Impedance and power ratings when using two cabs.

[SoulApprentice]

Hi all, and sorry if think that you have heard this one before...
I have two Ampeg cabs, an SVT 210AV and a PF-115HE.
They are both 8 ohm, so if I chain the two the resulting impedance will be 4 ohm.
I'm planning to use these cabs with an Ampeg PF-500, which at 4 ohm is rated 500 watt.
Now the question.
Since the power ratings of the cabs are 200 watt and 450 watt respectively, how will they "manage" the 500 watt provided by the head?
Since they have the same impedance, will they share equally the 500 watts?
If so, pushing the head at full volume will blow the 210AV?
Thanks,
Andrea

 

[pepj]

Equal, nominally.

If you push the signal really hard then you stand a chance of breaking the 210.
That is if you can tell the difference between where the stress or distortion might be coming from.
The amp or the cab.

 

[SoulApprentice]

That is if you can tell the difference between where the stress or distortion might be coming from.
The amp or the cab.

I'll try and not reach that point, then... gain and volume at 80% will probably suffice, and I'm pretty sure the overall volume would still be noticeably higher that using the PF-115HE alone...
Thanks!

 

[MrKpawz]

500w / 2 cabs = 250w per cab.
250w for 2 x 10" - each speaker will get more power than its rated for, take care about volume/EQ
250w for 1 x 15" - speaker should be okay

 

[Gearhead17]

I'll try and not reach that point, then... gain and volume at 80% will probably suffice, and I'm pretty sure the overall volume would still be noticeably higher that using the PF-115HE alone...
Thanks!

Knob position does not mean anything in regards to the power output. You will need to listen to your cabs for signs of distress.

 

[SoulApprentice]

Knob position does not mean anything in regards to the power output. You will need to listen to your cabs for signs of distress.

I agree, and will obviously be careful.
Having said that, maybe I'm overthinking, but if the head at full will provide 250 watt, and the SVT 210AV can only handle 200 watt, I have to run the amp at less than 80% of its max power, and gain and volume at 80% (plus an EQ reasonably flat) can't be anywhere near it...

 

[two fingers]

I agree, and will obviously be careful.
Having said that, maybe I'm overthinking, but if the head at full will provide 250 watt, and the SVT 210AV can only handle 200 watt, I have to run the amp at less than 80% of its max power, and gain and volume at 80% (plus an EQ reasonably flat) can't be anywhere near it...

Do NOT rely on knob positions. Simply use your ears. Dozens of factors can determine how much power is actually being produced as various knobs positions, not the least if which is pot taper. But your EQ matters as well.

Honestly? The 115 in your case blows away the 210 in both power handling and frequency response. If I were you, amd needed more volume, I would sell the 210 amd put the funds toward another identical 115.

But if you decide to proceed, keep your ears tuned to that 210 cab. It's not designed to handle nearly as much of anything (power, low frequencies, etc.) as that 115 is. Be careful. Those cabs are not equal. Not even close.

 

[SoulApprentice]

If I were you, amd needed more volume, I would sell the 210 amd put the funds toward another identical 115.

I never considered adding another PF-115HE, the PF-500's at 8 ohm is 300 watt, and it has always been more than enough... now (and quite exceptionally) I need to add a bit of volume for a gig tomorrow night, and it's too late to get another 15'' (which I'll probably never need again...).

Those cabs are not equal. Not even close.

I totally agree...
I compared my PF-350 with 2 SVT 210AV (350 watt at 4 ohm) and the PF-500 with the PF-115HE (300 watt at 8 ohm): theoretically the former combination should have had more volume, but my ears (and a db meter...) say otherwise... quite obviously the cab made a huge difference.

 

[pepj]

I'm pretty sure the amp will sound not great if you really wind it up...ie, around 3 oclick or even before, on the dial.

This is where it can be difficult to hear what is stressing. If you run pedals, even more so.

So, because plenty of us have broken speakers we know the deal and you become very wary of it happening again.

Warning signs:
Horrible sound at volume. not generally good at all.
Run at very high volume for a long period can cause a type of speaker fatigue and it just dies from an overload.
There are tech terms and reasoning but dont worry about that for now.

All I do, it turn amp up to about 1 o clock on the vol
and test if it sounds clean.
That then becomes my very top level.
And realistically at a gig, that is ear ache loud.
Ie, if you get to that on a 500w amp, everyone should turn down, esp gtrs.

The other variables are gain and input settings and how hot you are running the signal in.

 

[agedhorse]

IME, most players can not hear a speaker being stressed to damage. If they could, we wouldn’t need replacement speakers and recone shops. I had a good friend who owned a large recone shop, they reconed ~100 speakers per week for many years.

 

[dbsfgyd1]

I'll try and not reach that point, then... gain and volume at 80% will probably suffice, and I'm pretty sure the overall volume would still be noticeably higher that using the PF-115HE alone...
Thanks!

Being extremely careful may keep you from a very expensive repair, but I think the point has been made that you might not know when damage occurs.

Actually, as to which cab produces the most dBs that is going to depend on the efficiency of the cabs, as they will be getting the same amount of power.

 

[Lenny JG]

That means full power into your cabs would be around 500w or 250w each. Don't crank it all the way and you'll be fine.

Think of your master dial as fractions of a whole. Each 1/5 is 100w. Don't exceed 4/5, and even then you might stress something if you amplify your signal elsewhere.

There's other variables but this is like general rule of thumb most of the time.

 

[chris_b]

Hi all, and sorry if think that you have heard this one before...
I have two Ampeg cabs, an SVT 210AV and a PF-115HE.
They are both 8 ohm, so if I chain the two the resulting impedance will be 4 ohm.
I'm planning to use these cabs with an Ampeg PF-500, which at 4 ohm is rated 500 watt.
Now the question.
Since the power ratings of the cabs are 200 watt and 450 watt respectively, how will they "manage" the 500 watt provided by the head?
Since they have the same impedance, will they share equally the 500 watts?
If so, pushing the head at full volume will blow the 210AV?
Thanks,
Andrea

All you have to do is mind the 210. Your amp will put 250 watts into each cab. But if you run your amp flat out it will sound bad. if you run your amp so it doesn't sound bad you'll be putting less into both cabs.

I had an Ampeg SVT3-PRO, which I used through an Ampeg 210 and 115. The advice in the user manual was to run the master as loud as you could, in my case that was at 3 o'clock, and run the gain to where it needed to be. My gain, even for loud bands, didn't go past 12 o'clock. So that's a lot less than 500 watts. I'd guess 300 watts at the most. That's 150 watts into each cab.

If the cabs are suffering they will let you know, by sounding bad. If they sound bad turn down. If that's not loud enough get a more powerful 210.

 

[Deleted member 389437]

Each cab would be getting half of the output if the load is 4ohm and the minimum of the head is 4ohm. You would be sending each cab 250w and you risk blowing your speakers. If your careful and dont play too loud and listen to hear any fizz, distortion, or speakerfarts you should be ok

 

[bherman]

IME, most players can not hear a speaker being stressed to damage. If they could, we wouldn’t need replacement speakers and recone shops. I had a good friend who owned a large recone shop, they reconed ~100 speakers per week for many years.

@SoulApprentice this is the voice of wisdom and experience, just be cautious and you'll likely be ok. Pay particular attention to your eq - as in, don't crank the bass control way up or put heavy overdrive into the signal chain. I have often run higher-powered amps into lower-powered cabs, just need to be aware of what is happening. Only blew a speaker once and it was as @agedhorse describes - it didnt sound like it was being stressed, but in hindsight I can see that I was pushing it too hard (112 rear-ported cab in an outdoor setting).

 

[Rich Fiscus]

IME, most players can not hear a speaker being stressed to damage. If they could, we wouldn’t need replacement speakers and recone shops. I had a good friend who owned a large recone shop, they reconed ~100 speakers per week for many years.

This is particularly true with the 210AV, which starts sounding like it’s being pushed hard at a very low volume. I can’t imagine you would hear anything out of the ordinary until it stopped making noise entirely.

 

[Engle]

I’m not sure how similar the PF-115HE is to the SVT-115E, but the 210AV doesn’t sound great paired with the SVT-115E.

It seems that Ampeg doesn’t publish the sensitivity spec for the 210AV, but based on personal experience, its not as loud as my ported Ampeg Classic cabs.

I found the best thing to pair a 210AV with is another one.

 

[dbsfgyd1]

IME, most players can not hear a speaker being stressed to damage. If they could, we wouldn’t need replacement speakers and recone shops. I had a good friend who owned a large recone shop, they reconed ~100 speakers per week for many years.

Probably from back in the days when I was your and dumb..LOL..

 

[NKBassman]

I'll try and not reach that point, then... gain and volume at 80% will probably suffice, and I'm pretty sure the overall volume would still be noticeably higher that using the PF-115HE alone...
Thanks!

Put the 210 vertically on top of the 115 to get it closer to your ears. You'll be able to hear yourself better at lower volume just by the way of having some speakers closer to your ears rather than blasting you in the shins.
I used two 210AVs stacked vertically for years and it allowed me to gig with very low volume on stage while still being able to hear myself perfectly.

 

[Turnaround]

Do NOT rely on knob positions.

Good advice. The most that knob position can tell you is that as the numbers increase, so does the loudness. If you have your volume set at 10, but your bass is set at zero, how many watts is your 500 watt amp putting out? Likewise, if your master is set at 10, but your gain is zero - what's the output? If your tone controls are all set to -10? Or +10? The only way to tell what your amp is really putting out is to measure it, and then it will be frequency dependent anyway.