alexa3020 Posted January 17 Share Posted January 17 800w class D into a 200w 4ohm Cab is not a good idea right ? However... Will I get away with it if the head is not cranked. The head is a TC BH800 (renowned for overexaggerating wattage) and did I read something about not having to worry so much when dealing with class D heads? Thanks Alex Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted January 17 Share Posted January 17 The range of power usefulness is 4:1. With a 200w cab amps ratings of between 50 and 800 watts is appropriate. Frankly if you blow a bass cab it's entirely your fault, because it will severely distort long before it will blow. 5 Quote Link to comment Share on other sites More sharing options...
Baloney Balderdash Posted January 17 Share Posted January 17 (edited) As noted above not unless you keep turning your amp up above the point where it actually sounds good. Edited January 17 by Baloney Balderdash 1 Quote Link to comment Share on other sites More sharing options...
alexa3020 Posted January 17 Author Share Posted January 17 Cheers guys Quote Link to comment Share on other sites More sharing options...
tauzero Posted January 17 Share Posted January 17 I use a Tecamp Puma 900 with a 100W BC micro cab for open mic nights. No problems. 2 Quote Link to comment Share on other sites More sharing options...
Paul S Posted January 17 Share Posted January 17 Sorry! I thought this might be a thread about parliament. As you were. 17 1 Quote Link to comment Share on other sites More sharing options...
Crusoe Posted January 17 Share Posted January 17 1 minute ago, Paul S said: Sorry! I thought this might be a thread about parliament. As you were. Order! Order! 1 Quote Link to comment Share on other sites More sharing options...
stevie Posted January 17 Share Posted January 17 1 hour ago, tauzero said: I use a Tecamp Puma 900 with a 100W BC micro cab for open mic nights. No problems. Question for you: would you be happy to let one of the open night punters play through that rig? 1 Quote Link to comment Share on other sites More sharing options...
Downunderwonder Posted January 18 Share Posted January 18 A good rule of thumb is if it stops getting appreciably louder when you turn it up then you should turn it back down a bit instead. Fix the lack of volume some other way, usually by getting guitar player to point his cab at his own head. 1 Quote Link to comment Share on other sites More sharing options...
sandy_r Posted January 18 Share Posted January 18 (edited) 12 hours ago, alexa3020 said: 800w class D into a 200w 4ohm Cab is not a good idea right ? ...... Will I get away with it if the head is not cranked. The head is a TC BH800 ... the clue is on the backplate: the manufacturer is stating that the effective operating power drawn by the amp (including the PSU) is typically 200W av. just before onset of clipping (ie. less than 200W will be output to the speaker) Whether this is a meaningful measure is another matter So, if your speaker rating is valid, then technically your setup is ok as long as you keep the max drive level in the clean output region (personally, i'd feel happier with a higher-rated speaker, to avoid ...Oops!) This is why you have to be careful using Drive/Fuzz effects, 'cause it can mask the fact that a speaker is being overdriven - and, in the case of the BH800, there's up to another 600W where that came from, just ready & waiting to to weld the speaker coil to the magnet pole As others have said, proceed with caution! Edited January 18 by sandy_r Quote Link to comment Share on other sites More sharing options...
tauzero Posted January 19 Share Posted January 19 On 17/01/2024 at 20:56, stevie said: Question for you: would you be happy to let one of the open night punters play through that rig? Yes, as long as I supervised them plugging in. It was easily loud enough to compete with the PA they were using. But as I was the only bassist, it didn't matter. Quote Link to comment Share on other sites More sharing options...
agedhorse Posted January 22 Share Posted January 22 On 17/01/2024 at 19:11, sandy_r said: the clue is on the backplate: the manufacturer is stating that the effective operating power drawn by the amp (including the PSU) is typically 200W av. just before onset of clipping (ie. less than 200W will be output to the speaker) Whether this is a meaningful measure is another matter So, if your speaker rating is valid, then technically your setup is ok as long as you keep the max drive level in the clean output region (personally, i'd feel happier with a higher-rated speaker, to avoid ...Oops!) This is why you have to be careful using Drive/Fuzz effects, 'cause it can mask the fact that a speaker is being overdriven - and, in the case of the BH800, there's up to another 600W where that came from, just ready & waiting to to weld the speaker coil to the magnet pole As others have said, proceed with caution! No, that is not what it means. That is the power that is drawn by the amp at 1/8-rated audio power in rms metrics, into the minimum rated load. It's a minimum labeling requirement by the global safety regulations (assuming that it does comply with IEC 62368-1. The actual amount drawn can't exceed 200 watts but may in fact be less to account for any duty cycle additions beyond 12.5% that the manufacturer wishes to address. It's fairly easy to take that power consumption number and calculate the approximate rated audio power... Since the average efficiency of a SMPS + class D amplifier is 85%, take 800 watts RMS, multiply it by 0.125 and divide the result by 85% and this number must be less than 200W. (800 x .125)/.85 = 118W which is less than 200W. Now is this amp a good idea for a 200 watt/4 ohm speaker? It's perfectly fine as long as you don't have an accident, have a lapse in good judgement or have unrealistic expectations of the speaker's capabilities. It's one reason why we see blown speakers, nobody's perfect. 5 Quote Link to comment Share on other sites More sharing options...
Gypsyfolk Posted January 22 Share Posted January 22 Octave and distortion pedals seem to cause speakers to let go more than loud clean IME Quote Link to comment Share on other sites More sharing options...
sandy_r Posted January 22 Share Posted January 22 7 hours ago, agedhorse said: No, that is not what it means. Well, we'll obviously have to agree to differ on that then - interestingly we don't disagree on the bottom line that the amp can be used carefully (ie. "less than 200W.") with that speaker, as long as the system is operated below clipping You are obviously very welcome to have your own opinion on why the guideline value of "1/8 max. Power" (which i showed in a photoclip) was chosen by the regulating bodies to be at that level Have a nice day 😊 1 Quote Link to comment Share on other sites More sharing options...
sandy_r Posted January 22 Share Posted January 22 3 hours ago, Gypsyfolk said: Octave and distortion pedals seem to cause speakers to let go more than loud clean IME Yes, It's a fact - as the signal waveform alters from basically Sinewave form (ie. 'Clean') and heads towards Squarewave form (ie.the sum of the fundamental tone plus all the odd-harmonics) the average power content of the signal can nearly double - hence why you should be careful not to overdrive the speaker when using effects like distortion, octavers ...or just by driving the amp into clipping (again, it starts to increase the average output power content) It's a good idea to over rate speaker power compared with the amp - and make that at least double if you want to use effects which take the signal out of the 'clean' zone Quote Link to comment Share on other sites More sharing options...
alexa3020 Posted January 22 Author Share Posted January 22 This is becoming quite an interesting thread. I have decided to power the speaker with a markbass LM3 500w instead of a tc bh800. I'm slightly more comfortable with a lower wattage amp although I know I still have to be really careful and use my ears for any distortion because the amp is still possibly overpowered. The aim for this rig is to use it as an alternative lightweight rig for when playing smaller venues or when I know I'll have decent PA support and I just need to use it for monitoring onstage. I played a gig in my local pub and my current rig was overkill. Ideally I would have got a higher rated speaker, but I didn't want to spend huge amount and the cab came up fairly locally & speaker sounded plenty loud enough when driven by a GK MB200. 1 Quote Link to comment Share on other sites More sharing options...
Japhet Posted January 22 Share Posted January 22 On 17/01/2024 at 19:24, Crusoe said: Order! Order! 2 pints of lager and a packet of crisps please. 1 1 Quote Link to comment Share on other sites More sharing options...
Frank Blank Posted January 22 Share Posted January 22 On 17/01/2024 at 19:22, Paul S said: Sorry! I thought this might be a thread about parliament. As you were. ☝️ actual genius. 1 Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted January 22 Share Posted January 22 6 hours ago, Gypsyfolk said: Octave and distortion pedals seem to cause speakers to let go more than loud clean IME Only in the sense that when you use them they can mask the distortion that results from pushing drivers past their linear excursion limit. The distortion doesn't affect the drivers at all, if they did guitar players would be swapping them from gig to gig, if not from set to set. But guitar drivers have far more leeway between when they reach xmax and when they reach xlim (look up those terms) than bass drivers. https://speakerwizard.co.uk/thiele-small-parameters-what-are-they-for/ 1 Quote Link to comment Share on other sites More sharing options...
sandy_r Posted January 22 Share Posted January 22 (edited) 8 hours ago, Gypsyfolk said: Octave and distortion pedals seem to cause speakers to let go more than loud clean IME 1 hour ago, Bill Fitzmaurice said: Only in the sense that when you use them they can mask the distortion that results from pushing drivers past their linear excursion limit. The distortion doesn't affect the drivers at all, if they did guitar players would be swapping them from gig to gig, if not from set to set. But guitar drivers have far more leeway between when they reach xmax and when they reach xlim (look up those terms) than bass drivers. https://speakerwizard.co.uk/thiele-small-parameters-what-are-they-for/ No argument about the masking issues of distortion-type effects (in fact, someone made that point a few posts earlier ...hey -you could look it up! 😉) Amps overdriving the speakers into clipping (presenting as distortion) is an indication that the speakers will suffer thermal damage if exposed to continued power in excess of their rated power handling If guitarists aren't swapping their drivers out every set, then either that is a strawman argument, or the guitarists are 'cleantone'-loving gentle souls, or just maybe ...sheesh... their speakers are suitably over rated for their amps ...can we all get back on topic to blowing up the speaker @HoP now? Edited January 22 by sandy_r Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted January 22 Share Posted January 22 49 minutes ago, sandy_r said: Amps overdriving the speakers into clipping (presenting as distortion) is an indication that the speakers will suffer thermal damage if exposed to continued power in excess of their rated power handling Only when those drivers are tweeters and the occasional midrange. The increase in power density {look it up} only occurs in the harmonics, not the fundamentals. That being the case woofers are unaffected. It's different with respect to tweeters and some midranges. The power density of a normal clean signal drops by 3dB with each octave increase of frequency. That's why pink noise is used to test speakers, as it also drops in power density by 3dB per octave increase in frequency. For this reason the actual thermal capacity of a tweeter rated for use in a 100w speaker will seldom be more than 10 watts. Clipping upsets the apple cart by delivering more high frequency content than normal, so said 10w voice coil may receive 20w or more. That's why clipping can thermally kill tweeters. The power density of the signal to the woofer is unaffected, so clipping doesn't affect them at all. This goes to the Myth of Underpowering, a myth long ago debunked, but like most myths it refuses to die the death it deserves. 4 Quote Link to comment Share on other sites More sharing options...
alexa3020 Posted January 22 Author Share Posted January 22 Is the RMS power rating for an amp head based on everything at max including EQ? Quote Link to comment Share on other sites More sharing options...
sandy_r Posted January 22 Share Posted January 22 29 minutes ago, Bill Fitzmaurice said: ... The increase in power density {look it up} only occurs in the harmonics, not the fundamentals ... The power density of the signal to the woofer is unaffected, so clipping doesn't affect them at all. ... This goes to the Myth of Underpowering, a myth long ago debunked ... Er, yes - the difference between a basic Sinewave and Square IS the harmonics - A Woofer can easily reproduce at least the 5th harmonic (no Strawman Inc. Tweeter needed 😉) So, the power density of the signal to the woofer IS affected (as by clipping) I think you are Myth taken - it's ok, it's just humour (look it up) Quote Link to comment Share on other sites More sharing options...
sandy_r Posted January 22 Share Posted January 22 (edited) 32 minutes ago, alexa3020 said: Is the RMS power rating for an amp head based on everything at max including EQ? It's an upper limit to the total clean conversion of Input Power into a load - if you connected, say, a 4 ohm non-inductive resistor at the amp output and had a suitably math-capable 'scope monitoring the output voltage, then the scope should show that the amp can achieve an undistorted ouput signal at its max RMS rating indefinitely, regardless of how the EQ profile is set (N.B. the gain or volume may need to be adjusted after changes to the EQ to restore an undistorted max RMS value) [Edit] so to clarify for your 'everything at max' - no, the amp may be capable of overdriving the output (ie. into distortion) with everything at max - in that case you could have all the EQ at max, have to reduce either Vol or Gain appropriately, but still achieve the max RMS rated output Edited January 22 by sandy_r 2 Quote Link to comment Share on other sites More sharing options...
Lfalex v1.1 Posted January 22 Share Posted January 22 (edited) Quite apart from judicious use of the master volume control, some sort of compression and possibly an HPF (or something that acts like one) can be a worthwhile addition. Tames nasty peaks, and prevents unwanted low frequencies that the cab can't reproduce from making it past the HPF. Edited January 22 by Lfalex v1.1 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.