Amp vs cab wattage

[Powertripper]

Hey guys,

I'm a bit confused and wondering if you can help. I primarily use a Burman 100 amp through an Ashdown MAG410 (450 watt) cab, sometimes with an extension ABM115 (also 450 watt) cab. My spare amp is an [solid state] Orange OB1500 which I use as a backup. I lent the Orange and 115 (essentially my 'secondary' rig) recently to a friend playing in a pub, and both blew. This cost me some £150 in repairs. Frustratingly, the bassist using my rig (totally unapologetic after break) was using the amp at full at the time, which I thought given the venue wouldn't be the case, but hey. So presumably, the 500w overpowered the 450w cab, which shorted the amp, hence why both blew.

Now, with both repaired, I'm very apprehensive about using the Orange 500 through any cab that has an RMS rating of lower than that, even though I've done so many times successfully because it wasn't running at full. So, my question here would be - is it safe to run a 500w amp to a 450w cab as long as it's not running at maximum? I.e. if the volume is up halfway on a 500w solid state amp, am I only using 250w, therefore I am safe?

I've done a bit of reading into over and underpowering cabs now (including on here), but know of many people (including myself until now) who run higher wattage amps into lower wattage cabs. On the other hand, people talk about 'underpowering', but if I've never understood this? Is my Burman 100w (valve) really at risk of damaging a 450w cab?

Apologies for perhaps not grasping what has already been said; it took me years to even understand ohmage and impedance.

Any advice, wisdom or knowledge would be gratefully appreciated as this has been a costly mistake and I'm naturally concerned about it happening again.

Thanks guys,
H.

Edited February 13, 2017 by Powertripper

[xgsjx]

Yes. Forget watts. Check ohms if using more than 1 cab & use your ears.
Your watts theory is incorrect. If your cab is 8 ohm & the amp's min load is 4 ohm, then your amp will put about 350 watts out at most. You're more likely to be averaging about 100 from the amp.

Edited February 13, 2017 by xgsjx

[Powertripper]

[quote name='xgsjx' timestamp='1486945424' post='3235830']
Yes. Forget watts. Check ohms if using more than 1 cab & use your ears.
[/quote]

I've since totally changed and elaborated on my problem but thank you for responding to the original post, much appreciated.

[xgsjx]

[quote name='Powertripper' timestamp='1486945574' post='3235833']
I've since totally changed and elaborated on my problem but thank you for responding to the original post, much appreciated.
[/quote]
Oddly enough, I was editing mine at the same time.
The answer is still the same as my original edit.
Use your cabs with the amp. Use your ears. Bill the fandango for the repairs & don't let anyone use your rig again unless you're there & have some trust in them.

[Powertripper]

[quote name='xgsjx' timestamp='1486945907' post='3235836']
Oddly enough, I was editing mine at the same time.
The answer is still the same as my original edit.
Use your cabs with the amp. Use your ears. Bill the fandango for the repairs & don't let anyone use your rig again unless you're there & have some trust in them.
[/quote]

We agreed to go halves. Difficult politics as borrower (promoter) is a friend. I'm hoping to make the difference back in free gig entries haha. But yes, I won't be lending gear again - I do music full time (regrettably a gear theory amateur) and can't afford to burn my work tools like that. Thanks man

[xgsjx]

You'll find plenty of information in these pages. Another good place to read is Barefaced bass cabs' website. Alex has put a lot of good info on there.
Also go to Bill Fitzmaurice (BFM) website. The forums there are a vault of info too.

[Phil Starr]

bad luck, The truth is your amp shouldn't have blown your speaker and even if your speaker did short, which is extremely unlikely, the amp should have been able to protect itself.Without being there we will probably never know what actually happened.

Underpowering is a bit of a myth. Without getting too technical an amp can produce a little more power than it's ratings under very limited conditions but that isn't going to blow your speaker. Your Burman is perfectly safe to use.

It's not simple to be absolute about matching amp and speaker power. Amps are measured in terms of their electrical output with a test signal and speakers by how much power they can continuously take without over heating but music isn't a test signal, it has loud and quiet bits. The biggest variable is the person using it. If you turn your amp down a notch you are probably halving the power. Your 500W amp can be a 1W amp if you turn it right down. You've been using it without problem for years and with it mended nothing has changed. You can go on using it in exactly the same way without worries.

There is one other possibility, It could simply be coincidence, your amp may have been about to blow anyway and the friend was just unlucky enough to be the guy playing when it happened. Broken amps can pump a lot of power into a speaker under certain conditions. It might well be bad luck and him paying half the repair bill a fair income. I'd take that for peace of mind rather than walk around feeling hard done by, especially since you will never knoe the truth.

[Powertripper]

[quote name='Phil Starr' timestamp='1486977964' post='3235910']
bad luck, The truth is your amp shouldn't have blown your speaker and even if your speaker did short, which is extremely unlikely, the amp should have been able to protect itself.Without being there we will probably never know what actually happened.

Underpowering is a bit of a myth. Without getting too technical an amp can produce a little more power than it's ratings under very limited conditions but that isn't going to blow your speaker. Your Burman is perfectly safe to use.

It's not simple to be absolute about matching amp and speaker power. Amps are measured in terms of their electrical output with a test signal and speakers by how much power they can continuously take without over heating but music isn't a test signal, it has loud and quiet bits. The biggest variable is the person using it. If you turn your amp down a notch you are probably halving the power. Your 500W amp can be a 1W amp if you turn it right down. You've been using it without problem for years and with it mended nothing has changed. You can go on using it in exactly the same way without worries.

There is one other possibility, It could simply be coincidence, your amp may have been about to blow anyway and the friend was just unlucky enough to be the guy playing when it happened. Broken amps can pump a lot of power into a speaker under certain conditions. It might well be bad luck and him paying half the repair bill a fair income. I'd take that for peace of mind rather than walk around feeling hard done by, especially since you will never knoe the truth.
[/quote]

Yeah that's how I've been looking at it really, just thinking about the future. I've been thinking 'oh I must get a 500w cab now' but that's a bit of a drag financially and just a hassle. I won't bother now, will just be cautious with the 500w in the future. Thanks for your thoughts.

[Chienmortbb]

Phil is right and the jump from 450-500 watts is unlikely to has caused the problem. Just take it as a random failure and as it has been fixed it is unlikely to blow in the same way again.

[Powertripper]

Report I got back: "[font=arial, sans-serif][size=3]The amp's output transistors were shorted and the power amp PCB needed to be replaced. What is almost certainly the case is that your speaker failed short circuit and, in turn, shorted the amp's output section.[/size][/font]

[Bill Fitzmaurice]

Speaker short circuit failures are rare. When a voice coil gets toasted it usually results in an open circuit. The usual reason for a short circuit is failure of the speaker cable. I'd check the cable and the interior wiring of the speaker.

[Chienmortbb]

Just one question, Jacks or Speakon? If your amp has jack outputs that could be the culprit. I remember one amp manufacturer putting a very high percentage of power amp failures down to shorted jack cables.

[Phil Starr]

It probably doesn't matter because you'll never know, and there is no reason not to check your leads and speaker wiring. Just a thought though, what repairs were made to the cab, which I assume is now working?

'Almost certainly failed short circuit' implies that either he didn't actually check the speakers or wasn't the person who repaired them.

[Powertripper]

[quote name='Chienmortbb' timestamp='1487324267' post='3238900']
Just one question, Jacks or Speakon? If your amp has jack outputs that could be the culprit. I remember one amp manufacturer putting a very high percentage of power amp failures down to shorted jack cables.
[/quote]

[quote name='Bill Fitzmaurice' timestamp='1487300295' post='3238784']
Speaker short circuit failures are rare. When a voice coil gets toasted it usually results in an open circuit. The usual reason for a short circuit is failure of the speaker cable. I'd check the cable and the interior wiring of the speaker.
[/quote]

[quote name='Phil Starr' timestamp='1487332334' post='3239015']
It probably doesn't matter because you'll never know, and there is no reason not to check your leads and speaker wiring. Just a thought though, what repairs were made to the cab, which I assume is now working?

'Almost certainly failed short circuit' implies that either he didn't actually check the speakers or wasn't the person who repaired them.
[/quote]

The cable used was a speakon>jack, which seems to be all fine. So, Orange repaired the cab and had no involvement with the speaker, and Ashdown sent me a new speaker, which I just clipped in.