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Church and H.O.W. Forums for HOW Sound and AV - Your Displayed Name Must Be Your Real Full Name To Post In The Church and HOW Forums => Church Sound Archive => Topic started by: greg molina on September 17, 2010, 09:51:18 am

Title: 2 ohm load on a qsc rmx 1450 amp?
Post by: greg molina on September 17, 2010, 09:51:18 am
hello peeps, tnx in advance for all inputs shared. for spoken words in a catholic church with enough ac current on the whole pa system, can i get away with hooking up 4 ev sx-80/8 ohm cabs per channel for the main system? normal church temp. where the main pa cab is around 85 deg f. the pa is used twice a day, except sunday, where it's 4x.i can probably put an external mini fan to cool the amp.
Title: Re: 2 ohm load on a qsc rmx 1450 amp?
Post by: David Sharp on September 17, 2010, 09:28:23 pm
I think you'll be fine for just spoken word. 2ohms in stereo mode is within the specs of that amp:

http://www.qsc.com/products/amps/rmx/rmx.htm
Title: Re: 2 ohm load on a qsc rmx 1450 amp?
Post by: Jonathan Johnson on September 18, 2010, 04:36:20 pm
While you're at it, you should get that shift key looked at. It doesn't seem to be working.  Wink
Title: Re: 2 ohm load on a qsc rmx 1450 amp?
Post by: Arnold B. Krueger on September 19, 2010, 08:47:18 pm
greg molina wrote on Fri, 17 September 2010 14:51

hello peeps, tnx in advance for all inputs shared. for spoken words in a catholic church with enough ac current on the whole pa system, can i get away with hooking up 4 ev sx-80/8 ohm cabs per channel for the main system? normal church temp. where the main pa cab is around 85 deg f. the pa is used twice a day, except sunday, where it's 4x.i can probably put an external mini fan to cool the amp.


Another alternative is to hook the 4 speakers in series/parallel.

Make up two pairs os speakers in seires, and then hook the two apirs of speakers in parallel. Results: amp load = 8 ohms.

This is not to dtract from the suggestion that you run the speakers in parallel for a resulting load of 2 ohms - just another alternative that may help you in the future.
Title: Re: 2 ohm load on a qsc rmx 1450 amp?
Post by: Brad Weber on September 20, 2010, 08:21:48 am
How are the cabinets arranged?  If the eight speakers are distributed, say four down each side of the space or similar, then you may have some level adjustments delay or other processing that relate to specific boxes rather than to all of the speakers.  Maybe that is handled by the two channels addressing two 'zones' of speakers, but you probably want to be sure that you are not limiting yourself by paralleling four speakers on each channel.

A good example here of looking at the details in that while the EV Sx80 is a nominal 8 Ohm impedance, it is less than 8 Ohms between roughly 170Hz and 250Hz, being 7.2 Ohms at around 200Hz, while it is greater than 8 Ohms at other frequencies, in fact up around 3kHz the impedance is over 150 Ohms.

At the same time, the QSC RMX1450 shows only an EIA 1kHz, 1% THD rating at 2 Ohms, it does not show a 2 Ohm FTC 20Hz to 20kHz, 0.1% THD rating as it does for 4 and 8 Ohm loads.

This combination of the speaker impedance and amp rating details indicates that you could potentially be pushing the amp very hard.  However, given the Catholic church, speech only application you may be just fine.