Tube amps watts vs decibels

Ask questions and get answers about how to make music in any particular way. Hardware or songwriting or whatever.

Moderator: Mods

Lunkhead
Princess Zelda
Posts: 5183
Joined: Sat Sep 25, 2004 12:14 pm
Instruments: many
Recording Method: cubase/reason/mac/tascam4x4
Submitting as: Berkeley Social Scene, Merisan, Tiny Robots
Location: Berkeley, CA
Contact:

Tube amps watts vs decibels

Postby Lunkhead » Tue Jul 28, 2015 11:59 am

Starting a dedicated thread for this topic to keep the "Deals on Gear and Software" thread more focused.

http://www.300guitars.com/articles/ampl ... -decibels/

jb wrote:I've been looking into tube amps recently, and I just scrolled back and saw that Bugera amp from May-- 120w. Which makes me really confused, because in reading I see that a Vox 15w will apparently blow your head off and 30w is enough to play a pretty big room. So what the fuck do you do with a 120w tube amp? And how do you keep it from catching on fire from just being so loud?

And there there is this thing: http://www.musicradar.com/reviews/guita ... 800-615917

840w per channel?!?!?!?!?!?! (and light enough to carry in a backpack) What kind of god damned speaker do you hook that thing up to and do you get a whole Michael J Fox in Back to the Future type thing happening if you do?

(Contrast this with solid-state amps, where the wattage required to be loud is a lot higher. My Princeton 112+ is 65w for example and is just enough for a small rock club and still probably needs to be mic'd.)


fluffy wrote:Do they mean watts of power draw or watts of sound power? Because sound power watts are massively loud (10W is around 130dB) but a lot of amps are crazy inefficient at converting one to the other.


AJOwens wrote:You need to think also about how the power output is measured. 10W RMS is not the same as 10W peak.

Bass amps tend to need massive power. Put a 60W RMS guitar amp and a 60W RMS bass amp on stage, and you're going to have an extremely frustrated bass player. To get a clean sound in a modest venue, a bass player would probably want 200W RMS as a minimum.
User avatar
jb
Notable Hylian
Posts: 3535
Joined: Sat Sep 25, 2004 10:12 am
Instruments: Guitar, Cello, Keys, Uke, Vox, Perc
Recording Method: Logic X
Submitting as: The John Benjamin Band
Location: WASHINGTON, DC
Contact:

Re: Tube amps watts vs decibels

Postby jb » Tue Jul 28, 2015 12:45 pm

Just in case there was doubt, you guys are NOT making this easier to understand.
User avatar
AJOwens
Skull Kid
Posts: 726
Joined: Mon Jul 20, 2009 6:50 am
Instruments: bass, guitar, keyboards, drums, flute
Recording Method: Reaper, Reason Adapted, M-Audio 1010LT + 2496 (Windows XP)
Submitting as: James Owens
Location: Ottawa, Canada

Re: Tube amps watts vs decibels

Postby AJOwens » Tue Jul 28, 2015 1:14 pm

jb wrote:Just in case there was doubt, you guys are NOT making this easier to understand.


For RMS vs. peak, this page may help:
http://myhometheater.homestead.com/RMS.html

The solid-state amp thing sounds like a red herring. Whether a signal is amplified by gating the big electron source in a slab of silicon or sucking it across a vacuum with varying intensity shouldn't really make any difference. Probably the solid-state amp is rated 65W peak, meaning it won't be as loud as a 65W RMS amp.

[EDIT: The owner's manual says it's 65 W RMS. Maybe the speaker is not as efficient as some.]

Ten watts RMS is loads of sound for a small room, assuming the amp is cranked to the max. But when you crank an amp to the max, you're pushing it to its design limits, and depending on the designer, that many mean some level of clipping or distortion. The designer is trying to squeeze the maximum performance from physical parts with physical limitations. If you've got parts with the balls to handle 60W at their limit, they'll be real cool with 10W. You can turn down, and it will sound a whole lot sweeter than your 10W amp.

Part of this is escalation. If you are in a room with someone who likes to turn up, and they go to 60W, it's actually not going to sound six times louder for whatever reasons (the whole decibels and human hearing thing.) Nevertheless, in terms of physically pushing air, your 10W amp is going to be buried. If everybody just used 10W amps to play, no one would miss any notes by a long shot, and you'd still hear the upright piano too. But human nature being what it is, somebody will come in with a 30W amp, and then -- even though the 30W level is comparably tolerable to the ear -- you can't hear the piano or anybody else's amp. Personally I blame loud drummers for making 30W amps necessary in small rooms.

Then there are huge venues. I believe the Beatles played Shea Stadium with their usual VOX amps, probably in the 30-60W range, and it wasn't enough. Lesson learned.

[EDIT: Apparently they were 100W amps; still not enough.
http://www.voxshowroom.com/uk/amp/ac100mkII.html
https://answers.yahoo.com/question/inde ... 923AAhccuL
]

As for why bass players need the power, I don't know. Something about moving massive magnets, I guess. With modern speakers that may have changed a bit.
Lunkhead
Princess Zelda
Posts: 5183
Joined: Sat Sep 25, 2004 12:14 pm
Instruments: many
Recording Method: cubase/reason/mac/tascam4x4
Submitting as: Berkeley Social Scene, Merisan, Tiny Robots
Location: Berkeley, CA
Contact:

Re: Tube amps watts vs decibels

Postby Lunkhead » Tue Jul 28, 2015 1:37 pm

This Q&A seems potentially informative.

http://music.stackexchange.com/question ... escription

The approved answer doesn't provide source links, but this quote if true could explain things:

...an amp's wattage rating is traditionally listed as the amount of power it can produce while keeping the total harmonic distortion (THD) of the output under a certain percentage


Solid state amps can amplify a lot more with a lot less distortion than tube amplifiers, I think, right? So they can be rated higher, assuming this guy's comment is true.

Lots more complicated details here:

http://www.gmarts.org/index.php?go=216
User avatar
AJOwens
Skull Kid
Posts: 726
Joined: Mon Jul 20, 2009 6:50 am
Instruments: bass, guitar, keyboards, drums, flute
Recording Method: Reaper, Reason Adapted, M-Audio 1010LT + 2496 (Windows XP)
Submitting as: James Owens
Location: Ottawa, Canada

Re: Tube amps watts vs decibels

Postby AJOwens » Tue Jul 28, 2015 2:02 pm


Return to “Help and How To”

Who is online

Users browsing this forum: No registered users and 1 guest