Axiom Home Page Forums General Discussion Home Theater HT in-progress

Thanks Trevor.

Yeah, I kind of go a bit overboard of design and test. Back when I was doing software consulting some managers loved me and others hated me. You loved me because you knew the design and code would be right the first time (at least no major bugs), well tested, and very maintainable. You hated me because I took so long. Have a few funny stories about that but we will save them.

Save them for a trip to Boston?
Don't know if i'll be through there anytime soon.

I put up the electrical wall. It's OSB, floor muffler, and green glue wall-board sandwich so I can screw all the electrical power stuff to it. It's about 3' wide and held by 6 rows of channel with 2 clips a piece. It's rattling badly. So I tested the front wall which currently has a single layer of wall board. It also rattled a bit but not as much.

I'm plagued with this rattle stuff. I've looked at it a few times now and discover something off each time. The list of (possible/probable) rattle problems found before this were:

• Over torquing a wall board screw pulls the screw hole in the channel outward causing the hole to enlarge. Now besides the screws rattling in the hole they no longer hold the wallboard onto the channel. Not good if the ceiling falls on you! At the time, I thought this might be causing the rattle. Now I think the rattle was really something else.
• the vertical alignment of the clips was off. This had the issue of having the wall weight distributed unevenly over the set of clips. The clips holding the wall would be forced downward sometimes shorting to the wall while some clips had no weight allowing the channel to rattle in them,
• The studs were not all in the same plane. Some were bowed, others miss aligned. This pushed/pulled the clips twisting the channel. So some clips wanted to twist up and others down. Again some clips had no weight and were probably rattling. If you look closely at the pictures of the open wall with channel over it you will see the clips had to be shimmed out to get them onto the same plane.

This time I'm pretty sure I know what's going on. But you're gonna have wait for the next post to find out.

[quote=chesseroo]Save them for a trip to Boston?/quote]
When this is fully finished I'll throw a party

Ah geez that sucks for sure. One of the negative things i read about use of metal channels for HT came back to potential for rattles. For us living in lower Manitoba means building/living on mud, essentially. The house moves seasonally, or parts of it. Cracks, lifts, slopes, in walls, ceilings, floors, drywall, all very common. In putting our HT together, we stuck with materials that wouldn't rattle if such a house shift popped a screw or misaligned something.
There's pluses and minuses.
All that being said, i mentioned long ago about some rattle in our back wall that relates to the QS8 located near the sound, but i've never been able to track it down beyond something in the wall structure in the general area. Thankfully it only presents itself on loud, bassy occasions and once all the new surrounds come in, things will be adjusted. However, that could make it worse rather than better.
We'll see.

In our old house we had a rattle that showed up after we got all of our 5.1 Axiom system. I narrowed that one down to the electrical panel enclosure door. A few soft door bumpers solved the issue.

Perhaps setting up the new sub in the room and playing back some bassy material will help as you search for the rattling source.

Ok, I think, the weight of the wall pulls the top of the channel down creating a gap with-in the clips top slot. This allows the channel to slide up and down in the clip as the wall vibrates. My thinking is that the channel then whacks into the clip slot’s end and creates the metallic rattle sound. (Note: whack is my official engineering term which comes form slap’in your brother upside his head when he’s annoying you . )

Pict 1 weight of wall creates small gap at top of clip

pict 2 wall vibration causes the top of the channel to slide upward causing the rattle noise


Before moving to solve this … could it be a non-issue as:

• my hand vibration technique may be more extreme then sound vibration would be
• it's behind a sealed wall, so the rattle would not be heard
• It will be masked by the sound that created it
• It must be present at other installations of this system. If it was an issue it would have been taken care of already
  

Let’s play it safe and assume it’s a problem. To show my thinking (so you can run though this with me) the lists below state a theory and in blue my thoughts on it.

• The channel may not have enough spring to keep it fully engaged in the clip when under load. this might be the intent of the clip's design. Supporting this theory is that the channel ends which have less spring are more likely to rattle than the clips in the middle. The problem solving this is that I would have to try a different manufacture’s channel or try to bend the channel I have. Both solutions are not appealing and have risks (not to mention monetary and time impact). I'm also not really sure it's the designer intent
• The clip may be a bit rough causing chatters if the channel moves. clips look pretty smooth. Don't think this is an issue
• The whack is the main cause of the rattle. Very probable
• The slot's top curve pushes the channel back causing channel vibration. possible
• What ever the cause it's the channel's vibration you hear think this is key

Not sure I preventing the whack or movement is the way to go here. The design could be that the channel should move in the slot. I think I'll try to dampen the channels vibration and see if that works ...

While checking this out more ... when the channel is pulled down it has a bit of play to vibrate in the slot. So this is my new main theory.

I'll test out both dampening the channel vibration and dampening this movement.

Have you thought about contacting the channel manufacturer to confirm how this should fit together and if this is expected?
Just looking at the metal on metal contact there makes me cringe.
How many hangers are there that could vibrate and potentially create a noise from this?

Right now I'm waiting for some acoustic caulk to set for a bit. I've applied it to the joints where the channel mets the clip. On one test where I allowed it to sit for an hour it seems to have worked incredibly well. Let's see how it does after giving it more time.