100 watt amp not as loud as a 30 watt amp... Why?

[JASON_NORTH_BLUES_BAND]

Hey I wonder if anyone can answer this... My 2150 100watt 1x12 JMP two channel four input combo isn't as loud as my jtm45 (30 watts) or my JCM800 2204 (50 watts). Even when I use an extension speaker with the combo, making it a 2x12 at 4 ohms.
I can even use either of my two Marshall heads with my 100 watt 1x12 speaker and they're still alot louder.
This makes me think a) the speaker in the combo is not very good or b) the bias on the combo is out. There is nothing wrong with the valves in the combo as I have replaced them recently. Maybe c) the transformer is on it's way out.
It's very frustrating though, because I had a 2150 years ago, and it just seemed to be clean, clean, clean. With this one, it starts breaking up at about volume two or three, which gives a great bluesbreaker sound at low volumes. The problem is though, that at gigs I'm having to really work it at about 6 or 7 on the master volume. This means that all I'm getting is creamy Marshall overdrive heaven... but not a hint of clean. Not a problem some would say? Well I like a bit of clean now and again, especially for blues. My jtm45 can do it, why can't the 2150?

 

[bosrocker51]

is it the stock speaker? if so it should be matched to the amp. maybe a higher wattage speaker would helP? try taking it to a tech...

 

[timstoel]

Speaker efficiency is probably the difference. Some speakers put out 89dB at one watt measured 1 meter from the speaker (89dB 1W/1M) some can put out 102dB 1W/1M. Efficient speakers are a GREAT way to upgrade a quieter amp. The Eminence speakers in my Peavey (gasp!) Duel are 103dB 1W/1M and that amp will smoke many half stacks and some full stacks volume wise.

There's a lot more to say too -- for example, car speakers are made of thick polypropylene, which is VERY heavy when compared to paper. Some of those high end car audio speakers only have an efficiency of 85dB, 18dB quieter than the speakers in some guitar amps. That means the car speaker takes 64 times the power to produce the same volume! They do this because the denser cone materials can get to lower frequencies in a smaller volume enclosure because of the weight of the cone. Car speakers are also very sluggish in responding to transients as compared to musical instrument speakers.

Another aside -- If you ever shop for PA speakers, be sure to take efficiency into account because it can make the difference between buying a 250 watt amp and a 2000 watt amp.

Tim

 

[AndyHighTides]

The thing that throws me is how it breaks up so early. If it were the speakers you would expect the opposite. I would be suspicious of a preamp tube. If you have any extras, try trading them out one at a time.