A question on wattage NOT impedance

[KickingBass]

Ive found plenty of info on impedance online but for some reason I can't find an answer to my question. If there already is an answer please send me a link I don't want to waste anyone's time. My simple question is: to power two 8ohm cabinets rated at 500w rms would I need a 1000w head? Or would a 500w head work? I'm just not sure if the two wattages are added or not. Thank you in advance for any answers, I created an account to ask this haha

 

[CL400Peavey]

You can power any cab with any amp.

If you use your ears, and what is between them.

 

[lfmn16]

Plenty already written on this subject. You may want to start here:
http://www.talkbass.com/threads/amp...overunderpowercabs-diy-techtalk-links.166225/

 

[GeoffB]

The 500w rating is the maximum power you can put into the speaker. Beyond that, you could burn up the voice coil. To answer your question, if you ran 2 500w cabinets, you could put 1000w into the pair.

Running the two 8 ohms cabs in parallel would present a 4 ohm load to the amp so you'd want an amp that's rated 1000w into a 4 ohm load.

In practice, any amp in the 300-800w range would probably run fine. If the amp is too powerful, you burn up speakers. If the amp is under powered, you might run it so hard that is distorts and that can also cause speaker damage.

 

[HolmeBass]

GeoffB is right in so far as you can run less power than the speakers are rated for without issue, for the most part, but use your ears. If you boost the bass freqs a lot you could still subject your speakers to over-excursion, resulting in farting.

But the idea that "underpowering" your speakers can hurt them is widely recognized as a canard, especially on TalkBass. Check the stickies in the Amps sub-forum (this sub-forum).

The main point is the wattage rating on speaker cabinets is a thermal limit of the *maximum* wattage you should safely use, and there is no inherent issue with sending them less power than the max.

The reality is that the thermal limit is rarely exceeded, and some people will use as much as twice the rated power without issue. They mind their volume and listen to the speakers for audible signs of distress.

 

[BassmanPaul]

A Canard you say!!

A Canard!!!???

May I remind you that this is Talk Bass and no "big" words are allowed!

Besides it should be Canuk!!

 

[KickingBass]

Thank you all very much, this was helpful

 

[samson3382]

Don't ever go below minimum impedance.
Other than that, just don't make fart/bad noises. -works for life in general too.

 

[Downunderwonder]

Insofar as 500W + 500W = 1000w that is well and good.

The problem comes when the 1000w amp has headroom well above that, but the 500W cabs ran out of clean power handling about 250w each.

 

[monkeyfinger]

Just remember that the wattage ratings on most commercial cabs are useless for bass. The 500W rating is usually the thermal rating, not the mechanical rating. The mech rating is usually much, much lower. So your 500w RMS cabs can probably handle 100-150W continuous at 100Hz and maybe 300-400 watts for very brief peaks. This is not as bad as it seems as most of the basses signal is at 10-15% of the amps output. Personally I would throw a 1000-1500 watt power amp at it and just be judicious with the volume control.

 

[KickingBass]

I will probably go with a 1000 watt amp, thank you for the advice, I'm surprised how fast I got responses, the bass community is legit ha

 

[pedrodelawasp]

I hope you don't mind me jumping in here!

Another scenario:

If I have a 500w in to 4ohm head, and want to add two 8ohm cabs to the set up, what would be the minimum power handling level for the cabs I should be looking at? For example, would a 115 rated for 150w @ 8ohms and a 410 rated for 300w @ 8ohms handle the 500w? Am I being a dumbass thinking it looks like they're pairing up and coming 50w short?

Thanks in advance.

 

[monkeyfinger]

This is like asking 'if I want to drive to a store, how big a gas tank do I need?'. If you hook up two cabs, each with an 8 ohm load, into a power amp with a 4ohm min load, each cab will see about 1/2 the output. So in your scenario, each cab would see about 250 watts at max output. (However, the average output is usually about 1/8 power.)

 

[Humbled]

Amp Watts are a rather nebulous number.

I routinely power a "1200 Watt" GK 412 Neo with the paltry "200 Watts" of a Sunn Model T, and rarely turn the amp channel volume over 4, master on 10, although the output is actually higher with the master on 7. Go figure.

Works for me.

 

[NoGraveConcern]

I hope you don't mind me jumping in here!

Another scenario:

If I have a 500w in to 4ohm head, and want to add two 8ohm cabs to the set up, what would be the minimum power handling level for the cabs I should be looking at? For example, would a 115 rated for 150w @ 8ohms and a 410 rated for 300w @ 8ohms handle the 500w? Am I being a dumbass thinking it looks like they're pairing up and coming 50w short?

Thanks in advance.

Naive maybe. I wouldn't call you a dumb ass.

They each get half[ish] of the total power. This is determined by resistance. Since they are both 8 ohm they both get (for our purposes, though technically the impedance curves won't be exactly the same) the same amount of power, which is equal to half of whatever the amp is outputting at that instant.

So I wouldn't want 2 cabs with that much of a difference in thermal power handling or cone area. The risk is that you will blow that 15 because you won't hear it distressing with the much more capable and sensitive 4x10.

If you have to mix drivers, and you shouldn't, a 15 is a better match to a 2x10, all things being equal which they never are.

 

[HolmeBass]

I hope you don't mind me jumping in here!

Another scenario:

If I have a 500w in to 4ohm head, and want to add two 8ohm cabs to the set up, what would be the minimum power handling level for the cabs I should be looking at? For example, would a 115 rated for 150w @ 8ohms and a 410 rated for 300w @ 8ohms handle the 500w? Am I being a dumbass thinking it looks like they're pairing up and coming 50w short?

Thanks in advance.

Ah, the classic peril of the 115 plus 410 combination!

Each cabinet would get 1/2 of the amp's output power in this scenario. The 410 would be pretty much in it's sweet spot, getting 250 of its rated 300 watts, but the 115 will be close to taking double it's rated power!

So you will be stressing the 115 if you run very loud at all, and when doing so the 410 will barely be breaking a sweat. If the 410 is more efficient (has a better "sensitivity" rating), as is very commonly the case with this pairing, it could be so much louder that you won't even hear the 115 crying for mercy! Counter to conventional wisdom, which is actually somewhat lacking for this particular case, put the 410 on the bottom and the 115 on top so you know what the weak link is going through when using this combination. It can work great. It can also lead to blown 115s. In some cases, depending on the specific 410 and 115 you are using, you might find the rig is actually *louder when run with just the 410*!!

 

[pedrodelawasp]

Naive maybe. I wouldn't call you a dumb ass.

They each get half[ish] of the total power. This is determined by resistance. Since they are both 8 ohm they both get (for our purposes, though technically the impedance curves won't be exactly the same) the same amount of power, which is equal to half of whatever the amp is outputting at that instant.

So I wouldn't want 2 cabs with that much of a difference in thermal power handling or cone area. The risk is that you will blow that 15 because you won't hear it distressing with the much more capable and sensitive 4x10.

If you have to mix drivers, and you shouldn't, a 15 is a better match to a 2x10, all things being equal which they never are.

Ah, the classic peril of the 115 plus 410 combination!

Each cabinet would get 1/2 of the amp's output power in this scenario. The 410 would be pretty much in it's sweet spot, getting 250 of its rated 300 watts, but the 115 will be close to taking double it's rated power!

So you will be stressing the 115 if you run very loud at all, and when doing so the 410 will barely be breaking a sweat. If the 410 is more efficient (has a better "sensitivity" rating), as is very commonly the case with this pairing, it could be so much louder that you won't even hear the 115 crying for mercy! Counter to conventional wisdom, which is actually somewhat lacking for this particular case, put the 410 on the bottom and the 115 on top so you know what the weak link is going through when using this combination. It can work great. It can also lead to blown 115s. In some cases, depending on the specific 410 and 115 you are using, you might find the rig is actually *louder when run with just the 410*!!

Thanks for the swift replies!

I had an idea this would be the case - it's a little surprising that such a set up is offered on so many websites as a bundled package.

I'm in the process of selling my Micro VR and 210AV. I was going to get a second 210, but it really just won't keep up with my band. The other issue is that a lot of our gigs also involve having to bring our heads along and use venue cabs or cabs shared between bands - normally something the Micro just doesn't have the guts for. The plan, at the moment, is for a PF500 and two matched cabs that will each handle the 350w it can put in to 8ohms so I have the option of using one or both, depending on the gig. Now I just need to decide on which cabs...

 

[HolmeBass]

Two 115s isn't a bad option at all, but two stout 210s is also good. I went with a 4 ohm 212, which is another way to skin the cat. Then I also have two different 112s for smaller gigs.

 

[Downunderwonder]

Thanks for the swift replies!

I had an idea this would be the case - it's a little surprising that such a set up is offered on so many websites as a bundled package.

I'm in the process of selling my Micro VR and 210AV. I was going to get a second 210, but it really just won't keep up with my band. The other issue is that a lot of our gigs also involve having to bring our heads along and use venue cabs or cabs shared between bands - normally something the Micro just doesn't have the guts for. The plan, at the moment, is for a PF500 and two matched cabs that will each handle the 350w it can put in to 8ohms so I have the option of using one or both, depending on the gig. Now I just need to decide on which cabs...

Perhaps you have no experience of doubling up cabs? It is completely different to pump 200w into two cabs cf one cab at reduced power. I wouldn't write off the rig you have just yet. Jimmy uses a new V4b with two of those cabs.

 

[pedrodelawasp]

Perhaps you have no experience of doubling up cabs? It is completely different to pump 200w into two cabs cf one cab at reduced power. I wouldn't write off the rig you have just yet. Jimmy uses a new V4b with two of those cabs.

I definitely want to change the head - the Micro really doesn't want to have to try and power an 810 at any sort of volume! If I'm going to get a more powerful head, then I think I'm as well going for cabs that will be able to take it when I crank the gain!

Edit: Real world example from experience - my band opened for KEN Mode and Unkind last year. The promoters instructed us to bring our heads to use with the hired cabs for the touring bands. At soundcheck, when plugging the Micro in to the 4ohm Ampeg 810, with gain and volume both below 2, it went in to protection mode almost immediately. KEN Mode's bassist, luckily, is a very cool guy and let me use his amp.

We're actually opening for KEN Mode again in October. This time they're touring with HARK from Wales. Looking forward to that one!