Need help understanding power ratings...

[Lord Sausage]

[quote name='stingrayPete1977' timestamp='1338804094' post='1679327']
OK here is the laymans terms, I am one and this is how I see it but the others will be back to baffle you with electronic wizardry and have a debate about it Im sure!

I have a Morris Minor (realy ) it was designed for about 28bhp yet you can have a bigger engine like mine with about 39bhp or much more without upgrading the brakes and tyres etc, If you think of the car as the speaker cabs and the engine as the amp then I could drive it all day long without revving it up much and keep it below 20bhp which would be fine, I could drive it hard all the time until something broke but in reality I can drive it within a safe manner and exploit the extra power within reason once I have the feel of when its pushing it too hard (farting speaker constantly etc).
[/quote]
Thanks pal!

[Bill Fitzmaurice]

[quote name='Lord Sausage' timestamp='1338802455' post='1679298']
Does it matter if the amp is more powerful than the speakers.
[/quote]Only if it has no volume control.

[chris_b]

[quote name='Lord Sausage' timestamp='1338802455' post='1679298']
....Does it matter if the amp is more powerful than the speakers....
[/quote]

Do you [i]have[/i] to take the risk?

Always have more speaker watts than amp watts and never run your amp flat out, then you won't need to worry about blowing cabs.

[stingrayPete1977]

[quote name='chris_b' timestamp='1338813471' post='1679519']
Do you [i]have[/i] to take the risk?

Always have more speaker watts than amp watts and never run your amp flat out, then you won't need to worry about blowing cabs.
[/quote]

Thats not really that helpful is it?

I have a few amps and a few cabs but to always run with them having your ideal world would be impossible. Im using a shuttle 3 with a little 1x10 in the house but I could blow the speaker if I wanted but at that volume its never going to happen, I run my shuttle 6.0 into the 1x12 300w cab all the time yet the head is rated at 375watts into that cab that Genz Benz supply as a combo for over a thousand pound. My Neox 2x12 is only rated at 600watts which it runs at with the 6.0 head as its a 4 ohm cab, many people have that same cab for use with streamliner 9.0's etc with no trouble at all.

Who here has a rig that in each combination[u] always [/u]has speaker wattage higher than the amps rated wattage?

[JTUK]

[quote name='stingrayPete1977' timestamp='1338815159' post='1679558']
Thats not really that helpful is it?

I have a few amps and a few cabs but to always run with them having your ideal world would be impossible. Im using a shuttle 3 with a little 1x10 in the house but I could blow the speaker if I wanted but at that volume its never going to happen, I run my shuttle 6.0 into the 1x12 300w cab all the time yet the head is rated at 375watts into that cab that Genz Benz supply as a combo for over a thousand pound. My Neox 2x12 is only rated at 600watts which it runs at with the 6.0 head as its a 4 ohm cab, many people have that same cab for use with streamliner 9.0's etc with no trouble at all.

Who here has a rig that in each combination[u] always [/u]has speaker wattage higher than the amps rated wattage?
[/quote]

me... 2x112 (600w) from 400w or 550w amps.. and 2x210 at 700w.

I am not interested in running these cabs as singles and I brought them as they are easier to carry that a 212 or 410.
That is the config I play with... no exceptions outside the house.

I have been in too many situations where you can hear the speaker struggling..admittedly, more yesteryear than of late, but it stays with you.
I have blown a 12" in a 2x112 stack.. but put that down to faulty chassis...but hey, that happens as well.
The other cab coped ok...being one speaker down, so what I got out of that is that I trust and understand the single speaker volume capacity of that rig..not that I want to demo it again..

So, rule number one for me..always have more in hand that the chassis maker of cab maker specifies and way over what the amp will put out at full..which nobody really runs too anyway...hopefully.

[Lord Sausage]

Also what about ohms?
If you have say an amp that's 500w at 4ohms and 350w at 8 ohms and you run it thru a 4x12 that handles 500w at 8 ohms, i take it you'll get 350. If you add say a 1x15 cab that is 8 ohm would you still get 350 or do the ohms increase or decrease. Would i have to buy 4ohm cabs.

Do you worst, I can handle condescension due the my arrogance and giant intellect in other areas!!! ha ha!

[Bill Fitzmaurice]

[quote name='Lord Sausage' timestamp='1338828441' post='1679756']
Also what about ohms?
If you have say an amp that's 500w at 4ohms and 350w at 8 ohms and you run it thru a 4x12 that handles 500w at 8 ohms, i take it you'll get 350. If you add say a 1x15 cab that is 8 ohm would you still get 350 or do the ohms increase or decrease. Would i have to buy 4ohm cabs.

[/quote]The watts just don't matter, you have to increase them by a factor of ten to sound twice as loud. Always buy 8 ohm cabs so that if you need to add a second you can. And the last thing you'd add to a 412 is a 115, a 115 can't even keep up with a 212.

[Lord Sausage]

[quote name='Bill Fitzmaurice' timestamp='1338828840' post='1679761']
The watts just don't matter, you have to increase them by a factor of ten to sound twice as loud. Always buy 8 ohm cabs so that if you need to add a second you can. And the last thing you'd add to a 412 is a 115, a 115 can't even keep up with a 212.
[/quote]
So what do 1x15 give you then is it more low frequencies or is that bollocks! Just to be clear then, a 500w amp that only gives out 350 due to ohms would be plenty loud.

[Bill Fitzmaurice]

[quote name='Lord Sausage' timestamp='1338829278' post='1679763']
So what do 1x15 give you then is it more low frequencies or is that bollocks!
[/quote]Bollocks. Cone size in and of itself only affects one function, the angle of dispersion, The larger the driver the narrower the angle. All other aspects are determined by the driver specs. Same specs, same results, no matter what the cone size.

[Mr. Foxen]

Important thing to remember about power handling figures is that it is thermal power handling, and the likely cause of damage to speakers from overpowering playing bass guitar is not thermal but mechanical, so the mechanical damage limit is the important one, known as maximum excursion, and farting is the warning that you are approaching it. The actual amount of power it takes to reach the limit varies with frequency by a pretty massive amount, so it can't be expressed in a single number.

[Musky]

[quote name='Lord Sausage' timestamp='1338828441' post='1679756']
Also what about ohms?
If you have say an amp that's 500w at 4ohms and 350w at 8 ohms and you run it thru a 4x12 that handles 500w at 8 ohms, i take it you'll get 350. If you add say a 1x15 cab that is 8 ohm would you still get 350 or do the ohms increase or decrease. Would i have to buy 4ohm cabs.

Do you worst, I can handle condescension due the my arrogance and giant intellect in other areas!!! ha ha!
[/quote]
If you add a second 8 ohm cab impedance will halve, giving you a total load of 4 ohms. That means the amp will now be producing 500w. The total thermal power handling of your speakers will be 500w plus the wattage of your extra cab, with the power being shared equally between them. Transistor amps will have a minimum impedance they can work with - most often that's 4 ohms but some amps will drive down to 2 ohms. Unless your amp has a minimum impedance of 2 ohms using two 4 ohm cabs will blow the amp.

Valve amps work differently in that they always have the maximum stated wattage available, but must be switched to the correct impedance (they'll either have a switch or separate speaker outputs marked with the appropriate impedance). Using a valve amp at too high an impedance (or without any speakers connected) will leave you with an expensive repair bill - too low and you'll shorten the life of the valves.

[icastle]

[quote name='Musky' timestamp='1338851716' post='1680166']
If you add a second 8 ohm cab impedance will halve, giving you a total load of 4 ohms. [/quote]

That's absolutely true in this case, but the 'halving rule' only works if both cabs have the same impedance.

If you're mixing impedances then [url="http://ampservice.de/impcalc.php?lang=e"]this[/url] is quite a handy little tool.

[Mr. Foxen]

[quote name='Musky' timestamp='1338851716' post='1680166']
The total thermal power handling of your speakers will be 500w plus the wattage of your extra cab, with the power being shared equally between them. [/quote]
In that scenario its double the power handling of the weakest cab, since power is shared equally, it doesn't go to the higher one once the weaker one is 'full'

[quote name='Musky' timestamp='1338851716' post='1680166']
Valve amps work differently in that they always have the maximum stated wattage available, but must be switched to the correct impedance (they'll either have a switch or separate speaker outputs marked with the appropriate impedance). Using a valve amp at too high an impedance (or without any speakers connected) will leave you with an expensive repair bill - too low and you'll shorten the life of the valves.
[/quote]

Too low is apparently OK, the output jacks are shorting to stop death in case of no load, its plugged in to amp with nothing on the lead that is the killer, since that opens the short. Basically, a full circuit on the secondary means the transformer still works as a transformer due to current being able to pass through the completed coil giving it an inductance value, instead of an electromagnet, where the field collapses and puts a voltage spike back through the valves. This is bit on the limits of my understanding, but that is how I currently picture it.

[Musky]

[quote name='Mr. Foxen' timestamp='1338853198' post='1680183']
In that scenario its double the power handling of the weakest cab, since power is shared equally, it doesn't go to the higher one once the weaker one is 'full'[/quote]
Good point.

[quote]
Too low is apparently OK, the output jacks are shorting to stop death in case of no load, its plugged in to amp with nothing on the lead that is the killer, since that opens the short. Basically, a full circuit on the secondary means the transformer still works as a transformer due to current being able to pass through the completed coil giving it an inductance value, instead of an electromagnet, where the field collapses and puts a voltage spike back through the valves. This is bit on the limits of my understanding, but that is how I currently picture it.
[/quote]
I understood that too low an impedance would run the valves hotter, shortening their life. Though not disastrous, blowing a valve is never a good thing.

[Mr. Foxen]

[quote name='Musky' timestamp='1338878986' post='1680296']
I understood that too low an impedance would run the valves hotter, shortening their life. Though not disastrous, blowing a valve is never a good thing.
[/quote]

With no reason to do so, probably better not doing it, but I've never heard any decent explanation of why that should be so that wasn't actually a misplaced description of the output of solid state amps, between that and the shorting jacks, have been inclined to think there isn't much trouble from it aside from sounding a bit wrong.

[chris_b]

[quote name='Musky' timestamp='1338878986' post='1680296']
....too low an impedance would run the valves hotter, shortening their life. Though not disastrous....
[/quote]

If you run a valve amp at anything other than its correct impedance you will damage the valves, and the biasing circuitry. You will probably blow fuses so the amp will stop dead in its tracks.

That will be an expensive repair job.

[JTUK]

[quote name='Bill Fitzmaurice' timestamp='1338830436' post='1679776']
Bollocks. Cone size in and of itself only affects one function, the angle of dispersion, The larger the driver the narrower the angle. All other aspects are determined by the driver specs. Same specs, same results, no matter what the cone size.
[/quote]

Which is why people with 15" complain they can't hear the bass ...so have to feel it across the stage..which is NOT what you want, IMO. Of course, you hear the bass, but it can be too droney.
So then, they raise it upto ear level or add another cab...when the 115 only scores from being compact anyway. It is one of the reasons why I have always said it is NOT a one cab solution
but there you go. It might suit some.

So, couple this with a bass emphasis from the cab you are starting too far down the hill to get anywhere. The bass lacks focus from a positional sense and it degrades even further.
You might rescue it to a degree by playing with an aggressive pick style but probably not.

Adding a 210 might sharpen things up a bit... but a 2x210 would do the whole job better, IMO/IME.

Which is why the standard tends to 410.

[Mr. Foxen]

[quote name='chris_b' timestamp='1338893027' post='1680552']
If you run a valve amp at anything other than its correct impedance you will damage the valves, and the biasing circuitry. You will probably blow fuses so the amp will stop dead in its tracks.

That will be an expensive repair job.
[/quote]

Can you explain why? Especially for low impedance loads.

[Mr. Foxen]

[quote name='JTUK' timestamp='1338893562' post='1680570']
Which is why people with 15" complain they can't hear the bass ...so have to feel it across the stage..which is NOT what you want, IMO. Of course, you hear the bass, but it can be too droney.
So then, they raise it upto ear level or add another cab...when the 115 only scores from being compact anyway. It is one of the reasons why I have always said it is NOT a one cab solution
but there you go. It might suit some.

So, couple this with a bass emphasis from the cab you are starting too far down the hill to get anywhere. The bass lacks focus from a positional sense and it degrades even further.
You might rescue it to a degree by playing with an aggressive pick style but probably not.

Adding a 210 might sharpen things up a bit... but a 2x210 would do the whole job better, IMO/IME.

Which is why the standard tends to 410.
[/quote]

4x10 in standard format is more direction than a 1x15 because it has a broader cone area, so it makes the inaudibility issue worse.

[Musky]

[quote name='Mr. Foxen' timestamp='1338895138' post='1680625']
Can you explain why? Especially for low impedance loads.
[/quote]
Oxblood posted an informative post ages ago. http://basschat.co.uk/topic/5427-valve-amp-heat/page__view__findpost__p__57345

He knows his stuff as well - he virtually rebuilt a VA350.

[JTUK]

[quote name='Mr. Foxen' timestamp='1338895239' post='1680632']
4x10 in standard format is more direction than a 1x15 because it has a broader cone area, so it makes the inaudibility issue worse.
[/quote]

2x120 stacked traditionally is the config I use over all else and won out against 115 and 2x10, 2x112 and a 410... and hearing myself on a decent size stage where I will move offline is
just not an issue.

I suggest that people who have problems hearing have a bigger problem with their sound in general and should look elsewhere for the solution.

[Mr. Foxen]

[quote name='Musky' timestamp='1338896056' post='1680664']
Oxblood posted an informative post ages ago. [url="http://basschat.co.uk/topic/5427-valve-amp-heat/page__view__findpost__p__57345"]http://basschat.co.u...dpost__p__57345[/url]

He knows his stuff as well - he virtually rebuilt a VA350.
[/quote]

That says a short causes no harm at all, which is as I said, low impedance is not an issue for damage concerns.

[chris_b]

[quote name='Mr. Foxen' timestamp='1338895138' post='1680625']
....Can you explain why?....
[/quote]

No.

I have experience of someone running the wrong cabs with a valve amp and this is what happened.

[Musky]

[quote name='Mr. Foxen' timestamp='1338897483' post='1680708']
That says a short causes no harm at all, which is as I said, low impedance is not an issue for damage concerns.
[/quote]
You know what - I've taken that post as gospel for years, only to now discover that I'd misread/misunderstood it!

Stll can't use my Trace without hooking up a second cab though.

Edited June 5, 2012 by Musky

[Bill Fitzmaurice]

[quote name='Mr. Foxen' timestamp='1338897483' post='1680708']
That says a short causes no harm at all, which is as I said, low impedance is not an issue for damage concerns.
[/quote]+1. Most tube amps use a closed circuit switching output jack that shorts the output if there's no speaker plugged in. That's to prevent damage from what really does bother tubes, which is no load. They're not happy with a load higher than the tap rating either, but a load lower than the tap rating is to a tube as water is to a duck.