speaker stands?

[Dr. Parthipan]

OK. Buy a cheap wobbly lite weight speaker stand and get ready to pick your speaker up from the floor, with a ding or two.

Its simple physics. If the speaker is heavier than the stand it will be top heavy. The speaker should have a good substantial broad base also.

If the stand is light and unstable enough then as the cone is driven forwards, the speaker will move backwards. That is simple Newtonian physics, but I doubt you have heard of him.

No i havent heard of him but read what the previous poster wrote: Get an explanation how this happens. What is the threshold of movement that is audible with music in a listening room. Good luck.

Can you see he doesnt seem to agree with what you say?

Yes the cone motion creates a force but you will never see the speaker moving. So the question is what is the threshold of audibility for such movements? Is it significant?

 

[zhimbo]

That the speaker stand shouldn't be too lightweight I hope is common sense, if only for stability. If it is light and wobbly enough, it WILL counter the motion of the driver (basic physics cannot be overcome). If your stand is noticeably vibrating in response to the speaker, that can't be good.

No stand will *improve* a speaker. That's silly. It's possible (and at some point theoretical point, certain) that it can harm a speaker's sound. Whether that is a practical concern or not for a reasonably stable and solid stand, I don't know.

 

[shadyJ]

I can't see a plausible scenario where the stand's vibrating can cancel out the woofer's motion to an extent where it audibly affects the sound. I think you would have to have some serious excursion going on for that to even begin to crop up, and if that happens, you have bigger problems to worry about. The speaker would probably fall of the stand or tip it over.

 

[TLS Guy]

Its often reported that higher mass stands give you extra bass extension. Its not physically possible to lower the bass extension but it is perceived to happen and requires investigation as to what could cause such a perception. The stands often are fillable with sand too to experiment with the bass weight. This is different to the snake oil used to market audio cables.

Isaac Newton's (who you have never heard of) has a second law of motion. F(Force)= Mass X acceleration.

Now both force and acceleration are vectors. This is to say, that they have both magnitude AND direction. One can not exist independent of the other for a vector.

Now the acceleration forces on a speaker cone are very high and significant in a small bookshelf. The acceleration and therefore the force are highest when the cone is stationary between going from forward to backward and vice versa. So that is how the vibrations get caused. Vibrations mean loss of energy and that has to come from the loudspeaker cones energy. That means reduced output which will be frequency dependent. So the total mass of speaker and stand must be greater than the mass of the cone at least a 1000 fold preferably a lot more. So you do need a stable stand and the speaker needs to physically bond to the stand by friction or other means.

I get an example of this all the time. I have just come of the JD two cylinder in my Avitar. The tractor is two cylinder and the cylinders fire 180 degress in phase. As the pistons move to and for, the whole tractor visibly moves to and for. The tractor and loader weigh at least 7500 pounds. Yet two pistons, and they move horizontally and not vertically in these tractors, move the tractor visibly two and fro and yet the tractor is at least 3000 times heavier than the pistons.

It is the same with a speaker. People misjudge the force required to rapidly change the direction of even relatively light objects.

As an aside everyone should be familiar with Isaac Newton and know and understand his laws. That is just an essential fount of common knowledge. Yes, everyone should know this, there is no excuse not to.

 

[JerryLove]

Woofer cone = light
Speaker enclosure = heavy

If you had a speaker enclosure moving in complete sync with the bass driver; you can subtract the enclosure XMAX from the driver XMAX (actual movements, not theoretical maximums) to determine destructive interference.

I don't think it would be significant on the vast bulk of designs.

 

[twoeyedbob]

Why ..if the stability/rigidity of spkrs is so important...
why Have i never come across the suggestion they should be fixed to the floor...via stands if necessary..
In fact i mentioned wall swivel bracket's once ...
Very unsuitable...apparently

As an aside i recently made some stands ...definate improvement..although i'm sure the improved placement/height was 100% of it



Sent from my HTC Vision using Tapatalk 2

 

[TLS Guy]

Woofer cone = light
Speaker enclosure = heavy

If you had a speaker enclosure moving in complete sync with the bass driver; you can subtract the enclosure XMAX from the driver XMAX (actual movements, not theoretical maximums) to determine destructive interference.

I don't think it would be significant on the vast bulk of designs.

OK now you are forcing me to get technical.

The acceleration of a driver in Meters per second for a moving coil driver, is BL/moving mass in Kg.

So lets take a 6" woofer commonly used in bookshelf speakers, a Reveltor from Scanspeak.

a (acceleration in m/sec = BL/moving mass in Kg

a = 5.1/0.0054 which equals 944.44 m/sec.

From Newton's second law F + ma, we get 944.444 X 0.0054 which equals 5.1 Kg. So that is the force transmitted to a loudspeaker cabinet. Not a great deal of force for a large tower even with multiple drivers, but highly significant for a small bookshelf. That is the physics of it.

 

[Dr. Parthipan]

OK now you are forcing me to get technical.

The acceleration of a driver in Meters per second for a moving coil driver, is BL/moving mass in Kg.

So lets take a 6" woofer commonly used in bookshelf speakers, a Reveltor from Scanspeak.

a (acceleration in m/sec = BL/moving mass in Kg

a = 5.1/0.0054 which equals 944.44 m/sec.

From Newton's second law F + ma, we get 944.444 X 0.0054 which equals 5.1 Kg. So that is the force transmitted to a loudspeaker cabinet. Not a great deal of force for a large tower even with multiple drivers, but highly significant for a small bookshelf. That is the physics of it.

where have you taken into account the mass of the whole speaker in your calculations (which can only be a simplification by the way. I dont know how accurate your calculations are)? and what are the other symbols you are using? If you want to explain it, you had better do a good job of it or what is the point?

 

[PENG]

OK now you are forcing me to get technical.

The acceleration of a driver in Meters per second for a moving coil driver, is BL/moving mass in Kg.

So lets take a 6" woofer commonly used in bookshelf speakers, a Reveltor from Scanspeak.

a (acceleration in m/sec = BL/moving mass in Kg

a = 5.1/0.0054 which equals 944.44 m/sec.

From Newton's second law F + ma, we get 944.444 X 0.0054 which equals 5.1 Kg. So that is the force transmitted to a loudspeaker cabinet. Not a great deal of force for a large tower even with multiple drivers, but highly significant for a small bookshelf. That is the physics of it.

I am not going to check your math, the formula is correct but one slight correction to your units, accelaration is in m/sec/sec or m/sec^2. I am sure you know that and just forgot the one of the /sec.

 

[JerryLove]

OK now you are forcing me to get technical.

The acceleration of a driver in Meters per second for a moving coil driver, is BL/moving mass in Kg.

So lets take a 6" woofer commonly used in bookshelf speakers, a Reveltor from Scanspeak.

a (acceleration in m/sec = BL/moving mass in Kg

a = 5.1/0.0054 which equals 944.44 m/sec.

From Newton's second law F + ma, we get 944.444 X 0.0054 which equals 5.1 Kg. So that is the force transmitted to a loudspeaker cabinet. Not a great deal of force for a large tower even with multiple drivers, but highly significant for a small bookshelf. That is the physics of it.

And a 5.1kg push applied to (let's say) a 5.1kg speaker enclosure for 0.05 seconds will, in that 0.05 seconds move it how far? (enclosure XMAX).

If you want a simpler question: Given an equal force applied: What's the resulting speed difference between a 5.1kg mass and a 0.0054kg mass (this would be Newton's third law)?

Fa = -Fb
5.1 = 5.1 * a^2
a=1

So the 944.44 m/sec speed of the cone is offset by the 1m/sec speed of the 5.1kg enclosure.
assuming instant acceleration: your cone moved 44m @20hz and ..

Wait. We have a problem somewhere. Cones don't move 44m. How long did our cone take to get to its XMAX? Wasn't 0.05 seconds it seems. Crud.

All right: let's run this backwards. Let's assume the cone moved 0.044m (it's really the ratio we care about anyway), that would be 0.00005sec.
In that case: the cabinet moved 0.00005m.

So the net impact on the cone is that, instead of moving 0.04400m (as it would if the cabinet was braced), it move 0,04395m, costing it some volume.
Wanna compute how much?

 

[mtrycrafts]

..
In that case: the cabinet moved 0.00005m.

..?

You mean it moved less than a mm???

 

[shadyJ]

My contribution to the argument of the physics of speaker stands:

 

[Dr. Parthipan]

You mean it moved less than a mm???

yep. For every cone excursion. But over time it accumulates.

 

[JerryLove]

yep. For every cone excursion. But over time it accumulates.

I gotta know how you came to that conclusion.

 

[Dr. Parthipan]

I gotta know how you came to that conclusion.

well you calculated that figure for each cone excursion no? So more cone excursions means more distance moved on average.

 

[Steve81]

well you calculated that figure for each cone excursion no? So more cone excursions means more distance moved on average.

OTOH, the cone moves in both directions.

 

[JerryLove]

well you calculated that figure for each cone excursion no? So more cone excursions means more distance moved on average.

No.

Average would, in fact, be 0, because there's a negative vector for every positive vector. Sum would also be 0 (again, negative vectors cancelling positive ones) Absolute average (average of the absolute value of each movement) would be 0.00005m.

If you actually created a positive only sum for some reason (and I cannot think of a good one); you'd also have to sum the cone excursions the same way... so again it would cancel out.

The effect of our hypothetical is that an immobile speaker with a 0.04400m cone movement per peak would, with no coupling to a solid object, experience 0.04395m cone movement per peak instead.

 

[mjcmt]

I personally find a good high mass stand makes an improvement to a good quality monitor speaker. Better soundstage presentation, tighter bass and better dynamics.

 

[j_garcia]

I personally find a good high mass stand makes an improvement to a good quality monitor speaker. Better soundstage presentation, tighter bass and better dynamics.

Perhaps you haven't read the rest of the thread? The only alteration a stand can cause is a coloration IMHO. In no instance will it improve anything about the speaker. Ideally a stand ADDS NOTHING to the speaker, because the idea is to let the speaker do its job. A higher mass stand will do this better than one that does not properly manage resonance, but that would mean little more than selecting a stand that does its job as well. That resonance can easily be remedied by decoupling the speaker from the stand while the stand is coupled to the floor to provide proper stability for the speaker. I don't think it will take math to explain why that works.

Why ..if the stability/rigidity of spkrs is so important...
why Have i never come across the suggestion they should be fixed to the floor...via stands if necessary..
In fact i mentioned wall swivel bracket's once ...
Very unsuitable...apparently

As an aside i recently made some stands ...definate improvement..although i'm sure the improved placement/height was 100% of it

Speakers can be coupled or decoupled. Coupled would mean directly supported by whatever it is contacting and also directly transmitting vibration. Decoupled would mean isolated by some method (vibration damping material, hanging by string/chain, etc...) It depends on the speaker in question how each method will affect the sound of that speaker. I am of the opinion that decent speakers are better off decoupled - allowing them to sound exactly how they were designed, not vibrating another object along with them, which adds a new set of resonances and alters what you hear. My main stands weigh 26lbs each with no fill and they resonate when the speaker is directly placed on them. My speakers are 38lbs each and very solid; they aren't going to be moving around.

The reason you want a solid speaker cabinet is because the cabinet itself will resonate and color the sound. A solid cabinet does that a lot less, allowing you to hear the drivers not the cabinet.