The "Voodoo" of Vibration in Loudspeakers

[Tenson]

Following up on vibration in wires... I know some Greek high-end designers who did some tests.

I don't know the specifics but they got some wire and suspended it on fishing line. They then sent very large current through the wire. The effect was obvious to the naked eye; the wire was moving, rippling to the current bursts.

Now take this the other way. You move a wire, and electrical current is induced! Obviously this will be on a much smaller scale but it will still happen. How obvious is this to the ear? I am not sure. But I suspect it is small. Still the ear can hear small differences if it is the right sort. What if the wire that connects to the power amp input is resonating like mad at a certain frequency?? Hmm..

 

[ScottG]

Of course, the above is a simplistic treatment, but, it does show that there are more important issues to worry about than the actual movement of the box itself. Now, panel resonances...

I think this is a case of "try before you buy". Having done this myself, I've found that in many intances its quite important. (i.e. it is something to "worry about".)

Additionally, (looking at the driver) is the cone the only thing moving? (or perhaps more accuratly is mms only at "play" here?) In otherwords how much force is being transmitted through the driver (in totality) to cause momentum, (in the same plane of movement no less), in the loudspeaker? Note: a correlary here are actuators used in audio (i.e. "But thumpers").
Still, I agree that in most instances the movement is very low - but the question has never been how "low", but rather what makes an audible difference (..and that I can only surmise based on personal experience).

 

[ScottG]

Re: Vibration.. ad nauseum

Those insisting that vibrations in wires, transistors, working capacitors, etc. would paint a more convincing argument that effects are significant if they'd actually provide some sort of rational empirical (aka actual measurements) or at least an engineering evaluation of the magnitudes of said effects.

If one does the math one would find that phonon noise in wires / electronics from thermal lattice motion would swamp any extra "vibration" from external sources at anything above absolute zero by many orders of magnitude.

With speaker enclosures, with resonance effects, there definitely are effects, but then, what live performance doesn't also suffer from such effects (concert hall modes / resonance... sounding board coloration in pianos / violas / guitars) etc.?

How about some actual MEASUREMENTS rather than speculation masquerading as fact and generalizations about what must be because it's intuitively obvious, etc...


auplater

Hmm, correct me if I'm wrong - but vibration of wire in general (as an electrical conductor) was not the point of this thread. In fact if there was a "continum" here of most significant to least significant - wire would have to be at the very end of least significant.

 

[redunzelizer]

Simple Newtonian physics.

Lets say a cone weighs 50 grammes, and the enclosure weighs 10 kilos, a not unreasonable assumption I feel. If the cone is moving, by Newton's conservation of momentum the forces must balance. The ratio of cone movement to to enclosure movement is therefore 50/10 000, which gives us a maximum possible movement in the box of 0.005% of the movement of the cone. And that's with a box that's not coupled to anything, and is completely free to move. I'm not that worried.

While the "usual suspect" calculus error has already been corrected, you example is lacking an important detail.

In case of said 0.5% reactive movement of the box, you should reckognize that the box itself has quite some "cone area". In fact the complete front plate will now have excursions of 0.5% of the driver's value, but the area of said front usually is a lot larger that the driver's cone. You might not want to believe it, but this front panel is now distributing sounds too, which you probably never wanted it to do.

Even worse, the back panel of the box will distribute sound with this example also. There naturally will be a delay with that one, of course, because of the different speed of sound within the cabinet material and air.

So this first oversimplyfied cone-mass/cabinet-mass inertia observation won't work at all. Instead, you created two additional parasitic sources, while simultaneously "distorting" the original source (the driver).

So here's the next (still oversimplified) calculus:
99,5% driver (now tumbling)
plus:
0.5% mass-relation * parasitic area quotient (front)
plus:
0.5% mass-relation * parasitic area quotient (back, delayed!)
give...

You name it: "High End", cause that's definitely not HiFi

regards

 

[ScottG]

Scott,
Spikes are springs, don't you believe?
(perdone me for the provocation)

Cheers,
Inertial

Spikes are usually metal and considering their shape - they are neither compliant (subject to compression) nor store/release energy that would cause a spring like action to any significant degree in this application. So I guess - No.

Now this doesn't mean that there might not be spring like action at the coupling point of the spike (depending on the material and its shape).

 

[forr]

Spikes are sometimes called mechanic diodes. What's the idea underneath ? Some guys have used them upside down.

 

[ShinOBIWAN]

While the "usual suspect" calculus error has already been corrected, you example is lacking an important detail.

In case of said 0.5% reactive movement of the box, you should reckognize that the box itself has quite some "cone area". In fact the complete front plate will now have excursions of 0.5% of the driver's value, but the area of said front usually is a lot larger that the driver's cone. You might not want to believe it, but this front panel is now distributing sounds too, which you probably never wanted it to do.

I think that its far too complicated for us to model casually. What about propagation delay of the vibration through the material? Not to mention that certain frequencies are boosted due to the non-linear composition of a material and also the size and shape. These will all interact. So these are a few more elements to include in the equation that will help determine how significant this movement is in a more accurate way.

If you disect it even further than the scope becomes almost impossibly complex in terms of the final result and its accuracy. Eventually it becomes a joke and you can't see the forest for the tree's.

Do like Scott said and try it. He's made suggestion to the same effect before when I was constructing some speakers not long ago. I've got the bits to try it out and will do in the future. For now I'm on the side of pinkmouse but with an open mind and will explore this at some point.

 

[pinkmouse]

Redundaliser, my badly worked example was purely to show the interaction of the cone and the box in terms of conservation of momentum. It does not deal with the internal pressures of the system, or panel resonances. It was meant to demonstrate, as SY spotted, that movement of the box, even in a frictionless ideal enviroment would cause minimal IM distortion, and that one part of this complex problem could be disregarded in the real world with friction, air pressure, etc. It was not meant to explain the whole issue, and if anyone can't see that, I apologise, I was obviously being too subtle.

 

[ScottG]

Do like Scott said and try it.

Actually I'm not even going that far for the general population.

To me its more a point of considering problems that are perhaps effectivly overlooked, and contemplating solutions.

Any solution may be eperimented with, but thats another step in the "process".

The point then is to keep an "open mind" so that experimentation (in a particular "avenue") is not "foreclosed" - especially if its effect would have signifigance to that person had it not been previously dismissed.

Of course to some though - the "try before you buy" experimentation is neccesary for them to admit a potential problem and solution (or conversly to find no problem in need of a solution). (..so its somewhat of a cyclical process for them.)

All of which is the "long-winded" version of my original closing remark:

"Well I hope that this has given you something to contemplate and perhaps incorporate in your next design."

 

[pinkmouse]

For some make-up points:

Assume a 1cm p-p displacement at 50 Hz with masses as in your example. There is a midrange mounted on the same enclosure. How much Doppler distortion will that 0.5% motion cause at 1kHz, with a 2mm p-p midrange displacement?

OK, well, here goes nothing!

First assumption, I believe we can ignore the relative frequencies, we are merely looking at the proportions of the displacement caused by the movement of the bass driver on the movement of the mid driver, the frequency would seem to be irrelevant as long the peak to peak movement of the mid is constant with frequency. Second assumption, I will ignore the flexibility of the mid suspension, which will act to dampen any movement of the mid range cone from induced external forces.

If the bass driver is moving 10mm, by Newton, we can show that the box is moving 0.05mm. With a mid range movement of 2mm, this gives a possible error range of 2.05 to 1.95mm in it's position, or 0.1mm. This is one part in 20, or 5 percent, (sorry, my 5 key is still not working, time for a new keyboard methinks!). Getting towards significant in a frictionless enviroment!

Will that do?

 

[Nemophyle]

Re: Re: Vibration.. ad nauseum

Hmm, correct me if I'm wrong - but vibration of wire in general (as an electrical conductor) was not the point of this thread. In fact if there was a "continum" here of most significant to least significant - wire would have to be at the very end of least significant.

that's because of the stupid site you quoted in your first post scott !

Some people say, they cannot hear the difference between two CD-players. Others can easily. Some can hear the difference of a coin put under one foot of the player. Even others can distinguish whether a piece of paper is put below an external DAC device.

short extract. I finally understood your post wasn't about that

Following up on vibration in wires... I know some Greek high-end designers who did some tests.

well if they are high end designers they are certainly not objective then

anyway, when i slap a cap of my amp, wether music is playing or not, i can't hear nothing, do you think i miss the golden ear ?

 

[Tenson]

High-end = not objective? mm.. maybe. They certainly design their equipment by the subjective sound but I guess you need to have good objective understanding to be able to tailor the sound the way you like it.

You slap your caps and then you can’t hear anything? I think you got electrocuted! If I slapped my cats I think I would hear it.

Anyway... I'm not saying you can hear the effect, I'm just saying it exists and so maybe it is not such nonsense that people want to avoid vibration in equipment. How about such effects inside a microchip?

 

[redunzelizer]

I think that its far too complicated for us to model casually. What about propagation delay of the vibration through the material? Not to mention that certain frequencies are boosted ....

Of course, I just wanted to show that any such oversimplified calulations lead to nowhere. Regarding the questions if any such parasitic effects should be allowed or dfeated - even if not at all theroretically covered, and hardest to measure, if ever - this is one's own desicion. In case you allow to produce artificial sound(s) by alltoomany other parts than the drivers, and in allto large quantities, you'll have to live with the involved problems and output. I won't.

Originally posted by ShinOBIWAN
Do like Scott said and try it.

Definitely no need to with me. I've done uncounted listening and measurement experiments with both tight(est) and loose(st) (un)coupling, adding lots of mass and what not for nearly two decades. Thus I've found my personal conclusions and preferences of speaker mounting issues long ago.

A small "excerpt" anyone?

Thou shalt not have other radiating devices than your drivers.
Thou shalt not neglect thy precious drivers by bad mounting.
Thou shalt not let any energies wander and echo.
Thou shalt not move thy cones at the wrong time.
Thou shalt not tune thy "sound" by mangling parasitic dissipation.
Thou shalt not and never claim any acoustical artifacts as quality.

Go continue, in case you want to, else never mind, It's just my way...

regards

 

[ScottG]

Re: Re: Re: Vibration.. ad nauseum

that's because of the stupid site you quoted in your first post scott !

Sorry.

Actually which one?
..there are a lot of people that would have a problem with both Positive Feedback AND Mother-of-Tone.

Oh.. and as a reference point - Lynn Olsen (the one I pulled the quote from) is every bit as much an "objectivist" as a "subjectivist" (..actually more of an objectivist). The point here is that he understands the vast complexity of audio reproduction and our reaction to it (both from an engineering standpoint and a psychoacoustic standpoint), and not only does not dismiss something that others would think is pure cr@p (i.e. the M-O-T site) - but would go so far as to embrace it for a point of experimentation.

Its all about perspective..

as a side-note to the M-O-T site.. here is a recent review (obviously subjective) by DO who has listened to a L O T of DA converters over the years (both poor in "measuring" and excellent in that respect)..

http://www.enjoythemusic.com/magazine/equipment/0506/zero_oversampling_dac.htm

 

[auplater]

Vibes... or not

Re: Vibration.. ad nauseum Post #23
quote:

Originally posted by auplater

Those insisting that vibrations in wires, transistors, working capacitors, etc. would paint a more convincing argument that effects are significant if they'd actually provide some sort of rational empirical (aka actual measurements) or at least an engineering evaluation of the magnitudes of said effects.


How about some actual MEASUREMENTS rather than speculation masquerading as fact and generalizations about what must be because it's intuitively obvious, etc...

auplater

__________
Scott G. wrote:

Hmm, correct me if I'm wrong - but vibration of wire in general (as an electrical conductor) was not the point of this thread. In fact if there was a "continum" here of most significant to least significant - wire would have to be at the very end of least significant.

__________

From your original post...

Scott G wrote:

OK then - exactly what am I getting at here?

That control of vibration is not "voodoo". Whether it is an electrical component "part" via chassis & heatsinks (which are coupled to other "parts" in some manner), active devices like tubes or semi-conductors, transformers/inductors, capacitors, resistors, and yes even wire/cables - control of vibration is important. Perhaps in these components, each "part" alteration is subtle, (..maybe even inaudible in double-blind testing), and yet the cumulative effect may be rather signifigant. Certainly as a component contains FEWER "parts", each alteration of vibration takes on a more significant character - becoming less subtle, perhaps to the point of signifigantly altering the sound (..in certain instances). (..and note that this is not to say other effects beyond vibration control are not effecting the sound.)
_________

So, since you mentioned wires and the like in support of your speaker vibes thread... it is in fact relevant to the discussion.

In case you didn't notice, I 'm more in agreement with your point of view than in disagreement... it's just much easier to discuss various aspects of engineering (yes that's what makes things work) if numbers are supplied to draw conclusions from.. rather than feelings and perceptions (which are valid, but only for the individual expressing them).

auplater

 

[ScottG]

Re: Vibes... or not

So, since you mentioned wires and the like in support of your speaker vibes thread... it is in fact relevant to the discussion.

auplater

I suppose in some respect it was intended to be support, but only very minimally - particularly with respect to wires. In other words it was intended to be a point of reference to effectivly say "hey - it is *really* important in loudspeakers".

Of course what I'm afraid of is the thread mutating into a discussion on wires and vibration, when there is a LOT to discuss here just with respect to loudspeakers.

 

[ShinOBIWAN]

Go continue, in case you want to, else never mind, It's just my way...

regards

Sounds good.

That's what this is all about; doing what we want and how we want.

I feel that Scott has he head screwed on tighter than virtually all the folks on here(it goes without saying but: me included) when it comes to audio. I've never seen subjectivity really get in the way of his arguments and most are of a technical nature.

I think that when he mentions something then it likely has value but what this means to the end user and how competantly they implement those suggestions are another thing altogether.

 

[ShinOBIWAN]

Re: Re: Vibes... or not

Of course what I'm afraid of is the thread mutating into a discussion on wires and vibration, when there is a LOT to discuss here just with respect to loudspeakers.

Face it Scott, its inevitable.

If a cable is mentioned in any audio related thread it quickly spirals out of control

 

[pinkmouse]

Good point Shin, from now on any cable related stuff will be split off.

 

[ShinOBIWAN]

OK, well, here goes nothing!

First assumption, I believe we can ignore the relative frequencies, we are merely looking at the proportions of the displacement caused by the movement of the bass driver on the movement of the mid driver, the frequency would seem to be irrelevant as long the peak to peak movement of the mid is constant with frequency. Second assumption, I will ignore the flexibility of the mid suspension, which will act to dampen any movement of the mid range cone from induced external forces.

If the bass driver is moving 10mm, by Newton, we can show that the box is moving 0.05mm. With a mid range movement of 2mm, this gives a possible error range of 2.05 to 1.95mm in it's position, or 0.1mm. This is one part in 20, or 5 percent, (sorry, my 5 key is still not working, time for a new keyboard methinks!). Getting towards significant in a frictionless enviroment!

Will that do?

Interesting figures Al. They certainly look correct if we're looking at a simple and easy to understand model.

If these do relate to Scotts original observations then clearly there's plenty to be discussed.

How much of a difference would the coupling to the additional mass of the floor create? Can we just include it in the mass of the cabinet calculation?