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BGM68 July 2011 BAREFACED BASS BUT THIS GOES TO 11... But This Goes to 11… About The Author Welcome to the world of bass rigs. C. ALEXANDER CLABER What Exactly Is through zero, then the peaks – the average level will be close Alex rst picked up a bass RMS Power? have to be noticeably higher to zero due to all the muted when studying engineering at Technically this isn’t correct than the average. In fact, as sound while the peak on the university, and his quest for sonic terminology, but as ‘watts ampli ers are rated with a sine slap may take your amp right perfection led him to found RMS’ are used in the European wave the peak power has to be to its limits. Barefaced Audio, while also standards we’re stuck with at least 1.414 x (ie sqrt2) higher than the RMS power. leading The Reluctant, an alt-ska/ them. Regardless, the crux of The Joys Of Processing funk out t. the matter is that power in Recently I had the fun of using music is never constant – if some of our Big Series bass the voltage doesn’t vary then Crest Factor – It’s Not cabs as a rather ne PA system you won’t hear any sound About The Whiteness IN ASSOCIATION WITH playing recorded music (in because music is made up of Of Your Teeth! this case mostly drum ’n’ bass). pressure changes in the air Therefore, if we compare the These cabs are not hugely and you won’t get them from peak and average voltage of a e cient (trading o sensitivity a loudspeaker without voltage sine wave the ratio is 1.414:1, for bass depth) but, despite changes. And if voltage isn’t thus the peak and average This column is brought to you in that, a handful of cabs reached constant then neither is power! power is 2:1, or in audiospeak association with Barefaced Ltd deafening club SPL in a fairly However, peak power ratings 3 dB. We call this ratio the ‘crest who manufacture high-output large venue without being aren’t terribly useful because factor’, and it describes the ratio speaker cabs for the gigging driven remotely hard. Here’s they’re not a great indicator of peak to average height of bassist. Barefaced have recently why: let’s say that the amp that of real-world performance, so any wave – so it can be applied launched their new Big Baby and was driving them produces we have to use average ratings to ocean waves too. If a tsunami Big Twin cabs, the most accurate 1000 W/ch into 4 ohms and and the way to get them is to happens on an otherwise still and extended range bass cabs conveniently (often the case multiply the square root of the day then the crest factor will be ever made. An archive of previous with PA amps) has a ladder of articles plus a glossary of terms can mean of the voltage squared huge, while a stormy day may LEDs on the front showing how be found at with the square root of the exhibit a very large average much power it’s producing. www.barefacedbass.com mean of the current squared. wave height but the largest One LED for -20 dB, one for That sounds quite complicated, waves may be little larger than -10 dB and one for -3 dB. Once but the reason is that the mean the typical waves, hence the things start getting loud the (average) voltage of a sine wave crest factor is low. -20 dB LED stays on almost is zero because half the wave constantly and the -10 dB LED is positive and half is negative. Fig 2 – Crest Factor ickers frequently. The -3 dB Square the voltage and it all LED never lights. To put this in goes positive, then square root perspective this means that the the mean to get the values system is almost continuously correct. Ditto for current. putting out between 20 W (-20 And so we have our RMS dB from 2000 W total power) power thing. and 200 W (-10 dB from 2000 W) and frequently putting out So how does this relate to more than 200 W, but never Fig 1 – Peak vs RMS Power playing bass guitar (or double reaching the 1000 W half- bass)? Well, if we take a double power point. bass and bow quarter notes Take a bass guitar, play fortissimo, then the average it through a clean preamp level will be high but the peaks and this same amp and will be little louder than the complement of speakers and average so the crest factor will turn things up until the -10 dB be low. Likewise, if we play LED is frequently ickering. At You may have now put two steady but loud 8th notes this point the -3 dB LED will also and two together and realised ngerstyle on bass guitar then be ickering occasionally (and that your ampli er can thus the crest factor will be low. On if there’s a clip LED that might deliver more power than it’s the other hand, if we play just light now and again) and it will rated for – because if you’re one very loud slapped note be loud and thunderous, but calculating average power and once every couple of bars then no one would say it’s as loud the alternating wave passes the crest factor will be very high as that recorded music. Then 66 BASS GUITAR MAGAZINE Barefaced Bass_1nw.indd 1 02/06/2011 12:57 BAREFACED BASS BUT THIS GOES TO 11... get a compressor and use it words by compressing the density as you go higher in clipping (thus further lowering to squish down the peaks of bass guitar we’ve decreased the frequency so it more closely the crest factor) it becomes the louder notes from the bass crest factor. matches real music) through it much easier to reach a high guitar and you’ll notice that with a crest factor of 6 dB. This average power level and thus you can turn things up more means that the peaks are four overheat voice coils. without any more activity from What On Earth Is The times the average level. So a the -3 dB LED. Then add a soft Point Of All This? loudspeaker rated at 500 W will limiter before the compressor, Last time we investigated the have withstood being driven by Overexcursion Issues tweak the compressor further power distribution of a typical a 2000 W ampli er so hard that When you push a speaker too and you can turn things up bass guitar and what happens the ampli er almost clips on hard in the lows it overexcurses, even more. At this point the -3 when you clip that signal. Our the peaks, yet averages 500 W causing increased distortion dB LED is never lighting, yet the main point was that clipping continuous power output over and compression. Continue bass guitar is starting to sound increases the proportion of a number of hours, without with this and you can cause almost as loud as the recorded power in the high frequencies, thermal failure. This doesn’t damage to the speaker. music with similar -10 dB LED and that although this is a take into account how far the Fortunately, with clean bass activity. For the nal step stick serious issue with PA systems speaker can move without sounds this is pretty obvious an overdrive pedal in front of it isn’t an issue with clean bass distortion or damage, which is and a good warning sign to the soft limiter and you’ll be guitar because there’s so little the main limiting factor with back o the volume or the bass able to get even more loudness power up there to start with. bass guitar, but we don’t have knob. However, with dirtier without the -3 dB LED lighting But if we start running our bass space to discuss that here. bass sounds it can be hard to – in fact this tone might be so through various e ects most of detect the di erence between squished that it sounds even them will add extra mid range a deliberately grindy pedal/ louder than the recorded music and treble energy, especially Clipped Signals amp or distressed loudspeaker! at a similar peak level. overdrive, distortion, fuzz and And Crest Factor The key point in these ve synth pedals. If you then run Last time round our main examples (recorded music, those signals with greater treble concern regarding clipping Bass Rig Power Matching clean bass guitar, compressed content through an ampli er was how it changes the Rule Of Thumb #2 clean bass guitar, limited and that’s clipping, you’ll further distribution of sound energy, If you’re someone that likes compressed clean bass guitar, increase the treble energy skewing it towards the high messing with serious dirt and limited and compressed and that’s when tweeters start frequencies. This was because e ects, then it’s wise to use overdriven bass guitar) is that complaining. Fortunately this we were looking at more a larger rig than if you were despite all having relatively usually sounds pretty nasty, so typical, relatively clean and playing with a clean sound in similar peak levels, the average most players will back o on the relatively uncompressed bass the same band, and wise to level is much higher for the treble or volume before things guitar sounds which exhibit use speaker cabs with power heavily processed recorded go pop, but this isn’t always the very high crest factors.
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