Whitehoose Posted March 31, 2012 Share Posted March 31, 2012 Hello, without out failing to maybe seem like a complete tool, what does power rating on cabs mean in RMS and Continuous? I've never really learned for myself and never had any problems running cabs (I was told many years ago to make sure the wattage of the cab was higher than the head by a fraction and to hold regard for impedance). So what do both terms mean? If anyone could explain that would be great Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted March 31, 2012 Share Posted March 31, 2012 In practice, it all means nothing. Actually better to ignore it an pay attention to other things. Quote Link to comment Share on other sites More sharing options...
Mog Posted March 31, 2012 Share Posted March 31, 2012 RMS is the only one you need to keep an eye on. Basically its the most accurate rating of the cabs power handling capability. Continuous is sometimes referred to as peak power. Generally it refers to the upper limit of what the cab can tolerate. Quote Link to comment Share on other sites More sharing options...
chris_b Posted March 31, 2012 Share Posted March 31, 2012 There are lots of numbers involved but you don't need to know about most them. This is the simple version. RMS is the only industry standard and gives you an idea of the power rating of the cab and of the amp. Don't bother about any other numbers yet. I aim to have more cab watts than amp watts and I aim to have more amp watts than I need because what I want a clean sound. I never drive an amp flat out, so one of my rigs is a 500 watt amp through 600 watts of cabs. I usually never go over half on the amp volume so, on my amp, that might be about 200 watts through 2 8ohm 300 watt cabs, which means each cab is getting about 100 watts. Everything is working well within its limits. Some cabs are more sensitive which makes them louder but this has worked for me as a rule of thumb with many rigs for many years. Quote Link to comment Share on other sites More sharing options...
chris_b Posted March 31, 2012 Share Posted March 31, 2012 [quote name='chris_b' timestamp='1333186341' post='1598450'] .... that might be about 200 watts through 2 8ohm 300 watt cabs, which means each cab is getting about 100 watts.... [/quote] ps I don't play this rig at heavy rock or metal band volumes (I have other cabs for that) but this rig is as loud as any pub gig can take. Quote Link to comment Share on other sites More sharing options...
subrob Posted March 31, 2012 Share Posted March 31, 2012 RMS means 'root mean squared'. It near literally means 'average' power, but because a bases output (like music in general) us full of big dynamics and lots of different frequencies, your amp can put out maybe 8 times as much, if only for a small fraction of a second, as what it can do for averaged over a few seconds of usual playing. there are only really ways of approximating what your typical music program source actually makes an amp and speaker arrangement do, in terms of transducing electricity into sound. so what you're up against is a load of different ideas about what the best approximation is. And that's when the manufacturers marketing geeks get hold of it, and the figures can magically grow of their own accord... Lots are guilty of this, but that's another thread. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted March 31, 2012 Share Posted March 31, 2012 RMS is what engineers use when desiging gear. All else is what marketeers use when advertising it. Quote Link to comment Share on other sites More sharing options...
xgsjx Posted March 31, 2012 Share Posted March 31, 2012 The other thing you mentioned was impedance, that's the only one you need to take caution with. Have a read at the wiki. Quote Link to comment Share on other sites More sharing options...
crez5150 Posted March 31, 2012 Share Posted March 31, 2012 RMS, AES are the more truthful options..... Continuous at a push.... Everything else is FAIL! Quote Link to comment Share on other sites More sharing options...
xgsjx Posted March 31, 2012 Share Posted March 31, 2012 Oops, wiki is missing! Been a while since I last looked at it too. [url="http://basschat.co.uk/topic/135-impedance-etc/"]Try this. [/url] [url="http://barefacedbass.com/bgm-columns.htm"]& also this is worth a spot of reading.[/url] See you next week. Quote Link to comment Share on other sites More sharing options...
Musky Posted April 1, 2012 Share Posted April 1, 2012 Yeah, the wiki disappeared with the site revamp. It was an underused resource for sure, but then it was so tucked away that most people didn't seem to know it was there. Anyway, it's archived at the Wayback Machine. http://web.archive.org/web/20110609144632/http://wiki.basschat.co.uk/info:amps:impedance_and_wattage Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted April 1, 2012 Share Posted April 1, 2012 Essentially speaker rating is about not breaking your speakers and to a lesser extent about avoiding distortion. RMS ratings are about how much electrical power a speaker will take. The more you put in the hotter the speaker will get until eventually it burns out. There are minor fiddles a manufacturer/advertiser can indulge in but essentially it is a test anyone can do and so is easily checked and tends to be a reliable and convenient way of measuring. The only thing is that it only measures one aspect (heat dispersal) and so doesn't relate too well to musical abilities. Most manufacturers also give music/programme ratings and peak ratings. Music is usually double the RMS value and peak 4x. Music isn't continuous so the speaker normally cools down in the quiet bits and you can usually put a lot more power through a speaker for a fraction of a second so these are meant to be a 'real world' figure. However these are only rules of thumb and there is nothing to stop a peak claim of almost any figure, if it is short enough in duration. If they stick to 2x and 4x then it doesn't tell you anything more than the RMS value, unless you don't know your two times table. The main thing you need to know as a bassist however is that there are two other good ways of destroying a speaker or at least making it sound bad. The first is over excursion, pushing the cone beyond its limits. The lower a note is the bigger the excursion and there are plenty of bass speakers that, given a really low note will only handle a tenth of their RMS power. That 300W speaker might be only 100W for a 4 string or 30W with a 5 string. Finally wear and tear will knacker a speaker, run 600W through a 300W speaker night after night and it won't last as long as it will with just 100W through the same unit. Hope this helps Quote Link to comment Share on other sites More sharing options...
flyfisher Posted April 1, 2012 Share Posted April 1, 2012 The basic problem is how to characterise a music waveform. Because it is very complex and entirely dependent on the type of music being played, it's very difficult to determine the average power. At a given amplifier volume setting, two different pieces of music will deliver two different amounts of power. From a speaker's perspective, some power is used to move the cone but most will just heat up the voice-coil. The more power sent to the speaker, the hotter it will get until - at some point - the voice-coil will burn out. To help us match speakers to amps, the industry uses 'RMS' to specify power capabilities. It may not be an exact science but it's a good guideline. In general, if the speaker rating is higher than the amp rating then things should always be OK. But like most guidelines, the 'rules' can be safely broken if you understand the implications. The golden rule seems to be that if it sounds good then it is good, but a distorted/farty sound is really a cry for help. Quote Link to comment Share on other sites More sharing options...
Whitehoose Posted April 3, 2012 Author Share Posted April 3, 2012 Right then, thats cleared up, cheers y'all! Quote Link to comment Share on other sites More sharing options...
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