Has anyone used 'inward tension' using line/rope/long bolts to stiffen a cabinet? - diyAudio
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Old 15th September 2009, 01:34 AM   #1
sardonx is offline sardonx  Canada
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Default Has anyone used 'inward tension' using line/rope/long bolts to stiffen a cabinet?

Well this is an idea I heard when I was working for a local speaker builder which I want to implement in my current project and wanted to know if anyone has done this and what the results were. The method is basically having say a typical speaker cabinet made of plywood, drilling a hole in two opposite panels (at the same location) and running something like aircraft cable or even a long bolt through it. Then if using a bolt, simply tighten while listening to music until you feel it sounds good. Of course you'd have to be careful not to over tighten and crack/collapse the cabinet.
Now this got me thinking. And this is a bit of a nutso idea and a lot on here will not like it. What if you were to use a series of strings (say bass guitar strings) and actually tighten and tune them to certain notes, or all 7 whole notes. The issue would be that not all music is played on instruments tuned to A440 but I'm wondering if the right combination of stiffness and damping were used, along with the tuned strings, would this blur the music or would the specific resonances enhance the experience..? Maybe for stringed instruments it would work, but what about wind, brass, synths etc.. ?
I will probably try this sometime for the hell of it. But for the current project I'm staying on planet earth and using half inch bolts and tightening a half inch baltic birch floorstander in two locations. The bolts will be covered in some sort of goop to help deaden any ringing that may occur (maybe I will brace the bolts themselves) and some sort of sealant will be used at the ends to seal air gaps. There will also be a typical wood brace that is not too close and not too far away from the tension points to prevent the walls from flexing in too much in the center (for visual reasons) and to help stiffen the walls further by having an extra tension point. Any thoughts?
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Old 15th September 2009, 02:07 AM   #2
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Quote:
Originally Posted by sardonx View Post
And this is a bit of a nutso idea and a lot on here will not like it.



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Old 15th September 2009, 02:23 AM   #3
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Yup! I've seen long crossbolts used in stage gear at concerts.

One cab was labeled Pioneer and was an open backed 16x12 that stood about 12' high. Four sets of crossbolts in that one (one crossing behind every four speakers).

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Old 15th September 2009, 02:27 AM   #4
Key is offline Key  United States
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Well I kinda like the idea about inward tension but not so much the idea of the guitar strings. The way I am thinking about it you can either damp them or let them resonate - no in between or you will just cause buzzing. Also over time I would expect the strings will stretch out and become "dead". At least if you are going for a hi-fi speaker or one meant for program material I would ditch the idea of the resonance but keep the idea of being able to adjust the tension.

Now for a colored instrument speaker that utilizes resonance the idea might be worth experimenting a little with. Of course musicians have enough doo dads to tinker with and have to tune already and I tend to stick with things that just sound good with minimal need for tweaking in terms of what I use on instruments. And I don't think I tune to strict A 440 haha.

Anyway I would still try it regardless of anything said in this thread I am stubborn like that with ideas.
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Old 15th September 2009, 02:47 AM   #5
sardonx is offline sardonx  Canada
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Nice signature, John.

I wonder if those cross bolts for the Pioneer stage gear was to help the sound or to help them from falling apart!

I'm not sure the strings would keep stretching out. After a certain point they either stop stretching or break. And since nobody would be physically plucking at them I don't think they'd break. I always thought they became dead due to the acid and gunk that comes out of my pores! And humidity and temperature play a role in de-tuning over time as well. And I bet the actual guitar is just as much the culprit here as the string if not more. But I'll stop assuming.
The thing is that the more you tighten the string the more inward tension and the less uncontrollable vibration of the walls. So with a very stiff material to begin with the actual resonance would probably be on a small scale but maybe just enough to add some sweetness. I am putting on the fire retardant suit now.
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Old 15th September 2009, 02:51 AM   #6
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On the surface inward tension seems to create less stress on the glue joints but isn't it "half a dozen or six of the other" scenario?
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Old 15th September 2009, 02:53 AM   #7
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Quote:
Originally Posted by Geek View Post
Yup! I've seen long crossbolts used in stage gear at concerts.

One cab was labeled Pioneer and was an open backed 16x12 that stood about 12' high. Four sets of crossbolts in that one (one crossing behind every four speakers).

Cheers!
A lot of car audio SPL competitors do the same thing. Lots of pressure in those enclosures.
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Old 15th September 2009, 03:33 AM   #8
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Well yeah there would more things that would contribute to strings breaking on a real guitar which is being used. But strings do lose there elasticity over time - it might just take more time in your case. I find this is the number 1 cause of broken strings with guitarists - either too much elasticity because they didn't stretch the strings as they added tension and strung the guitar (which can lead to slippage) or a lack of elasticity from age and wear.

And also thinking about it they might not be as adjustable as you would need for this application since they will break if they are tuned higher than concert pitch.

My problem with the idea of resonance is you can't control it. It can only add inaccuracy and get in the way of realism (says the hypocrite who loves his Bass Reflex speakers)
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Old 15th September 2009, 03:48 AM   #9
sardonx is offline sardonx  Canada
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I guess it depends on how the box is constructed and how much tension is applied. I think i know what you are saying though. If a box is made with 45 degree edges then inward stress is the right kind. And the glue joints would break with outward force before they did if inward force was applied.
But you are right that it's the same thing whichever way the pressure is applied I just think this method is probably the easiest and most practical way of tightening the walls to the brink.
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Old 15th September 2009, 04:55 AM   #10
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Wasn't it Triangle that had the philosophy (if you can call it a philosophy) of building their speakers to resonate (after a fashion) like musical instruments? I remember hearing some of their stuff maybe ten years ago and liking them quite a bit.

If I wanted to play with tension I think I'd try something like one of these maybe even going so far as make the faces slightly convex by making them out of smaller triangles with the vertex at the centre of the face so that applying tension from vertex through the interior of the enclosure to opposing vertex makes the face itself more rigid. . . . The trouble is, with forms like these all the internal cables will want to pass through exact centre so they'll all try to displace each other unless you build an internal hub. Oh, and all the face edges will want to be beveled at the proper angle so they won't pull by each other when you're tightening them up
. . . . .
Gee, it's starting to sound like quite a project . . . . . better get started!
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