Why is the material not changing based on the playbackloudness?

For some reason this is not working, I already felt that before but can someone please help me with this, thanks for looking -JustSxript

Script in part (LocalScript)

local sound = workspace:WaitForChild("Sound")
local Fire = script.Parent

sound:GetPropertyChangedSignal("PlaybackLoudness"):Connect(function()
    local PlaybackLoudness = sound.PlaybackLoudness

    Fire.Material = "Plastic" - (PlaybackLoudness / "Neon")
end)