Adding mass lowers resonant frequency, raising stiffness raises resonant frequency. Damping dissipates energy by converting resonant mechanical energy into heat and thereby lowers and broadens resonant peaks. In general a damper produces a force resisting motion that is proportional to the velocity of the motion...a classical example is a shock absorber or damper in a vehicle suspension.
Need some serious kit to do that. At any level of useful info anyway.
I have seen at least a few AES papers, and KEF published some sruff, Maybe B&W as well. Klippel might have some stuff.
dave
The net result is a lower Fs. Don't believe me, try to use a massively rigid construction to raise Fs an octave above a woofer's pass band.
Well, I've seen woofer cones deflect in prosound apps and many mids-up drivers are designed to flex to get the desired frequency response.
Back in the 80s B&W showed off with laser interferometry to measure cone deformation of their midranges. KEF did use laser interferometry too, to check performance of driver suppliers. I still have some drive units from Focal and Audax with magnesium oxide covered domes lying around.
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Fired clay? Why bother? Use sand, it works very, very well.
Tap on a clay pot, then tap on a bag of sand. Which resonates more? 😉
Tap on a clay pot, then tap on a bag of sand. Which resonates more? 😉
So if making a double walled box to be separated with a layer of sand would 1” gap all the way around be enough? And how would one keep the inner box from shifting…..maybe soft rubber/sorbathane blocks of the same width as the gap? And lastly would it be best to secure the outer box to the floor (if possible) or just use some sort of feet usually used for a regular box?
Edit……on further reflection you’d probably need a ring of silicone around the driver to seal the sand in so inner box never touches the outer? Or maybe that little bit of contact around the driver wouldn’t be a issue?
Edit……on further reflection you’d probably need a ring of silicone around the driver to seal the sand in so inner box never touches the outer? Or maybe that little bit of contact around the driver wouldn’t be a issue?
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These what-if question while the objective of this thread, require quite complex and intricate analysis with all dimensions and material properties defined in order to even begin to obtain specific and meaningful answers. Fifty years ago when I was a mechanical engineering student there were at least four semesters of statics, dynamics and systems analysis that dealt with these kind of structural issues. So while it's very easy and directionally correct to say thicker = stiffer = higher resonance trying to balance the interplay between mass, stiffness and damping in a complex structure is not amenable to armchair guesstimates.
Something else that hasn't been mentioned is the practice of placing a sack of sand in the cab as a damper. How effective would this be? Volume can be calculated to accommodate and the bonus in that is the ability to precisely fine tune the cab volume to the particular driver being used. Mission designed a series with the option of placing sand in the bottom of the cab. I had a pair of V63 years ago but didn't bother trying it. Those cabs were very stiff as is.
I’ve seen sacks of lead shotgun shot used in that capacity https://www.amazon.com/Magnum-Lead-Shot-2-25-Pound/dp/B001QV1A0Q
Sand would be a heck of a lot cheaper!
Sand would be a heck of a lot cheaper!
Ah! Think surface area, i.e. lbs/in^2, ergo the cab pressure will 'feel' a rigid piston, IOW it will rip its surround out first if the presumed air mass is a ~uniform particle density [UPD].
If it's a cab eigenmode [non UPD], then it gets complicated and where drivers designed to flex in said UPD will in some cases have an audible response plot somewhat different, with a measurable undercurrent of peaks/dips to 'muddy up' the response.
How often are you tapping on the speaker box when you are listening to it. As long as that (in this case typically HF) potential resonance is not excited.
Fired clay is not well damped, sand is an excellent damper but needs to be constrained (otherwise you listening room will become a waterless beach). It damps because it can move and the friction sucks up the energy.
dave
As a general rule just think in terms of weight with at least 2 - 2.5x as a starting point and only add more in other ways if audibly required, so if a double walled cab = 200# then need at least 200 - 250# of sand.
That said, better to make a well braced cab and add a removable weight on top Vs the half a$$ way of tossing a bag of it inside the cab.
Make it heavy enough and it won't need anchoring. 😉 If the floor 'floats', i.e. not a resonant free concrete slab or similar, then some form of isolation is desirable.
??? Make the baffle single panel with add on pieces to brace via added thickness/density as shown in the article.
Double wall construction in French, but lots of pictures: Caisson W sable – Onken
Real world example done to [empirically] prove how much weight needs adding to a typical so-so box construction + plastic? horn to sufficiently damp it:
Mass Loading A7s, VERY inexpensive, reversible, needed -
Mass Loading ALTEC A7 VOTT 825 enclosures - drlowmu - High Efficiency Speaker Asylum
Adding MASS to an A-7 825 enclosure
Audio Asylum Thread Printer
https://www.audioasylum.com/cgi/vt.mpl?f=hug&m=175100