Bill Fitzmaurice

The rear ported are that way because there's not enough room to fit them on the front. Larger box equals lower response with the same drivers used.

[quote name='Mr. Foxen' timestamp='1338897483' post='1680708'] That says a short causes no harm at all, which is as I said, low impedance is not an issue for damage concerns. [/quote]+1. Most tube amps use a closed circuit switching output jack that shorts the output if there's no speaker plugged in. That's to prevent damage from what really does bother tubes, which is no load. They're not happy with a load higher than the tap rating either, but a load lower than the tap rating is to a tube as water is to a duck.

[quote name='Lord Sausage' timestamp='1338829278' post='1679763'] So what do 1x15 give you then is it more low frequencies or is that bollocks! [/quote]Bollocks. Cone size in and of itself only affects one function, the angle of dispersion, The larger the driver the narrower the angle. All other aspects are determined by the driver specs. Same specs, same results, no matter what the cone size.

[quote name='Lord Sausage' timestamp='1338828441' post='1679756'] Also what about ohms? If you have say an amp that's 500w at 4ohms and 350w at 8 ohms and you run it thru a 4x12 that handles 500w at 8 ohms, i take it you'll get 350. If you add say a 1x15 cab that is 8 ohm would you still get 350 or do the ohms increase or decrease. Would i have to buy 4ohm cabs. [/quote]The watts just don't matter, you have to increase them by a factor of ten to sound twice as loud. Always buy 8 ohm cabs so that if you need to add a second you can. And the last thing you'd add to a 412 is a 115, a 115 can't even keep up with a 212.

[quote name='Lord Sausage' timestamp='1338802455' post='1679298'] Does it matter if the amp is more powerful than the speakers. [/quote]Only if it has no volume control.

[quote name='CraigPlaysBass' timestamp='1338409734' post='1674271'] Could someone please explain to me clearly what the difference is between DC and the clipped waveform? [/quote]DC is constant polarity and has no phase. AC has phase, and with each passage of 180 degrees of phase polarity is reversed.

[quote name='GregBass' timestamp='1338402599' post='1674085'] Good question. I posted what I felt was reasionable advice, but a couple of "experts" decided to rip into what I said. I responded. Things got silly. [/quote]Well, if you're going to give expert advise the first requirement is that you be an expert. My credentials as such are a matter of public record. I also have a personal rule that I'm here to teach those wishing to learn, not argue with those who don't. As you clearly have no desire to learn, only a penchant to argue that which you don't comprehend, with you I am done.

[quote name='GregBass' timestamp='1338387450' post='1673703'] And isn't a flat voltage waveform actually a direct voltage? [/quote]No. [quote] Go run a fast Fourier transform on your 'square' wave and see what harmonics you get [/quote]+1. Or run it through a low pass filter to remove the harmonics. What will remain is a sine wave. A woofer voice coil is a low pass filter. One of the design characteristics of guitar drivers is low Le, so that the harmonics aren't filtered at too low a corner frequency. .

[quote name='GregBass' timestamp='1338384355' post='1673631'] Clipping is EXACTLY putting DC in short bursts across the speaker. [/quote]It does not. DC does not alternate between positive and negative. [quote]Think of the theory. Consider a sine wave. When it clips the top of the waveform goes flat - that's basic waveform analysis. [/quote] That's flawed waveform analysis. The difference between a sine wave and square wave is the harmonic content. A sine wave has none, a square wave has all the harmionics of the fundamental occuring at the same voltage swing as the fundamental. [quote] the Fane technical department describe it as precisely that when they explain that over pushing the amp is more likely to damage speakers than driving them too hard.[/quote] If that's the case they're incorrect as well. I doubt Celestion would make such a grievious error, knowing that the tone of a guitar is pretty much predicated on clipping not only the amp but the driver as well. This document is the source of the myth of underpowering. If readers all paid attention to the key phrase 'high frequency components' the myth might not have arisen. But like all myths it grew with each retelling. [url="http://www.jblpro.com/pub/technote/lowpower.pdf"]http://www.jblpro.co...te/lowpower.pdf[/url] And as to why cliiping has no effect whatsoever on woofers, not only does the added harmonic content of a clipped signal not increase the maximum voltage swing, the majority of the added harmonic content is filtered out by the inductlve and capacitive reactance of the voice coil.

[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.