{"id":1143,"date":"2012-03-02T23:54:52","date_gmt":"2012-03-02T22:54:52","guid":{"rendered":"http:\/\/svarthaletracing.se\/?p=1143"},"modified":"2012-05-01T15:02:21","modified_gmt":"2012-05-01T14:02:21","slug":"hur-hogt-later-en-pulsjet","status":"publish","type":"post","link":"https:\/\/svarthaletracing.se\/?p=1143","title":{"rendered":"Hur &#8221;h\u00f6gt&#8221; l\u00e5ter en pulsjet?"},"content":{"rendered":"\n<!-- powered by embed-javascript plugin ver. 1.1 beta (sw-galati.ro) -->\n<span style=\"font-size:10px;\"><a href=\"http:\/\/wordpress-plugins.sw-galati.ro\/\">Powered by Wordpress Plugins<\/a> - <a href=\"http:\/\/wordpress-plugins.sw-galati.ro\/\">Get the full version!<\/a><\/span><br><script type=\"text\/javascript\" width=\"100%\" height=\"900\" src=\"http:\/\/svarthaletracing.se\/linusn_js\/calculateDb.js\"><\/script>\n<p>Det h\u00e4r med ljudtryck kan l\u00e4tt bli lite sn\u00e5rigt, och en s\u00f6kning p\u00e5 Google g\u00f6r inte saken klarare f\u00f6r den oinvigde. Den enhet man normalt anv\u00e4nder f\u00f6r att ange hur &#8221;h\u00f6gt\/mycket&#8221; n\u00e5got l\u00e5ter \u00e4r decibel (dB). Detta \u00e4r inget absolut m\u00e5tt, utan anv\u00e4nds f\u00f6r att ange hur ett v\u00e4rde f\u00f6rh\u00e5ller sig till ett annat. I detta fall referenstrycket 20 mikropascal (\u03bcPa), vilket anses vara den l\u00e4gsta ljudniv\u00e5n som det m\u00e4nsliga \u00f6rat kan uppfatta.<\/p>\n<p><a href=\"http:\/\/en.wikipedia.org\/wiki\/Sound_pressure\" target=\"_blank\">Den engelska Wikipediaartikeln<\/a> om detta \u00e4r betydligt b\u00e4ttre \u00e4n den svenska.<\/p>\n<p>V\u00e5rt instrument visade 125.4 dB. D\u00e5 kanske n\u00e5gon undrar, &#8221;hur mycket \u00e4r det egentligen?&#8221;. Faktum \u00e4r att en s\u00e5dan angivelse \u00e4r ganska intets\u00e4gande utan ett avst\u00e5nd. Ta den svenska Wikipediaartikeln om ljudtryck som exempel. D\u00e4r finns en tabell, d\u00e4r det bland annat anges att 120dB motsvarar en dieselmotor. D\u00e5 fr\u00e5gar vi oss; upplever man ljudet fr\u00e5n en dieselmotor som lika &#8221;h\u00f6gt&#8221; oavsett om man st\u00e5r 1 meter eller 100 meter ifr\u00e5n den. Sj\u00e4lvklart inte!<\/p>\n<p>I den engelska Wikipediaartikeln d\u00e4remot, s\u00e5 anger man ljudniv\u00e5n vid ett visst avst\u00e5nd. T.ex att en vuvuzela ligger p\u00e5 runt 120dB vid 1 meter, och jag tror att man skulle uppleva det ljudet som <span style=\"text-decoration: underline;\">mycket<\/span> mer besv\u00e4rande \u00e4n en dieselmotor p\u00e5 samma avst\u00e5nd (om den inte k\u00f6r utan avgassystem f\u00f6rst\u00e5s).<\/p>\n<p>Om man har uppm\u00e4tt en ljudniv\u00e5 p\u00e5 ett visst avst\u00e5nd s\u00e5 kan man ungef\u00e4rligt ber\u00e4kna ljudniv\u00e5n p\u00e5 ett annat (st\u00f6rre eller mindre) avst\u00e5nd enligt formeln nedan:<br \/>\n<img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-1159\" title=\"dbCalc\" src=\"http:\/\/svarthaletracing.se\/wp-content\/uploads\/2012\/03\/dbCalc.gif\" alt=\"\" width=\"155\" height=\"36\" srcset=\"https:\/\/svarthaletracing.se\/wp-content\/uploads\/2012\/03\/dbCalc.gif 155w, https:\/\/svarthaletracing.se\/wp-content\/uploads\/2012\/03\/dbCalc-150x36.gif 150w\" sizes=\"auto, (max-width: 155px) 100vw, 155px\" \/><br \/>\nD\u00e4r L1 \u00e4r uppm\u00e4tt ljudniv\u00e5, R1 \u00e4r avst\u00e5nd till ljudk\u00e4llan, R2 \u00e4r det avst\u00e5nd man vill ber\u00e4kna ljudniv\u00e5n vid och L2 \u00e4r ber\u00e4knad ljudniv\u00e5 vid valt avst\u00e5nd.<\/p>\n<p>Eller s\u00e5 anv\u00e4nder man formul\u00e4ret nedan. De v\u00e4rden som \u00e4r f\u00f6rifyllda \u00e4r de som vi m\u00e4tte upp vid v\u00e5r <a href=\"http:\/\/svarthaletracing.se\/?p=1108\" target=\"_blank\">andra provk\u00f6rning<\/a>, snett framf\u00f6r pulsjetens front.<br \/>\n(Om inte formul\u00e4ret funkar, prova det alldeles utm\u00e4rkta <a href=\"http:\/\/www.wolframalpha.com\/input\/?i=L2+%3D+L1+-+20+*+log10%28R2+%2F+R1%29%2C+L1%3D125.4%2C+R1%3D3%2C+R2%3D10\" target=\"_blank\">Wolfram Alpha<\/a>)<\/p>\n<form>\n<table>\n<caption>Ber\u00e4kna ljudniv\u00e5 vid ett annat avst\u00e5nd till ljudk\u00e4llan<\/caption>\n<tbody>\n<tr>\n<td>Uppm\u00e4tt ljudtryck (L1):<\/td>\n<td><input id=\"measuredDb_input\" type=\"text\" name=\"measuredDb_input\" value=\"125.4\" \/><\/td>\n<td>(dB)<\/td>\n<\/tr>\n<tr>\n<td>M\u00e4tpunktens avst\u00e5nd till ljudk\u00e4llan (R1):<\/td>\n<td><input id=\"measuredAtDist_input\" type=\"text\" name=\"measuredAtDist_input\" value=\"3\" \/><\/td>\n<td>(m)<\/td>\n<\/tr>\n<tr>\n<td>Ber\u00e4kna ljudtrycket vid detta avst\u00e5nd fr\u00e5n k\u00e4llan (R2):<\/td>\n<td><input id=\"calculateAtDist_input\" type=\"text\" name=\"calculateAtDist_input\" \/><\/td>\n<td>(m)<\/td>\n<\/tr>\n<tr>\n<td>Ber\u00e4knat ljudtryck vid angivet avst\u00e5nd (L2):<\/td>\n<td><input id=\"calculatedAtDist_input\" type=\"text\" name=\"calculatedAtDist_input\" readonly=\"readonly\" \/><\/td>\n<td>(dB)<\/td>\n<\/tr>\n<tr>\n<td><\/td>\n<td><input onclick=\"javascript:calculateDbAtDistance_form();\" type=\"button\" value=\"Ber\u00e4kna!\" \/><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/form>\n<p>En kollega som bor p\u00e5 andra sidan Kvitslestr\u00f6mmen h\u00f6rde v\u00e4ldigt v\u00e4l n\u00e4r vi dundrade ig\u00e5ng motorn. L\u00e5t s\u00e4ga att det \u00e4r 1400m \u00f6ver till honom. Detta ger ungef\u00e4r 72 dB, vilket enligt <a href=\"http:\/\/www.sengpielaudio.com\/TableOfSoundPressureLevels.htm\" target=\"_blank\">denna sida<\/a> motsvarar en dammsugare p\u00e5 1 meters avst\u00e5nd. Detta \u00e4r f\u00f6rst\u00e5s h\u00f6gst ungef\u00e4rligt (man vet ju inte vad det \u00e4r f\u00f6r dammsugare), och utr\u00e4kningen \u00e4r v\u00e4ldigt f\u00f6renklad, men det ger i alla fall en indikation.<\/p>\n<p>(Jag reserverar mig mot eventuella faktafel)<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Det h\u00e4r med ljudtryck kan l\u00e4tt bli lite sn\u00e5rigt, och en s\u00f6kning p\u00e5 Google g\u00f6r inte saken klarare f\u00f6r den oinvigde. Den enhet man normalt anv\u00e4nder f\u00f6r att ange hur &#8221;h\u00f6gt\/mycket&#8221; n\u00e5got l\u00e5ter \u00e4r decibel (dB). Detta \u00e4r inget absolut &hellip; <a href=\"https:\/\/svarthaletracing.se\/?p=1143\">Forts\u00e4tt l\u00e4sa <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1,26],"tags":[],"class_list":["post-1143","post","type-post","status-publish","format-standard","hentry","category-allmant","category-faktarutorguider"],"_links":{"self":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts\/1143","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1143"}],"version-history":[{"count":22,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts\/1143\/revisions"}],"predecessor-version":[{"id":1158,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=\/wp\/v2\/posts\/1143\/revisions\/1158"}],"wp:attachment":[{"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1143"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1143"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/svarthaletracing.se\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1143"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}