Trevor,

i've been so busy i havent had time to phone but as soon as i know i'll post here.

am up north this weekend so maybe i'll check out some places up there.

i cant even remember how to switch the home theatre on its been that long.

john

Actually you can calculate the delay with the following formula. Sound travels in air at normal room temperature at 1130 fps....

t=d/c

t = time in feet or meters.
c = the velocity of sound in fps or mps.
t = time in seconds.

Remember to keep the units the same... so for example. If you were 12 feet away from the speaker and in a normal temp room...

t = 12/1130

t = .016 seconds of delay from this speaker to your ear. Or 16 mS.

Use the speakers the furthest away delay time and then subtract the closer's from it. Say your rears are only 4 feet away.

t = 4/1130

t = 3 mS

16 mS - 3 mS = 13 mS, that is the delay you would want to use on your rear speaker for the sound to arrive at the same time.

Matt, could it be that D = DISTANCE in feet or meters?

12/1130 actually equals 0.0106, or 10.6ms.
4/1130 actually equals 0.00354, or 3.54ms.
1(ft)/1130(ft/sec) equals 0.000885(sec), or 0.885ms./ft.
That works out to:
13.56 inches per millisecond

Conclusion: compensation for distance differences should be one millisecond per 13.5 inches closer than the farthest speaker.

Larry

My rear speakers are closer to the listening position than my mains. This suggests to me that I need negative delay for the rear speakers.

Or is the idea to make the rears sound further away than they really are?

-Nick

LOL sorry about the miss typing...yes you are correct D = distance in feet or meters..

yeah, and I missed the zero in there..what can I say, sorry.

Anyway, you get the point and yes Nick, you want the sound to arrive at the same time, so you need to add delay to your rears to make the sound arrive at the same time as your front speakers. (Delay makes the sound come out of your speakers later than the base time)

Thanks for the correction Larry.

ps: So in the example, you would delay your rear speakers 7 mS (or so) not the 13 I miss calculated.



This message was edited by Matt on 11/19/01 19:29.57.