Magic Matt Posted September 8, 2014 Share Posted September 8, 2014 I freely admit the whole "match the amp watts and speaker watts" thing has had me confused for a long time. I never seemed to get a conclusive answer to whether you should have speakers more powerful than amp, or match, or amp more powerful than speakers... This link suddenly turned a light on for me - I think I get it now! - so I'm sharing in case others find it helpful too. http://brain21.net/blues/blog/?p=432 Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted September 8, 2014 Share Posted September 8, 2014 The problem is that it's incorrect, because like most laymen he's considering watts and that's not what matters. Voltage swing and driver excursion are. Suffice it to say that where watts are concerned if your amp is rated anywhere between one half and twice what your speakers are rated for you're fine. Quote Link to comment Share on other sites More sharing options...
dincz Posted September 8, 2014 Share Posted September 8, 2014 I got as far as multiplying wattage by 1.414. He obviously doesn't understand what he's writing about. Quote Link to comment Share on other sites More sharing options...
karlfer Posted September 8, 2014 Share Posted September 8, 2014 [quote name='Bill Fitzmaurice' timestamp='1410141005' post='2546532'] The problem is that it's incorrect, because like most laymen he's considering watts and that's not what matters. Voltage swing and driver excursion are. Suffice it to say that where watts are concerned if your amp is rated anywhere between one half and twice what your speakers are rated for you're fine. [/quote] Thank you for that Bill, it's something I've never got my head round. So, if I follow that, my Carvin BX700 COULD be used with cabs from 350watt to 1400watt quite safely? I always thought a bit more speaker watts than amp watts, so with the Carvin I would have looked min 800watts cabs. Mind I think my understanding was from my demo model 20 watt valve Marshall bass head, 50 watt Marshall bass cab bought for my Christmas present (on tick ) in Dec 73. I finished paying for my half in 75, immediately sold if for £30 to fund a HH combo. The last Marshall half stack that I saw, exactly like the one I had, was on FEEBay a couple years back at £2500 Shoulda kept mine then Quote Link to comment Share on other sites More sharing options...
xgsjx Posted September 8, 2014 Share Posted September 8, 2014 IIRC, how they measure the watts on an amp is by using a dummy load and a sine wave & measure the voltage with an oscilloscope. Now depending on what frequency the sine wave is, the amount of watts can vary greatly. Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted September 8, 2014 Share Posted September 8, 2014 [quote name='karlfer' timestamp='1410170694' post='2546682'] I always thought a bit more speaker watts than amp watts, so with the Carvin I would have looked min 800watts cabs. [/quote]Most cabs reach maximum driver excursion at no more than half their rated power, so that's all you need to get full output from them. You can have more power on tap if you wish, but you simply won't use it. The same applies to PA. Where PA differs to some extent is with respect to high frequency drivers. They can be harmed by clipping, so plenty of amp power used to be a necessity to prevent that, but clipping is very effectively prevented with electronic limiting, something which was not an option when this was written: http://www.jblpro.com/pub/technote/lowpower.pdf As for the link's take on guitar speakers, he misses that by an even wider margin. Most guitar drivers have such short xmax, 1mm or less, that they reach maximum uncompressed output in the lows with only 10-15w input. The power required where guitars get most their decibel output, between 500 and 2kHz, is quite low, and doesn't require massive driver capacity to handle it. Anyone doubting that has never been on the receiving end of a Vox AC-30. Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted September 8, 2014 Share Posted September 8, 2014 [quote name='Bill Fitzmaurice' timestamp='1410178204' post='2546782'] Most cabs reach maximum driver excursion at no more than half their rated power, so that's all you need to get full output from them. You can have more power on tap if you wish, but you simply won't use it. The same applies to PA. Where PA differs to some extent is with respect to high frequency drivers. They can be harmed by clipping, so plenty of amp power used to be a necessity to prevent that, but clipping is very effectively prevented with electronic limiting, something which was not an option when this was written: http://www.jblpro.com/pub/technote/lowpower.pdf As for the link's take on guitar speakers, he misses that by an even wider margin. Most guitar drivers have such short xmax, 1mm or less, that they reach maximum uncompressed output in the lows with only 10-15w input. The power required where guitars get most their decibel output, between 500 and 2kHz, is quite low, and doesn't require massive driver capacity to handle it. Anyone doubting that has never been on the receiving end of a Vox AC-30. [/quote] Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted September 8, 2014 Share Posted September 8, 2014 (edited) As I have owned both an AC30 and a Selmer Selectatone 30 ( i wish I still had them both) ,I can atest to their volume. Not as beefy as a 4x12 with a Marshall/Sound City/HiWatt/Simms Watt head but plenty where it reallly mattered. Is it me or was their just more balls in those early british valve Combos? Got to also say the AC30 bass was a POS. Edited September 8, 2014 by Chienmortbb Quote Link to comment Share on other sites More sharing options...
Magic Matt Posted September 8, 2014 Author Share Posted September 8, 2014 Try replacing the stock valves with some nicer ones. I replaced the valves in my Traynor YCV40 with some GEC tubes (new old stock) and it sounded much better. They were relatively new Sovtek valves I was replacing, so I do wonder if some of it may be down to simply valve characteristics. Even though the valves are rated the same the output jumped up a little bit and it sounds a bit punchier - maybe a little better response in the mid-range? Whatever it is, I like it. As for the link... I'll pop off and shoot myself later, lol Quote Link to comment Share on other sites More sharing options...
Bill Fitzmaurice Posted September 8, 2014 Share Posted September 8, 2014 [quote name='Chienmortbb' timestamp='1410215722' post='2547311'] Got to also say the AC30 bass was a POS. [/quote]So were 60s Fenders that were basically guitar rigs without reverb. Best guitar amp ever? '59 Bassman... with outboard reverb. Quote Link to comment Share on other sites More sharing options...
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