BM mkIII FAQ

[Electrodynamic]

Our web guy is out of commission for a few weeks, so until he gets better here is the BM FAQ:

What is the mounting depth if mounted on a normal ¾” piece of material?

When mounted to a ¾” piece of MDF or other material the mounting depth of the BM mkIII is 2.75”.


What size enclosure can I put the BM mkIII in?

For optimum performance the enclosure volume can anywhere between 0.42 ft^3 and 0.55 ft^3 sealed. We highly recommend stuffing any sealed subwoofer enclosure with polyfill and/or fiberglass insulation.


Can I put the BM mkIII in a smaller enclosure or a larger enclosure?

Yes you can. However, power handling and/or low frequency extension will be affected. The BM mkIII has been engineered to provide optimum performance in 0.5 ft^3 sealed. Making the enclosure volume significantly smaller than recommended will cause a reduction in low frequency extension. On the other side, making the enclosure volume larger will significantly reduce the power handling of the driver.
If you make the enclosure smaller than recommended (0.5 ft^3 sealed), we highly suggest using an aperiodic membrane such as a ScanSpeak Variovent.
Making the enclosure larger will diminish power handling as follows: In 0.75 ft^3 power handling is reduced to 400 watts RMS. In 1 ft^3 the power handling is reduced to 300 watts RMS.


How much room does the BM mkIII take up inside the enclosure?

The BM mkIII 12” subwoofer displaces 0.05 ft^3.


How much room do I need behind the subwoofer?

If you have no other choice, you can put the back of the BM mkIII 1/8” away from the back of your enclosure. Ideally there should be ¼” to ½” of space behind the BM mkIII.


Does the BM mkIII need 450 watts RMS to perform?

Absolutely not. The new BM mkIII is a very efficient subwoofer thanks in part to its XBL^2 enabled motor and it does not need every bit of its power handling limit in order to perform well. In its recommended enclosure volume of 0.5^3 sealed, the BM mkIII’s ideal power range is 200 to 450 watts RMS.

[ma_ttcald]

Great post. Looks like I'm going to go easy on my gain, since my amp is rated @ 500rms.

edit: why the need for stuffing?

[Electrodynamic]

Originally Posted by ma_ttcald

Great post. Looks like I'm going to go easy on my gain, since my amp is rated @ 500rms.

edit: why the need for stuffing?

Stuffing an enclosure (we recommend lining the walls with fiberglass insulation over using polyfill) reduces internal resonances which smooths out the overall response. It also fools your subwoofer into thinking it's in a larger enclosure. For instance, if you had an enclosure that was 1 ft^3 and you stuffed it with a pound of polyfill the subwoofer would think it's in 1.25 ft^3. I.e. it will play lower.

[ma_ttcald]

Originally Posted by Electrodynamic

Stuffing an enclosure (we recommend lining the walls with fiberglass insulation over using polyfill) reduces internal resonances which smooths out the overall response. It also fools your subwoofer into thinking it's in a larger enclosure. For instance, if you had an enclosure that was 1 ft^3 and you stuffed it with a pound of polyfill the subwoofer would think it's in 1.25 ft^3. I.e. it will play lower.

Even if my box is at .5 cu ft, stuffing is still a good idea? If so how much?

[Electrodynamic]

Originally Posted by ma_ttcald

Even if my box is at .5 cu ft, stuffing is still a good idea? If so how much?

Stuff is always a good idea for any size sealed enclosure. Simply apply the general rule I posted in my previous post. In your case, stuff the enclosure with a half of a pound of polyfill since your enclosure volume is 0.5 ft^3.

But we still prefer fiberglass insulation lining most of the interior walls to polyfill because of the acoustic benefits over simply using poly.

...actually I didn't say it was a general rule in that post did I? Anyway, the general rule for stuffing sealed enclosures is: 1 lb of polyfill per 1 ft^3 of volume. If you have 1.4 cubes, use 1.4 lbs. If you have 0.37 cubes, use 0.37 pounds.

[dantonel]

What Fiberglass Lining do you recommend?

[Electrodynamic]

Something like this. The smallest, tiniest roll you can find. Don't smother the subwoofer, but line the walls with it.

[Mid Life Crisis]

I was just going to put in my order for 2 BM MkIII but was not sure what Ohm load they carry? Are they 4ohm or 2ohm?

Also, what is the release date for the preorders? If I order now will I still get them within the 60 days?

Thanks!!!

[Electrodynamic]

The VC configuration is stated on the right hand side of the BM mkIII's web page, "2.5" diameter, dual 4ohm, voice coil".

We're still putting some test drivers through power testing right now but I'll have an update on the ETA for actual shipment in the next week or so.

[Mid Life Crisis]

Originally Posted by Electrodynamic

The VC configuration is stated on the right hand side of the BM mkIII's web page, "2.5" diameter, dual 4ohm, voice coil".

We're still putting some test drivers through power testing right now but I'll have an update on the ETA for actual shipment in the next week or so.

Gotcha..... I completely missed that part! One more question.... I know I read that it was designed for .5cubes and a larger enclosure will reduce the power handling, but what will it do to the longevity of the driver? If say its in .66cubes will it change the sound charictaristic to be more of a boom rather than tight thump?

Sorry for the questions. Just trying to get all the info I can so when I purchase them I am 100%.

Thanks again!