SP395 SoundPro Audio Integrator
Form7492
Operation Manual
42
To measure Initial Time Delay Gap (ITDG)
ITDG is the time between the direct sound and the first lateral sound reflection that is within 10
dB of the direct sound. This time clues the brain as to the room size - longer ITDGs mentally
equate to larger spaces, while too short ITDGs cause early reflection problems. For good home
theater acoustics, the ITDG for all speakers should be at least 10 mSec. ITDG time can be
lengthened by adding sound absorbing material to the speaker mirror points to reduce early
reflections.
1.
Follow the steps outlined above for "Identify Loudspeaker Reflections".
2.
Set the Horizontal measurement to time (mS).
3.
After you obtain a good display, turn off the generator to freeze the graph.
4.
Set the cursor to the direct sound (first peak). Note the dB level and the time.
5.
Move the cursor towards the right until you encounter a next peak that has an SPL level
that is within 10 dB of the direct sound level. Measure this time.
6.
Subtract the time of the reflection that is within 10 dB of the direct sound level (time in
step #5) from the direct sound arrival time (time in step #4).
Measuring RT Times
Reverberation time is how long it takes for the sound pressure level to decay by a specified dB
amount after the sound source is removed. The ETG function allows you to determine RT times
from RT10 to RT60.
1.
Follow steps 1-6 above for obtaining an Energy-Time graph
. Use A-weighting.
2.
Select the desired RT time (RT10, RT20, RT30, RT40, RT50, or RT60).
3.
Position the
RT
cursor to the start of the decay slope (to the right of the initial sharp decay)
.
4.
Position the measurement cursor to the end of the decay slope
.
5. Read the equivalent RT time for the decay slope.
RT60 Time ETG Measurement
Once you have a good decay graph, turn off the generator to freeze the graph. Select the RT
Cursor by clicking on the field below the vertical dB axis, and move the RT Cursor until it is
above the start of the linear decay slope, just after the initial sharp decay. This cursor will only
move up to the main Measurement Cursor, so you may need to move the main cursor first. Then,
select the main cursor and move it to the end time of the decay slope. The RT60 time for the
decay slope you have selected will be computed and shown in the RT Time field, at the upper
right.
Real-time Interface
The ETG function can be used with the TerraLink computer software program to provide real
time measurements on a PC screen. See the TerraLink Control – Real Time Computer Interface
section of this manual for more information.
