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[Dan Kok]

Jason Lavoie wrote on Thu, 23 October 2008 08:49

Dan Kok wrote on Wed, 22 October 2008 12:58 Would a counterweight extending straight down (and offset back to miss the mast of the stand) from the bottom of the mechanism move the CG down?  If so, would allowing that counterweight to be adjusted up and down a shaft allow you to put the CG wherever you wanted allowing the size of the mechanism to be fixed yet allowing its use over a larger range of speaker sizes (because you can move the CG)?  Using something like this it would seem a larger range of speaker sizes could be balanced on your mechanism allowing them to be adjusted to some position where they would stay and be clamped to stay in place rather than the clamping part of the mechanism having to carry weight. a counterweight like you describe would make his device obsolete.. if you added enough weight you could move the center of gravity to the pole socket point, and then tilt at any angle without worry.. (except the added weight on the stand, but at least it would be balanced) Jason

My point was to use the device _and_ a counterweight.  Together, both the device and the counterweight can be smaller.  Separate, each has to be bigger.  Without his device the counterweight would probably add an unacceptable amount of weight to the stand.

--
Dan

[Arjan van Gog]

I'm wondering, how necessary is a device like this really? If you tilt 12 degrees and assume that the cog is at 300mm from the bottom of the speaker, the cog has shifted

0.3m x sin 12 = 0.0624m = 2.45 inches

off-center horizontally. Or with 8 degrees

0.3m x sin 8 = 0.0418m = 1.7 inches

Is that actually something to worry about? I mean, how wide is the base of your stand compared to that? Doesn't this mean that your horizontal tip-over safety margin has been reduced by 2.45 or 1.7 inches respectively, measured at the top?

If you assume that the top is at 2m (6.5ft) that would translate to a reduction of the rotational stability safety margin 1.7 degrees (12 degree tilt) or 1.2 degrees (8 degree tilt).

Again, is that really something to worry about? And if it is, wouldn't you maintain the original non-tilted safety margin by extending your base by 2.45 inches in every direction?

Again I'm just wondering, not bashing the idea or anything like that.

[Mac Kerr]

Jason Lavoie wrote on Thu, 23 October 2008 09:57

jeffhtg (Jeff Kenney) wrote on Wed, 22 October 2008 20:34 1. and tilt adjustment must have a secure locking system - none of those drum clamp screw downs.. something that can slip is dangerous. Speaker angle slips.. cabinet tilts foward and falls off stand as the CG moves foward. Someone gets hurt - you get sued. I think you're missing the point of the adapter. even if the setting slips, the center of gravity doesn't move front or back. it might make an awkward shift, but if the design is right you should be able to move the speaker though its full travel with one hand and without any lateral weight shifts. Jason

More to the point, with the COG centered over the pole there is no moment arm to cause the speaker to tilt more. it is balanced on its COG, there is no unbalanced force to cause it to move. Theoretically it should stay in place with no locking mechanism at all. Since not all speakers have the same COG there will be some variation, and in practice locking will be required, but the forces should be small.

Since it is the height of the COG above the adapter that will cause the differences, maybe there could be a couple of versions for a couple of narrow ranges of speaker COG heights. Or maybe a couple of different attachment points for the bottom of the rear arm that has the long slot, to accommodate different COG.

Mac

[Charlie Zureki]

Arjan van Gog wrote on Thu, 23 October 2008 09:48

I'm wondering, how necessary is a device like this really? If you tilt 12 degrees and assume that the cog is at 300mm from the bottom of the speaker, the cog has shifted 0.3m x sin 12 = 0.0624m = 2.45 inches off-center horizontally. Or with 8 degrees 0.3m x sin 8 = 0.0418m = 1.7 inches Is that actually something to worry about? I mean, how wide is the base of your stand compared to that? Doesn't this mean that your horizontal tip-over safety margin has been reduced by 2.45 or 1.7 inches respectively, measured at the top? If you assume that the top is at 2m (6.5ft) that would translate to a reduction of the rotational stability safety margin 1.7 degrees (12 degree tilt) or 1.2 degrees (8 degree tilt). Again, is that really something to worry about? And if it is, wouldn't you maintain the original non-tilted safety margin by extending your base by 2.45 inches in every direction? Again I'm just wondering, not bashing the idea or anything like that.

+1

 As Mac had alluded to in an earlier post, the Center of Gravity IS the Center of Gravity.  Putting the Center of Gravity directly over the Top of the speaker stand is the main concern.

Cheers,
Hammer

[Mac Kerr]

Mac Kerr wrote on Thu, 23 October 2008 11:24

More to the point, with the COG centered over the pole there is no moment arm to cause the speaker to tilt more. it is balanced on its COG, there is no unbalanced force to cause it to move. Theoretically it should stay in place with no locking mechanism at all. Since not all speakers have the same COG there will be some variation, and in practice locking will be required, but the forces should be small.

My mistake. Looking at this again, there will be a force trying to tilt the speaker forward. There won't be a force trying to bend the pole, but as the hinged pivot point moves back, the weight of the speaker acting through the COG will be an unbalanced off center force in relation to that point trying to tip the speaker forward. It has been a long time since I was an engineering student, and I am not up to the math, but I still believe the forces will be small, although locking will be required.

Mac

[David R Allred]

Here is what I did for my Yorkville E12's.
Can be set at 10 or 15 deg by moving the cabinet socket insert and the elevator bolts. Although any angle for any cabinet can be used.
With a gravity angle level (the kind that sets on a surface and the dial tells you the angle) set on top of the cabinet.  Set the cab on a sturdy table or case with e front feet off the edge.  hold the cabinet at the angle that you what and slide the cabinet forward until it teeters.  That is the center of gravity.  Measure the distance from the front of the cab (bottom) to the edge of the table and trig out the offset of the speakers pole socket for the pole.  My tilter is made of steel and aluminum (pole and socket inserts)and welded a hinge on the fulcrum end.  Wood could be easily used.  I strapped the elevated end together to avoid a push from the back side causing a total forward flip if it push or lifted beyond the teeter point.  Note: As the angle increases the teeter "point of no return" get narrower.

[Arjan van Gog]

Quote:

As Mac had alluded to in an earlier post, the Center of Gravity IS the Center of Gravity. Putting the Center of Gravity directly over the Top of the speaker stand is the main concern.

I'm not really sure how Mac's allusion is related to my calculations.

BTW I do think that the speaker would want to tilt forward further. It's easier to see why if you imagine a simple static structure that tilts the speaker and shifts the speaker. The actual horizontal shifting of the cog has no bearing on the force exerted on the link between the angled pole and whatever it's mounted on.

Although the imbalance introduced by the tilting my be relatively small to make tipping over of structure as a whole unlikely, I'm actually more worried about whether the pole mounts inside the cabinet will be able to deal with the non-vertical forces as they may not have been designed for that.

It would depend greatly on how the pole mount is secured to the cabinet itself internally and what arms of force come into play. When you use fly points they are located on the outside a good distance from the cog and any stress on the mounting points caused by the rotational force would be relatively small.

Am I way off here or does this make sense?

(Edit: grammar)

[Nimrod Webber]

Thanks for the interest…
I am just starting the prototype here and you are already placing orders…  

Indeed the concept and operation of the BT are simple and straight forward.
This was my goal.

Some details and features don't appear in the drawing but are part of the design.

Here goes,

There will be one tightening knob for securing the BT onto the pole and another for locking the tilt angle.

The design allows smooth and easy adjusting of the tilt angle even while loaded by the cab's weight.
There is only about 5mm (3/16") vertical displacement of the cab across the tilt angle range,
so tilting shouldn't be hard to do by grabbing top and bottom of the cab.
Much easier then tilting a cab on its base edge.  

With this adaptor there is no need to rotate the cab at the stem/top hat,
more so it is even desirable to prevent rotation at this point.
Therefore, the design includes an internal locking mechanism inside the stem.
This lock will be automatically activated by the cab's own weight and will lock the top hat (and cab…) from rotating.

If this design is to be compatible with a wide(r) range of loudspeaker cabs, each with its specific COG location,
a means of trimming and calibrating should be incorporated into the design
This is of coarse possible, but would have made this prototype more complicated
and therefore beyond what I was ready to undertake at this stage.

Of coarse there is the option of different models to suit specific COG heights,  as was suggested.

I'll keep you updated.

N.Webber

[Arjan van Gog]

Quote:

BTW I do think that the speaker would want to tilt forward further. It's easier to see why if you imagine a simple static structure that tilts the speaker and shifts the speaker. The actual horizontal shifting of the cog has no bearing on the force exerted on the link between the angled pole and whatever it's mounted on.

I'm actually having second thoughts about my own statement. Sure there's a force but I don't think it's in the right direction to cause further tilting. It looks like Nimrods design would keep the cog in the exact same place (not just horizontally but verrtically too) regardless of tilt (if the speaker matches the design perfectly) so I guess at least in theory it would stay put in any position.

The force I mentioned would be a rotational force that exerts its power exactly on the joint between tilting pole and its support, or to put it another way, that joint moves in a perfect (very wide) circle around the cog which stays in the exact same place. I'm not sure if that is what Nimrods design does but it looks like it.

(Edit: clarification added)

[Scott Deeter]

Arjan van Gog wrote on Thu, 23 October 2008 14:53

Although the imbalance introduced by the tilting my be relatively small to make tipping over of structure as a whole unlikely, I'm actually more worried about whether the pole mounts inside the cabinet will be able to deal with the non-vertical forces as they may not have been designed for that. It would depend greatly on how the pole mount is secured to the cabinet itself internally and what arms of force come into play. When you use fly points they are located on the outside a good distance from the cog and any stress on the mounting points caused by the rotational force would be relatively small. Am I way off here or does this make sense?

Arjan,

I can understand what your trying to say. If I did the cab tilt, I'd make sure the cup had a backplate on the inside with the use of nuts, washers & bolts (recessed bolts of course), not just rely on the wood-screws going into the bottom of the cab as I've seen. Even though this has nothing to do with Nimrod's design per say, it's a safety factor to consider with the use of it though.