using a higher wattage cabinet with low wattage amp head

[rm -rp ./Matt*]

Hi all,
This is more of an amp question, but this forum has been really helpful over the past couple of days so I thought I'd throw in another question

Reading up on amp heads and cabinet wattage in here has really changed my perception on needed wattage values.

It seems most diy amp projects are either for micro amps or 15-18w amp heads, both of which people seem to use with 2x12 cabinets (60-80w?) fine.

I'd like to know if I build a 15w tube amp with a 60-80w 2x12 cabinet will it get loud enough to play in a small live environment unmiked? I'm not playing heavily harsh or overdriven music, and I'm fine with my effects pedals doing all the talking when it comes to this.

And is there any info out there that can help me with this whole head/cab wattage difference?

[Derringer]

It all depends how loud your drummer is.

Will you never have the opportunity of mic'ing it?

[km-r]

yes it will. match the output impedance of the amp to the cab to get almost 100% of the power...
your 15w amp may get a lil overdriven if you want it to sound over the drums though...

[CodeMonk]

As long as the total wattage for the cabinet is higher than than the amps maximum output, you should be fine.
I've got a Vox AC30CCH (30 watt) head, hooked to either a 1x12 or a 2x12 cabinet each with Celestion G12K-85 speakers (thats 85 watts for each speaker). And let me tell you, that thing can get DAMN loud.
And the amp handles it just fine.
Well, except for a few weeks ago at a jam session. We went for 6 hours straight and the head overheated a bit. Some idiot (me) had also set a rack mounted processor on top of it covering one of the vents

[rm -rp ./Matt*]

thanks for your replies, I guess I'm not really sure how loud it's all going to be, maybe a better question would be to compare setups.

Would a diy 15-18w valve head with a vox 60watt(2x30w) 2x12 cabinet be as loud or louder than a Marshall 80w solid state amp?

Currently I'm running my solid state at 8 out of 10 volume and that competes fine (for my liking) with the drums and bass.

[petemoore]

  What's the speaker effeciency ?
  It can make enourmous difference in SPL's and percieved loudness.
  Bass tends to eat watts, if trebly speaker or amp voicing it'll be different also.
  15w 'cranks' a 12'' speaker [opinion and rig specific of course], by that I mean it'll make a 12'' sound plenty loud, about as loud as a 12'' gets and still sounds sweet, YMMV.
  But when cranking the 12, there won't be much clean available, especially if bass is big...if you want the 'plank' of a string hit hard to sound kinda loud, you'll need more watts, sounds real sweet though driving 2x12's.
  18w push pull is quite a bit louder, and drives 2x12's to loud, enough to get more than loud enough for my bands, but with the rooms' we're playing mostly, it is morgan enough.
  YMMV and when you're up against say a cranking 50w nearby, clean / ligible is pretty much squelched by the bigger amp...really depends on how loud the environment around the amp is.

[CodeMonk]

From what I have heard (haven't tested myself much), that a lower wattage tube amp will blow away a higher wattage solid state amp. How much higher I don't know. I've tried to compare my AD50VT against my AC30, but my ears started hurting (my studio/workshop is rather small).

[Darkness, Darkness]

Here is my point of view :

- Usually tube amps sounds louder than solid state at the same power rating
- 15 W should be OK to play with a drummer that don't play heavy metal  but if the amp design is vintage like, you might not have clean tone with enough volume
- Speaker choice is important : the higher sensibility of the speaker, the higher the volume (for example 96db for the greenback, 100db for the vintage 30) 
- 4x12 will sound lounder than 1X10.... more speakers surface to move the air (but adding speaker does not add more power to your amps !)
- Open back cab will diffuse the sound in the room while a closed cab will project the sound mostly in real front of the cab
- One more tips to have your guitar (or other instrument, voice ....)  to sound a bit louder.... use a compressor

Here are a good link explaining volume things (well this site is more on how to reduce the volume...):
http://www.amptone.com/g183.htm
http://www.amptone.com/g112.htm
http://www.amptone.com/speakers.htm

[MarcoMike]

+1 on the sensitivity thing... then, I don't know about your specific amp, but mine is a 50-60 watter (2xEL34) and with volume at max I never went over 2-3 of gain at rehearsal. probably a 15W is good enough for rehearsal, maybe a little undersized for live concerts in football fields....

[StephenGiles]

My mum used to say "I don't know why you need to play so loudly" - and that was with a Watkins Westminster 10 watt amp!!

[geertjacobs]

As mentioned above: speaker efficiency can compensate for the lower wattage of the amp.
for example an Eminence Red Fang has an efficiency of 103dB!