D.I. Joe Posted November 12, 2012 Share Posted November 12, 2012 An interesting conversation that I had at an open mic last week... According to the chap I was speaking to, you are more likely to blow a speaker by using an under-powered amp than by using an over-powered amp. I guess in the context of power ratings - whereby, say, a 1200w amp could happily power a 600w speaker at a reasonable volume whereas if the values are reversed, the amp tops out and sends a heavily clipped signal which causes the speaker to fail. I'll point out now that I do not know a great deal about the mechanics of speakers and PA systems. I know some basic principles, but don't know much about crossing/loading etc. and I guess the impedance rating of the speakers would play a part as well. I can see the logic - a speaker emitting a squared wave pattern will be moving more violently than one which is producing a sine wave. Thoughts anyone? Joe Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 12, 2012 Share Posted November 12, 2012 Basically, never listen to what that that guy says. Totally doesn't work like that. Only thing is a clipped wave (amps can't actually put out square waves, needs infinite bandwidth) can toast tweeters an midranges if there is a passive crossover. Quote Link to comment Share on other sites More sharing options...
bremen Posted November 12, 2012 Share Posted November 12, 2012 Doesn't really apply to bass or guitar speakers. It's important for hifi or PA speakers though. The LF speakers are designed to take more power as there's more LF energy than HF in a musical signal. Clipping creates high levels of HF that the HF drivers just can't take. A single speaker can deal with a square wave just as easily as a sine (at the same power). Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 12, 2012 Share Posted November 12, 2012 Plenty of bass speakers have HF elements in them. Quote Link to comment Share on other sites More sharing options...
LawrenceH Posted November 12, 2012 Share Posted November 12, 2012 (edited) The guy you were talking to is wrong, but it's a poorly-understood topic and there is an element of truth in the idea that clipping can be dangerous. As has been said, in a system employing passive crossovers it is a particular issue. But something that's often overlooked is that speaker thermal power handling is rated in watts RMS, an average power value. A sensible measure for a driver where heat dissipation is a limiting factor. Amplifier outputs are also rated in watts RMS, however this will be to a rated or derived distortion value. Amps are often limited by peak voltage output. By driving an amplified into clipping, you can (if the amp's power supply is good enough) push out an average power value beyond its clean RMS capability. If you get really extreme, this could allow an amp to fry a speaker despite the RMS rating suggesting otherwise. The solution assuming you need more volume isn't a more powerful amp though - that'd allow you to push out a cleaner signal but the average power to get to similar perceived level would still be too high -you need more speakers. Edited November 12, 2012 by LawrenceH Quote Link to comment Share on other sites More sharing options...
iiipopes Posted November 12, 2012 Share Posted November 12, 2012 It's not that a person is "more likely" to blow a speaker underpowered, but it can happen. In a nutshell, it's this: when the amp is peaked out and can't deliver any more power, it clips the signal. These clips are, in essence, immediate DC going to the speakers. Because it is a clip, the ramp on the front side of the wave form is pretty steep compared to non-clipping signal. So one or both of two things can happen: 1) the speaker perceives an immediate jump in signal, and if it's too compliant, can blow its extension on the overshoot, and 2) DC means amperage, which means heat, which over time, if the speaker coil can't dissipate the heat, it will burn out the coil or disintegrate the coil form from the heat, or even kill the magnet (old Alnico speakers) Most new speakers, especially musical instrument and reinforcment drivers, are designed to take at least some abuse. But the best bet is, going in, match everything so that the rated load of the speakers is at least the rated power ouput of the amp, if not more, and always watch the power amp to make sure it doesn't clip. Most modern amps have some sort of protection circuit or "soft clipping" circuit that also helps prevent too much DC from clipping from going to the speakers, and/or a thermal protection shutdown. And occasional "red" peaks are no big deal, but the amp should always be monitored visually to make sure it isn't constantly clipping, if for no other reason than the deterioration of the sound quality from the distortion. Quote Link to comment Share on other sites More sharing options...
Noisyjon Posted November 12, 2012 Share Posted November 12, 2012 (edited) A useful read on the subject: [url="http://barefacedbass.com/technical-information/mythbusters1.htm"]http://barefacedbass...ythbusters1.htm[/url] Edited November 12, 2012 by jonthebass Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 12, 2012 Share Posted November 12, 2012 [quote name='iiipopes' timestamp='1352759555' post='1867214'] It's not that a person is "more likely" to blow a speaker underpowered, but it can happen. In a nutshell, it's this: when the amp is peaked out and can't deliver any more power, it clips the signal. These clips are, in essence, immediate DC going to the speakers. Because it is a clip, the ramp on the front side of the wave form is pretty steep compared to non-clipping signal. So one or both of two things can happen: 1) the speaker perceives an immediate jump in signal, and if it's too compliant, can blow its extension on the overshoot, and 2) DC means amperage, which means heat, which over time, if the speaker coil can't dissipate the heat, it will burn out the coil or disintegrate the coil form from the heat, or even kill the magnet (old Alnico speakers) Most new speakers, especially musical instrument and reinforcment drivers, are designed to take at least some abuse. But the best bet is, going in, match everything so that the rated load of the speakers is at least the rated power ouput of the amp, if not more, and always watch the power amp to make sure it doesn't clip. Most modern amps have some sort of protection circuit or "soft clipping" circuit that also helps prevent too much DC from clipping from going to the speakers, and/or a thermal protection shutdown. And occasional "red" peaks are no big deal, but the amp should always be monitored visually to make sure it isn't constantly clipping, if for no other reason than the deterioration of the sound quality from the distortion. [/quote] There is no DC from a not broken amp. Doesn't work like that. Even if it did, dc doesn't break speakers, you can put a 9v battery across a speaker and it is fine. Quote Link to comment Share on other sites More sharing options...
51m0n Posted November 13, 2012 Share Posted November 13, 2012 [quote name='Mr. Foxen' timestamp='1352764298' post='1867287'] There is no DC from a not broken amp. Doesn't work like that. Even if it did, dc doesn't break speakers, you can put a 9v battery across a speaker and it is fine. [/quote] +1 Yup, used to do that to check 15" cones were all wired in right on old PA kit, they'd all push to the front a bit and sit there, if on ewas wrong it would pop to the back. Probably not hugely good for them, but having said that I never, ever blew a speaker in my life..... (note to self, could try harder??) Quote Link to comment Share on other sites More sharing options...
Musky Posted November 13, 2012 Share Posted November 13, 2012 It's at times like this I wish this site still had a wiki. Quote Link to comment Share on other sites More sharing options...
BOD2 Posted November 13, 2012 Share Posted November 13, 2012 This discussion seems to pop up on all of the music forums on a regular basis - and it always refuted successfully. But then it appears again... It seems to have stemmed from a misinterpretation of this article by JBL [url="http://www.jblpro.com/BackOffice/ProductAttachments/lowpower.pdf"]http://www.jblpro.com/BackOffice/ProductAttachments/lowpower.pdf[/url] However, if you read the very first sentence of the article it qualifies the article and shows why this does NOT apply, in general, to bass guitar rigs - "We occasionally hear of JBL owners who damage the [u][i]high frequency components[/i][/u] of their loudspeaker systems using amplifiers that are rated at less - rather than more - power output than recommended" (my italics) Note the italics. It seems every other person who reads this article chooses to ignore that first sentence ! Quote Link to comment Share on other sites More sharing options...
bertbass Posted November 13, 2012 Share Posted November 13, 2012 If it was true, you'd blow the speakers every time you stopped playing, turned the amp down, packed the gear away, loaded the cab in the van / car, etc., etc. Quote Link to comment Share on other sites More sharing options...
BILL POSTERS Posted November 13, 2012 Share Posted November 13, 2012 (edited) [quote name='Mr. Foxen' timestamp='1352764298' post='1867287'] There is no DC from a not broken amp. Doesn't work like that. Even if it did, dc doesn't break speakers, you can put a 9v battery across a speaker and it is fine. [/quote] If it clips into a square wave, that is DC, although only in very short pulses, isnt it ? But still 60 volts in short bursts is going to warm the speech coil up a bit. Cant see it doing damage unless you did it for a long time though. and as it would sound really bad thats unlikely. although with old speakers pushing the cones past their limits would soften them after a while and make them sound farty. Edited November 13, 2012 by BILL POSTERS Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 13, 2012 Share Posted November 13, 2012 [quote name='BILL POSTERS' timestamp='1352832999' post='1868126'] If it clips into a square wave, that is DC, although only in very short pulses, isnt it ? But still 60 volts in short bursts is going to warm the speech coil up a bit. Cant see it doing damage unless you did it for a long time though. and as it would sound really bad thats unlikely. although with old speakers pushing the cones past their limits would soften them after a while and make them sound farty. [/quote] Nope, the flat bits are on both sides of 0v line. You can tell a square wave isn't DC by the way 'wave' is in the name. Voice coil warms up anyway, incandescent light bulbs work off AC, they get warm. Most of the energy that goes to speakers is lost as heat due to inefficiency, regardless of waveform. Quote Link to comment Share on other sites More sharing options...
iiipopes Posted November 13, 2012 Share Posted November 13, 2012 (edited) [b][url="http://sound.westhost.com/clipping.htm"]http://sound.westhost.com/clipping.htm[/url][/b] "The composite input signal is made up of a 3.3V peak-to-peak sinewave at 1kHz, added to a 2kHz 3.3V P-P sinewave whose phase is shifted by 90° to obtain an asymmetrical waveform that has a peak amplitude that is almost twice as great in the negative direction as in the positive direction." ... "Before we continue, it is important to understand just [i]how[/i] clipping the waveform can introduce a DC voltage. First, look at the basic waveform details (two complete cycles are shown), both before and after it is clipped ... [center] [b][size=2]Figure 2.3 - Input Waveform Detail[/size][/b][/center] The total shaded area shows that the area above the zero volt line is exactly equal to the area below, therefore, the signal is perfectly balanced and there is no DC at all. When the amplifier chops off (clips) the section below the line marked 'Clipping Level', the two areas are no longer the same - the area in the lower part of the waveform is smaller because some of it has been removed when the amplifier overloads. Since the upper (positive) section of the waveform now has more area than the lower (negative) section, the overall waveform has a positive bias - this is seen as a DC voltage. No tricks, no special effects, just plain old physics at its most basic level." ... "Given the right (or wrong) signal and sufficient clipping, there is the real risk that a loudspeaker driver may even be damaged. The voicecoil may be slammed into the rear polepiece of the magnetic circuit, suspensions may be stretched and the assembly's alignment compromised. This will lead to eventual driver failure." ... "As noted, for power amplifiers used to drive a transformer, the DC component is even more of a problem. A typical transformer for these applications may have a primary resistance of well under 1 ohm, so even a small DC level will cause a very high current to flow. This will cause transformer saturation and possibly amplifier failure." Edited November 13, 2012 by iiipopes Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 13, 2012 Share Posted November 13, 2012 Yeah, copy pasted wrong, is still wrong. It is wrong from the first sentence: "Although it is recognised that a power amplifier should never be subjected to (overload) clipping". The existence of driven amps sounding awesome in music shows that is wrong. Quote Link to comment Share on other sites More sharing options...
51m0n Posted November 13, 2012 Share Posted November 13, 2012 Wow, a signal with a DC offset, like about 99.8% of music then (if you measure a short enough amount of it, like half a cycle) Quote Link to comment Share on other sites More sharing options...
bremen Posted November 13, 2012 Share Posted November 13, 2012 [quote name='iiipopes' timestamp='1352837336' post='1868237'] "As noted, for power amplifiers used to drive a transformer, the DC component is even more of a problem. A typical transformer for these applications may have a primary resistance of well under 1 ohm, so even a small DC level will cause a very high current to flow. This will cause transformer saturation and possibly amplifier failure." [/quote] This is apalling horseshit, as we electrical engineers say. Valve amps with transformer outputs are exactly what 99% of guitarists use, and 99% of that 99% regularly drive them well into clipping 99% of the time. Quote Link to comment Share on other sites More sharing options...
iiipopes Posted November 14, 2012 Share Posted November 14, 2012 (edited) Yes, but don't beat around the bush. Tell me how you really feel. I love a good debate. Now, I own a Marshall Master volume 2203 from 1975, and have played both guitar and bass (and keys, and tuba, and...) since then, and trumpet since 1973 and piano since 1970. I've been cranking the stuffing out of the preamp knob on my 2203 for probably longer than many of the people posting on the forum have been alive. My amp is just fine. My Celestion Vintage 30's, and before that my Jensen Concert Series speakers (a notoriously low-power handling, but great tone for jangle speaker), are just fine. I wondered how much flak this post would receive. I expected gentlemanly disagreement, but not the emotional outbursts. There you have it. The only speakers I have ever blown, personally, were those which had damaged or deteriorated suspensions, and therefore were going to blow anyway in time, or from massively overpowering them. (100w through a 25w speaker, bass through a guitar speaker in an open back instead of sealed or ported cabinet, etc.) Edited November 14, 2012 by iiipopes Quote Link to comment Share on other sites More sharing options...
bremen Posted November 14, 2012 Share Posted November 14, 2012 Apologies, no offence intended, it was Mr Eliott's statement I was robustly addressing. The rest of your post, above, I have no argument with and it matches my experience. Neither of us appears to have blown speakers with underpowering. Quote Link to comment Share on other sites More sharing options...
iiipopes Posted November 14, 2012 Share Posted November 14, 2012 (edited) What concerns me more about blowing amplifiers is dissipation of heat. Even when operated "in parameters," valve/tube amps can get mighty hot. That's how I got my 2203. Someone had killed it - it had gotten so hot the top plastic vent plate melted down into a trough! (It's now a great place for putting spare connectors, preamp tubes, picks, etc. for the gig). I had it rewired for EL-34's instead of the stock 6550's that it had for the American market, and I run a pair of Electro-Harmonix "big bottle" 6CA7's (think 6L6GC on steroids -- clean, with a nice breakup -- 6550 plates but EL34 grid bias). Properly ventilated, biased and loaded, when I played more guitar, I could run it all night cranked with two of the four output tubes pulled, run a 32 ohm cab (wired four nominal 8-ohm speakers in series) instead of a 16 ohm cab so I could push it harder to get tone without necessarily increasing volume, and it would run all night only moderately warm, keeping it away from the back wall and not putting anything on top of it. Yes, these new class D amps are great for efficiency, cooling, clean tone, and light weight, and I run a new Carvin MB12 with an extension cab as my gigging bass rig for both electric and double bass, but nothing beats what Jim Marshall's large power transformers can do for guitar for the output stage of his amplifiers! You don't worry about underpowering. You worry about damaged ear drums and loosening fillings, with tone! Edited November 14, 2012 by iiipopes Quote Link to comment Share on other sites More sharing options...
dincz Posted November 14, 2012 Share Posted November 14, 2012 [quote name='Mr. Foxen' timestamp='1352734861' post='1866702']amps can't actually put out square waves, needs infinite bandwidth [/quote] Hmm, the same logic would suggest that square waves don't exist. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 14, 2012 Share Posted November 14, 2012 (edited) [quote name='dincz' timestamp='1352925266' post='1869509'] Hmm, the same logic would suggest that square waves don't exist. [/quote] Yep. They are entirely theoretical. you can have them exist in the digital realm sort of, because that's theory, but not in substance. Any component with an inductance or capacitance immediately limits your bandwidth and rounds off the wave. Edited November 14, 2012 by Mr. Foxen Quote Link to comment Share on other sites More sharing options...
tauzero Posted December 4, 2012 Share Posted December 4, 2012 [quote name='dincz' timestamp='1352925266' post='1869509'] Hmm, the same logic would suggest that square waves don't exist. [/quote] They're the product of an infinite series of odd-order harmonics (which is why clipping produces a sound which has lots of odd-order harmonics in it). But in the real world, there's things like slew rate and damping to consider. Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted December 7, 2012 Share Posted December 7, 2012 [quote name='iiipopes' timestamp='1352911738' post='1869325'] nothing beats what Jim Marshall's large power transformers can do for guitar for the output stage of his amplifiers! [/quote] Wha? Marshall tone is all about the underrated transformers. Quote Link to comment Share on other sites More sharing options...
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