20w head into 15w 1x10? Safe?

[Cazualwhiteguy]

Hey guys,

Any danger in running a 20w Friedman Runt head into a Marshall C110 1x10 cabinet with a 15w speaker? I'm by no means cranking this amp, home levels only.

Just want to be safe with this head! The cab just matches really well aesthetically, salt and pepper Marshall cabs seem to be tough to come by.

 

[Radspin]

Probably OK if you don't crank it...I have a similar situation and have never blown a speaker because I don't turn the amp up much.

 

[telemnemonics]

I'd just buy a higher wattage speaker for the cab.
Till then, make sure nobody else plugs in!

A cranked 20w tube amp might put out 25 or 30w, since watts should be rated "at clipping", meaning at the loudest clean sound, or when the amp is slightly distorted AKA 5%THD.
Generally speaking, a 20w speaker is not enough power handling for a 20w amp, you want 50% more power handling than the amps rated output.

 

[Wyatt]

I wouldn't.

Wattage is not constant. That amp can be peaking well over 15 watts before you get to 3 on the Vol knob.

Edit: forgot the word "not"

 

[MilwMark]

First step would be to make sure the OHMS match. Then worry about speaker wattage. If you are keeping the volume really low it might work for awhile. If you get feisty and crank the amp, you might blow the speaker.

 

[Wally]

If the impedance matches and you keep the volume down, the speaker should not be at risk. However, if you play evil rock and roll or cheatin’ & drinkin’ country at necessary volume, the speaker’s safety as well as your immortal eternal well-being are both at risk!!!!!!

Eeeeehaw......

 

[thegeezer]

Hey, it's your call. I gig my old Deluxe with a '59 P12Q in it. Jensen claimed they were a 25 watt speaker but Ted Weber always said they were good for about 15 and Weber's exact copy of it (12A100T) is rated at 15. The original P12R is really only good for about 12 watts and a lot of them dry rotted before they blew up...mine did.

Anyway, I crank mine pretty hard on stage and hit it with an Xotic BB when I want full on ridiculousness. Hasn't blown up yet and we're talking several hundred on stage hours on the old P12Q already. Now, I'm running about 1:1 in terms of amp output to rated speaker power...but the speaker is almost 60 years old so it might not be good for that many watts anymore.

I'd say you're good just playing for grins at home, but don't come looking for me. I've been wrong before!

 

[Wally]

The vintage...old not new vintage Italian Jensen....Jensen P12Q was listed as a 15, iirc. The old P—N’s weren’t even 25 watt speakers. 18 or maybe 20 max.

 

[nojazzhere]

Hey, it's your call. I gig my old Deluxe with a '59 P12Q in it. Jensen claimed they were a 25 watt speaker but Ted Weber always said they were good for about 15 and Weber's exact copy of it (12A100T) is rated at 15. The original P12R is really only good for about 12 watts and a lot of them dry rotted before they blew up...mine did.

Anyway, I crank mine pretty hard on stage and hit it with an Xotic BB when I want full on ridiculousness. Hasn't blown up yet and we're talking several hundred on stage hours on the old P12Q already. Now, I'm running about 1:1 in terms of amp output to rated speaker power...but the speaker is almost 60 years old so it might not be good for that many watts anymore.

I'd say you're good just playing for grins at home, but don't come looking for me. I've been wrong before!

Many older (50's and 60's) amps came with lower wattage speakers 'cause the manufacturers never dreamed we would be turning them up to distortion levels....but we did. And many of those speakers are still going strong. The only speaker I've ever blown was the cheap replacement speaker (probably from an old Hi-Fi) that was in a blackface Princeton I bought at a guitar show....I rarely turned that amp much over 10...! Even at higher than living room volume, I seriously doubt that a 15 watt speaker with a 20 watt amp would ever have a problem....but, like thegeezer I've been wrong once or twice before.....go buy a 100 watt JBL and not have to worry about it.

 

[Wyatt]

I should add that if you do burn out the voice coil on the speaker, then the output transformer will be the next to die because of the open circuit.

 

[telemnemonics]

15w Celestion Blue singles blew in AC15s and pairs blew in AC30s, 25w Greenback quads blew in 100w Marshalls, pairs of 25w GBs blew in JTM45s, even JBLs blew in Twins.
I blew an old Celestion 15w (gray frame) Blue in a 12w Musicmaster Bass amp at low volume, but that speaker was 50 years old.

 

[Cazualwhiteguy]

Thanks for the info guys, now just to reiterate, I play at living room and SEMI LOUD living room levels, nothing loud enough to keep up with a drummer or anything. Seems maybe a speaker replacement would be the SAFEST option, but what's the difference in a 100w head pushing 4 25w speakers or so? That's a much bigger difference in power but it seems to be done often, just trying to figure this all out.

 

[jackal]

Because 4X25=100 watts power handling. Same in series or parallel.

 

[telemnemonics]

Thanks for the info guys, now just to reiterate, I play at living room and SEMI LOUD living room levels, nothing loud enough to keep up with a drummer or anything. Seems maybe a speaker replacement would be the SAFEST option, but what's the difference in a 100w head pushing 4 25w speakers or so? That's a much bigger difference in power but it seems to be done often, just trying to figure this all out.

The 25 watt speakers blew regularly.

 

[Cazualwhiteguy]

The 25 watt speakers blew regularly.

I feel like you guys are referring to playing at say gig volumes or so, I'm talking living room levels. Does anybody actually blow a speaker at living room levels..?

 

[JustABluesGuy]

I use some lower wattage vintage speakers with no problems (yet), but I am very careful with them.

For example, I have a '73 CTS alNiCo that I only run with my 2 watt amp just to be safe. I have a 2x10 with '73 CTS ceramics that I "rate" at 15 Watts. I also use that with the 2 W amp as well though they can handle more I'm sure.

I've used all of these speakers with my 15 watt amp as well, but I was very careful with the volume and didn't do it for extended periods.

If you don't have to worry about idiot friends or bandmates diming your amp and wailing away, and you don't use lots of gain or fuzz you will probably be ok.

 

[Frodebro]

Thanks for the info guys, now just to reiterate, I play at living room and SEMI LOUD living room levels, nothing loud enough to keep up with a drummer or anything. Seems maybe a speaker replacement would be the SAFEST option, but what's the difference in a 100w head pushing 4 25w speakers or so? That's a much bigger difference in power but it seems to be done often, just trying to figure this all out.

The sensitivity rating of a typical guitar speaker is around 90dB-97dB, measured with one watt of input power from a distance of one meter.

What this means is that just one watt of power is going to produce volume levels approximating that of a lawnmower in your living room. Typical "living room/bedroom" levels are around 70dB or thereabout. If you are generally always running your amp at these living room/bedroom levels, you're seldom going to be pushing more than 0.5 watts through your speaker. It doesn't matter if the amp is a five watt amp or 100-at living room levels it's not putting out even close to its full rated output.

I run my Boogies (90W and 100W) through a 1x12 with a single 25W Greenback ALL THE TIME at home and the speaker isn't even breaking a sweat, because it's not getting more than one watt of power in that situation.

Bottom line: You're not going to hurt a healthy 15W speaker with a 20W amp if you're only playing at television levels.

 

[Dacious]

Marshall Plexis blew Greenbacks (originals were rated 20w BTW) because a healthy Plexi cranks out 130 watts. Similarly, AC30s with Topboost easily top 33. Part of the reason they can flame out output transformers. Brian May runs four non-Topboost AC30s at gigs but regularly blows them. The Brits used to rate amps pre-distortion.

If you crank an amp like them a la Hendrix and Townshend guess what - speakers become consummables. Just over- watting speakers does not guarantee they'll survive lots of square waves; a speaker tries to move both directions when the poweramp clips hard so all of us who love cranking to distortion are shortening lives of our output sections.

To the OP - I think you're safe unless living room is bombproof and you play metal.

 

[Frodebro]

Marshall Plexis blew Greenbacks (originals were rated 20w BTW) because a healthy Plexi cranks out 130 watts. Similarly, AC30s with Topboost easily top 33. Part of the reason they can flame out output transformers. Brian May runs four non-Topboost AC30s at gigs but regularly blows them. The Brits used to rate amps pre-distortion.

If you crank an amp like them a la Hendrix and Townshend guess what - speakers become consummables. Just over- watting speakers does not guarantee they'll survive lots of square waves; a speaker tries to move both directions when the poweramp clips hard so all of us who love cranking to distortion are shortening lives of our output sections.

To the OP - I think you're safe unless living room is bombproof and you play metal.

I've heard that Marshalls hit close to 180 watts with everything dimed, but there was no mention of which model that was. Regardless, most tube amps are going to exceed their rated output wattage by a fairly generous margin when you push them into full distortion. My Boogies (Mark V/90 watts and Stiletto Deuce ii/100 watts) are literally painful to stand in front of when cranked up through a 4x12. I may have even sterilized myself, who knows...

 

[telemnemonics]

I feel like you guys are referring to playing at say gig volumes or so, I'm talking living room levels. Does anybody actually blow a speaker at living room levels..?

"Living room levels" is not a technical term, but I'll admit that while I've cranked 50w Marshalls in living rooms, 100 watters need more space.

If your LR is carpeted and has sofas and Lazyboys, I would personally have no problem blowing 20 watts with a 20w amp turned to 3 without getting divorced.
Vintage Marshalls typically hit full rated watts around 2 on the volume.

We had a pretty long and technical thread this year where a player wanted to know how to figure out where on the volume know his amp was at the speakers rated wattage. IIRC he had some pretty special speakers he didn't want to blow.

If you are convinced that you and everyone else will never turn up, you're fine. But you knew that, right?
We can't really know. All we can do is answer in technical terms.
Lots of players post the exact same question here.
"If I don't turn up my amp, can I use a speaker that's way under rated?"
Generally a 20w tube amps needs a 50w speaker, so a 15w speaker would be way under rated, not slightly under rated.
Lots of us have blown speakers, with the best intentions.

If you spent your life savings on that high end amp, and are now on disability, so will never be able to save up $60 to buy a speaker that is suited to your $1200 amp, then you know what you must do.

If you want a cosigner to approve the suitability of your mismatch...

Sorry, just trying to be truthful rather than supportive.