Not your daddy's dipoles

[fernandov]

Just finished an OB design that incorpoartes some interesting concepts. I spent the weekend listening and I am favorably impressed.

Here's a quick summary and some pics...

Type: OB dipole up to approx 5.5k Hz. Biamped helper woofer, actively crossed and EQ'd. Coaxially mounted single point source pro audio driver w/traditional 1" fabric dome tweeter (Morel MDT-20). Acoustically dampened and isolated panels w/closed cell foam suspension. Visco-elastic anti-vibration feet.

Helper Woofer: Peerless 10" Nomex XXLS woofer (PE Buyout). 250Hz lowpass filter @ 24dB/octave.

Mids: Eminence Acoustinator CX2008 8" poly coax, 1 3/8" 18 TPI threaded chamber, allowed to roll-off naturally.

Highs: Morel MDT-20 mounted coaxially, 1.8uf single cap, 6dB per octave.

Initial crossover points surprisingly good. Will spend some time tweaking. The drivers produce some respectable SPL's w/o strain. These were initially designed with many genres in mind. The acoustinator's mida are slightly dark, but still make for a realistic presentation. The voicing is very pleasing to me. They are just as apt to produce electronic music, possibly due to a very satisfying lower mid presentation... thus the title of this thread.

[fwater]

Re: Not your daddy's dipoles

Fascinating. I love to see builds with differents ideas and approaches.

How is the tweeter mounted to the mid? Was there a need for padding it down, and have you rolled any other XO parts through? Is there anything about the Morel unit that you feel makes it better suited to this implementation? Lastly, plz describe the suspension used to mount the drivers (the pics are a little fuzzy).

[fernandov]

Re: Not your daddy's dipoles

Fascinating. I love to see builds with differents ideas and approaches.

How is the tweeter mounted to the mid? Was there a need for padding it down, and have you rolled any other XO parts through? Is there anything about the Morel unit that you feel makes it better suited to this implementation? Lastly, plz describe the suspension used to mount the drivers (the pics are a little fuzzy).

The tweeter is actually mounted to a 18 TPI to 2 bolt horn driver flange adapter. The Emi CX2008 is a poly mid woofer that accepts a 1 3/8" screw in driver. Once mounted, the acoustic center of the Morel closely matches the center of the mid/woofer, offering a true point-source arrangement.

The sensitivity of both drivers is roughly the same; 90dB @ 1w/1m so padding is not needed. The morel is crossed with a single cap and the CX2008is allowed to run full range; it's upper rolloff is quick and graceful starting at about 6k. I mounted and auditioned 11 tweeters for this project. The warmer Morel was the most pleasing driver, helping to offset the darker voicing charasteristic of the CX2008.

As far as the driver mounting goes, the sub and mid woofer are first mounted to their own MDF panel. Each panel is then suspended from an MDF backer. The panels and backer are seperated by a layer of closed cell foam. The mounting hardware is also unique in that it is set-up to minimize vibration transfer from the 2 baffles to the common backer. Similar to acoustically isolated drywall clips in a well built home theatre room, the bolts and lock nuts do not come in direct contact with walls of the panels. The end goal is to prevent vibrations emitted from the high-ish moving mass of the sub from negitively impacting the mid/high coax assembly. If you touch the upper panel and lower panel, you can easily feel the difference in their movement.