BM mkIII dimensions

[Electrodynamic]

Here is a technical drawing of the BM mkIII's basket for all of your mounting depth and cutout desires. All the dimensions are in mm.

[Electrodynamic]

And to save you all some time:

Overall diameter without the gasket is 12.36"
OD with the gasket is 12.6"
Cutout diameter is: 11.023"
Mounting depth is: 3.4" (or 3.2" without the gasket)

[zacjones99]

So what are the recommended enclosure volumes?

.4cf sealed for 300w and .5cf sealed 500w? How about ported?

Do the above sealed enclosure sizes account for any polyfill or fiberglass insulation being stuffed into the enclosure? Does that mean we can go down to .3-.4cf sealed if we stuff with polyfill?

[Subwoofery]

The bigger you go the less power you can apply to the driver.
Eg: 0.5cuft sealed with 500rms --//-- 0.6cuft sealed with 400rms --//-- 0.4cuft sealed with 300rms

Kelvin

[Electrodynamic]

You can ultimately do whatever you want to do. We cover the BM mkIII drivers for 450 watts in 0.5 ft^3 sealed. However you want to manipulate the enclosure volume is up to you. However, in 0.5 ft^3 sealed, the BM mkIII's will handle 450 watts RMS without a problem.

But as Subwoofery said, the larger enclosure you choose, the lower the power handling.

[Invinsible]

What will be the Qtc with 0.5 cu.ft of enclosure?

I understand that in car environment cabin gain too plays the role in boosting low end output. Can it be played in bigger enclosure size ?

[zacjones99]

So what is the volume displacement of the driver when top mounted? Trying to get the box just right...

[Electrodynamic]

The volume displaced by the driver is 0.05 ft^3.

Qtc is a 1.2 in 0.5^3 sealed. You can place the driver in a larger enclosure if you absolutely have to, but power handling will go down substantially. In a car audio environment there is no reason to put the driver in a larger enclosure unless you want an over-exaggerated bottom end and greatly reduced power handling. In a vehicle, hitting your target F3 (it should be in/around the mid 40's) is the most important aspect. Qtc is valid for home applications, but not so much for cars due to the +12 dB/octave gain you get starting at approximately 45 Hz.

[zacjones99]

Nick thanks for that reply on the volume displaced and qtc, target f3.

So I had just about given up trying figure out if these puppies will fit into the box I have room for behind the seat. I tried bassbox and that wouldn't tell me. Modeling it in autocad would have been a chore, for what little I learned last time I needed it I have most likely forgotten. But then it dawned on me... keep it simple stupid! So I just modeled it on paper with a ruler and scissors and voila~ they will fit!

My calculations tell me that this driver will just barely fit in an enclosure 15" tall, 7" deep at the bottom, and 4" deep at the top, recess mounted 3/4" into a double baffle so that it is top mounted to the first baffle. I feel kind of silly fretting over this for a while now when all I had to do was scratch it out on paper! Anyway I'm happy to know that it will fit. I may end up having to scratch away a little with a chisel inside the box, but I don't think so. Is there a minimum clearance at the corners of the back of the driver? I wouldn't think so, just so that they're not touching the enclosure right?

For anyone else wondering about minimum enclosure size... this is it with this baffle angle, unless you want to use something other than 3/4" material or like I said chisel away inside the box and maybe cover it up with a couple layers of fiberglass.

Nick you're not selling grilles for these are you? Can someone recommend a really sturdy one? The grille is likely going to be in some contact with the back of the seat, and I'm going to need a pretty substantial one to protect the driver. I'm a big fat ****er and I'd hate to bend a grille sitting back into my seat and have the driver start smacking into it!

[zacjones99]

One more thing... and I'm sorry if I'm a pest, as I know I have asked this question before.

To get the .5cf requirement I have to make the enclosure 15.125" tall x 23" wide x 7" bottom depth x 4" top depth. If I tuck these enclosures in out of sight behind the seat, I have room for two of them but that only leaves me 6" between them for an amp rack.

The amp I'm looking at for these is the Zed Kronos and it's 9.7" wide with heat sinks on the sides. It'd be nice to allow 12" for the amp between the speaker boxes. I could accomodate the amp there by cutting the enclosures down to 20" wide, and compensate for the lost volume by:

(1) Adding a little fiberfill to bring the Qtc of the .424cf enclosure down to the recommended 1.2 Qtc.

(2) Reducing the front baffle thickness to 1.25 and adding a little fiberfill to bring the Qtc of the .461cf enclosure down to the recommended 1.2 Qtc.

(3) Reducing the front baffle thickness to 1" and adding a couple fibrous strands to bring the Qtc of the .497cf enclosure down to the recommended 1.2 Qtc.

Reducing the thickness of the front baffle does, however, push the driver and grille farther into the seat.

So which of these of these would you consider to be the best compromise? If you think all of them would represent a significant compromise then I could mount the amp under the seat, but that would involve putting the seat up on risers and a fair amount of extra work. I also wouldn't be able to look at that beautiful amp whenever I felt like it. Work that I'm willing to do and a sacrifice I'm willing to make for quality sound, however, if necessary.

Anyway thanks for your patience Nick. If I was a little more knowledgeable about acoustics and speaker and enclosure design I wouldn't need to ask these questions. I think the answers to these questions might be useful to others as well, as I imagine there will be others like me looking for that last little piece of real estate back there too.