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question regarding imedance and speaker combinations

R

rockiesfan

May 29, 2008
13
0
#1
I have a Peavey Firebass amp (700 Watts). I currently am using it with a 2x10 cabinet. I am looking to add a 15 cabinet to this rig.

My 2x10 cab is 4 ohms with 175 watts continuous and 350watts program. the 15 I am looking to add is 8ohms at 400watts RMS and 800 Watts continuous.

I believe that in parallel the impedance of my cabinet combo will be 2.66 ohms. My firebass amp puts out 700 watts at 2ohms.

I would be either running the cabinets out of my parallel outputs with each cabinet having its own separate output from the amp or by connecting the cabinets with a y-cable out of one jack.

Am I risking any damage to speakers and/or amp by doing this?

I am hoping to not have to buy another amp, which I can do and use the crossover on my Firebass.

Thanks much!
 
#2
Since your amp is rated to 2 ohms the 2.6 load (your 4 ohm cab + 8 ohm cab in parallel) will be just fine.

Your 4 ohm cab will get 2/3 of the power from the amp and the 8 ohm cab will get 1/3.

You don't want to present a lower resistance load than your amp is rated to or else you risk damaging it.
 
#3
I just noticed that you mentioned a crossover on your amp, this suggests/requires two separate amps or channels so you would be presenting two separate loads to each of the amps/channels. This is no problem but it kind of negates the parallel load question.
 
#4
Thanks LowLee,

I was thinking about getting a separate amp/combo with a 15 in case the combo doesn't work with only the firebass amp.

If the 4ohm cab gets 2/3 of the amps power and the 8 ohm gets 1/3 of the amps power would that meant that the 4ohm cabinet would be louder? I am looking for an even sound. :hmm:

And, also what about the power needs of each cabinet. would the 15 cab get enough power and not stress it ultimately ruining the cabinet? It is a 400 watt RMS cabinet and if it only gets 1/3 of the amps power it would only be getting 233 watts while the 2x10 cab gets the rest (466 watts)? :hmm:

Also the power specs on my amp are:
Rated Power and Load:
700W RMS into 2 ohms
475W RMS into 4 ohms
275W RMS into 8 ohms

Thanks a bunch so far...
 
#5
A little over 400 watts into a 175 watt cab will probably be pushing it. Cab power ratings are not set in stone, but you should probably avoid cranking it unless you get a more even distribution with another 4 ohm cab, or better yet, 2 4 ohm cabs that can handle it.

Edit: just saw your new post. You cannot damage a cab by underpowering it, contrary to popular belief.
 

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