This is Crazy! Delay your surround sound speakers!? Consider this: the most important aspect of any kind of listening environment is speaker placement. Get into stereo and both speakers must be equidistant to the listener AND in the magic triangle. Get into Quad and all four have to be equidistant in TWO magic triangles. Get into 5.1 surround and the Center and LFE channels must ALSO be equidistant…and on it goes. But what happens when you CANNOT get the speakers equidistant? Are you screwed? This article will show you how to unscrew yourself and delay your surround sound speakers.
It happens a lot. Your speakers – for whatever reason – cannot be equidistant to each other. The architecture of the room, positioning of gear, whatever. It’s common. And if it’s not dealt with, your mixes will NEVER translate outside of your listening environment. DO understand, however, that your speakers must be ANGLED correctly…there’s no getting around that. You can’t have your speakers pointing 15º away from the sweet spot of listening. But if we’ve got great speakers pointed in the right direction, but some are closer than others, what do we do to fix it?
What’s the Big Deal?
“Well, Mark, why is it a big deal anyway?”
Good question. Two things:
- Inverse Square Law: it means the closer a sound source (speaker) is to the listener, the louder it gets – on a geometric scale. That means that a 90 decibel signal at 1 meter, will be 84 dB at 2 meters (four times softer and two times softer to the brain), and will be 78 dB at 4 meters (eight times softer and four times softer to the ear). You can imagine what a foot of difference would do between speakers: catastrophe. Even a few inches will cause major issues in your mix because of inverse square law – but there’s an even bigger issue:
- Speed of Sound. The speed of sound at 72ºF at sea level is 1.1308 feet/ms. That means for every foot sound has to travel in space, it takes 1.1308 ms to traverse it. Right away you can see the horrors involved in even a foot of difference between speakers. Specifically and particularly between any stereo pair (front/surround): it would be impossible to create phantom mono. You’d have all manner of phase issues not to mention a perceived “quietness” from the farther speaker – on top of the issue of Inverse Square Law – you’ve got a mess. And simply “turning up the speaker to match the others” only exacerbates the issue.
The solution comes in creating “delay lines” for all channels and delaying the closest speakers to coincide with the farthest.
For Example: If you have a stereo pair, and the left speaker is 6″ closer than the right, this means that the left speaker is both louder and earlier than the right. Once we correct the time discrepancy we can correct with volume. And that math goes like this:
([farthest speaker] – [closest speaker ]) X 1.1308 ms = delay of closest speaker.
In this case .5 X 1.1308 = 0.5654 ms.
Now that not seem like much, but try balancing the room with that speaker 6 inches away, add the delay, and see if you’re not at least 1 dB wrong.
Surround systems are much the same. Imagine you’ve got a 7.1 system in a narrow, long room. The LCR speakers are at 8 feet, the Mid-sides are at 5 feet, and the surrounds are at 10 feet with the LFE at 9. This is a horrific situation which no amount of EQ, or volume can solve. Since the Mid-sides are closest we solve from them:
LCR delay = [(8-6)] X 1.1308 = 2.2616 ms
Surround delay = [(10-6)] X 1.1308 = 4.5232 ms
LFE delay = [(9-6)] X 1.1308 = 3.3924 ms
How do we delay these channels? Either using a multi-mono compatible delay plugin on the master surround output or splitting the channels into reasonable “final busses” and delaying them accordingly: a Front LR stereo bus, a Surround LR stereo bus, a mono LFE and a mono Center…or whatever distances are causing issues.
From here you’ll return your listening environment to optimal and you can tune your room accurately once again.
MAJOR CAUTION!!!! If you’re applying the delay line as a plugin before or on the master channel BE SURE TO TURN IT OFF BEFORE YOU BURN YOUR MASTERS or the resulting file will have those delays burned in…which will certainly not apply in someone else’s listening environment.
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