aj5string Posted September 18, 2007 Share Posted September 18, 2007 Right, i dont really get the whole RMS, 8 ohms, 4 ohms etc thing, so be gentle Im buying a new head + cab. Ideally i want to get a 2x10. Thing is, they dont seem to have very high power handling capabilities. Looking around, most seem to have around 200w into 4ohms or 8ohms - where as the heads i've been looking at seem to be around double that (a couple on ebay...). Am i being stupid? I really just want/need the one cab at the moment... Cheers. Aj. Quote Link to comment Share on other sites More sharing options...
alexclaber Posted September 18, 2007 Share Posted September 18, 2007 A power ratio of 2:1 either way is absolutely fine. Speakers make bad noises when you push them too hard. If you ignore these noises can be blown with less than their rated power handling whilst if you're aware of these noises and react when you hear them they can safely handle far more than their rated power handling. Alex Quote Link to comment Share on other sites More sharing options...
bass_ferret Posted September 18, 2007 Share Posted September 18, 2007 Depends which end of the market you are looking at. Lots of high end 2x10's are 500 watts. There is something on the wiki that explains all about ohms. Quote Link to comment Share on other sites More sharing options...
aj5string Posted September 18, 2007 Author Share Posted September 18, 2007 Cool... I was looking at the SWR 2x10 in the for sale section (200w 4ohms) because its quite local to me. Headwise, I've been offered an Ashdown ABM 500 EVO II at a good price, but am starting to think it might be a bit too pokey for the cab... what do people think? Alex. Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted September 18, 2007 Share Posted September 18, 2007 [quote name='aj5string' post='62171' date='Sep 18 2007, 03:00 PM']Cool... I was looking at the SWR 2x10 in the for sale section (200w 4ohms) because its quite local to me. Headwise, I've been offered an Ashdown ABM 500 EVO II at a good price, but am starting to think it might be a bit too pokey for the cab... what do people think? Alex.[/quote] It really is difficult to generalise Alex but the Asdown into the SWR should be absolutely fine; however, follow the advice given previously by (the other) Alex... listen to your equipment. Ensure none of the gear is exhibiting nasty noises before you even start using it but I'd like to hope that if the seller were an established user of this forum (check feedback) then they'd be upfront about any issues. Quote Link to comment Share on other sites More sharing options...
paul, the Posted September 18, 2007 Share Posted September 18, 2007 You could always keep an eye out for replacement speakers if you're turning the volume up. You see them coming up in pairs sometimes on ebay. Quote Link to comment Share on other sites More sharing options...
paul, the Posted September 18, 2007 Share Posted September 18, 2007 What I find interesting is valves with speakers. Surely a transistor amp starts clipping before it's using its full wattage - have modern speaker specifications changed to cater for this? Sorry if this is a silly question. Quote Link to comment Share on other sites More sharing options...
alexclaber Posted September 18, 2007 Share Posted September 18, 2007 The power output of an amp is simply the maximum voltage swing squared divided by the specified load. The maximum voltage an amp can put out is equal to the rail voltage of the amp. As the impedance decreases the amp gradually runs out of current capability to keep the voltage rails at full voltage, thus the power output does not keep on doubling every time you halve the impedance. This remains true for any class or type of power amp, from Class A valve to Class D transistor. An amp playing typical recorded music that is turned up to just clip occasionally on the loudest peaks will only put out 1/8 power on average. An amp playing particularly demanding recorded music that turned up to clip frequently and severely will put out 1/3 power on average. Typical bass playing is even less demanding than 1/8 power. What exactly did you mean by this? [quote name='paul, the' post='62210' date='Sep 18 2007, 04:21 PM']What I find interesting is valves with speakers. Surely a transistor amp starts clipping before it's using its full wattage - have modern speaker specifications changed to cater for this?[/quote] Not quite sure what you're getting at! Alex Quote Link to comment Share on other sites More sharing options...
Bernmeister Posted September 18, 2007 Share Posted September 18, 2007 Hi all, I believe one of the cabs he's aiming he questions towards is the swr 2x10 i have up for sale. i have pm'd him offering him a chance to demo the said item as he lives not too far away from me. Oh! Aj pm sent Quote Link to comment Share on other sites More sharing options...
paul, the Posted September 18, 2007 Share Posted September 18, 2007 [quote name='alexclaber' post='62276' date='Sep 18 2007, 07:03 PM']What exactly did you mean by this? Not quite sure what you're getting at! Alex[/quote] Well you see early 15" drivers with 50watts on them - designed to power a 50 watt valve amp, perhaps in a combo. Presumably, that speaker would break up and distort with a 100 watt valve amp turned up full. If you powered that speaker with say a 150 watt SS head, I would have thought you would still get the amps optimum of quality and volume. -- I realise that terminology such as 'distort' and 'volume' have multiple meaning in this context. Quote Link to comment Share on other sites More sharing options...
alexclaber Posted September 18, 2007 Share Posted September 18, 2007 [quote name='paul, the' post='62297' date='Sep 18 2007, 07:42 PM']Well you see early 15" drivers with 50watts on them - designed to power a 50 watt valve amp, perhaps in a combo.[/quote] I'm going to be pernickety but one has to be if you want to know what's going on! For starters drivers do not power amps, the reverse is what happens. A speaker has two things that affect the thermal power handling - how quickly the voice coil can dissipate heat (the bigger the voice coil and more extensive the heatsinking the better) and what temperate the voice coil wire and former can stand before damage occurs (insulation melting causing short circuit or former warping from heat). The power handling rating on a speaker states how much power it can continuously dissipate without overheating. The reason modern speakers can handle much greater power is the combination of larger voice coils and more high temperature materials. If you put too much continuous power into a speaker so that it overheats it will just suddenly die without any warning. You will not hear distortion from the speaker beforehand but you may notice that turning the amp up more has no effect because of the extreme power compression. However it is almost impossible to put too much continuous power into a speaker without clipping the amp, because of the continuous to peak power ratio I described in a previous post. This is why clipping is bad because it allows you to get more continuous power out of the amp, not because it causes DC or because speakers don't like square waves etc - these points are both untrue. [quote name='paul, the' post='62297' date='Sep 18 2007, 07:42 PM']Presumably, that speaker would break up and distort with a 100 watt valve amp turned up full.[/quote] If you turn any amp up full, unless you're putting a very quiet signal into it, the amp will distort. The speaker may not but the amp will and you're unlikely to be able to distinguish that from speaker distortion. There is another (and for bass, more important) type of power handling that matters. This is excursion limited or mechanical power handling. The main issue when it comes to speakers' mechanical power handling is the Xmax and Xlim of the speaker - the former is how far the cone can move before exceeding 10% distortion, the latter is how far the speaker can move before breaking. Mechanical power handling is never quoted because it is dependent on the cab volume and tuning as well as the speaker specs. It also decreases dramatically below the tuning frequency. Most bass cabs have far less mechanical (excursion limited) power handling than they have thermal power handling - often as little as 1/4 as much. The reason Acme cabs can cope with such powerful amps is that they have more mechanical power handling than they have thermal power handling but they are unique in this respect. Mechanical power handling only matters in the lows - hence its importance to us. Every time you go an octave lower you quadruple the cone excursion for an equal input power. Also whilst the peak thermal power handling is vastly higher than the continuous thermal power handling, the peak mechanical power handling is the same as the continuous thermal power handling. The sound of a speaker being overdriven (by a clean non-clipping amp) is that of it exceeding its mechanical power handling rating - cone going beyond Xmax. This will not usually cause damage but it rarely sounds good. However go far enough beyond Xmax and you hit Xlim, which equals instant speaker death. The sound of exceeding Xmax is a good warning sign! Alex Quote Link to comment Share on other sites More sharing options...
paul, the Posted September 19, 2007 Share Posted September 19, 2007 Lovely. Sorry about the question, it was written whilst watching TV. Thanks for the detailed response Alex, I'm now a little wiser. Quote Link to comment Share on other sites More sharing options...
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