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steve
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I was reading [url="http://www.doctorproaudio.com/doctor/temas/powerhandling.htm"]this web article[/url] which states right at the bottom

[quote]5. Selecting amplifier power

In general, the amplifier power needs to be larger than the speaker's rated power. This is because an amplifier only delivers its rated output power with sinewave signal, and delivers much less with a real signal with dynamics. As ageneral guideline, it is recommended to use an amplifier delivering 50% more power than the speaker's average ("RMS") power. For example, for a speaker with 450W average power, an amplifier with an output of 700W may be used. If a small amplifier is used, sufficient level will not be reached, nor the perception that it is attained, so the signal will tend to be clipped to compensate, thus endangering the integrity of the speaker."[/quote]

Is this correct?

If so, I assume my 450W into 4ohm Ampeg head be well matched to Hartke 2.5XL and a 115XL (or another 2.5XL), which are both 200W @8ohms.

Could anyone confirm this?

thanks chaps

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[quote name='steve' post='101410' date='Dec 8 2007, 04:21 PM']I assume my 450W into 4ohm Ampeg head be well matched to Hartke 2.5XL and a 115XL (or another 2.5XL), which are both 200W @8ohms.[/quote]

Yes. For a sensible amp:cab power rating ratio I'd recommend within a 2:1 either way, i.e. an amp with between 200W and 800W power for the Hartkes.

Typical power draw with program material (i.e. recorded music) with your amp running at full volume (i.e. clipping on the peaks) is 1/8 power. So an 800W amp will only be averaging 100W power output. For live bass guitar this ratio tends to be even larger.

Alex

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[quote name='alexclaber' post='101419' date='Dec 8 2007, 04:38 PM']Yes. For a sensible amp:cab power rating ratio I'd recommend within a 2:1 either way, i.e. an amp with between 200W and 800W power for the Hartkes.

Typical power draw with program material (i.e. recorded music) with your amp running at full volume (i.e. clipping on the peaks) is 1/8 power. So an 800W amp will only be averaging 100W power output. For live bass guitar this ratio tends to be even larger.

Alex[/quote]

That's brilliant, and thanks for responding so quickly Alex.

So I've actually got enough headroom with my 2 Hartkes. Cool :)

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I think that article is quite misleading on a number of levels - it appears to be written with a home stereo in mind, with a "given" level of volume. yes, for a particular volume level a smaller amp will have to be run higher on the dial.

after that, sorry, it makes rather absurd assumptions on speaker sensitivity vs power handling, with no basis for it because there is no basis for it. my 500 watt 15" is a far more sensitive "loud" speaker than my 300 watt 10", and will be far louder with virtually ANY wattage amp. all things being equal - which they never are - I'd rather have my speakers rated waaay higher than my amps rated output, the higher the better, as long as they have sufficeient frequency response and sensitivity.

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[quote name='gypsymoth' post='101445' date='Dec 8 2007, 12:34 PM']I think that article is quite misleading on a number of levels -[/quote]
+1. It verges on a retelling of the Myth of Underpowering. Some valid points are raised as far as hi-fi and PA are concerned, but pretty irrelevent with regard to instrument amps.

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[quote name='steve' post='101475' date='Dec 8 2007, 02:10 PM']@ gypsymoth and bill

so are you saying in your respective (and respected) opinions,that I haven't got enough headroom with the Hartkes?[/quote]
The average cab won't take more than 1/2 its rated power before exceeding xmax, and many won't even take that much. Having more is not going to make things any louder. It won't hurt, but it isn't a necessity. There's a very simple way to know if your amp/speakers have adequate power. Are they loud enough? If so, they do.

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[quote name='gypsymoth' post='101581' date='Dec 9 2007, 07:45 AM']if your 450 watts is rms (ss @ 4 ohms) and your two cabs (combined 4 ohms) are rated for 400 watts - I sure wouldn't turn the volume up very high.
I prefer double or quadruple speaker ratings to amp output - some people do get away with a lot less, it depends on how you play.[/quote]

:) Ahhh SH*T I'm screwed then... my cab is rated at 2100watts! Anyone got a 4000 - 8000 watt amp spare :huh:

As has already been stated there is a lot of claptrap written on this subject and just as many variables to skew any judgement. Many experienced Basschatters will have driven speaker cabs with amps rated higher and lower then the recommended amounts and will have done no harm. The more 'mature' section of our user base may well goggle at the ratings of some of the amps and cabs produced today (even taking into account spurious power claims). I have personally driven a 200 watt 2x10 cab with a 1000 watt pre/power set-up and had absolutely no problems.

I'd be happier using an amp with more power than the cab was rated at as hopefully I wouldn't need to push it to get the required output. Ultimately I use my ears and common sense and in my 25+ years of gigging experience I've yet to fry a driver or horn/tweeter (and that includes PA use).

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[quote name='steve' post='101475' date='Dec 8 2007, 07:10 PM']so are you saying in your respective (and respected) opinions,that I haven't got enough headroom with the Hartkes?[/quote]

If it sounds bad, turn down. That's all you need to remember. If you want to know why search for some of my old posts on this subject.

Alex

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you have my opinion backwards.
if I had a 500 watt amp, I would want a cab capable of 1000 or more watts. my biggest head is 200 watts, my cabs range from 300 to 800 watts, depending on the number of speakers I use.

if you are running an amp with double the power of your speakers ratings, and not smoking those speakers, all it means is that you are not turning it up, and are not putting out (utilizing) much of that amps power. maybe you don't need anywhere near a thousand watts - you aren't using them :)

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The big difference in instrument amplifiers as apposed to hi-fi / pa amplifiers is the gain level required to produce audible output and the nature of the signal being processed.

hi-fi and pa systems are most often run with nice, "loud" line level signal, its easy to predict and control its output level, so tolerances can be very tight with regards to getting volume out of a pa speaker. you can run a 1000w (peak) amp into a 500w RMS cabinet with no problems - provided you know what you're doing...

an instrument signal is much much "quieter", the gain applied to the signal is much higher, the dynamic range of that signal is massive (in terms of output voltage) and so you need to make sure your cabs can handle anything your amp kicks out - as the tolerance has to be that much higher.

At least, from where I'm standing that seems to be the reason. Either that or I'm talking sh*t, and I'm sure someone will point that out!

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an amp makes power - it's kinda like an engine. if you attach a 500hp Aston Martin engine to a transmission and clutch from an Austin anything, it will work. as long as you don't actually step on the gas and create power - in which case things would start breaking.
the difference is that you are likely to smoke your head if you first smoke your speakers.
but if you never step on the gas, the Aston engine isn't putting out those 500 horsies anyway, so you could get away with it.

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[quote name='DrGonzo' post='101821' date='Dec 9 2007, 01:20 PM']At least, from where I'm standing that seems to be the reason. Either that or I'm talking sh*t, and I'm sure someone will point that out![/quote]
Pointed. Distorted signals have excess high frequency power content that can toast tweeters, so hi-fi and PA systems need plenty of amp headroom to minimize the possiblility of distortion. Instrument speakers are designed to handle distorted signals so amp headroom is not a requirement; where guitar is concerned it can be detrimental to tone. Bass cab tweeters can have problems with distorted signals if they aren't robust enough to handle distorted signals, but most are designed to do so.

Edited by Bill Fitzmaurice
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