Amp/cab question

joeturbodiesel@ · #1 04-01-2011, 12:01 AM

What happens if the cab you want to play through is rated for way more than your amp puts out? Like a cab with 400 watts capacity @8 ohms and an amp that only puts out 170 watts @ 8 ohms. Will it sound good?

fourstringburn · #2 04-01-2011, 12:09 AM

It's not that it wont sound good, but it is better to have more amp power than cab rating power. You can blow an amp being way under powered for a cab. That shouldn't be the case with what you specified. Most modern cabs can handle 2 times their rated power. Check with your cab's manufacture if a peak/program rating isn't listed in the cab's specs.

kramj · #3 04-01-2011, 12:32 AM

under-powering?

JimmyM · #4 04-01-2011, 12:33 AM

Quote:

Originally Posted by fourstringburn

It's not that it wont sound good, but it is better to have more amp power than cab rating power. You can blow an amp being way under powered for a cab. That shouldn't be the case with what you specified. Most modern cabs can handle 2 times their rated power. Check with your cab's manufacture if a peak/program rating isn't listed in the cab's specs.

whoa! who told you that? i thought you'd been hanging around here long enough to know that the exact opposite is true. you cannot blow a cab with an amp that's underpowered. i do it all the time and have never lost a cab once, but i have seen plenty of folks blow cabs with twice the rated power of their cabs because they believed it was better to overpower. and most modern cabs can only handle about half their rated power.

joe, you won't be the loudest guy on the block, but you'll be fine with that rig.

fourstringburn · #5 04-01-2011, 01:18 AM

ampeg rates their cabs at program power which is 2 times the rms power. I should have specified that in the first post that it is 2 times the RMS power, my mistake! A 810e is 800 watts rms but 1600 watts program. I do run 1500 watts into each one of mine and do drive them hard and haven't had a problem yet. I checked with ampeg tech support to verify and it was confirmed it will handle it just fine.
QSC audio recommends the same, in fact check their website on use their amp/ speaker calculator and you will see the same conclusion. There is a big misconception about rms power and peak/program power and what is better and/or safe. The catch maybe that this doesn't apply to all manufactures so that's why I stated to check and see what or if a cab has a program power rating..

As for under powering, I could research and post the info I have read but to sum it up, I recall reading how being way under powered can cause an amp into clipping due to trying to get more out of the amp that it can deliver to the given speaker load which is a primary reason why amps can fail. There is many postings on this forum and through out the net for that matter that supports this.

I never ran any amps under powered for any cabs I have owned so yes, I'm and relying on what seems like credible info agreed upon by many including the engineers on this forum.

JimmyM · #6 04-01-2011, 02:32 AM

Quote:

Originally Posted by fourstringburn

ampeg rates their cabs at program power which is 2 times the rms power. I should have specified that in the first post that it is 2 times the RMS power, my mistake! A 810e is 800 watts rms but 1600 watts program. I do run 1500 watts into each one of mine and do drive them hard and haven't had a problem yet. I checked with ampeg tech support to verify and it was confirmed it will handle it just fine.

ampeg is also one of the very few companies out there that rates their cabs based on what they'll do in the real world, not just where the voice coils will burn out. most companies just tell you where the voice coils burn out, so that can't be trusted in real world usage.

Quote:

QSC audio recommends the same, in fact check their website on use their amp/ speaker calculator and you will see the same conclusion. There is a big misconception about rms power and peak/program power and what is better and/or safe. The catch maybe that this doesn't apply to all manufactures so that's why I stated to check and see what or if a cab has a program power rating..

qsc sells pa amps, and in pro sound that is what's usually done. but you're also talking about people who know the limits of their gear and don't try to exceed them or even come close. bass players are usually not that judicious.

the one thing you have to worry about clipping is if it exceeds the power handling of the speaker. but that's not "underpowering," it's "overpowering." but an amp rated for peak well below the power handling of the cab will never blow it, even if it clips. i've turned up a b-15 head all the way into two cabs that are rated for about 250w each and it's yet to cause any damage whatsoever.

the one caveat is tweeters. a good clip can blow a tweeter. but again...the clip has to overpower the tweeter to get it to blow.

Quote:

As for under powering, I could research and post the info I have read but to sum it up, I recall reading how being way under powered can cause an amp into clipping due to trying to get more out of the amp that it can deliver to the given speaker load which is a primary reason why amps can fail. There is many postings on this forum and through out the net for that matter that supports this.

I never ran any amps under powered for any cabs I have owned so yes, I'm and relying on what seems like credible info agreed upon by many including the engineers on this forum.

none of the engineers on here will tell you that underpowering blows speakers. not a single one of them.

Lowtonejoe · #7 04-01-2011, 03:13 AM

Quote:

Originally Posted by fourstringburn

It's not that it wont sound good, but it is better to have more amp power than cab rating power. You can blow an amp being way under powered for a cab. That shouldn't be the case with what you specified. Most modern cabs can handle 2 times their rated power. Check with your cab's manufacture if a peak/program rating isn't listed in the cab's specs.

It's not that you can blow an amp that is rated lower than your cabs power handling capacity, it's that if your amp is underpowered you will be tempted to run it fully cranked...which can be very bad.

You will NEVER ruin an amp by running it with a cab with a higher power rating. Period. No argument allowed.

Joe.

alexclaber · #8 04-01-2011, 03:27 AM

Barefaced Bass - Mythbusters #1 - amplifiers

joeturbodiesel@ · #9 04-01-2011, 01:27 PM

I was thinking about buying a swr 410 cab rated for 400 amps and want to run it with my ha 5000 until I come across a more powerful amp. That's the reason for the post.

Lowtonejoe · #10 04-01-2011, 02:35 PM

Quote:

Originally Posted by joeturbodiesel@

I was thinking about buying a swr 410 cab rated for 400 amps and want to run it with my ha 5000 until I come across a more powerful amp. That's the reason for the post.

Unless there is already a problem with the amp or cab you will have zero problems with this setup. Just don't max out your amp.

Listen to it. If it sounds bad, turn down until it doesn't.

Heh heh, that's almost a joke!

Joe.

joeturbodiesel@ · #11 04-01-2011, 05:37 PM

Thanks!

joeturbodiesel@ · #12 04-01-2011, 05:40 PM

Its got to sound better than the 210 Hartke cab that I'm using now for my top cab. Right? I was trying to get just a little more umph combining it with the b15 ampeg cab.

billfitzmaurice · #13 04-01-2011, 05:42 PM

Quote:

Originally Posted by JimmyM

none of the engineers on here will tell you that underpowering blows speakers. not a single one of them.

We will say the exact opposite, ad infinitum unfortunately, as this myth refuses to die.

joeturbodiesel@ · #14 04-01-2011, 05:45 PM

Quote:

Originally Posted by billfitzmaurice

We will say the exact opposite, ad infinitum unfortunately, as this myth refuses to die.

Are you saying that under powering the cab Will cause problems Bill? Sorry for the ignorance but how else can I learn if I don't ask the question?

Lowtonejoe · #15 04-01-2011, 06:06 PM

Quote:

Originally Posted by joeturbodiesel@

Are you saying that under powering the cab Will cause problems Bill? Sorry for the ignorance but how else can I learn if I don't ask the question?

Bill is an engineer/cabinet artist.

He's saying that as an engineer he would say exactly the opposite of 'underpowering blows speakers'.

Joe.

joeturbodiesel@ · #16 04-01-2011, 11:26 PM

Thanks. I am also curious, if you daisy chain two 8 ohm cabs together do you still have an 8 ohm circuit or a 4 ohm or a 16 ohm circuit? Thank you again.

5StringBlues · #17 04-01-2011, 11:33 PM

2 8ohm cabs = 4 ohm load. 2 4 ohm cabs= 2 ohm load.

Chris K · #18 04-01-2011, 11:42 PM

Quote:

Originally Posted by alexclaber

Barefaced Bass - Mythbusters #1 - amplifiers

Definitely worth the read, thanks Alex. My favourite quote from that site:

Quote:

"Read between the lines of all anecdotal (forum!) evidence as little of this is collected with a scientific mindset."

joeturbodiesel@ · #19 04-01-2011, 11:51 PM

Thank you so much guys. I really do appreciate y'all taking the time to help me with this. I can only hope that some day this will all pay off as some one being able to say, " man the bass player SOUNDS real good" and will be because a few good guys took the time to help another Tbr to become a little bit better. I know my guitar player appreciates it for sure! Thanks again. When I am able to pick up the 410 cab I will let y'all know how it sounds. Well, at least as best as I can describe it anyway. Joseph