BM mkIV 12" sub prototype

Just got this email from stereo integrity.
The BM mkIV prototype landed a few weeks ago and was tested with good results. The initial prototype used a very stiff rubber surround that simply would not give us the specs that we wanted so about a week after we received the prototype we sourced a much more compliant (softer) rubber surround so we rebuilt the driver with the new soft rubber surround and took more measurements. This time around the numbers are where we want them. With a stiffer suspension/surround than the mkIII the Fs is up a tad but is still below 20 Hz. **Here are the parameters for the BM mkIV 12" shallow subwoofer:*Re: 6.26< p>Fs: 19 HzQes: 0.54Qms: 7.97Qts: 0.50Le: 3.97Sd: 453.7 cm^2Vas: 71.3 litersBL: 19.9Mms: 287.5Xmax: 14mmXsus: 19mmSPL: 82 dB (1W/1M)*The rubber surround and traditional gasket with holes for easier mounting are a real advantage. You no longer have to call three of your friends to help mount the driver like you did with the mkIII with the hidden screw holes gasket. And the rubber surround is more durable than the foam surround found on the mkIII's.**Even though we are improving the parts and the peak excursion of the driver we are still going to rate the woofer at 450 watts RMS in our specified sealed enclosure volume of 0.5 ft^3. The mkIV, like the mkIII, will be a sealed only subwoofer.**Here is a video that we took of the prototype before we tore it down and rebuilt it with the better surround:*http://www.youtube.com/watch?v=7BK205IVVWM

 

I blew up 4 of those before Nick admitted there was an issue with them. Glad to see development has continued to make them better after my bad experience.

For those of you who haven't seen this woofer before, it's basically an exercise in how thin you can go and still get great low end response. It's a lot like the JL thin subs but not quite as expensive. And the enclosure size of 0.5 cubic feet is very small. Just make sure you have a solid 500 watts on tap because it's about as inefficient a sub as you'll find.

 

very exciting news, and just when i thought I had settled on 3 SD10's sealed, this comes along....gonna have to reconsider now

 

Email from stereo integrity

BM mkIV pre-ordering is open!



Today we received the final, correct, BM mkIV prototype and pre-ordering for the BM mkIV's is now open. We have given the official GO to our build house to finish full production so we should have the drivers by January or February 2014.

The BM mkIV has the proper aluminum diaphragm, correct spider, rubber surround, basket and metal color finish, etc. Everything is where we want it.

We did go ahead with the driver even though the shorting ring is not copper. The shorting ring is brass instead of copper so the price on the mkIV will not be $412. The price of the BM mkIV will be $398.

Pre-or dering is open right now for the BM mkIV's at $269 until November 18'th 2013 at which point the price will become $329 from then until the drivers are in stock at/around January or February of 2014 when the price will return to normal

 

thanks for the update. can't wait for the reviews.