semi OB/isobaric?

Yeah, folks have done that. You can look at my Lii F15 thread for a post by Dadbeh, #164, which shows a drawing having such "extended side panels".

Regarding the isobaric, I've heard it commented that by simply running both woofers in the normal way doubles the effective cone area. This follows a general rule "there's no replacement for displacement" - which I believe is valid for both woofers and piston gasoline engines.

You can imagine with two cones operating in concert, they only have to move half as much to push/pull the same air volume. The shallower movement keeps suspensions more nice and linear, voice coils more centered in the magnetic gap. You can see plenty of designs that use two large woofers in this way, which I spose substantiates the idea...

Some of the big woofers only move 2mm max, two of 'em could do it only moving a mm. The isobaric would still move the full 2mm, but there must be some other advantage I dont understand...
 
Hi Pete,


Bert Doppenberg from The Netherlands once had a pretty clever design with a Feastrex 5-inch on the narrow front part and 2 bass drivers on the wider wings of the baffle, but I can´t find it anymore in the net. Of course this had nothing in commen with an isobaric design.
Some time ago, I planned to adapt his design for another 5-inch on front and 2 10-inch on the sidewings, the 2 bass drivers of course wired in phase, but I never built it so far. All in all, a pretty clever design which requires a little bit of woodwork skills.
Another thing is a construction with 2 or more bass drivers situated behind each other (Kronos Gaia, Legacy and others). This configuration acoustically simulates a larger baffle than physically available, works only in the bass region, and takes away a little stress of the woofers, but does not halve it. Of course, in parallel you´re halving impedance and thus have better efficiency at 2,8 volts (not with 1 watt...).
Hope that might have helped... if not, I didn´t understand the TO´s question well. A sketch might help.


All the best


Mattes
 

Disco-Pete

Member
Paid Member
2009-11-30 10:04 pm
Hi Pete,


Bert Doppenberg from The Netherlands once had a pretty clever design with a Feastrex 5-inch on the narrow front part and 2 bass drivers on the wider wings of the baffle, but I can´t find it anymore in the net. Of course this had nothing in commen with an isobaric design.
Some time ago, I planned to adapt his design for another 5-inch on front and 2 10-inch on the sidewings, the 2 bass drivers of course wired in phase, but I never built it so far. All in all, a pretty clever design which requires a little bit of woodwork skills.
Another thing is a construction with 2 or more bass drivers situated behind each other (Kronos Gaia, Legacy and others). This configuration acoustically simulates a larger baffle than physically available, works only in the bass region, and takes away a little stress of the woofers, but does not halve it. Of course, in parallel you´re halving impedance and thus have better efficiency at 2,8 volts (not with 1 watt...).
Hope that might have helped... if not, I didn´t understand the TO´s question well. A sketch might help.


All the best


Mattes
Right. I meant another woofer shrouded by the side panels on standoffs facing the same direction as the one on the baffle. Standoffs/ side panels' length tuned to suit.
 
Some of the big woofers only move 2mm max, two of 'em could do it only moving a mm. The isobaric would still move the full 2mm, but there must be some other advantage I dont understand...
Yes, that can be applied also to smaller woofers. I think that it's the very reason of why isobaric was born, to extend a little the bass from older units, as it's not a new idea. The woofers were a little stiffer, so Cms and Vas would benefit from such arrangement. Indeed, I did try it with old woofers and it worked, putting new ( rubber surround and 4 mm excursion one way ) resulted in a broken/rubbing former in a woofer, probably suffering from the elasticity of air in the chamber between them.;)