Postioning weld doesn't work either does rotating?

Here is what you have to fix.

local radio = script.Parent
local weld2 = Instance.new("Weld")
local Spectrum = game.ReplicatedStorage.Parts.Spectrum:Clone()
Spectrum.Parent = radio.mesh
Spectrum.Position = Player.Character.HumanoidRootPart.Position + Vector3.new(0,-6,0)
weld2.Name = "Spectrum_Weld"
weld2.Part0 = Player.Character.HumanoidRootPart
weld2.Part1 = Spectrum
weld2.C0 = Player.Character.HumanoidRootPart.CFrame:Inverse()*CFrame.new(Player.Character.HumanoidRootPart.Position)
weld2.C1 = Spectrum.CFrame:Inverse()*CFrame.new(Player.Character.HumanoidRootPart.Position)
weld2.Parent = Player.Character.HumanoidRootPart

Edit: Sorry, here is explaination:

Here is your script:

weld2.C1 = Spectrum.CFrame:Inverse()

This is just the Inverse of Spectrum's CFrame Ex. 1 -> -1 , -3 -> 3

The correct should be distance between 2 parts that is welded. 1.) Find the first position. (in the form of CFrame)

local FirstPosition = Player.Character.HumanoidRootPart.Position

CFrame.new(FirstPosition)

2.) Subtract the first position with the second position. To subtract the cframe, yoou will need to inverse the cframe first and then sum it.

local FirstPosition = Player.Character.HumanoidRootPart.Position

CFrame.new(FirstPosition) * Spectrum.CFrame:Inverse()
--or 
Spectrum.CFrame:Inverse() * CFrame.new(FirstPosition)

Now you got the distance between 2 parts, put it in weld.C1 because the center position of the weld(0, 0, 0) is weld.Part0 Position.