18’’super scooper VS. 1850 horn

is it still 8ohms when run passively because of the cross over? as two 8ohm drivers in parrallel would normally be 4ohms....i'm trying to sort out my own passively x-over 2way high freq design at the moment and am a little unsure of the effects of passive x-overs on the total resistance of the speaker system

cheers

.....i've read that just about everything effects the actuall end resistence of the speakers.....i'm just trying to get an idea of how much power each cab will required to drive the individual components to decent levels...and avoid running my amp's into an impeadence which is too low..

cheers for the advice..

phil

silworm: if you're going to run them with a passive crossover, then you have two options:
if you don't mind missing out on the stereo, you could bridge that qsc amp (it will give 1600w@4ohm bridged) and run both x15s parallel off that.
if you need the stereo still, then you'll need an amp that will give you about 800w@80hms per side, which is actually pretty hefty (qsc 3402, or nfinite6 maybe?)

however passive crossovers always waste some energy. after all (and much to dubsuctions confusion recently ;) ) they have a resistance themselves and so there is a voltage drop across the x-over as well as the speakers. ideally you would run your whole system actively, in which case for stereo you would need one amp that gave about 600w@8 per side and one that gave about 2-300w@8 per side

dubsuction: a passive crossover (always, as far as i know? and of course nominally, dont worry martin ) just acts as its given resistance in series with the other components. the vx crossovers' resistances aren't stated on the p.a.p site, but i think it's very likely they would be 4ohm, which would make the overall resistance of the system two 4ohm loads in series, i.e. 8ohm

some learning for me now....
martin:
nominal values aside, don't these 'bumps' in the impedance of a speaker/crossover system directly translate to bumps in its acoustic output? box resonances and phase cancellations obviously taken into account as well, wouldn't the impedance relate to the response pretty straightfowardly?
or do resonant modes in the speaker and suspension itself also greatly affect the response?
how much of a reverse e.m.f. effect does the mechanical resistances/resonances of a speaker in a box have? i.e. how much change will you see in the impedance of a driver when you load it into a long horn
cheers mate

joe

AFIK the bumps are as a result of interaction with the various components which are different in regards to electrical phase too (it gets rather complex)

An ideal filter with resisticv elements substituted for speakers would in theory result in an impedance that's relatively flat or has a small bump at x-over I think (I am an active person, so I don't really care too much about passive x-overs)

The problem is that in some poor crossover designs the impedance can dip very low. This is not only bad for the amp i.t.o current, but also means that the components of the x-over need to be rated at much higher currents.

Now unfortunately speakers' impedances are anything but flat, so one has to take a lot more care. In the end it's not about the filter characteristics of the x-over components on the theoretical "nominal" resistance of the speaker but the interaction of filter components that are wired in series/parallell with the drive unit which result in the most desirable outup. This is not limited to on-axis response, but also effects the response off-axis response/ distortion/ etc.

Unfortunately I'm not too knowledgable on passive x-overs (apart from having come up with one design in speaker workship for hi-fi use which worked out alright)

Regards

Martin