{"id":236532,"date":"2021-12-28T16:21:04","date_gmt":"2021-12-28T15:21:04","guid":{"rendered":"http:\/\/tyxcisv.cluster031.hosting.ovh.net\/?p=236532"},"modified":"2025-09-18T17:40:35","modified_gmt":"2025-09-18T15:40:35","slug":"acoustic-basic","status":"publish","type":"post","link":"https:\/\/www.majorcom.fr\/en\/acoustic-basic\/","title":{"rendered":"Acoustic basics (Fundamentals)"},"content":{"rendered":"\n<div class=\"et_pb_legacy\">\n<div id=\"header\" class=\"et_pb_section\">\n<div class=\"et_pb_row\">\n<div class=\"et_pb_column\">\n<div class=\"et_pb_text\">\n<h1>Acoustic basics (Fundamentals)<\/h1>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"et_pb_section\">\n<div class=\"et_pb_column\">\n<div class=\"et_pb_row_inner\">\n<div class=\"et_pb_column_inner\">\n<div class=\"et_pb_text\">\n<h2>Sound acoustics<\/h2>\n<p> <\/p>\n<h3>1. Concept of acoustics :<\/h3>\n<p> <\/p>\n<p><u>GLOSSARY :<\/u><\/p>\n<ul>\n<li><u><strong>Sound :<\/strong><\/u> A sound is a pressure variation around the atmospheric pressure expressed in Pascal (Pa).\n<br>Human ear is sensitive from 20\u00b5Pa to 200Pa. A sound wave is propagated at a speed of 340 m\/s at 20\u00b0C in air. A perfect human ear perceived sounds from 20Hz to 20 000Khz.  <\/li>\n<\/ul>\n<p> <\/p>\n<ul>\n<li><u><strong>dB :<\/strong><\/u> Logarithmic unit that expresses a level of pressure (0 dB = 20\u00b5Pa, 94 dB = 1Pa, 114 dB = 10Pa).<\/li>\n<\/ul>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Echelle-du-bruit-Majorcom.jpg\"\/><\/figure>\n<div class=\"et_pb_text\">\n<div>\n<p>The sound level pressure in dB (SPL) decrease of <strong>6 dB<\/strong> in free field when the distance is doubled :<\/p>\n<\/div>\n<div class=\"pmedia-item pmedia-center\"> <\/div>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Image-perte-Majorcom.jpg\"\/><\/figure>\n<div class=\"et_pb_text\">\n<p>The free field is a space devoid of reflection. In this case, the acoustic wave loses <strong>6 dB<\/strong> per doubling of the distance.<br\/>Unlike a free field, the reverberating field is an acoustic propagation area where the acoustic wave encounter obstacles that gives reflections (for example an empty apartment behaves like an echo chamber). In this case the decrease of <strong>6dB<\/strong> can\u2019t be applied.<br\/>The SPL of a loudspeaker is increasing by <strong>3dB<\/strong> when the power is doubling. If a loudspeaker have a SPL of 90dB 1W\/1m, when this loudspeaker is wired on 2W the SPL will be 93dB at 1m and for 8W the SPL will be 99dB at 1m.<\/p>\n<p><strong><u>dBA :<\/u> <\/strong>Is a SPL unit weighted according to the human ear perception. Indeed the human ear behaves like a filter that enhance human speech frequencies. Below against the weighting curve of dBA.<\/p>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Courbe-de-ponderation-Majorcom.png\"\/><\/figure>\n<div class=\"et_pb_text\">\n<p><u><strong>Background noise :<\/strong><\/u> Background noise is the level of pressure that occurs in normal use without any message or music being played. For example, background noise in a restaurant is around 50 dBA. <\/p>\n<p><u><strong>Reverberation time :<\/strong><\/u> The time it takes for an impulse to lose X dB of pressure level, where X corresponds to 60 dB for the TR60 or 30 dB for the TR30. It is due to the geometry of the room and the materials used. <\/p>\n<p><u><strong>Reflections :<\/strong><\/u> Reflection is a phenomenon caused when a sound wave encounters an obstacle. There are two types of reflection: early reflections (important for intelligibility) and late reflections (harmful for intelligibility). <\/p>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Relexion-du-son-Majorcom.png\"\/><\/figure>\n<div class=\"et_pb_text\">\n<p><u><strong>Absorption :<\/strong><\/u> Ability of a material to dissipate the energy of an acoustic wave and thus reduce the level of the reflected wave. All materials have an ability to reflect or absorb sound. This capability is defined by the absorption rate which is between 0 and 1. 0 is a reverberant material and 1 is a fully absorbent material.<\/p>\n<p><u><strong>Resonance :<\/strong><\/u> Ability of an object, a wall or a place to vibrate at a specific frequency. For example a glasses broken by an singer.<\/p>\n<p><u><strong>Intelligibility :<\/strong><\/u> Percentage of message comprehension. This percentage depends on the ratio between the direct wave and the reflected wave, and on the reverberation time. It is expressed in <strong>RASTI, STI or CIS<\/strong>. The higher the percentage, the better the intelligibility.<\/p>\n<p><u><strong>Mask effect :<\/strong><\/u> This effect appears when the pressure level of the message or the music broadcast is close to the level of background noise. To understand a voice message, we admit a difference of 15-20 dB between these two levels.<\/p>\n<p><strong><u>Delay :<\/u><\/strong> Delay is used in the case of multiple speakers are used. The delay time is determined by the distance between speakers and the sound velocity. In case we don\u2019t use delay, phase shift phenomena may occur.<\/p>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Retard-du-son-Majrcom.png\"\/><\/figure>\n<div class=\"et_pb_text\">\n<p><u><strong>Phase shift :<\/strong><\/u> This is identical to that known in electronics. When two speaker broadcast toward to the same point are not wired in phase, loss of sound pressure level can appear by the addition of the two waves.<\/p>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Dephasage-du-son-Majorcom.png\"\/><\/figure>\n<div class=\"et_pb_text\">\n<p><u><strong>Sensibility of a transducer :<\/strong><\/u> Sound pressure level (SPL in dB) provided by a speaker when is supplied by a power of 1W at 1 meter.<\/p>\n<p><strong><u>Directivity of a loudspeaker or microphone :<\/u><\/strong> Vertical and horizontal angle of sound dispersion from the axis of the loudspeaker depending on the frequency. The most used directivity for microphone are: cardioid, hyper-cardioid or omnidirectional. They are given by a polar diagram.<\/p>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Directive-du-son-Majorcom.png\"\/><\/figure>\n<div class=\"et_pb_text\">\n<div>\n<p>For loudspeaker more the frequency is high more the directivity is reduced. Tweeters are more directive while a subwoofer is considered omnidirectional.<\/p>\n<\/div>\n<div>\n<h2> <\/h2>\n<h2>STI Index :<\/h2>\n<p>  0% &#8211; 30% : Very bad<br\/> 30% &#8211; 45% : Bad<br\/> 45% &#8211; 60% : Correct<br\/> 60% &#8211; 75% : Good<br\/> 75% &#8211; 100% : Excellent<\/p>\n<p><strong>STI conversion table \u2013 CIS (common inteligibility scale) :<\/strong><\/p>\n<\/div>\n<\/div>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/11\/Tableau-Majorcom.png\"\/><\/figure>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"et_pb_column\">\n<div class=\"et_pb_blurb\">\n<h3>MAJORCOM<\/h3>\n<figure><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/10\/unnamed-3.jpg\" alt=\"\"\/><\/figure><p><\/p>\n<p>Expert in Public Address and Voice Alarm systems for the past 50 years.<\/p>\n<\/div>\n<div class=\"et_pb_button\"><a class=\"et_pb_button_link et_pb_button_0\" href=\"https:\/\/www.majorcom.fr\/en\/public-address-system\/\">See our Public Address solutions<\/a><\/div>\n<div class=\"et_pb_button\"><a class=\"et_pb_button_link et_pb_button_1\" href=\"https:\/\/www.majorcom.fr\/en\/professional-sound-systems\/\">See our professional sound solutions<\/a><\/div>\n<div class=\"et_pb_button\"><a class=\"et_pb_button_link et_pb_button_2\" href=\"https:\/\/www.majorcom.fr\/en\/voice-alarm-solutions\/\">See our Voice Alarm solutions<\/a><\/div>\n<\/div>\n<\/div>\n<div class=\"et_pb_section\">\n<div class=\"et_pb_row\">\n<div class=\"et_pb_column\">\n<div class=\"et_pb_text\">\n<div>\n<div style=\"height:var(--wp--preset--spacing--70)\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n<h2><span style=\"color: #333333; font-size: 26px;\">Our other documentation<\/span><\/h2>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<div class=\"et_pb_section aide-sections-list\">\n<div class=\"et_pb_row\">\n<div class=\"et_pb_column\">\n<div class=\"et_pb_blurb\">\n<h3>Installation advice and information<\/h3>\n<figure><a href=\"https:\/\/www.majorcom.fr\/en\/installation-advice-information\/\" target=\"_blank\"><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/10\/La-technologie-100V-et-ses-principes-Majorcom.png\" alt=\"\"\/><\/a><\/figure><p><\/p>\n<p>Majorcom provide ranges of professional installation loudspeakers for indoor and outdoor PA applications \u2026<\/p>\n<p><a href=\"https:\/\/www.majorcom.fr\/en\/installation-advice-information\/\">Read more<\/a><\/p>\n<\/div>\n<\/div>\n<div class=\"et_pb_column\">\n<div class=\"et_pb_blurb\">\n<h3>How to measure a speaker line impedance<\/h3>\n<figure><a href=\"https:\/\/www.majorcom.fr\/en\/measure-speaker-line-impedance\/\" target=\"_blank\"><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/10\/Calculer-la-charge-dune-ligne-Haut-Parleur-Majorcom.png\" alt=\"\"\/><\/a><\/figure><p><\/p>\n<p>Impedance is a measure of the opposition to the flow of an alternating current in a circuit; the aggregation of its resistance \u2026<\/p>\n<p><a href=\"https:\/\/www.majorcom.fr\/en\/measure-speaker-line-impedance\/\">Read more<\/a><\/p>\n<\/div>\n<\/div>\n<div class=\"et_pb_column\">\n<div class=\"et_pb_blurb\">\n<h3>Omnidirectional speakers<\/h3>\n<figure><a href=\"https:\/\/www.majorcom.fr\/en\/omnidirectionnal-speakers\/\" target=\"_blank\"><img decoding=\"async\" src=\"https:\/\/spcdn.shortpixel.ai\/spio\/ret_img,q_cdnize,to_webp,s_webp\/www.majorcom.fr\/wp-content\/uploads\/2021\/10\/LOmnidirectionnel-Majorcom.png\" alt=\"\"\/><\/a><\/figure><p><\/p>\n<p>Recognized since 1992 and protected by an international patent, so far the omnidirectional speakers created by MAJORCOM \u2026<\/p>\n<p><a href=\"https:\/\/www.majorcom.fr\/en\/omnidirectionnal-speakers\/\">Read more<\/a><\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Acoustic basics (Fundamentals) Sound acoustics 1. Concept of acoustics : GLOSSARY : Sound : A sound is a pressure variation [&hellip;]<\/p>\n","protected":false},"author":17,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10721],"tags":[],"class_list":["post-236532","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.3 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Acoustic basics (fundamentals) - Majorcom<\/title>\n<meta name=\"description\" content=\"Acoustic basics (fundamentals) | A sound is a variation in pressure around atmospheric pressure ... - Majorcom\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.majorcom.fr\/en\/acoustic-basic\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Acoustic basics (fundamentals) - 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