Now we're getting to the heart of the matter. You say:
Plywood panels can be easily made to vibrate, and not just at a few resonant frequencies. The thinner a panel is the less energy it will take to make it vibrate.
So in my posts I've been questioning whether thin, stiff cabinet walls are good for subs, as you claim. Now maybe you're right. Maybe resonance, which implies energy storage, is all we really have to worry about. Maybe the limited sound attenuation of a thin plywood panel at low frequencies is enough, so long as energy is not stored. But I'm not convinced.
Moving on, I wrote "a speaker is not a musical instrument. I never said it is!" You replied:
That's what I don't accept. You are very focused on resonance, but resonance is a subset of vibration, and I'm talking about vibration more generally. You say everything resonates. You're right. But I'd say its worse than that: everything vibrates.
Plywood panels can be easily made to vibrate, and not just at a few resonant frequencies. The thinner a panel is the less energy it will take to make it vibrate.
So in my posts I've been questioning whether thin, stiff cabinet walls are good for subs, as you claim. Now maybe you're right. Maybe resonance, which implies energy storage, is all we really have to worry about. Maybe the limited sound attenuation of a thin plywood panel at low frequencies is enough, so long as energy is not stored. But I'm not convinced.
Moving on, I wrote "a speaker is not a musical instrument. I never said it is!" You replied:
Sorry, Dave, but that's a total misreading of my posts, and quite a bizzare one, if i may say so. I'll make the point again: you're the one arguing for subs made with thin, stiff wood cabinet walls. I'm the one pointing out that many musical instruments use thin, stiff (and braced!) wood panels as soundboards, because they vibrate so readily.
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Not only as soundboards, but also as echo chamber. 😉
Furthermore, in my humbe opinion, the "thin" concept would be a bit to deepen since it is also to relate to the size of the instrument itself.
In some cases it may be less thin than one would expect, because it is a function of what the designer (the luthier) had as the final goal of its resulting sound.
However, after writing something on another thread, if I may I would like to highlight a fact.
Simplifying as much as possible: sound is vibration, the propagation of sound is through (not the movement, but) the vibration of air (or water, or something else), the eardrum vibrates and thanks to the fact that the eardrum vibrates we hear and we can "listen to" that sound.
IMHO A resonance is something else, it is always vibration and as such certainly audible, but it is another thing because I guess that a resonance is a peak (of a variable amplitude) of vibrations and therefore an accentuation of a certain segment of the original vibration.
In some acoustic musical instruments this is exploited artfully and there are soundboards and sound box (echo chamber) that amplifies the sound coming from strings plucked and/or rubbed by a bow whose hairs are impregnated with rosin and that segment (of whatever amplitude it is) and its type I think characterizes and differentiates the sound of the same kind of instruments and also their timbre.
The same thing happens (voluntarily or involuntarily) also with the cabinets of loudspeakers or subwoofers, contributing to the final sound characterization of them.
In the piano and even more so in a pipe organ whose extension is (almost) practically equal to that of the audible spectrum, I believe that there are more than only one resonances, with all the relevant annexes.
Since sound reproduction is a different theme compared to sound propagation, the two themes will certainly intersect in at least one or more points, while remaining two parallel "worlds".
Even the ear canal (the external ear) has its own resonance (on average 3kHz) and this fact (even if not hugely variable) is probably also one of the elements that differentiates the listening sensations of different listeners, but this is a different story.
Anyway, since I'm neither an expert technician nor even an expert, I don't think I can add much else because it rightly doesn't have the slightest authority so I ask an expert, if he wants, to expand on the topic of resonance.
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No, that's not what you said.
No, that's completely wrong! The ear is much more sensitive to high frequencies, therefore it will be much more audible.
Here you can see, at 100Hz the sensitivity is already over 30dB more sensitive than at 50 Hz! (Music range, mind you) You cannot catch up to that in a light box. And it goes on on higher frequencies too. Lighter materials can work fine but please, PLEASE stop claiming heavy speakers are worse!
Exactly the opposite. A low Q res can often not be distinguished or is often not even audible at all. A high peak (=high Q) is MUCH easier to hear and identify. Always! Use a parametric EQ and try for yourself
MDF isn't brute force. It's working very well if used right, and there's nothing crude about it.. The savings at the materials are what I'd call elegant too.
Light subs with drivers with a very high Mms move around like nothing. Even if they don't, the impulse to the enclosure takes off from the first peak amplitude, That eats up precision and not too little, it's as much difference as P-P to a single driver sub.
Sandwich panels with highly absorbent material filling like quartz sand. Or composite concrete (not that it's practical but effective.
In the 70s Sony had a turntable built from a metal and composite mixture, it was resonance free (below the measurement sensitivity in the tests back then). It was light and didn't sell that well. And it's the same principle, light isn't always better.
Thinking more about how panels behave, I'm actually coming round (a little!) towards Dave's theory. 😱
A panel's vibrational behaviour can be analysed in a way similar to that of a driver, I guess. Below its fundamental resonance, its movement will be primarily controlled by compliance (how its held in place, really) and above resonance its behaviour will be primarily mass controlled. Now, drivers still vibrate, below resonance. In fact the amplitude of that vibration is often greater below resonance than above, for a given energy input. However the acoustic output reduces below resonance, because the amplitude would have to increase by even more than it actually does, if acoustic output were to be maintained. So for low frequencies, cabinet vibration may not matter too much, because the amplitude of the vibration won't be sufficient to create much acoustic output.
If that's so, then what you need in a sub cabinet is stiffness and what you have avoid is stored energy. Thin, light panels store less energy but are less stiff. Where's the sweet spot?
A panel's vibrational behaviour can be analysed in a way similar to that of a driver, I guess. Below its fundamental resonance, its movement will be primarily controlled by compliance (how its held in place, really) and above resonance its behaviour will be primarily mass controlled. Now, drivers still vibrate, below resonance. In fact the amplitude of that vibration is often greater below resonance than above, for a given energy input. However the acoustic output reduces below resonance, because the amplitude would have to increase by even more than it actually does, if acoustic output were to be maintained. So for low frequencies, cabinet vibration may not matter too much, because the amplitude of the vibration won't be sufficient to create much acoustic output.
If that's so, then what you need in a sub cabinet is stiffness and what you have avoid is stored energy. Thin, light panels store less energy but are less stiff. Where's the sweet spot?
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Hi thank you for the very interesting and valuable advice
I understand better now about the goal of moving the resonance frequency outside the working range of the speaker
As i said the woofer cabinet is the only real challenge in speaker design Really
A great solution for playing back frequencies below 200Hz is all what i need Above that it will be a joke Almost any decent 2 ways will work maybe with some added mass to the cabinet
It makes very much sense to me
A very clever way yo design a sub cabinet that reminds me of the B&W Matrix concept for instance
I much prefer the old 801 style by the way used as monitor by famous studios
I guess that a sweep test could be a great way to chek at what frequency the cabinet starts to resonate
I still wonder how to enhance that resonance to make it more evident
So if i understand well increasing stiffness moves the resonant freq up
Increasing mass cabinet instead will move the resonant freq down
If i understand well lower resonances are less impacting in the overall sonic performance ?
this could be the reason why i got better sound adding mass to the cabinet
I moved resonance down in a less audible range ?
i ask because in my mind it could be easier to increase mass than stiffness after all
Bracing is not an easy mod for sure
I have no access to the needed tool to cut wood and i am scared by them
I understand better now about the goal of moving the resonance frequency outside the working range of the speaker
As i said the woofer cabinet is the only real challenge in speaker design Really
A great solution for playing back frequencies below 200Hz is all what i need Above that it will be a joke Almost any decent 2 ways will work maybe with some added mass to the cabinet
It makes very much sense to me
A very clever way yo design a sub cabinet that reminds me of the B&W Matrix concept for instance
I much prefer the old 801 style by the way used as monitor by famous studios
I guess that a sweep test could be a great way to chek at what frequency the cabinet starts to resonate
I still wonder how to enhance that resonance to make it more evident
So if i understand well increasing stiffness moves the resonant freq up
Increasing mass cabinet instead will move the resonant freq down
If i understand well lower resonances are less impacting in the overall sonic performance ?
this could be the reason why i got better sound adding mass to the cabinet
I moved resonance down in a less audible range ?
i ask because in my mind it could be easier to increase mass than stiffness after all
Bracing is not an easy mod for sure
I have no access to the needed tool to cut wood and i am scared by them
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The sweet spot probably depends on finances, very often. It is possible to have both lighter and stiffer (e.g. materials like carbon fibre and foam composites). I don't know the exact answer, or even if there is one, but when working with similar materials (e.g. qualities of plywood) it is possible to compare them at least in a relative sense. Even then, I think once you get beyond the cheapo nasty stuff, ever smaller improvements tend to hit the wallet ever harder.
This is one reason why bracing is key, and often underrated IMO. It needn't be exotic or expensive to bridge gaps between two walls quite effectively. Obviously that divides/shortens the wavelengths at which side panels will resonate. But if the designer can bring themselves to avoid symmetry, it will also vary or spread the frequencies over which the higher resonances occur, so they don't sum into something loud. I think this is a useful extra tip and only costs the effort of placing the braces slightly more thoughtfully. Pushing the resonances out of band makes them harder to excite to a loud degree, and avoiding even those from summing can be quite an effective combo.
This is one reason why bracing is key, and often underrated IMO. It needn't be exotic or expensive to bridge gaps between two walls quite effectively. Obviously that divides/shortens the wavelengths at which side panels will resonate. But if the designer can bring themselves to avoid symmetry, it will also vary or spread the frequencies over which the higher resonances occur, so they don't sum into something loud. I think this is a useful extra tip and only costs the effort of placing the braces slightly more thoughtfully. Pushing the resonances out of band makes them harder to excite to a loud degree, and avoiding even those from summing can be quite an effective combo.
Lowering the frequency with added mass of panels is useful for higher frequency cabinets, as you can lower resonances below their frequency range. Sometimes an absorbent lining can be useful (and might include adding some weight), since higher frequencies are easier to damp.
But it is hard to do for bass and sub-bass cabinets, partly because the in-band frequencies can be so low that it gets hard and heavy to get panels resonating low enough below the intended band. Partly because it is much harder to absorb/damp low frequencies with adding linings. I would only go for adding weight if it is an indirect repercussion of adding significant stiffness; materials like concrete might work in some cases, for example.
Though weight can still be useful 'in other areas', like preventing cabinets from walking or transferring vibration to the floor. Mostly by having too much mass for the available sound/vibration energy to affect very much, though it could also be absorbent and preferably not prone to resonance.
But it is hard to do for bass and sub-bass cabinets, partly because the in-band frequencies can be so low that it gets hard and heavy to get panels resonating low enough below the intended band. Partly because it is much harder to absorb/damp low frequencies with adding linings. I would only go for adding weight if it is an indirect repercussion of adding significant stiffness; materials like concrete might work in some cases, for example.
Though weight can still be useful 'in other areas', like preventing cabinets from walking or transferring vibration to the floor. Mostly by having too much mass for the available sound/vibration energy to affect very much, though it could also be absorbent and preferably not prone to resonance.
It may be true, but AFAIK the baffle edges diffraction at (mid)-high frequencies seems to me not even a joke. 😉
Go study some physics.
A practical aplication in our field are tweeters. Why are some cerami, diamond, or diamond coated? To push the fundemental resonance up… they all have a substantial HF peak, but nothing below.
And woofers like this (https://www.seas.no/index.php?optio...08-w22nx001&catid=49:excel-woofers&Itemid=359):
The idea is to push rresonances up above the used bandwidth. Same idea with the cabinet.
dave
A vibration is a resonance, usually more associated with something with lower Q, they are 2 words for the same thing.
dave
Toole’s work says the opposite.
It may be easier to identify, but it is also much harder to excite. And if it is never exciterd it is as if they do not exist.
I get teh feeling you are missing the point. The idea is to accept that resonances will happem so let sput them somewhere they will not be an issue. As opposed to blungeoning them and trying to make them disappear (requires extreme brute force — like the 5-6 figure price of things like Rockports (some clever engineering there too) or the Martens (sheer brute force).
Finese.
dave
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Well, resonances are also induced at 1/2, 1/4, 2x 4x etc. That's why 1/4 wavelength horns, Reflections apply too, therefore also 1/3 etc lambda resonances also appear with multiple reflections and TMLs etc with 'unreasonable' length work too (okay, that's also depending on it's physical construction/dimensions). You keep to ignore that. You can't choose which physical laws apply and which not.
Where? May I see the context please?
No, that's where you are wrong again. The higher the Q, the easier it is to excite them and how long they retain the energy! It may be happen rarer but if it does, oh boy! Any high Q res have to be avoided for the speaker to be able to reproduce any music. Having high Q resonances makes speakers selective to music choices but a good speaker has to be able to reproduce any music equally good, otherwise it's not actually a good speaker.
I get the principle very well. But there are instances where it's not working that well and other principles are more universally applicable and advantageous or even vastly superior and that's the point you are not missing but ignoring, vehemently denying, or even lying about. There is more than one way to Rome.
What?! Please excuse I'm not a native speaker but I cannot for my life fathom what you mean by that.
Now we are getting somewhere. What happens to the resonance if you can’t put any energy into it?
A LF low Q resonance is easy to pump energy into than a high Q HF resonance. The excitation is the music you play.
With music how often to you get a HF note held for long enuff to load the HQHF resonance with sufficient energy to get it going.
The inflection point (where it lies on the x-axis) is aneducated guess, the 2nd order curve is easy to show, but there are good arguments for the forth order curve. Likliehood of music providing sufficent energy to get a resonance going.
dave
A lighter panel of the same stiffeness will outperform a heavier one. Stiffmess goes up with the cube of thickness.
So you can take the elegant way go light with clever engineering, or brute force by just using thicker walls. But budget is a compromise few of us can ignore.
dave
The energy required to set off a HiQ resonance has to be within the resonances bandwidth. With music how much continuos energy is pumped into the box at those HFs?
A low Q resonance has a much broader bandwidth so can feed off much more of the music. And there is more energy in the LF notes so if the resonance is also lower in frequency it is easier to excite.
dave
You don't get it. You can apply absorption, bracing (even with absorption!) and construction methods? Like MDF with braces which are connected to panels with (one side) alubutyl? Or sandwich panels? Don't you ever think about what combinations of materials and methods are possible? Why do you constantly deny such possibilities? Why do you insist 'light' is the only possible way to go? Honestly, I find it hard to believe you seem to understand the principle of light build but not seem to understand the principle of heavy build. I don't want to believe that it's you do not understand it (you're too smart for that!) nor that it's willfully ignorance. What's needed for you accept there are viable alternatives?