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4 ohm Head into 8 ohm cab

#23
Running an 8 ohm cab and a 4 ohm cab into a single channel will create a load on the amp of 2.6 ohms.
If your amp is only rated down to 4 ohms - DO NOT DO THIS.

If your amp is stable down to 2 ohms, you will be fine.
otherwise, you should use 2 x 8 ohm cabs.
 
#24
Mr Grady said:
so...what would happen if you ran a 100w 4Ohm amp through 300w 8Ohm speakers?

i understand that the speakers would be limited by the amps output, i just want to make sure no damage can happen

as i understand it, as long as you didnt crank the amp up too high it wouldnt be a problem.......(each speaker is connected by a jack to seperate outputs) makes sense?

cheers
Click to expand...

You'll be fine. Your amp's output will be reduced to about 60 watts, so you won't get a lot of volume out of the cab. Don't try to get more from this minimal setup than it can put out. If you start to hear distortion, you're going to have to turn it down. If you need loud, this rig won't produce it.
 
#25
I have got a question that should fit in here:

Let's say I want to buy a bass head with 300W at 4 ohm and 180W at 8 ohm. I want to connect two 8 ohm cabinets, which will result into a total impedance of 4 ohm meaning 300W of power. Do the cabinets need to be able to handle 300W each or do they "share" the power and only have to handle 150W?

In other words: is it safe to use 2 cabinets that say 200W at 8 ohm with a head that says 300W at 4 ohm?
 
#27
I have a question... I'm buying a Traynor DynaBass 800H that runs at 800watts for 4 ohms, but the cab im buying with it runs at 300 watts for 4 ohms. Would this work and would it be loud enough to play a good-sized gig at? Would I have to worry about blowing a speaker?
 
#28
tjhabsman said:
I have a question... I'm buying a Traynor DynaBass 800H that runs at 800watts for 4 ohms, but the cab im buying with it runs at 300 watts for 4 ohms. Would this work and would it be loud enough to play a good-sized gig at? Would I have to worry about blowing a speaker?
Click to expand...
If you run a head rated at 800W at 4 ohms into a 4 ohm 300W cabinet and you turn it all the way up, then yes, you can blow up the cab.
 
#29
WaywardSon said:
I have got a question that should fit in here:

Let's say I want to buy a bass head with 300W at 4 ohm and 180W at 8 ohm. I want to connect two 8 ohm cabinets, which will result into a total impedance of 4 ohm meaning 300W of power. Do the cabinets need to be able to handle 300W each or do they "share" the power and only have to handle 150W?

In other words: is it safe to use 2 cabinets that say 200W at 8 ohm with a head that says 300W at 4 ohm?
Click to expand...
they do indeed "split" the power between them, so yes, that would be safe.
 
#33
jeffgnr90 said:
so if i were to run my 2ohm 600w head into 2 2 svt210av's and an acoustic b115neo, I would be running at 2.67 ohms right? Would all my speakers be putting forth the same volume? And how could I get this potential rig down to 2ohms??
Click to expand...

Holy 9 Lives thread.

Some cabs are more efficient than others at turning power into sound (higher sensitivity ratings) so different cabs will not have the same volume at the same power level.

If you want to get your load to 2 Ohms, get a pair of 4 Ohm cabs but there is no requirement to run your amp at maximum load.
 
#34
Big Brother said:
Holy 9 Lives thread.

Some cabs are more efficient than others at turning power into sound (higher sensitivity ratings) so different cabs will not have the same volume at the same power level.

If you want to get your load to 2 Ohms, get a pair of 4 Ohm cabs but there is no requirement to run your amp at maximum load.
Click to expand...
hey, at least he's not starting new threads with the same old topic!

+1 to this answer.

if all 3 are 8Ω, it'll work; how well it works, mixing two little sealed 2x10s and one ported 1x15 is anybody's guess. he'd be better off with a 3rd 210AV.
 
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#35
also, just because you can run your amp at 2Ω doesn't always mean you should.

you're pushing the amp to the wall when you do that, which can spell long-term trouble for cheaper amps.
 
#36
I have a Fender Rumble 350 and have a Eden 4x10 cab and want a 15 inch cab. My output says 4 ohms. If I get a 8 ohm 15 will the amp be running efficiently? I want to add more bottom. Thanks for the help.
 
#37
I=V/R (Or in this case I=V/Z)

Watts=VA (DC)

Impedance in Parallel = 1/(1/R1+1/R2+....)
Impedance in Series = R=R1+R2+...

The Ω your amp is running is determined by the load present (the cab/s you have hooked up to it). Hook up an 8Ω cab and you run at 8Ω etc. Hook up 2 8Ω cabs and...

1/(1/8+1/8) = 1/(.125+.125) = 1/.250 = 4Ω

According to Ohm's law (1st formula) the lower the resistance the higher the current - we can assume voltage remains the same. Higher current means higher power output by your amp. Run your amp at higher than it is rated and it will melt. Typically a decent amp will be rated for at least 4Ω. The lower the Ω your amp is rated the better. Not that it is better to run at lower Ω's - just that it can take more abuse.

If you want to get really funky and you have multiple cabs with multiple speakers you can do some fancy series-parallel wiring to get the most bang for your buck. But you better read this first:

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imped.html

Good luck. All information for entertainment purposes only. You blow your stuff up don't blame me. I barely know what I'm talking about anyway...

-Rock on! :bassist:
 
#39
tjhabsman said:
I have a question... I'm buying a Traynor DynaBass 800H that runs at 800watts for 4 ohms, but the cab im buying with it runs at 300 watts for 4 ohms. Would this work and would it be loud enough to play a good-sized gig at? Would I have to worry about blowing a speaker?
Click to expand...

I'll answer this one. The cab "rated" at 300 watts does not mean that you can send 300 watts to it. Most (I won't say all) ported, or vented, cabs will start to distort at a power level that is much less than the (rated) power level. It depends on the design of the cabinet and the parameters of the speakers. I don't know about your specific cab, but most (again, not all) cabs will start to distort at about 2/3 of that "rated" power. That means that you can really send only 200 watts to that cab before it starts to sound distorted. So, is 200 watts enough to play a good-sized gig? I use about 200 watts for indoor band practice and "small" indoor gigs. For my idea of "good-sized" gigs, I use about 350 watts. IRMV
 
#40
Hi all.
I have a question concerning this topic.
So, I have a Hartke VX410 cabinet (300watts at 8ohms) and I plan on getting a Marshall MB450H amplifier (300watts at 4ohms, 450watts at 2ohms). Which means if I connect these two together I get about 260watts output since the cabinet is 8ohms?
Ok, what if I got an additional 2x10 cabinet (say, 150watts at 8ohms). This would make the amps load a total of 4ohms. Right? So each speaker (4 + 2) would get 50watts of power each. Am I right?
Would this setup be good at all? Will it be loud enough for a heavy metal gig?

Thanks in advance!
 

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