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Total noob questions about impedance and ohms

Jjango

Jjango

Nov 16, 2007
1,329
116
Los Angeles, CA
#1
Sorry for the noob question – I've always used combo amps, so I have no idea about stuff like matching amps with cabs.

The [Invalid or Expired Link Removed] says it has an output power of "300W RMS @ 8 ohm, 500W RMS @ 4 ohm".

The [Invalid or Expired Link Removed] says that it comes in two versions, one with 8 ohms, and one with 4 ohms.

Total noob questions:

  1. If I use the LMII with the 8 ohm cabinet, do I have a 300 watt amp setup?
  2. If I use the LMII with the 4 ohm cabinet, do I have a 500 watt amp setup?
  3. Say you wanted to use TWO of these cabs – would you need to use the 8 ohm versions, or the 4 ohm versions?
  4. If you did use two of these cabinets, what wattage would you then be running at?
Any help you can offer in setting this noob straight would be greatly appreciated. :)
 
#3
PS: I did read the sticky at the top of this forum, but stuff like this –

Total impedance = 1/(1/a + 1/b + 1/c ... + 1/n). When all the cabinets or speakers are the same impedance, all you have to do is add up the # of speakers and divide the resultant number into the # of ohms of each speaker. For example, three 16 ohm speakers wired in parallel in a cabinet = 3/16, or 5.333333.… ohms. With a 4 ohm cabinet and an 8 ohm cabinet run in parallel the formula is 1/(¼+1/8). You can’t add ¼ to 1/8 without having the same denominator, so you have to reduce ¼ to 2/8 so they match. Then adding 2/8 to 1/8 gives you 3/8, dividing 8 by 3 gives you 2.67. So, hooking up an 8 ohm cabinet and a 4 ohm cabinet in parallel to your amp gives the amp a load of 2.67 ohms to power.
Click to expand...
– is way, way, WAY over my head.
 
#5
RedLeg said:
you want (2) 8 ohm cabs to bring you to 4 ohms total

impedance of single cab / number of cabs = total impedance
Click to expand...
Thanks for your response RedLeg :), but I'm embarrassed to admit that even that is beyond my understanding. I'm a real dummy when it comes to this stuff.

So if someone could answer my questions 1 through 4 with "yes" or "no" answers, I'd really appreciate it. I'll admit, I don't even know if my questions make any technical sense!

:help:
 
#7
[*]If I use the LMII with the 8 ohm cabinet, do I have a 300 watt amp setup?
Click to expand...

Yes... your amp can put out 300W maximum into an 8ohm cab.


[*]If I use the LMII with the 4 ohm cabinet, do I have a 500 watt amp setup?
Click to expand...

Yes, your amp can put out 500W. But be careful, the cab is rated that it can handle 400W safely.
This means you must be careful not to turn the master volume of the amp fully open.

General rule: use your ears to find out how much you can push your rig.


[*]Say you wanted to use TWO of these cabs – would you need to use the 8 ohm versions, or the 4 ohm versions?
Click to expand...

2 8ohm cabs. This will result in a 4 ohm load on your head. The cabs can handle about 800W togheter, so there is less (even none) risk of turning the master volume on your amp full open.
Don't even think about using 2 4ohm cabs. That will result in a 2 ohm load and the amp can't handle that.


[*]If you did use two of these cabinets, what wattage would you then be running at?
Click to expand...


500W maximum if Markbass's specs are correct.





And, many will say read the FAQ.

But I am in a good mood to give you the simple answers. :)



Get the LMII with two 8ohm cabs... and you're good to go.
 
#10
no problem at all dude



You know, a year ago I wouldn't know the answers to these questions either. (Wich seem sooo trivial to me now.)
Hanging out on TB and in the amp forum has teached me a lot about amps.


Sometimes the regulars around here forget that not everyone is technicly minded.
The FAQ can be difficult to understand for a newbie to amps.



Maybe I should write an "amps explained for dummies" version of the FAQ. :)

I know I'm at least qualified for that.
 
#12
From the FAQ:

With a 4 ohm cabinet and an 8 ohm cabinet run in parallel the formula is 1/(¼+1/8). You can’t add ¼ to 1/8 without having the same denominator, so you have to reduce ¼ to 2/8 so they match. Then adding 2/8 to 1/8 gives you 3/8, dividing 8 by 3 gives you 2.67.

It's probably just me, but this "common denominator" explanation seems much more complicated than it needs to be. 1/8 = .125 and 1/4 = .250 Add them together and divide into one. SIMPLE.
 

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