Building Resonance Free Subwoofers

@terry9 Thanx!  I have never heard the DWM. I assume you are using Magnepan loudspeakers. Where does the Isobaric sub come in?

It is important to note for the gallery that properly made cylindrical subwoofer enclosures do not require any bracing as they are inherently extremely stiff. Another interesting trait of the decadron cylinder is if you travel around the long axis in radians the enclosure wall thickness is constantly changing from 1 15/32" to just over 2 " at the joints. The enclosure wall dampens itself.  

I use four modern Quads, modified. They are crossed over at 18dB, 200 Hz (factory), but they need stabilizing, which is easily done with a platform box of baltic birch with a non-resonant top. Each box is stabilized with a Bryston mono block on the lower shelf, so I use the mass instead of it using me. Soon the DWM's will be further stabilized by Al bracing, a la Mye.

I am building an active crossover, must get back to it.

Subs are also a dipole isobaric, premium 10" Scanspeak woofers, crossed at 50Hz, 18dB. Both DWM’s and Scanspeaks are unusual in having good transients and linearity extending more than 4 octaves above the crossover point, so that the transitions are pretty seamless (to me, another Quad user, and a Magnepan owner). Sub drivers are also Bryston powered - bass doesn’t need more, but it also sounds a lot better than less. IMO.

You are so right about active control over the bass. Would never go back. Both of my bass systems are actively controlled in terms of volume, but only the sub has an electronic crossover.

@terry9 Go for it! IMHO there is no such thing as too much power for subwoofers. With the amount of gain required at 20 Hz and the corrections room control makes some frequencies are going to be plus 15 to 20 dB. That is 6 to 8 times the amount of power required!

Mini DSP makes a very inexpensive digital subwoofer crossover. You might want to try playing around with one. You can get slopes up to 96 dB/oct! Even if you do not use it in the end it will help you determine what the best crossover points and slopes are.

ESLs are the best! 

And DIY forever!