Stop brodcastig in 3 external soundcard

Question

Hello,
I want to stop the broadcasting of a sound wave in looping.I've used this method but to no avail:

private void btnStop_Click(object sender, EventArgs e)
{
if (output != null)
{
if (output.PlaybackState == NAudio.Wave.PlaybackState.Playing)
{
output.Stop();

}
}


}
I use the play function follows:

 public void PlaySoundInDevice(int deviceNumber, string fileName)

        {

            if (outputDevices.ContainsKey(deviceNumber))

            {

                outputDevices[deviceNumber].WaveOut.Dispose();

                outputDevices[deviceNumber].WaveStream.Dispose();

            }

            

                var waveOut = new WaveOut();

                waveOut.DeviceNumber = deviceNumber;

                WaveStream waveReader = new WaveFileReader(fileName);

                LoopStream loop = new LoopStream(waveReader);

                waveOut = new WaveOut();

                waveOut.Init(loop);

                waveOut.Play();

                // hold onto the WaveOut and  WaveStream so we can dispose them later

                outputDevices[deviceNumber] = new PlaybackSession { WaveOut = waveOut, WaveStream = waveReader };}
Ihave 3 external soundcard and the wave out of the 3 sond card

Is anybody can help me please and thank you in advance.