{"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\/da\/calculators\/noise-distance-attenuation\/","title":{"rendered":"Ideel overf\u00f8rsel af SPL fra punktsource i frit felt | 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>Gratis st\u00f8jd\u00e6mpningsberegner til afstand. Beregn lydniveauet i enhver afstand ved hj\u00e6lp af den inverse kvadratlov: 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\/da\/wp-json\/wp\/v2\/calculator\/100168","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/da\/wp-json\/wp\/v2\/calculator"}],"about":[{"href":"https:\/\/vibromera.eu\/da\/wp-json\/wp\/v2\/types\/calculator"}],"version-history":[{"count":4,"href":"https:\/\/vibromera.eu\/da\/wp-json\/wp\/v2\/calculator\/100168\/revisions"}],"predecessor-version":[{"id":102505,"href":"https:\/\/vibromera.eu\/da\/wp-json\/wp\/v2\/calculator\/100168\/revisions\/102505"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/da\/wp-json\/wp\/v2\/media?parent=100168"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/da\/wp-json\/wp\/v2\/categories?post=100168"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/da\/wp-json\/wp\/v2\/tags?post=100168"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}