Mounting huge TV+sound bar above TV with down&out mount - AVS Forum
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post #1 of 13 Old 10-03-2011, 02:11 PM - Thread Starter
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I'm about to mount a large TV + soundbar above a fireplace and I'd like to hear some thoughts about my plan before I go ahead with it.

I've attached a picture that roughly shows the location of some studs as well as the location of where I plan to attach the mount to the wall. Note that this is the "down & out" mount which swings away from the wall, allowing the TV to come down to eye level. The two large green rectangles in the picture roughly show the position of the TV in the high and lowered positions.

Specifications: Total weight: 95 lbs slightly under mount's max load of 110 lbs.

Questions:
  • Shear load: Should I be worried about 95 lbs of shear on the wall or studs at all?
  • Tensile load: I plan on screwing the four 3/8" x 3" lags that came with the mount into the studs. Because the studs are quite a bit off-centered versus the TV, the left-most top lag will be taking most of the tensile load due to the torque of the TV. I talked to the mount manufacturer and he said that the top bolt or bolts will take about 300 lbs of pull-out force for a 100 lb TV (I assume this is only if the TV is in the pulled-out position, and it will normally be in the down or up position).
  • I'm using 2 different stud finders so that I can make sure to hit the center of the studs. One is an edge finder and the other is a center finder. I figure that getting the center of the stud will be pretty important?
  • Pilot hole size for 3/8" lags. I tested some pilot holes on a 2"x4" and the suggested 1/4" pilot hole didn't seem that tight to me. I tried going all the way down to 1/8" pilot hole and I still didn't cause the 2"x4" to split, even with a hole drilled near the edge of the stud. This stud perhaps a bit softer than what is in my 30 year old walls, however. Anyways, I may use a 15/64" or 7/32" pilot hole just to get a bit more holding power there. Does anyone have any experience with pilot holes for 3/8" stud and what they recommend?
  • I was going to use 4 SnapToggles as well, will these actually do anything?
  • I didn't see the point of putting some plywood or 2x2 backing or anything. I can't see how that will make any difference. Anyone disagree? In the end, all the forces will still transfer to the studs or the drywall. Hopefully they will help spread the load a bit?
This is the first time I have ever mounted a TV, that's why I'm being extra careful. I have done a bit of DIY stuff around the house but I've never hung anything heavy from a ceiling or hung anything ridiculously heavy from the wall. I'm hesitant about having an installer do this as I doubt they are aware of this mount and will not read the instructions for it as carefully as I have. I also don't trust them to take the time to do it right.
LL
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post #2 of 13 Old 10-04-2011, 02:12 PM
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Welcome to the above the fireplace crowd!

We just moved in August and put the TV above the fireplace. But the "studs" above the fireplace aren't at 16" OC, just evenly spaced, with one in the direct center of it. So my mount was only able to land on one stud, without having the TV offset crazy.



I just used 2 of the 3/8" lags and two drywall anchors on each end. By some info I've found on the web, even a 1/4" bolt has a shear of 200 lbs and tensile of 160 lbs. So two of those **should** be strong enough to hold the weight. And the anchor (snap toggles for you) keep the thing from twisting funny.

I don't know the exact size of pilot hole, but my quick Googling says 15/64", which is a hair under 1/4". The general idea would be to make the hole just ever so slightly bigger than the shank of the lags.

Good luck!
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post #3 of 13 Old 10-04-2011, 02:18 PM - Thread Starter
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I think you mean "The general idea would be to make the hole just ever so slightly smaller than the root diameter of the lags." At least that sounds like what you meant.

Thanks for the information! Very helpful. :-)
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post #4 of 13 Old 10-04-2011, 03:54 PM
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1. drill whatever hole is recommended for the size lag bolt you are using -- there are specs available

2. the drywall toggles certainly wont hurt, drywall is a structural element of walls to prevent racking forces from wind, it is amazingly strong

3. static loads dont really matter as this is an articulating mount. i would be concerned that you are so close to its weight tolerance (unless it is rated for a 110# load with dynamic factors accounted for)
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post #5 of 13 Old 10-04-2011, 04:07 PM - Thread Starter
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Quote:
Originally Posted by longtimelurker View Post

1. drill whatever hole is recommended for the size lag bolt you are using -- there are specs available

I've seen many numbers for pilot hole sizes. I finally found this today:
http://bbs.homeshopmachinist.net/sho...86&postcount=9
which gives the best detail I've seen on where these numbers come from. My studs are Hem-Fir, I might go 3/16" which is 70% of root diameter, or at least 7/32" or 15/64"...1/4" as suggested by mount company seems needlessly large though.

Quote:
Originally Posted by longtimelurker View Post

3. static loads dont really matter as this is an articulating mount. i would be concerned that you are so close to its weight tolerance (unless it is rated for a 110# load with dynamic factors accounted for)

You mean the static loads are not significant?

What dynamic factors do you mean exactly?

Thanks.
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post #6 of 13 Old 10-05-2011, 05:35 AM
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Quote:
Originally Posted by dgrant View Post

I think you mean "The general idea would be to make the hole just ever so slightly smaller than the root diameter of the lags." At least that sounds like what you meant.

Thanks for the information! Very helpful. :-)

I did mean bigger. I was always taught for woodworking that you just want the threads of the screws cutting into your wood. Not the shank bulldozing it's way through. The threads are what keeps the screw from pulling out. The smooth shank doesn't help in that respect.
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post #7 of 13 Old 10-05-2011, 05:40 AM
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Quote:
Originally Posted by dgrant View Post


You mean the static loads are not significant?

What dynamic factors do you mean exactly?

Thanks.

I hadn't noticed it was an articulating mount either. But what he's saying is when the mount is pulled fully out, you don't have just the static load of the TV. At least not the weight just pulling straight down. You'll be dealing with whats called "the moment." This is the weight of the TV pulling down on the end of the mount out from the wall, similar to a lever.

Personally I wouldn't be concerned with coming close to the rated load. I mean things are designed with a certain safety factor, right?
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post #8 of 13 Old 10-05-2011, 07:04 AM
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One thing to consider is that you are discussing the shear and tensile strength of the SCREW, which is likely to be higher than the strength of the WOOD.

The pilot hole is really important to prevent splitting and compressing of the wood, both of which will seriously compromise the strength.
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post #9 of 13 Old 10-05-2011, 09:25 AM
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Quote:
Originally Posted by dgrant View Post

What dynamic factors do you mean exactly?

As the display extends from the wall, it's in motion (obviously). Once it reaches the full extension of the mount, if you haven't stopped it already (by exerting a force on it) the mount must not only support the tension and moment of itself and the display, it must also supply the force required to stop the display. Depending on how everything is designed and how you use it, the display could come to a stop in a very short distance (as the mount travel is maxed out). If that happens, the force required to bring the display to a stop is increased compared to stopping the display over a longer distance, more gradually. This dynamic (changing) force can be quite high. It could be as though you were trying to yank the whole thing off the wall.

For a more familiar comparison, consider an air-bag in a car. By inflating the air bag a foot in front of the steering wheel, the distance over which your body is brought to rest in increased, and the force diminished greatly.

The good news is that the mount is most likely built with enough internal friction in the joints that the display will never get moving quickly enough for this to become a problem. The engineers are fully aware of the dynamic forces the wall and display would encounter, and all of that is taken into consideration when the load rating is issued. Follow the instructions, use the mount as indicated, and you can expect it to perform as advertised. That includes, of course, securing it to the wall properly, using the supplied hardware and guidelines.
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post #10 of 13 Old 10-05-2011, 10:56 AM
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1. Looks like you use the fireplace for fires. I would be concerned that the soundbar will melt with the TV up. No mantel.

2. I'd have concerns that someone would bring the TV down with a fire in the fireplace. It could easily burn down your house if that happens. I suggest you do something to 'disable' the fireplace permanently, so that can never happen.

3. If you have kids or kids' friends or toddler relatives, I suggest you install 'blocking' - remove the drywall, make it VERY strong. Kids swing on things like that. Kids can get seriously hurt if that's not hung correctly. I can't imagine killing a friend's child because I didn't want to spend $50 to buy some lumber, drywall mud, and paint, to hang it right. 100 pound static load + 50 pound child = tragedy.

Edit - sorry to be a dick. Very cool mount, though.

Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

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post #11 of 13 Old 09-17-2012, 08:23 AM
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Hey There,

Here are photos and pictures of my installation of the DOWN AND OUT MOUNT.
I had the same issue as you, having the TV mounted above my fireplace.
REALLY HAPPY now that I can move it down to my level to watch it....no more neck straining.
My A/V guy mounted it in less than 30 mns.
Now I just have to move the outlet behind the TV a little lower so you can;t see the chord.



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post #12 of 13 Old 12-03-2012, 09:10 PM
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So, I was a bit nervous about mounting the down and out mount with a Bose Videowave which depending on which doc you read, can be 96lbs-106lbs.
Turns out its all good. Mine is the 1st gen Videowave with 46" LCD screen. Looks like it weighs 96lbs, as I did not need to use the max counter weight.
This mount is great. Installers had a bit of hard time with it, but once I started to read the instructions, and gave them direction, it all was pretty easy. Some things like counter weight and tilt setting are counter intuitive, before you adjust, you will think, this does not make sense, but it does exactly as it says when you follow the instructions. Well worth the money.

Due to location of studs and power, we could only mount 7" above 8" deep mantel.
Still the result was very good. Bose adaptiq calibrated for up position. Down position is for my 4yr old to watch his cartoons.

http://www.DynamicMounting.com

Up position


out position


down position


http://www.DynamicMounting.com
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post #13 of 13 Old 12-03-2012, 09:47 PM
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hope this video works...
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