Dear Fellow SC IVA owners

Hello all, I have researched D'Appolito designs quite a bit and built my first speakers in 1979.
"A true D'Appolito design requires a 3rd order 18bd per octave crossover allowing the drivers to have the same horizontal dispersion characteristics".
The above statement used to be accurate, but no longer is. D'appolito started that way and used 3rd order electrical slopes. Today, he has changed most of his designs to 4th order acoustical slopes. He specifically found that with the tweeter at ear level, this crossover improved the Symmetrical dispertion pattern maintaining good phase and amplitude summation.
4th order (linkwitz riley) acoustical puts your acoustical slope 6db down at the crossover point. Time alignment and proper phasing are much easier to achieve here and D'Appolito did tons of research of lobing and cancelation effects in vertical alignment.
I am currently useing D'appolito I use 12/18 electrical slopes to achieve 24/24 acoustic.
I am not speaking for Dunlavy in anyway, I have not seen crossover schematic for SC IVa

Also, Just looked at the SCIVA... The only thing in common with D'Appolito is that they use a wmtmw arrangement. Totally different design parameters. These Dunlavy's are extremely well thought out speakers. Dunlavy achieves time alignment through voice coil alignment, he keeps speakers very cohesive by using 6 db per octave slopes, he handles baffel step compensation by the use of felt...He tackles every problem.... in a different way and by what I can tell with terrific results.

I'd like to clean up a few points here before the end of the year. ;-)

Yes, I was wrong to call Dunlavy designs D'Appolito arrays. I do know John Dunlavy liked symmetrical driver arrays because they simulated a point source speaker when matching mid and woofer pairs equal distance (respectively) from the tweeter. I believe all of John's designs had first order crossovers to maintain time and phase coherency. Whatever D'Appolito uses or did use, it apparently was not first order.

Rrog called me out saying SC IV measurements were at 10 feet, not 3 meters. Well, I was referring to the Princess which had factory measured responses made at 3.5 meters, thus my suggestion for 10-11 feet listening distances. And as I think we agree, each room will be different so there is NO specific formula. Trial and error is necessary unless you are extremely lucky.

The third point is my agreement with Rrog in not understanding how adding a subwoofer will help the midrange when the main speakers and amp(s) are not being rolled off. My introduction to good subwoofers came from a dealer who demoed a sub set up by playing s solo violin recording! When the approximately lowest two octaves (20-80 Hz) are removed from the signal going to the main amp and speakers, their job becomes easier and improvements in upper bass and midrange can be realized, in addition to potential extended bass response. Now I cannot say that Jonathan did not hear improvements extending into the midrange (I was not there), but I will suggest he will hear a greater improvement if he reconfigures his system to roll off his SC IVAs and main amp within the range of 50-100 Hz. The best point must be determined in his system.

Lastly, Dunlavy utilized stepped baffle designs, in addition to wool felt, in his Duntech speakers. As I recall the DAL speakers have a flat front baffle but still utilize the wool felt and crossovers to assist the time and phase alignments. Yes John was among the relatively small group of truly great speaker designers.

Hi Pryso, the wool was strictly diffraction control. I agree with you on the subwoofer points also.

Pryso, the Dunlavy's also have stepped baffles, in order to maintain proper time alignment.