Mr. Foxen

[quote name='chris_b' timestamp='1338414557' post='1674390'] ....and you need to know all of this in order to buy a bass amp and cab! [/quote] The right bass amp and cab, more specifically. Although people can get away with the wrong ones quite well.

[quote name='CraigPlaysBass' timestamp='1338409734' post='1674271'] This is great guys, don't stop, I feel like I'm learning loads! (No sarcasm intended). So... Could someone please explain to me clearly what the difference is between DC and the clipped waveform? I get that they look the same on the graph but aren't, why? I expect it was somewhere in the thread but there were lots of angry rebuttals in-between... [/quote] DC isn't a waveform, its current flowing. Kind of like the difference between the sea doing tides and waves, and a river flowing. The waves are higher harmonics and the tides are the fundamental (which is sort of irrelevant to previous sentence, but its sort of a neat way of putting it). And if you pass a clipped/square wave into an electrical component other than a perfect resistor, the graph won't be square any more, it will round off according to the inductive or capacitive qualities of that component, namely a speaker (obviously some components do other stuff, but couldn't think of a term to cover both resistors, capacitors and things that have resistive or capacitive effect). Basically, whatever shape the wave is, if its a wave, then it is AC.

[quote name='GregBass' timestamp='1338404576' post='1674138'] Hmm. Note that we can't see the x-axis scale. That horizontal portion could be 10ns or 10 minutes. Are you saying that if it's 10 minutes, we are not seeing DC? At which point does it stop being a blip on a waveform and start being DC? Just asking - because if you connect a scope to a battery via an open switch, close the switch for a while then open it again you see a square wave (try it). Does this mean the battery does not produce a direct voltage? Or would you have to be selective about which bit of the waveform you look at? BTW, I did acknowledge that I had misread your statement. [/quote] [quote name='dincz' timestamp='1338404929' post='1674145'] The polarity and the direction of current flow don't alternate so it's not AC - just pulsating DC. [/quote] It has already been said a bunch of times, that if you put an inductive or capacitive load on the output, then you don't get the flat bit. a capacitor will block DC, but pass AC (up to a point given its specification). This is what makes the difference between resistance and impedance, and a speaker is not a purely resistive load. an if you connect a battery to one, the cone just moves to a point and stays there, and that is it.

Nope, nominal impedance is a fairly useful speaker spec in comparison to thermal rating.

Would definitely make life easier if they didn't mention output power at all and just gave a voltage swing and min/max operating conditions.

Shoot up some pics, inside and out, they might be a rebadged something else that is better known.

[quote name='GregBass' timestamp='1338398956' post='1673992'] Wow Bill - so if you have a trace that's completely flat at a voltage other than 0, its not a direct voltage? Maybe physics doesnt apply in your universe. [/quote] The part where you say 'waveform' and try and claim it is DC is where you are wrong. You can have one or the other. [quote name='stingrayPete1977' timestamp='1338399126' post='1673999'] What's all the electronics talk about? [/quote] From the thread title: [size=3]"[/size][size=3]Need help understanding power ratings..."[/size]

[quote name='dincz' timestamp='1338397758' post='1673973'] Ah, 'square wave' as opposed to square wave I need to study the rules of this game. [/quote] Everything needs to relate to reality, in order to facilitate understanding. Every example you've cited as fact in opposition to people who already understand relies on removing the reality. Hence the use of quotes in the instruction.

[quote name='dincz' timestamp='1338396686' post='1673946'] I've got no way of doing that at the monent, but I'd expect to see what others have seen: [/quote] That is for an ideal square wave, and not a clipped wave. In the real world you don't get ideal square waves because they require infinite bandwidth. Hence the suggestion of applying a real world observation, rather than demonstrating your limited understanding of the subject matter, and claiming others have seen the impossible to try and back up your claims.

Go run a fast Fourier transform on your 'square' wave and see what harmonics you get.

There isn't a way of power rating speakers that isn't frequency dependent though. Sensitivity would be useful, but there isn't a standard for that as applied to cabs, you get one with speakers though, so you can sort of extrapolate onto a cab if you understand a bunch of other factors. The fact that sensitivity is the determining factor between voltage swing from the amp and spl renders watts meaningless.

[quote name='GregBass' timestamp='1338390130' post='1673783'] I think you may have missed the bit where I said "for that short period while the line is flat". [b]If you ignore the rest of the waveform,[/b] for that short time there is DC applied across the speaker. For that short period, the speaker is pushed (or pulled) and held in a particular position. There's no sound generated, but there may be a bit of heat. This, as you say, is not a good idea - and that was actually my initial point. [/quote] So if you ignore the fact it is a wave, then it isn't a wave. However, it isn't flat if you have a speaker on it: [quote]If you scope it, you do not see a constant flat line above or below 0v which is DC, and you only see a flat top into a purely resistive load, an inductive (such as a speaker) load rounds them off, because the impedance varies with frequency. Basic physics is that if its a waveform, it is alternating, otherwise is isn't a wave, its a flow.[/quote] And the suggestion that a clipping amp makes no sound is a bit silly, don't you think? Edit: And to the OP, give an idea of what sound you want, and we can get on tot he gear suggestions. My tendency in recommendations is to figure what sort of amp is suitable, then match it up with a Barefaced cab, since they cover most ground, and don't have too much sound of their own so don't introduce further sound variables. But if you want to mix it up some, I'll work with what you are after.

[quote name='Bill Fitzmaurice' timestamp='1338385955' post='1673665'] If readers all paid attention to the key phrase 'high frequency components' the myth might not have arisen. But like all myths it grew with each retelling. [/quote] This aprt is why it needs correcting every time someone decides to start retelling it.

[quote name='GregBass' timestamp='1338384355' post='1673631'] So you haven't blown your speakers while not power matching them - good. Just to complete the picture, the power handling of the speakers in my rig is currently double what the amp can kick out at full blast. Guess what - I haven't blown any of the speakers either. Does that actually prove anything? As a general rule, I would say it's a decent idea to make sure your speakers can handle the power you intend to kick out of the amplifier. The simplest way to do this is to look at the power ratings, and make sure that the amp is not going to be chucking out more than the speakers are rated to handle. As a sort of rule of thumb, I hardly think that's contentious. Clipping is EXACTLY putting DC in short bursts across the speaker. Think of the theory. Consider a sine wave. When it clips the top of the waveform goes flat - that's basic waveform analysis. A flat waveform is a short burst of DC, that's basic electronics. In fact, the Fane technical department describe it as precisely that when they explain that over pushing the amp is more likely to damage speakers than driving them too hard. I have a nice little Hartke 4x10 which goes down to 30Hz. My 1x18 EV sub does too. That's two out of two. Not bad considering virtually none do, eh? Maybe I'm just lucky. It's actually very useful for the heavy rock I play, mostly without house PAs to play through. I didn't mention anything about the benefits of valves, so I fail to understand why you are using that criticise my input to the discussion. [/quote] You can blow 500w rated speakers with a 200w rated amp, because thermal ratings don['t tell you the power it takes to blow a speaker. This is why watt rating have no meaning and thus should be ignored. Clipping does not put out short bursts of DC. This is fact. If you scope it, you do not see a constant flat line above or below 0v which is DC, and you only see a flat top into a purely resistive load, an inductive (such as a speaker) load rounds them off, because the impedance varies with frequency. Basic physics is that if its a waveform, it is alternating, otherwise is isn't a wave, its a flow. Let's see these SPL charts and waterfall plots from the cabs you claim have useable output capacity at 30hz then.

[quote name='Bill Fitzmaurice' timestamp='1338382721' post='1673594'] It must be a constant, otherwise the amp simply won't work. Hook up an tone generator to an amp with flat response, the amp to a speaker. Measure the voltage as you sweep across the spectrum, it will remain constant even though the speaker impedance is not. If it's not constant the amp, or generator, does not have flat response, and you'll see the same voltage fluctuation into a resistive load. [/quote] Think the guy meant it isn't constant in the sense there is no voltage when you are playing a rest etc. Its output varies massively when in use, but its output across the frequency band for a given input voltage/signal strength is constant. Bearing in mind music won't have a constant strength across the band.

[quote name='GregBass' timestamp='1338382198' post='1673580'] Wow, man, you are really aggressive on here aren't you? So let's get this straight. You reckon it's OK to use a 25W speaker with a 500W amp? Do your speakers last more than a few weeks? You reckon that driving an amp to saturation doesn't cause clipping? That clipping is not "flattening off: at the peaks of the waveform? That valves don't sound "warmer" to most people? Congratulations - you have just rewritten the rules of science all on your own. maybe a Nobel prize comes next. For the OP - if you follow what this man says you will blow your speakers at the very least. [/quote] Its ok to use any amp with any speaker if you aren't an idiot about it. I've had one speaker develop a voice coil run in all the time I've been playing really loud bassy detuned music, and that was likely to do with storage conditions. Clipping doesn't cause DC, and doesn't upset bass drivers. I run my amps in clipping all of the time. Pretty much no commercial bass cabinets go as low as 30hz, and it isn't a useful frequency for bass guitar anyway. There are various benefits to valves, and a bunch of them are down to clipping. And a bunch of the others are down to the properties of the output transformer, in particular its ability to filter out extremely low frequencies.

[quote name='dincz' timestamp='1338378349' post='1673479'] Test an amp into a purely resistive load and the effect can easily be seen. Use a reactive load like a loudspeaker and a fixed frequency and you'll see the same. Vary the frequency and the situation becomes more complicated but the same basic relationship still holds. [/quote] This is jsut saying that if you do a bunch of stuff that isn't applicable to the actual situation you don't get the result that you do in the actual situation. And the actual situation is more complicated. Whereas the people you are arguing with already know about the more complicated situation and are talking about it, because they deal with it in reality not in experiments where key variables have been removed. This is about learning to deal with those variables, because it is engineering and those variables are always there. Music varies in frequency, and speakers vary in impedance, those are factors that have to be considered, as soon as you don't consider them, you aren't talking about amplifying music, and thus should be posting about it in another forum.

[quote name='StraightSix' timestamp='1338373740' post='1673380'] No, that is your implication. Why do you think the long-standing manufacturers/designers will have more knowledge...? [/quote] Its more important that they are current designers, and thus an understanding of how amplifiers work is really important when designing devices to play well with amplifiers. Long established ones can just keep remaking the old design and telling people its their own fault that they don't work very well with new designs.

[quote name='GregBass' timestamp='1338370850' post='1673315'] OK there are a few rules that make for a good match: Ideally speakers should have a higher power rating than the amp driving them (check the amp power at the appropriate impedance for the cab) Always have an amp with plenty of power output. If you drive the amp to its limits, it will clip (the tops and bottoms of the waveforms are flattened, which effectively puts DC across your speakers for a short period). Check the frequency bandwidth of your cabs - down to 30Hz is what you should be looking for to give deep bass (all decent bass amps do this so you shouldn't need to check the amp). Valves and transistors produce different harmonics (higher frequency "overtones" of the fundamental frequency). To most people's ears, valves produce a warmer tone. [/quote] Dunno if you are trolling on purpose, but pretty much all of this is wrong. Valve amps totally do make a massive difference, its more to do with the output transformer acting as a high pass than the valves themselves, but it means your power is massively more efficiently used and your cabs are less stressed, so you can get louder without farting out. Main thing to o is start by being clear in what you want to achieve. Also ignore anyone who says a bunch of stuff from the above quote.

[quote name='dincz' timestamp='1338354523' post='1673108'] What flaws do you see? Was Mr. Ohm wrong? [/quote] He was right about resistance, but this is impedance, which he is also right about, but they are different things. I don't think you've really understood the really big fundamental differences between them and how they apply to amplifying signal. [quote name='GregBass' timestamp='1338361619' post='1673133'] This cannot be true. At any specified frequency, the impedance of the speaker is fixed. That's how impedance is defined. If the voltage is constant and the impedance is fixed, then Ohm's Law tells us that the current must also be fixed, meaning that at any frequency, the power from the amp is always the same. This is clearly not the case. [/quote] We are talking maximums. You only get one maximum under a given set of criteria. You could put out full power from an amp at the top or the bottom of its frequency band, but probably wouldn't want to do the top one.

Better explanation would be where those ideas come from, because I've seen stuff like that posted a few times, and usually claiming some sort of authority from 'experimentation' or a formula that doesn't apply to the situation, whilst ignoring the massive flaws in the internal logic of the situation.

There is more to matching speakers to a cab than ohms and watts. In fact, ohms and watts aren't very relevant at all. Do a search for "winISD' on here and there'll be a ton of threads running through how it works.

[quote name='Musky' timestamp='1338317467' post='1672709'] On a side note, my Harley Benton BA500 (500w at 4 ohms) has a specified power consumption of 170w. I thought it was a typo until Mr Foxen pointed out that other class D amps he'd been looking at had similar power demands. Anyone have an explanation of why this is? I would have sided with Dincz in saying that this is completely impossible, but now I'm totally confused. Something strange going on with the power factor perhaps? [/quote] Basically RMS isn't putting out the absolute maximum it can forever. Music isn't like that, and that is why RMS is the more relevant value to music.

Speakers aren't a resistive load. And you need to have a scope or other means of determining when you are at max clean output, or it doesn't tell you anything relevant.