Confused about ohms and watts!

[stingrayPete1977]

To be fair Saxy your amp is quite unusual having the ability to be working as 4 ohms on its own and still 4 ohm when you add an extra 8 ohm cab, clever but not so easy to describe.

[SaxyBassist]

[quote name='Dad3353' timestamp='1423944649' post='2690784']
Try this first; come back here if questions subsist...

[url="http://www.studybass.com/gear/bass-amps/"]Bass amps and cabs, beginner's guide...[/url]

There's no problem with asking questions. Sooner or later it will 'click'. It's not rocket surgery.
[/quote]

I'm not so sure it will, I once started an Open Uni Music Technology course having completed 3 course at level 4, 5 and 6 (Humanities and Literature) and I whizzed the though music part but couldn't grasp the apparently simple maths - it was pure gobbledygook to me - I really struggled.....I even had a maths tutor visit me at home to go through it all...... "Eureka!!" I cried when he finished explaining it all.....then I sat down to complete the first assignment and it had all gone again so I bailed out of the course

[quote name='stingrayPete1977' timestamp='1423944738' post='2690787']
To be fair Saxy your amp is quite unusual having the ability to be working as 4 ohms on its own and still 4 ohm when you add an extra 8 ohm cab, clever but not so easy to describe.
[/quote]

Trust me to get the awkward one

[Dad3353]

[quote name='SaxyBassist' timestamp='1423924901' post='2690423']
I am a complete electronics numpty and just wondered if anyone could clarify something for me! I have a Promethean 3110 combo (300 watts 8ohms) and want to add a extension cab - a TC Electronics RS 210 (400 watts 8ohms)......... I've been told this will work, but if I ever wanted to add another RS210 I'd need a more powerful head.

My question is how comes the 400 watt RS210 is not to powerful for the Promethean 300watt Combo? and also what amp head would I need for 2 RS210s ? thanks in advance (ps please imagine you are explaining to a small child )
[/quote]

I would ask 'What is the perceived problem you're trying to solve..?'.

Cabs are never 'too powerful' for amps (or combos...). The 'watts' referred to are telling us how many it would take to blow it up. Amps (and combos...) watts are telling us how many they can deliver when pushed to their limit. Normally, one can reasonably assume that you're fairly safe if the cab watts are more than the amp watts, preferably by a factor of 1.5 (300w cab, or more, for a 200w amp...).
Adding an extra cab will not, in your case, enable the combo to deliver more power, as it is already optimised with its built-in speakers. An extra cab with more than one speaker (ie: a 2x10 or more...) will, however, push more air around, and so an increase in volume. Not massive, however; it won't lift your skirts.
So... What problem are you trying to solve..? I'm sure there'll be good enough advice if the question was formulated towards that.
Hope this helps.
([i]Have you finished your homework..? ... and turn that racket down..! What..? A pocket money increase..? I don't know what you find to spend it on..![/i])

[3below]

If you want more SPL (volume) then another way forward would be a more efficient extension cab - e.g. Barefaced compact or similar. Not all cabs (speaker + box) are created equal, some deliver greater SPL per input Watt than others. Treat most manufacturer figures with caution.

[stingrayPete1977]

Loads in parallel get divided between the number of loads, the load being in ohms
two 8 ohm cabs equals 4 ohms
two 16 ohm cabs would be 8 ohms
Four 16 ohm cabs would be 4 ohms
a single 4 ohm cab is just that same as 8 or 16 ohms all would be above the 4 ohms minimum required by most non valve amps most of us have.

Loads in series adds the total so
two 8 ohm cabs equals 16 ohms
two 16 ohm cabs would be 32 ohms
four 16 ohm cabs would be 64 ohms

To do that you need a special series lead, why would you you ask? Well you could pair two 4 ohm 2x12 cabs in series to give 8 ohms then do the same again and put both pairs into the head in parallel giving 8x12 speakers and the 4 ohm load the wants to produce its full power!

Your amp has the two 8 ohm loads pre wired in parallel inside tricking the amp into thinking you have already added an extra speaker cab, when you plug into it one gets disconnected (probably by the jack socket pushing a contact open) so if you plug a lead in it will see 8 ohms then let you add another 8 ohm load giving the amp a 4 ohm load as before but with more drivers pushing more air.


To complicate it more you could put two 2x10 8 ohm cabs with a series lead between them and plug into the head from the first one and have the combo driver and both 2x10s running at a total of 4 ohms (does anyone else agree?)

[stingrayPete1977]

[quote name='3below' timestamp='1423946243' post='2690806']
If you want more SPL (volume) then another way forward would be a more efficient extension cab - e.g. Barefaced compact or similar. Not all cabs (speaker + box) are created equal, some deliver greater SPL per input Watt than others. Treat most manufacturer figures with caution.
[/quote]

I think the problem here is (and I've answered my own question above) is that you are quite correct that the extension cab would be great......until the next time you plug the combo in on its own to find the internal speaker no longer...well...speaks?! The nice sounding barefaced would mask all the power destroying the single 8 ohm speaker in the combo?

Edited February 14, 2015 by stingrayPete1977

[SaxyBassist]

[quote name='stingrayPete1977' timestamp='1423943662' post='2690758']
Most combos run 4 ohms min load and an 8 ohm built in speaker (unlike the unusual one the OP has), so you can add another 8 ohm cab underneath to get a 4 ohm load (2 8s divided by 2 cabs equals 4) that will give you the full 180 watts the amp can produce hence you get more power and more driver area, double whammy upgrade! If the head can be unplugged from the combo cab you could run any combination of cabs as long as they combine to a total of at least 4 ohms (4 x 16 ohm 2x10 cabs all wired in parallel, 2 x 8 ohm 4x10 cabs, a single high quality 4 ohm 2x12, etc etc
[/quote]

So what I've got is good then? - Not going to go up in smoke or anything? No the head doesn't come unplugged, (I think the 3115 does)

ps I read the idiots guide to amps and cabs and it went straight over my head, I'm afraid I really am dyscalculic and will never really understand any of it also I found a couple of switches on the back of the Promethean one says ground or lift and one that says 0db or -20db, haven't a clue which ones it should be set on

Edited February 14, 2015 by SaxyBassist

[stingrayPete1977]

Adding the extra cab should give you more air being moved but no more power unlike most combos with an extra cab due to that clever switching inside, adding any cabs is always an unknown area tone wise, adding a matching cab with 8 ohms is the normal advice but even that is not so easy as they wont actually be matching drivers as your combo one will be running at half capacity if that makes sense?

Take your combo to a good bass amp shop like bass direct or bass gear and they will let you try your combo with other cabs and try some other amps and cabs to see what you like, two RS2x10s and a TC head maybe but you can see why many of us run a 1x12 combo or head and cab with a second identical one for bigger gigs, I've actually got a 1x12 and a 2x12 as I bought the 2x12 first.

Edited February 14, 2015 by stingrayPete1977

[stingrayPete1977]

Dont worry about those switches they are for when it's plugged into a pa via the DI built in.

[taunton-hobbit]

I preferred my answer, but then I'm old & frail (shuffles off for Ovaltine laced with bootleg Vodka).

[stingrayPete1977]

[quote name='taunton-hobbit' timestamp='1423943276' post='2690751']
If it says minimum, it means it won't like 2 ohms a lot (burning smell) - I'd talk to Ashdown, but I think, like many, you are trying to get out of a situation at the minimum cost - nothing wrong with that, but 'yer gets wot yer pays for' at the end of the day...............


[/quote]
[quote name='taunton-hobbit' timestamp='1423949611' post='2690868']
I preferred my answer, but then I'm old & frail (shuffles off for Ovaltine laced with bootleg Vodka).




[/quote]
Well it was a good reply but just as flawed as my earlier TC advice as it's not an Ashdown, lol

[RickyV]

[quote name='stingrayPete1977' timestamp='1423943662' post='2690758']
Most combos run 4 ohms min load and an 8 ohm built in speaker (unlike the unusual one the OP has), so you can add another 8 ohm cab underneath to get a 4 ohm load (2 8s divided by 2 cabs equals 4) that will give you the full 180 watts the amp can produce hence you get more power and more driver area, double whammy upgrade! If the head can be unplugged from the combo cab you could run any combination of cabs as long as they combine to a total of at least 4 ohms (4 x 16 ohm 2x10 cabs all wired in parallel, 2 x 8 ohm 4x10 cabs, a single high quality 4 ohm 2x12, etc etc
[/quote]

[RickyV]

[quote name='stingrayPete1977' timestamp='1423943662' post='2690758']
Most combos run 4 ohms min load and an 8 ohm built in speaker (unlike the unusual one the OP has), so you can add another 8 ohm cab underneath to get a 4 ohm load (2 8s divided by 2 cabs equals 4) that will give you the full 180 watts the amp can produce hence you get more power and more driver area, double whammy upgrade! If the head can be unplugged from the combo cab you could run any combination of cabs as long as they combine to a total of at least 4 ohms (4 x 16 ohm 2x10 cabs all wired in parallel, 2 x 8 ohm 4x10 cabs, a single high quality 4 ohm 2x12, etc etc
[/quote]

Ok, thanks for that. I think that makes sense now. The head can be unplugged so that makes it more flexible than I thought. Cheers for your help.

[BassBunny]

SaxyBassist.
I bet after this you want to stick to Sax.
If you want to add an RS210 to your combo then YES YOU CAN. It will be perfectly safe and if you like the sound, it's your right to spend your money how you wish. In fact any 8 Ohm cab will do but I would stick to 10" speakers. Mixing speakers can have varying results.
On the up side it will handle considerably more power than you are going put through it and if you decide the combo won't deliver the power you want for gigging, you can just buy a more powerful amp head and off you go.
I am a bit OCD, and would want to pair the combo with it's matching extension cab, ie the Ibanez 1x10, just so it would look right. That would snooker the upgrade path though.
Hope that answers what you asked as this post seems to have gone into information overload.

[stingrayPete1977]

That is all well and good saying it has "gone into information overload" but the internal speaker will be rated at only 150 watts max with the 2x10 added, "add any 8 ohm cab" is great advice unless it hides the combo driver crapping out with 300 watts going through it that a 400 watt or more ext cab will happily handle? This is not like any other combo where the 300 watt rating of it's driver remains constant is it?

Edited February 14, 2015 by stingrayPete1977

[Dad3353]

[quote name='stingrayPete1977' timestamp='1423952853' post='2690929']
That is all well and good saying it has "gone into information overload" but the internal speaker will be rated at only 150 watts max with the 2x10 added, "add any 8 ohm cab" is great advice unless it hides the combo driver crapping out with 300 watts going through it that a 400 watt or more ext cab will happily handle? This is not like any other combo where the 300 watt rating of it's driver remains constant is it?
[/quote]

With an 8 ohm extension cab, surely the remaining internal speaker will simply receive its current wattage..? What difference would it make having an extension cab, compared to its neighbour..? It won't even notice the difference, I'd say. If the extra cab is more efficient than the second, disconnected, combo speaker, there'll be more volume (albeit not enormously more...), but the amp and 'working' speaker won't be affected.

[Musky]

[quote name='Dad3353' timestamp='1423953333' post='2690935']
With an 8 ohm extension cab, surely the remaining internal speaker will simply receive its current wattage..? What difference would it make having an extension cab, compared to its neighbour..? It won't even notice the difference, I'd say. If the extra cab is more efficient than the second, disconnected, combo speaker, there'll be more volume (albeit not enormously more...), but the amp and 'working' speaker won't be affected.
[/quote]
This echoes my thoughts as well.

The speaker is unlikely to crap out as it can handle 300W with both coils engaged and presumably has enough excursion to handle that adequately. As I understand it all that is happening is one of the coils is being switched out of the circuit (and so handling the same amount of power as before) while the cone is now being pushed less hard as it's only seeing 150W?

[Dad3353]

[quote name='Musky' timestamp='1423954349' post='2690952']
This echoes my thoughts as well.

The speaker is unlikely to crap out as it can handle 300W with both coils engaged and presumably has enough excursion to handle that adequately. As I understand it all that is happening is one of the coils is being switched out of the circuit (and so handling the same amount of power as before) while the cone is now being pushed less hard as it's only seeing 150W?
[/quote]

No, no and thrice times no. In combo mode, the 2 speakers share the power from the amp. Assuming amp is giving its maximum (very unlikely, but just for the numbers...), each speaker will receive 150w of the 300w total. Once an external cab is connected, one of the speakers receives nothing, the other shares the 300w in exactly the same fashion as before, ie: 150w for the combo speaker,150w for the external cab (assuming equal impedance of internal speaker to external cab...).
There. I hope small children can follow that, at least.

[stingrayPete1977]

Lots of presuming there though isn't there? If we are presuming then I'm presuming the 150 watt voice coil will get ruined by the possible maximum wattage going through it?

Unlike a regular amp all you can do is send half the original power to an eternal driver, it's more like cutting a 2x10 cab in half than actually adding a cab, so adding a 2x10 is like having an 8 ohm 150 watt max 1x10 and 400 watt 2x10 in parallel, would we normally advise that as a good setup?I'd say no?

[Musky]

[quote name='Dad3353' timestamp='1423954812' post='2690956']
No, no and thrice times no. In combo mode, the 2 speakers share the power from the amp. Assuming amp is giving its maximum (very unlikely, but just for the numbers...), each speaker will receive 150w of the 300w total. Once an external cab is connected, one of the speakers receives nothing, the other shares the 300w in exactly the same fashion as before, ie: 150w for the combo speaker,150w for the external cab (assuming equal impedance of internal speaker to external cab...).
There. I hope small children can follow that, at least.
[/quote]

This [i]is[/i] getting confusing. Isn't that what I said? Well sort of - this is a 1x10 combo we're talking about, albeit with a tricksy 2 8 ohm coils in parallel. So the point I was attempting to describe was that the cone wouldn't crap out as it was designed to handle 300W on it's own.

[Musky]

[quote name='stingrayPete1977' timestamp='1423954977' post='2690961']
Lots of presuming there though isn't there? If we are presuming then I'm presuming the 150 watt voice coil will get ruined by the possible maximum wattage going through it?

Unlike a regular amp all you can do is send half the original power to an eternal driver, it's more like cutting a 2x10 cab in half than actually adding a cab, so adding a 2x10 is like having an 8 ohm 150 watt max 1x10 and 400 watt 2x10 in parallel, would we normally advise that as a good setup?I'd say no?
[/quote]
Assuming each driver had the same excursion capabilities that scenario would usually be advised against because the 1x10 would be likely to run out of Xmax before the 2x10. But in this case there's a 1x10 which still has the excursion capabilities of a 300w speaker.

Of course that does presume comparable excursion capabilities of the speakers, which may be a big presumption...

[chris_b]

[quote name='SaxyBassist' timestamp='1423924901' post='2690423']
I am a complete electronics numpty and just wondered if anyone could clarify something for me! I have a Promethean 3110 combo (300 watts 8ohms) and want to add a extension cab - a TC Electronics RS 210 (400 watts 8ohms)......... I've been told this will work, but if I ever wanted to add another RS210 I'd need a more powerful head.
[/quote]

Well, I don't quite know what the last 40 posts were about.......

You can connect the TC 210 cab to this combo and it will work just fine. It'll sound much louder because it has more speakers making more sound and IMO that will give it a better tone. Nothing will break or sound bad because you have caused a problem by adding the extra cab. Take your combo and bass to try it with the 210 cab, so you can check you like the sound, before you buy. You can also try other cabs as long as they are 8 ohms.

Ask about another 210 cab later, if you find out your 310 rig doesn't do what you want.

[stingrayPete1977]

[quote name='BassBunny' timestamp='1423927652' post='2690463']
I think if you check further you will find the 3110 is already running at 4 Ohms, and thus the maximum 300W. The internal speaker has two 8 ohm voice coils wired in parallel thus you have the full 300 watts with the internal speaker. When you plug in the external speaker one of the 8 ohm windings is disconnected.
So although an additional speaker will move more air, you already have the full 300W as the combo stands.
Here's the info from the user manual.
[attachment=183888:Promethian.png]
[/quote]
[quote name='chris_b' timestamp='1423968649' post='2691073']


Well, I don't quite know what the last 40 posts were about.......

You can connect the TC 210 cab to this combo and it will work just fine. It'll sound much louder because it has more speakers making more sound and IMO that will give it a better tone. Nothing will break or sound bad because you have caused a problem by adding the extra cab. Take your combo and bass to try it with the 210 cab, so you can check you like the sound, before you buy. You can also try other cabs as long as they are 8 ohms.

Ask about another 210 cab later, if you find out your 310 rig doesn't do what you want.
[/quote]

That's fine not understanding all the other posts but as you can see from the picture BassBunny found it is showing a 150 8 ohm cab to pair it with, of course they want you to purchase that but at the same time you would be able to hear both matching drivers starting to fart with their recommened setup, you wont hear that 150w 1x10 dying with a TC 2x10 400 watt cab in it's stride. The maths mean nothing really so I'll ask you this, the amp will put 300 watts max into the internal driver or 150 watts into each 8 ohm load (half of the internal driver plus extra cab) so the maths say it can cope? Now run the amp on maximum with some 5 string bass through it, do you think the internal driver would cope or like every other combo on the planet things would start to get messy with the single driver?

[taunton-hobbit]

WOW! All this from a simple(?) question........
I'd like to see what Bill Maurice or Alex Claber think..
...imo if you stick another speaker in circuit that cuts out one of the existing pair, and space it as good distance away from the amp, you will spread your sound, which can give the illusion of 'more'.

[RickyV]

[quote name='BassBunny' timestamp='1423952189' post='2690921']
If you want to add an RS210 to your combo then YES YOU CAN. It will be perfectly safe and if you like the sound, it's your right to spend your money how you wish. In fact any 8 Ohm cab will do but I would stick to 10" speakers. Mixing speakers can have varying results.
[/quote]

Ok, last question(s) from me. Is the statement above about speaker sizes a generally held view or is it more down to personal taste? My Ashdown combo has a 12" speaker so would, say, a 2 x 12 or another single 12 extension cab give me the best results or would a single 15 or possibly a 4 x 10 work just as well (assuming it is an 8ohm cab as established earlier)? I guess the tone that I am after comes in to the equation?