Question: Why is it so hard to get a straight answer about amp configurations?

PunkKitty

PunkKitty

Horny bag of electric meat
I posed this at another forum:

I'm getting to the point where I'm playing small clubs and small halls. I'm currently using a Carvin MB10 amp (250 watts) with a Carvin 115MB extension cab. I'm thinking of upgrading my amp and buying an amp head.

The 115MB will handle 400 watts. I also have a Epiphone 1x12 guitar cab that I installed a Sica SL12B25P neo woofer in it . According to the speaker specs, it is rated for 250 watts or 500 watts continuous program power. I have no idea what this means in plain English. I'm a bassist and not a sound engineer.

The speaker is a bass speaker. Let's set aside the issue about it being in a guitar cab. I realize that this isn't optimal. For my purposes I don't think it will matter much since I play rock and primarily punk.

Since both speakers are 8 ohm, I should be able to use them in parallel at 4 ohms.

I'm trying to figure out how powerful of a solid state head I should be looking at to use both cabinets.

Reading what I've found online leaves me thoroughly confused. I'm just looking for a straight answer in plain English.

Would I get more volume using something like an all tube Fender Bassman 100 with dual outputs totaling 4 ohms?


I'm getting all kinds of responses about how the guitar cab will blow up because it's not optimized for bass. It's frustrating. Just answer the damn question!!!
 
Continuous rating is if you're running compressed (ie: prerecorded) material through it. Live music has much more dramatic spikes, so it's harder on the voice coil of the woofer (they get warmer faster). You basically need the extra overhead when running live music to make sure the cones don't blow out or the coils seize. If you're DJing, you can run more power without fear that your speakers will melt because the levels are more consistent.

I would use the same warning in regard to a bass vs guitar cab. If the guitar cab is rated at 100 watts, I wouldn't hook up more than a 50 watt bass amp because the wave dynamics of the bass's low frequency is much harder on the speaker.

I read that as you want to plug a bass into a guitar speaker... I would only run half power until you can get a bigger bass cab. That's why many bass cabs are rated at 400 watts even though you only run 200 through them. Guitars don't have the same heavy wave dynamic (huge metal strings passing through the pickup field) so their output is a smoother dynamic.
 
Okay. Then I'm running two 8 ohm cabinets at 250 watts and 400 watts. In parallel they should run at 4 ohms. Does this change the output of the speakers in any way? What is the maximum that I can push through such a configuration?
 
In parallel the amp is running at 4 ohms, the speakers are running at 8...you need to match your amp power to your weakest speaker at it's rated ohm load, in this case 250 watts at 8 ohms...
 
PunkKitty said:
Okay. Then I'm running two 8 ohm cabinets at 250 watts and 400 watts. In parallel they should run at 4 ohms. Does this change the output of the speakers in any way? What is the maximum that I can push through such a configuration?
Click to expand...

On a side note...wattage is a rating of "heat dissipation." The speaker can dissipate XX amount of heat before it melts down. This is independent of impedance.

Jelloman is right be he omitted an important note...The 250w at 8 ohm amp has to be able to run a 4 ohm load (with would be 500w). You NEVER go below to posted minimum speaker load for a SS amp. Voltages will increase beyond part ratings.
 
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In regards to amps and ohms....


Think of your amp as a water source. A small amp is a faucet, a couple hundred watt amp is a fire hydrant.

When you have a speaker, or group of speakers rated at 16, 8, 4, or 2 ohms it's how much resistance they put up (16 ohm garden hose vs 4 ohm fire hose) to what's flowing out of the amp.

If you have two speakers of different ohms, the lower ohm side puts up less resistance, so more of the amps wattage flows that direction.

When you hook up multiple speakers in parallel, the wattage will flow based on the total load, but when you have multiple speakers, the power is divided up among them depending on their ohms load. That's how you get a power amp that can do (for example) 600 watts per side in 8 ohm stereo [600 x2 =1200 total], but if you run 4 speakers (8 oh + 8 ohm per side = 4 ohm) but that same amp is rated 1000 watts per side at a 4 ohm load, each speaker sees 500 watts that way [500 x4 =2000].
 
I'm going to see how things work out with what I have. I decided not to mix the cabinets. If I need a second cabinet, I'll buy a matching Carvin cab. Then I should be able to use a 500 watt amp with no problems.
 
Do the clubs you play have a PA? Back in the early 90s I gigged up and down the east coast with a peavy rig that was a 150 watt head and 15 inch cab and that was more than enough with a PA.


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If I were buying a bass rig, it would be a TC Electronic. Very small, lightweight, built in tuner, and supports a second cab. They offer it in a 1x15, 2x8 and 2x10.

13720.jpg
 
baimun said:
If I were buying a bass rig, it would be a TC Electronic. Very small, lightweight, built in tuner, and supports a second cab. They offer it in a 1x15, 2x8 and 2x10.

13720.jpg
Click to expand...
Built in tuner? In all the years I gigged on a bass, I never used a tuner. Tuner are for guitar players :grin:
 
matching amp ohmage to cabinet ohmage is the right way to go.

but just to be clear (if i read the OP right).....you have installed a bass speaker in a guitar cabinet (the epi cab)......the cabinet does not care what speaker is in it....just wood, glue and screws.....now it might sound kinda thin compared to a bass cabinet.....but it will not "blow up".....it's just wood.
 
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