uses
  MMSystem;

procedure SetVolume(const volL, volR: Word);
var
  hWO: HWAVEOUT;
  waveF: TWAVEFORMATEX;
  vol: DWORD;
begin
  FillChar(waveF, SizeOf(waveF), 0);
  waveOutOpen(@hWO, WAVE_MAPPER, @waveF, 0, 0, 0);
  vol := volL + volR shl 16;
  waveOutSetVolume(hWO, vol);
  waveOutClose(hWO);
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  SetVolume(14000, 14000);
end;