|  IP: Logged

 |  IP: Logged

 |  IP: Logged

 |  IP: Logged

Five 8 ohm speakers in parallel comes out to 1.6 ohm. That already below the minimun. Since impedance is usually defined at 1kHz, in actual operation, it could get much lower.

This is taken from the instruction manual for the QSC models USA 370, USA 850, USA 1300:

"The USA series amplifier has adequate current capaiblity to fully drive loads down to two ohms. However, many high performance 8-ohms loudspeakers, especially multi-way systems with passive crossovers, have impedances at some frequencies which are far lower than the average rating. (snip) For this reason, impedance curves should be consulted before connecting speakers in parallel. (snip) Two ohm loads should be approached with caution, as there is no further margin for impedance dips. (snip) For these reasons, operation with two ohms loads should be tested throughly before being put into use."

I'm assuming that for this application, where it says, "two ohms," it means at two ohms or less.

70v systems (actually it was 70.7v; sound familar!?) were originally meant for large area speaker distribution. The voltage was stepped up so you could buy thinner (cheaper) wire; nice if you are wiring, say, a large stadium. All speakers connected to that line, and transformers did the voltage reduction and impedance matching. You could buy different 70v transformers to increase or decrease the volume in different areas. Suppose there was a small corner of a stadium where you didn't want the sound to be too loud. You connected a different 70v transformer to the same 70v line and it was reduced.

The only QSC cinema amp that is rated to 1.6 Ohms ( at the momenet) is the DCA1222. In fact, it was designed with just that in mind so connect up!

A series/parallel connection is really to be avoided if possible...the series connection will muddy up the bass a bit. As a fun experiment at home...try putting a power resistor in-line with your speakers and hear what happens to the bass. Some people even like the effect.

The USA line of amps (and the remaining series 1 amp, the 1400, which is the USA 850/900 with a different input module) really should be targeted for 4-8 Ohms. At 2-ohms they will tend to breath rather hot out of the front of the amp.

The MX line (my favorite) is just fine down to 2-ohms as are the rest of 2-channel DCA amps.

The new 4-channel DCA amps offer other options (besides the obvious Surround-EX implications) in that one can break the surround array up to avoid impedance problems without going to a series connection. Also, one can have front and rear zones to better balance the level of the surrounds with the stage channels as one moves back in the auditorium.

Steve

And thanks to Steve for bumping the topic (and me!) in the right direction.

Although the QSC page is a little confusing: the DCA 1222 amp's spec page says down to 2 ohms, but the app note says it can go to 1.6 ohm.

Ya gotta admit, 1.6 ohm is a little unusual!

Also, if I remember correctly, impedance won't always split correctly with speakers wired in series. The slightly different mechanical characteristics of each speaker effect it while in use.