Absorbation of energy in a given medium:
I keep on seeing the debates on what constitutes a good build material. Well like anything there are positives and neagtives to any material selection and application.Its covered in engineering materials.
Absorbtion of mechanical energy depends on density and elasticity of a medium given that the medium is a near constant in mass. This is more like MDF. It has a reflective index based on mass and impedance value and an abosrbation based on thickness. Many do not like the sound of MDF but that is due to the lower resonance frequency of the material for a given wavelength. In a strictly BR or TL alingment it will perform in an adequate manner as even a TL may be a totally resonante device, its dependant primarly on a given pressure and phase point and not on harmonics at a given frequency.
Horns are different as they depend primarly on harmonics to blend in with different actions. A good material for BLHs is a multi layered composit as the harmonic range is greater than a constant mass/density material which is more monocromatic in resonance. On the opposite side is the fact that a composit material can abosrbe more energy due to the fact that as any energy that traveles thru the mass is faced with different impedance values and the energy loss is greater due to the many interfaces of different impedance values.
ron
I keep on seeing the debates on what constitutes a good build material. Well like anything there are positives and neagtives to any material selection and application.Its covered in engineering materials.
Absorbtion of mechanical energy depends on density and elasticity of a medium given that the medium is a near constant in mass. This is more like MDF. It has a reflective index based on mass and impedance value and an abosrbation based on thickness. Many do not like the sound of MDF but that is due to the lower resonance frequency of the material for a given wavelength. In a strictly BR or TL alingment it will perform in an adequate manner as even a TL may be a totally resonante device, its dependant primarly on a given pressure and phase point and not on harmonics at a given frequency.
Horns are different as they depend primarly on harmonics to blend in with different actions. A good material for BLHs is a multi layered composit as the harmonic range is greater than a constant mass/density material which is more monocromatic in resonance. On the opposite side is the fact that a composit material can abosrbe more energy due to the fact that as any energy that traveles thru the mass is faced with different impedance values and the energy loss is greater due to the many interfaces of different impedance values.
ron
The appliance of science... hard to argue with that really, Ron. 🙂 I suspect it also explains why QW & related boxes (Onken types etc) seem to work well with ply.
Larry Lomax said:
Hi Larry,
Have fun building and testing all of those boxes. It'll be time well wasted, if my experience is any indication.
What "glue mystery"?
marce said:
Hi marce,
I take no offence to your jester comment. I do try to inject a little humour (my own brand) into the proceedings. Occasionally, a stuffy individual or two decides they need to teach me some manners. Water off a ducks back.
Thanks for coming to my defence. 🙂
AndrewT said:
For the typical panel size of the typical speaker, MDF is as stiff as plywood. Where it suffers in comparison to plywood is elasticity.
Mdf has a simple mechanical structure - a kind of sandwich, with (slightly) softer material in the middle, between two outer compressed "layers". Plywood, especially Baltic birch, has a more complicated structure, with it's multiple cross-grain layers.
MDF damps vibration better than plywood due to it's lower elasticity and simple structure. Plywood resonates higher due to it's complex structure and high elasticity.
Which is better? High elasticity or low? Low damping or high?
It's my contention that when used in the typical speaker cabinet, there's no audible difference between the two.
MJL21193,
Careful John. Best toadie up and toe the party line ...... You have already alerted the thought police.🙂
Cilla
Careful John. Best toadie up and toe the party line ...... You have already alerted the thought police.🙂
Cilla
MJL21193 said:
ronc said:
John,
I would tend to agree with you for 'typical speaker cabinet', but it would be interesting if you (or someone) had a chance to build a couple of simple Back Loaded and Front Loaded horns to test out this proposition. If measurements do not come to a conclusion, then it's back to the old 'ears' equation.
It may not be a simple thing, as the horn might need to be quite large to 'excite' the appropriate material. The cone would probably only need to have 2 built - it could be used for both the BLH and FLH for each test (just attached to the appropriate enclosure section).
🙂 "Man does not live by words alone, despite the fact that sometimes he has to eat them." 🙂
pdan said:
Hi Cilla,
I have always been too much of an individual to let someone else do my thinking for me. This is, apparently, a bad thing here.
🙂
Cloth Ears said:
Hi Jon,
The horns that I've heard didn't arouse my interest, therefore I've never built one. All the same, isn't it true that horns use controlled exponential expansion of the sound wave for it's effect? And that the enclosure itself should not "excite" or resonate, but rather just guide the wave?
If this is the case, there shouldn't be a notable difference there either.
Man does not live by words alone, despite the fact that sometimes he has to eat them."
Never had to do yet. If you apply logic and physics to any given question you usually are correct.
ron
Never had to do yet. If you apply logic and physics to any given question you usually are correct.
ron
Ron,
A philosopher said : "When the problems of science have been solved, the problems of life remain." Do you think he should have eaten his words?
Cilla
A philosopher said : "When the problems of science have been solved, the problems of life remain." Do you think he should have eaten his words?
Cilla
There’s something I still miss. Energy absorption, what is it? Where do goes energy? In a closed box energy comes from the speaker and hit the inside of the box and it is reflected back and fort depending on the conformation of the box itself. Some of that energy at some frequencies and changed of phase will return to the speaker, and some is converted to heat and exchanged with the outside via the walls of the box. (You’ll never feel this heat with your hands off course, but it does).
If you fill up the interior of the box with fluff, the mechanical waves from the speaker will be absorbed by the fluff a some frequencies and converted to pneumatic pressure, and feed back to the speaker at the fundamental frequency or at the resonance frequency of the box plus the fluff. This is true for frequencies with their wavelength longer than the enclosure size. Lets say that under 660Hz, about 50Cm or 18” of wavelength. Higher frequencies tends to cross the material of the enclosure via the material itself at a speed higher than the speed of sound in the air. But I still don’t see where energy is absorbed and where it gets hidden. I have a sensation that I still miss something or I have a misconception of “energy absorption”. The conduction of some frequencies by the case material (MDF or Ply) may be higher in plywood than in MDF its evident by the way they are made. This could result in brilliance of the Ply or in the dull of the MDF. But, for definition a good enclosure should be passive. It will never exalt a determined frequency, the reproduced spectrum should be flat. Unless, you are looking for an exaltation of something lost by the way in the speaker or in the cross over. So, I still feel uncomfortable with that concept of “energy absorption” some hints?
Cheers
Larry.
If you fill up the interior of the box with fluff, the mechanical waves from the speaker will be absorbed by the fluff a some frequencies and converted to pneumatic pressure, and feed back to the speaker at the fundamental frequency or at the resonance frequency of the box plus the fluff. This is true for frequencies with their wavelength longer than the enclosure size. Lets say that under 660Hz, about 50Cm or 18” of wavelength. Higher frequencies tends to cross the material of the enclosure via the material itself at a speed higher than the speed of sound in the air. But I still don’t see where energy is absorbed and where it gets hidden. I have a sensation that I still miss something or I have a misconception of “energy absorption”. The conduction of some frequencies by the case material (MDF or Ply) may be higher in plywood than in MDF its evident by the way they are made. This could result in brilliance of the Ply or in the dull of the MDF. But, for definition a good enclosure should be passive. It will never exalt a determined frequency, the reproduced spectrum should be flat. Unless, you are looking for an exaltation of something lost by the way in the speaker or in the cross over. So, I still feel uncomfortable with that concept of “energy absorption” some hints?
Cheers
Larry.
Yes, I've always been a bit bothered by the 'stores energy' concept too. Loudspeaker cabinets as batteries?
Remember that not everyone believes a good enclosure should be entirely passive & contribute nothing of itself to the sound. As it happens, I do too, most of the time anyway (given there are exceptions to almost everything -look at Bosendorfor's range). But the cab as an instrument approach is just as valid; it simply has different values, even if they don't suit / match everyone's definition of what a 'good' enclosure should be. Name your poison. Barkeep! Make mine a triple Midleton! (discerning lovers of Irish will know it. 😉)
Re energy absorbtion, I don't think you are missing anything really, it's back to interpretation of phrases. Based on my rubbish physics knowlede, energy doesn't just disappear; there has to be a conversion of it into something else. The conversion itself is somewhat lossy, depending on the efficiency with which it occurs, and the term absobtion by my understanding (Ron?) simply refers to how the box recieves the energy and converts it into a different form. Storing energy is another one that depends on how you interpret the phrase (Latin didn't have half as many problems as English). To use one basic example, remember that the speed of sound varies in different mediums. The number of boundaries in a medium will also affect this.
Re energy absorbtion, I don't think you are missing anything really, it's back to interpretation of phrases. Based on my rubbish physics knowlede, energy doesn't just disappear; there has to be a conversion of it into something else. The conversion itself is somewhat lossy, depending on the efficiency with which it occurs, and the term absobtion by my understanding (Ron?) simply refers to how the box recieves the energy and converts it into a different form. Storing energy is another one that depends on how you interpret the phrase (Latin didn't have half as many problems as English). To use one basic example, remember that the speed of sound varies in different mediums. The number of boundaries in a medium will also affect this.
Stretch a spring = stored energy.
Bend a leaf spring = stored energy.
Bend a panel of wood product = stored energy.
Springs use materials with a high Q, low damping and manage to release most of that energy without converting that energy into heat. That's why we have dampers on our motor vehicles.
Panels made from wood product have a much lower Q. They have some damping. Natural wood, bent along it's grain, has low damping (high Q) and releases most of it's energy (a bow for shooting arrows). Manufactured boards generally have high damping in comparison to natural springy wood.
Our panels store energy when they bend (deflect) and release some of it back as acoustic power and some is converted to heat. The portion that gets neither converted to heat nor sound, bends the panel in the other directon. Could we call this resonance?
I see that my analogy begins to look like a damped spring.
Bend a leaf spring = stored energy.
Bend a panel of wood product = stored energy.
Springs use materials with a high Q, low damping and manage to release most of that energy without converting that energy into heat. That's why we have dampers on our motor vehicles.
Panels made from wood product have a much lower Q. They have some damping. Natural wood, bent along it's grain, has low damping (high Q) and releases most of it's energy (a bow for shooting arrows). Manufactured boards generally have high damping in comparison to natural springy wood.
Our panels store energy when they bend (deflect) and release some of it back as acoustic power and some is converted to heat. The portion that gets neither converted to heat nor sound, bends the panel in the other directon. Could we call this resonance?
I see that my analogy begins to look like a damped spring.
I disagree with this conclusion.
AndrewT said:
That's two of us. Some exact comparisons would be interesting however. I'm not sure what a 'typical speaker' size is though. For those using WB or FR drivers, it can vary like anything else, but is often much larger than for a regular multiway as some form of horn loading is popular.
Re the horns BTW John, kind of. Depends what type of horn you're refering to. I don't like the term 'acoustic transformer' that's popular as to me it's a wooly way of saying they are impedance matching devices. But they don't have to use exponential expansion, and the problem with most dometic horns is that due to size restrictions (in free-space a 40Hz horn would need a mouth circumference of ~340in & a length of at least 170in & preferably more) they aren't really horns in the LF at all. They use QW action for the lowest frequencies & there is a transition (more or less gradual, depending on the design) to horn loading as frequency increases and the acoustic-impedance match improves. Also, you have the potential for standing waves between the parallel walls most have to use, bends introduce their own issues (some negatives, some can be useful if you take them into account) etc etc. So it all gets rather more complicated than the basic theory suggests, and ergo, the construction materials become a major factor, at least for bass-horns. Less so for a properly sized midrange device as they're a) much smaller and b) generally work above the natural resonance frequencies of the construction material.
About the bending Andrew, funny you should bring that up because Ron & I are discussing stresses etc along bends in our PMs at the moment. I have a particular interest in this as my current research in late 19th - early 20th century (large) cruisers involves aspects of their hull and armour design.
Colin said:
This is misplaced term for decay time of a resonance. A mechanical system will vibrate for a given amount of time depending on how it is damped. Higher damping = shorter decay time.
AndrewT said:
Resonance is the natural tuning frequency of a mechanical system (panel), the frequency where it's oscillations will be of the highest amplitude.
Stiffness is a measure of deflection due to an applied force. For smaller panel sizes, given the smaller forces involved, stiffness is not a factor.
Bends!
is this any good to you?
M/I = sigma/y = E/R
M=applied moment.
I=moment if inertia.
sigma (greek symbol) = extreme fibre stress.
y= distance from centroid to that same extreme fibre.
E=Young's modulus.
R= radius of bend.
is this any good to you?
M/I = sigma/y = E/R
M=applied moment.
I=moment if inertia.
sigma (greek symbol) = extreme fibre stress.
y= distance from centroid to that same extreme fibre.
E=Young's modulus.
R= radius of bend.
MJL21193 said:
AndrewT said:
I should have worded that better, as I can see everyone will jump on that statement.
I meant that with small panel sizes at the forces involved, the difference between the stiffness of MDF and plywood is negligible. A bigger factor is elasticity and damping.
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