Does anyone know the volume of basket, magnet, etc (ie in-box volume of driver)for the FF85K?
I've got some on order, but it will be a while before they get here.
Thanks.
I've got some on order, but it will be a while before they get here.
Thanks.
not much
My grade 8 math is a bit rusty, but here goes - calculating the volume of a cylinder with the diameter of the magnet, the gross volume (i.e. from rear of mounting flange to magnet) would be pi*R^2*H = 31.76 cu in/ .018 cu ft or .52 liters
Remember that this is a very shallow driver (i.e. net mounting depth of 43mm = 1.69") ) - if front mounted on 3/4" baffle the driver will "intrude" into the cabinet by less than 1" , almost all of which is magnet. The numbers for that would be approx 17.67 cu in, .0102 cu ft or .28 liters.
I'd recommend taking any/combination of several methods to ensure clearance of basket frame/ magnet to the mounting baffle; i.e. rebating, separate mounting plate of thinner material (1/2" or less - say 1/8" aluminum or ABS) or champhering of the rear of driver cut-out on thicker material.
Whatever mounting method you choose, unless you're contemplating a very small enclosure, the volume consumed by the driver is minimal, and could certainly less than any cabinet bracing that might be employed.
Hi,
The whole box is gong to be 1/2" actually, desktop bipole.
So, 3.6L box with two drivers. So, I think volume of bracing and drivers might be fairly critical.
I guess I should have thought about it as a cylinder and done the calcs before asking. I seems like this would be available from driver specs. Maybe no because of different baffle thicknesses. Anyway, Thanks.
The whole box is gong to be 1/2" actually, desktop bipole.
So, 3.6L box with two drivers. So, I think volume of bracing and drivers might be fairly critical.
I guess I should have thought about it as a cylinder and done the calcs before asking. I seems like this would be available from driver specs. Maybe no because of different baffle thicknesses. Anyway, Thanks.
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Well, my number was a very rough quick calculation - Mr Dlugos had actually arrived at a much more accurate figure for the driver volume as part of his design for a small desktop monopole for this driver - perhaps he can pipe in with that number.
I don't want to assume anyone's experience with this driver - it might seem that 1/2" material would be more than adequate for enclosure construction, but don't underestimate the power of its motor. While the X-max and Fs are certainly limited compared to larger drivers, it can still shake a poorly braced box.
In the case of the enclosure design referenced above, 1/2" BB plywood was used, along with a horizontal holey brace connecting the back of the magnet to the rear panel. In addition, the full width port slot panel and full depth spacers provide a fair degree of bracing. Indeed, the funnest part is applying the (felted cotton) panel damping in the fairly tight confines of a 2 liter box.
An externally hosted image should be here but it was not working when we last tested it.
http://homepage.mac.com/tlinespeakers/FAL/box-plans/microFonken-0v9-map.pdf
The amount used up by the basket & the cone is very close to the volume gained by mounting them on an opened up 12mm baffle, so in the end one needs to just calculate the amount taken up by the magnet. I used 0.09 litres for this. The holey brace in the uFonken takes up 0.116 litre. All of this is calculated into the net volume of uFonken
dave
intuitive
analytical
and that's not a particularly big brace
note that the driver brace is not indicated in the 3-D phantom view on linked drawing, but as shown in section and plan views, is 102mm wide by approx 84mm deep(depending on depth of front baffle, and whether rebated)
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I'm going to use 1/2 MDF or Bird's Eye Maple, depending on availability and price. Definitely with bracing, even though I'll be listening at low SPLs, I want the best sound possible given my constraints.
I was thinking stuffing. Is felt better for a tiny box?
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Driver brace?
The driver brace actually touches the driver and braces it against vibration? Doesn't that require extremely close tolerances to make it both brace against the magnet and also seat correctly?
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that's been our experience - lining the walls with 1/2" felted cotton (reclaimed from old speaker boxes) or recycled denim insulation
http://www.creativesound.ca/details.php?model=UltraTouch Insulation
An externally hosted image should be here but it was not working when we last tested it.
whatever material is used, it's important in this particular family of enclosure designs to avoid occluding the internal opening(s) to port slot(s) - the required resistance is already calculated in their length/aspect ratio.
The brace couples the driver to (usually at least 3 panels of ) the shell of the enclosure, and rather than "bracing against vibration", assists in distributing and dissipating that energy through those panels
Yup, but the cutting doesn't really require any more precision than it takes for the rest of the parts to fit accurately. The trick is to fully assemble the box with one panel off (usually the side), and mount the driver to determine a "just right" dry fit of the brace. Even after dozens of pairs of boxes, it can still take me several trims, and you can always err on the loose side and use a small dab of duct-seal putty, blu-tak or PSA felt pad (not silicone ) to fill the gap
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