{"id":306842,"date":"2023-09-14T14:06:52","date_gmt":"2023-09-14T14:06:52","guid":{"rendered":"\/forum\/forums\/topic\/i-meet-a-4-db-gap-in-cfd-post-spl-calculation\/"},"modified":"2023-09-14T14:06:52","modified_gmt":"2023-09-14T14:06:52","slug":"i-meet-a-4-db-gap-in-cfd-post-spl-calculation","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/i-meet-a-4-db-gap-in-cfd-post-spl-calculation\/","title":{"rendered":"I meet a 4 dB gap in CFD-Post SPL calculation"},"content":{"rendered":"<div>Hello,<\/div>\n<div>&nbsp;<\/div>\n<div>I start studying acoustics by CFD-Post these days. And I know the formula of SPL (sound pressure level) is SPL=20*log10(P\/ref), ref=2e-5. So while P=1 Pa, the SPL should be 93.9794 dB.&nbsp;<\/div>\n<div>&nbsp;<\/div>\n<div>But when I use a sin signal to test the settings in CFD-Post, I do FFT and turn Y axis from magnitude to SPL, then I find it give a SPL 97.9588 dB at P=1 Pa. There is a 4 dB gap with the 93.97 dB it should be.<\/div>\n<div>&nbsp;<\/div>\n<div>Dose anyone meet the same problems? Can anyone tell me how to fix it, thanks very much.<\/div>\n<div>&nbsp;<\/div>\n<div><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/09\/14-09-2023-1694700240-403555d8b0ac69b17b461c76c09559b.png\" alt=\"\"><\/div>\n<div><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/09\/14-09-2023-1694700260-3cd2ed954602f7725751ffe0a0eba41.png\" alt=\"\"><\/div>\n<div><img decoding=\"async\" src=\"\/forum\/wp-content\/uploads\/sites\/2\/2023\/09\/14-09-2023-1694700282-fe24ae0ce66c22ac244b11387132775.png\" alt=\"\"><\/div>\n","protected":false},"template":"","class_list":["post-306842","topic","type-topic","status-closed","hentry","topic-tag-cfd-post"],"aioseo_notices":[],"aioseo_head":"\n\t\t<!-- All in One SEO 4.9.10 - aioseo.com -->\n\t<meta name=\"description\" content=\"Hello, I start studying acoustics by CFD-Post these days. And I know the formula of SPL (sound pressure level) is SPL=20*log10(P\/ref), ref=2e-5. 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