1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Amp wattage ratio to speaker rating?

Discussion in 'Glowing Bottle Tube Amp Forum' started by natec, Dec 8, 2020.

  1. natec

    natec Tele-Meister Silver Supporter

    Posts:
    152
    Joined:
    Mar 21, 2009
    Location:
    Portland Oregon
    If replacing a speaker in a 'low-ish' powered amp (AC4) - should I expect that one with a 15w to 25w rating would have less headroom (break up sooner) than a speaker with a 50w or more rating?

    My gut says yes, but my gut does not have an electrical, radio, or any other STEM degree....

    Nate

    p.s. - Putting this in the tube forum, as I also expect the answer may vary for SS amps...
     
  2. Wally

    Wally Telefied Ad Free Member

    Posts:
    38,174
    Joined:
    Mar 17, 2003
    Location:
    Lubbock, TX
    I’ve got an EV SRO 12L that will not break up before that amp gives out....if that is what you are looking for?!?! (8^0
     
    old wrench likes this.
  3. Jakedog

    Jakedog Telefied Ad Free Member

    Posts:
    20,489
    Joined:
    Mar 26, 2003
    Location:
    The North Coast
    I like to try and have a speaker that is rated to handle at least double the wattage of the amp. I like preamp breakup. I like power amp breakup. I like pedal breakup. I hate speaker breakup.

    I currently have a 15 watt amp with a 50 watt speaker in it, and a 20 watt amp with a 70 watt speaker in it. I also have a 50 watt ext cab that I use with an 18 watt head.

    My 120 watt combo only has a 150 watt speaker in it. But I like the way it sounds stock, and I never turn that thing up enough to have to worry about it.
     
    BelairPlayer, Askwhy, PhredE and 2 others like this.
  4. natec

    natec Tele-Meister Silver Supporter

    Posts:
    152
    Joined:
    Mar 21, 2009
    Location:
    Portland Oregon
    Thanks. For a 4 watt amp (AC4 Vox) - is there any advantage to speakers over 15w (assuming all else equal)?
     
  5. ahiddentableau

    ahiddentableau Tele-Meister

    Posts:
    415
    Joined:
    Jul 8, 2018
    Location:
    Middle of Nowhere
    I think as a generalization what you say is true. All things being equal a speaker with higher power handling will probably have more headroom. But power handling is still it's own thing and not necessarily related to breakup characteristics. Put another way, I'm sure if you dig around you can find a speaker that handles 30W that breaks up easier than a different model speaker that handles 20 or 25W. So you probably want to be a bit careful.

    And no, there is no particular advantage to great levels of power handling for an AC4 if that's the only amp you're going to use with that speaker. However, you might want to consider whether you'll want to use the speaker with different amps in the future. In other contexts higher power handling could be desirable.
     
    Jakedog, fatcat, PhredE and 3 others like this.
  6. old wrench

    old wrench Tele-Afflicted

    Posts:
    1,968
    Joined:
    Feb 2, 2017
    Location:
    corner of walk and don't walk
    As a starting point for minimum speaker power rating- if you double your amps output rating, that will give you a pretty safe number for speaker power rating. It's a place to start, anyhow :).

    A speaker with a higher rating is probably going to sound "smoother".

    There are a lot of factors that determine stuff like "headroom" including speaker cone design. Smooth cones tend to "breakup" earlier than ribbed cones.

    I put quotation marks around those words because they are somewhat subjective (!) and different folks interpret them in different ways ;).

    If you haven't already, you might check out the Weber speaker site and browse through some of the speakers and speaker descriptions. I find their descriptions pretty interesting, and as a Weber speaker user, they also seem pretty accurate based on my experience.

    Weber Speakers – www.tedweber.com

    .
     
    drewg, Digital Larry, PhredE and 2 others like this.
  7. BigDaddyLH

    BigDaddyLH Tele Axpert Ad Free Member

    Posts:
    56,055
    Joined:
    Sep 1, 2009
    Location:
    Kelowna, BC, Canuckistan
    Is there a difference with SS/tube amps?

    I still feel, with a few notable exceptions, there's a difference in SS-vs-tube Watts.
     
    Chiogtr4x likes this.
  8. MuddyWolf

    MuddyWolf Tele-Meister

    Age:
    58
    Posts:
    424
    Joined:
    May 11, 2017
    Location:
    Paradise, Ca
    The 2 to 1 rule is generally good. But you can still blow a 200 watt speaker with a 50 watt amp. I've done it. So the answer is listen to the speaker . You can hear it stressing when it is in the red zone. Then back it off or enjoy a short time of glorious tone right before it smokes.
     
    spellcaster, MLHull and PhredE like this.
  9. Dacious

    Dacious Poster Extraordinaire

    Posts:
    9,284
    Joined:
    Mar 16, 2003
    Location:
    Godzone
    I would not use a very high rated speaker with a 4 watt amp. There's no practical reasons you can't. It's just the amp has to move the motor - that's the voicecoil, spider and cone of the speaker. To me, massively over-speakering a small guitar amp will reduce its sonic performance.

    Headroom defined as volume before breakup on an AC4 is never going to be high. You can improve it with a better speaker than the one Vox uses. Tube selection too. Vox doesn't use the best tubes in these.

    If you ask Celestion or Eminence or Jensen today what speaker to use they will tell you to match the RMS wattage rating to the amp's. Speaker breakup is influenced by many things - weight of cone, doping, surround; stiffness, voicecoil diameter and gaige. Of course with higher wattage speakers these are all stiffer, harder and therefore so will the amp's response be at low volume IMO.

    It's true a 50 watt amp can peak at 100 watts. But a 50 w RMS speaker can also cope with that as long as it isn't sustained. If it is, you'll cook something in the amp eventually.

    People started over speakering amps because Plexis popped speakers - two quad boxes of Greenbacks only gave you 160 watts of speaker and the amp could produce that much power without any overdrive or distortion or treble boosters in front.

    Ditto AC30s, which can produce 36 watts into Celestion Blues rated 15 watts just on topboost.

    The moment people started hitting them with treble boosters, Fuzzfaces, Maestros they started futzing out speakers with gay abandon.

    Modern speakers have better materials and especially glues. plus many amp makers advertise power by peak rather than undistorted as Marshall and Vox used to. A JTM45 was rated 33 watts and it was - prior to distortion.
     
    Last edited: Dec 8, 2020
    drewg, Paul G., Jakedog and 1 other person like this.
  10. BobbyZ

    BobbyZ Doctor of Teleocity

    Posts:
    13,402
    Joined:
    Jan 12, 2011
    Location:
    Snellman MN
    Generally a higher wattage speaker will break up at a higher volume/wattage. But there's more involved there. Remember what sets the wattage, the voice coil, up to a point, then voice coil diameter and magnet size come in.
    That said, with small amps I might actually crank up, I like some extra wattage capacity.
    With big amps I don't worry too much, volume and the police keeps me from getting a 100 watt amp anywhere close to 100 watts.
    I just laugh when I see a guy with a 100 watt master volume amp, that lives in town worried if he ain't got 200 watts worth of speakers. I know guys like that, they wet themselves when you turn up a Deluxe Reverb past 6. Then ask if it has a master volume. :)
     
    natec and beanluc like this.
  11. schmee

    schmee Doctor of Teleocity

    Posts:
    13,884
    Joined:
    Jun 2, 2003
    Location:
    northwest
    I generally like about a 2 to 1 ratio. Your assumption of less breakup with higher wattage is generally correct. Also, generally, higher wattage will give you more low end.
    HOWEVER, in your case that little amp will break up early and a lot, if it does that, any speaker will just amplify that sound!
    A good case in point is the last SF Champ I had. For giggles I tried various speaker cabs with it, including a 4 x 10 connected with my monster EV15! (the combo made a 4 ohm match.) Did it sound better than the decent 820H combo speaker I had? A little but not much when I pushed the amp.
     
  12. Chiogtr4x

    Chiogtr4x Poster Extraordinaire

    Posts:
    9,279
    Joined:
    Mar 29, 2007
    Location:
    Manassas Park, VA
    I'm just amazed that the 20 watt Vox/Celestion 8" speaker ( came out of my dead Vox Cambridge 15), in my 15 watt Vox Pathfinder...

    ( always goosed by an OD pedal which almost doubles the amps apparent volume),

    ...does not explode into dust every time our little band gets cookin' - like a Blues band meets Crazy Horse.

    Our band is not insanely loud but sometimes I feel like I'm pummeling that little speaker, but it takes it!
     
  13. kbold

    kbold Tele-Afflicted

    Posts:
    1,965
    Joined:
    Jul 21, 2015
    Location:
    Australia
    I see no advantage going above 15 to 20 Watts. A larger wattage speaker will need more power to get it moving, so that's a loss for a 4 watt amp.
    Another consideration is speaker efficiency (the volume output for a given input) which varies considerably between speakers. Worth looking at this rating esp. for a low power amp.

    The main difference between valve and s/s (besides the opinion that valves sound better) is how they overdrive. Overdrive a s/s amp and it flat-lines (while a valve will still have squiggles). The s/s flat-line = DC, which speakers dislike (watts from your amp are converted into heat instead of noise).
    You don't want the magic smoke escaping from your precious speaker: it's really hard to get it back in.

    This is why I would argue that for a s/s amp you should not overrate your speakers. (i.e. 50W speaker for a 50W s/s amp)
    The unpleasant sound of speaker breakup is IMO less damaging than the amp flat-lining into the speaker.
     
  14. Askwhy

    Askwhy Tele-Meister

    Posts:
    375
    Joined:
    Dec 18, 2019
    Location:
    Utah
    Double (or more) is a good rule of thumb to be safe, no need to get more complicated than that. In terms of how loud it will be, sensitivity is much more important than wattage, assuming a safe wattage choice. As one poster mentioned, the much higher wattage speakers will sound a bit smoother (or another mans dead and blanket covered). Double is a good spot.
     
  15. marshman

    marshman Poster Extraordinaire Silver Supporter

    Posts:
    5,364
    Joined:
    Feb 1, 2007
    Location:
    SE PA
    Efficiency, or the ability of your amplifier to turn the maximum amount of energy from the amp into sound energy, is measured in dB and generally referred to as SPL. This number is, as I understand it, completely unrelated (at least mathematically) to the amount of power a speaker can process before it fails, which we refer to as power handling, generally measured in watts.

    It was my observation years ago regarding older speakers (with no actual data to back it up) that the design techniques used to make speakers rated for higher power output made speakers less efficient, given the same size speakers. Modern technology and techniques seem to have moved that bar considerably, given the typical modern Eminence 12" guitar speaker is rated for 100-ish watts AND 100+ dB.

    Other unsubstantiated observations are that typical push/pull tube amps are capable of making roughly 40% more power than their ratings for very brief (1 or 2 seconds) when pushed really hard. I would imagine a single ended tube is less, but even if that were true, your worst-case scenario for power spike from an AC4 would probably be 6 watts. Highly distorted signals are said to be pretty rough on speakers, so even if we were to double THAT, we're talking about 12 watts, so if were sure you only expect to use this speaker with the AC4, anything rated for 15 watts should be more than up to the task, and looking at dB will help you guesstimate how loud it will be.

    My personal experience is that even the stock 8" speaker in my 5-watt Epiphone Valve Jr is capable of generating a bit of window rattle when playing hard barre chords in the upper levels of the amps volume capacity ergo, well past maximum clean tone.

    Happy hunting!
     
    natec and Cali Dude like this.
  16. BobbyZ

    BobbyZ Doctor of Teleocity

    Posts:
    13,402
    Joined:
    Jan 12, 2011
    Location:
    Snellman MN
    I get what your saying, but sensitivity ratings are always done at 1 watt. A Swamp Thang has a wattage rating of 150 and puts out 103db at 1 watt. That's a pretty high wattage rating and about as loud as a sensitivity rating goes.
     
  17. kbold

    kbold Tele-Afflicted

    Posts:
    1,965
    Joined:
    Jul 21, 2015
    Location:
    Australia
    Wow ...wow! I didn't know speaker sensitivity went that high.

    That's a good Swamp Thang going on there. Sounds like a good option ... certainly won't overdrive the speaker.
     
  18. BobbyZ

    BobbyZ Doctor of Teleocity

    Posts:
    13,402
    Joined:
    Jan 12, 2011
    Location:
    Snellman MN
    Well I was wrong, it's 102db.:D
    It's a speaker I've heard great things about and I think I'd like it, but that sensitivity rating keeps me away. It's 2020, who needs louder?
     
  19. Frodebro

    Frodebro Doctor of Teleocity Ad Free Member

    Age:
    51
    Posts:
    16,328
    Joined:
    Aug 17, 2012
    Location:
    Seattle
    There is no difference in watts when comparing tubes to SS. A watt is a watt is a watt. Tubes, however, are capable of putting out nearly double their rated clean wattage when pushed hard (and still sound good). Solid state doesn't behave in this way-once it hits its rated clean output you're just about out of gas. From there it goes into hard clipping and sounds horrid (as well as melting speaker voice coils).
     
  20. BigDaddyLH

    BigDaddyLH Tele Axpert Ad Free Member

    Posts:
    56,055
    Joined:
    Sep 1, 2009
    Location:
    Kelowna, BC, Canuckistan
    I guess that's what I meant: tube amps can be pushed above their clean wattage so we have the rule of thumb about doubling the wattage valuer for the speaker. No need to do that with a SS amp?
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.