Volume of FF85K for internal box size calculations

[roadsterdriver]

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.

[chrisb]

Originally Posted by roadsterdriver

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.

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.

[roadsterdriver]

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.

[roadsterdriver]

Just got them in.

Wow! These are small!

[roadsterdriver]

Just got them in.

Wow! These are small!

[chrisb]

Originally Posted by roadsterdriver

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.

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.




http://homepage.mac.com/tlinespeaker...en-0v9-map.pdf

[chrisb]

Originally Posted by roadsterdriver

Just got them in.

Wow! These are small!

they certainly don't sound that way though

[planet10]

Originally Posted by chrisb

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.

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

[chrisb]

Originally Posted by chrisb

not much



Whatever mounting method you choose, unless you're contemplating a very small enclosure, the volume consumed by the driver is minimal, and could certainly (be) less than any cabinet bracing that might be employed.

intuitive

Originally Posted by planet10

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

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)

[roadsterdriver]

Originally Posted by chrisb

...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.

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.

Originally Posted by chrisb

Indeed, the funnest part is applying the (felted cotton) panel damping in the fairly tight confines of a 2 liter box.

I was thinking stuffing. Is felt better for a tiny box?