Bertiebee

Isolation on the cheap

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Super Dealer

I don’t expect you to believe me, write to these people,

http://www.speirsrobertson.co.uk/microscope-platforms-and-tables/2-active-air-isolation-tables.html

Speirs make isolation devices for laboratories ,universities, these products have to work.

Keith

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40 minutes ago, PuritéAudio said:

I don’t expect you to believe me, write to these people,

http://www.speirsrobertson.co.uk/microscope-platforms-and-tables/2-active-air-isolation-tables.html

Speirs make isolation devices for laboratories ,universities, these products have to work.

Keith

What does that tell anyone about whether isolation/damping under a speaker may be of benefit or not? I've used pneumatic isolation tables in a lab setting for ultrasonic measurements but short of knowing that they 'work' I don't really think this is particularly relevant here.

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1 hour ago, PuritéAudio said:

Bless, have you been reading those marketing brochures again...

Keith

Guess this paper must be invalid!?! (even though it is not for hifi speakers per se, but about reducing the effect of vibration on a speaker cone in a TV enclosure.... it should, by extension, apply to ANY speaker cone in ANY enclosure)...

http://www.j-mst.org/On_line/admin/files/08-J2011-1240-2003.pdf

Let's discuss this with suitable studies we can find. This doesn't seem to be a well studied area from a brief trawl on Google Scholar. 

2 hours ago, PuritéAudio said:

Unless the speakers are creating an audible resonance there is no need to isolate

My view on the above statement...

It assumes that only resonance induced distortion is needed to be dealt with via isolation, when vibration induced distortion doesn't have to be resonant.

My view of the study above is that it shows that vibration affects the velocity (and by extension the air displacement) of cone movement, which is therefore going to have an effect on the accuracy of reproduction of certain frequencies if the required cone velocity cannot be accurately obtained due to the influence of vibrational energy.

No marketing blurb was used to reach this viewpoint.

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Super Dealer
7 minutes ago, MartinC said:

What does that tell anyone about whether isolation/damping under a speaker may be of benefit or not? I've used pneumatic isolation tables in a lab setting for ultrasonic measurements but short of knowing that they 'work' I don't really think this is particularly relevant here.

Isolation may be beneficial under a loudspeaker, if that loudspeaker is creating an audible structural borne resonance , or if the resonance is being propagated to a neightbour for example.

Speirs engineers visited here some years back and took some measurements using a three plane accelerometer we discussed loudspeaker isolation , I have some photographs somewhere, it was interesting.

Keith

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24 minutes ago, PuritéAudio said:

Isolation may be beneficial under a loudspeaker, if that loudspeaker is creating an audible structural borne resonance , or if the resonance is being propagated to a neightbour for example.

This re-iterates my concern about thinking that only vibration causing resonance is an issue, where I said...

34 minutes ago, Metatron said:

It assumes that only resonance induced distortion is needed to be dealt with via isolation, when vibration induced distortion doesn't have to be resonant.

And...

26 minutes ago, PuritéAudio said:

Speirs engineers visited here some years back and took some measurements using a three plane accelerometer we discussed loudspeaker isolation

Yes, that measures the vibration of a cabinet/enclosure, not whether energy has been transmitted back to a cone and damped its velocity. This is a very key difference.

I'm afraid to say that they only measured cabinet resonances, not whether vibration of the entire cabinet is affecting the cone. It also isn't testing if the pistonic action of a cone causing energy transfer to the cabinet, then stand, to floor and reflected back up is affecting the cone.

If you are suggesting that if a cabinet has a acoustic resonance that stands won't help, then I am with you. But if the momentum energy transferred to a stand is transmitted to and reflected off the floor and back into the cabinet, that's a different issue.

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Super Dealer

You have to trust that the loudspeaker’s designer has  made an enclosure which does not store energy that  leads to  audible resonance, isolation will not cure this, stored energy will not be magically drained away.

Keith

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23 minutes ago, PuritéAudio said:

You have to trust that the loudspeaker’s designer has  made an enclosure which does not store energy that  leads to  audible resonance, isolation will not cure this, stored energy will not be magically drained away.

Keith

Most 'isolation' will in practice add some damping as well.

What did the Spiers engineers measure when they visited and what were the results?

(BTW I don't have a strong view either way on the usefulness of isolation/damping under loudspeakers.)

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2 minutes ago, PuritéAudio said:

You have to trust that the loudspeaker’s designer has  made an enclosure which does not store energy 

We cannot trust that at all, because it is not possible.

Even if we assume a cabinet cannot store energy, it implies it instantly disposes of energy applied to it.. that is, it converts the applied energy to another form instantly (e.g. kinetic energy, heat energy, or some other form). The energy applied is kinetic via the driver. If it becomes potential, it is 'stored', if it remains kinetic, it transmits to whatever it is coupled with.

A perfect speaker cabinet should perform two conflicting goals for it to NOT store energy or flex/vibrate: 1) infinite stiffness 2) infinite damping

Only if it can succeed on those two ideals will it not store energy or be subject to vibration. It's physically impossible to fulfill either, let alone both. That part is understood and communicated in books on speaker building. 

What follows is my understanding from the physics involved, but I could be wrong...

As noted in the study, a degree of combining rigid (stiff) materials with soft (damping) materials is required to get a good amount of isolation from vibration. This is isolating the cone/cabinet from vibration effects. Since most speaker cone baskets are coupled to the stiff exterior cabinet, there is an inherent problem of energy transfer between them. How bad that is, is mostly down to the momentum of the pistonic action and the relative mass (mass ratio) of driver to cabinet. When a magnet moves a driver in one direction, there is an equal and opposite force applied along the pole piece anchored to the basket, anchored to the cabinet, hence applied to the cabinet. It's inescapable.

So energy the driver applies is not exclusively to the cone, but also to the cabinet. If the cabinet is coupled too harshly to a stand, energy will transfer through the stand and reflect from the ground back up and potentially re-enter the cabinet (delayed) and ultimately back to the moving component - the cone - albeit damped via the cone rubber surround. I believe you somewhat understand this aspect as it's why you've mentioned spiked feet not being ideal in the past. Anyway, this energy reflection affects the cones ability, even marginally, but may be exacerbated at some frequencies. How audible it is depends on the speaker, the masses involved (especially driver to cabinet relative masses due to F=ma, so a heavy cabinet is preferable), the springiness of the cone suspension, the strength of the magnet and the type of coupling between the cabinet base and the stand/floor.

One might think that the physics suggest that a tweeter will be unaffected as they produce negligible energy with which to affect a cabinet, but in audio playback we still have the bass driver movement creating significant vibration, which if transmitted through the structure to floor and reflected, will affect all drivers to some degree. Naturally, the magnitude of a bass vibration containing much energy will affect a tweeter more relative to the other drivers, because while they share applied force of a vibration equally, the light tweeter will undergo more velocity change (acceleration) due to F=ma.

Happy to look at a proper targeted study that refutes the need to consider damping/isolating a speaker from vibration effects.

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3 hours ago, PuritéAudio said:

Bless, have you been reading those marketing brochures again...

Keith

Never.  Nor do I want DSP as a cure for everything.  Or anything, actually. :roll:

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