Speaker Rigging, again.

Ok, I need some advice from you CB experts. My church is undergoing a major building program and as a part of it we're getting a new pre-school worship room. For whatever reason the design and installation of the AV systems for this room were not included in the AVL contractors scope. As such, the church technical ministry is handling the design and installation internally. I'm a volunteer in the technical ministry and happen to enjoy this sort of thing, so of course I've been heavily involved in both the design and the installation.

We're hanging Renkus-Heinz CFX121 speakers on either side of the stage. The speakers have M10 rigging points built in. The building contractor provided a single piece of unistrut on each side of the room to hang the speakers from. I added to this 3 more pieces on each side to make a grid to give us the appropriate mounting points. Now the unistrut is properly installed with all the appropriate hardware (strut nuts, flat washers, lock washers, etc.). The problem is attached the speakers to the unistrut. Paying attention to all the recent threads we've had here about overhead rigging, I went with forged M10 eye-bolts, stamped 5/16" quicklinks, and 1/4" grade 30 proof coil chain. We did the install and everything went great.

Now the problem. I'm not sure who, but somebody decided that the chain wasn't as visually pleasing as desired. Those who make the decisions (not me) decided that GAC would be used instead. Now I haven't seen how the GAC was installed, but I don't think thimbles were used and I believe that all the hardware came from a big box store. I think the GAC is 1/8", uncoated.

Is this change a problem that I should make a stand against? I'm just a volunteer here and I'm not getting paid. However, I am a Professional Engineer and I want to be very careful about any liability that might come back to me.

Your thoughts?

Signs that the GAC should be done away with:

+ No thimbles.
+ Oval compression sleeves aren't copper.
+ Oval compression sleeves look like they are mushed by someone striking them with a hammer.

If the G30 chain is a problem, spray paint it a desired color and it'll look less noticeable.

GAC isn't inherently awful for something like this, but if it wasn't done properly then it shouldn't be used. It's also just kind of a pain to use GAC because you can only slightly modify the lengths of the wire rope cables via turnbuckles for the sake of aiming the speakers.

If they even used compression sleeves, for all we know they used cable clamps.

techieman33 said:

If they even used compression sleeves, for all we know they used cable clamps.

Click to expand...

Well there's nothing wrong with cable clip s, PROVIDED they were installed correctly.

epimetheus, besides a visual inspection, you need to find out WHO did the re-rig, and whether they are competent. If they used hardware from the local home center, the second question answers itself.

The particular speakers you are dealing with have a spec weight of 52.5 lbs, so 1/8" GAC is more than adequate for the job.......if installed correctly. Your original installation sounds spot on except I would strongly prefer forged shackles vs: the quick links. For the weight of your speakers, 3/16" chain and hardware would also be OK.

Installed correctly of course means forged hardware, thimbles in all eyes, correct # of clips (2) if using clips and tightened to the correct torque.

===================================================================
Cable Clip Application
Recommended Method of Application of Cable Clips
1. Turn back the specified amount of rope from the thimble. Apply the first clip one base width from the dead end of the wire rope. Place the U-bolt over the dead end; the live end rests in the clip saddle. Tighten the nuts evenly to the recommended torque.

2. Apply the next clip as near the loop as possible.Turn on nuts firm, but do not tighten.

3. Space additional clips, if required, equally between the first two. Turn on nuts, take up any rope slack, and tighten all nuts evenly to the recommended torque.

4. Apply the initial load and re-tighten the nuts to recommended torque. The rope will stretch and shrink in diameter when loads are applied. Inspect the clips periodically and re-tighten.

Recommended torque values are based on the threads being clean, dry and free of lubrication.

IMPORTANT: Failure to make termination in accordance with instructions, or failure to check the recommended torque periodically and re-tighten, will cause a reduction in the efficiency ratings of the clips.


CABLE CLIP USAGE
Cable Size in Inches Minimum Number of Clips Amount of Rope Turnback/Inches Torque in Ft. Lbs

1/8...............................2......................................3-3/4......................................4.5
3/16.............................2......................................3-3/4......................................7.5
1/4...............................2......................................4-3/4......................................15
5/16.............................2......................................5-1/4.......................................30
3/8..............................2.......................................6-1/2.......................................45
=====================================================================

If using swage sleeves, correctly means a copper sleeve installed with the correct # of crimps for the tool used.

For most Sleeves and hand operated crimping tools, 3 presses is the correct #, however many mechanical tools only require 1 or 2 presses. Make sure the # of crimps matches the tool and die used and make sure it has been checked with the proper Go-No Go gauge.

If the installation is done correctly, don't make waves. If it is incorrect, speak up.

First off there is a lot of questioning going on here for a "supposed" change. the author has not seen the cable or the installation and is guessing as to what is actually there. He needs to go actually look at the install and then ask if it is alright. We all can speculate all day long. We all know the you should use a thimble with Aircraft cable, and we all should know that clips are alright, Sleeves are even better. It depends on whether or not the install was done correctly, and this is what we do not know. So go back take a look and use this general rule of thumb..."if it hurts your eyes, there is a good chance it will hurt your head."

spribil said:

First off there is a lot of questioning going on here for a "supposed" change. the author has not seen the cable or the installation and is guessing as to what is actually there.

Click to expand...

The OP knows it was changed, and was already advised to take a look at it, and given info as to what it should be to compare to what it is once he gets a look at it.

Mpowers gave the rundown of what to look for and then summed the whole thread up nice and concisely,

MPowers said:

If the installation is done correctly, don't make waves. If it is incorrect, speak up.

Click to expand...

MPowers post was pretty much what I was looking for. And thanks to all those who have commented. I haven't seen the installation since it was changed from what I spec'ed out and installed. I'll compare with the instructions above once I get a look at the modifications.