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Fender Bassman 100T + Acme Low B2 = Farty?

J-Dub

J-Dub

Feb 13, 2011
381
295
Austin, TX
#1
My rig is farting out at louder volumes. It's not terrible, but its getting low-end distortion that I don't want. I'm running the Fender Bassman 100T @ 4ohms into two Acme Low B-2 2x10 8ohm cabs (total 4x10s @ 4ohms).

This is my first tube all tube head so I could just be hearing power tube distortion and not know it. The amp sounds great at lower volumes but is having trouble keeping up with my louder bands without getting farty. But I also wonder if it could be the cabs. Any suggestions on a better cab setup? I like bassy and dubby, but warm. I love this amp, and really don't want to get a bigger 300W tube head if I can avoid it. I've considered 12 or 15" speakers, but 10" speakers seem to be the golden standard for loud rock music. Or maybe 4x10's simply isn't enough?

Another thought that occurred to me is getting a solid state power amp to bypass the tube power when its not enough, but I might as well go back to my Ashdown ABM hybrid if I'm gonna do that, right?
 
#5
At 93 dB efficiency, you have to push the head a lot further to get the volume you need. You are running into amp breakup. You need more efficient cabinets or more power. While not as low as some Acmes, this is still quite lower than most commercial bass cabinets.

Efficiency is not an indication of quality. In order to get extended low end, and high excursion, efficiency suffers. These speakers are not the right fit for you.

Acme recommends 400-500 watts for this cabinet.


http://www.acmebass.com/pdf/b2.pdf
 
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#9
Steve Dallman said:
At 93 dB efficiency, you have to push the head a lot further to get the volume you need. You are running into amp breakup. You need more efficient cabinets or more power. While not as low as some Acmes, this is still quite lower than most commercial bass cabinets.

Efficiency is not an indication of quality. In order to get extended low end, and high excursion, efficiency suffers. These speakers are not the right fit for you.

Acme recommends 400-500 watts for this cabinet.


http://www.acmebass.com/pdf/b2.pdf
Click to expand...

Yeah I'm starting to think they're simply not a good fit either. Definitely quality build and sound great at lower volumes, just not what I need.

Any recommendations for loud rock? I can stand the typical Ampeg offerings, but I'd prefer something deeper sounding with less mids.
 
#11
Naturally it will sound bad. You simply do not have enough power to drive the cabinets properly. As an example: I own four 4Ω B2s. I use a pair at a time driven by a power amp that can put 500W into each cabinet. It sounds wonderfull. The amp can also power all four cabinets should I desire such an excess!! :D
 
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#14
To me Acme cabinets are very special. I consider them amount the best bass speaker cabinets out there. They go very low, are quite small and easy to tote. The downside is that they are inefficient. They NEED to be driven properly. The OP's 100W tube amp will not even adequately drive one B2 let alone two. If one buys into Acme one has to be cognizant of the necessities involved in using them.
 
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#16
I've got a pair of 8 ohm B2s. I tried my Music Man HD-130 thru them and it wasn't a good fit. Similar to what you found. I've been told that this is due to the "damping factor" of either the head or speakers. Don't know which and don't know if that is in fact true. They do sound great with my MarkBass F500 and my Genz Benz Streamliner 900.

Just looked up "damping factor". Sounds like it could indeed be the culprit. As well as the need for more power.

Definition. Amplifier damping factor (DF) is defined as “the ratio of the load impedance (loudspeaker plus wire resistance) to the amplifier internal output impedance.” This basically indicates the amplifier's ability to control overshoot of the loudspeaker, i.e., to stop the cone from moving.
 
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#17
As others have mentioned, that particular amp and cab pairing is not ideal, because of the way a 100W tube amp breaks up fairly early, starting with the part of the signal that is wanting the most power.

Those cabs sacrifice (for better or worse), efficiency for low end. So if your low end is causing low end amp break up you're going to hear it.

You either need more amp or more speaker. Something along the lines of 6x10 or 8x10.

Having owned tube amps up and down the power spectrum and cabs of all different tastes, I'll always opt for more power.
 
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#20
How about borrowing/hiring a powerful amp and see if the same thing happens? Drag all your stuff to a local GC and run a GK or MB or high power Ampeg and do the experiment. I predict an "aha" moment

BTW I had a B2 with a Markbass LM2 and it was just cutting it so I feel that, as most other posters have pointed out, you are severely UNDERPOWERED. B2 is a nice speaker and 2 are twice as nice!

GOOD LUCK AND let us know how you solve things.
 
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