Bass Traps

I have no first-hand experience with DBA or with the C20.  However, according to PSi, the C214 is more efficient (and well as better looking) than the C20 and one would have predicted a more pronounced effect than shown by Katz.  Nonetheless, my FR measurements with the C14s were consistent with Katz' and did not seem to correlate with the audible effects which were immediately apparent to me.  That motivated me to examine decay times.

@OP I have experience of both products. The Synergistic box, at best, does nothing. If you look at it in the context of the laws of physic, that's not surprising.

The PSI AVAA C214 is a completely different animal. It is highly effective and the effect is readily audible. It takes a little bit of time to fine tune placement and the gain adjustment. When dialled in it is very effective at smoothing out the bass and has consequential effects up into the midrange.

While I'm a happy custoemr of GIK, another good source is ATS Acoustics.  Also always worth checking the AM Acoustics Room Mode Simulator for help understanding your problems and tips on speaker/listener positions

I tried first one and then two Avaa C214's in my room.  They did not do enough in my room to justify the costs.  One of them I got on loan from a local audiophile and he had the same experience.  If I had money to burn I would have kept them as they did tighten up the lower boom just a bit but ultimately I did not find them revolutionary in any sense, but many people I have spoken with do find them to be must haves...so maybe it was me??  

 I did not find them revolutionary in any sense, but many people I have spoken with do find them to be must haves...so maybe it was me??  

Nope. It is probably your room.  There is no one-size-fits-all solution.