diff --git a/eos/file_reader.py b/eos/file_reader.py
index 1c8d452..3bc1806 100644
--- a/eos/file_reader.py
+++ b/eos/file_reader.py
@@ -572,18 +572,16 @@ class AmorEventData(AmorHeader):
     def read_beam_monitor_stream(self, packets):
         if self._beam_monitor is None:
             return None
-        _signal = self._beam_monitor.signal
-        _time = self._beam_monitor.time
         plse = np.array([0, 5, 6, 11])
         base = np.array([2, 3, 8, 9])
-        i = 0
-        beam_monitor = np.recarray(shape=np.shape(packets.time)[0], dtype=BM_TYPE)
-        for tt, tme in enumerate(_time):
-            if (tme>=packets.time[0])&(tme<=packets.time[-1]):
-                beam_monitor.value[i] = _signal[tt][plse].sum() - _signal[tt][base].sum()
-                beam_monitor.time[i] = tme
-                i += 1
-        return beam_monitor[:i+1]
+        _time = self._beam_monitor.time
+        fltr = (self.eventStartTime<=_time)&(_time<=packets.time[-1])
+        _time = _time[fltr]
+        _signal = self._beam_monitor.signal[fltr]
+        beam_monitor = np.recarray(shape=_time.shape[0], dtype=BM_TYPE)
+        beam_monitor.time = _time
+        beam_monitor.value = _signal[:, plse].sum(axis=1) - _signal[:, base].sum(axis=1)
+        return beam_monitor
 
     def info(self):
         output = ""