Bill Fitzmaurice

[quote name='Chienmortbb' timestamp='1408779601' post='2533353'] In my experience it is the same in the UK Bill. [/quote]I'd imagine you mainly have PA in the inner cities where it's a big enough hassle even bringing in amps in your car, let alone a lorry full of PA.

[quote name='Phil Starr' timestamp='1408717314' post='2532911'] Sorry to spoil the party but dispersion isn't the only factor affected by cone diameter. First of all you can't vary cone size without changing either its mass or cone thickness both of which will alter the sound it produces. [/quote]If you look at the Mms specs for various drivers you'll see that they have little to no relationship to driver size. For instance, the LAB 12 is 146g, the Sigma Pro 18 is 130g. By the same token Fs and cone size are far from directly related.

[quote name='HowieBass' timestamp='1408650030' post='2532285'] I always wondered about the reason for the vertical stacking of speaker cabs you see at big gigs, now I know (I think)... [/quote]Read this (and the subsequent chapters). http://www.gtaust.com/filter/05/07.shtml

[quote name='chrismuzz' timestamp='1408646062' post='2532224'] Really? We're very lucky over here! In my current band I've only ever done like three gigs where I wasn't through the PA.[/quote]In the US it's SOP that the band provides the PA. The worse the job pays the more likely that you have to provide the sound. Since most bands don't want to pay for or carry any more gear than they have to the average PA is a powered mixer and a couple of cheap boxes on sticks, hardly something you'd run your bass through. The same applies to sound engineers, if you want one you'd better bring one with you. Consequently most bands mix from the stage. Maybe one in ten venues has PA, and those are mainly larger clubs in major metropolitan areas. Outside of cities you'll be lucky to find one in a hundred clubs that has PA.

[quote name='Painy' timestamp='1408642779' post='2532187'] So out of interest, what effect is made to the dispersion in cabs where you have 2 drivers but positioned across the diagonal rather than immediately side by side or one above the other? [/quote]The overall width of the radiating planne determines the angle of horizontal dispersion. If a diagonal placement reduces that width compared to side by side it's better, but it still won't be as narrow as vertical drivers. [quote]Dispersion be damned; there's a PA for that..! [/quote]On this side of the pond I doubt that one in ten bass players is in the PA.

[quote name='chrismuzz' timestamp='1408626296' post='2531952'] This might be a ridiculous question, but if you filled a cab with like 32 tweeters would you get good low end response with better dispersion on the highs? [/quote]No, because tweeters are made with specs optimized for the band width that they operate in. You can get a very good result with a large grouping of smaller drivers which do have specs appropriate for electric bass. But they must not be placed side by side, or the dispersion angle shrinks back to that of a single driver of the same width. The right way to do so is to have them in a single vertical line. For that matter that's how a 4x10 should be made, but they aren't, because what sells cabs isn't technology, it's how they look. [quote]I sort of thought that would be because the 10" cone can react quicker.[/quote]All drivers 'react' with the exact same 'qiuckness', as that 'quickness' is determined by the speed at which an electron wave passes through the voice coil, about 0.7 times the speed of light. What does tend to be different with smaller drivers is their transient response, which is related to the inertial forces of the moving mass. But as you can find somes tens with higher moving mass than some eighteens here again you can't judge the end result by size alone. Your wife/girfriend will give you confirmation on that.

[quote name='LukeFRC' timestamp='1408571394' post='2531538'] so.... thinking out loud and hoping to take advantage of your knowledge.... if the only real factor is dispersion.... what would you use as optimum for bass? I know you use a 12 loaded horn loaded cab yourself.... [/quote]I use the largest cab that I can comfortably carry, that's a JackLite 12, as opposed to the larger JL15 or smaller JL10. If it wasn't loud enough I'd probably use two JL10s, which would give higher output while still fitting in my car with ease. I have a JL15, I've only used it a couple of times, those being before I built the JL12. I just don't need its output capability, and it's a PITA to fit into my car.

[quote name='Painy' timestamp='1408567731' post='2531486'] At the risk of displaying my ignorance, could you define dispersion? Are we basically just talking about spread of sound e.g. how well we hear the sound is affected by where we are positioned in relation to the speakers? [/quote]Yes. [quote]Or in other words, will 3 vertically stacked 15s fill a venue with bass more completely and evenly than the classic 8x10 fridge configuration at the same volume? [/quote]Yes, although the difference will be heard in the mids and highs, not the bass. [quote]So what am I 'hearing' because in a blind test I swear I could tell the difference between a 10", 12" and a 15" speaker[/quote]If all speaker sizes had a 'signature sound' then all tens would sound the same, as would all twelves and all fifteens. Not only is that not the case, but you can make the same driver sound different by loading it into a different enclosure. For that matter you can realize literally dozens of audibly different sounds using the same driver with different cab configurations.

[quote name='Painy' timestamp='1408564532' post='2531457'] So my question is, what difference does driver size actualy make to the sound? If there's really no difference between them then why do we need the range of sizes we have available? [/quote]The only factor determined by size alone is the angle of dispersion. The larger the driver the smaller the dispersion angle as frequency goes higher. That's why guitar drivers beam like mad in the highs. It's also the primary reason why tweeters are smaller than midranges, and midranges smaller than woofers. The main advantage to a larger cone is that it takes fewer of them to reach a given combination of low frequency extension and output, but at the expense of dispersion. In theory one may use, for instance, eight tens to get the same low frequency output as three fifteens, without giving up dispersion. But if you put those tens in two rows side by side the dispersion angle becomes the same as a twenty-one, so an 8x10 has narrower dispersion than a vertical stack of three 1x15s.

[quote name='Highfox' timestamp='1408451779' post='2530254'] Funny, in the last year I have myself gone from liking a pure clean tone with flats, to a slightly overdriven sound with rounds, how's that! [/quote]I did the same thing...in 1972.

[quote name='TheDaivisch' timestamp='1408441233' post='2530089'] I suppose by toppier, I mean the quickness/airiness (in the upper mids, I suppose) and the extra tightness in the lower frequencies of 10s and 12s thats inherent in the woofer, rather than just the top end sparkle of the tweeter [/quote]If that's what you're after you need to add midrange drivers, 6 or 8 inch, and a crossover. Ten and twelve inch woofers are still woofers, they're not going to make that much difference in the midrange.

[quote name='LukeFRC' timestamp='1407772789' post='2523841'] I read in interesting paper about flaired ports and investigating them from a aero fluid dynamic POV. The main thing I can remember that in a straight exit port the air forms laminate layers at the length of the port. Flaired ports , ideally on both ends induce eddies that break up the laminates reducing resistance on air flow. A bit like the dimples on a golf ball or sharks skin [/quote]If you want to see the effect of a port of insufficient area model the cab in WinISD Pro. Open the Advanced tab in the Box window, change the Qp value to 5 (BTW, it should be at 50 if the port models with port velocity less than 20) to see the effect of a seriously undersized port. It shows the result of friction. Dimples reduce friction, they're used by some duct manufacturers.

[quote name='Ghost_Bass' timestamp='1407506189' post='2521300'] So you're saying that feeding 100w (sorry to use watts but i think is better to example) to a single 4 ohm driver and feeding 100W to two 8 ohm drivers the voltage delivered from the amp to the cab system will be exactly the same? [/quote]Forget about watts. You'll never really understand how speakers work when your thinking is wattage bound. FWIW 100w into a 4 ohm load is 20 volts, and two 8 ohm drivers in parallel is 4 ohms, so yes, the voltage swing will be the same as into a single 4 ohm driver.

[quote name='Ghost_Bass' timestamp='1407495849' post='2521097'] That's what i'm trying to explain here, this analogy is wrong in the OP's POV. [/quote]It's a perfect analogy. The sails are equivalent to cones, the wind speed equivalent to voltage swing.

[quote name='Beer of the Bass' timestamp='1407433505' post='2520555'] I've seen it suggested elsewhere (and in older forum posts by BFM) that the increase in sensitivity from coupling closely spaced woofers is 3dB, though only where they are spaced at less than 1/4 of the wavelength. So the quoted 6dB increase in SPL when adding a second cab or driver to a solid-state amp is 3dB from doubling the amps power output and 3dB from the increased sensitivity, if I've understood this correctly (and if I haven't, feel free to explain why!). [/quote]That's another way of viewing the result of doubling driver count while maintaining the same voltage swing. For that matter if you double the displacement via doubling the excursion with one driver, which is accomplished by doubling the voltage swing, the result is also 6dB. It's very clear when you look at it from the standpoint of displacement and voltage swing, but as clear as mud when you look at it from the standpoint of power and impedance. That's one reason why when engineering speakers we look at volts, not watts.

[quote name='Ghost_Bass' timestamp='1407344588' post='2519657'] , you have two identical amps set to give exactly the same output signal to two different speaker systems, the first with two identical cabs (8ohm each) and the second to a single 8 ohm cab identical to the other two. Wich system would sound louder? Maybe i'm wrong and didn't read well the OP. [/quote]I don't think you read post #5. The difference will be 6dB.

[quote name='Count Bassy' timestamp='1407327376' post='2519440'] Obviously if you put two drivers in parallel then, as bill says, they each seems the same voltage so so you'd shift twice the air. Providing that the amplifier can drive twice the current. And I suspect that this is where most of the "two drivers is better than one" thing comes from. However, as ghost says, if you have one 4 ohm driver, or two 8 ohm drivers being driven by the same amp at the same settings, then the total electrical power delivered would be the same. I guess, as someone else said, the cone gets harder to move as the excursion increases due to the spring effect of the surround, so the two 8 ohm drivers might actually be more efficient (less energy loss in the surround), but by how much? Ignoring this, if the one 4 ohm speaker cone taking 100 watts moves twice as far as each of the 50 Watt 8 ohm speakers then surely the total air shifted is the same? [/quote]This points out why power alone is meaningless. Driver output is determined by cone excursion, cone excursion is determined by voltage swing. One can no more anticpate the output level in decibels based on watts than one can the output of a lightbulb in lumens based on watts. If engineers ruled the roost you wouldn't see watts used at all, but we don't. Watts are the darlings of marketing departments.

[quote name='Chienmortbb' timestamp='1407251484' post='2518791'] It is often said on here that if you have two cabs rather than one it is louder. Is that really the case and if so is it always the case? [/quote]The number of cabs doesn't matter, the number of drivers does. Maximum output is limited by the total driver displacement, T/S spec Vd. The displacement of two drivers is double that of one, the resulting increase in maximum output by doubling the driver count is 6dB. It doesn't matter if the two drivers are in one cab or in two cabs with the same net internal volume. By the same token when you plug a second identical cab into your amp the voltage swing into each cab remains constant, the total driver displacement doubles, and you get a 6dB increase in output. But you can only do so if the halving of the impedance load doesn't go below what your amp can deliver.

[quote name='MoJo' timestamp='1407240752' post='2518635'] Purely out of curiosity Bill, could it be improved with modern drivers? [/quote]Yes, but instead of an underperforming monstrosity you'd have a fairly well performing monstosity. It would still be a monstrosity. A far better investment would be modern drivers in a modern cab half the size and weight that works better.

[quote name='Painy' timestamp='1407074119' post='2517026'] what on earth would possess anyone to design such a thing? [/quote]When it was designed 30 odd years ago the driver limitations of the day (note that it only handled 400 watts) made such monsters useful. Today you can top it with a good 2x12.

[quote name='Chienmortbb' timestamp='1406988177' post='2516470'] I was paraphrasing the blurb on the Precision Ports site Bill and my worry always was that, as in plumbing, the flow is dictated by the smallest bore in the system. Whilst turbulance may be reduced, the air velocity and c the pressure is still high. So is this treating the sympton rather than the disease? [/quote]When the port is too small there are friction losses; that's what will result in reduced output. That friction, coupled with higher velocity of the air mass vibration than in a correctly sized port, causes chuffing noise. By flaring the port you reduce the friction in that section, and allow a transition from high velocity within the smaller diameter of the port to lower velocity within the flare section, which reduces dB losses and chuffing noise. But if you simply make the port the right size to begin with there are no losses or noise. The obvious question is [i]'why would one make the port too small', [/i]the answer is to reduce cab size. It's the classic clash between what size cab the consumer wants, versus how low and loud he wants it to go.

[quote name='Chienmortbb' timestamp='1406969848' post='2516273'] Flared ports supposedly give you an extra 3dB [/quote]They don't. An undersized port can cost you 3dB. By using a flare you can recoup some, if not all, of that loss, but it won't give you 3dB more than a port that's correctly sized to begin with.

[quote name='JuliusGroove' timestamp='1406880196' post='2515482'] I have the mark bass CMD 102p 2x10 combo, I have recently started playing with a samba band and the bateria leader thinks my amp won't cut it as it's only a 2x10. [/quote]The purpose of the backline is to provide enough volume for you and the others on stage to hear you. A 210 should be sufficient for that. Covering the room is the PA's job. not yours.

[quote name='funkle' timestamp='1405971318' post='2507134'] Again, I'll ask though - in general - if you have a woofer which suits the job in hand, and enough power to drive it with, and it can take the power thermally and mechanically, but it isn't efficient, can applying extra power provide the extra volume to match another woofer with lower Xmax but higher efficiency? [/quote]Perhaps. If you give up 3dB of sensitivity you need to increase excursion by 70% and double thermal power handling for equal output. Plus almost invariably the price of high xmax isn't just lower sensitivity, it's also less midrange. Changing driver parameters isn't like playing checkers, it's like playing 3 dimensional chess.

[quote name='funkle' timestamp='1405963650' post='2507016']. Does high Xmax (with high power handling, thermal and mechanical) + sufficient power compensate for low efficiency of a woofer? I'm thinking of e.g. the 3012LF vs the 3012HO here... [/quote]You should not choose between those two based on that criteria. Use the LF if you either don't desire much midrange or if you have a separate midrange driver, and you need the lower frequency response that the LF is capable of in a cab of sufficient size.