What's the problem?
It goes like this:
Modern audio processing like Dolby Atmos, DTS:X and Auro:3D can deliver wonderfully convincing spatial audio, but it's no good if only one or two seats get the benefit.
We should do whatever we can to give everyone a great result. First, we do our best with placement, and make sure no-one's too close to any one speaker.
The next problem is that speakers only give their best performance when pointed straight at the listener, and up to 20 degrees either side - we call that the listening window. Outside the listening window, the speaker response gets more and more uneven, and it's also lower in level - so any SPL (Sound Pressure Level) calculations - if your provider has done them - will be a bit off too.
We can use toe-in to put more listeners inside the sweet spot of each speaker:
Typical - flat to the wall
Better - speakers toed-in
When the Left and Right speakers sit flat against the screen wall, a lot of the energy bounces off the side walls. This creates a lot of reflected sound, and because that sound arrives later, it messes up the clarity of the words.
By toeing the speakers in, we reduce the reflections - less energy bounces off the walls, so there's less stray sound to absorb, and the words are clearer.
What is cross-firing?
The next-level answer is a technique called cross-firing.
Cross-firing is an advanced form of toe-in which creates a more even performance for more of the audience.
Think about it like this:
The listener in the left seat, is a little bit too close to the left speaker compared to the listener in the centre. The listener in the right seat, is a similar amount too far away from that left speaker.
So we should point our left speaker directly at the person on the right - and actually, point it at their left ear. That turns their level up a bit, and turns it down a bit for the person on the left. (the centre seat is fine, because the system gets calibrated to that centre position).
Repeat for all speakers - so that the left speakers point at right listener / right speakers point at left listener - and that's cross-firing!
You can't do it for a centre speaker - but it's okay, because that speaker already has almost all the listeners within its listening window.
You can also use cross-firing for multiple rows - always point each speaker towards the listener furthest away. In our showroom, though, we optimised for the front row, because it's a demonstration space and we expect clients to sit at the front.
For projects, we'll find out about the typical uses of the room and optimise for that.
Cross-firing in the Cinemaworks showroom
Want to know more?
Trinnov have produced a consumer version of their placement guidelines. It's pretty technical.
Our cinema uses cross-firing throughout - we've also gone wider than usual with our front speakers, so that we sit within ITU guidelines. We talk about the placement in part 1 of this series.
So then we had a choice - Should we fit the fabric walls flat over the angled speakers, making the room smaller, or make a feature out of it?
Looking at the room layout, it was clear that we'd have more room to come and go if we built our fabric walls around the angled speakers.
It also lets us vary the thickness of the flat sections, so we can use thicker acoustic treatments in some areas, for improved bass response. The side walls nearest the screen aren't needed for seats or access, so we built them out 140mm.
After a lot of design work around the lighting, angles, track fabric, ceiling coffer and ergonomics, it looks really cool!
But it's not the only option - one of our upcoming projects is technically very similar, but has traditional styling - we're hiding the Front Wides and Surround speakers in a flat section, and then making a 'bay' feature out of the very sharply angled Surround Backs and L/R speakers;
Whether you want traditional, ultra-modern, or somewhere in between, we'll build you a better cinema - because we're one of a small handful of providers in this country who understand the issues properly.