DIY Surround Sound Speaker Delays You Don’t Know

DIY Surround Sound Speaker Delays You Don’t Know

Now that folks are realizing that Cinema Sound is THE resource for independent media creators, consumers are starting to realize that we’re the place to go for understanding how to set up their surround systems. We get about a dozen questions a week about this, so we’re going to put out several articles about this – in addition to the Cinema Sound Education. Let’s get this surround sound placement and speaker delays thing handled!

The Basics:

Placing surround speakers is easy – once you know how it all works. If you don’t, then it’s a hunt-and-place madness which never sounds or feels right. In the professional arena, there are few tolerances, and most of what you need to know is covered in the Workspace Volume of the Cinema Sound education and in articles here. But for consumers, there’s a lot more leeway about where speakers can go, room acoustics and construction constraints.

The bottom line is this: to be truly accurate and correct with your placement, these are the rules,

  1. All speakers must be equidistant from the listening position. ALL SPEAKERS. Including the subwoofer and the surrounds and – especially – the Center channel – which is the most often misjudged distance between them all.
  2. All speakers must be equal volume to each other – in accordance with Dolby standards. This means they’re NOT the same volume. Yep. That’s right. If you’re listening at a 80 dB dialog norm, then your L, C, R speakers are 80 db, your surrounds are 77 dB and your subwoofer is 85 dB. I know. Crazy. But there’s good reason for it which is covered in the education.
  3. All speakers must be focused toward the listening position at the same relative angle of incidence plus-or-minus 5 degrees from all axies. Of course, if you’re doing a theatrical system, this nearly impossible because of the area style seating and the need to put speakers on the ceiling – also due to the fact that the “listening position” is nearly the entire room. But for your home theater, this is very doable.

Now, that said, to the extent that you differ from this, to the extent of the difference, means you’re breaking the rules, and you’re not going to get a good result. Let’s just say this. It DOESN’T MATTER if you have a special intelligent room EQ, or smart microphone  with a head unit with built in delays or whatever – if you’re not doing the above 3 things, you’re not going to get an optimal result. If I had a $$$ for every idiot who screams on our Youtube channel something like, “that’s what [automated microphone systems] do!” I’d be super rich.

The Solution

As to what rules you should consider breaking when you must, which ones are “okay” to break? 

Only #1. 

The other two cannot be recovered from without causing all kinds of other issues – and with #2, you’re just not going to hear anything right if you’ve gotten this wrong.

As for #1, how to we solve a situation where speakers aren’t equidistant – or even close to equidistant – to the listening position? Easy. Now, to be clear, this solution does solve the issue of speaker distance, but creates other issues around primary and secondary reflections which can’t be resolved without significant acoustic treatment of the room (which probably isn’t a bad idea to treat anyway – and is, again, covered in the Workspace Volume).

Here we go. The solution:

Delay. Volume won’t do. The reason you can’t just turn up a speaker x-dB when it’s farther away is that the brain will always think the earlier sounds it hears is louder. In fact, sound that comes even 1 ms later can get completely masked – not to mention the massive amount of comb filtering and phase issues with just turning a further-out speaker up louder. No. Volume only makes it worse.

Delay is your only course. And, again, while this makes other issues, they’re far less bad than having speakers unaligned.

We like to say that in a 72-75ºF room at sea level, sound travels at roughly 1.1308ms/ft. This means, for every foot sound travels, it takes it 1.1308 ms to do so. This means if your Center speaker is in a straight line with your left and right speakers, your Center speaker is TOO CLOSE. Or your L/R speakers are too far – either way, your Center speaker will appear louder than your L/R speakers even if the amp has them the same. If, by using a tape measure, you discover that, say, the Center speaker is 1 foot/12 inches closer (a large distance indeed), then you’d delay your center speaker 1.1308 ms, and everything is fine. If, however the Center speaker is only 6 inches closer, then you’d delay the speaker, .5654 ms (1.1308ms X distance in feet) and you’re good.

The issue comes when the subwoofer is on a wall somewhere, the Center channel is in a line with L/R and the surrounds are, horrifically, on the ceiling in the back of the room. That’s far more normal in a home setup – and I pray is never the case in a studio or home-studio setup. Still, let’s say the Center Channel is 6″ closer than the L/R speakers which are in the right place. The Sub is 4 feet further than the Center and the surrounds – now “ceilings” – are 9 feet farther Rs and 10 feet farther Ls. Let’s also say that the optimum magic triangle is 4 feet.

How do we compute 1.1308ms X distance for all these? Easy. We add a variable: (Longest distance from listening position – Distance of Speaker) X 1.1308ms.

Take the farthest speaker away as your base. In this case, the Ls. All other speakers are delayed to suit based on this farthest figure. It goes like this:

  • Ls = 10 feet from listening position. The farthest out and therefore cannot be delayed.
  • Rs = 10 feet (Ls) – 9 feet (Rs) X 1.1308ms = 1.1308ms
  • Sub = 10 feet – 6 feet X 1.1308ms = 4.5232ms
  • L/R = 10 feet – 4 feet (since L/R are correct, but still must be delayed), X 1.1308ms = 6.7848ms
  • Center = 10 feet – 3.5 feet X 1.1308 ms = 7.3502ms

Notice for clarity, the closest speaker is delayed the most.

Do you need to get this to the dead accurate decimal? No. In fact if you’re at rounded ms, you’re probably okay. Once you have the delays set up, THEN AND ONLY THEN do you balance for volume.

I have several articles on this, and all kinds of things to manage the levels of your speakers as well, but let this be the end of the delay issues!

If you want to learn more, just use the search field in the blog or – even better – buy or rent the Cinema Sound Volume: Workspace!

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