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Home FAQ Amp & PA Questions How Many Speakers Can I Hook Up?
 
How Many Speakers Can I Hook Up? PDF Print E-mail
Written by Bari   
Monday, 06 April 2009 23:19

 

POWER AMP IMPEDANCE RATING
SPEAKER CABINET IMPEDANCE
# OF CABS YOU CAN SAFELY HOOK UP
2 Ohms
4 Ohms
2
8 Ohms
4
16 Ohms
8
4 Ohms
4 Ohms
1
8 Ohms
2
16 Ohms
4
8 Ohms
4 Ohms
0
8 Ohms
1
16 Ohms
2
16 Ohms
4 Ohms
0
8 Ohms
0
16 Ohms
1

 

 

One should respect the manufacturer's minimum impedance or you'll be paying your local tech to repair the output section of your amp.

If an amp is rated for 100 watts output power at 4 ohms, then any speaker combination that takes you below 4 ohms is inviting trouble. In this case a a load that is 4 ohms or greater is OK. For maximum safe power output from your amp you would want to match the speaker impedance exactly (ie  100 watts @ 4 ohms rating on amp + 4 ohm speaker impedance = full rated output of 100 watts without risking damage to amp). If you make the speaker impedance higher than the amp, you will get less power out but the amp will be working in a comfortable zone. Some guitar players will actually increase the speaker impedance in order to derate the output power of a an amp. Lets say you have a single 12" combo amp and the amp puts out 50 watts into an 8 ohm speaker. If you change the speaker to a 16 ohm speaker, the amp will in effect only produce 25 watts.

 

So, there are 2 components to consider: the minimum ohms rating on your amp + the actual impedance of your cabinet(s).  When you have multiple cabinets such as is the case with many PA systems you need to do a little calculation as to how many speakers you can connect to the amp (or refer to the above chart).


 

In case you're a math dog here is the formula to calculate ohms (the resistive component of impedance) for multiple speaker cabinets or speakers hooked in parallel:

1
-----------------   =  ohms,   where r1, r2, r3 .... are the speaker cabinet impedances
1  +  1  +  1
---    ---     ---
r1    r2      r2

One last note: If you have a speaker cabinet that is rated for 100 watts and you push it with a 500 watt amp, don't be surprised when the voice coils on your speakers burn up!!!

Last Updated on Monday, 20 April 2009 23:43