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Old 17th November 2012, 12:47 AM   #91
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Not sure but can we call them shelf braces? I am confused by window braces as it already has a meaning.
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Old 17th November 2012, 07:58 AM   #92
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Originally Posted by planet10 View Post
To start a resonance you 1st have to pump sufficient energy into it at just the right frequency to get it going.
Wrong. No matter how much energy you put into it, the resonance is always there. And, at resonance, the panel is more likely to receive the energy, because both impedances, mass and stiffness, cancel out and there's only the resistance (the damping) working.

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Fighting this is the natural energy dissipation of the material which is related to the relative dimensional differences between the material thickness and the wavelength in question.
What?
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Old 17th November 2012, 08:03 AM   #93
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No matter how much energy you put into it, the resonance is always there.
The potential for resonance is always there. But if you never put sufficient energy into it to excite it, it is as if it isn't.

A tuning fork always has the potential to resonant, but if you keep whacking it with a wet noodle it isn't going to make any sound.

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Old 17th November 2012, 09:07 AM   #94
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So you're not filtering out a driver's cone resonance?

What happens if I play a dirac impulse? Will these signals excite the resonances?
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Old 17th November 2012, 09:45 AM   #95
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So you're not filtering out a driver's cone resonance?
That is a band-aid. The resonance is still there. If i have a resonance that is an issue i'll tackle it mechanically

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What happens if I play a dirac impulse? Will these signals excite the resonances?
Who cares, i don't listen to dirac impulses, i listen to music. And i don't gohitting my speakers with a hammer while listening.

If of sufficient magnitude a good excitation if you want to find where resonances are

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Old 17th November 2012, 09:54 AM   #96
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That is a band-aid. The resonance is still there.
But if you filter it, you reduce the energy transferred into that resonance. According to your argumentation above this would be a good thing. Because it can't resonate any longer.

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Who cares, i don't listen to dirac impulses, i listen to music.
Did you know that you can represent music as a sequence of Dirac impulses? So, if you can excite a resonance with a Dirac, you can excite it with music.
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Old 17th November 2012, 10:32 AM   #97
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But if you filter it, you reduce the energy transferred into that resonance. According to your argumentation above this would be a good thing. Because it can't resonate any longer.
true, but you'd need to have a steep notch to remove the energy which would screw up the FR and that filter in the signal path all to often does way more harm than good.

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Did you know that you can represent music as a sequence of Dirac impulses? So, if you can excite a resonance with a Dirac, you can excite it with music.
Like a CD? You can excire the resonances with a dirac of sufficient magnitude. Doesn't mean that energy exists in the music.

A dirac is like the whack you give a tuning fork to get it ringing. The tuning fork takes the energy available at the frequency of its resonance, and if it is sufficient it starts ringing.The whack has to be large enuff...

As implied above the best way to introduce a dirac into a cabinet is to whack it with a hammer.

You can also decompose music into sins. That hasn't proven very good at predicating the real-world performance of a device.

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Old 17th November 2012, 10:39 AM   #98
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The tuning fork takes the energy available at the frequency of its resonance, and if it is sufficient it starts ringing.
What is sufficient energy?
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Old 17th November 2012, 10:45 AM   #99
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Did you know that you can represent music as a sequence of Dirac impulses? So, if you can excite a resonance with a Dirac, you can excite it with music.
Just because you 'can' doesn't mean 'it' will.

But you admit that resonance isn't there, as P10 said, unless you hit it with the right frequency, for the right amount of time, at a volume sufficient to overcome the natural properties of the panel in question?

The Albert Bridge crosses the Thames near Chelsea. The sign below was posted many years ago due to a mechanical resonance being created when troops from Chelsea Barracks marched across it. It just took a certain number of men marching at a certain pace. They could however all walk across it at the same time with no ill effect. No doubt that frequency was produced by them walking as well, just not at a volume necessary to overcome the bridges natural structural rigidity.

You do not have to filter out 700hz (for example) just because at high volumes with one or two tracks in you collection you can manage to excite a panel. That would be deleterious to ALL music. You would be better off bracing or better yet not playing those tracks at high volume.

As Keriwena noted most normally braced cabinets of average size (75% of this forum maybe?) will NOT have an issue. Big efficient drivers in big cabinets "create a situation where panel resonances in the midrange need special attention."
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Old 17th November 2012, 10:50 AM   #100
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What is sufficient energy?
Sufficient energy would be enuff that every man women & child would not want. And it would need to be clean. We are a ways off...small fusion generators would be a good start.

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