• John

    Great writeup! I appreciate all the great info. My room is 13x18x8. I use a 7.1 setup. I sit 6 ft 10 inches from the back wall. I am going to treat the first reflections that need to be treated based on the ITU standard for the side walls and ceiling using absorption. I am going to treat the rear wall with diffusion. This should create a ISD gap of about 12 ms. Correct? Again, using the the ITU standard, would I treat my surround speakers’ first reflection points? If so, would I use diffusion or absorption? Also, should my surround speakers be towed in like my fronts to get the flattest response or be straight forward? Thanks for your time.

    • Hi John. Glad you like it! Looks like this message slipped through my radar.

      Yes, that’s right. Your ISD gap is about 12 ms. Reflection points for surround speakers are not as critical. I’ve used both absorption and diffusion on the front wall to treat them, but your choice depends on the overall response and goals for the room. In general, diffusers or hybrid absorber-diffusers on the front wall are a safe bet.

      If space and budget is no concern, one solution that works well for surround sound (and stereo) mixing is a room with deep bass absorption on all walls + ceiling, with hybrid absorption-diffusion overtop. Like this: http://www.myroom-acoustics.com/hosted/myroom-acoustics/MyRoom_Design-white_paper.pdf

      Whether or not you should toe in your surround speakers would depend on their dispersion characteristics. Your best bet is to consult the speaker manufacturer, and you can also measure the resulting response using Room EQ Wizard. If you want to get scientific with speaker placement, the best source of information I know is the book Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms: http://www.amazon.com/gp/product/0240520092/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=0240520092&linkCode=as2&tag=arqen-20&linkId=3AJPDV6NPHR6V3IT

      Cheers,
      Tim

  • James Sandwell

    Hello, a lot of really great information here!
    There is something bugging me though. The EBU / ITU criteria is the best thing we have for general specifications that should be met for a professional control room. But can we assume their standards are probably slightly lax for full range audio as they primarily deal with the human voice (is that fair to say?). As far as i’m aware, with ITD we can localise sound well down to 200Hz or so extremely well… I know it is very hard to get information on monitor polar responses but can we assume that most are omni-directional below 500Hz? Should we therefore not be treating the front wall with absorption? Sorry if the tone of my question comes off as rude. I have been reading about acoustics for the last year now and the general consensus seems to be that treating early reflections down to 1kHz is acceptable and i’m really frustrated! Am i missing something?
    Thanks a lot,
    James.