Designing cinema systems
Following a recent change made by Dolby to the recommended angles for the surround speakers for 5.1 and six channel Atmos systems, I felt like now would be a good time to put together a piece on cinema design.
Everyone specifying and designing cinemas should be aware of the changes made by Dolby and note that it is in addition to the front wide speaker positions added a little while back for 9.1 systems.
Due to the changes in recommended angles for the surround channels in a 5.1 system and a set of 6 Atmos speakers, it’s now somewhat more difficult to sell an upgrade path from 5.1 to 7.1 or 9.1 and equally to go from two Atmos channels to six.
It also means that 5.1 systems now have better coverage for the surround channels, so it’s not all bad.
Aside from the now ubiquitous Dolby Atmos standard we should also consider DTS-X with its central voice of God channel which differs from Dolby’s two channel Atmos position. Generally, this is overcome in the surround processor but this channel (or multiples of it) can be included in systems above Dolby Atmos 9.1.6.
There are numerous different video standards for cinema designers to consider, from THX and SMPTE. Generally, it is possible to design most rooms to accommodate all of these as they mainly refer to viewing angles to achieve a good field of view for most seats.
There are also the recently updated CEDIA cinema design standards for audio and video. It’s a good idea to reference these, especially when creating a design for a project that you might want to enter for a CEDIA award.
Next up is the various different theories and standards on bass performance. These vary wildly basically because there is no way to guarantee great bass response and coverage across all seats for all room sizes, due to the sheer size of the lowest audible frequencies and the way these interact with the room boundaries.
As a general rule of thumb, we will start by avoiding the null points in the room for sub and seat positions alike (null points are 25 per cent of the room size in from each side and front and back).
Then start by positioning the subs with centres at 1200 off the floor and either side of the centre speaker and then run this through a piece of bass response calculation software to look for big dips in the response at the seated head height points.
Then it’s a question of adjusting the sub positions or adding more (and in some extreme cases adjusting the seat positions) around from there to remove the big dips. We tend not to worry about peaks as these can be equalised out but big dips are much harder to equalise.
The importance of accurate room dimensions cannot be overestimated, speaking from bitter experience there is no substitute to obtaining accurate room dimensions. If the cinema is a new build then architects drawings can take care of this easily. If we are working in an existing room which doesn’t come with any as built drawings then this is a very different matter.
The first rule is you can’t measure a room to build a cinema in with a tape measure, it’s simply not accurate enough, use a laser measure. If you don’t have one, invest, it could save you thousands on site if you measure without one and then have issues with dimensions during construction (my bitter experience with a job in Dubai!).
Where to start with design, this is probably the most common question I get asked about cinema design. Over the years we have built up a nice CAD based template for use in cinema design. This is based on the work we did in creating the Dolby Atmos protractor for Artcoustic. It includes all the recommended Dolby angles including Atmos plus a paper space tab for each view; plan, plus front, back, left and right walls.
This is the starting point we always use and we draw up or drop the existing room into this to start the design process.
Then we go off searching for CAD drawings of all the speakers, subwoofers, screen, projector and seats before adding the null lines.
Then we start adding in the CAD drawings of the equipment or drawing up the items we could not find CAD for (there is always at least one of these in every cinema!). This gives us a pretty good start on the design.
Design is all about finding the best compromise and cinema design is no different. It is a physical impossibility to design a perfect cinema, there will always be seats that sound better than others.
What is important here is to ensure we know where in the room the customer(s) will spend the most time and design to give the best audio and visual performance at this position(s).
Another route I have seen some people take is to position the hot spot of the audio and video in between the front and back rows. The aim here is to give an evenly compromised performance for both rows.
Personally, I favour the first option as it’s important to deliver a great result to the customer(s) in their preferred seat(s) as they are the ones who will foot the bill for the cinema.
I have already covered bass response above, but this is a big consideration for the seat and subwoofer positions and there is no substitute for using software simulation to avoid any large dips in response across all seats in the room.
Often in cinema rooms there will be a physical obstacle right where we need to place a speaker. It’s important to take a pragmatic approach to this: If a 7.1 speaker layout places a surround speaker where there is such an obstacle then try a 5.1 layout which might work better. At the end of the day we are trying to deliver the best performance we can for the specific room and to suit the client’s preferences and budget, it’s not about selling as many speakers as we can fit in the room.
Room treatment, some believe this is a black art, again this is a very common question and to put it simply, no, you just need to know where to look for guidance. For treatment we follow the simple guidelines set out in Genesis Technologies CATS Packs guide. For methods used to isolate the room go to: https://www.customaudiodesigns.co.uk or talk to one of the more experienced distributors of cinema equipment.
There are only a couple of things to note here: It’s well worth asking the customer at an early stage in the sales process if they intend to use their finished cinema at reference levels. If they will it’s highly recommended to try to convince them to have some level of room isolation, to help avoid disturbing neighbours or other rooms in the house near the cinema. Reference levels are very, very loud!
In terms of treatment this is one area where less is more. Generally we like to leave some liveliness in the room as overdoing the acoustic treatment can leave the acoustics of the room feeling a bit unnatural and dead.
Visualisation and Virtual Reality (VR) is becoming an increasingly important part of cinema design and our partners at Sinemas are recognised as one of the best in the industry, just as we are for design and documentation.
The power of visualisation and even more of VR should not be underestimated, it really can be a massive help to convince what could be an otherwise unwilling customer to invest in a cinema.
The Sinemas VR that our partner is producing these days is so realistic when you first experience it, it can actually be disorientating. Once you get used to it though it is simply stunning and an extremely persuasive means of selling cinemas.
As I’m sure most of us know there is a well-known piece of automated design software for cinema rooms out there and I get asked a lot, is this worth shelling out for? Well the short answer is yes but there are a few shortcomings to be aware of:
Firstly, while this is an excellent tool to help accurately specify cinema equipment, I believe the report it generates is far too technical and wordy to be given to an ordinary client. If your client is a technical boffin then it’s great but most people buying cinemas are buying for the experience and to add value to their homes, they are probably not particularly interested in the standards used to obtain the design or the SPLs achievable with the chosen specification, let alone masses of detail about each product chosen for the final solution.
Furthermore this software can only deal properly with perfectly rectangular rooms which is fine if you are building a new box style room but less useful if you are trying to shoehorn a cinema system into an existing room that has less ideal characteristics in terms of shape and size.
All this said this tool is still the quickest, easiest way to come up with a good cinema specification and produce a quick set of technical drawings, if that’s what you need.
Keith Jones studied product design at Central St. Martins where he graduated in 1996. He has had a successful career working in numerous high-end audio outlets, culminating in owning his own successful AV installation company from 2001-2008. After a career break, he started Jones designs in August 2009 which morphed into limited company designflow, in 2015. Designflow aims to increase awareness of design in AV and help installers win more jobs and create proper documentation for them.