Mainly that the former will act without even considering cabinet resonances. It will also participate in a rocking mode with the suspension due to the vertical displacement of the moving mass from the anchor points.
I think I am getting an idea of the distinction you are seeking to make but vibration analysis needs to considers all modes/resonances including the rigid body ones if the speaker has unphysical constraints such as a friction free floor. The reason being that the forced response function (i.e. the frequency response of points on the cabinet to the applied forces) is evaluated from a weighted sum of the mode shapes. Many numerical methods for determining the modal frequencies and shapes will fail if the 6 rigid body motions are not fully constrained by the boundary conditions whereas others will work though the combination of predicted orthogonal mode shapes won't be known. It may seem a bit nit picking but vibration analysis does predict the lot.
I really like when these discussions regularly are grounded both by physics we can't ignore, and also actual testing that provides some information on parts of the problem. When starting out on this hobby 20 years ago i got onto the wrong path several times by individuals that were partly right but fully confident, I've probably been that guy myself a few times. In danger of doing that now, i will try to summarize what we know, please correct me if i got the basics wrong:
Electrical energy is converted to mechanical energy by the transducers. Very little mechanical energy is converted to sound as we know, some turns into heat and quite a bit of the energy will transfer into the enclosure. Whatever energy is not absorbed by damping in the enclosure walls will either cause the walls to vibrate or the whole enclosure as a unit to vibrate. This vibration can either be transfered as sound through the air, or mechanically through the mounting system. (Over time it will dissipate as heat in the walls)
By looking at STC numbers for wall systems we can maybe deduce that even quite hefty enclosures will transmitt some energy. If i understand physics correctly most (if not all) of this is transmitted as vibrational energy. If we connect a vibrating surface rigidly to another surface two things will happen; the first surface will vibrate less, and the new surface will vibrate more (than before they were in contact). Depending on the difference in mass (the impedance) this can either lead to less sound or more sound being radiated.
Dissipating some of this energy through the mounting system might be a reasonable thing to do. (Allthough i suspect quite far down on the list of things to prioritize)
Electrical energy is converted to mechanical energy by the transducers. Very little mechanical energy is converted to sound as we know, some turns into heat and quite a bit of the energy will transfer into the enclosure. Whatever energy is not absorbed by damping in the enclosure walls will either cause the walls to vibrate or the whole enclosure as a unit to vibrate. This vibration can either be transfered as sound through the air, or mechanically through the mounting system. (Over time it will dissipate as heat in the walls)
By looking at STC numbers for wall systems we can maybe deduce that even quite hefty enclosures will transmitt some energy. If i understand physics correctly most (if not all) of this is transmitted as vibrational energy. If we connect a vibrating surface rigidly to another surface two things will happen; the first surface will vibrate less, and the new surface will vibrate more (than before they were in contact). Depending on the difference in mass (the impedance) this can either lead to less sound or more sound being radiated.
Dissipating some of this energy through the mounting system might be a reasonable thing to do. (Allthough i suspect quite far down on the list of things to prioritize)
Last edited:
Essentially all the energy ends up as heat. Most is lost in the electrical circuitry but the proportion of the rest that is sound for a while should be reasonably high. In a good design there isn't much energy tied up vibrating the cabinet. Quantifying this would make a nice article.
The movement of the cabinet (kinetic energy) is dissipated directly as heat by damping forces opposing the motion or transferred to the air by working against the opposing forces in the air. The energy transferred to the air will be transported away as sound, vorticity and entropy waves. Energy can also go the other way from the air to cabinet but this is normally signfiicantly less than from the cabinet to the air.
STC numbers relate to transferring sound in the air in one room through a wall into the air in a neighbouring room. That is a speaker fully decoupled from the room boundaries creating the sound. If a speaker is coupled to a room boundary this will be additional energy.
If there are open windows, air ducts, or similar creating a path for air-borne sound this will be additional to the structure-borne sound through the building structure. If the STC value is for a single wall the structure-borne sound through the other room boundaries might be additional depending on how the STC number was created. These sorts of numbers can provide useful guidelines if your setup and the setup used for the measurements are close but not otherwise. They aren't much use for speaker cabinets.
Often but it depends on how the coupled system responds. For example, it may resonate strongly at the driving frequency when coupled but not when uncoupled.
The difference in impedance determines the degree of energy transfer but impedance is force / velocity not mass. For example the specific impedance for a 1D acoustic wave is given by the material's density * speed of sound (maths for 1d acoustic wave omitted). So at the interface between two materials with the same density but different speeds of sound (i.e. stiffness/Youngs modulus) energy will be reflected. This indicates why the stiffness of the floor (sprung vs solid) makes a substantial difference to the amount of energy transferred from the cabinet.
If the resonant frequency of the speaker on the isolating soft spring is well below the speaker's frequency passband then damping will be harmful due to significantly reducing the effectiveness of the isolation in the speaker's frequency passband as shown in a plot earlier. The damping is providing a force coupling the speaker and floor/desktop.
I meant to use the STC-numbers of a wall only for the data it provides on how even quite massive cross-sections of material will transfer vibrational energy, sorry that this wasn't clear.
Thank you for clarifying the definition of impedance!
If there is vibrational energy in the enclosure, I still think it can be made an argument for trying to damp it through the suspension-system instead of isolating it. Thereby dissipating the unwanted energy to a greater degree/faster.
Thank you for clarifying the definition of impedance!
If there is vibrational energy in the enclosure, I still think it can be made an argument for trying to damp it through the suspension-system instead of isolating it. Thereby dissipating the unwanted energy to a greater degree/faster.
A home-size room that doesn't have absorbers at the side-wall reflection points is simply incapable of good imaging. Reflections from the left speaker get into your right ear, and vice versa. Even reflections from the same side change the delay times with minute head movements, which also makes stable imaging impossible. One big problem with discussions like this is most people who consider themselves to be audiophiles, or serious home theater enthusiasts, have no acoustic treatment at all. They have no idea what they're missing because they never heard proper imaging. Such reflection treatment, or optionally angled side walls, is standard practice in every million dollar recording studio's control room. If you want to experience what the mixing and mastering engineers heard as they fine-tuned the music you love, you need a similar setup.
So to your point, room acoustics might not be the only thing that affects imaging, but it's surely 90+ percent of it. All a loudspeaker can do is have good or not so good off-axis response. But even that too affects mainly how the side-wall reflections arrive at the listeners ears. (Ceiling and floor reflections can also be a factor.) I'm not sure what other technical property of a loudspeaker would affect imaging.
Yes, exactly, you're making my point for me! It's not the speaker that affects imaging, but rather how the speaker sends untamed reflections around the room. And those reflections are what harm imaging.
I assure you that I miss nothing in this discussion. 😎 Yes, of course I "do"diffusers:
I see in some other posts a lot about measuring loudspeaker cabinet vibration, and experiments that can test a cabinet coupling to the surface it rests on. But none of that matters! Regardless of how much cabinet excursion you measure, the only thing that matters is how the sound in the room is affected. This is what I measured in the article I linked in my first post to this discussion. The glass of water on the subwoofer was an extra point, and not my main evidence as several people seem to think. The article in my first post showed that speaker isolation made no difference using response and waterfall graphs. That is the relevant proof.
Counter example: my listenng room. It is very revealing wrtn imaging/soundstage, something particularily important to me.
Mine has no “artificial” room treatments (the one i made sits on the floor blocking the car door).
I’d suggest that migh be/is a too high estimate. Depands heavily on the loudspeaker and placement.
Sloped ceiling is better (in general). y room has such.
The speaker is the source, it cannot be discounted, you diminish its importance. Toole has shown that some reflections are necessary. If i needed something i’d first lookn at diffusors, noit absorbers. Do you have anything more interesting looking in difusors than the ones shown in the video.
For n=diyers, a graduate thesis from Simon Fraser has some very interesting and fairly designs. Vertical like yours.https://p10hifi.net/forum/DIYdiffusers.zip In Y2K i started writing a program to calculate diffusors with square wells. Brute force. It vecame obvious a recursuve algoritm would be needed.
A hifi is system, nothing can be discounted,
dave
It is primarily the properties of the floor/wall/desktop that determines if speaker isolation is needed. If it isn't then cabinet damping could indeed be used in the suspension system. But then how would the cabinet be adequately damped for the situations where the speaker does need to be isolated?
Reducing sound radiation from a speaker cabinet is not a major task if the relevant principles are understood. That is, where it is beneficial to introduce stiffness, damping or mass. The manufacturer's of professional studio monitors rarely mention the subject because it isn't a relevant distinguishing feature of well designed speakers.
I'm also known as Oldhvymec, in other circles.
No. The simple answer is to look at all things using a suspension in all things that are on the highway, heavy-duty equipment, aerospace, and underwater. If not for decoupling/damping/isolators, you would see the world using a set of plow mules, oxen, or work horses to plow the fields.
If not for the modern tractor in the field, the transportation from the fields to the cleaning, curing, packaging, canning and packing facilities we would have at least 1/2 the population we have, if that.
The food survives because of the way it is harvested, transported, packed, and then delivered to your door or your store.
There is not a single powerplant in any modern piece of industrial, commercial, recreational, public, private transportation or production facility that doesn't use carefully thought-out engineering, backed by thousands of years of learning.
Decoupling is simple to understand in the music world. Take care of the cabinet first with bracing and reduce ALL resonant issues that are not wanted. Some cabinets are made to resonate a certain way, EX, a violin or a spruce horn cabinet that was and still is popular in some circles.
Second, you DECOUPLE by using springs, pods (bellows), air-ride, accumulators (shocks), or cable isolation suspension using inline adjustable cable springs. Decoupling is NOT exclusive to ONE thing, it could be a combination of several things, LIKE. The tire or part on the ground could be pneumatic, solid rubber, or even a track. As we go from there to the operator's seat, a moving suspension mounted with isolation materials or very tough materials like nylon etc, then springs, shocks. cab isolation by using a soft isolator, pods/springs, or accumulators with springs for a return to center, THEN we get to the seat where the operator is actually set apart from the environment, the powertrain, and the surface they are on, including air or water.
So the question you posed is asked and answered and has been since Rolls-Royce rolled out some of the finest decoupled carriages in the world along with Cadillac, Bentley, Duesenberg, and anything racing to ever place in a race, including chariot racing over 3000 years ago.
Sometimes some people just don't know where to look.
I use springs, and air ride, EX, an inner tube in a given box that will fit under the thing to be decoupled, and usually not add to the height for the purpose of driver alignment and the listener's ear (tweeter for example). Shocks are also a real thing.
The little spring pack you seem to be dismissing are PART of the puzzle. Now take those spring packs, disassemble them, get some @Flex Seal (aerosol or brush style), coat all the springs, and housings let it dry and insert memory foam earplugs in the number of springs you determine it takes to get 1/2 the total spring compression after the cabinet has settles on 4-8 spring pack.
My cabinets are 410 lbs. each, and the front baffle is 225 lbs. of HDF. Tell me all about decoupling cabinet. 🙂
BTW you will never see a spiked powerplant unless the cage or cabinet is completely isolated from the power plant to any surface, any diesel would crack the stand to pieces without complete isolation from the bolted or spiked surface.
At 70 and a retired master mechanic, I've seen some strange stuff behind things being way too rigid or way too soft. One can be just as bad as the other. You have to keep tires on the ground or they will cup or wear out. THAT is the main reason for shocks to keep the tires ON the ground, not to cushion your back, that is the job of a great cab isolation and seat that moves up and down, front to back, and side to side, all in moderation. They use shocks, air-ride, and 3 way movement on most operators' seats, including many aircraft.
Hope this clears up some of your misunderstandings.
With great regard.
Last edited:
Two requests:
1. Can you explain how you define imaging? I think that will help this discussion a lot.
2. Would you post a photo of your listening room? Best is to stand all the way in the back of the room, then take a wide shot toward the front so everything can be seen in context in that one photo.
From my perspective QRD diffusers are the best type, and those look like a useful variant, though possibly not deep enough to diffuse to a low enough frequency. But that type of surface won't avoid the imaging shifts you get when placed at reflection points. Only absorption can do that.
More a rhetorical ploy, nearly moral: if footers work, the speaker is 'incompetent'. Left to be demonstrated is the percentage of market speakers meriting the competent badge. Often those that go to extreme lengths in this regard - Magico, Acora - are dismissed as woo. Those that don't are nearly memes, the larger Klipsch for example.
Is the intent to show footers do nothing in all scenarios? That table top's lowest resonance is nearly 300 hz. Extending conclusions from such a light weight structure to floors at bass frequencies is quite the stretch. Using standard construction estimates my small living floor weighs about 1800 lbs. That tabletop is 10 lb? Placing a 20 lb (?) speaker on my floor alters its fundamental resonant behaviour not one bit, implying a benefit from isolation. On that table top the resonant reduction is almost certainly dramatic by placing the unisolated speaker on it, not illustrated with a second tap test. The experiment compares footers against a table top mass loaded by a appreciable weight. Viewed from an alternate perspective, footers on a floorstanding speaker are as effective as mass loading the floor with comparable weight, i.e. many hundreds of pounds?
It's unclear how a 1/4" or 1/8" speaker movement causes large response changes at 5 to 10 foot wavelengths. Graphs illustrating this are mentioned but I'm not seeing them. If it's room related, are the measurements not gated? How dramatic is beaming on that speaker below 500 Hz?
Approximately, 90 db + 90 db = 93 db. 87 db + 90 db = 92 db. A 2 db change means the secondary source is around 3 db below the primary source and can't be casually dismissed. Nor is the nature of that change investigated. For a protocol that begins with a demonstration of the harmonic behaviour of a support surface, harmonic distortion measurements are a consideration.
A post with a lot of good stuff.
Suspensions are pretty well understood. Spring/mass/damper physics fine tuned by mechanics/engineers in te field.
The tweeter mount on the Pearl PR2 was my first exposure to this in hifi. He goes intomore detail in his PR2 paper/short book.
At a veryndifferent scale one has to be impressed with the suspension on the Apple"Flying Saucer/Ring" … designed to let the building “surf” an earthquake,
dave
The auditory scene that the ear/brain creates from the information a stereo hifi (with a good piece of software) can produces,
It relies heavily on the small bits/clues. And the timing of those bits.
https://www.diyaudio.com/archive/blogs/comments/comment1028.html
dave
Last edited:
Something tells me your responses cater to pre-existing speakers. A competent DIY speaker with controlled directivity will not do poorly in it's matching room with no acoustic treatment.