[{"data":1,"prerenderedAt":642},["ShallowReactive",2],{"site-footer-common":3,"glossary:near-field-far-field":45,"glossary-related:near-field-far-field":151},{"id":4,"extension":5,"footer":6,"meta":40,"navbar":41,"stem":43,"__hash__":44},"common\u002Fcommon.yml","yml",{"tagline":7,"links":8,"sections":9},"Acoustic cleaning intelligence for industrial fouling, soot, ash, dust and build-up.",[],[10,19,31],{"title":11,"links":12},"Product",[13,16],{"label":14,"to":15},"How it works","\u002F#product",{"label":17,"to":18},"Cost assessment","\u002F#hero",{"title":20,"links":21},"Company",[22,25,28],{"label":23,"to":24},"What we build","\u002F#about",{"label":26,"to":27},"Careers","\u002F#careers",{"label":29,"to":30},"Contact","\u002F#contact",{"title":32,"links":33},"Resources",[34,37],{"label":35,"to":36},"Blog","\u002Fresources\u002Fblog",{"label":38,"to":39},"Glossary","\u002Fglossary",{},{"links":42},[],"common","YocmZRy1AYfBbpgGVms-zhdiABlF8VTxHx6h4rDmZBA",{"id":46,"title":47,"aliases":48,"body":51,"category":132,"description":133,"extension":134,"meta":135,"navigation":136,"path":137,"relatedTerms":138,"seo":141,"sources":144,"stem":148,"term":149,"__hash__":150},"glossary\u002Fglossary\u002Fnear-field-far-field.md","Near field \u002F far field",[49,50],"acoustic near field","acoustic far field",{"type":52,"value":53,"toc":125},"minimark",[54,78,83,91,94,98,101,105],[55,56,57,58,62,63,68,69,72,73,77],"p",{},"The ",[59,60,61],"strong",{},"near field"," is the acoustic zone immediately surrounding a sound source — typically within one ",[64,65,67],"a",{"href":66},"\u002Fglossary\u002Fwavelength","wavelength"," — where pressure and particle velocity are out of phase and SPL does not follow a clean 1\u002Fr² fall-off. The ",[59,70,71],{},"far field"," is the region beyond, where the wave behaves as a simple radial expansion and the ",[64,74,76],{"href":75},"\u002Fglossary\u002Finverse-square-law","inverse-square law"," applies.",[79,80,82],"h2",{"id":81},"why-the-distinction-matters-for-cleaning","Why the distinction matters for cleaning",[55,84,85,86,90],{},"Cleaning targets immediately adjacent to a horn's ",[64,87,89],{"href":88},"\u002Fglossary\u002Fbell-horn","bell"," are in the near field. The pressure environment there is intense and irregular and is what actually does the cleaning. Further targets sit in the far field, where the simpler radial model predicts the SPL.",[55,92,93],{},"For a 60 Hz horn (λ ≈ 5.7 m) the near field extends several metres. For a 400 Hz horn (λ ≈ 0.85 m) the near field is much smaller. Multi-horn arrays in large vessels deliberately overlap near-field zones so every target surface sees high-intensity coverage.",[79,95,97],{"id":96},"why-it-matters-for-measurement","Why it matters for measurement",[55,99,100],{},"Nameplate SPL is normally measured at 1 m — close enough to the source that the result depends on whether that point falls in the near or far field for the horn's frequency. Apples-to-apples comparisons between vendors require knowing where the measurement was taken.",[79,102,104],{"id":103},"related-terms","Related terms",[106,107,108,114,120],"ul",{},[109,110,111],"li",{},[64,112,113],{"href":66},"Wavelength",[109,115,116],{},[64,117,119],{"href":118},"\u002Fglossary\u002Fsound-pressure-level","Sound pressure level",[109,121,122],{},[64,123,124],{"href":75},"Inverse-square law",{"title":126,"searchDepth":127,"depth":127,"links":128},"",2,[129,130,131],{"id":81,"depth":127,"text":82},{"id":96,"depth":127,"text":97},{"id":103,"depth":127,"text":104},"acoustics-physics","The near field is the acoustic zone immediately surrounding a sound source — typically within one wavelength — where pressure and particle velocity are out of phase and SPL does not follow a clean 1\u002Fr² fall-off. The far field is the region beyond, where the wave behaves as a simple radial expansion and the inverse-square law applies.","md",{},true,"\u002Fglossary\u002Fnear-field-far-field",[67,139,140],"sound-pressure-level","inverse-square-law",{"title":142,"description":143},"Near field and far field — measurement zones around a sonic horn","The near field is the complex acoustic zone within roughly one wavelength of the source. The far field is the simpler region beyond, where the inverse-square law applies.",[145],{"title":146,"url":147},"Wikipedia — Near and far field","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FNear_and_far_field","glossary\u002Fnear-field-far-field","Near field and far field","gt3fuBeZGRr0VEtbkOdAg0ZuR-1fYKLBGU5D4XkzYjI",[152,317,499],{"id":153,"title":113,"aliases":154,"body":157,"category":132,"description":302,"extension":134,"meta":303,"navigation":136,"path":66,"relatedTerms":304,"seo":308,"sources":311,"stem":315,"term":113,"__hash__":316},"glossary\u002Fglossary\u002Fwavelength.md",[155,156],"acoustic wavelength","sound wavelength",{"type":52,"value":158,"toc":297},[159,169,173,249,252,256,269,271],[55,160,161,163,164,168],{},[59,162,113],{}," is the spatial distance over which one full cycle of a wave repeats. It is calculated as λ = c \u002F f, where c is the speed of sound in the medium (~343 m\u002Fs in air at 20 °C) and f is the ",[64,165,167],{"href":166},"\u002Fglossary\u002Ffrequency","frequency"," in hertz. For industrial acoustic cleaning the wavelength is the single most informative dimension because it predicts how the horn's sound field will fill the vessel.",[79,170,172],{"id":171},"wavelengths-for-industrial-sonic-horns","Wavelengths for industrial sonic horns",[174,175,176,189],"table",{},[177,178,179],"thead",{},[180,181,182,186],"tr",{},[183,184,185],"th",{},"Frequency",[183,187,188],{},"Wavelength in air at 20 °C",[190,191,192,201,209,217,225,233,241],"tbody",{},[180,193,194,198],{},[195,196,197],"td",{},"12 Hz",[195,199,200],{},"~28 m",[180,202,203,206],{},[195,204,205],{},"30 Hz",[195,207,208],{},"~11 m",[180,210,211,214],{},[195,212,213],{},"60 Hz",[195,215,216],{},"~5.7 m",[180,218,219,222],{},[195,220,221],{},"75 Hz",[195,223,224],{},"~4.6 m",[180,226,227,230],{},[195,228,229],{},"125 Hz",[195,231,232],{},"~2.7 m",[180,234,235,238],{},[195,236,237],{},"230 Hz",[195,239,240],{},"~1.5 m",[180,242,243,246],{},[195,244,245],{},"400 Hz",[195,247,248],{},"~0.85 m",[55,250,251],{},"Wavelengths in hot flue gas are longer than in cool air because the speed of sound rises with temperature — at 200 °C the speed of sound is about 436 m\u002Fs, stretching a 75 Hz wave to roughly 5.8 m.",[79,253,255],{"id":254},"why-long-wavelengths-penetrate-further","Why long wavelengths penetrate further",[55,257,258,259,263,264,268],{},"Acoustic energy diffracts efficiently around obstructions smaller than its wavelength. A 5-metre 60 Hz wave bends around tube rows, electrode spacings and baffles that would scatter or absorb a 1-metre 350 Hz wave. This is the underlying physics of why ",[64,260,262],{"href":261},"\u002Fglossary\u002Flow-frequency-acoustic-cleaner","low-frequency acoustic cleaners"," clean large open vessels better than ",[64,265,267],{"href":266},"\u002Fglossary\u002Fhigh-frequency-acoustic-cleaner","high-frequency"," units.",[79,270,104],{"id":103},[106,272,273,277,281,287,292],{},[109,274,275],{},[64,276,185],{"href":166},[109,278,279],{},[64,280,119],{"href":118},[109,282,283],{},[64,284,286],{"href":285},"\u002Fglossary\u002Fstanding-wave","Standing wave",[109,288,289],{},[64,290,291],{"href":261},"Low-frequency acoustic cleaner",[109,293,294],{},[64,295,296],{"href":266},"High-frequency acoustic cleaner",{"title":126,"searchDepth":127,"depth":127,"links":298},[299,300,301],{"id":171,"depth":127,"text":172},{"id":254,"depth":127,"text":255},{"id":103,"depth":127,"text":104},"Wavelength is the spatial distance over which one full cycle of a wave repeats. It is calculated as λ = c \u002F f, where c is the speed of sound in the medium (~343 m\u002Fs in air at 20 °C) and f is the frequency in hertz. For industrial acoustic cleaning the wavelength is the single most informative dimension because it predicts how the horn's sound field will fill the vessel.",{},[167,139,305,306,307],"standing-wave","low-frequency-acoustic-cleaner","high-frequency-acoustic-cleaner",{"title":309,"description":310},"Wavelength — how long is a sonic horn's wave inside a vessel?","Wavelength is the distance a sound wave travels in one cycle. At 60 Hz in air a wave is 5.7 m long; at 400 Hz it is 0.85 m. Wavelength governs how far a sonic horn's cleaning reach extends.",[312],{"title":313,"url":314},"Wikipedia — Wavelength","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FWavelength","glossary\u002Fwavelength","yrWaX9232a1ZSNJwMET2GxJuJPt98k9__zwmIHdRPuk",{"id":318,"title":319,"aliases":320,"body":323,"category":132,"description":481,"extension":134,"meta":482,"navigation":136,"path":118,"relatedTerms":483,"seo":487,"sources":490,"stem":497,"term":119,"__hash__":498},"glossary\u002Fglossary\u002Fsound-pressure-level.md","Sound pressure level (SPL)",[321,322],"SPL","sound pressure level dB",{"type":52,"value":324,"toc":475},[325,345,349,419,423,432,436,452,454],[55,326,327,329,330,334,335,339,340,344],{},[59,328,319],{}," is the logarithmic measure of sound pressure relative to the 20 µPa human-hearing reference, expressed in ",[64,331,333],{"href":332},"\u002Fglossary\u002Fdecibel","decibels",". It is the primary specification figure for any ",[64,336,338],{"href":337},"\u002Fglossary\u002Fsonic-horn","sonic horn"," or ",[64,341,343],{"href":342},"\u002Fglossary\u002Facoustic-cleaner","acoustic cleaner"," and the metric used to size noise-exposure controls at the work area.",[79,346,348],{"id":347},"industrial-reference-values","Industrial reference values",[174,350,351,361],{},[177,352,353],{},[180,354,355,358],{},[183,356,357],{},"SPL (dB)",[183,359,360],{},"Reference",[190,362,363,371,379,387,395,403,411],{},[180,364,365,368],{},[195,366,367],{},"0",[195,369,370],{},"Threshold of human hearing",[180,372,373,376],{},[195,374,375],{},"60",[195,377,378],{},"Normal conversation",[180,380,381,384],{},[195,382,383],{},"120",[195,385,386],{},"Threshold of pain",[180,388,389,392],{},[195,390,391],{},"140",[195,393,394],{},"Industrial sonic horn (lower-output models)",[180,396,397,400],{},[195,398,399],{},"160",[195,401,402],{},"Typical cement \u002F ESP sonic horn",[180,404,405,408],{},[195,406,407],{},"180",[195,409,410],{},"Upper limit of pneumatic industrial sonic horns",[180,412,413,416],{},[195,414,415],{},"194",[195,417,418],{},"Theoretical maximum for an undistorted sine wave in air",[79,420,422],{"id":421},"spl-and-cleaning-effectiveness","SPL and cleaning effectiveness",[55,424,425,426,428,429,431],{},"Cleaning energy scales with intensity, which doubles for every 3 dB rise. A 150 dB horn delivers roughly twice the energy of a 147 dB horn at the same distance. SPL is not, however, the only selection criterion: ",[64,427,167],{"href":166}," determines ",[64,430,67],{"href":66}," and therefore penetration. A 150 dB low-frequency horn typically out-cleans a 160 dB high-frequency horn in a large open vessel.",[79,433,435],{"id":434},"spl-and-exposure","SPL and exposure",[55,437,438,439,441,442,446,447,451],{},"Reported nameplate SPL is measured at 1 m on the bell axis. Real exposure at the work area falls with distance per the ",[64,440,76],{"href":75}," and through enclosure attenuation. Compliance with ",[64,443,445],{"href":444},"\u002Fglossary\u002Fosha-29-cfr-1910-95","OSHA 29 CFR 1910.95"," and ",[64,448,450],{"href":449},"\u002Fglossary\u002Feu-directive-2003-10-ec","EU Directive 2003\u002F10\u002FEC"," is calculated from exposure, not from nameplate SPL.",[79,453,104],{"id":103},[106,455,456,461,465,471],{},[109,457,458],{},[64,459,460],{"href":332},"Decibel",[109,462,463],{},[64,464,185],{"href":166},[109,466,467],{},[64,468,470],{"href":469},"\u002Fglossary\u002Fsound-power-vs-sound-pressure","Sound power vs sound pressure",[109,472,473],{},[64,474,124],{"href":75},{"title":126,"searchDepth":127,"depth":127,"links":476},[477,478,479,480],{"id":347,"depth":127,"text":348},{"id":421,"depth":127,"text":422},{"id":434,"depth":127,"text":435},{"id":103,"depth":127,"text":104},"Sound pressure level (SPL) is the logarithmic measure of sound pressure relative to the 20 µPa human-hearing reference, expressed in decibels. It is the primary specification figure for any sonic horn or acoustic cleaner and the metric used to size noise-exposure controls at the work area.",{},[484,167,485,140,486],"decibel","sound-power-vs-sound-pressure","sonic-horn",{"title":488,"description":489},"Sound pressure level (SPL) — definition, industrial-cleaning ranges","SPL is the logarithmic measure of sound pressure in decibels relative to a 20 µPa reference. Industrial sonic horns operate at 140–180 dB SPL.",[491,494],{"title":492,"url":493},"Wikipedia — Sound pressure","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FSound_pressure",{"title":495,"url":496},"Acoustical Society of America — Sound Pressure Level","https:\u002F\u002Fasastandards.org\u002F","glossary\u002Fsound-pressure-level","ayEoQNuJweSv9WGpwDPcx5CMESsbiPd4QPUpIoyQA6M",{"id":500,"title":124,"aliases":501,"body":504,"category":132,"description":628,"extension":134,"meta":629,"navigation":136,"path":75,"relatedTerms":630,"seo":633,"sources":636,"stem":640,"term":124,"__hash__":641},"glossary\u002Fglossary\u002Finverse-square-law.md",[502,503],"1\u002Fr² law (acoustic)","geometric spreading",{"type":52,"value":505,"toc":622},[506,517,521,524,578,582,593,597,605,607],[55,507,57,508,510,511,513,514,516],{},[59,509,76],{}," states that the intensity of a point-source sound wave falls as 1\u002Fr² with distance. Expressed in ",[64,512,333],{"href":332},", ",[64,515,321],{"href":118}," decreases by approximately 6 dB for every doubling of distance from the source in a free field.",[79,518,520],{"id":519},"worked-example-for-a-sonic-horn","Worked example for a sonic horn",[55,522,523],{},"A horn rated at 150 dB SPL at 1 m on the bell axis will produce, in free-field conditions:",[174,525,526,536],{},[177,527,528],{},[180,529,530,533],{},[183,531,532],{},"Distance",[183,534,535],{},"Approximate SPL",[190,537,538,546,554,562,570],{},[180,539,540,543],{},[195,541,542],{},"1 m",[195,544,545],{},"150 dB",[180,547,548,551],{},[195,549,550],{},"2 m",[195,552,553],{},"144 dB",[180,555,556,559],{},[195,557,558],{},"4 m",[195,560,561],{},"138 dB",[180,563,564,567],{},[195,565,566],{},"8 m",[195,568,569],{},"132 dB",[180,571,572,575],{},[195,573,574],{},"16 m",[195,576,577],{},"126 dB",[79,579,581],{"id":580},"where-the-rule-breaks-down","Where the rule breaks down",[55,583,584,585,587,588,592],{},"Three real conditions modify the textbook result. Inside a vessel, reflections from walls and tube banks reinforce the sound field and slow the fall-off; geometry no longer behaves as a free field. In the ",[64,586,61],{"href":137}," of the bell, the simple 1\u002Fr² rule does not apply. And at long distances and high frequencies, ",[64,589,591],{"href":590},"\u002Fglossary\u002Fattenuation-acoustic","attenuation"," absorbs additional energy beyond geometric spreading.",[79,594,596],{"id":595},"why-it-matters-for-noise-exposure","Why it matters for noise exposure",[55,598,599,600,339,602,604],{},"Worker exposure assessments work backwards from the inverse-square law: knowing the nameplate SPL and the operator-station distance, the predicted exposure can be compared with ",[64,601,445],{"href":444},[64,603,450],{"href":449}," action levels.",[79,606,104],{"id":103},[106,608,609,613,618],{},[109,610,611],{},[64,612,119],{"href":118},[109,614,615],{},[64,616,617],{"href":590},"Attenuation (acoustic)",[109,619,620],{},[64,621,47],{"href":137},{"title":126,"searchDepth":127,"depth":127,"links":623},[624,625,626,627],{"id":519,"depth":127,"text":520},{"id":580,"depth":127,"text":581},{"id":595,"depth":127,"text":596},{"id":103,"depth":127,"text":104},"The inverse-square law states that the intensity of a point-source sound wave falls as 1\u002Fr² with distance. Expressed in decibels, SPL decreases by approximately 6 dB for every doubling of distance from the source in a free field.",{},[139,631,632],"attenuation-acoustic","near-field-far-field",{"title":634,"description":635},"Inverse-square law — sound pressure halves every doubling of distance","In free-field conditions sound intensity falls as 1\u002Fr². Sound pressure level drops by approximately 6 dB for each doubling of distance from the source.",[637],{"title":638,"url":639},"Wikipedia — Inverse-square law","https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FInverse-square_law","glossary\u002Finverse-square-law","EYJdDFIbE5CXCp0ONbKYLs6jeZE8zRgWkX6myn6g82k",1782613716034]