[andyr]

OK, you engineers, speaker mfrs and general "Lab Forum" gurus ... I'd like to know if speaker stands are supposed to do more than just raise the box off the floor (so that the tweeter is roughly the same height as your ears when you're sitting in your favourite listening chair)?   

Now obviously - well, to me anyway - apart from raising the tweeter, the stand is supposed to hold the speaker cabinet fairly rigid, positional-wise ... so it doesn't rock backwards when the driver wants to move forwards suddenly. 

But, for instance, is the stand supposed to provide a path to drain the inevitable cabinet vibrations down and out to the floor?     If so, it seems to me this could be a problem if your listening room has a suspended wooden floor!    Yet if you had a concrete slab, this might be a good thing!   

Regards,

Andy

[bgewaudio]

No secondary function at all!  raising the speaker to optimum listening height is really the only purpose for a stand.  It is all of the sonic discrepancies that they introduce while elevating it that forces us to make critical decisions on what materials to use and what way to implement them.

As for the statement about pathing vibrations to the floor, this is not ideal either.  Also known as the "footfall" effect, these vibrations will travel up you equipment rack and into your components causing resonance.

The only thing that would help this would be to maybe install some acoustic fibre under the floor to help damp floor vibrations, other than that not to much.  Probably why isolation products were introduced?

[andyr]

No secondary function at all!  raising the speaker to optimum listening height is really the only purpose for a stand.  It is all of the sonic discrepancies that they introduce while elevating it that forces us to make critical decisions on what materials to use and what way to implement them.

Hi bgewaudio,

I don't actually have any problem with floor vibrations but I posted because of an experiment I did recently.

I had some new speaker stands made up for some small 2-ways (9" x 11" x 13").   

These 2-ways used to sit on fairly conventional, 2' high stands ... a small top plate under the speaker, a larger bottom plate (with spikes) and 2 rectangular steel tubes about 1" x 2", filled with lead shot.

The floor of this room is suspended sheet flooring.

I had the new speaker stands made up from aluminium. These consist of:
* a 1/4" top plate, the same size as the steel one in the other stands
* 4 splayed, tubular legs (1" diam, 1/8" thick walls) with spikes on the end. The tubes are filled with a lightweight damping material (oil-absorbant clay granules - bentonite) and the spikes form a square about 2' a side.

With the original (steel/lead shot) stands, I could feel the floor vibrating with heavy bass transients when standing next to the speakers. I believe this is because the massive lead-filled steel tubes form a nice sonic transmission path for speaker cabinet vibrations to get to the floor.

With the new aluminium stands, the floor vibrates considerably less. It still certainly vibrates but it's less ... so it would seem these stands do not provide a transmission path for the cabinet vibrations?   

So which is better?  Some people might say of the original steel stands "great, the stands are draining the cabinet vibrations away"!! ) However, another way of looking at this is to say the stands are exciting the floor - so we now have a much larger panel area vibrating!!   

IMO, this cannot be a good thing ... so I believe "light & stiff" (ie. aluminium and a lightweight damping filler such as bentonite granules) is a better solution than "heavy" (ie. steel/lead shot or sand), as it excites the floor less.  But this means it is perhaps not draining away cabinet vibrations as well as the original stands?   

So I was interested to hear what others thought ... hence my question about potential secondary function of stands - are they supposed to drain away cabinet vibrations?

Regards,

Andy

[DSK]

Andy, if you are right that there is energy disappearing between the speakers and the floor, I would imagine that it is due to two things. Firstly, due to greater flex of the aluminium. Secondly, due to more efficient damping (aluminium will resonate at a higher frequency than steel and this is easier to damp). This last reason is why "light & stiff" equipment racks are preferred by many people ... they are easier to excite but will resonate at a higher frequency and lower amplitude and are easier to damp.

[andyr]

Andy, if you are right that there is energy disappearing between the speakers and the floor, I would imagine that it is due to two things. Firstly, due to greater flex of the aluminium. Secondly, due to more efficient damping (aluminium will resonate at a higher frequency than steel and this is easier to damp). This last reason is why "light & stiff" equipment racks are preferred by many people ... they are easier to excite but will resonate at a higher frequency and lower amplitude and are easier to damp.

Hi Darren,

I hadn't thought of it as "energy disappearing between the speaker and the floor" ... I had feared that perhaps the vibration energy was staying in the cabinet (since it wasn't appearing in the floor!  ).  However, feeling the legs, I noticed they were vibrating a bit (but I never felt the steel tubes in the old stands, so I can't compare).  So maybe you are right in the sense that the stand still draws out vibrations from the cabinet but vibrating legs, by themselves, produce less sonic damage than a vibrating floor?   

BTW, aluminium is stiffer than steel!  So if the ally legs were the same length as the steel ones, they would flex less ... but because they're splayed, they're longer and so may flex more.   

Regards,

Andy

[DSK]

BTW, aluminium is stiffer than steel!  So if the ally legs were the same length as the steel ones, they would flex less ... but because they're splayed, they're longer and so may flex more.

Andy, it is the other way around. Steel has greater stiffness than aluminium which is relatively flexible.

[Russell Dawkins]

If I'm picturing these stands properly, it sounds like the significant difference is the geometry, more than the materials used.
If the new stands couple through spikes into the floor at points 2 feet apart, then the base is wider, deeper and thus more rigid than the typical stand.

In the typical scenario the fore and aft speaker enclosure movements which are the reaction to the bass drivers' action are fairly tightly coupled to the stand top plate. This rocking motion results in a largely vertical input into the floor (let's assume it is wood) within a small area of maybe one foot square.

The relatively unfavourable leverage relationship resulting from the height of the stand vs the short distance between the front and rear floor spikes combined with the relatively lossy coupling of floor to stand, even with brass cups under the spikes results in a speaker box not held very rigidly in space and a floor (as tympanum) being excited from what can be considered one point. This has a lot in common with the way the bridge vibrates the top on a typical steel string guitar. The varying tension of the vibrating strings results in a rocking force being transmitted from the bridge to the top.

Contrast this with the second stand. The splayed legs form an inherently more rigid support system. The energy is introduced into the floor at 4 widely separated points and not vertically, but maybe 30º off vertical. This is a better recipe. The floor is more rigid to tangential forces than right angle forces.

I have long felt that the single best way a small stand mounted speaker (or floor stander, and especially planar) could be improved, aesthetics and room placement permitting, would be to brace the stand to the nearest floor/wall junction by almost any means - a broom handle would be functionally sufficient because the energy is flowing in compression and tension. Slim sticks of wood are plenty strong in tension and compression. I say floor/wall junction because these are often available behind speaker stands at about the right distance and this is the most rigid surface in the average room.

Getting back to your stands I think the reason the floor vibrates less is mainly that 1/4 the energy of this rocking is entering the floor down each leg over an area of 4 square feet vs the 1 square foot of the other arrangement. This plus the aforementioned advantage of the greater angle of the legs.
I think you would feel the same effect even if the legs were the same steel filled with lead shot.

You didn't mention the sonic effects of the new stands compared to the old. Were there any?

[Kevin Haskins]

They are just there to raise the speaker to the correct height. 

You want them dead so sand-filled columns work well.    I suppose MDF filled with sand would be preferable to metal but like many overkill techniques of doing something you enter the land of seriously diminishing returns and its easy to let your imagination take the lead.

One important area is the interface between the cabinet and the stand.   I prefer rubber mounts that are designed to absorb shock/vibration for the given weight of the loudspeaker.   I use industrial motor mounts that are designed for the purpose.   You can find them at McMaster Carr.

[bgewaudio]

I also think solid wood stands would be superior to metal because sound travels faster through metal than wood and metal would resonate at a higher frequency the would be (according to the Fletcher Munson Curve) more detectable by the human ear.

However, the stands I am using for my B&W 805s are similar to the ones you have, top and bottom metal plates and 2 parallel rectangular tubes down the middle.  I have filled these with 00 silica sand, given the finer qualities of this sand it allows me to maintain the mass to volume ratio resulting in less resistance to tipping and better sound dampening qualities.  Having implemented this my stands are virtually resonant free, the speaker also helps with this as well given it's extensive Matrix Bracing System.

[PhilNYC]

Andy, it is the other way around. Steel has greater stiffness than aluminium which is relatively flexible.

Is this true?  Coming from a mountain biking background, I can remember the days when aluminum bike frames were becoming all the rage.  The first time I rode one (back in the days of rigid forks, not a suspension fork), I remember my arms and knees feeling incredibly beaten-up on a ride that I had done a million times on my steel bike with no problem...and that the aluminum frame was incredibly stiff relative to my steel bike.  So my impression has always been that aluminum was stiffer than steel.

[tianguis]

Phil:

       You might also remember that the cross section of the aluminum tubes used was much larger than the steel tubes. The overall result was a stiffer frame.
And, yeah, they did tend to beat one up more.

Larry

[DSK]

Is this true? 

Sure is. Just do a quick Google on '+aluminium, +steel, +stiffness' and you won't even have to read the articles ... the first sentence in each site listed says steel is stiffer than aluminium. It's probably also why we use steel girders in buildings and bridges, not aluminium ones.

EDIT: Here is a blurb specific to bikes, that says ... "Compared to other metals steel is very stiff, far more so than Aluminium or Titanium," http://www.bretonbikes.com/stee.htm

[DSK]

I also think solid wood stands would be superior to metal because sound travels faster through metal than wood and metal would resonate at a higher frequency the would be (according to the Fletcher Munson Curve) more detectable by the human ear.

The point of raising the natural resonance as high as possible (as in light & rigid racks) is that higher frequency resonances are far easier to damp and remove (not just shift in frequency).

...it allows me to maintain the mass to volume ratio resulting in less resistance to tipping and better sound dampening qualities.  ...

I hope you mean MORE resistance to tipping, I'd hate to see your speakers come crashing to the floor!

[andyr]

Thank you all for your responses.  Many have raise Qs in my mind so perhaps I could list these and beg your indulgence to take the time to respond.

bgewaudio ... OK, I agree the essential purpose of a stand is to raise a speaker to the appropriate height - and, Russell pointed out, keep it rock steady - and that the properties of various potential stand materials make them a crucial decision.   

However, is it a good thing to drain away cabinet vibrations?     I would agree with you that if you have a wooden floor, you do not want it to vibrate (so draining away cabinet vibrations is not desirable) but if you have a massive, ground-floor slab then the same level of vibration frequency (in the 50-500Hz region?) that would excite a suspended sheet floor would not do anything to the slab ... so if the stands can drain away cabinet vibrations, this should be doing some good?   

And I've commented below about sand vs. lead shot.  If you're interested in "maintaining the mass-to-volume ratio", using lead shot would increase this ... or lead shot in the bottom half of the tube and sand in the top half, for further stability and sound damping.

DSK ... thanks, my mistake!  Now I've read up about Young's modulus in Wikipedia, I realise steel is about 3 times as stiff as steel!    

Russell ... yes, you pictured my stands correctly!     I can see that the different geometry probably was the main factor in causing the floor to vibrate less.  However, if we assume the legs of a steel stand which was made up the same way as my ally ones (the legs being filled with lead shot) would vibrate less than my ally legs ... is this a good thing or not?

IE. is the fact that the legs of my ally stands are vibrating (but the floor doesn't) a problem?

And re. your point about stand mounting planars ... see here for a picture of my MG IIIa stands:
http://www.audiocircle.com/gallery/displayimage.php?&pos=-5562   

Kevin ... I agree you want the stands as dead as possible but I suggest there are two philosophies of achieving this:

1.  as DSK has pointed out, "light & stiff".
2.  the other is mass-loading.

The reason for filling steel tube with sand or lead shot is to dampen it - otherwise the steel tube would ring when excited by particular frequencies.  However, I believe the only thing that sand or lead shot does is increase the mass of the tube ... so this increased mass is excited less (compared to a lighter, unfilled tube).  To my simple mind, this is "damping by secondary means" (adding mass) - whereas wrapping the tube with something like Dynamat Extreme is "damping by primary means" (forming a CLD structure).

I did an experiment filling lengths of steel tube with different substances (lead shot, sand, mortar and expanding polyfoam) - and I invite anyone to try this out themselves.  Lead shot gave by far the greatest damping when I struck these steel tubes with a hammer ... ie. the resulting sound was significantly less.  But I admit, I didn't try any Dynamat Extreme!   

Therefore, as lead shot is so much heavier than the same volume of sand - however small its particle size - I suggest "anything sand can do, lead can dooo better!"     So using sand to fill tubing is a compromise chosen by people who fear using lead.

And I'm afraid I don't agree with you that the interface between the cabinet and the stand should be flexible.  IMO, the cabinet should be fixed to the stand, so it doesn't move backwards when the driver moves forward; your industrial motor mounts will not do this.

The easiest way of doing this is using a small ball of Bostik "BlueTac" under each corner, which is compressed into a pancake about 1" in diameter when the speaker is pressed down onto it.  If you're worried about seismic vibration coming up through your speaker stands and into the cabinets, where they interfere with the action of the drivers ... that's a completely different problem which needs a completely different method of solution.

Regards,

Andy

[DSK]

The reason for filling steel tube with sand or lead shot is to dampen it - otherwise the steel tube would ring when excited by particular frequencies. 

Correct!

However, I believe the only thing that sand or lead shot does is increase the mass of the tube ... so this increased mass is excited less (compared to a lighter, unfilled tube).  To my simple mind, this is "damping by secondary means" (adding mass) - whereas wrapping the tube with something like Dynamat Extreme is "damping by primary means" (forming a CLD structure).

I'm not an expert in this field but my understanding is that every object has its own 'natural resonance frequency' that will depend upon its material, dimensions and density. For example, a piece of MDF will have a lower natural resonant frequency than a smaller piece of MDF. Likewise, a higher density piece of MDF will have a lower resonant frequency than a piece of MDF of the same size but lower density. Materials with lower resonant frequencies are more difficult to set resonating but are also more difficult to stop resonating (like inertia of a heavier object). Typically, the thicker the substrate, the thicker the damping layer needs to be to have any effect.

The two methods you mention (Dynamat & lead shot) will both damp resonance by transferring energy to heat. I would imagine that in the case of lead shot filled stands, the minute resonance waves sent through the stand legs would be trying to physically move the lead shot particles that rest against their surfaces, so some resonant energy may be being transferred into 'work' as well.

Perhaps someone with a science background can confirm or correct this?

[andyr]

The two methods you mention (Dynamat & lead shot) will both damp resonance by transferring energy to heat. I would imagine that in the case of lead shot filled stands, the minute resonance waves sent through the stand legs would be trying to physically move the lead shot particles that rest against their surfaces, so some resonant energy may be being transferred into 'work' as well.

Hi Darren,

That's verry inneresting ... I'd actually never considered that the lead shot inside the tube, as well as adding weight (mass!), would actually damp because the walls of the tube, when vibrating, would press the outermost layers of shot - which are in contact with the walls - against the inner layers.  And hence would transfer resonant energy into heat!   

But the nub of the problem remains ... is the best arrangement for speaker stands lightweight ally legs (with some lightweight damping material) or heavy, shot-filled steel legs?   

Which transfers less vibration to the floor?
Which damps (transfers?) the inevitable cabinet vibrations better?
Is the fact that the stand legs might vibrate, an issue?

Are there any other considerations?

Regards,

Andy

[DSK]

Is the fact that the stand legs might vibrate, an issue?

Unless you implement isolation techniques to prevent energy reaching the stand legs, they will certainly resonate. It is just a case of damping this resonance as efficiently as possible.

The constrained layer damping technique (CLD) you mentioned earlier is appropriate when trying to isolate one material from another (eg. layers within a platform for a component) with a lossy layer and works best when there is no rigid connection between the layers (eg screws) that provide a bypass for the resonance. CLD is also useful to damp resonance in large metal panels. With speaker stands, the top plate, legs, bottom plate are all rigidly coupled (welded) together. So, my understanding is that you are better off using the traditional method of lead shot, sand, kitty litter, or a combination thereof. If you do this, strike the legs with a hard object and hear no rrrriinnngggg after the sound of the initial strike, then I think that is about the best you can do. If the speakers are rigidly coupled to the stands and the stands are rigidly coupled to the floor, then it is likely that your floor (and the neighbour's floor if joined dwellings) will still vibrate. The only way to minimise this is to adopt isolation somewhere in the path. An example of this is the cork/rubber pads used under some heavy industrial equipment.

[bgewaudio]

if you have a massive, ground-floor slab then the same level of vibration frequency (in the 50-500Hz region?) that would excite a suspended sheet floor would not do anything to the slab ... so if the stands can drain away cabinet vibrations, this should be doing some good?   

Yes I would agree.....If you have a rigid floor such as concrete, coupling would be beneficial, and if you're working with a floating or wood floor, decoupling would be the best option.

Happy listening!

 

[PhilNYC]

Phil:

       You might also remember that the cross section of the aluminum tubes used was much larger than the steel tubes. The overall result was a stiffer frame.
And, yeah, they did tend to beat one up more.

Larry

That would explain it...!