Adjustable speaker ‘delays’ allow the processor to automatically compensate for your room size, and for situations where for example, the rear speakers are positioned closer to your seat than the front speakers. If you didn’t add a slight delay to the sound in such circumstances, there’s every chance you’d hear the rear speakers before the fronts, which would sound very strange indeed. To set delays, you need to measure the distance from each speaker to your seat and enter those values into the ‘delay’ section of your amp or receiver’s set-up.
Most modern receivers and amps offer the choice of metres or feet for precise speaker delay calibration. However, some older kit requires you to enter in values to account for milliseconds of delay (which effectively does the same job, but which simply means you have to do the calculations yourself, rather than the processor). To work out these delays, use the following calculation: first, measure the distance from your front-left speaker to your seat. Then do the same for your left-rear speaker. You’ll have two numbers. For every 30cm of difference between these two figures, add 1ms (millisecond) of delay. For example, 300cm to front speakers, 150cm to rears = 150cm of difference, so 5ms of delay.
Finally, you’ll need to set the relative volume level of each speaker and your subwoofer. This can be done using the receiver’s built-in test tone, which can be used to both ensure you’ve wired each speaker up correctly, and to adjust each speaker for an even level of volume at the listening position. This is best done using a sound pressure level meter. Sit in your listening position, and point the meter straight upwards, not at your speakers. Set the meter’s sensitivity to 80dB and flick the selector switches to ‘C’ weighting, and ‘Slow’ response. Turn on your receiver’s test tone, and turn up the main volume dial until you get a reading from the front-left speaker of 75dB. Then use the volume trims on your receiver’s remote to adjust the volume from every other speaker in the system until it shows that level.