\/vibromera.eu\/calculators\/\"},{\"@type\":\"ListItem\",\"position\":3,\"name\":\"Ideal Free-Field SPL Transfer\",\"item\":\"https:\/\/vibromera.eu\/calculators\/noise-distance-attenuation\/\"}]}<\/script>\n\n<style>\n:root{--nd-bg:#f3f5f7;--nd-card:#fff;--nd-ink:#17212b;--nd-muted:#52606d;--nd-soft:#eef3f6;--nd-line:#ccd6dd;--nd-accent:#176b87;--nd-accent-dark:#0e536b;--nd-good:#17693b;--nd-warn:#8a4b08;--nd-danger:#a12b2b;--nd-radius:10px;--nd-shadow:0 1px 2px rgba(23,33,43,.06),0 8px 24px 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0;font-weight:700;cursor:pointer}.nd-faq details p{padding:0 0 14px;margin:0}.nd-footer{margin-top:24px;text-align:center;color:var(--nd-muted);font-size:13px}.nd-footer a{color:var(--nd-accent-dark)}@media(max-width:680px){.nd-grid,.nd-result-grid{grid-template-columns:1fr}.nd-field-wide,.nd-result-primary{grid-column:auto}.nd-header{padding:28px 16px}.nd-card-head,.nd-form,.nd-results,.nd-section{padding-left:16px;padding-right:16px}}@media print{.nd-actions,.nd-error{display:none}.nd-card{box-shadow:none}.nd-results[hidden]{display:none}}\n<\/style>\n\n<main class=\"nd-app\" id=\"nd-app\">\n  <header class=\"nd-header\">\n    <p class=\"nd-kicker\">Reference worksheet \u00b7 geometric spreading only<\/p>\n    <h1 class=\"nd-title\">Ideal Free-Field Point-Source SPL Transfer<\/h1>\n    <p class=\"nd-lead\">Transfer one explicitly identified sound-pressure-level descriptor between two distances using ideal spherical spreading. The result is conditional\u2014not a complete outdoor-noise, indoor-noise, exposure, or compliance prediction.<\/p>\n    <div class=\"nd-tagrow\"><span class=\"nd-tag\">same source state<\/span><span class=\"nd-tag\">same level descriptor<\/span><span class=\"nd-tag\">far field<\/span><span class=\"nd-tag\">free field<\/span><\/div>\n  <\/header>\n\n  <div class=\"nd-notice\"><strong>Scope gate:<\/strong> use this worksheet only when both receiver positions meet every stated assumption. If ground, reflections, barriers, air absorption, weather, source directivity changes, near-field behaviour, or extended-source geometry matters, this single-term model is incomplete.<\/div>\n\n  <section class=\"nd-card\" aria-labelledby=\"nd-input-title\">\n    <div class=\"nd-card-head\"><h2 id=\"nd-input-title\">Recorded inputs<\/h2><p>No example values are preloaded. Enter the measurement or documented source basis you actually have.<\/p><\/div>\n    <form class=\"nd-form\" id=\"nd-form\" novalidate>\n      <div class=\"nd-grid\">\n        <div class=\"nd-field-wide\">\n          <label class=\"nd-label\" for=\"nd-descriptor\">Acoustic level descriptor used at both positions<\/label>\n          <input class=\"nd-input\" id=\"nd-descriptor\" type=\"text\" maxlength=\"80\" autocomplete=\"off\" placeholder=\"e.g. Lp,Z for the same one-third-octave band\" aria-describedby=\"nd-descriptor-hint\">\n          <span class=\"nd-hint\" id=\"nd-descriptor-hint\">Record the physical quantity plus frequency weighting\/band, time weighting or averaging interval, as applicable. \u201cdB\u201d alone is not a descriptor.<\/span>\n        <\/div>\n        <div class=\"nd-field-wide\">\n          <label class=\"nd-label\" for=\"nd-record\">Reference measurement\/source record<\/label>\n          <input class=\"nd-input\" id=\"nd-record\" type=\"text\" maxlength=\"160\" autocomplete=\"off\" placeholder=\"e.g. source ID, operating state, instrument record and receiver direction\" aria-describedby=\"nd-record-hint\">\n          <span class=\"nd-hint\" id=\"nd-record-hint\">Identify the evidence behind L\u2081 so that unchanged operation, position and directivity can be checked.<\/span>\n        <\/div>\n        <div>\n          <label class=\"nd-label\" for=\"nd-level\">Reference level L\u2081 (dB)<\/label>\n          <input class=\"nd-input\" id=\"nd-level\" type=\"text\" inputmode=\"decimal\" autocomplete=\"off\" placeholder=\"e.g. 90.0\" aria-describedby=\"nd-level-hint\">\n          <span class=\"nd-hint\" id=\"nd-level-hint\">A finite signed decimal is accepted. Use either decimal point or decimal comma.<\/span>\n        <\/div>\n        <div>\n          <label class=\"nd-label\" for=\"nd-unit\">Common distance unit<\/label>\n          <select class=\"nd-select\" id=\"nd-unit\" aria-describedby=\"nd-unit-hint\"><option value=\"\">Select unit<\/option><option value=\"m\">metre (m)<\/option><option value=\"ft\">foot (ft)<\/option><\/select>\n          <span class=\"nd-hint\" id=\"nd-unit-hint\">Both distances must use this same unit; it cancels in the ratio.<\/span>\n        <\/div>\n        <div>\n          <label class=\"nd-label\" for=\"nd-r1\">Reference distance r\u2081<\/label>\n          <input class=\"nd-input\" id=\"nd-r1\" type=\"text\" inputmode=\"decimal\" autocomplete=\"off\" placeholder=\"e.g. 1\" aria-describedby=\"nd-r1-hint\">\n          <span class=\"nd-hint\" id=\"nd-r1-hint\">Positive source-to-receiver distance in the selected unit.<\/span>\n        <\/div>\n        <div>\n          <label class=\"nd-label\" for=\"nd-r2\">Target distance r\u2082<\/label>\n          <input class=\"nd-input\" id=\"nd-r2\" type=\"text\" inputmode=\"decimal\" autocomplete=\"off\" placeholder=\"e.g. 2\" aria-describedby=\"nd-r2-hint\">\n          <span class=\"nd-hint\" id=\"nd-r2-hint\">Positive source-to-receiver distance in the selected unit.<\/span>\n        <\/div>\n        <div class=\"nd-field-wide nd-check\">\n          <input id=\"nd-basis\" type=\"checkbox\">\n          <label for=\"nd-basis\"><strong>I have checked the model basis:<\/strong> one stable point-like source; unchanged operation and emission; the same level descriptor; both positions in the source\u2019s far field and the same directivity sector; unobstructed free-field propagation; geometrical spreading is the only change being calculated.<\/label>\n        <\/div>\n      <\/div>\n      <div class=\"nd-actions\"><button class=\"nd-button\" type=\"submit\">Calculate transfer<\/button><button class=\"nd-button nd-button-secondary\" id=\"nd-reset\" type=\"reset\">Clear<\/button><\/div>\n      <p class=\"nd-error\" id=\"nd-error\" role=\"alert\" aria-live=\"polite\"><\/p>\n    <\/form>\n\n    <div class=\"nd-results\" id=\"nd-results\" aria-live=\"polite\" hidden>\n      <h2>Conditional result<\/h2>\n      <div class=\"nd-result-grid\">\n        <div class=\"nd-result nd-result-primary\"><span class=\"nd-result-label\" id=\"nd-out-level-label\">Predicted target level L\u2082<\/span><output class=\"nd-result-value\" id=\"nd-out-level\">\u2014<\/output><\/div>\n        <div class=\"nd-result\"><span class=\"nd-result-label\">Signed level change \u0394L = L\u2082 \u2212 L\u2081<\/span><output class=\"nd-result-value\" id=\"nd-out-change\">\u2014<\/output><\/div>\n        <div class=\"nd-result\"><span class=\"nd-result-label\">Geometrical term subtracted, G<\/span><output class=\"nd-result-value\" id=\"nd-out-term\">\u2014<\/output><\/div>\n        <div class=\"nd-result\"><span class=\"nd-result-label\">Distance ratio r\u2082\/r\u2081<\/span><output class=\"nd-result-value\" id=\"nd-out-ratio\">\u2014<\/output><\/div>\n        <div class=\"nd-result\"><span class=\"nd-result-label\">Sound-pressure ratio p\u2082\/p\u2081<\/span><output class=\"nd-result-value\" id=\"nd-out-pressure\">\u2014<\/output><\/div>\n      <\/div>\n      <p class=\"nd-result-note\" id=\"nd-out-note\"><\/p>\n      <div class=\"nd-actions\"><button class=\"nd-button nd-button-secondary\" id=\"nd-copy\" type=\"button\">Copy recorded result<\/button><\/div>\n    <\/div>\n  <\/section>\n\n  <section class=\"nd-card\">\n    <div class=\"nd-section\">\n      <h2>Model and dimensional check<\/h2>\n      <p>For spherical waves from an ideal point source in a lossless free field, far-field sound-pressure amplitude is proportional to 1\/r. Therefore the pressure-level difference is:<\/p>\n      <div class=\"nd-formula\">G = 20 log\u2081\u2080(r\u2082\/r\u2081)<br>L\u2082 = L\u2081 \u2212 G<br>\u0394L = L\u2082 \u2212 L\u2081 = \u221220 log\u2081\u2080(r\u2082\/r\u2081)<\/div>\n      <p>Here L\u2081 and L\u2082 are the <em>same specified sound-pressure-level descriptor<\/em>, in decibels; r\u2081 and r\u2082 are positive distances in the same unit. The ratio r\u2082\/r\u2081 is dimensionless, so taking its logarithm is dimensionally valid. The associated ideal pressure-amplitude ratio is p\u2082\/p\u2081 = r\u2081\/r\u2082.<\/p>\n      <p>A doubling gives G = 20 log\u2081\u2080(2) = 6.0206 dB\u2014not exactly 6 dB. If r\u2082 &lt; r\u2081, G is negative and the model predicts an increase; the worksheet reports the sign rather than disguising it as \u201cattenuation.\u201d<\/p>\n    <\/div>\n    <div class=\"nd-section\">\n      <h2>Applicability checklist<\/h2>\n      <div class=\"nd-table-wrap\"><table class=\"nd-table\"><thead><tr><th>Condition<\/th><th>Required for this worksheet<\/th><th>If not satisfied<\/th><\/tr><\/thead><tbody>\n        <tr><td>Source and operation<\/td><td class=\"nd-pass\">Same stable source power, spectrum and operating state<\/td><td class=\"nd-fail\">Do not attribute the observed difference solely to distance<\/td><\/tr>\n        <tr><td>Acoustic quantity<\/td><td class=\"nd-pass\">Same named level descriptor, weighting\/band and time basis<\/td><td class=\"nd-fail\">Levels are not directly transferable<\/td><\/tr>\n        <tr><td>Geometry<\/td><td class=\"nd-pass\">Point-like at both distances; both points in the validated far field<\/td><td class=\"nd-fail\">Use a source\/geometry-specific method<\/td><\/tr>\n        <tr><td>Direction<\/td><td class=\"nd-pass\">Same source directivity sector<\/td><td class=\"nd-fail\">Include documented directivity<\/td><\/tr>\n        <tr><td>Propagation<\/td><td class=\"nd-pass\">Free field; no relevant reflecting or screening objects<\/td><td class=\"nd-fail\">Model reflections, ground and barriers<\/td><\/tr>\n        <tr><td>Medium and weather<\/td><td class=\"nd-pass\">Their change is negligible over the path for the stated purpose<\/td><td class=\"nd-fail\">Use frequency-dependent atmospheric and meteorological modelling<\/td><\/tr>\n      <\/tbody><\/table><\/div>\n      <p class=\"nd-small\">\u201cFar field\u201d is not established here by a universal distance preset. It depends on source dimensions, wavelength, radiation behaviour and measurement purpose.<\/p>\n    <\/div>\n    <div class=\"nd-section\">\n      <h2>What this worksheet deliberately does not calculate<\/h2>\n      <ul class=\"nd-list\">\n        <li>It does not calculate sound power level from sound pressure level.<\/li>\n        <li>It does not model a road, railway, pipe, fa\u00e7ade or arbitrary \u201cline source.\u201d A universal 3 dB-per-doubling rule is not assigned to those cases.<\/li>\n        <li>It does not combine octave bands, A-weight a spectrum, or convert among instantaneous, maximum, peak, time-weighted, equivalent-continuous or exposure levels.<\/li>\n        <li>It does not include atmospheric absorption, ground effect, reflections, screens, foliage, buildings, terrain, wind or temperature gradients.<\/li>\n        <li>It does not establish a safe distance, worker dose, community-noise rating, legal limit or regulatory compliance.<\/li>\n      <\/ul>\n    <\/div>\n    <div class=\"nd-section\">\n      <h2>Standards boundary and sources<\/h2>\n      <p><strong>Classification of the equation:<\/strong> general acoustical\/physical relation for ideal spherical geometrical spreading. It is not presented as a formula prescribed by ISO 9613-2.<\/p>\n      <ul class=\"nd-list nd-ref\">\n        <li><a href=\"https:\/\/www.osha.gov\/otm\/section-3-health-hazards\/chapter-5\" target=\"_blank\" rel=\"noopener noreferrer\">OSHA Technical Manual, Section III, Chapter 5<\/a> \u2014 official explanation of the point-source free-field distance relation and limits of real sound fields.<\/li>\n        <li><a href=\"https:\/\/www.iso.org\/standard\/74047.html\" target=\"_blank\" rel=\"noopener noreferrer\">ISO 9613-2:2024, Edition 2<\/a> \u2014 current outdoor engineering method; its public scope lists geometrical divergence, atmospheric absorption, ground effect, reflections, screening and meteorology. A draft Amendment 1 is under development and is not used here.<\/li>\n        <li><a href=\"https:\/\/www.iso.org\/standard\/17426.html\" target=\"_blank\" rel=\"noopener noreferrer\">ISO 9613-1:1993, Edition 1<\/a> \u2014 published, currently under review; frequency- and weather-dependent atmospheric absorption. No coefficients from its licensed text are reproduced here.<\/li>\n        <li><a href=\"https:\/\/www.iso.org\/standard\/59765.html\" target=\"_blank\" rel=\"noopener noreferrer\">ISO 1996-1:2016, Edition 3<\/a> \u2014 current basic environmental-noise quantities and assessment procedures; its public note warns that the underlying acoustic quantity must be identified.<\/li>\n        <li><a href=\"https:\/\/www.iso.org\/standard\/64978.html\" target=\"_blank\" rel=\"noopener noreferrer\">ISO 80000-8:2020, Edition 2 + Amendment 1:2025<\/a> \u2014 current names, symbols, definitions and units for acoustical quantities.<\/li>\n        <li><a href=\"https:\/\/webstore.iec.ch\/en\/publication\/5708\" target=\"_blank\" rel=\"noopener noreferrer\">IEC 61672-1:2013, Edition 2<\/a> \u2014 sound-level-meter specifications distinguish frequency-weighted, time-weighted, time-averaged and sound-exposure measurements.<\/li>\n      <\/ul>\n      <p class=\"nd-small\">Official public records checked 13 July 2026. Clause-level ISO propagation algorithms and coefficients require the controlled standard text and are outside this worksheet.<\/p>\n    <\/div>\n    <div class=\"nd-section nd-faq\">\n      <h2>Questions that prevent common misuse<\/h2>\n      <details><summary>Is \u201c90 dB\u201d enough information?<\/summary><p>No. Record what level it is\u2014for example a Z-weighted band level, L<sub>Aeq,T<\/sub>, or another defined quantity\u2014plus the relevant time\/frequency basis and operating state. ISO 1996-1 explicitly warns that different acoustic quantities can all be expressed in dB and normally differ.<\/p><\/details>\n      <details><summary>Can I use an A-weighted level?<\/summary><p>Only as the same fully specified A-weighted descriptor at both positions and only when every propagation assumption is met. This worksheet applies the same frequency-independent geometrical term to the unchanged source spectrum; it does not calculate frequency-dependent losses or A-weight a spectrum.<\/p><\/details>\n      <details><summary>Does the equation work indoors?<\/summary><p>Not as a prediction of the total room level. Reflected\/reverberant sound generally prevents the total level from following ideal spherical spreading. A separately isolated direct-field component may be analysed only with a defensible measurement model.<\/p><\/details>\n      <details><summary>Why is there no line-source switch?<\/summary><p>Because selecting \u201cline source\u201d does not prove cylindrical spreading. Real extended sources can be finite, incoherent or directional and can transition with distance; roads additionally require traffic, spectrum, ground, screening and meteorology. A generic switch would produce unjustified precision.<\/p><\/details>\n      <details><summary>Can this choose a hearing-safe distance?<\/summary><p>No. Hearing risk depends on the applicable A-weighted or peak descriptor, duration, temporal pattern, multiple sources and governing requirements. Verify exposure using suitable measurements or a complete validated assessment.<\/p><\/details>\n    <\/div>\n  <\/section>\n\n  <p class=\"nd-footer\">Reference worksheet by <a href=\"https:\/\/vibromera.eu\/\">Vibromera<\/a> \u00b7 calculation is conditional on the recorded assumptions.<\/p>\n<\/main>\n\n<script>\n(function(){\n  'use strict';\n  function byId(id){return document.getElementById(id)}\n  var form=byId('nd-form'),descriptor=byId('nd-descriptor'),record=byId('nd-record'),level=byId('nd-level'),unit=byId('nd-unit'),r1=byId('nd-r1'),r2=byId('nd-r2'),basis=byId('nd-basis'),error=byId('nd-error'),results=byId('nd-results'),copy=byId('nd-copy');\n  function parseDecimal(raw){\n    var s=String(raw).trim().replace(\/\\u2212\/g,'-');\n    if(!\/^[+-]?(?:\\d+(?:[.,]\\d*)?|[.,]\\d+)$\/.test(s))return null;\n    if(s.indexOf('.')!==-1&&s.indexOf(',')!==-1)return null;\n    var n=Number(s.replace(',','.'));\n    return Number.isFinite(n)?n:null;\n  }\n  function signed(n){var clean=Math.abs(n)<0.00000000005?0:n;return(clean>0?'+':'')+clean.toFixed(4)+' dB'}\n  function fixed(n,d){var clean=Math.abs(n)<Math.pow(10,-d)\/2?0:n;return clean.toFixed(d)}\n  function ratioText(n){if(!Number.isFinite(n)||n<=0)return'\u2014';return(n>=1000000||n<0.0001)?n.toExponential(6):n.toFixed(6)}\n  function hide(){results.hidden=true;copy.disabled=true}\n  function fail(message,field){hide();error.textContent=message;if(field)field.focus();return false}\n  function calculate(event){\n    if(event)event.preventDefault();error.textContent='';\n    var name=descriptor.value.trim(),sourceRecord=record.value.trim(),L1=parseDecimal(level.value),d1=parseDecimal(r1.value),d2=parseDecimal(r2.value);\n    if(!name)return fail('Identify the acoustic level descriptor used at both positions.',descriptor);\n    if(!sourceRecord)return fail('Record the reference measurement\/source evidence and operating state.',record);\n    if(L1===null)return fail('Reference level must be one finite decimal number, without units or extra text.',level);\n    if(unit.value!=='m'&&unit.value!=='ft')return fail('Select the common distance unit.',unit);\n    if(d1===null||d1<=0)return fail('Reference distance must be one finite number greater than zero.',r1);\n    if(d2===null||d2<=0)return fail('Target distance must be one finite number greater than zero.',r2);\n    if(!basis.checked)return fail('Confirm the model-basis checklist before calculating.',basis);\n    var logRatio=Math.log10(d2)-Math.log10(d1),G=20*logRatio,L2=L1-G,change=-G,ratio=d2\/d1,pressure=d1\/d2;\n    if(!Number.isFinite(G)||!Number.isFinite(L2)||!Number.isFinite(ratio)||!Number.isFinite(pressure)||ratio<=0||pressure<=0)return fail('The entered distance ratio is outside the calculator\u2019s finite numerical range.',r2);\n    byId('nd-out-level-label').textContent='Predicted target level L\u2082 \u2014 '+name;\n    byId('nd-out-level').textContent=fixed(L2,4)+' dB';\n    byId('nd-out-change').textContent=signed(change);\n    byId('nd-out-term').textContent=signed(G);\n    byId('nd-out-ratio').textContent=ratioText(ratio);\n    byId('nd-out-pressure').textContent=ratioText(pressure);\n    if(d2>d1)byId('nd-out-note').textContent='The target is farther away: ideal geometrical spreading predicts a level decrease of '+fixed(Math.abs(change),4)+' dB.';\n    else if(d2<d1)byId('nd-out-note').textContent='The target is closer: ideal geometrical spreading predicts a level increase of '+fixed(Math.abs(change),4)+' dB. This is not attenuation.';\n    else byId('nd-out-note').textContent='The two distances are equal, so this geometrical-spreading model predicts no level change.';\n    results.hidden=false;copy.disabled=false;return true;\n  }\n  form.addEventListener('submit',calculate);\n  form.addEventListener('input',function(){hide();error.textContent=''});\n  form.addEventListener('change',function(){hide();error.textContent=''});\n  form.addEventListener('reset',function(){window.setTimeout(function(){hide();error.textContent='';descriptor.focus()},0)});\n  copy.addEventListener('click',function(){\n    var text=['Ideal free-field point-source SPL transfer','Descriptor: '+descriptor.value.trim(),'Reference record: '+record.value.trim(),'L1: '+level.value.trim()+' dB','r1: '+r1.value.trim()+' '+unit.value,'r2: '+r2.value.trim()+' '+unit.value,'L2: '+byId('nd-out-level').textContent,'Delta L: '+byId('nd-out-change').textContent,'Geometrical term G: '+byId('nd-out-term').textContent,'Distance ratio: '+byId('nd-out-ratio').textContent,'Pressure ratio: '+byId('nd-out-pressure').textContent,'Basis: ideal spherical geometrical spreading only; not a complete environmental\/exposure\/compliance prediction.'].join('\\n');\n    if(navigator.clipboard&&navigator.clipboard.writeText)navigator.clipboard.writeText(text).then(function(){copy.textContent='Copied';window.setTimeout(function(){copy.textContent='Copy recorded result'},1200)}).catch(function(){copy.textContent='Copy unavailable'});\n  });\n  hide();\n})();\n<\/script>\n\n","protected":false},"excerpt":{"rendered":"<p>C\u00f4ng c\u1ee5 t\u00ednh to\u00e1n suy gi\u1ea3m \u00e2m thanh theo kho\u1ea3ng c\u00e1ch mi\u1ec5n ph\u00ed. T\u00ednh to\u00e1n m\u1ee9c \u0111\u1ed9 \u00e2m thanh \u1edf b\u1ea5t k\u1ef3 kho\u1ea3ng c\u00e1ch n\u00e0o b\u1eb1ng c\u00e1ch s\u1eed d\u1ee5ng \u0111\u1ecbnh lu\u1eadt ngh\u1ecbch \u0111\u1ea3o b\u00ecnh ph\u01b0\u01a1ng: L2 = L1 \u2212 20\u00b7log10(d2\/d1).<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-100168","calculator","type-calculator","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/calculator\/100168","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/calculator"}],"about":[{"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/types\/calculator"}],"version-history":[{"count":4,"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/calculator\/100168\/revisions"}],"predecessor-version":[{"id":102505,"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/calculator\/100168\/revisions\/102505"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/media?parent=100168"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/categories?post=100168"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/vi\/wp-json\/wp\/v2\/tags?post=100168"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}