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Home Forums Home Theater The home theater build code-named THT Reply To: The home theater build code-named THT

  • Chedwin

    February 25, 2023 at 1:07 pm

    This will be a long post but stick with me here. This is based on a mix of my own experience delving into the creation and mixing side of atmos with the Dolby Atmos Renderer and other info I found digging around the Dolby Professional support docs

    A small correction to start, Dolby is not a home theatre provider. They are a fundemental part to the production and distribution of content throughout the entire TV and film industry. Dolby as a company are a technology provider creating inovation in audio and video formats and providing standardisation and certification of both creation and playback systems from 5.1 HT scale to the 400 speaker certified Dolby Cinema in Leicester Square. They dont generally involve themselves in the creation side of content

    When I say studio in a Dolby Atmos context I do not mean a recording studio for capturing audio. I am refereing to a mixing and mastering studio for music or rerecording stage for film, these are the room where an atmos mix is done by the sound engineers. These types of rooms fall into 2 size categories, they are near field and mid field. The third category would be large scale cinema which is far field

    Near, mid and far field is as simple as it sounds, it desribes the general proximity of the speakers to the listener. Home theatres generally fall into near field with smaller mixing studios. Example of blackbird studio atmos room Rerecording (aka dubbing) stages are a step up from a HT and aim to provide mixing engineers with a closer representation of how a film will sound played back in full scale cinema. Rerecording stages are similar in size to smaller commercial cinema screens of around 30-40 seats. Example of a rerecording stage from skywalker sound

    As far as I can tell based on the additional info supplied in the cinema spec only 2 versions of the speaker placement guide are needed to cover any size atmos system. Home theatre and smaller studios will use the same speaker layouts, the difference being the distance, size and power of the speakers. If you compare the blackbird studio atmos room to the 9.1.6 layout in the HT PDF although the room at blackbird is shorter depth with the MLP much closer to the screen/main LCR other than that they match up very well. Anything larger than that will be built to the cinema spec as the cinema spec doesnt have fixed position diagrams but instead provides formulars for calculating speaker positions based upon room dimmentions and relative positions to other speakers.

    If you really wanted to you could use the cinema formulas to work out your own home theatre room but I’m pretty sure you will end up with almost exaclty the same as Dolby already reccomend in the HT PDF, the layouts they provide are based upon the same calculations they have just simplified it by doing alot of the maths for you. For example in the professional cinema spec side surround are mounted above head hieght to cover the whole audince. The angle for overheads is then calculated as 45 plus 1/2 the vertical angle of side surrounds from head height. As home theatre places the main 5/7/9 speakers at head height this makes the overhead angle always be 45.

    In summary, unless you have the luxury of building a big enough room to need the formulaic calculations of the professional cinema guidance use the home theatre PDF, just be sure to read it carefully and fully understand the extra information provided in the text sections e.g. that the overhead aiming angle is based on dispertion of the speaker and dolby dont actually say it should always point straight.

    Do note that the top down diagrams are not shown in reference to the rooms walls, they show the relation of each speaker to the screen, the MLP and the other speakers. I feel this is a common mistake to make when interpretting the diagrams.

    If any of this needs further clarification or you have more questions do let me know, always happy to help as much as I can with my pro audio knowledge