It’s easy to surprise someone, setting sound to mute=off and sound at 100% using that code :

[void][reflection.assembly]::LoadWithPartialName("System.Windows.Forms")
If(-not(Test-Path "c:\temp")){
    mkdir C:\temp
}
cd c:\temp
Add-Type -TypeDefinition @'
using System.Runtime.InteropServices;

[Guid("5CDF2C82-841E-4546-9722-0CF74078229A"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IAudioEndpointVolume {
  // f(), g(), ... are unused COM method slots. Define these if you care
  int f(); int g(); int h(); int i();
  int SetMasterVolumeLevelScalar(float fLevel, System.Guid pguidEventContext);
  int j();
  int GetMasterVolumeLevelScalar(out float pfLevel);
  int k(); int l(); int m(); int n();
  int SetMute([MarshalAs(UnmanagedType.Bool)] bool bMute, System.Guid pguidEventContext);
  int GetMute(out bool pbMute);
}
[Guid("D666063F-1587-4E43-81F1-B948E807363F"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IMMDevice {
  int Activate(ref System.Guid id, int clsCtx, int activationParams, out IAudioEndpointVolume aev);
}
[Guid("A95664D2-9614-4F35-A746-DE8DB63617E6"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
interface IMMDeviceEnumerator {
  int f(); // Unused
  int GetDefaultAudioEndpoint(int dataFlow, int role, out IMMDevice endpoint);
}
[ComImport, Guid("BCDE0395-E52F-467C-8E3D-C4579291692E")] class MMDeviceEnumeratorComObject { }

public class Audio {
  static IAudioEndpointVolume Vol() {
    var enumerator = new MMDeviceEnumeratorComObject() as IMMDeviceEnumerator;
    IMMDevice dev = null;
    Marshal.ThrowExceptionForHR(enumerator.GetDefaultAudioEndpoint(/*eRender*/ 0, /*eMultimedia*/ 1, out dev));
    IAudioEndpointVolume epv = null;
    var epvid = typeof(IAudioEndpointVolume).GUID;
    Marshal.ThrowExceptionForHR(dev.Activate(ref epvid, /*CLSCTX_ALL*/ 23, 0, out epv));
    return epv;
  }
  public static float Volume {
    get {float v = -1; Marshal.ThrowExceptionForHR(Vol().GetMasterVolumeLevelScalar(out v)); return v;}
    set {Marshal.ThrowExceptionForHR(Vol().SetMasterVolumeLevelScalar(value, System.Guid.Empty));}
  }
  public static bool Mute {
    get { bool mute; Marshal.ThrowExceptionForHR(Vol().GetMute(out mute)); return mute; }
    set { Marshal.ThrowExceptionForHR(Vol().SetMute(value, System.Guid.Empty)); }
  }
}
'@
[Audio]::Mute=$false
[Audio]::Volume = 1.00

If(-not (Test-path "c:\temp\giphy.gif")){
    Invoke-WebRequest -URI "https://media.giphy.com/media/YTbZzCkRQCEJa/giphy.gif" -OutFile "c:\temp\giphy.gif"
}
If(-not (Test-path "c:\temp\hb.wav")){
    Invoke-WebRequest -URI "http://www.thewavsite.com/Birthday/bday02.wav"-OutFile "c:\temp\hb.wav"
}
$file = (get-item 'c:\temp\hb.wav')
$file2="c:\temp\giphy.gif"
$img = [System.Drawing.Image]::Fromfile($file2);
[System.Windows.Forms.Application]::EnableVisualStyles();
$form = new-object Windows.Forms.Form
$user=$env:username
$form.Text = "Happy Birthday $user"
$width=$img.Size.Width + 100

$form.Width =$width;
$Height=$img.Size.Height + 100
$form.Height =  $Height
$pictureBox = new-object Windows.Forms.PictureBox
$pictureBox.Width =  $img.Size.Width;
$pictureBox.Height =  $img.Size.Height;
$pictureBox.Image = $img;
$form.controls.add($pictureBox)
$form.Add_Shown( { $form.Activate() } )
Add-Type -AssemblyName PresentationCore 
$_MediaPlayer = New-Object System.Windows.Media.MediaPlayer 
$_MusicFiles = Get-ChildItem -path "c:\temp" -include *.wav -recurse
$duration = $null
[uri]$_song = $file.FullName
 do {
     $_MediaPlayer.Open($_song)
     $_songDuration = $_MediaPlayer.NaturalDuration.TimeSpan.TotalMilliseconds
     }
until ($_songDuration)
$form.Top
$_MediaPlayer.Play()
$form.ShowDialog() 

$_MediaPlayer.Stop()
$_MediaPlayer.Close()