I design FR loudspeaker and it has proven to work very well. There is much less energy in the higher frequencies to excite any resonance and there are rarely any HF energy that is continuously transmitted into the enclosure in the narrow bandwidth required to excite that resonance. Add damping and the Q drops allowing a wider bandwidth of energy to drive the resonance (and also lowering its frequency) making it more likely to move.
You can certainly light those resonances up with an aproppriate artifical signal, but we are playing music, not sine waves.
The approach decidely breaks many “common knowledge” rules, but since it works, and works well, those guidlines are moot.
dave
You can certainly light those resonances up with an aproppriate artifical signal, but we are playing music, not sine waves.
The approach decidely breaks many “common knowledge” rules, but since it works, and works well, those guidlines are moot.
dave
Which you did not say very well.
If you want it to be a 1/2 wave line it has to be a half-wave long, for the back-wave to be absorbed the trip to the end and back has to be a wavelength.
Modern modelers have shown us that the physical length can be shorter to achieve the same acoustic length as required by tapering large to small.
Now for practical purposes one may give up some of that absolute absorption and so reduce the line, but it becomes a 1/2 wave line of a higher frequency.
dave
Looking at the images I posted the backwave is being absorbed more so than if not in a line, which is all I really mean to point out about the sealed TL's. If one did not study TL, they might not come across this useful information...not the end all be all, but a lot of useful information, regarding all enclosures, is exposed within the study of TL.
An aperiodic TL whether vented or sealed...has a response closeth to a sealed....anyone who uses a sealed enclosure for bass might appreciate some of the fundamentals I speak of... If you hang out on Martin Kings facebook group long enough you'll see that a lot of people have abandoned the practice of fully stuffing the vented TL (actually they offset the driver and use no stuffing), so most TL's being aperiodic, might of been true at one point....but now we have to talk about where TL ends and MLTL and BR begin...you being one of the experts on the topic, know how it goes... If one were to learn what it takes to mute the backwave...one may give up some of that absolute absorption...for practical purposes...vented and sealed alike.
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Lets try looking at some evidence which is hard to find but there is some such as this from KEF. On page 11 you can see plots of a stiff relatively undamped cabinet pushing resonances high up into the midrange where the ear is most sensitive. Note adding stiffness raises the frequency of the resonances but leaves the level unchanged which is typical. Are you really advocating this as a good idea?
Highly effective damping in this case knocks the peak down 30 dB pushing the cabinet radiation down to 40 dB below the signal to likely inaudible levels. It doesn't matter if low Q resonances at 40 dB down are driven or not if they are too low in level to be heard.
A quick look at the paper does not explicitly say what the driving force of the FEM is, if it is not music it is artificial. I do not dispute that the (potential) resonances exist, but that with music they do not get excited.
Also, if the brace is as shown in the illustration i would consider that inadequate. Tappan showed decades ago that that syle of brace was poor.
dave
Also, if the brace is as shown in the illustration i would consider that inadequate. Tappan showed decades ago that that syle of brace was poor.
dave
The floor of my floating (sound proofed) room is made of a layer of sheetrock sandwiched with 2 layers of plywood, and I'm sure that it works extremely well to reduce resonance. I learned this method from a music studio construction book, and I remember that they call it German something.
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The cabinet construction is just one piece of producing excellent music in your listening room. Understanding What-to-Build and Why is the most important.
Room interaction
1) Dr. Earl Geddes "Directivity in Loudspeaker Systems"
2) "LOUDSPEAKERS AND ROOMS - WORKING TOGETHER" 3 parts
by Floyd E. Toole, Ph.D. Vice President Acoustical Engineering, Harman International
3) Sketch or CAD your living room with dimensions and angles.
4) Download free room resonance simulators.
Room treatment products
Capabilities of DSP with 1amp/driver
Interesting production speakers. Copy off the Smart Kids.
1) Horns control directivity (+ Multiple Entry Horns )
2) Dipoles control directivity
3) Front baffles control directivity
Understanding What-to-Build and Why is the most important.
Room interaction
1) Dr. Earl Geddes "Directivity in Loudspeaker Systems"
2) "LOUDSPEAKERS AND ROOMS - WORKING TOGETHER" 3 parts
by Floyd E. Toole, Ph.D. Vice President Acoustical Engineering, Harman International
3) Sketch or CAD your living room with dimensions and angles.
4) Download free room resonance simulators.
Room treatment products
Capabilities of DSP with 1amp/driver
Interesting production speakers. Copy off the Smart Kids.
1) Horns control directivity (+ Multiple Entry Horns )
2) Dipoles control directivity
3) Front baffles control directivity
Understanding What-to-Build and Why is the most important.
You want an very large resin printer....why? Why not go for PLA?
13.2 × 7.9 × 11.8 in for 10 thousand dollars?.... I am curious to what resin may offer a horn or enclosure that a PLA printer can't handle.
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Very true. A meticulously constructed cabinet which is the wrong size/shape for the driver is worthless, actually less than worthless because a lot of time and effort was sunk into it...
But back to the discussion between Andy19191 and Dave Planet10... Quoting myself from an earlier thread: Many great examples of excellent cabinets have been built, going back over several decades. We know what works: Answer - all of the methods under discussion have produced excellent sounding cabinets. Massive brute force cabinets, highly damped cabinets, high stiffness cabinets, CLD cabinets. MDF cabinets, plywood cabinets, fiberglass, high density polymer, concrete, aluminum.
This is not an either/or black/white issue. All cabinets have mass, stiffness, and damping. The question is how do we balance and compromise those three elements along with size, shape, interior access, and mobility.
However Andy19191, you seem to be saying that a high stiffness cabinet will not work
I can offer numerous examples of highly regarded speakers which used the high stiffness approach (1) the original B&W 801 Matrix enclosure was highly braced, but no structural dampening (2) Celestion SL600 series used aluminum skinned aluminum honeycomb panels which were very stiff and lightweight, but very low damping (3) Theil CS series used very thick MDF walls and extensive bracing, combining high mass and high stiffness (4) Magico's current lineup of Q series aluminum cabinets. (6) Barefoot Audio (7) Wilson (8) you get the idea.
Did you really mean to imply that a high stiffness cabinet will perform poorly, in all cases, no exceptions?
Much higher quality, betty surfaces, more material options. This is not only for play, it is for production.
dave
I meant what I said which wasn't that.
To repeat, if cabinet resonances are not in the frequency passband of the driver then stiff is the way to go although very high stiffness is not necessary. Separate subwoofer cabinets and woofer cabinets isolated from the midrange cabinet would be examples of this.
To repeat, It is impractical to move cabinet resonances out of the passband of a midrange making high damping the requirement with stiffness being relatively unimportant. I showed an example of what happens if you are unwise enough to have high stiffness with low damping. You get high Q resonances in the frequency band where the ear is most sensitive to resonances that are not much quieter than signal at their peak.
To expand on my comment about targeting stiffness. The rate of work (force * velocity in direction of force) put into vibrating the cabinet around the lowest resonant frequencies comes primarily from the drivers hammering on the baffle. The force is the reaction to the motion of the cone and is fixed (assuming the driver isn't isolated on rubber grommets) but the velocity can be reduced by making the baffle stiff. So a stiff baffle is always desirable but once the work has entered the cabinet then stiffness (and mass) will do absolutely nothing to remove it. It is removed by damping (desirable) and radiating away as sound (undesirable). So the other panels require high damping with stiffness being relatively unimportant but since high damping comes at the expense of stiffness this tends to mean a choice between low stiffness or medium stiffness for the other panels.
To expand my comment on modes shapes which has a bearing on low vs medium stiffness for the panels that are not the baffle. A structure is easier to bend in the lower modes because it takes less deformation of the material. The amount of damping follows from the amount of deformation (strictly the right type of deformation) and so having higher order modes at frequencies where the ear is most sensitive rather than low order ones should lead to more damping and lower radiated sound.
PS Can you link to evidence of your examples having high stiffness, low damping and low cabinet sound radiation.
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Wouldn't it be preferable that the cabinet walls didn't move, and therefore that they be more stiff as long as they have sufficient damping?
As has been clearly shown with real-world examples it is not impractical and while the KEF document shows the existance of those resonances (in a poorly braced box, so not as high in frequncy as possible) in practise they will not be excited by music. We do not make a habit of playing sine waves or listening while someone is tapping the enclosure with a hammer.
The physics is not disputed, potential resonances wil be there, but given the available energy provided with music as a stimulus, and the high unliklihood of any very sustained note at the exact frequency of the resonance to get it moving it is highly unlikely it wil ever be excited so it is, in effect, non-existant.
One could go over the top and tune the frequencies of the (potential) resonances to where they do not fall into any frequency produced by the well-tempered music scale (or any unusual music YOU play) to further decrease the already really low probability of excitation.
It is an elegant and cost-effective approach tha uses finesse instead of brute force. It is an absolute no-barainer at low frequencies, and if one takes advantage of teh active reactive force cancelation of a push-push arrangement of the woofers one can get away with quite thin building material as our test build of a dual 10" sub with 15mm BB has shown.
dave
The second fights the 1st, and in practice is unneeded. Use of many-ply plywood with every transition from ply-to-ply providing damping is more then often sufficent. More could be achieved but it is, in practice, guilding the lily.
dave
I suspect this is what Andy is saying, that damping requires movement and stiffness stops movement. Yet no movement is the goal and the less stiffness, the more movement there might potentially be.
54 posts and no hint, unless I missed it that an enclosure is merely one approach to speaker design. While the talented engineer who developed them is no longer with us his designs are, and in the humble opinion of this engineer it is well worth your time to explore his work.
Linkwitz Lab - Loudspeaker Design
Linkwitz Lab - Loudspeaker Design
Well Planet10 this is from the OPs first post, nothing I see here or in the rest of the post suggests that the OP is aware that there are other options besides enclosures. It's good that you have concluded that only enclosures can satisfy, but thousands of others would strongly disagree. The OP being an engineer I would expect that he is equipped to review and decide for himself. But since you have decreed that only enclosures can produce acceptable results I guess that's settled! 🙄
If an automotive engineer told me he wanted to know how to design a bitchin' solid axle rear suspension I'd advise him that there were better options, just like this!