Bill Fitzmaurice

[quote name='vintage_ben' timestamp='1344023180' post='1758944'] My hunch is that the Ampeg 8x10 was much more expensive to develop than a modern day equivalent. [/quote]The 'engineering' required to develop the SVT cab took perhaps a week. It's a sealed box, how difficult is that? Theile modeling was not being used at that point, having been developed only a few years before and was only known of in Australia until 1971. Drivers using Theile parameters didn't come along until a few years after that. The SVT drivers already existed, guitar drivers BTW, which were also used in some Fender guitar combos. They were chosen based solely on their 32 ohm impedance, allowing a simple parallel wiring harness that the assemblers would be less likely to screw up than a complicated series/parallel scheme. If some 32 ohm twelves had been readily available they likely would have been used instead and quite possibly tens would never have become the standard for electric bass. The SVT driver has changed over the years, but it remains an inexpensive stamped frame unit that costs Ampeg about $30 each. The neo drivers used by Barefaced, for instance, come in at least four times that.

[quote name='Mog' timestamp='1343905577' post='1757057'] This confuses me. Is the only thing that can cause this proximity to the stage floor or is it some new fangled physics I haven't heard about. [/quote]The physics of dispersion by a sound source were quantified in the 1930s. [quote]The thing is you don't want the bass to go everywhere on a controlled stage as it is a bugger to get rid off if it bleeds into other signals.[/quote]The low frequencies [i]always [/i]go everywhere. Below roughly 250Hz the radiation pattern of a typical bass cab is 360 degrees. Above that dispersion progressively narrows as the wavelengths become shorter. The wider the source the greater the disparity between low frequency and high frequency dispersion. That disparity is minimized by keeping the source as narrow as possible. Contrary to popular belief this is why midrange drivers are smaller than woofers, and tweeters are smaller than midranges. As the operating range of drivers goes higher in frequency the size of the drivers is reduced not for the purpose of extending the operating range of the driver higher in frequency but rather to counteract the narrowing of the system angle of radiation with increasing frequency. [quote]True - but Jacks don't produce a real arse-shattering sub-type bass, though.[/quote]Jacks produce at least as much low end as direct radiating cabs using the same drivers. Where they differ is that they produce stronger mids. And they're not rear-loaded horns, they're front loaded horns. [quote]Isn't it strange that if the sound man does manage to get a reasonable sound out front during a sound check how it suddenly changes to rubbish during the gig.[/quote]The room acoustics are totally different when the room is empty versus full with an audience. [quote]For instrument monitoring we just hear each other on stage as normal.[/quote]That's even more of a challenge than having uniform sound in the audience, as the cone shaped midrange and high frequency dispersion pattern is much smaller close to the amps. With a typical stage setup the mids and highs from amps can only be heard directly in front of them. Only by running the instuments through the monitors may what's heard on stage be as close as possible to what's heard out front. Since the low frequencies as noted are omni-directional there's no need to have them in the monitors, so the instrument feeds to the monitors should be high-passed.

[quote name='KingBollock' timestamp='1343857819' post='1756572'] Would tipping the cab up, so that it was in a more diamond style configuration, so one speaker above another and then one either side at middle height, help? [/quote]It would be better. Horizontal dispersion is inversely proportional to the width of the source. By making it narrower dispersion is widened. Of course this makes the head placement a bit of a task. BTW, the entire reason why drivers were placed horizontally in the first place was to accomodate a wide amp, first in combos, then in separates. No consideration was ever given to the dispersion issue because the amp designers weren't aware of it.

[quote name='BluRay' timestamp='1343847483' post='1756345'] This thread's taken a turn for the better [/quote]It should have ended at post #3. That's when the answer to the original question was given, most of what has been posted since has been silly catterwallering. Little wonder Alex seldom comes here any more. If one doesn't want the opinion of an expert in the field one should not ask the question to begin with. Unless they be trolling, of course.

[quote name='alexclaber' timestamp='1343814974' post='1755517'] I'd have thought I'd have already said enough in my columns and on our website to get my view across and hopefully increase people's understanding of acoustics. [/quote]Said thinking obviously falls into the wishful category.

[quote name='shizznit' timestamp='1343774579' post='1755208'] Dispersion is only a problem if you need your backline to fill a venue if you are not going through the FOH. [/quote]But most of us don't. By placing two tens side by side the midrange dispersion is less than that of a 1x15, or vertically aligned 2x15s. Tens naturally have the widest dispersion of the usual driver sizes, but only if kept in a vertical line. Want the tone and output of a 4x10 with wide dispersion so that the audience can hear them, and with the drivers high enough so that you can hear them? Stack two 2x10s vertically.

[quote name='Pbassred' timestamp='1343591996' post='1752517'] You might possibly want to check out the Eminence web site. [/quote]When you do spend time here: http://www.eminence.com/support/understanding-loudspeaker-data/ The only factor influenced by cone size alone is the dispersion angle. Where response is concerned there are tens that go lower than some fifteens, and fifteens that go higher than some tens, so to say that 'tens do this and fiteens do that' has no basis in fact. [quote]The benefit a 15 has over a 10 is that it moves more air (the surface area of cone is more)[/quote]The amount of air moved is determined by the driver displacement, not cone area. Some tens have more displacement than some fifteens, so how low/loud you want to go isn't a matter of cone size. .

[quote name='icastle' timestamp='1343584308' post='1752367'] Turn the scenario on it's head - if there was any real benefit in using a crossover in a bass cab then all the mid to high tier manufacturers would be fitting them, and they aren't... [/quote]The reason they don't is that the vast majority of players would not be willing to pay the added cost, lacking the understanding of how speakers work and therefore why a well designed and built cab is worth a lot more than a few drivers tossed into a box.

[quote name='Pbassred' timestamp='1343552150' post='1751885'] Surely you would want to use the 10" for Highs only and 15" for lows only Otherwise it would sound bad or be inefficient. [/quote]If the tens and fifteens used were optimized for highs versus lows this would be true. But they aren't. There's precious little difference in the response of electric bass tens through fifteens, and for that reason precious little benefit to mixing them, if any.

[quote name='Mr Fretbuzz' timestamp='1343069408' post='1744784'] I've kept that link thanks but all I've bought are shop cables so far... The last was a retro looking Fender Custom Shop cable in the smallest length I could find as I'm told that the smaller cable you can get away with the better the signal. One thing that I've been thinking about though is that i used to get gold plated connections for my tv surround/ play station etc.... Not seen any gold plated bass ones in the shops... How come as I thought you'd get a better signal etc with them ?.. [/quote]Cables should be kept as short as you need them because longer cables are extra cost and kit that you don't need. Gold plating doesn't corrode, but unless your installation is on a boat or in a beach house that's not a concern. Overpriced/overhyped cables are the number one ripoff in the world today, don't believe 1/10th of what you see in advertising for them.

[quote name='HotelEcho' timestamp='1343049091' post='1744242'] does anyone have any preferences for speaker cables from one manufacturer over any of the others? [/quote]Copper is copper. All you want to be sure of is adequate gauge, 16 will do for 1.5m, and the use of Neutrik connectors. Since Neutriks are more expensive than generic el-cheapos if they're employed it's a safe bet that the cable is also of decent quality. [quote]I'm slightly sceptical at spending £35 on a 1.5m lead [/quote]As you should be, for that length it's at least twice what you should spend.

[quote name='bigjohn' timestamp='1342973768' post='1743305'] Nowt wrong with the speakers. Cab belonged to my mates dad from new I believe and wasn't overworked. It's then spent some year being an occasional guitar cab / stored in a studio. [/quote]It's not a matter of anything beiong wrong with them, just the fact that 50 watt fifteens of that era generally were displacement limited to perhaps 30 watts before farting out. That's a mighty big box to haul about for such a small result.

To be gig worthy you'd need to replace the drivers, brace, port and line the cab. Otherwise it would be an oversized underperforming albeit cool looking curiousity. If you or a mate have the skills to do that it might be worth the hundred, much or all of which you could recoup selling the drivers to a collector.

[quote name='bremen' timestamp='1342705117' post='1739632'] You're telling me the spiltter transformer was invented in 1980? [/quote]I doubt that, but they would not have been common items in everyone's kit. True FOH consoles as we know them today were still few and far between even in 1980. Most of what was being used through the 70s for touring was studio gear, and most of that prior to 1975 was originally made for broadcast, not live sound. Even balanced mics using XLR connectors weren't standard until the mid 70s. They existed, but most PA mixers made prior to 1975 had unbalanced 1/4" inputs.

[quote name='bremen' timestamp='1342701437' post='1739544'] Seems an odd way of going about it. Why not just use one mic, one transformer, two mixers? [/quote]Easy to say that today, in the 70s not so much. Much of what we take for granted today didn't exist then. Keep in mind that in 1970 the Shure Vocal Master was state of the art.

[quote name='BRANCINI' timestamp='1342695420' post='1739386'] They always seemed to be two different mics, rather than two the same, probably a reason for that. [/quote]If the mics are not identical the technique won't work, so if that's the case the mics are being fed to two different consoles. That was done a lot in the 70s, using one console for the FOH and the other for the recording, as most consoles then didn't have the ability to do both simultaneously. [quote]with the mics, say, 5cm apart a bit of back-of-a-fag-packet maths says that they'll already be out-of-phase at around 3300Hz, [/quote]Not if the elements are on the same plane.

[quote name='bremen' timestamp='1342538589' post='1736797'] It'd be messy to wire them in series. Easier to stick each through its own preamp, invert the phase on one, and sum them. [/quote]You'd parallel wire them into a single channel, one with the cable reverse polarity, using a dedicated Y connector to do it.

[quote name='bremen' timestamp='1342526600' post='1736527'] It's anti-feedback. They are wired out-of-phase, so sound arriving at both (ie from the PA) is cancelled out. You just sing into the one, so you don't get cancellation. [/quote]+1, a technique pioneered by the Dead, necessitated by their Wall of Sound. They didn't use monitors, rather the entire system provided both the FOH and personal monitoring as they were set up in front of it. That required the nearly 100% common mode rejection of sound that was picked up by both mics while not affecting the sound picked up by only the one mic that they sang into.

[quote name='ivansc' timestamp='1342450895' post='1735249'] Bought BF's 2x10 Jack plans, as I happen to have acquired a pair of the 300 watt Celestion Neos at a really silly price. [/quote]Be sure they meet the required specs. Watts matter little, T/S specs and response matter a lot.

[quote name='Balcro' timestamp='1342261354' post='1732424'] For entertainment / musical instrument loudspeakers it doesn't matter, but purist hi-fi people tend to design loudspeakers with the frame flush to the baffle or with a surrounding trim piece to blend the frame into the baffle. Their argument is, that it minimises unwanted sound diffractions from the sharp edges of the cut baffle board. The ultimate aim or obsession being a flat frequency response. Putting loudspeakers inside the baffle means the drive unit fires out into a 15-18mm deep tunnel, but as its for guitarists, who cares. Maybe Bill will have a technical opinion on the validity of this "hi-fi" claim. Balcro. [/quote]For our purposes it's not true. For diffraction to be significant the obstacle must be at least 1/4 wavelength in dimension; at even 4kHz that's nearly an inch, so the driver positioning on the baffle doesn't matter with electric bass or guitar. In a hi-fi cab what can happen is that a woofer frame extending beyond the baffle can cause diffraction of the wave from a tweeter adjacent to it, so inlaying the woofer flush to the baffle may be beneficial, depending how thick the frame is.

It's easier to build a front loaded cab, as the back doesn't have to be removeable. Otherwise there's no particular advantage to either arrangement.

[quote name='LawrenceH' timestamp='1341500534' post='1720115'] From a dispersion perspective I think it's better to cross as low as possible to avoid off-axis nulls due to destructive interference between drivers in the crossover region [/quote]That's much more of a concern with PA than electric bass. So long as you use at least 3rd order filtering on the midrange the response overlap zone is slight enough to minimize ill effects to the point of being virtually inaudibile, especially when compared to a typical commercial cab with woofers horizontally aligned and no midrange driver at all.

[quote name='dincz' timestamp='1341413832' post='1718602'] I suspect the answer will be no, but is there a standard for this e.g. +ve on the tip moves the cone out? [/quote]The standard is outward excursion with a positive voltage applied to the tip on a 1/4" plug or the + pole of a Speakon.

[quote name='4 Strings' timestamp='1341410777' post='1718545'] ...you mean like maple fingerboards sounding 'bright'. [/quote]Actually rosewood and ebony are brighter, being more dense than maple. More dense body woods are also brighter and sustain longer than less dense varieties. Here also there's nothing the least bit magical about it, it's simple physics. But as Clarke said any sufficiently advanced technology is indistinguisable from magic, even when that technology is as simple as a block of wood. If you're a luthier you understand the technology. If not you may not.

[quote name='dincz' timestamp='1341247347' post='1715719'] Just a thought. Correct me if I'm wrong but the potential problems with mixing cabs are to do with dispersion and comb filtering. [/quote]The main issue is the different phase responses of different cabs. When combined they may work OK, or they may not, and there's no way for the user to predict it. With identical cabs there are no issues. The theory behind mixed cabs, with tens and fifteens being by far the most popular configuration, is based on the notion that fifteens go lower, tens go higher, and that by combining them you get the 'best of both worlds'. The fly in that ointment is that fifteens don't necessarily go lower than tens, and tens don't necessarily go higher than fifteens. The only inherent difference is that tens do have wider dispersion in the mids and highs. But when tens are placed side by side their dispersion in the mids is halved, resulting in narrower dispersion than a fifteen, and the highs are combed. And where output capability is concerned one fifteen can't match four tens, so the ubiquitous 115/410 combination makes no sense from any perspective.