Jump to content
Why become a member? ×

RSM/Continuous, help.


Whitehoose
 Share

Recommended Posts

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 :)

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

[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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Oops, wiki is missing! Been a while since I last looked at it too. :search:

[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. :D

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...