Bill Fitzmaurice

[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.

[quote name='fleabag' timestamp='1405945301' post='2506748'] Even if you use 5 or 6 string bass ? [/quote]The f3 of a Fridge is 58Hz, it doesn't seem to bother most five and six string players.

[quote name='LukeFRC' timestamp='1405894438' post='2506329']I notice the preamp has a switch on giving me a 12dB high pass filter at 80Hz. And it sounded ok! It made me think about how our rig can/ or can't produce the low end.... and the effect it has. [/quote]That filter compensates for the difference in response between an electric bass cab and a PA with subs. 80Hz is a bit high, 60Hz would be better. When you go to a concert with big PA and bass that's all boom and rumble with no definition, or for that matter even pitch, it's because the soundman has no clue what electric bass is supposed to sound like, nor how to use his PA kit to get it. By the same token one shouldn't go after an electric bass rig with flat response to 30Hz. If you get it you'll probably regret it.

It depends on the amp. Many, most notably Fender, employ a closed circuit switched output jack that shorts the output transformer when no speaker is plugged in. That would be death for a SS amp, but prevents damage to a tube amp with no load. Not having a load won't bother a tube amp at idle, only when it's being played through. [quote]My mates mesa boogie 400+ was left on standby for 15 mins with no speaker connected. The amp is now f****d.[/quote]When on standby only the heater voltage is active, the B+ voltage is not, so even if being played through no damage is possible. I haven't seen Mesa schematics but being basically upgraded Fenders I very much doubt that they don't use switched output jacks.

[quote name='GrammeFriday' timestamp='1404643449' post='2494333'] but he was using an all-TC rig last time I saw him (playing with Supersilent) and the sound was amazing. [/quote]You mean the sound of the PA was amazing. You probably couldn't hear a note from the backline.

[quote name='Painy' timestamp='1404601722' post='2494143'] Good to know thanks. Oh, and Mrs Painy says thanks too - seeing as I won't need to spend the money on a replacement speaker now, she says I can use it towards a present for her birthday next week! [/quote]Manolo. Trust me.

[quote name='Painy' timestamp='1404597555' post='2494108'] would there be any risk of damage to either the amp or cab in continuing to run it as is? [/quote]No. If anything the higher total impedance load will let your amp run cooler.

Don't worry about not getting the full 500 watts out of it. You can't hear watts. You do hear decibels.The difference between running a 4 ohm versus 8 ohm extension cab might be at best 2 decibels, which is roughly the difference between running your volume control at 7 versus 6.75. It's simply not worth changing the driver, the advantage being so slight. You also do not want to run a 4 ohm 4x10. If you do each ten in the combo will receive twice the power as each ten in the extension. Probably the best extension option would be a 4 ohm 2x10 loaded with the same drivers as those in the combo.

[quote name='bassmachine2112' timestamp='1404329127' post='2491684'] I don,t know the physics side [/quote]I do. They sound exactly the same as one of the same drivers, the Eminence Deltalite II 2512, will sound in a cabinet of twice the net internal volume with the same tuning. After accounting for the space taken up by the second driver and the space in between them the actual size savings is perhaps 40%. But most manufacturers don't load drivers into a cab as large as they should, because that's not what most customers want. Speaker design always boils down to compromise. If you have more money than pack space an SP may make sense for you. If you have more pack space than money a correctly sized cab may be the better option. The trick lies in finding a correctly sized cab, as very few are.

If you run them together each cab will receive the same power. That means each driver in the 2x10 will get twice that which those in the 4x10 do. For a correct match the impedance of the 2x10 should be twice that of the 4x10.

[quote name='LukeFRC' timestamp='1403976887' post='2488296'] At which point I don't know why they bother giving those figures. It's so so different to the PA world where everything is spelled out. [/quote]Bass players get gigs by being competent playing their instruments. That doesn't require a high level of technical knowledge.PA guys get gigs by being competent producing good sound. That requires a high level of technical knowledge. I'm generalizing of course, not all working PA techs are competent by any means. I'm in Montreal for the jazz festival. Last night I saw concerts at five outdoor venues, only one sounded good. Not concidentally it was at the largest/most important venue. It's a very safe bet the crew there got the gig by having a reputation for knowing what they're doing. It's also a very safe bet they got paid a lot more than the hacks at the other venues. Knowledge may be its own reward, but it carries a lot of other perks as well.

Headroom is mainly defined by the capacity of the power supply. Wattage ratings have skyrocketed, but the actual capacity of the power supplies has not.

[quote name='LukeFRC' timestamp='1403952681' post='2487973'] It all depends at what point they are measuring the frequency point from! -3dB, -6dB or -10dB - without that information the frequency response info isn't really that useful.[/quote]They're probably -20dB. Those numbers are utterly silly where electric bass speakers are concerned. They simply don't go that low, by about an octave. [quote]I would google around for Bill Fitzmaurice's advice on mixing speaker sizes.... and make your choice from that. [/quote]In a word, don't.

No witchcraft, just simple physics. Two drivers coupled allows the cab size to be smaller. But there's no such thing as a free lunch with physics. The price paid for the smaller cab is that the output is the same as with only one driver in a larger cab. IMO a 2x12 that only goes as loud as a 1x12 isn't worth the slight net savings in size compared to a standard 1x12.

[quote name='Ben Jamin' timestamp='1403476933' post='2483147'] I'm thinking it be much more efficient to split my signal and send the subs to the SWR and the rest to the Compact, [/quote]Probably not. I doubt that the Big Ben goes much lower, if at all, than the compact, and doing this might end up giving you less low end.

[quote name='fleabag' timestamp='1403103896' post='2479811'] Its hard to imagine why the Beymas are cheaper than Betas. [/quote]In the US the Beymas are $130, the Betas are $80. The US price for the Deltalite II 2510 is $140.

[quote name='MoonBassAlpha' timestamp='1402923497' post='2477892'] A sealed cab of appropriate dimensions will give a gentle bass roll-off, yes?[/quote]Yes, and no. The roll off is lower slope but the f3 is much higher, so you don't get better low end, you get less. On average a sealed cab only works better than ported below 30Hz, which is of no benefit for electric bass.