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Wall mounting heavy monitors?

Engineer here, and also plenty of DIY experience hanging heavy things on walls (eg cabinets, bookshelves, kitchen units, TVs etc.). Very rough back of envelope calculation but a 20kg speaker mounted on a bracket 15cm off the wall, with 4 screws spaced 10cm vertically (not an unusual bracket configuration, is going to produce a max tensile load on the screw of about 90N. This is well within the load capacity of many fixings, e.g. I've used these two extensively (click "Additional Documents" -> "Load Table") and e.g. the Duotec recommended shear and tension loads start at 200N.

https://www.fischer.co.uk/en-gb/pro...scher-duotec/537261-fischer-duotec-10-s-ph-ld
https://www.fischer.co.uk/en-gb/products/standard-fixings/plastic-fixings/duopower

If you can find a stud, you're laughing (see pull out force for wood screws here https://www.engineeringtoolbox.com/wood-screws-allowable-withdrawal-load-d_1815.html). If you're in plasterboard, you'll be fine too as long as you take care with the fixing. (Solid walls are of course totally fine.) This back of envelope calculation is consistent with my practical experience (i.e. our bathrooms, kitchen are still up and a lot of this was mounted into stud walls!). A couple of other fixings of note: Gripits and Corefix work great in dot and dab plasterboard. I've not used but they look great (I have some ready to try) https://www.geefix.com. Nine times out of ten though, the two Fischer products above will do the trick.

Edit: as per the last post, yes, cutting out the plasterboard and fixing some timber to mount into is also a good solution but more faff.
 
Kitchen cabinets produce shear forces - they are hung, and how much does a loaded one normally weigh????? Anything thin, and hence with a centre of gravity near the wall, produce very little pull-out/tensile strain/load. Book shelves - usually several brackets along a length and also a load very close to a wall, usually 8-12cm at a guess.

27kg, centre of gravity probably 30cm, quite possible more, from a wall and above the fixings, so producing a mechanical advantage (as in a lever, in effect a 1st order one, as in a crowbar) that works AGAINST you....…………

Solid walls - a walk in the park. Anything else...………………….
We still don't know from the OP what he has, so far as a quick scan of replies tells me.

Irrespective of what the wall construction is, a stand/bracket that suspends the speaker below the fixing is by far the best mechanical design, and would be 1000 times easier to safely attach to a stud wall, because the load would be far more in shear - same principle as a kitchen cabinet - you'd be hanging the speaker and the lever would work in your favour - the load would be nearer the fulcrum that the effort (the fixing).
 
You're fundamentally correct, there are two levers at play (the load * distance from the wall), and the bracket/screw holes (tensile force on the screw * distance to the screw from the lower edge of the bracket, which acts as the fulcrum as the load rotates out). But crunch the numbers and the forces in play are not that great, e.g. 30-50Nm moment generated by the load, and most sensible brackets will not exert a tensile force on the screw in excess of about 100N, well within the load capacity of the toggle-style fixings (steel unbrellas, Fischer duotec, geefix, gripit). Evidenced by the real world, TV mounts are the closest thing:
 
There is just one lever involved - a lever, by definition is load, fulcrum and effort, in any order, not just two of them. And the smart Alec in the vid has loads/centres of gravity, VERY close to the wall.

The two halves in this case - 1st order lever - are load-fulcrum and fulcrum-effort.

My 45-year-old applied maths says -

In the case of a speaker on a bracket, the force is mass, multiplied by g, multiplied by horizontal distance from fulcrum (effectively the wall), so we have something like 27 x 9.8 x 0.3 = c.80Nm (we could just as easily skip g, and use Kgmf).
The other half of the lever depends on design -
Say the bracket attaches to the wall on a 10cm deep/tall plate, the actual bracket holding the speaker being welded in the centre -
Force on the fixing(s) is c.80/0.1 = 800Nm (actually quite a bit more as this assumes the fixings are on the edge of the plate).
Say the wall plate is 60 cm long, the fixing(s) at the top and the actual bracket is welded to near the bottom of the plate -
Force on the fixings is c.80/0.6 = 133Nm

Force on the fixing of a "standard" bracket, small plate, fixed near the fulcrum is a crowbar - it is as simple as that.

Unless my 45-year-old maths is out.
 
jamington2004 said:
I hope the OP has a a cup of tea in hand when he finally joins in :)
Click to expand...

But he's deathly quiet. After that barrage of maths, physics and DIY suggestions, he'll need a lot more than a cup of rosy. We don't even know what kind of wall it is, let alone the model or dim's of the speaker.
 
Ah well we can keep going anyway - I have been on the same subject about my Kii Three so loving it :)

And the new mounting plates just arrived, made to attach to the ceiling bracket I have, and tilt the speakers down at precisely a 20 degree angle (Thanks Vinny! :) )

Damn speakers aren’t here yet so have an anxious wait to check the holes are drilled in the right place to bolt them on!!
 
LLOL.
My pleasure, although I would hope that you will have some lee-way in the 20 degrees by either fitting spacers on some of the fixings, or whatever. Hopefully it should be near enough though.
 
Vinny said:
There is just one lever involved - a lever, by definition is load, fulcrum and effort, in any order, not just two of them. And the smart Alec in the vid has loads/centres of gravity, VERY close to the wall.

The two halves in this case - 1st order lever - are load-fulcrum and fulcrum-effort.

My 45-year-old applied maths says -

In the case of a speaker on a bracket, the force is mass, multiplied by g, multiplied by horizontal distance from fulcrum (effectively the wall), so we have something like 27 x 9.8 x 0.3 = c.80Nm (we could just as easily skip g, and use Kgmf).
The other half of the lever depends on design -
Say the bracket attaches to the wall on a 10cm deep/tall plate, the actual bracket holding the speaker being welded in the centre -
Force on the fixing(s) is c.80/0.1 = 800Nm (actually quite a bit more as this assumes the fixings are on the edge of the plate).
Say the wall plate is 60 cm long, the fixing(s) at the top and the actual bracket is welded to near the bottom of the plate -
Force on the fixings is c.80/0.6 = 133Nm

Force on the fixing of a "standard" bracket, small plate, fixed near the fulcrum is a crowbar - it is as simple as that.

Unless my 45-year-old maths is out.
Click to expand...

Close, but a) you have typically 4 fixings per bracket so load sharing and b) the load on the mounting plate of the bracket is independent of where the arm of the bracket (to the speaker) attaches (assuming a "stiff and thin" bracket, which is a fair assumption). But you're right bracket plate geometry plays a big role (the reason for saying there are two levers in play is that you effectively construct two moment equations to solve for the loads on the fixings). I'll post a worked solution when I get a moment, it's useful to know how to do this properly because then you can make quick and dirty (but effective) practical decisions!
 
Lliure, where oh where did I mention number of fixings?

Lliure said:
the load on the mounting plate of the bracket is independent of where the arm of the bracket (to the speaker) attaches (assuming a "stiff and thin" bracket, which is a fair assumption).
Click to expand...

Really? Very interesting.
We have a 60cm tall wall plate and it matters not where the bracket is attached? How about welding it to the top v the bottom? That isn't changing the length of one half of the lever?
The same applies to a 10cm tall plate, but the change of position possible is of minor consideration.

Please tell me the TWO levers involved, a lever being 3 points.

So far as I can see the bottom of the wall plate is the fulcrum, the load and effort can be considered interchangeable, but are the speaker and the top fixing(s).
 
Yes, it is genuinely independent of the location of the attachment to the wall plate, because the distance to the attachment point doesn't figure (the load is parallel to the plate, there is no load perpendicular to the wall plate at the attachment point to give rise to a moment). I think what you're trying to square is the intuitive effect of the length of the wall plate on the fixing loads - and there is an effect due to the geometry of the plate, i.e. longer is indeed better - but the location of the application of the load doesn't matter, the geometry only affects their distribution. See worked example here https://photos.app.goo.gl/a6EBQDkF1ayFW7MZ6 , taking e.g. this bracket https://prolight.co.uk/product/speaker-wall-bracket which is rated to 25kg (geometry here https://www.prolight.co.uk/ftp-in/BRAC03_TD01.pdf). According to my working, the top 2 fixings in this example will experience a combined load of 250N each (with a 25kg load on the bracket at 30cm) - this will require "care" but could be totally fine with the right fixing in plasterboard. Knowledge is power in this case - either in the choice of bracket, or the fixing method! The other interesting result is that the bottom fixings only experience 87N, i.e. totally fine with a regular decent wall plug, so you only need to really worry about the top ones.

Hope this makes sense, I think the analysis is sound (could maybe be more elegant about the way the geometric terms are expressed); the key "trick" being in step 2 (the principle of Virtual Work https://en.wikipedia.org/wiki/Virtual_work, which you'll generally only find in university engineering 1st or 2nd year mechanics courses).
 
Yeah I am well pleased - I used the same ceiling brackets with the Phantoms which were much less tall so the brackets were a lot more visible.

With these they are pretty much covered, and the plate is well hidden, so looks like the speakers are floating :)

I added a close up of of the connector. I left a bit too much safety gap on the fit - so they actually have too much room and tilt a bit more than planned under weight. Plus a bit of flex in the steel plate.

When I get time will try and fit a washer to tighten the gap up a bit.

https://flic.kr/p/2htRb4y
 
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