4ohm mids on MTM D'Appolito???

Hello,

I'd like be interested in a few opinions.

I'm trying to do the front 3 (left, center, right) of a Home theater and was looking for shielded 6.5" drivers. Most of the designs I've seen use 2 eight ohm mids in parallel yielding 4 ohms nominal.

I saw some 4ohm 6.5" drivers and was wondering if there was any sonic reason I couldn't wire them in series and make an 8 ohm impedence characteristic? Does a D'Appolito design work any better (or worse) with the mids in series or parallel?

If I were to wire the two mids in series would I attach a zobel to the the top of the series and use an 8 ohm? Or would I attach a zobel using a 4 ohm to each?

Thanks
Bob
 
Hi Bob,

There are no sonic issues in using 4Ohm drivers in series.
Compared to the parallel wiring, the good is that your amp will see an easier load, the bad is that your speaker will be less efficient (at the standard 2.83V reference measurement)
Some brand produces (nominal) 8 Ohm drivers with a high DC resistance (I remember Focal had a series with 7.7 Ohm DC), typically a nominal 8 Ohm speaker has DC res of 6 Ohm.
With this high DC you can parallel the 2 mids w/o problems of low impedance load.

D'Appolito MTM design was originally intended for optimal disperdion in the crossover freq. range, it is dependent from the acoustical behavior of the speakers and the x-over freq, slope and phase (plus, of course, the geometrical position). So doesn't matter the impedance of the used drivers assuming that the filter is calculated properly.

For the x-over, zobel calculation and the box bass alignement you can assume the 2 drivers as a virtual one with the following parameters:

REv = RE x 2
VASv = VAS x 2
BLv = 2 x BL
MMSv = 2xMMS
CMSv = CMS/2
DBSPLv = DBSPL (at 2.83 V input)
All Q factors are unchanged

bye
sandro