Bill Fitzmaurice

[quote name='GregBass' timestamp='1338383506' post='1673611'] I read your statement as meaning that under normal usage the output voltage of an amplifier is constant. [/quote]You misunderstood.

[quote name='dincz' timestamp='1338353498' post='1673105'] We're talking at cross purposes here. You're talking about an amp's behaviour under normal operating conditions. I'm talking about maximum available output voltage swing i.e. at clipping. [/quote]Since most players tend to use their amps under normal conditions that's what's pertinent. [quote name='JTUK' timestamp='1338371447' post='1673334'] But to follow that on logically, you have to put their opnions and thoughts below the producers who sell volumes of the stuff. [/quote] I can't speak for Alex, but I've designed dozens of speakers for said producers, the majority of whom do not employ engineers, and are not engineers themselves, relying on independants such as myself to do their design work. [quote name='GregBass' timestamp='1338376958' post='1673451'] Ah - I took the quote at face value (that the voltage must be constant). That was what I disagreed with. The output voltage of an amplifier is absolutely no constant. [/quote]It must be a constant, otherwise the amp simply won't work. Hook up an tone generator to an amp with flat response, the amp to a speaker. Measure the voltage as you sweep across the spectrum, it will remain constant even though the speaker impedance is not. If it's not constant the amp, or generator, does not have flat response, and you'll see the same voltage fluctuation into a resistive load.

[quote name='dincz' timestamp='1338322148' post='1672821'] Connect an 8ohm load, measure the maximum output voltage swing and then repeat with a 4ohm load. It'll be different on every single amplifier. Not even debatable, just a demonstrable as well as theoretical fact. [/quote]Explain then why a speaker doesn't reproduce every note at a different level, when this is what a typical speaker's low frequency impedance looks like:

[quote name='dincz' timestamp='1338311001' post='1672561'] On this I have to say that's absolutely untrue. Every amp I've ever bench-tested could deliver a higher voltage swing into an open circuit than with a load connected. The power rail voltage and maximum available output voltage swing reduce as you drop the load impedance. No surprises there, just Ohm's Law and real-world imperfect power supplies. [/quote]An open circuit doesn't deliver a load. Within the operating load ranges actually presented by speakers amps must deliver a constant voltage, otherwise they simply won't work.

[quote name='dincz' timestamp='1338307063' post='1672485'][b][i](to a specified load)[/i][/b] [/quote]Amps deliver the same voltage swing irrespective of load impedance. They have to, otherwise every note would be heard at a different volume, as impedance is not the slightest bit a constant. Current varies with load.

[quote name='dincz' timestamp='1338283581' post='1671971'] There seem to be only two points of view around here: 1. Power is everything 2. Power is meaningless [/quote]Point one comes from those who do not understand how gear works. Point two comes from those who do. What really matters is voltage swing. It takes a given voltage swing to drive a speaker to full output; if the amp can deliver that voltage swing you'll get full output. If it can't you won't. Voltage swing removes power factor and duty cycle from the equation, and all of the spec fudging that they allow. Amplifier and transducer engineers are well aware of this fact, so voltage swing is what they consider when designing your gear. Marketing departments and the vast majority of consumers don't.

[quote name='samkeen' timestamp='1338286161' post='1672024'] Can anyone tell me, is it possible to convert a 1x12 4 ohm cab to 8 ohms? [/quote]Only by taking it to a music store and trading it in.

Ignorance, coupled with Gear Stockholm Syndrome. The good thing about this particular version of identification with their captors is that escape only involves the simple act of learning.

[quote name='thinman' timestamp='1338123452' post='1669819'] Just an observation but I often see comments in threads such as this like "My XXX is putting out n Watts into my YYY cab" as though the amp's output is somehow a constant and is providing output even during silence rather than ranging from 0 Watts to whatever in proportion to the output signal. It may be the way I read some comments but on the other hand it may be a popular misconception! [/quote]It's both popular and a total misconception. FWIW, amps don't 'put out watts' at all, they provide voltage. How much power is being drawn in the process is determined by the voltage swing and current draw; current draw is based on load impedance, and the load impedance varies over about a 10:1 range depending on frequency. A speaker could be burning 100 watts at 100Hz but only 10 watts at 50Hz, while producing the same output at both frequencies. But that kind of information doesn't sell amps, so you won't find it in any marketing literature.

[quote name='Marvin' timestamp='1338009322' post='1668561'] [url="http://www.carvinworld.com/products/BR118-4"]http://www.carvinwor...roducts/BR118-4[/url] [url="http://www.carvinworld.com/products/BR118-8"]http://www.carvinwor...roducts/BR118-8[/url] Apparently these are new. Be interesting to know what they sound like. [/quote] [i]a tight, punchy, slap & pop high-end.[/i] [b]Freq. Resp: 30 to 2K Hz -3dB [/b] Those statements are diametrically opposed. [quote]Does anyone on here use a Trace 410/118 Rig?[/quote]Better than a 410/115 I suppose, but still illogical. Demands on drivers increase exponentially as frequency decreases, so you don't need four tens to keep up with one eighteen, you only need one. Want to add big bottom to a 410? Try four 118s.

[quote name='ThomBassmonkey' timestamp='1337983826' post='1668468'] Wattage isn't too important. Speaker surface area (combined) is probably the most important factor followed by sensitivity. [/quote]Where maximum output is concerned that's governed by driver displacement, not surface area. You can have a 1x12 with the same displacement as a 4x10, so both could be equally loud. Sensitivity, however, is directly related to both the size of the cab and the number of drivers used. Said 1x12 would probably require four times the power to reach the same levels as the 4x10. So if you opt for a small high displacement driver cab and want to get high output from it you may need a new amp as well.

[quote name='xgsjx' timestamp='1337864185' post='1666577'] So is it worth buying an Ampeg driver & sticking it in a decent cab? [/quote]Only if you can get the specs, and Ampeg won't tell you. Besides, they're Eminence OEM anyway. It's not that the Ampeg OEM are any better than stock Eminence, it's just that Ampeg may rate a driver at 200w when the coil is actually a 300w or higher coil. They rate the SVT driver at only 100w, while the stock B810 is rated at 150w. They do so to discourage users from overpowering the cabs beyond what the displacement will allow them to make use of. That's a reversal of the usual marketing technique of advertising as high a power rating as possible, despite the fact that it may be three times what the driver can actually make use of.

[quote name='xgsjx' timestamp='1337858157' post='1666413'] According to Ampeg's website it's 200w. [/quote]Not that it matters all that much, as output is limited by the driver displacement, not the power rating. Ampeg drivers tend to be very conservatively rated, so a 200w Ampeg driver may have the same displacement as another company's 400w driver.

[quote name='incubass' timestamp='1337213769' post='1657356'] So which cab would be louder and as a standalone cab? The obc115 or the sp212? [/quote]The OBC 115. It has a driver displacement of 343cc. The twelves used in the SP212 have a displacement of 255cc each, and if used in a standard alignment they would go louder with a total 510cc displacement. But when mounted in an isobaric alignment only one driver's displacement moves air, creating sound, so it's 343 versus 255. [quote]I've heard the obc115 is a really good cab,[/quote]I consider it a bass cab made by a guitar cab company to guitar cab standards. It's a far cry from Barefaced; compare the displacement numbers for yourself: http://barefacedbass.com/technical-information/Volume-displacement.htm

[quote name='dannybuoy' timestamp='1337214157' post='1657359'] You will lose a little bass response from the higher cab due to loss of floor coupling [/quote]Nothing is lost. The drivers are close enough together so that they mutually couple in the lows, acting as one. Vertical stacking of drivers is how it always should have been done. It wasn't for purely cosmetic reasons.

You need to match the driver to the cab using T/S specs and a response modeling program.

[quote name='glefty' timestamp='1337009823' post='1653916'] I also posted this question on TB but as it is largely American, I figured most wouldn't really concern themselves with or even be aware of these issues as much as UK, EU, AU, NZ, SA & others outside North America. [/quote]And there's your answer. Manufacturers who do little distribution outside N. America aren't going to increase their build cost by using dual primary power transformers.

Read this: http://barefacedbass.com/technical-information/Volume-displacement.htm The Midget's 330cc displacement is equivalent to three average tens.

[quote name='Bass_man219' timestamp='1335987392' post='1639243'] Does valve preamp distortion wreck speakers? [/quote]If the distortion is severe enough tweeters can be at risk. Woofers, no.

[quote name='MarshallBTB' timestamp='1335962592' post='1638646'] I've seen the reviews, both good and bad. For that price with the thomman return policy its worth a go. [/quote]I agree the price is good, just be aware that these aren't holding up well over time, and that you may have issues after the warranty/return period has expired.

[quote name='MarshallBTB' timestamp='1335951600' post='1638405'] cant be bad for that kind of money! [/quote]They've been replaced, that's why the price cut on old stock. The originals garnered quite a bit of criticism for their lack of bracing, no damping, and a propensity for the hardware to come loose. It remains to be seen if the new version has addressed these issues, or if all that's changed is the grille.

[quote name='chrismuzz' timestamp='1335769055' post='1635531'] is this true? So would this mean that the famous 4x10 cabinet is not as great as it could be? [/quote]It's the poster child for how not to build a speaker.

[quote name='dannybuoy' timestamp='1335290067' post='1628773'] How about a guitar cab? A sealed 1x12 from Orange or Matamp for example. [/quote]+1. Bass cabs are made to run clean, guitar cabs are made to run dirty.

[quote name='AndThenSome1' timestamp='1335270032' post='1628321'] is this pairing not potentially able to damage the cab, given that the amp puts out 500w? [/quote]Did you get one with no volume comtrols? BTW, thermal wattage ratings of drivers are meaningless. What counts is the displacement, and that of the Kappa 15 used in the OBC is only 340cc, which translates to about 100w actual capacity before reaching maximum output. For some perspective you should compare that to the listed displacement figures at Barefaced Bass, keeping in mind that doubling displacement quadruples the usable power handling.

[quote name='Jazz Bass 65' timestamp='1335203213' post='1627229'] Why oh why won't Ashdown make available a power amp version of their Little Giant? [/quote]Probably because Alto (who makes the modules) won't agree to it. Buy an Alto instead.