Speaker Break In - Page 3 - AVS Forum
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post #61 of 86 Old 07-11-2003, 06:35 PM
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Grifin----I said metal suspensions, not cones. I'm aware that there have been aluminum cone woofers for many years, going back at least as far as an 8" driver from Bozak about 40 years ago. Bit I'm unaware of any metal cone drivers with metal suspensions.

I think any audiophile that doesn't take into account the fact he may be ********ting himself about what he hears is not thinking things through or being realistic about things. One must at least consider the possibility.
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post #62 of 86 Old 07-11-2003, 06:50 PM
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""Sushi's got it in a headlock!!"" hes usually right on the money!!!
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post #63 of 86 Old 07-11-2003, 07:46 PM
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Quote:
Originally posted by DigitalGriffin
ASTM manual of materials. Warning: It will give you back problems if you try to lift it. It will also set you back five benjamins. :-)
I believe what you are referring to may be a strain hardening that occurs in the actual manufacturing of the raw fiber. I'll check ASTM and ASM and see what they have to say. However, once in the fiber or composite form these materials, including Kevlar, don't have the elastic/plastic regions corresponding to typical ductile metal behavior. Take a look at some published stress/strain curves for typical composites (Kevlar/epoxy, S2/epoxy, E-glass/vinylester, carbon/epoxy, etc.). There isn't a plastic region. There is no strain hardening effect. It is much closer in behavior to a brittle material such as some grades of cast aluminum, or a ceramic. Composites typically don't have a yield strength, they only have an ultimate strength. Exceed that and it's broken.

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The author who wrote this book I believe wrote other books on the break in, lifetime, and characteristics of materials that are subject to mechanical stress...You might be able to contact him if you want to know more.

http://www.wiley.com/WileyCDA/WileyT...471510599.html
I've taken advanced fatigue and fracture courses. Let me tell you... that is one area of solid mechanics that still has a lot of work to be done. You really get the feeling learning such material that all the equations are just pseudo-emperical instead of derived from first principes (that isn't always the case in F&F, but it is sometimes, often a mix of the two) - they work, in some cases, usually with some degree of accuracy, but there's always that nagging thought that the smartest people in the field still don't really konw what is happening. Just the statistical aspect alone is enough to be discouraging. That being said, I highly suggest taking such courses, as in the future it will be more and more important for engineers to have such knowledge.

OK, now that I've covered that tangent thought, I should point out that fatigue in metals doesn't cause a change in modulus. It might eventually cause plastic deformation which results in a stiffness change in a given member, but that is a geometric effect and not a material effect.

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BTW: What's a matter? Don't believe in metal fatique/work hardening? I tell you what, why don't we stick you in an aircraft frame that has been subjected to loading and vibration for 100,000 hours. Do you feel safe that the characteristics of that frame is the same?!?!?
Perhaps you should briefly revisit those texts you have handy. As I clearly stated previously, work hardening produces a change in material strength, not elastic modulus. And the characteristics of an airplane that you should be worried about are the strength and crack lengths, not material stiffness. That hasn't changed, no matter how many hours are on the clock. I'd be worried to be sure, but not for the reason you are assuming.

Oh, and I'd list my credentials but don't see the need, though you can rest assured that I'm not speaking from my as* either. ;)

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post #64 of 86 Old 07-11-2003, 07:56 PM
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Quote:
Originally posted by sushi


1. If the inter-specimen variability is large, all you need is a larger number of specimens to increase the statistical power of the study. A large variability surely makes the study more involved and costly, but it does not automatically render the study unsubstantial or irreproducible. Ill-controlled experiments and statistics are what make the study unreliable. On top of these general points, I would say (as Bigus would probably do), a large inter-unit variability usually suggests a poor engineering.

2. First, you shouldn't underestimate the power of today's loudspeaker measurement methodologies. The old simple era of steady-state frequency responses and distortion measurements were long gone. Second, the "subjective" assessments from well-controlled listening tests are perfectly acceptable "hard data" for the science of loudspeaker engineering. What separates between science and pseudo-science is not whether the data are derived subjectively by human listeners, but whether the listening session is properly designed and controlled.

What I meant in #1 is that the break-in effects, if exist, may vary with material used as well as designs. Therefore, it's not about the size of specimens, but rather how one could draw conclusions.

Unlike microelectronics technology, audio is relatively "low-tech", and the evolution has been approaching to the summit since long. Further, the art of sound to hearing is similar to that of a paint to seeing or cuisine to tasting, many factors are not measurable or not definable by measurements. However, I agree with you that a well-controlled listening tests may be valid in these type of experiments. BTW, forgive my ignorance, but I'm not aware of any Ph.D. programs on hi-fi audio in the States at present.

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post #65 of 86 Old 07-12-2003, 12:32 PM - Thread Starter
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Sushi,

"My own observations in this and other audio forums are in fact totally opposite of what you said.

I observe that, in general, people who believe in lab testing and physical measurements are also firm proponents of well-controlled (blinding is one of the absolute prerequisites here) subjective listening tests.'

While I don't doubt that this is your experience, it has been exactly opposite of mine. I find that those who see bench tests argue for human testing and vice versa.

That having been said, I know that if either had been done in both the first few hours I played my speakers and now, the results would have been the same - they are different. My real point is, it wouldn't have proven anything or changed the argument for anyone who already has a strong opinion about this. That just seems to be the nature of the beast.

Doug

Turn it UP!!
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post #66 of 86 Old 07-12-2003, 02:37 PM
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I'm in an odd camp on this issue. I am a big advocate of level-matched double blind testing and have participated and conducted several of them. The results of these have cast considerable doubt in my mind on several common audiophile claims, such as their being substantial differences between power cords, most interconnects and speaker cables, amplifiers, isolation devices, speaker stands, and more.

However, using the same methods have led me to give more credence to the phenomen of speaker break-in (but not cable or component break-in). While I have not found differences in all new vs used speakers, I have found it quite easy to discern differences in some cases.

Why this is true, I don't know. But as I did it, and was able to repeat it, and even found it very easy to hear differences, I can't dismiss the claim.
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post #67 of 86 Old 07-12-2003, 03:11 PM
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What length of break-in periods were you comparing to "fresh out of the box", Tom? Did a couple of hours of break-in sound different than say...100 hours when compared blind?

Thanks.
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post #68 of 86 Old 07-12-2003, 04:02 PM
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I wish I had conducted trials at more periods, but it is a lot of work and I didn't.

I have done comparisons on 5 different pairs of speakers, breaking in one and leaving the other "new." I did not hold all testing conditions consistent from pair to pair, which were done over about a 6 year span.

What I did was to compare brandnew to brandnew out of the box, using a mono signal to a stereo amp and making sure both channels were level-balanced to under 0.1dB (using a true-RMS multimeter to measure the amp's output). And then the almost brandnew (with maybe 30-60 minutes on it) vs the other one that now had 20-50 hours on it. Then I put many hours back on the first speaker and compared them "used" to "used."

In 2 of the 5 cases, I could not consistently discern a difference at any time. One time I felt I could tell a slight difference between the "almost new" vs "used", never completely passing to 95% confidence, but always getting about 65%-70% of my guesses correct.

On the other 2, I had no problems whatsoever telling the "almost new" from the "used" speaker. And on one, I was able to measure differences in the bass response between the two. Differences that disappeared both audibly and measurably after I "broke in" the first speaker. I was able to swap the speakers and repeat the tests and still pass with ease, scoring 100% on any number of trials.

The conditions were not so controlled that I would hold up the results to intense scrutiny.

I have also tried to discern differences on two other speakers, under less controlled conditions, but using test tones & music and written notes taken from the before and after listening sessions. Neither of these produced conclusive results.

So being the skeptic that I am, I remain quite dubious of the claims that all speakers have substantial break-in periods, after which their sound will be much improved. I believe that the vast majority of break-in (in speakers) is listener acclimation to a different sonic signature. I believe that it is likely that all of the claimed improvements in cable and component break-in is due to psychological effects.

However I cannot dismiss that it may well be true that some speakers/drivers really need a break-in period, of perhaps several hours in duration, to sound their best. The results from 2 of my 7 attempts to discern break-in effects were too dramatic for me to wave the claim off.

But I am not so confident that I would guarantee that under rigorously controlled conditions, that someone would be able to find speakers/drivers that would prove this beyond the shadow of doubt.
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post #69 of 86 Old 07-12-2003, 04:14 PM
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Interesting. Thanks for the follow-up.
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post #70 of 86 Old 07-12-2003, 07:16 PM
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Quote:
Originally posted by Tom_Bombadil


So being the skeptic that I am, I remain quite dubious of the claims that all speakers have substantial break-in periods, after which their sound will be much improved. I believe that the vast majority of break-in (in speakers) is listener acclimation to a different sonic signature. I believe that it is likely that all of the claimed improvements in cable and component break-in is due to psychological effects.

And I think the same applies to smoking pot. It takes a while to get used to the new smoke you just bought, compared to the stuff you've been smoking, but after a while it seems to be just as good or better than what you had. Lighten up guys and enjoy your equipment, that is what it is for. Over study and delving into the technicalities is great, but the main thing is to enjoy it, and after reading some of the posts, it appears too many are into head games and not enjoying their equipment. Speaker break in, cable break in, $300 cables vs $4 cables, can we give this a break? You got it, spend it! You don't, don't! No knock against the poster I quote or anyone, just get over it already, get over it.
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post #71 of 86 Old 07-12-2003, 08:31 PM
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I'll have to trust you on the pot smoking analogy.
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post #72 of 86 Old 07-13-2003, 12:32 AM
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Tom,

An obvious thought is that the speakers that appreciably change after a break-in period uses different types of materials (in the spider, surround, etc) than those in the speakers that do not seem to change.

So, do you have any info with regard to the driver materials on those 1 or 2 speakers that seemed to change, as compared to the materials used in the other 3?
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post #73 of 86 Old 07-13-2003, 10:31 AM
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My first guess Tom would be an excess of resin/varnish on the spider of the speakers that noticeably change. This is still the only plausible explanation I've heard. And I still think such a condition is due to either poor quality control in manufacturing, or less than optimum decisions made by the design engineers.

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post #74 of 86 Old 07-13-2003, 10:55 AM
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Bigus, foam vs. rubber surrounds can make a difference in break-in time as well. If rubber surrounds are used, the spider will likely take longer to become compliant that the surround. If foam is used, all bets are off and I don't think that's been a factor in some of these tests. Nevertheless, foam is still used in some otherwise very good driver designs. (unfortunately!)
--------------------------------

A take on driver break-in from Tom Nousaine:

"I've conducted several experiments examining speaker break-in. Two of them
involved drivers that were claimed to require 48 and 150 hours of break-in
respectively. In both cases the sound quality and measured performance of a
fully broken-in one and one fresh out of the carton were smaller than the unit to unit variations one would expect from two samples.

There was a measureable change in compliance (drop in Fs and increase in Vas)
noticable immediately after the break-in period, but the changes were exactly
offsetting in terms of speaker system design.

In a later experiment I used a driver than was said by the manufacturer to
require 48 hours of break-in. Before the break-in period the system resonance
of the driver in a 1.5-cubic foot sealed enclosure was 53 Hz.

I then broke the unit in for 48 hours according to instructions. Immediately
following break-in the system resonance was 49 Hz. (nearly an 8% drop) and the
dcr had risen by 0.4-ohms. However with a few minutes of rest the resonance had
risen to 51 Hz. The following morning it was back to 53 Hz and dcr was as
before.

So while it might be said that speakers "warm-up" (the voice coil certainly
does heat up with use) it all occurs quickly and is fully restorable with rest.

An engineer from a large OEM and aftermarket home and auto speaker company once
told me "yes, drivers do break-in, but it all happens with the initial stroke at
end-of-line QC."
-------------------------------------
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post #75 of 86 Old 07-23-2003, 03:18 PM
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To wake up a sleeping dog again... :D

It is well known that wood lumbers continue to become harder (increase stiffness) over many years, as they continue to lose the cellulose-bound water molecules (in some cases, it continues over 100's of years, as has been scientifically demonstrated in certain Asian wooden temple/shrine structures).

So, how about the MDF used in the vast majority of speaker cabinets? Does MDF material also experience a long-term change in its stiffness and other acoustic characteristics over many years? If so, could this be possibly related to the alleged changes in sound quality after a "break-in" period, in some selected cases?

Naturally, I presume that the "aging" process of MDF, if any, would not require the speaker to be actually worked out. In that sense, this is different from what is normally referred to as "break-in." Still, it might be some thing to think about...
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post #76 of 86 Old 07-23-2003, 09:35 PM
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Quote:
Originally posted by Tazmania
You learn something new everyday :)
Yea just listen to the State Of The Union, its full of good info :P
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post #77 of 86 Old 07-23-2003, 10:21 PM
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Quote:
Originally posted by sushi
To wake up a sleeping dog again... :D

It is well known that wood lumbers continue to become harder (increase stiffness) over many years, as they continue to lose the cellulose-bound water molecules (in some cases, it continues over 100's of years, as has been scientifically demonstrated in certain Asian wooden temple/shrine structures).
I'm not a wood expert, so my knowledge about wood properties is somewhat limited. I would like to point out however that hardness and stiffness are not the same thing, nor are they directly related. Hardness and strength have a fairly stong correlation. Hardness and stiffness much less so.

To illustrate the point: 1010 steel, 1050 steel, and heat treated 4340 steel have significantly varying strengths, have significantly varying hardnesses that are closely correlated to their strength, yet all have practically identical stiffnesses. The same is true for essentially all aluminums, from soft cast aluminums to brittle cast aluminums to very strong, tough, and hard forged aluminum alloys - they all have the same stiffness.

Now, perhaps wood actually does become stiffer with age (as I said, we didn't really cover wood materials that much... that's the realm of civil engineers primarily), but the fact that they become harder doesn't dictate that they become stiffer. They could do both, but I wanted to make sure you are talking about the right mechanical property here.

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post #78 of 86 Old 07-23-2003, 11:39 PM
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I agree with Sushi. While varnish, metal fatigue, wood shrinkage etc. are all possible culprits to explain break-in, good old fashioned empirical data would be a good starting point.

On the psychological side, one big factor is likely cognitive dissonance. For example, if you just spent $200 on an interconnect, your desire to hear a difference in sound (which justifies your purchase) is strong.

For me, to be worthwhile, scientific testing has to show measurable physical differences in sound that are also detectable by a normal listener in a double-blind listening test. Some bench testers get excited about statistically significant but audibly undetectable differences and this can be as big a problem as the anecdotal zealot who has little basis for their faith in speaker break-in and yet tells every customer that visits their store that break-in is needed.

Today I listened to speakers and smiled respectfully when the salesperson told me that one set of speakers only had 30 hours on them so they were at a distinct disadvantage to those with about 100 hours on them.

From an engineering perspective, it would seem easier to develop a product that works well new rather than developing it so that material degradation gets you to the optimal level of performance.

BTW, thousands of years of solid anecdotal evidence by millions of people suggested the earth was flat. I suppose we could have all just enjoyed the flatness of the planet without bothering with all that thinking stuff...

Outlier

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post #79 of 86 Old 07-24-2003, 12:28 AM
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I had never heard of or thought about break-in a few years ago when one of my friends bought a new pair of JBLs that I immediately fell in love with. I had been happy with my Polk sattelites for the previous 7 years, but I was enamored with the midrange his JBLs offered and ultimately decided I had to get a pair myself. The excitement I had when they finally arrived quickly waned as soon as I hooked them up - they sounded terrible. I'm not sure how that can be measured, but they sounded absolutely awful. I experimented with different placements but nothing worked.

I hadn't figured it out at the time but the next day they didn't really sound too bad, and I eventually felt the same way about them as I did my friend's.
The idea of break-in to me now is a reality. I don't even consider that it may be a myth, although some things seem to be affected more than others. My current Paradigms sounded good to me right out of the box, but both of the SACD players I've bought, while not sounding terrible, didn't sound at all at first like they did later. Both had very constricted soundstages and dynamics compared to what they eventually became.
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post #80 of 86 Old 07-24-2003, 10:28 AM
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Bigus, when I wrote "wood lumbers continue to become harder (increase stiffness) over many years" above, I used the word "hard" as a layman's generic term, while I used "stiffness" as a technical term. Sorry I should have been more precise.

Anyway, my understanding is that wood materials increase their stiffness over time as they loose water. I do not know whether or not the hardness also changes.

An increase in material stiffness directly results in an increase in resonance frequency, everything else being equal, correct? How about Q? An increase in stiffness results in an increase in Q in general? Also, what are the effects of a change in hardness on the acoustic properties of the material?
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post #81 of 86 Old 07-24-2003, 11:16 AM
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WOW! What a stretch, Sushi.....LMAO

I presume that the 100 year old 'timbers' used in the temples started life out as green and not kiln dried. To air dry wood, the general rule of thumb is that it takes at least a year per 1" of thickness to achieve some reasonable stable state (less than, say, 30% moisture content). And could be much longer for heavy dense exotics.

Furniture hardwoods (deciduous trees, the ones that have leaves) are kiln dried to about ~7% moisture content. Softwoods (coniferous trees, the ones that have needles) are dried to a much higher state ~15%.

Once these materials are placed into a stable environment (your room) they will vary (slightly) with the relative humidity level in that location, due to the fact that the internal 'cell' structure are like vessels (think of a log cell structure as a cluster of soda straws). If you place a board endgrain down into a shallow bucket of water, eventually it will 'wick' up to the opposite end.

There is a condition called 'air hardened' where a board is dried out to fast such that the outer surface becomes harder and more brittle than the interior (creates surface 'check' or cracks').

I would be very interested to see any studies that show that standard materials such as MDF (which are basically dry as a bone (nearly)) changing in such an environment (assuming the resins within were properly cured).

I would suggest the room atmospheric conditions could have a larger effect on all the variables (not the wood), than a on the cabinet itself.

Are you all barking up the wrong tree (pun intended)?:D
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post #82 of 86 Old 07-24-2003, 11:29 AM
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Quote:
Originally posted by sushi
An increase in material stiffness directly results in an increase in resonance frequency, everything else being equal, correct?
That would be correct.

Quote:
How about Q? An increase in stiffness results in an increase in Q in general?
The Q will be more affected by relative damping than by stiffness, though if the damping is held constant and the stiffness is increased I believe there will be an accompanying increase in Q as well. My guess here is that the abscence of water will change the Q more by way of decreased damping than by increased stiffness.

Quote:
Also, what are the effects of a change in hardness on the acoustic properties of the material?
In and of itself, a change in hardness shouldn't have a marked impact on the acoustic properties. AFAIK, work hardening a steel rod to 30% higher strength (and roughly the same increase in hardness) doesn't change resonant frequency, and it shouldn't appreciably affect the overtone series. Those things are tied to stiffness, not strength. Though, in a material like wood or a composite, a change in hardness could be an indicator of a larger physical change (like the evaporation of water) that does have an acoustic impact.



Even so, this change in wood stiffness is something due to material aging, not material cycling. Fatigue doesn't decrease stiffness, just strength. I wouldn't argue with anyone that claimed a speaker sounded different 10 years down the road, because things like natural rubber and even synthetic foams might have property drift as a result of age, but I am a bit skeptical of someone who claims a speaker sounds markedly different 20 hours later. Whatever break-in is required should be taken care of at the factory.

There may be the extraordinary exceptions, and in that case I'm very much interested in hearing a legitimate explanation. Thus far excessive resin is about the only plausible one offered.

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post #83 of 86 Old 07-24-2003, 11:33 AM
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Here's a report on MDF moisture content changes with Relative Humidity and temperature, as can be seen from the tables in your room, a point or two variation is all.

http://www.cape.canterbury.ac.nz/Apc...ata/886rev.pdf
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post #84 of 86 Old 07-24-2003, 11:44 AM
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Thanks, Bruce, for an expert account. I am convinced that we don't have to worry about the "aging" of MDF. (But do we still have to worry about the speaker break-in? :D )

Your post reminded me that our grand piano has to be tuned slightly down every summer. The frame lumber of the piano slightly expands due to the high humidity of Dallas summer, stretching the strings and making the pitch sharp, sometimes by up to several 10's of cents.
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post #85 of 86 Old 07-24-2003, 12:47 PM
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Thanks, Bigus.

Okay then, from the materials engineering point of view in general, what determines the "relative damping" of a material? Is it possible that the inherent damping of a material changes with "normal" use/cycling?
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post #86 of 86 Old 07-24-2003, 01:52 PM
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This whole subject of material damping gets fairly complex. For metals and many other structural materials, there is an inherent natural damping that comes from Coloumb damping, but due to the way it affects a cyclic stress-strain curve it is more commonly referred to as hysteresis damping. I know that for metals and a host of other materials (like ceramics, glass, and many natural stones and gems) this damping coefficient is a material property that remains relatively constant over a wide variety of frequencies. In general, the energy dissipated in one cycle due to hysteresis damping is proportional to the material stiffness and to the square of the amplitude of vibration. There can also be internal damping due to plasitic deformation, but I don't think we need to get into that for most loudspeakers.

When moving to most polymers and some natural materials like rubber, things get more complicated. Here we find that the stiffness of the material is not really a constant, but is dependent on the frequency of vibration. When you write out and solve the differential harmonic oscillator equation without making the assumption that elasticity is a constant, you define a class of materials known as viscoelastic. In these materials the energy dissipated in one cycle is relative not only to the amplitude but also to the frequency. The modulus of elasticity is a complex modulus, not a constant. However, I must stress that this complex elasticity does include a constant component, even if it is a coefficient to something variable (frequency). I've never studied about a phenomenon whereby cycling changes this coefficient value. It is for all practical purposes a fixed material property just like the elasticity of steel is fixed, but is also dependant on frequency whereas steel is not (for most reasonable frequencies at least).

I hope that answers your question sushi. I'll do some more digging and see if I can find any reference to something like decreased yield strength having an effect on the material damping coefficient. I'd also like to know if it is more related to material class (like stiffness) or material condition (like strength). i.e., I'm curious as to whether different grades of steel have varying damping properties. I do not believe that they do, simply because I figure I should have heard of that at some point... but occasionally I do miss something fairly important. :)

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