View Full Version : Am I nuts to go isobarik with LE15A's?

07-08-2005, 03:07 PM
I've got four 1960's LE15A's with original cones. The re-surround kits are on their way. I'm thinking about what kind of cabinets to put them in. I'm limiting myself to a cabinet volume of 4 ft3 for, let's just call it, family reasons. I of course want to use all for drivers because more is better.

I see that iso-barik designs yield a great 3db roll off for given size cabinet. My question is this: Are these speakers too old to go iso-barik?

I'll be using a 375 for mid and 075 for highs.

Ian Mackenzie
07-08-2005, 03:21 PM
What sort of sysem were you planning?

07-08-2005, 03:33 PM
I don't know looks like it could work. 2 in 4cuft 32Hz tuning


07-08-2005, 03:33 PM
Home stereo for living room. Two separate cabinets each with 2ea LE15A's, 1 ea 375 compression driver with H93 horn and one each 075 bullet ring radiator. Using LX5 and N7000 for crossovers. I don't own the acoustic lens for the midrange horn. I might try to buy one or fabricate one. Thanks for asking!

07-08-2005, 03:37 PM
Yep, I've been playing with the same program. I'm concerned about the drivers ability to handle the extra stress I *imagine* that the isobarik configuration introduces on 40 year old cones. Glad to see someone else using winisd!

Ian Mackenzie
07-08-2005, 04:30 PM

I just did a qucik sim im bassbox 5.1, allowing for 10% increase in QTs due to crossover dcr and amp X output impediance and using normal fill Bassbox gave an opimum Vb of 4 cu ft 3, Fb 31.7 and f 3 of 45 hz and using (2) 4inch ports 1.8 inches long

Now, if you were to compound the drivers in push pull (back to back or face to face) you half the Vas in theory and 1/2 the Vb becomes 2 cu ft 3 and port length 8.4 inches. Fb remains 31.7.

This configuration will yield lower 2nd and 3rd harmonic distortions as the drivers operate in anti phase where the cones are inverted.

Assuming room gain of +3db at 50 hz the response is flat to 30 and -3 at 20hz. Max spl is 124 db at Fb
You could also apply a small amount of LF boost around Fb to give more extension. If you are game and have the patience to tweak you could try a KB Keele Jnr 6th order system with push pull compound configuration but they are more critical to tune in practise than the above alignments.

Bassbox by the way has a very high degree practical accuracy in modelling bass response.


07-08-2005, 06:20 PM
LE15A Isobarik, BB6 recommended "Extended bass" alignment. Isobarik gets you lower distortion and half the box size. Excursion limits still apply, tho, and you've got to deal with aesthetics. If you mount the drivers back to back in a tube, total box size is 4.795 cuft.

07-08-2005, 10:27 PM
Thank you Ian and Zilch. Good stuff. I'll check out BassBox.