2ohm or so loads

rmb

Any recommendations on running 5, 8 ohm monitors from one QSC MXA 2000 amplifier? One side would be running a different load than the other.
Monitors are a combination of 12inch JBL and 15inch EAW.In the QSC manual the amp is rated for 2 ohm use . I always try to stay on the safe side.

Dra

Just take the average of the 2 speakers and then divide by 2 (# of cabs)for the load to the amp.
((8+5)/2)/2 =
(13/2)/2 =
6.5/2 =
3.25 ohms

A 5 Ohm cabinet?


DRA

kpippen

It's no problem to have a different loads on each channel... I would try not to chain more than three monitors on a channel...

Cheers!

Kev

kpippen

Dra wrote:

A 5 Ohm cabinet?

DRA

Dra,

I think they are saying five 8-ohm monitors... So I would recommend three on one channel and two on the other...

Kev

rmb

Thanks , I am running out of rack sapce so I wanted to remove one amp that I was using for just one monitor. And yes it is five 8 ohm monitors.

Dra

:oops: :oops: :oops: :oops:
Ahhhhhhhh! Bach! (You get that one, K?)
Kevin is right.

DRA

3 cabs = 2.7
2 cabs = 4

bones442

You can run differently loaded channels with most amps, however...

As the spec sheet indicates the amp has ~1000w @2 ohms.

So... with the idea that one wants decent headroom on any given channel, the more speakers you add, the less power you will have for each individual speaker.

With the QSC's ratings in mind and an 8ohm monitor, 1 monitor gives 450W, 2 gives 325W each, and 4 gives 250W each.

The amp may be able to produce more power as the load increases, but your headroom will decrease and so will your max volume.

When the smoke is released, It's awful hard to get it back in...

Fanman20

Hi All

Speakers in parrell

Speaker A impedance 8 ohms
Speaker B impedance 8 ohms
Total impedance 4 ohms


Speaker A impedance 8 ohms
Speaker B impedance 8 ohms
Speaker C impedance 8 ohms
Total impedance 2.666666667 ohms


Speaker A impedance 8 ohms
Speaker B impedance 8 ohms
Speaker C impedance 8 ohms
Speaker D impedance 8 ohms
Total impedance 2 ohms

Calculations

1/(1/speaker 1 impedance + 1/speaker 2 impedance + 1/speaker 3 impedance )
1/(1/8 + 1/8 + 1/8 )
1/(3/8 )
1/0.375
2.666666666666


Try Duncan's calculator

http://www.duncanamps.com/technical/impedance.html

Kev will like it

Mark

P.S. bones442 is \"dead\" right when he says \"When the smoke is released, It's awful hard to get it back in...\"

Fanman20

5 Speakers

5 x 8 ohm speakers on 1 side of amp =

1/(1/speaker 1 impedance + 1/speaker 2 impedance + 1/speaker 3 impedance + 1/speaker 4 impedance + 1/speaker 5 impedance)

= 1/(1/8 + 1/8 + 1/ 8 + 1/8 + 1/8 )
= 1/(5/8 )
= 1/0.625

= the smoke gets out!!! :shock:

1.6 ohms

bones442

Some amps are capable of 2 ohm and lower loads, but I don't like doing that... thats almost like taking a shorting bar and dropping it across the outputs of the amp! The current draw is HUGE also so you better have a LOT of EDISON available! As I said we ran 6 each labsubs ( @ 3.2 ohms per cab) three per channel on a Digam 5000...and the smoke stayed in! You could feel the low end 1/2 mile away outdoors... :shock: man I would have loved to have the Digam K10 :twisted: that day...
G

rmb

What I am doing is adding ONE 8 ohm monitor to my existing setup. So I have Three 8 ohm Monitors at 2.7 ohm on channel one and TWO 8 ohm monitors on channel 2 at 4 ohms using a DRPA for processing. Vocals only. The drummer has a separate mix, x-over, monitor,sub and power amps .I have been using a driverack pa for a few years on the FOH system and just picked up a used DRPA for monitors.If the 2.7 is marginal or not reccommened I have other power amps I can use but I was trying to save some rack weight and space.

bones442

Older convention mode power supply amps will exhaust quickly @ that load and you'll risk the voice coils on your speakers... the good thing is that you are only running vocals through the monitors...Do they need to be STUPID loud like most monitors? Do the stage volumes get crazy loud.. if the answer to either is yes.. my recommendation is no. If it's like Acapella vocals then maybe but I suspect that with a drummer were talking stupid loud stage volumes...You will most likely be sorry....

G

jhague

rmb wrote:

Any recommendations on running 5, 8 ohm monitors from one QSC MXA 2000 amplifier? One side would be running a different load than the other.

I have done this - three 8ohm wedges on 1 channel and two on the other - with a QSC MX1500a and even a QSC USA900 (which isnt even rated for 2 ohm loads) and had no problems with the "smoke gettin out" but only when I couldnt convince the musicians that 4 wedges would be better than 5.
As others have said, you need to make sure that you leave yourself enough power. The amp will put out more power with three 8 ohm wedges because of the lower overall load but the power is now being split across 3 wedges instead of 2 so each 1 probably wont get as much as if there were only 2. Even dropping the load in half usually doesnt actually souble the output. In some cases you actually wind up with lower overall SPL.

Gadget

Well you have it kinda backwards but the jist is there...the load is GREATER the closer you get to -0- ohms, not less... It's hard on the amps though.. and draws tons of edison...It's like the light bulnb you have that can do 100 watts... run it full brightness and it lasts a few thousand hours...run it at 50% and lasts YEARS...

Gadget...