In April of 2020 we hosted a webinar with audio guru Anthony Grimani discussing room layouts and speaker placement. This is a 2 part series (these were the questions from pt 1). If you happened to miss the pt 1 session live you can find the replay here:
We had some great questions during the session. Here they are with answers from Anthony. If you have any additional questions feel free to leave a comment or you can always email me directly at firstname.lastname@example.org
-If only using 2 subwoofers, should they both be in the front or opposite corners?
Best is middle of the Left and Right walls, or Middle of the Front and Back walls. Other location pairs can work OK too, but will take some experimenting and measurements.
-I missed it, but does the Left and right wall baffle also serve as a bass trap, or do additional traps need to be placed?
You can actually build the baffle to include bass absorption functions. Simplest way is to stuff the back of the baffle with mid-density fiberglass or rockwool, and leave a 12” gap at top or bottom.
-What rules do you follow when you equalizing acoustics? no more then +6dB?
While there are lots of legends, there aren’t really that many rules. Basic ones are:
If the speaker is decent, and has reasonable frequency response, you don’t need to do much above 500Hz. You can measure the speaker in the nearfield, at about 24” in front of the tweeter/midrange drivers. If it’s smooth enough, look at response of 4 mics around the seating area. There will be some deep narrow notches, and it’s not really worth filling those in. Look at knocking down peaks and filling in larger dips, which could be as much as 8~10dB. If you have the amplifier and drive headroom, that will be OK.
-What takes priority: L, C, R speaker placement relative to the listening position based on recommended degrees and screen location, or best measured in-room response but may not match the recommended placement?
Great question! It’s all about the best compromise. I would definitely get the center speaker to sound reasonably smooth, even if it isn’t exactly at the right location relative to the screen center. Same goes for the L/R, remembering however that you do want a reasonable 2 channel stereo phantom imaging pair.
-When you talked about full room depth, your picture showed the distance from the front wall and not the front of the front speaker (and/or when using an AT screen, the front of the screen). Just wanted to make sure I had that correct.
When I talk about room length, I do mean from the front to the back wall. The seat location guidelines for standing waves is taken from the front wall, not the speaker nor the screen.
-When we're referring to a 50-degree angle, are we referring to a 1.78:1 screen? Or a 2.35:1 screen? If 1.78:1, if we want CIH, could we allow the scope image to go beyond the 50 degrees?
Yes, that’s an interesting set of options. If you have variable aspect ratio, set the 2.35 image to about 50 degrees, and the 1.78 image will be smaller. That’s good for drama!
-2:35 aCOUSTIC SCREEN, SPEAKER PLACE AS IN SLIDE. TWO ROWS. iNVERT 38" TALL SPEAKERS? TWEETER ON BOTTOM?
The height of speakers depends on several factors, including the cancelation lobe between the midrange driver and the tweeter in the crossover region. Ultimately, you need a reasonable radiation pattern towards the listeners, emanating from around 46” above the floor (6” above seated ear height). Also watch out for mid bass errors from the vertical placement choices…
In other words, it’s complicated.
-Would you Reverse the L/R speakers to have the tweeters closer togeter for TV's?
Not sure what you mean by reverse. Up/down, or sideways?
-Do you consider woven screens the same as perforated?
Woven screens are generally much more acoustically transparent than perforated, and produce a much better picture. They do come in a range of types so do ask the manufacturer for acoustical and optical data. The materials made by Screen Excellence-Seymour, Screen Research, and the new Stewart woven screen, all work very well.
-How does the 45-degree front channel spacing remain compatible with the recommendation of 60-degrees (equilateral triangle) that's often specified for music reproduction? Is 45 degrees a recommendation that could go +/- some degrees?
45 degrees has some latitude and you can experiment in the balance between L-C-R separation and L-R soundstage quality. Note that some speakers to a better job of this than others, depending on their sound power response (Off axis response). I do think that the 60 degree recommendation is a bit wide for most 2 ch listening anyhow. Often times, the phantom center is lost, and you need to bring the speakers closer to each other.
-Is sonic "image" or "stage" priority or "broad" listening field the goal. I find competing opinions.
They are both important. Turns out that about 50/50 listeners like one or the other better. But you can set things up to have a really wide soundstage with pin-point imaging. It takes decent acoustics, speakers with a good and even sound power, and some calibration time and EQ. Yes it’s a shameless plug, but people often say that our new speakers and calibration do usually yield this non-competing ideal (www.grimani.tv)
-Is there a particular amount of absorption, or a particular room size that would almost or entirely eliminate standing waves in the bass?
No amount of absorption will eliminate standing waves without making the room a total dead space; that wouldn’t sound good. A room size with even standing wave distribution is better, an if you can stay with pretty flexible walls (1/2” sheetrock on studs with 24” centers) you can reduce the effects quite a bit.
-Wouldn't Atmos take the place of "top" channels? True Atmos channels are discreet; top speakers are synthesized.
I call Top channels the ones that up on the ceiling. That is also what Dolby calls them. They are true decoded channels, as long as the decoder has enough DSP horsepower.
-Is there a documented maximum angle that people are comforable viewing a screen? I'm seeing the screen at 15 degrees higher, but is that an 'acceptable range'?
It is documented that screens with centers above 15 degrees up are uncomfortable. We always design for less than that.
-Do you have a link on this Line acoustics Do you have a link for the line acoustics material for the front wall.
It is called Linacoustic by Johns Manville
It is available in various thicknesses. I would go with 2”