Bill Fitzmaurice

[quote name='alexclaber' timestamp='1446651008' post='2901157'] This article that I read years ago was what first got me thinking about it: [url="http://www.meyersound.com/support/papers/amp_power.htm"]http://www.meyersoun...s/amp_power.htm[/url] [/quote]Referencing the link, here's the issue: [i]Recently Meyer Sound measured a well-known dual 18” subwoofer system that came with a power amplifier. The amplifier’s power supply rail when it was not being driven sat at 160 volts. Using this rail voltage, we could calculate the instantaneous peak power for a 4 ohm (resistive) load to be: [/i][i] E[sup]2[/sup]/R = 160[sup]2[/sup]/4 = 6,400 watts per channel[/i] That's not how one measures amp output. The correct method is to feed the amp pink noise, turn up the volume until THD reaches the design spec into the specified load impedance, then measure the output voltage. Anything else is smoke and mirrors.

[quote name='Jono Bolton' timestamp='1446496506' post='2899874'] assuming that the cab is completely empty inside, would the vertical rods need to run the full height of it? I would have thought that that length of rod would have license to oscillate from the vibration. [/quote]With rods, and they can be square or round, of an inch diameter oscillation isn't an issue, as there are no forces in that direction, it's all tension and compression. FWIW I only use 1/2 inch plywwod, even with concert grade subs, and they don't vibrate. This illusltrates why: Using only the single red brace to connect opposed panels the vibration resistance of a 1/2" plywood panel is the same as a full inch of unbraced plywood. Using the blue braces as well increases the stiffness to the same as two inches of unbraced plywood. Commercial cabs tend to use thicker materials with inadequate or even no bracing, as that greatly reduces labor costs, and when corners are cut it's usually inside the cab, where it can't be seen.

[quote name='garyod7' timestamp='1446500800' post='2899920'] The stuff was 2 months old by the way just when you mention how long stuff lasts or doesn't! [/quote]At 2 months old it should be under warranty.

Nothing lasts forever. I'd only suspect a problem if you'd blown all four drivers. But don't assume that the knob positions have any relationship with the amp output. All that 12:00 indicates is that it's more gain than 11:00 and less than 1:00.

[quote name='dincz' timestamp='1446486503' post='2899773'] Their rated powers are measured differently. [/quote]No, a watt is a watt. A valve amp and SS amp of the same power will both deliver the same voltage and current into a given load. A valve amp can sound louder than an SS amp even though the delivered voltage and current from the valve amp is less because of the alteration of the waveform by the natural compression that valves impart. This begs the question as to whether you can duplicate the effect with SS by using a compressor, and the answer is yes.

[quote name='Jono Bolton' timestamp='1446472357' post='2899565'] Is it worth running a brace from top to bottom? Would I need one running width-ways across the middle to support it? [/quote]This is what the interior of a well made cab looks like. Few do.

[quote name='Jono Bolton' timestamp='1446455545' post='2899401'] My head is an Ashdown ABM 300 which is reasonably small and lightweight, when I got the cab I tried it out with a Mark IV which may have weighted the cab to stop it vibrating. [/quote]A heavy head would be less likely to vibrate atop the cab, but nonetheless the cab panels should not be vibrating in the first place. A well braced cab won't even cause a pint to vibrate off. That's how I test my cabs. Of course, you can't take the results of only one test as valid, only after a dozen or so pints can you be sure.

[quote name='Japhet' timestamp='1446458986' post='2899428'] why is it that a 200 Watt valve amp outperforms a 600Watt class D? [/quote]Signal compression. Valves do, SS doesn't.

Bracing in older, and for that matter many newer, cabs is often inadequate, if not missing entirely. That's what I'd check first.

[quote name='4-string-thing' timestamp='1446309701' post='2898522'] What I don't understand is why x4 the power makes no noticable difference. [/quote]Just because the Ashdown claims 4x more power that doesn't mean you were getting it. You'd only know for sure by measuring the output voltage of the two.

[quote name='fleabag' timestamp='1446302896' post='2898478'] So that guitarist was right ? [/quote]There's a first time for anything. [quote]1db is just noticable but only in the midrange ? [/quote]The midrange is what Bell Labs concentrated on, as their research was mainly related to telephone transmission, which in the 1920s was mainly in the midrange, for maximum intelligibility. They weren't so much concerned with audibility as they were transmission losses over long phone lines. Sensitivity varies with both frequency and with loudness, so 1dB as the threshold is by no means carved in stone.

[quote name='4-string-thing' timestamp='1446306541' post='2898501'] Any explanation why my 575w Ashdown Head is (seems) no louder than my 125w Acoustic head through the same cab? [/quote]To sound twice as loud as 125w you'd need 1250w. There's also the matter of maximum driver excursion. Once that's reached more power applied won't make it louder, it will only add distortion. If your cab is loaded with 40 year old drivers chances are they run out of excursion around 40-50 watts each.

The decibel scale was originally calibrated by testing a few hundred people to determine the smallest average variation that they could hear in the midrange at normal conversation levels. That variation is 1dB. 3dB is what you get with a doubling of power, 6dB is what you get with a doubling of voltage swing, while 10dB (ten times the power) is perceived as a doubling of volume level.

[quote name='4-string-thing' timestamp='1446301126' post='2898457'] This is why I find it fascinating, even though I don't really understand it.... If only it went up to 11..... [/quote]The volume control acts like a water valve. One may configure a valve to be fully open with 1/4 turn, 1/2 turn. 3/4 turn or for that matter with ten turns.

[quote name='4-string-thing' timestamp='1446291071' post='2898357'] 120 db from a 125w amp..... Maybe thats just marketing hype too? [/quote]If a cab has 100dB/1w sensitivity it only takes 100w to reach 120dB. [quote]And that it got no louder after about 3 on the volume pot![/quote]Google 'gain structure'. The position of the knob has no relationship with the output. If you were to change the volume pot value and/or taper you would change at what knob position full gain is achieved. [quote]I always thought a Watts were like a miles-per-hour rating, [/quote]They're the same as a horsepower rating. In that vein, which will go faster, a 200HP vehicle or an 800HP vehicle? That depends on issues totally unrelated to power. A 200HP BMW will go considerably faster than an 800HP tank.

[quote name='Nicko' timestamp='1446213371' post='2897790'] I'm pretty sure there is some correlation between wattage and sound power level (measured in dB). [/quote]Only in so much that with a given speaker as more power is applied SPL goes up. But there is no simple x watts= x dB calculation. [quote]The last thing we need is manufacturers confusing us with decibel ratings. [/quote]That's one of the reasons given by manufacturers as to why they don't produce measured SPL charts. It's a smokescreen for the real reasons, those being either they don't want you to see them, or they don't have them. Or both.

[quote name='cybertect' timestamp='1445424018' post='2891310'] Here's some actual testing data, that suggests there is no practical difference in the frequency response between Monster or any other cables (whatever claims they may make) [url="http://www.ovnilab.com/articles/cables.shtml"]http://www.ovnilab.c...es/cables.shtml[/url] [/quote]This is the significant point made, which is exactly what I've already said : [i]These charts demonstrate [b]that with a passive instrument [/b]a cable's capacitance has a direct correlation to the amount of high-frequency content it can carry effectively. [/i] [quote]turning the tone control down a little would achieve the same thing in a more controllable way. [/quote]Turning the tone control down a little duplicates the effect of a high capacitance cable, as it also puts a capacitive load across the pickup output. What differs is the value of the capacitor. Since a tone control is intended to roll off the highs at a fairly low frequency, 1kHz or so, the cap used has a higher capacitance value than one would usually find even in a particularly inferior cable.

[quote]The argument about cables affecting tone is pretty bogus -[/quote]I discovered the difference that cables make circa 1966, when high capacitance coiled cords (telephone handset type wire) came along and very nearly took over the market. At the time I knew nothing about capacitance, or why it could cause high frequency roll-off bordering on extreme with passive pickups, but the difference in tone was obvious and undeniable. With straight cords capacitance tends to be less of an issue, but high capacitance tone killing straight cords do exist, the Monster Bass being one example. [quote] "Tone wood" is a complete fallacy in solid electric instruments and just another device used to part the unwary from their cash. [/quote]It made a very large difference in the basses and guitars that I've built. A few decades of experimentation led me to my final choice, all rosewood neck-through with semi-hollow body chambers similar to Rickenbacker. Tone wise a solid rosewood body is even better, but the weight is too much. One might not be able to identify whether a body is made of basswood or poplar or ash without seeing the grain, but the tonal difference is considerable.

[quote name='Ghost_Bass' timestamp='1444823522' post='2886358'] My drummer is a light hitter and i love it that way. Much more comfort on stage and i don't finish my gigs with my ears ringing. We use a PA (x2 15" subs + x2 12" tops - RCF) and we send almost everything to the mix. Drum kit is mic'ed on the drums and hit-hat (no snare or cymbals), the rest is all in the PA and mixed according to the venue. This helps us keep a low on-stage volume and we can enjoy the gig better, hearing everybody, and not getting a headache. I also would say that the sound we feed to the audience is more balanced and with better dispersion doing it this way. A decent PA for pubs isn't very expensive and with class-D/Neo is small and light to carry. It will improve the band's overal sound and help you do your job better, with more quality, and win you more gigs. [/quote]I agree. The backline, including the drums, need only be loud enough to hear on stage, with the PA covering the room. For that matter I run our guitar player though the stage monitors as well so that we can hear him, since he plays a1x12 combo at sensible levels. Huge backline played at crazy levels made some sense when there was no such thing as good PA, but that hasn't been the case within the lifetimes of most players today.

The point is that the average club band doesn't have a big enough system. They need to get the most possible out of the least amount of gear. That very much takes cardioid sub arrays and freestanding subs off the table.

[quote name='ironside1966' timestamp='1444164850' post='2880888'] I personally don't see the point in putting the subs at the back [/quote]The reasons for not placing subs out front is the resulting cancellation notch from Allison Effect, and the loss of boundary loading. It's true that the vast majority of users don't wall load their subs, and they split them left/right under the mains. Those are the two most often seen errors in subwoofer placement, by users who don't know what Allison Effect, boundary loading and the power alley are. I wouldn't put them on stage, I'd put them to one side or the other. As for the rumble, since the output of subs is omni-directional it won't matter much to the band if the subs are in front of or behind them. That's also why off to one side or the other will work equally as well as directly behind.

Subs in the back, or off to the side but still close to the back wall, is what you want. But only subs, running no higher than 100Hz, not full range cabs.

[quote name='Tdw' timestamp='1444071221' post='2880091'] Out of interest, what sort of cable would you suggest between a passive bass and a valve amp? A short one, or is it more than that? [/quote]As short as possible with the lowest capacitance you can find and 100% shielding. There are capacitance specs available from various wire manufacturers, like Belden, Canare and Mogami.

[quote name='PaulWarning' timestamp='1444066723' post='2880026'] reminds me of the great speaker/connect cable debate in the world of HiFi. The cynic in me tends to believe that charge someone enough money for something and they'll convince themselves they've not been ripped off, but, like I said I'm a cynic, and one with hearing damage as well [/quote]Hi fi interconnects and speaker cables are a different beast entirely, and yes, there's no justification for high prices there either. But they differ in that they don't have to deal with high impedance pickups driving relatively low impedance loads, ie, valve amplifiers. It's that particular combination that demands very low capacitance cables for best results. That's not the the case with interconnects between line level devices or speaker cables, or low impedance mics, nor for that matter active basses.

[quote name='discreet' timestamp='1443982901' post='2879212'] I currently believe that a one-piece maple neck on a P has a sound all its own [/quote]It does. All of the wood parts have their effect, based on their density. A maple versus rosewood fretboard won't make as much difference as an ash versus poplar body, but there will be some.