A short review of the audio Development ESA Bass & Vipera F6 midbass speakers:

Before using the AD speakers, I had a pair of Dynaudio 650s in each door powered by a Brax Matrix MX4 with two channels bridged to each pair. They were in a 3-way setup with a band pass of around 80-450 Hz.

In a quest for increased low-end midbass with the special requirement of maintaining composure at high volume levels, and after discussing my goal with Jerry Niebur of High Definition Mobile audio and Emilios Mandalios of Audio Excellent, I first purchased a pair of the Vipera F6.

The F6 has a Xmax listed as plus or minus 13mm. It definitely provided the low-end midbass I was looking for, and performed very well at high volume levels with a high pass as low as 55-60 Hz. It is, however, more of a subwoofer than a true midbass, and was not as detailed and articulate as the 650.

I then decided to try the AD ESA Bass which is more of a true midbass. Immediately after installing them, I noticed the return of the detail I had with the 650. The ESA was smooth and articulate and very comparable - if not better than - the 650 in the 80-450 Hz range. Below 80 Hz, I feel like the ESA produces more output with more control at high volume levels. I currently have them on a high pass of 65 Hz.

The face of the ESA and F6 look very similar. The ESA is on the right at the front of the door, the F6 on the left. Sorry I don't have any pics of the rear of the speakers right now to post.

The ESA and F6 are currently on the same channel. I know this is not ideal, but they actually sound quite good this way after some tuning with a Helix DSP Pro. I hope to run a 4-way setup soon with each on its own channel.