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Loud Watts and quiet Watts


thinman
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It seems to be a common thing on this and other forums where people talk about a "loud" xxx Watts amp versus, I assume, "quieter" xxx Watts amps.

Surely most of this is just perceptual due to other factors such a different cab efficiencies, tone and differing ways of measuring amp output and, I suspect people comparing apparent volume for the same master gain knob position?

I'll give you an example:

I've got an Ashdown MAG300 1 x 15 combo (about 180w into 8 ohms) and a H&K bassbase 250 used with a BFM Omni10 (250w into 4 ohms). For similar EQ (flat) and input gain settings (as far as I can tell) and the master set to a third on both, the Ashdown seems louder despite the Omni 10 probably being more efficient and the the H&K being allowed to provide its full output into the lower impedance.

However, I have a suspicion that some amps are designed such that they reach their full gain for an average input level quite a low master setting. i.e. if I turned the Ashdown up further it will start getting nasty sooner than the H&K/BFM which will then show it can produce a higher SPL.

I reckon from the marketing point of view it's thought that someone will try an amp at reasonable volume in a shop and think "blimey - that's only on a quarter and it's pretty loud already" thinking it will get louder linearly as they turn it up, i.e. it's got "louder watts" than another amp!

OK, I realise that better amps will probably deliver their quoted output in a real life situation whereas others only do it under specific artificial situations but that's not really what I'm on about.

Maybe I'm just being cynical...

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I think this has been brought up before and similar conclusions reached. But here are a few points mentioned.

1. WATTS are a unit of power and not loudness, so it does not actually make any sense to use the Wattage of an amplifier to predict it's "loudness".

2. The volume of a rig is hugely dependent of the efficiency of the speakers used. It is not valid to compare amplifiers unless the same identical speakers are used.

3. As you suggest, the position of the volume control(s) is not an accurate measure of the power output. Half on the volume control does not mean that half the power is being used.

4. Apparent volume (to a listener) will be frequency dependent so the "tone" of an amp will have an effect on the perceived loudness. You would have to use proper measuring equipment to rule this out.

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[url="http://basschat.co.uk/index.php?showtopic=3730"]http://basschat.co.uk/index.php?showtopic=3730[/url]

Most confusion is due to variations in gain though frequency response and sensitivity are important too. You can also add distortion and compression into the gumbo.

The loudest amp to the layman will be the one with the most gain at low knob settings, the most midrange, the most distortion and the most compression.

Alex

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I always apply this rule of thumb... if a speaker cab weighs a tonne then it's likely to be LOUD. After all what you are paying for is big magnets... and generally big magnets have higher sensitivity.. of course the cab might be made of ebony with a lead lining... but that's another issue :) .

Richard

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[quote name='bass_ferret' post='170605' date='Apr 6 2008, 10:57 AM']You have not heard of light weight ply and neo magnets then?[/quote]

Neodymium? I have a Ph.D. in metallurgy, so yes. They are actually iron based so are not really lightweight. Either way you are paying for the ability to translate electric signals into air movement and big magnets do this better than small magnets.

Richard

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[quote name='Vasquez Rich' post='170484' date='Apr 5 2008, 11:19 PM']I always apply this rule of thumb... if a speaker cab weighs a tonne then it's likely to be LOUD. After all what you are paying for is big magnets... and generally big magnets have higher sensitivity..[/quote]

Bad rule of thumb. Is a speaker cab is big then it's likely to be loud. Big magnets may make guitar cabs louder but too much magnet lowers the Qts too much and you end up with less sensitivity in the lows, and we are bass players so sensitivity below 200Hz does matter.

Size matters, weight doesn't.

Alex

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