Bill Fitzmaurice

[quote name='Jack' post='119059' date='Jan 12 2008, 06:31 AM']Yup, head->cab 1->cab 2 is still parallel if thats what you mean. I think the reason Eden have series on some of their cheaper combos is so a beginner can plug in ANY cab and not have to worry about impedance.[/quote] More likely the internal driver(s) is already at the amp's minimum load rating to maximize output. For example, all the Nemisis save the 15 are 4 ohm rated with 4 ohm speakers.

A transformer capable of handling the power draw of an amp will require no less than the same VA rating as the transformer in the amp, so you might as well just replace that. Before doing so RTFM and be sure the amp doesn't have a dual primary that can be reconfigured for 240.

[quote name='Jack' post='118542' date='Jan 11 2008, 09:17 AM']I think Bill was more about 'ohmage' than 'resistance'. Hey, at least youre aware of 'it', more than a lot of people.[/quote] The problem with the quasi-word 'ohmage' is that it could refer to impedance, could refer to resistance, could refer to inductive or capacitive reactance. Being non-specific makes it useless in an engineering context, so while it does appear in the vernacular it is not used by the engineering community. Resistance is only used with respect to speakers in its context as a component of impedance.

Gentlemen, the term is [b]impedance[/b]. Bad enough that we butcher the Queen's English as badly as we do on our side of the pond with words concocted out of whole cloth.

[quote name='Hamster' post='117886' date='Jan 10 2008, 09:58 AM']Well don't keep us all in suspense Bill! - which one is best? Hamster[/quote] Fuschia.

[quote name='gilmour' post='117671' date='Jan 10 2008, 05:15 AM']Does that mean an SWR Redhead would go Faster? [/quote] Laugh you may, but I recall many extended discussions between ostensibly intelligent human beings on a forum who debated ad nauseum over which color shrink wrap tubing on wire connections sounded better.

[quote name='Gray' post='117469' date='Jan 9 2008, 05:15 PM']Turbosound decided to use the 'turbo blue' paint colour on their cabinets because it sounded 'better' in blind listening tests...[/quote]Or they got a good price on a boatload of blue paint that no one else wanted.

[quote name='Gray' post='117184' date='Jan 9 2008, 12:22 PM']In PA world (particularly in regards to driving bins) its fairly standard practice to use amps which are twice the rated RMS output of the speakers they are driving (i.e. 1000 Watt RMS amp driving a 500 watt RMS cone). Gray[/quote]In the instrument amp world the opposite is very often the case. With PA systems one does not wish to have distortion anywhere in the signal chain. With instruments distortion, sourced both within the amps and the speakers, is part and parcel of the instrument tone. Bass in general doesn't go to the extremes that guitar does in terms of the distortion density, but when a bass player refers to 'growl' in his tone distortion is the source.

[quote name='warwickhunt' post='117116' date='Jan 9 2008, 11:28 AM']no amount of charts and graphs can account for it![/quote] Actually, they do. The problem is obtaining accurate data, or more to the point where the electric bass cab industry is concerned, any data.

[quote name='Crazykiwi' post='113533' date='Jan 4 2008, 08:57 AM']EBS rate their 212 at 103dB.[/quote]That would have to be a peak reading. There are no twelve inch drivers capable of that level broadband averaged. Twelves do exist that have 100dB sensitivity (making a pair 103dB), even a bit more, but they only achieve that sensitivity above 200 Hz or so. Below 100Hz, where it counts, 98dB is the practical limit in a direct radiator cabinet.

[quote name='Hamster' post='113329' date='Jan 3 2008, 08:51 PM']IIRC, it's twice as loud as a speaker of 103db sensitivity if using the same input level. I may be wrong, but I think I'm right. No doubt Bill F or Alex C will be along soon to put me right Hamster[/quote]Close. A 3dB difference is equal to twice/half the power, but not twice/half the perceived volume. Hearing response is logarithmic, so it takes a 10dB difference to sound twice/half as loud. As for manufacturers SPL ratings, they're next to useless, because they aren't referenced to frequency. Some, like Ampeg, quote a legitimate average figure. Some, like Eden, quote a peak figure. Some quote figures that defy all known laws of physics. None save Phil Jones provide the all important SPL charts that allow one to know the facts.

[quote name='jamjarjay' post='111271' date='Dec 30 2007, 08:50 PM']how can I tell I'm running too hard without damaging my head? Thanks, JJJ[/quote] Clipping can't damage a head. But a clipped waveform greatly increases the high-frequency content of the signal, and that can lead to overpowering and possibly damaging tweeters. If you don't have tweeters don't worry about it.

[quote name='umph' post='110319' date='Dec 28 2007, 03:00 PM']if its ported you'd probly want the port on the floor so you get more low end. you can always put it in a corner to make it louder to.[/quote] No difference. A port's output is roughly from 40 to 80 Hz, and is omnidirectional. If it's within less than a quarter wavelength of a boundary it gets boundary reinforcement. A quarter wavelength at 80 Hz is 3.5 feet. [quote]There has been a tendency for some time now for hi-fi cabinets and multi-channel sound systems to follow this path. You don't see many cabs that don't try to keep a fairly narrow front face, making up internal volume with back to front depth as well as height. A narrow front face apparently helps to give a better stereo image when using two cabinets and helps the perceived location of sound in a room if using more than two in a multi-channel set-up. Even lateral dispersion is one of the factors affecting how well a pair of speakers create a believable stereo image.[/quote] That all has to do with diffraction, which is a different matter entirely. [quote]Some say that rounding off the edges of cabinets helps as well, but whether this would have any useful purpose on a bass cab is debatable.[/quote]Also a diffraction issue, and less than about a 2 inch radius has little to no effect.

[quote name='bass_ferret' post='108993' date='Dec 24 2007, 12:13 PM']I wonder how this baby will sound? [/quote] On the technical side, it's a bass reflex cab, like 90% of the cabs on the maket, loaded with Eminence dirvers, like 90% of the cabs on the market. But it does have the drivers vertically aligned the way they should be, not horizontal like 90% of the cabs on the market, so it's a step in the right direction. If it only had a midrange driver instead of a tweeter, so there would not be a midrange 'hole' in the response, and if the box were actually large enough to allow the woofers to work as well as they could, I'd call it a proper design.

[quote name='Hamster' post='108895' date='Dec 24 2007, 07:51 AM']IIRC, the argument is that it's always best to stack speakers vertically. It improves the vertical dispersion - which I can get my head around, and for some reason it improves the wider dispersion - which I don't understand I'm trusting the opinion of someone like Bill Fitzmaurice or Alex Claber on this. Hamster[/quote]Two reasons for vertical stacking. One, you can hear them better. Two, the audience can hear them better. That has to do with two other facts. First, the all important midrange frequencies travel in relatively straight lines. The further the speakers are below your ear level the more difficult it is to hear them. Second, the angles of dispersion are inversely proportional to the width and height of the source. A low wide source has narrow dispersion on the horizontal plane, wide dispersion on the vertical plane, and that's the precise opposite of what's desired. Wide horizontal dispersion, for the benefit of the audience, and narrow vertical dispersion, so as not to waste power scerenading spiders on the ceiling and mites on the floor, is what you want, and you get that from a source that is narrow and high. [quote]TBH you aren't talking HUGE difference when you do this.[/quote] Not necessary with one 2x10, but two stacked on end one over the other is significantly different than two side by side on the floor. That's why side by side cluster PA systems are landfill bound, being replaced by tall line arrays. Bass cabs should be tall and narrow too, but technologically the electric bass cab industry lags the PA industry by at least a decade, if not two.

[quote name='TimmyC' post='108048' date='Dec 22 2007, 06:23 AM']I thought he used an Ampeg B15n for a lot too?[/quote]For monitoring, his recorded sound was taken direct. The purpose of tweeters is to allow the full range of the bass to be reproduced. As noted previously the main defect usually lies in the implementation, not the device. Most bass cabs would be far better served using a midrange driver in lieu of or in addition to a tweeter, the main reason why they aren't is cost, pure and simple.

IMO combos are almost valueless. Where portability is concerned sticking the head and speaker in the same box just makes for a heavier box. Where sound is concerned, in the effort to keep the overall box size and weight manageable they're even worse than separates vis-a-vis using too small a cab for the drivers within. As for flexibility, I'd rather a separate head and well engineered cabs, using as many or as few cabs as the gig requires so that I'm neither lugging too much gear to a small gig nor under-gunned at a large one. The only combo I'd consider is for personal practice, where output and tone aren't a consideration.

[quote name='jammie17' post='104520' date='Dec 14 2007, 04:38 PM']McIntosh ARE professional power amps, Gratefull Dead toured with them for years and they are used for pa amplification....[/quote] McIntosh makes great gear, but they have always been a high-fidelity company, never pro-sound in the vein of Crown, Crest, QSC, etc. Decades ago they were often employed in pro-sound applications, but that's because at that time all amps were hi-fi and theatrical gear drafted into pro use. While one could use current McIntosh offerings in pro-sound applications, it's not their focus and they don't specifically market their products for pro-sound usage. So doing allows them to use features like autoformers in home and studio applications where the resulting extra weight and chassis size is not a concern. But you won't find an autoformer in an amp made for the pro-touring sound market.

[quote name='jammie17' post='104467' date='Dec 14 2007, 02:32 PM']Ahhh, you see I did not know that about them. So, an an amplifier that has say, three different outputs...say 2,4,8, ohms, has three Autoformers?[/quote] A tube amp doesn't have any. Tube amps use multiple tap secondary transformers. A transistor amp can use a single autoformer with multple taps, but no professional amps I know of do, it's an unnecessary expense and adds weight as well as cost.

[quote name='jammie17' post='104392' date='Dec 14 2007, 12:03 PM']The Autoformer creates an ideal match between the power amplifier output stage and the loudspeaker.[/quote]Autoformers are nothing new, they've been used for decades. They're only necessary if the impedance load is lower than the output stage can handle in a normal direct coupled configuration. While acting like transformers they have only one winding, so they are not preferred for use in audio, as there is no separation between a primary and secondary. Their advantage is that since they have only one winding they are cheaper to produce than a transformer.

[quote name='jammie17' post='104359' date='Dec 14 2007, 11:11 AM']Don't want to argue. Mc'Intosh uses output transformers called, "audioformers" with s/s power amps.[/quote]Once upon a time, before the invention of transistors capable of being direct coupled, all SS amps used output transformers. For the last 40 odd years direct coupled outputs have been preferred.

[quote name='jammie17' post='104039' date='Dec 13 2007, 03:01 PM']Ahh..thank you Bill...I did mis-state. Let me re-state. 300 watt amp with multipal taps on it. 2, 4, 8. Amplifier is claimed to deliver 300 watts into evey load, however, if you hook up the same load, say, 4 ohms, to the different taps, you get three different volume levels. Why? Three different Voltages delivered at those different outputs. Voltage = volume...so in the ohms law it would be best to have more voltage with less current....but then speaker control would suffer.[/quote] Irrespective of the tap used if you don't change the impedance of the load. ie., the speaker, then you are not changing the output voltage of the amp if the same power output is maintained. What you are changing by using a different tap is the number of turns on the secondary of the output transformer being utilized, and yes, that will alter the volume level, because it changes the output voltage available. But it does not alter the current available, that is a constant with a tube amp, so if the volume goes down it is because the voltage swing is also down. Doing so is also begging for trouble, as an impedance mismatch between the output transformer and speaker can fry everything from the output transformer to the output tubes to the input transformer, and everything in between. Most amps are built to withstand abuse of this sort, but many have found out the hard way that amps will only take so much.

[quote name='Peaty' post='103920' date='Dec 13 2007, 10:36 AM']Hi All, yup, I took it out of the cabinet and the speaker had no info on it what so ever, hence my question.[/quote] Confucius say "picture worth thousand words".

[quote name='jammie17' post='103682' date='Dec 12 2007, 09:16 PM']Well, that's not necessarily true. 300 watts with a lot of current vs voltage, or 300 watts with a lot of voltage vs current. [/quote] It's always true. Ohm's Law. For a given wattage in order to alter either the current or voltage one must also alter the load impedance. For instance, 300 watts into 4 ohms is 34.6 volts at 8.7 amperes, period.

[quote name='carlosfandango' post='102945' date='Dec 11 2007, 05:04 PM']Hmmmm that sounds interesting.....how does this work? Do you mean like you would use a compressor/limiter e.g when mastering a recording or in modern PA systems to create a "louder" mix?[/quote]That's pretty much it. The power output of an amp is limited by its voltage swing. Compression allows one to increase the density of the signal within a given voltage swing, therefore sounding louder without actually being louder. The one thing that sets valves apart is that they can compress the signal in both the pre-amp and output stage, while SS can only do so in the pre-amp, so while valve sound can be emulated it can't quite be duplicated.