impedance questions (4 ohm amp into 8 ohm cab)

booshin

booshin

Dec 1, 2017
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#1
Hello. I've been looking at an eden 410xlt (700 watts, 8 ohms) for a while now. I really like the tone it puts out and the store is selling it at a great price for its condition.

Problem is, I've been planning on getting a peavey tour 700 head, which is a 4 ohm amp. I've researched the subject a little bit, and from what I understand, mismatching impedance in this way likely wouldn't cause any problems aside from the speaker not being able to run at full capacity. I'm not too worried about this, as I play a peavey t-40 with extremely hot pickups and usually end up with my volume at about 9 o'clock either way, so I'd still have plenty of headroom. Regardless, I won't likely be in a situation where I'll need to push my amp for some time.

I just want to know if it's reasonable to run a 4 ohm head through an 8 ohm speaker like this. This will be the first time I've bought a larger setup, and I don't wanna do something stupid and regret it later. Any thoughts on the matter would be greatly appreciated.

Thanks
 
#2
No problem at all, it's quite common to run a 8 Ohm cabinet on 4 Ohm amp. That's the amp's minimum load.

http://www.musiciansfriend.com/amplifiers-effects/peavey-tour-700-bass-amp-head

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#5
If the solid state power output section of an amp is rated for X amount of power at 4 Ohms, that 4 Ohms is the minimum rated impedance you can run. You should go no lower than 4, but you can operate a higher than 4, so 8 Ohms is OK.

The amp running at 8 Ohms will not likely supply the full power of the amp to the speakers. That's not a problem. It will be down somewhere between 30% and 50% depending on the amp. In any case, the difference in power will be virtually negligible to your ears and you will have more speaker headroom.

It's all good. Unless the output section of your amp is tubes. Then different rules apply.
 
#5
Killed_by_Death said:
Your logical upgrade would be to get another 8 Ohm cabinet.
Click to expand...
This ^ is correct!
Roughly speaking, double the speakers, doubles the loudness.
You need roughly ten times the power to double how loud you get.
So adding another 8 Ohm speaker of the same configuration (preferably) is the most logical upgrade for later.
The two 8 Ohm speakers will then have the amp operating at 4 Ohms and allow it to provide it's full power.
 
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#7
Old Garage-Bander said:
If the solid state power output section of an amp is rated for X amount of power at 4 Ohms, that 4 Ohms is the minimum rated impedance you can run. You should go no lower than 4, but you can operate a higher than 4, so 8 Ohms is OK.

The amp running at 8 Ohms will not likely supply the full power of the amp to the speakers. That's not a problem. It will be down somewhere between 30% and 50% depending on the amp. In any case, the difference in power will be virtually negligible to your ears and you will have more speaker headroom.

It's all good. Unless the output section of your amp is tubes. Then different rules apply.
Click to expand...
The tour 700 amp is solid state so that shouldn't be a problem. Can you explain why tube amps are different?
 
#16
Killed_by_Death said:
Tube amps don't like higher impedance loads, because it makes the transformer work harder. (extra heat)
SS amps don't like lower impedance & will simple go poof if short circuited at the output.
Click to expand...
This ^.

In tube driven equipment, you get the maximum transfer of power from the amp to the speaker when the amp's output impedance matches the impedance of the load (speakers).

This is why some tube amps have an arrangement to match impedance to the speakers you have.
Some use an arrangement of jacks on the back of the amp, some use switches to set the amp's output impedance.
All of these arrangements work by taking the output from different "taps" of the output transformer.
So usually with tube amps the available power output is always the same regardless of load, within limits of course.

SS amps just let you load them as lightly (higher impedance) as you want. You just take a power output hit in relation to load.
No load, aka infinite impedance, aka nothing connected to the output results in Zero watts out.
But put too low of an impedance on a solid state amp, a short circuit being the most extreme case, and there's a good chance that things will go South in a hurry.
 
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#17
Bo, you sure you dont have that backwards. I have a Tour, they are 8ohm one speak, 4ohm with two connections. I didnt get the Eden because pf the mismatch which makes me think the Eden cab is 4 ohm.
 
#18
Whil57 said:
Bo, you sure you dont have that backwards. I have a Tour, they are 8ohm one speak, 4ohm with two connections. I didnt get the Eden because pf the mismatch which makes me think the Eden cab is 4 ohm.
Click to expand...
Are you sure? I didn't know that about the tour. However, I do know that the cabinet is 8 ohms.
 
#19
Looked in my book, one of the guys could answer- it has two ratings- 500w @8ohm and 700w @4ohms. It says the outputs are parallel. I thought i had asked about this and was told it depended on how many speakers i ran.
 
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