Setting amp Ohm when two different speaker loads

[GearBoxTy]

I apologize if this question has already been addressed, but I'm curious...

The amp I currently use for live work (Peavey Triple XXX 1x12 60-watt combo) has a 16-ohm built-in speaker load.  If I add an 8-ohm cabinet, what do I set the amp's ohm setting to? 4, 8, or 16?

Thanks!

~Ty

 

[Super Turbo Deluxe Custom]

Your new total ohm load is 5.33333.  My understanding is that the ohm value of the speakers must be equal to or higher than the amp for the amp's protection.  I'd set the switch on the amp to 4 ohm.  It's higher than 4 ohms, so you won't realize the full potential of the amp like you would with a 16, 8, or 4 ohms load and appropriate setting with the switch.

However, my main experience with impedance matching speaker loads with heads is SS bass head related.  Some apspects of tube and SS stuff behave the exact opposite.  I'd wait for one of the tube gurus.  

 

[mayfly]

I'd set it for 4 ohms and live with the small loss in efficiency

 

[-CB-]

Not familiar with that amp, but... here goes.

The 5.3 ohms is correct - sort of - since its impedance not resistance and speakers are not good followers of impedance rules when mismatched - being electro-MECHANICAL devices.

For tube output amps, using tubes, output transformer... you are better off going a little UNDER the rated output impedance of the transformer, not over.  Tubes and output transformers will tolerate that better.

For solid state - silicon - output, then you never want to go under the rated impedance of the output, or you're going to blow the finals, the fuses or breakers, or both.

Set the amp to 8 ohms, run it at 5.33....  IF YOU MUST

Here's the thing - its a terrible combination.  You'll have the 8 ohm speaker taking up lion's share of the current, and the 16 will be sitting there doing some bench shining.  Most of the loud will come from the 8 ohm speaker.    You might consider just using it, and leaving the 16 out of the picture.

 

[Super Turbo Deluxe Custom]

For tube output amps, using tubes, output transformer... you are better off going a little UNDER the rated output impedance of the transformer, not over.  Tubes and output transformers will tolerate that better.

For solid state - silicon - output, then you never want to go under the rated impedance of the output, or you're going to blow the finals, the fuses or breakers, or both.

Set the amp to 8 ohms, run it at 5.33....  IF YOU MUST

Some apspects of tube and SS stuff behave the exact opposite.  I'd wait for one of the tube gurus. 

See what I mean.

 

[-CB-]

Here's the thing - its a terrible combination.  You'll have the 8 ohm speaker taking up lion's share of the current, and the 16 will be sitting there doing some bench shining.  Most of the loud will come from the 8 ohm speaker.    You might consider just using it, and leaving the 16 out of the picture.

The part I hoped would get picked up on was THAT one above...!~!~!~!~

 

[Super Turbo Deluxe Custom]

That goes w/out saying.  It was picked up on by me, but wasn't really what he was asking about.

I've got a question, more of an observation, with impedance matching cabs.  I am running a 4 ohm 210 with a 4 ohm 112 for a total ohm load of 2 ohms, which is the load the head sees.  With this combo, the load is split equally between the 2 cabs.  The 210 has (2) 8 ohm speakers and the 112 has (1) 4 ohm speaker.  If the 112 had an 8 ohm speaker, all 3 would share the load equally because all three would have the same ohm value.  Is it better, sound wise, to have each cab share the output equally or better to have each speaker share the load equally?

 

[-CB-]

I am running a 4 ohm 210 with a 4 ohm 112 for a total ohm load of 2 ohms, which is the load the head sees.  With this combo, the load is split equally between the 2 cabs.  The 210 has (2) 8 ohm speakers and the 112 has (1) 4 ohm speaker.  If the 112 had an 8 ohm speaker, all 3 would share the load equally because all three would have the same ohm value.  Is it better, sound wise, to have each cab share the output equally or better to have each speaker share the load equally?

In your example - with the 2x8 ohms in the 210 you're getting 4 ohms, and sharing it with another 4 ohm load in the 112.  That gives you 2 ohms total load.

In your "what if" - you'll have 2x8 ohms in the 210 still giving 4 ohms, and you'll share it with 8 ohms for a total of 3.2 ohms (I think, if memory serves me tonite, or was it 2.8... whatever).

In the top example, each cabinet has the same current, in the bottom example, each speaker has the same current.  This is a bit of a toss up, but if its a closed back, cabinet for the 210, I'd run it with a 112 with a 4 ohm speaker, due to the interaction of the speaks in the 210, but your wattage would be split equally in the 2nd example.

 

[Dan025]

That goes w/out saying. It was picked up on by me, but wasn't really what he was asking about.

I've got a question, more of an observation, with impedance matching cabs. I am running a 4 ohm 210 with a 4 ohm 112 for a total ohm load of 2 ohms, which is the load the head sees. With this combo, the load is split equally between the 2 cabs. The 210 has (2) 8 ohm speakers and the 112 has (1) 4 ohm speaker. If the 112 had an 8 ohm speaker, all 3 would share the load equally because all three would have the same ohm value. Is it better, sound wise, to have each cab share the output equally or better to have each speaker share the load equally?

my opinion would depend on the power handling of each driver (speaker).

as cb said if you are mis-matching drivers in the same closed back enclosure id match the impedance of the driver but in different enclosures id balance the load according to the power handling, if there all the same id make the driver impedance the same, it really will only determine which cab is louder and which one is closer to its load limit and the difference in volume is surprisingly little to the ear and the driver efficiency plays into that big time.

but like i said just an opinion.

 

[Rouse]

For future reference for those who don't feel like doing the math: http://www.about-guitar-amps.com/speaker_ohms_calculator.html

 

[Super Turbo Deluxe Custom]

In your "what if" - you'll have 2x8 ohms in the 210 still giving 4 ohms, and you'll share it with 8 ohms for a total of 3.2 ohms (I think, if memory serves me tonite, or was it 2.8... whatever).

(3) 8 ohms in parallel is 2.667.

By switching the 112 to an 8 ohm instead of the current 4, each speaker would be as loud (or have the same output).  The 2.667 ohm load is a little weird, and my amp is 500w @ 2 ohms, so I'd lose a little bit of the efficiency, but not an issue as it's never really cranked anyway.  Switching the 112 to an 8 would really just let the flavor of the 210 be a little more dominant I guess. 

The 210 and 112 are both close backed, but they are shelf ported bass cabinets as this is a bass rig.