My first quick attempt at B139 DIY sub

[phidauex]

Please do at least SOME calculations! Even if its just plugging the driver's numbers into one of the many subwoofer calculators, and using whatever it spits out for a sealed enclosure.

Or even simpler, just use the manufacturer's recommendation for sealed volume.

If you deviate too much, you may end up with something really unfortunate. It doesn't matter when its cardboard, but if you are paying someone to build up 4 enclosures out of 1" MDF, its worth doing it right (or at least close to right)!

BTW, composite carpet padding foam makes pretty good damping material, for the cost. You'd need to layer it to get the right thickness though. Egg crate and other such homogenous foams are not so good.

peace,
sam

 

[ToTo Man]

I was going to use the page clmrt shows but that b139 driver is a later lighter model than my one so i'm not sure how far those values would deviate from my one. for example, the B139 1044 has an Fs of 25hz, but i'm sure the B139 6171 (my model) has an Fs of 20hz. would these deviations affect my calculations?

clmrt, is it better to have a sealed enclosure or a vented enclosure for the b139? what would the difference in -6db frequency be with a sealed enclosure?

 

[Clmrt]

Vented, since the Xmax is small. Plus, if possible, a hi-pass just below the tuning point. Or SMALL sealed....

Actually, I'm just running the numbers I find in that one spec sheet and from another web site. After I ran the first simulation, I found more info and added more parameters, and it changed things slightly.

The key is to download WinISD and play with it, get a feel for things. It's a simulation, though, not real world. Real world is the thing built and operationg in your room. A sim will show you if the bird has a chance to fly or not.

 

[Nat]

Putting a driver in a larger box to get lower bass is a technique left over from the days of stiff suspensions. It isn't as great an idea with high compliance woofers, which usually need the restoring force of the air in a small enclosure, and which already have a low resonance so slapping them in a bigger box may lower the resonance too far, giving you flabby bass and the potential for overdriving the woofer.
How shall I put this tactfully -- with a pair of drivers of the B 139 caliber, and so carefully speced (specced?) you really shouldn't avoid calculations. Either use KEF's suggested volume, or work out another alignment. There are tons of woofers out there that can be sacrificed to your learning curve, but the 139 shouldn't be the ones. If you simply want woofers, I'd be happy to trade, and I'm sure plenty of there people would be too.
I say this recognizing that they are your woofers, and you can do whatever you please with them. And that your random alignment might please you immensely -- most projects do delight their makers, even if no one else. And I'm as guilty as anyone else...

 

[ToTo Man]

Been playing round with WinISD and I agree that a vented design is a better option for the B139. Then its a case of weighing up the volume of the box with the tuning port frequency to get the 'best' compromise. I suppose the ideal one would be a volume of 200 liters and a tuning frequency of 25hz, as this gives 30hz at 0db and 20hz at -8db, but as Nat said this volume might be too large for the B139 to handle.

 

[Fast_Eddie]

I use two car stereo speakers in cardboard boxes in my garage. It's not perfect, but it works ok. I mean, it's better than when I had them stuck to a piece of conduit by the magnets.

 

[ToTo Man]

I suppose I could always just use my KEF Concertos as subwoofers and disconnect the mids and tweeters. I know its sacrilige, but the its an easily solution and the bass is flat down to 35hz. I don't like the overall sound from them anyway - they really are mid-range dominant and lack treble (reminds me a bit of my Kenwoods!), so I may as well put them to some use!