16 ohm speaker question.........

[Blueswede]

I"m sure this is a real novice question, but I'll ask it anyway. Is the only proper way to wire 2-16 ohm speakers in parallel, with a load of 8 ohms? Can you run them in series? I know you can run 2-8 ohm speakers either way. Just wondering.........

 

[GregR]

it's the only USEFUL way (parallel) if your amp doesn't have a 32-ohm tap on the O/T. the vast majority of guitar amps have 4 / 8 / 16 ohm outputs, so using two 16-ohm speakers you have to resort to parallel to get 8 ohms.

there's nothing inherently BAD about putting a pair of 16's in series. supposedly, putting speakers in series ehnances their characteristics, and putting them in parallel tends to even things out.

 

[StrykeBack]

what if your amp only has a 16 ohm output? and you've got a 2 12 cab thats empty right now but you plan on getting a mark iv later on that uses 8 ohms?

Any way to wire something up to make the amp think their is a second 2x12 cab? some kind of mass dump?

 

[John Phillips]

Running a 32-ohm cab from a 16-ohm amp is fairly safe - it's within the usual factor-of-two mismatch band. Running an 8-ohm cab is also safe though (probably safer) so I'd do that if you really need to use 16-ohm speakers.

But do you mean a Mesa MkIV? If so, that amp can run at 4 ohms too, so if you get two 8-ohm speakers, you can wire then in series for 16 ohms now, and swap them to parallel for 4 ohms later.

Yes, you can use a dummy load (or attenuator set to 'load') as a 'second speaker cabinet'. The impedance doesn't have to match the cab either - you just get a different range of power distribution if it doesn't. E.g. 16-ohm speaker, 8-ohm load sends 1/3 of the power to the speaker, and the amp needs to be set to 4 or 8 ohms (the actual load is 5.33 ohms).

 

[StrykeBack]

But do you mean a Mesa MkIV? If so, that amp can run at 4 ohms too, so if you get two 8-ohm speakers, you can wire then in series for 16 ohms now, and swap them to parallel for 4 ohms later.

Ahh thanks John for letting me know. I'l be aware of that now. Is their any tonal difference between two of the exact type of speaker but one is a 16 and the other an 8 ohm?


Also myashdown can not change ohm settings so i am stuck at 16 with it. Not exactly sure how I would do that setup you were trying to explain to me..but its not your fault. I'm an idiot sometimes in this department.

I was under the belief that if your amp is a tube amp then you need to match ohms exactly or you can burn it up. Also one rule was either that you can go from a higher impedence to a lower impedence but not go from a lower impedence to a higher impedence cab...Or that could be the other way around.

 

[John Phillips]

Here are the basic rules:

With tube amps, you can mismatch, in almost all cases by a factor of two in either direction (ie between half and double the correct impedance). There are a few exceptions I wouldn't try it with, and I'm not sure I would with a vintage amp run at very high power either.

It's usually safer to use too low an impedance (eg 16-ohm amp into 8-ohm cab), since the risk to tube amps comes not so much from drawing too much current, as from the 'flyback' voltages generated in the output transformer - that's also why you must never run a tube amp with no load connected to it. Running into a lower-impedance load is harder on the power tubes, and will reduce their life, but won't fry them immediately.

Smaller mismatches are correspondingly safer, eg the 'odd' impedances you get if you mix loads. It's always better to match though IMO. You get the most power, best reliability, and IMO best tone - although some people do like a mismatch, so that bit is down to taste.

With solid-state amps (which almost never have an OT), the rules are very different. Here, the impedance requirement is a minimum not a match, because the current is drawn directly from the output transistors, not via a transformer, and too much will fry them - much more quickly and completely than with tubes, too. So you must never connect a SS amp to too low an impedance. Conversely, it's usually entirely safe to run any impedance above the minimum, and even no load at all.

This can be a source of confusion to people who have been trained on one type of technology or the other!


Next: with an 'unknown' amp, it's best to be cautious. I don't know much about the Ashdown (other than that it doesn't have the best reputation for reliability, unfortunately), so I would avoid mismatching if at all possible, just in case there is a chance of damage.

Luckily, it's easy. Just use two 8-ohm speakers wired in series for 16 ohms. This also means you can later use the same speakers in parallel to give a 4-ohm cab, which is definitely OK with the MkIV too.

8- and 16-ohm versions of the same speakers do sound very slightly different, but not enough to worry about.

 

[Blueswede]

John- I really do appreciate your knowledge. You are incredibly helpful and informative. Every time I read a thread that you have replied to, I learn another snippet of great info. Thanks!!!