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A quick power/impedance question!

BassIan

BassIan

Apr 27, 2003
919
229
41
San Francisco, California
#1
I've tried searching pretty extensively, since I think I had read something about this before, but no luck finding my answer, so apologies if it was obviously found by anybody else.

The gear I am working with currently consists of a Fender 800 Pro head into an SWR Goliath Senior. I've recently ordered an SWR Big Ben to help the Senior out on the low end (it starts to drop off pretty early). The 800 Pro provides 800 watts into a 4 ohm load, and 1200 watts into a 2 ohm load.

1) Since the Goliath Senior is a 4 ohm cabinet, and the Big Ben is an 8 ohm cabinet, am I correct in saying that they'll put a 2.67 ohm load on the 800 Pro?

2) Would the Big Ben get half the power from the amp that the Goliath Senior does? If so, will that make their respective volumes too different?

3) If their respective volumes ARE likely to be too different, what possible solutions, short of buying a seperate power amp for one (or both) of the cabs, could there be to this problem?

Thanks in advance for your help.
 
#2
1. You are correct.

2. Yes, the Big Ben would get half the power of the Goliath Senior. I don't know if this will make their volumes too different, so I guess you'll just have to try them out and see.

3. Sell the Goliath Senior and get an 8 ohm Goliath III.
 
#3
BassIan:

1) Since the Goliath Senior is a 4 ohm cabinet, and the Big Ben is an 8 ohm cabinet, am I correct in saying that they'll put a 2.67 ohm load on the 800 Pro?
Click to expand...
[COLOR=dark red]Right.[/COLOR]

2) Would the Big Ben get half the power from the amp that the Goliath Senior does? If so, will that make their respective volumes too different?

[COLOR=dark red]It will get 1/2 the power, assumimg parallel connection. But, it gets worse. The BB is far less sensitive, and needs to see more than ten times the power than the GS to produce the same sound pressure level. This, according to the published online specs [/COLOR]

3) If their respective volumes ARE likely to be too different, what possible solutions, short of buying a separate power amp for one (or both) of the cabs, could there be to this problem?

[COLOR=dark red]Find a much more sensitive low frequency cabinet, or a less sensitive high frequency oriented one. That one would be a better match with a 2 X 10 that is 8 ohms.

Really, you probably want to be biamping. You'll need another amp and a crossover to get there. Since the cab's already coming, try to borrow or rent those, and see how it works for you. It'll probably do just what you need. Look at something like a Crown XLS amp if you want to keep the cost down. Behringer makes some crossovers that aren't expensive at all, and will fit in the rack with your new power amp.[/COLOR]:cool:

Thanks in advance for your help.

[COLOR=dark red]I think I'd try the Fender powering the Big Ben, and get something rated around 1200-1500 watts for the Goliath. Watch the bridged impedance ratings if you do that though, it's going to create problems with a fair number of amps. But, if the Fender drives the Goliath to your satisfaction, get a new amp for the BB. I'm guessing that part of your bass rolloff is due to underpowering the Goliath right now. I've never used one though, so...[/COLOR]

luck,

Charlie Escher
 
#4
The idea I had for longer-term, in order to really properly power each cabinet was to run the Big Ben off the Fender, and then get a good power amp for the Goliath Sr. I would need to get a bigger rack, and find a good power amp, but that'd definitely be the ideal situation.

I'll have to see how it goes with the current setup to determine how badly I need the power amp. I've had a look at QSC power amps, and those look good, I just don't really know what specifically I should be looking for in such a device.
 
#5
I'll have to see how it goes with the current setup to determine how badly I need the power amp. I've had a look at QSC power amps, and those look good, I just don't really know what specifically I should be looking for in such a device.

The PLXs are rated for 4 ohm bridged operation, are light(21 pounds), and only occupy two rack spaces. A PLX 1602 is good for 1600 watts bridged into 4 ohms. That's probably a nice match for the Goliath Sr., which is rated for 1000 watts RMS. Ask some other owners though, for sure.;)
 

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