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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Peter Kowalczyk on April 15, 2024, 07:52:15 PM
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Has anyone else had trouble with their M20 threaded Pole Cups?
I use Meyer X40 and 900-LFC with a single threaded pole, and found that setup was a bit wobbly, and that wobble led to one pole cup failing. A colleague had the same issue. So, I came up with a more robust solution and had these Truss Adaptors built.
I'm posting to see if there's enough interest in the community to build a small batch to share.
Mods, please move to a more appropriate forum if necessary....
These adaptors work with 35mm (1-3/8") pole cups that have an integrated M20 threaded socket, such as Penn-Elcom M1557/M20
https://www.penn-elcom.com/us/universal-speaker-mounting-top-hat-m1557-m20
These pole cups are standard on some Meyer Speakers, but I'm guessing are common with others, and are likely an easy retrofit for others still.
These adaptors use an off-the-shelf Global Truss F34 12" square base plate, with a 35-mm aluminum tube welded on. An M20 bolt fits through the tube to secure the speaker to the plate.
The end result is basically a Global Truss SQ-4137SAP with an M20 hole through the middle, except that the 'Speaker Pole' stud is welded instead of bolted on to allow for the coaxial hole.
I put a pair of these adaptors on each end of a stick of truss. I use 1.25m segments, naturally you can pick whatever length suits your need. Each end bolts securely into its respective speaker. The 12" footprint is far more stable than a single pole. Plus they look pretty cool 😎.
My cost for the first round was about $400 / pair in a batch of 8x. That includes a pair of plates, pair of bolts and washers. If there's enough interest and we can run a larger batch, we can hopefully get the cost down a bit. If you're interested in getting a set, please DM me (info <AT> sierraaudiosolutions <DOT> com) and we can talk!
Thanks!
PK
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... Addtional Photos...
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Very cool, but seems a bit overkill? :)
We ended up putting M20 pole sockets in the tops of our small Meyer subs, and bought some of the K&M speaker poles that have M20 on the bottom and 1-3/8" on top.
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Maybe I’m missing something, but why not just put an M20 bolt through the middle of the plate straight into the cup?
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Very cool, but seems a bit overkill? :)
We ended up putting M20 pole sockets in the tops of our small Meyer subs, and bought some of the K&M speaker poles that have M20 on the bottom and 1-3/8" on top.
Oh, its definitely overkill. ;)
However, after having an M20 pole cup fail at a gig, I don't trust the straight poles anymore. The weight of an X40 on top of a straight pole was able to apply enough torque to break a pole cup. Can you imagine with a UPQ? These truss assemblies feel solid with a UPQ on top of a 900LFC.
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Has anyone else had trouble with their M20 threaded Pole Cups?
The end result is basically a Global Truss SQ-4137SAP with an M20 hole through the middle, except that the 'Speaker Pole' stud is welded instead of bolted on to allow for the coaxial hole.
I put a pair of these adaptors on each end of a stick of truss. I use 1.25m segments, naturally you can pick whatever length suits your need. Each end bolts securely into its respective speaker. The 12" footprint is far more stable than a single pole. Plus they look pretty cool 😎.
I did this with F14 truss, which still has a very small visual footprint, but much more stable than a pole. This is an RCF NX-L24a on top of a JBL SRX818.
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Oh, its definitely overkill. ;)
However, after having an M20 pole cup fail at a gig, I don't trust the straight poles anymore. The weight of an X40 on top of a straight pole was able to apply enough torque to break a pole cup. Can you imagine with a UPQ? These truss assemblies feel solid with a UPQ on top of a 900LFC.
What did Meyer Sound have to say about the pole cup failure?
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However, after having an M20 pole cup fail at a gig, I don't trust the straight poles anymore. The weight of an X40 on top of a straight pole was able to apply enough torque to break a pole cup. Can you imagine with a UPQ? These truss assemblies feel solid with a UPQ on top of a 900LFC.
Is that plastic?! Very frightening if so. I get that manufacturers are trying to shave weight and cost where they can but this seems to be a very poor place to do that...
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Is that plastic?! Very frightening if so. I get that manufacturers are trying to shave weight and cost where they can but this seems to be a very poor place to do that...
May be aluminium, but I'm betting on white metal.
Chris.
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In the picture of the broken pole cup, is that some kind of dual mode cup? The M20 mounts on my subs are flush with the speaker cabinet such that the bottom of the air-assisted poles that I use make contact with the metal plate of the M20 mount when screwed down tightly. IOW - there's no "cup" at the bottom, just a solid metal plate. I've never felt like my speakers were wobbly on my poles. I agree that the speakers do look cool mounted on the truss!
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Oh, its definitely overkill. ;)
However, after having an M20 pole cup fail at a gig, I don't trust the straight poles anymore. The weight of an X40 on top of a straight pole was able to apply enough torque to break a pole cup. Can you imagine with a UPQ? These truss assemblies feel solid with a UPQ on top of a 900LFC.
That appears to be an axial type failure and not the result of excessive side loading. Probably dropped onto a fixed speaker pole that bottomed our or "shanked" and the lower supporting structure won the contest.
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In the picture of the broken pole cup, is that some kind of dual mode cup? The M20 mounts on my subs are flush with the speaker cabinet such that the bottom of the air-assisted poles that I use make contact with the metal plate of the M20 mount when screwed down tightly. IOW - there's no "cup" at the bottom, just a solid metal plate. I've never felt like my speakers were wobbly on my poles. I agree that the speakers do look cool mounted on the truss!
The Meyer X40 has a regular pole up with an extra hole in the bottom threaded for M20. The U-bracket comes with a little hole-filler that threads into the bottom of the cup and provides a flush threaded hole for the U-bracket bolt on that side of the speaker.
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Yeah, the lever arm on M20 and pole cups is scary, when you consider the weight on top.
I ended up making some flanges pressed into my 1 1/2 EMT poles to widen the footprint a bit.
I would think 8" truss would be way strong enough, and not be so bulky looking.
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That appears to be an axial type failure and not the result of excessive side loading. Probably dropped onto a fixed speaker pole that bottomed our or "shanked" and the lower supporting structure won the contest.
It could have been direct overload or fatigue from repeated side loading. The actual failure cross-section is shockingly thin, and one of the reasons I don't like pole cups. I use them grudgingly. My flanged poles put the vertical load onto the speaker body instead of the pole cup bottom, and reduces the bending from side loads.
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Meyer was kind enough to sell me a replacement part.
I believe the pole cup is a Penn Elcom M1557/M20
https://www.penn-elcom.com/us/universal-speaker-mounting-top-hat-m1557-m20
... I've since purchased a few of these direct from Penn Elcom. It accepts a 'standard' unthreaded pole or a hybrid threaded pole. Meyer sells a hybrid pole for use with them.
It appears to be made of cast aluminum or some similar alloy. White Metal? Sure, IDK...
I don't mean for this to be a critique of the product or design. Things fail; it happens... I just happened to find a weak point in this particular item.
Love the idea of using a narrower truss piece for this purpose. However, I think the appeal of this design is that it works with a 'standard' F34 truss; that makes it versatile.
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It appears to be made of cast aluminum or some similar alloy. White Metal? Sure, IDK...
At least that's better than plastic. The cup also doesn't look very deep which isn't helping either. All the cups on my speakers are single piece metal (pressed or machined) that are probably 4" deep or so - never once had one fail.
With a 12" top plate holding most of your load I don't think you need anything particularly fancy here. A simple M20 bolt up the middle into your speaker should be all you need to hold everything in place. I use a similar philosophy for ground stacking my Yorkville Unity rig. The boxes up on top are the easy part - what's not seen here are all the additional rigging components used to bolt the subwoofers together and provide rigid mounting points for the 1m box truss segments, in addition to overall load distribution for weight/balance considerations.
Obvious rigging disclaimer here that each case is unique and any proposed rigging solutions must be thoroughly evaluated before use.
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I believe the pole cup is a Penn Elcom M1557/M20
https://www.penn-elcom.com/us/universal-speaker-mounting-top-hat-m1557-m20
I also believe it is a M1557/M20. Reading the M1557/M20 specs and taking measurements of the actual Meyer part reveals that the I.D. of the cup is slightly oversized, I expect so as to not impede rotating a pole or u-bracket adapter into the 20mm thread. If you don't use the 20mm thread, however, this can leave the pole fit a bit wobbly. My solution for this is to replace the stock M1557/M20 pole cup with a Penn M1557 pole cup, which does not have the 20mm threaded portion and is .6 mm tighter I.D.
https://www.penn-elcom.com/us/3-1-8in-high-black-die-cast-zinc-top-hat-for-1-3-8in-poles-m1557
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Oh, its definitely overkill. ;)
However, after having an M20 pole cup fail at a gig, I don't trust the straight poles anymore. The weight of an X40 on top of a straight pole was able to apply enough torque to break a pole cup. Can you imagine with a UPQ? These truss assemblies feel solid with a UPQ on top of a 900LFC.
Switch to all steel pole cups. The cast ones like this are known to crack and break like that.
Best regards,
John
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Switch to all steel pole cups. The cast ones like this are known to crack and break like that.
I was thinking this, too. I have been using the Penn-Elcom one-piece spun (I think) steel cups and they appear very strong and have never had a failure. In general, mild steel is wonderful for critical structural applications as it plastically deforms (yields) very far before failing. Its chief shortcomings are low strength/mass and corrosibility.
The truss supports look great, by the way.
--Frank
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Thanks all
I am planning to order parts soon to build another small batch of these M20 truss plate adaptors. If anyone is interested in picking up a set, please DM me....