What is the rule on matching speaker ohms with amp output?

[donahue]

Hey guys, I'm in the middle of fixing up an old single-end and I"m trying to test the output transformer to match up ohms for speakers. How does it work again? Is it okay for the amp if the speakers are higher ohm than the output jack rating or if the speakers are lower that the output jack rating. ie. plugging 8ohm speakers into a 4ohm rated jack or vise versa. thanks.

 

[Rich_S]

Re: What is the rule on matching speaker ohms with amp output?

Obviously, matching the speaker to the amp's output setting is best. But for tube amps, if you must mismatch, having the speaker LOWER is better.

Speaker impedances that are higher than the amp are hard on the amp - the extreme case of an open circuit is often deadly to the OT. Many Fender amps have a shorting speaker jack that shorts the output whe no speaker is plugged in. A short is better than an open.

On the other hand, old Marshalls go up in flames when those infuriating impedance selector plugs get loose and fall out, causing an open circuit.

High OR low, a 2:1 mismatch is unlikely to hurt anything. For that Dukane you're working on, just use any 8 or 4-ohm speaker you have around, and keep the volume under control until you know more about how it's working.

 

[Lazarus1140]

Re: What is the rule on matching speaker ohms with amp output?

I hope someone else chimes here because I was under the total opposite impression. If the output jack is 8 ohm you should consider that a minimum. The extension jack on the Peavey that I gig with actually says 8 ohm minimum. I could be dead wrong, but I think the risk is in running an amp into a lower impedance.

 

[TheAbomb12]

Re: What is the rule on matching speaker ohms with amp output?

4 ohms requires more power than 8 ohms...

 

[ModestCargo]

Re: What is the rule on matching speaker ohms with amp output?

I hope someone else chimes here because I was under the total opposite impression. If the output jack is 8 ohm you should consider that a minimum. The extension jack on the Peavey that I gig with actually says 8 ohm minimum. I could be dead wrong, but I think the risk is in running an amp into a lower impedance.

In a solid state amp you are absolutely right. If it says 8 ohms minimum then you run 8, or 16, or 32, or whatever. Never under 8, and an open circuit (no speaker attached) won't do any harm whatsoever.

But we're talking tube amps here and it's a whole different ball game.

4 ohms requires more power than 8 ohms...

Not necessarily in a tube amp - at least, the amp probably won't put OUT any more power at 4 ohms if it's 8 ohms nominal. In fact there may be a power decrease. But as said previously running an amp designed for 8 at 4, if it's a tube amp, is most always perfectly fine.

 

[donahue]

Re: What is the rule on matching speaker ohms with amp output?

So i'm confused now, its worse to run the speaker thats less than the amp ohms, or more than the amp ohm speaker tap? For example is it worse to run an 8 ohm speaker into a 4 ohm tap or run a 4 ohm speaker into an 8 ohm tap?

 

[Rich_S]

Re: What is the rule on matching speaker ohms with amp output?

My post is correct for tube amps. Running with a speaker lower than the amp's setting is safer.

 

[YJM_Rocks]

Re: What is the rule on matching speaker ohms with amp output?

The best rules is to match them up 1:1.

 

[Lewguitar]

Re: What is the rule on matching speaker ohms with amp output?

With a good tube amp that wants to see 8 ohms you can use 4 ohms, 8 ohms or 16 ohms and probably be just fine...but not 2 ohms.

I'd try to match it though.

If your amp wants to see 4 ohms, you could probably use 2, 4 or 8...but not 16.

But it'd be best to match a 4 ohm amp to a 4 ohm speaker combination.

Lew

 

[TheAbomb12]

Re: What is the rule on matching speaker ohms with amp output?

its worse to run a 4 ohm amp with an 8 ohm speaker-- cause you are no providing enough load for the output transformer...

 

[Lazarus1140]

Re: What is the rule on matching speaker ohms with amp output?

Thanks for the lesson. I had it wrong for a very long time.

 

[LesStrat]

Re: What is the rule on matching speaker ohms with amp output?

The best rules is to match them up 1:1.

This is easiest.

OTOH, Scott warned sternly about NOT matching the speaker with the correct setting on my Celtic Franklin. It has 3 output levels, so you can select the matching level. BUT, he warned to make sure they match before firing it up.

 

[Scatterwound]

Re: What is the rule on matching speaker ohms with amp output?

I was asking this same question to myself last summer when I built a 2X12 wooden cabinet for my Traynor Custom 100 head.....(This is a tube head)...My speaker cabinet is wired up as 4 ohms to match my head...I did my research based on the responses of two major speaker manufacturers.....

From the Eminence website:

--------------------------------------------------------
Do I have to match my speaker's impedance with my amplifier's?

Yes, you should match up your impedances. One reason is that you will get maximum transfer of power. The other reason is that you can sometimes approach unsafe and dangerous conditions. When in doubt, it is safer to go higher in impedance to help protect the amplifier.
------------------------------------------------------------


And from an e-mail inquiry to Celestion that affirmed the statements from Eminence.....

 

[Lazarus1140]

Re: What is the rule on matching speaker ohms with amp output?

I was asking this same question to myself last summer when I built a 2X12 wooden cabinet for my Traynor Custom 100 head.....(This is a tube head)...My speaker cabinet is wired up as 4 ohms to match my head...I did my research based on the responses of two major speaker manufacturers.....

From the Eminence website:

--------------------------------------------------------
Do I have to match my speaker's impedance with my amplifier's?

Yes, you should match up your impedances. One reason is that you will get maximum transfer of power. The other reason is that you can sometimes approach unsafe and dangerous conditions. When in doubt, it is safer to go higher in impedance to help protect the amplifier.
------------------------------------------------------------


And from an e-mail inquiry to Celestion that affirmed the statements from Eminence.....

1. Did Eminence understand you were asking concerning a tube head?
2. Where is the Celestian response to your question?

 

[ModestCargo]

Re: What is the rule on matching speaker ohms with amp output?

Well, the people that work at those speaker companies don't always know everything.

 

[metlking]

Re: What is the rule on matching speaker ohms with amp output?

I'm seriously confused........Example: All my years of playing music I thought if you ran an amp at 8 ohms into a 16 ohm cab it was OK, not "ideal" but OK. I thought the problem was with (again, an example) say an 8 ohm amp into a 4 ohm speaker......

I've been told: As long as the amps output OHM's is lower than the speakers ohms everthing is cool.........Have I been wrong all these years!?!?!?!?!

 

[donahue]

Re: What is the rule on matching speaker ohms with amp output?

People are still saying opposite things. I thought I was confused b/f. The reason I really want to know, is that I don't know what my transformer's range is (its an old single ended project), and I want to find out or at least play on the safe side with a good guess. AWWWWWW!

 

[Fresh_Start]

Re: What is the rule on matching speaker ohms with amp output?

People are still saying opposite things. I thought I was confused b/f. The reason I really want to know, is that I don't know what my transformer's range is (its an old single ended project), and I want to find out or at least play on the safe side with a good guess. AWWWWWW!

I don't think people are saying opposite things exactly. If you are talking about a "single-ended" amp, I assume it's a tube amp. The +/- a factor of 2 is OK for a tube amp (e.g. 4-ohm output to 8-ohm speaker and vice versa). If you have a solid state amp, the rules are different.

Hope this helps,

Chip

 

[Rich_S]

Re: What is the rule on matching speaker ohms with amp output?

Scatterwound's responses from Eminence and Delestion are correct for SS amps, NOT for tube amps. Keep in mind that the customer-support folks at these outfits are not tube-amp experts, they are customer support techs for companies that make hundreds of different kinds of speakers for stereos, TVs, sound reinforcement, bass, etc. Out of all those speakers, only guitarists commonly use tube amps anymore, a small percentage of their product line. So, they gave out the stock response.