Hi Ethan
I'd have to take exception to that opinion. A lot of energy from a driver can be transferred into the enclosure. We've known that for a long time. But the solution is not to isolate the driver from the enclosure, that's a mistake, the driver wants to be rigid in space to radiate as it was intended. What needs to happen is to dampen the enclosure to dissipate the small amount of mechanical energy transferred to it from the driver as well as the acoustic source from the back radiation. This has been my solution for years and it works quite well. Structural damping of the enclosure can be tedious but worth the effort.
As far as I can tell, I'm the only person here who has actually tested this stuff. I see a lot of speculation, and comments like "We've known this for a long time," but no actual data. While you work out your plans to devises a suitable test to post here, this video is yet more evidence that common competent speaker cabinets do not vibrate and thus have nothing Ito transfer to the surface they rest on:
A solid demonstration that speaker panels don't resonate at 38 Hz.
Last edited:
You absolutely need to patent a speaker enclosure that doesn't vibrate. I'm relying on my vibration meter! Could the glass be in the wrong place?
If you don't understand the relevant physics how can you know what stuff needs to be tested? Following the scientific method is likely to be helpful because the process of formulating a hypothesis to predict what is going on and hence what needs to be measured to refute/support it can often reveal that one's understanding isn't quite sufficient to do it.
That's a pretty silly response, no? Apparently you believe you know "the relevant physics" involved, so you can devise a test that proves whatever it is you believe needs proving. I'll be glad to see your results.
Just put an accelerometer on a panel. The glass of water test is a very poor one. It doesn't take much vibration displacement to radiate sound. I have done these tests myself before, but I am not about to go dig up any data. I am sure that there will be data somewhere on the web.
And yes David, everything resonants somewhere. It's damping that dissipates that energy.
And yes David, everything resonants somewhere. It's damping that dissipates that energy.
It has drawn this typical response from you avoiding the topic being discussed, let readers know that your pontificating is not based on scientfic/technical reasoning (or at least suggested it for those that lack the technical knowledge to see it directly) and indicated how they might go about resolving matters for themselves using what they were taught at school. I would hope that was a useful rather than silly contribution to the thread.
As a general statement that might be unwise. Consider a subwoofer in a relatively light cabinet that moves around on the floor when playing loudly. Would decoupling be a better solution than placing something heavy on top of it or adding grippy feet?
There are a number of physical processes involved with loudspeaker drivers in a cabinet in a room and whether passive isolation is beneficial, harmful or irrelevant will depend on the masses, stiffnesses and damping involved.
The soundpressure inside the enclosure translates to the order of tens of Pascals, i would think nowhere near enough to deform the enclosure to an extend where it starts to radiate meaningful SPL. Unless of course it tries to do so near an eigenfrequency of the structure, of which there are plenty in all enclosures. I believe this is why no vibration happens at ie. 38Hz, but i bet you there are SPL-producing vibrations in the 500-800Hz area.
Regarding stands i'm curious myself, but have always landed on damping rather than isolation, I just use rubber feet with the lowest Shore-value i can get away with. This way i get decent isolation where the enclosure resonates, and limit any resonation of the suspension system due to the damping of the rubber. A fully isolated tower speaker would be difficult to manage because of the bending moment caused by the height. I will try to do some simulation on it.
Eigenfrequencies of 19mm MDF enclosure 1200x350x240mm:
Regarding stands i'm curious myself, but have always landed on damping rather than isolation, I just use rubber feet with the lowest Shore-value i can get away with. This way i get decent isolation where the enclosure resonates, and limit any resonation of the suspension system due to the damping of the rubber. A fully isolated tower speaker would be difficult to manage because of the bending moment caused by the height. I will try to do some simulation on it.
Eigenfrequencies of 19mm MDF enclosure 1200x350x240mm:
Last edited:
Except at low frequencies the forcing from the internal air is likely to be negligible compared to that from the drivers hammering away on the cabinet and is often ignored because the resonances which might be loud enough to be audible are at higher frequencies. Including the internal air pressure in a simulation isn't straightforward because both the background thermodynamic component of pressure as well as the acoustic component needs to be handled particularly for small sealed cabinets. This means a low Mach number compressible CFD scheme or perhaps a high Mach number compressible CFD scheme and putting up with computational inefficiency and dodgy speed of sound. This adds a lot of complexity for little gain beyond providing evidence that internal air pressure isn't important to the resonances. It might be of interest in checking how much the walls of a small sealed cabinet deflect and how that influences the cone movement but that could likely be done well enough with a simple lumped model.
I call the vibrations from the speaker cabinet that travel into the floor structure-borne sound. Bending waves and other wave types. Structure-borne sound disrupts all electronics. I find sylomer very effective for reducing this, both for speakers and electronics. Regards
Are you modelling the drivers given they typically have a strong influence on the most problematic modes. I assume you intend to use the surface displacements for an acoustic BEM simulation? What damping models are available because these are likely to determine the accuracy achievable in simulating vibration.
If you are using simulia remotely it would be useful to have a rough idea of cost in terms of time and money for the full set of simulations in order to compare with alternatives such as grinding away with freely available software (hard work, time consuming and with important bits missing) or locally run CAE packages (straightforward but prohibitively expensive for DIYers).
You are right Andy, the mechanical force from the cone moving transfering to the cabinet would be a significant contributor to exciting modes. Probably way more than air pressure. Thanks! At this point i don't know how to include that in the modeling.
My original idea was to run a steady state modal dynamic with an equivalent pressure on the walls, but this won't take what you mentioned into account. I just finished a class on Abaqus, but will have access to running simulations remotely for another year. This topic was not covered in the class, so im learning as i go.
My original idea was to run a steady state modal dynamic with an equivalent pressure on the walls, but this won't take what you mentioned into account. I just finished a class on Abaqus, but will have access to running simulations remotely for another year. This topic was not covered in the class, so im learning as i go.
I have never seen any test with identicaly sized enclosures, braced and without any bracing, maybe different materials or thickness with logical measurements. This would have been not that expensive, if someone really wanted it.
All these special constructions to made to make different materials resonate and record it, give to much discusable results and may seem to have no connection to reality for many.
I have done my own experiments, like identical subwoofer drivers, transfered from factory into hand build, braced cabinets. Then, a few builds of identical sub driver into different cabinets. I can say the results with subwoofers are impressive. If anyone still cares about sound, of course.
Anyway, as I don't have any doubtless mesurements and see no win for me to buy expensive gear, it is only an anecdote. Publishing own measurements in deeple controversal, nearly religious technical themes, is also a masochistic habbit. So I build my stuff to a price/ result ratio that my own experience, measurements and wide study of any information available dictate.
I see a problem with most people putting their focal point on the region they are most fluent with. The computer simulation guys, which I deeply appreciate, may completely miss some other factors in speaker building that count.
In the end, the speaker has to perform, in a room, with music. So never expect a final result or plan for an optimum from just one side of science. In fact, I see many that may build less perfect than possible constructions, just because they want the most expensive, exotic or unusual material or the stuff they know or get at best price for some reason.
Personaly, today I take ecological points into consideration. I recycle old furniture for panels and don't use toxic materials (like sheet lead) if I can avoid them.
All these special constructions to made to make different materials resonate and record it, give to much discusable results and may seem to have no connection to reality for many.
I have done my own experiments, like identical subwoofer drivers, transfered from factory into hand build, braced cabinets. Then, a few builds of identical sub driver into different cabinets. I can say the results with subwoofers are impressive. If anyone still cares about sound, of course.
Anyway, as I don't have any doubtless mesurements and see no win for me to buy expensive gear, it is only an anecdote. Publishing own measurements in deeple controversal, nearly religious technical themes, is also a masochistic habbit. So I build my stuff to a price/ result ratio that my own experience, measurements and wide study of any information available dictate.
I see a problem with most people putting their focal point on the region they are most fluent with. The computer simulation guys, which I deeply appreciate, may completely miss some other factors in speaker building that count.
In the end, the speaker has to perform, in a room, with music. So never expect a final result or plan for an optimum from just one side of science. In fact, I see many that may build less perfect than possible constructions, just because they want the most expensive, exotic or unusual material or the stuff they know or get at best price for some reason.
Personaly, today I take ecological points into consideration. I recycle old furniture for panels and don't use toxic materials (like sheet lead) if I can avoid them.