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Impedence setting

spindlebox

spindlebox

Guest
Apr 26, 2011
18
2
Kansas City, MO
www.alicesweetalice.com
#1
Hello! This is something that my head won't wrap around for some reason.

OK, so I have a Peavey VB-2 bass amp, and I am going to be running two 15" speaker cabinets. They are vintage 80's Peavey cabinets. I just bought a 2nd one, and it should be the same as what is pictured below as far as Model & specs. I have one just like it, and I replaced the original speaker with an 8 Ohm Emenence speaker. So, I guess the cabinet would be rated for the speaker, not the cabinet specs correct?

Basically, my existing speaker has an 8 ohm speaker, and the one I just bought might be rated for 4 Ohms.

My Peavey VB-2 has 3 settings, 2-4-8 Ohm. There are two outputs on the back of the amp, the manual for the amp says the outputs are "parallel".

What would I set the OHMs on when running these two cabinets? Thanks in advance!
 

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#2
spindlebox said:
Hello! This is something that my head won't wrap around for some reason.

OK, so I have a Peavey VB-2 bass amp, and I am going to be running two 15" speaker cabinets. They are vintage 80's Peavey cabinets. I just bought a 2nd one, and it should be the same as what is pictured below as far as Model & specs. I have one just like it, and I replaced the original speaker with an 8 Ohm Emenence speaker. So, I guess the cabinet would be rated for the speaker, not the cabinet specs correct?

Basically, my existing speaker has an 8 ohm speaker, and the one I just bought might be rated for 4 Ohms.

My Peavey VB-2 has 3 settings, 2-4-8 Ohm. There are two outputs on the back of the amp, the manual for the amp says the outputs are "parallel".

What would I set the OHMs on when running these two cabinets? Thanks in advance!
Click to expand...

Combining 4 and 8 ohm cabs results in a load that is between 2 and 4. Closer to 2.
Also, the 4 ohm cab will probably be much louder than the 8.
 
#5
If you have a 4 and 8 ohm cabinet, the 4 ohm cabinet will receive twice the power that the 8 ohm cabinet will. Generally, not the greatest combination for single driver cabinets.
 
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#8
lz4005 said:
Combining 4 and 8 ohm cabs results in a load that is between 2 and 4. Closer to 2.
Also, the 4 ohm cab will probably be much louder than the 8.
Click to expand...
The result will equal 2.67 Ohm which is the "well balanced" middle between 4 Ohm and 2 Ohm.
2.67 Ohm is same as close to 4 Ohm and 2 Ohm.

lz4005 said:
Also, the 4 ohm cab will probably be much louder than the 8.
Click to expand...
Any other things beeing equal except for impedance the 4 Ohm will be +3dB louder.
I think that +3dB more of loudness is commonly (and frequently considered at TB forum) as "a little bit more of loudness" rather than "much louder".
 
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#9
spindlebox said:
What would I set the OHMs on when running these two cabinets? Thanks in advance!
Click to expand...

As the amplifier output runs at something about 2.7 Ohm you may want figure if the 2 Ohm or the 4 Ohm setting fits better to your personal sound goals.
Amplifying wise 2.67 Ohm is just as close to 2 Ohm as is for 4 Ohm setting of the amplifier.
However you might experience some difference of sound between both output Ohm settings.
 
#10
ThisBass said:
As the amplifier output runs at something about 2.7 Ohm you may want figure if the 2 Ohm or the 4 Ohm setting fits better to your personal sound goals.
Amplifying wise 2.67 Ohm is just as close to 2 Ohm as is for 4 Ohm setting of the amplifier.
However you might experience some difference of sound between both output Ohm settings.
Click to expand...

Either way that's a pretty minor impedance mismatch, but IMHO the way the amp is setup should be considered in choosing 2 or 4 ohms. The general rule is tube amps are safer if the load is lower than the amp expects, but Mesa amps are setup to work better when the load is slightly too high. Since the correct advice varies by design, it's good advice to consult the specific manufacturer of your amp if you are going to run an impedance mismatch instead of relying on a general rule.
 
#12
Wasnex said:
Either way that's a pretty minor impedance mismatch, but IMHO the way the amp is setup should be considered in choosing 2 or 4 ohms. The general rule is tube amps are safer if the load is lower than the amp expects, but Mesa amps are setup to work better when the load is slightly too high. Since the correct advice varies by design, it's good advice to consult the specific manufacturer of your amp if you are going to run an impedance mismatch instead of relying on a general rule.
Click to expand...
By default I suggest the lowish going mismatch cause some "generic" EQ adjustment of the preamp might "rise" the average impedance to noticeable higher numbers (beyond 2.7 Ohm) at the low band of the total (average) spectrum.
Explained in other words, power density at the lows might be noticeable raised.
With a little bit of luck he might get a "real" 4 Ohm system in real practice yet 2.7 Ohm nominal.
 
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#13
ThisBass said:
By default I suggest the lowish going mismatch cause some "generic" EQ adjustment of the preamp might "rise" the average impedance to noticeable higher numbers (beyond 2.7 Ohm) at the low band of the total (average) spectrum.
Explained in other words, power density at the lows might be noticeable raised.
With a little bit of luck he might get a "real" 4 Ohm system in real practice yet 2.7 Ohm nominal.
Click to expand...

This is a very technical explanation. I have attached a speaker data sheet with a graph that shows the driver's impedance by frequency, so people can hopefully understand a bit better. By boosting lows you emphasize the relevance of the rising impedance below 150hz.
 

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