Limp mass trap idea

[dean1979]

What about this idea.

Just getting my head round traps and stuff, and I was thinking about making a limp mass trap.

Now what I am thinking is making like a tall floor standing pole with a large circular ring at the top about 1m diameter, and then hanging the vynil off of this so that it surrounds the pole and then maybe join it together so its like a hanging cylinder. Kind of wonder if the fact it uses such a big peice but in a smll space is a plus, and that it is kind of 2 layer with a gap due to it being a cylinder would be a plus as well.

What you think

[Rod Gervais]

Originally Posted by dean1979

What about this idea.

Just getting my head round traps and stuff, and I was thinking about making a limp mass trap.

Now what I am thinking is making like a tall floor standing pole with a large circular ring at the top about 1m diameter, and then hanging the vynil off of this so that it surrounds the pole and then maybe join it together so its like a hanging cylinder. Kind of wonder if the fact it uses such a big peice but in a smll space is a plus, and that it is kind of 2 layer with a gap due to it being a cylinder would be a plus as well.

What you think

Iit would have very little value - would tend to reflect mid and high frequencies by itself - and would do little for low frequencies........ look at their test data - it was a result of a free hanging test - you will see fairly high TL values in the mids to high and fairly low in the low frequencies - this reflects what dB levels are reflected back into the space - the remainder just passes through - they would pretty much still be in the room - very little destruction of sound through heat conversion here........ plus it would be MUCH MORE expensive than other DIY options you have -

Rod

[Glenn Kuras]

look at their test data

Link??

[dean1979]

See I thought suspended sheets of 10kg/m2 sound barrier mat absorbed bass, sound on sound etc seem to think so. Or am I ready things wrong

[Brainchild]

Nobody really knows what they're talking about in this specific area, but it doesn't look good.

[SAC]

Originally Posted by Brainchild

Nobody really knows what they're talking about in this specific area, but it doesn't look good.

If I may make a general comment aimed only at the 'notion' expressed.

The dynamics of a limp mass (mass-spring) system are WELL understood!

It drives me crazy to read almost daily of various aspects within audio and acoustics that SO MANY seem to think are so esoteric and beyond the understanding of physics and engineering. After all, to many, audio and acoustics are some mysterious esoteric art that transcends the understanding of science as evidenced by the amazing existence of SO MANY products that claim capabilities that far outstrip and confound our abilities to explain why they work!

Right?

Sorry folks, but that is absolute nonsense. There, I said it.

Now, we as individuals may not be intimate with every aspect of physics, but classical mechanics - as this has nothing to do with quantum - is well understood. And while the manufacturer or the end user may not be able to coherently describe or 'diagram' the mechanical or electrical systems at play, that DOES NOT make the system "too complex" nor unknowable. It simply demonstrates our lack of understanding. And in this sense to say it is beyond our understanding simply indicates hat we need to get more qualified folks to evaluate the 'system' - NOT that it is beyond understanding!

And understanding this limitation where our POV is the limiting function is critical.

There are indeed aspects of behavior which push the envelope of our understanding. And there are areas where the evaluative models so commonly employed do not exactly correlate 1:1 with the subjective experience of their behavior. But that does not account for audio having assumed an exceptional state in the realm of engineering and physics that justifies the all too common notion that it somehow transcends physics. I would suggest that in the VAST majority of cases it simply reflects the desire of many who are not well versed the disciplines of physics and engineering inability to adequately discuss or describe the behavior. And instead this mystery all too often represents the limited toolsets in the form of understanding that we too often bring to the table.

But even the realm where our understanding ceases to provide strict 1:1 correspondence with the subjective does not necessarily mean that we don understand the behavior of a electro-mechanical or acoustical system. And the interesting thing is that those who address this realm of psycho-acoustics have a pretty good understanding of the regions where the strictly 1:1 correspondence varies and offers multiple possible relationships. It is not that we simply do not have a clue. But rather it is a case where the possible results are not limited to a specific outcome.

And we encounter exactly such cases when we address various acoustical response models. Some folks simply, for whatever reason, have different preferences. While we can statistically state trends in preferences, we cannot state categorically that in all cases that a particular response is desired. But that does not mean that we do not understand that which is occurring. Nor is this meant to explore the limitations of that which we are capable of known, the irony being that even those limits are able to be identified!

After all, we can analyze the characteristics of ice cream with great precision and accuracy, but it does not necessarily tell us why one person likes vanilla, another chocolate, or another strawberry (etc.). Yet this does not mean that we do not or cannot understand the functional nature of ice cream.

Similarly, mechanical damping of an acoustic transformer in this particular case of a limp-mass absorber is NOT a case of "nobody knows". But it may indeed be a case where the folks involved here in the evaluation do not know!

Many of the variables are not easily quantified with the 'dining room tools' we too often bring to bear on the situation. And the refusal of so many to even acknowledge the existence of math (sorry!!!) which serves as a language that describes the behavior of single or multivalued models further makes our ability to evaluate mechanical or electro-mechanical or psycho-acoustical relationships difficult at best (heck, just look at the confusion that the mention of simple time based tools has wrought on this forum!).

But I hate to burst the bubble of so many who are want to assign the understanding of such behavior to mystical realms simply because we often do not apply the same rigorous methodology that other realms of science and engineering do.

I can only imagine the mysticism and awe that would envelop other areas of applied physics if those evaluating and attempting to implement systems and solutions lacked the ability or will to apply the tools and understanding that are well know. And if bridges were designed, evaluated and built in the same manner as much of acoustics and audio, I would be avoiding a GREAT many bridges!

So, if someone has the honesty to say "gee, I don't fully understand the complexity of that system", I respect that. Heck, in many cases we can commiserate!

And I happen to be one who delights in flirting with the fringes of what we know in the area, as this region beyond which there be dragons utterly fascinates me - and that is my own demon to tame. And thus I also tend to have a pretty good grasp of that which I personally do not fully understand - as that is personally what I find fascinating. But even I am aware that this has little relationship to the total limit of our understanding of all things acoustic.


But far too often by virtue of the subject involving audio or acoustics we hear the assertion that "it" is simply "too complicated" for "us" to have a suitable understanding of the behavior - when it really indicates that the problem isn't with the physics....

I wonder, would as many who have studied music be so tolerant of others who, lacking such in depth awareness, assert that "that music stuff" is just "too complicated" or when those who eschew a knowledge of notes, time signatures and harmonic structure and melody ascertain that music is just noise? ...After all, its just beyond 'our' comprehension and "nobody really knows what is going on". Right? ...And in discussing music analytically, don't anyone dare mention notes or chords or harmonic structure!

[Brainchild]

Originally Posted by SAC

The dynamics of a limp mass (mass-spring) system are WELL understood!

Specifically, this is a question about the absorptive properties of a limp-mass-as-limp-mass, not a mass-air system. The question has been raised before, and...

Originally Posted by SAC

...we need to get more qualified folks to evaluate the 'system'...

...mechanical damping of an acoustic transformer in this particular case of a limp-mass absorber [sic] is NOT a case of "nobody knows". But it may indeed be a case where the folks involved here in the evaluation do not know!

...from a factual standpoint, no one on this forum (up to and including every post in this thread) has ever offered any knowledge as to the absorptive behavior of a limp-mass-as-limp-mass in any configuration.

[avare]

Originally Posted by Brainchild

Specifically, this is a question about the absorptive properties of a limp-mass-as-limp-mass, not a mass-air system. The question has been raised before, and...

...from a factual standpoint, no one on this forum (up to and including every post in this thread) has ever offered any knowledge as to the absorptive behavior of a limp-mass-as-limp-mass in any configuration.

Noise Control and Acoustics by Rettinger covers it the in simplest terms. The text is 40 years old.

Andre

[DanDan]

Hi Dean, I haven't seen such a cylindrical design even hypothetically. I suspect that it would work if you could get the construction detailing right. It would need a fill of absorbent material, but not touching the vinyl. Difficult. Also isn't that material insanely expensive? I wonder if it would be more effective/much cheaper to use a smaller amount fronting a sealed box or corner? If you do proceed I recommend that you look up the BBC designs. They very effectively used asphalt impregnated roofing felt as a front surface in modular sealed box designs. Munro in the UK, specify limp panel traps in their designs. You could probably ask them directly about that. I think Primacoustic have a new product using a damped membrane. The Modex is certainly one.
I reckon a SuperChunk, fronted by some sort of airtight but light damped membrane should work well. However the only designs I have seen used extremely light membranes, e.g. light card or heavy paper, damped by proximity to, but not actually touching, the insulation fill.
I would worry that incoming sound might have difficulty vibrating the much heavier material you are looking at.

DD