Bill Fitzmaurice

[quote name='phatbass787' post='228673' date='Jun 28 2008, 01:43 PM']Ahh I forgot about that, i think from what ive heard the 4x8 is split into two 4 ohm 2x8's so you run an input into each side and get full whack, anyone heard or got one of these cabs? Be interesting to know what it sounds like[/quote] I doubt it would do the OP much good. Four eights probaly aren't going to have more displacement than his 1x15, possibly even less. IMO it's displacement that's his limiting factor, not power. If his Diesel is loaded with an EVM it can't make use of much more than 100 watts through most of the bass range anyway, so one channel of the Fly has enough to drive it to full output.

[quote name='LeftySteve' post='228089' date='Jun 27 2008, 10:15 AM']Much as I like my Superfly I am finding it's use restricted by the inability of it to work in bridged mode to give 500W into 4ohms. Steve[/quote] Even if you could you'd only get an additional 3dB output, and that assumes that you have a cab that's not displacement limited to 250 watts or less anyway. The displacement limited power rating of any cab is a secret more tightly held than Joan Collin's real age, but on average it's 50% of the thermal rating at best, and usually less. Ergo, if you really need more than what the Superfly will deliver with one channel into one cab chances are you need a second cab anyway.

[quote name='tauzero' post='227185' date='Jun 26 2008, 06:02 AM']If they're 1/2 wavelength apart, a little thinking about the geometry of the two drivers and the listener's ear will show that the only place you can get phase cancellation will be if you are in line with them, ie. at 90 degrees to the speaker axis. If they're .7 wavelength apart, you'd get phase cancellation outside 45 degrees off-axis. You can only get phase cancellation over the whole arc in front of the speakers with 1 wavelength separation, if my quick scribblings and mental arithmetic is correct.[/quote] Kal is only partially correct, but he's a reviewer, not an engineer. The 1/2 wavelength he's refering to is the center to center to center distance at the crossover frequency in a vertically aligned MTM, which has nothing to do with the required spacing of horizontally placed drivers to prevent combing within their operating bandwidth. That is one wavelength, measured center to center. In those frequencies where that distance is less than 1 wavelength combing will not occur, where it is longer it will.

[quote name='Biggsy' post='225130' date='Jun 23 2008, 11:20 AM']I don't think cabs get much more efficient than my current ones[/quote]Possibly not commercial cabs, but no direct radiating cab is particularly efficient. One of the reasons for DIY is not having to live with the inefficiency of direct radiators.

[quote name='obbm' post='224877' date='Jun 23 2008, 06:43 AM']I strongly recommend that you read paragraph 2 on page 8 of the Hartke 5500 User Manual.[/quote]The technical acronym for this proceedure is RTFM.

[quote name='bnt' post='223644' date='Jun 21 2008, 10:51 AM']The power lost as heat in these components is proportional to the [i]square[/i] of the current (P=I²R), so if you double the current, the losses are [i]quadrupled[/i].[/quote] That's part of the overall no free lunch equation, which also encompasses output device and power supply failure if you go too low with the load impedance. Were it not so we could use 0.4 ohm speakers. That would be a very good thing as far as the efficiency of the speakers is concerned, but would require an entire retool of the amp/speaker relationship from low voltage high current to high voltage low current. Unfortunately Tesla wasn't involved when the dynamic loudspeaker came about.

[quote name='Musky' post='223115' date='Jun 20 2008, 12:40 PM']why aren't at least some manufacturers making amps with power supplies that would be capable of delivering the kind of power needed to make the most of the amp? Expense and/or weight?[/quote]Physics and the reality that there is no such thing as a free lunch. In any event, power is not the limiting factor of how loud an amp will push a speaker. A speaker's output is determined by voltage swing, not power consumed. The entire concept of going to as low an impedance load as one can to 'get all the watts out' of an amp is intrinsically flawed. The main result of so doing is to cause the amp to generate higher heat levels, shortening component life.

[quote name='Musky' post='222991' date='Jun 20 2008, 10:08 AM']Or am I missing something obvious here?[/quote] Nope. You're pretty much there. Scenario 1: You run your 500 watt/8 ohm SS amp with a 28v output into an 8 ohm speaker. It will deliver 100 watts. Add a second 8 ohm speaker, leaving all the settings the same. The voltage swing will still be 28 volts, the current will double into the halved impedance load, and you will get 200 watts. Scenario 2: Run your 500 watt amp at full power into an 8 ohm cab. The output swing will be 63 volts. Add a second 8 ohm cab. You won't get 63 volts, because the amp's power supply isn't capable of delivering maximum voltage into all impedance loads. It generally drops by a factor of .7 for each halving of the load impedance, so instead of 1,000 watts into 4 ohms you might get 700. So while you will get a doubling of power with a halved impedance load if the amp is well below full power you won't get it at full power.

[quote name='gypsymoth' post='222372' date='Jun 19 2008, 01:27 PM']the fender/fender combination is IT and is unbeatable - because that is what this contraption is supposed to sound like - technically right or not.[/quote]My first Fender/Fender wasn't first generation, but close enough to it, 1965 Jazz/Bassman, bought new. The damn thing farted out on the first low E I hit and every one subsequent. Never satisfied with how inept it was at actually producing useful bass I studied audio engineering to find out why. Today I owe my livelihood to Leo Fender's never having done the same.

[quote name='lowhand_mike' post='222228' date='Jun 19 2008, 10:27 AM']the same as in cross firing?[/quote] +1, though you don't have to limit yourself to a pair of drivers, you can use four or more to get the added sensitivity of an array. [quote]it is perhaps worth noting that all these problems were recognised waaay back[/quote]+1, though waaay back starts in 1927, when films added sound. Until the 1970s most of the innovations in sound technology were driven by what was the single largest industry that employed sound reproduction, and that was the moving picture industry. The shift away from the movie industry as the leader in the field started with the introduction of the VCR, which made home theater a reality. In terms of units sold home theater now accounts for the largest slice of the audio pie.

[quote name='lowhand_mike' post='222016' date='Jun 19 2008, 06:31 AM']i can understand roughly what those guys were saying about wavelengths etc but are they actually talking about speaker positioning....where-as we are talking about the wave lengths coming from a single box,.[/quote]Both. The rules that apply for placement of speakers within a room also apply to drivers within a cabinet. Just think of the cabinet as a room within which drivers reside, and that what differs between the two scenarios is the size of the 'room'. [quote]centre speakers for home cinema and lots of centres have two woofers each side of a tweeter[/quote] Same rules, you need to cross the woofers to the tweeter no higher than the 1 wavelength center to center distance between the woofers. But that only addresses combing, not dispersion, which is better on the horizontal plane with the woofers vertical. The inability to place woofers vertically below a TV is problematic, but can be compensated for by having them in a concave array.

[quote name='bass_ferret' post='221834' date='Jun 18 2008, 06:55 PM']Now i am really confused - combing and beaming![/quote] Beaming is when the dispersion angle is so narrow that you can't hear the mids or highs if you move a foot to either side. It's why you can't hear the guitar cab four feet to your left and four feet in back of you, whilst the poor lady at the table in front of the guitar cab fifty feet into the club stuffs her ears full of napkins in a futile attempt at self-defense. Combing is when the frequency response of the cab constantly changes as you move across the soundfield and literally doesn't sound the same in any two spots. The other blokes complaining you were too loud while you couldn't hear yourself probably involved both beaming and room modes, where in the spot you were standing reflected waves off the walls and/or ceiling cancelled out much of your low frequency output, while elsewhere in the room that was not the case. None of these conditions are at all desirable.

[quote name='lowhand_mike' post='221575' date='Jun 18 2008, 12:40 PM']i guess thats what raggy, and myself were thinking. or would it be that because they are close to side by side that they still suffer?[/quote] Two factors are at work. The closer the driver centers are to vertical the higher the frequency before combing starts, which happens when the driver centers are more than 1 wavelength apart. Fully vertical there can be no combing, but if the driver only goes to, for instance, 3kHz, then a CTC of four inches is sufficient. The second factor is the total width of the radiating plane, outer cone edge to outer cone edge. As that exceeds one wavelength the horizontal dispersion angle shrinks, eventually to the point of beaming. So even if combing isn't an issue dispersion is, especially considering that four inch wavelength at 3kHz. Even a single ten will be beaming up that high. Now consider a 2x12 or 4x12 guitar cab with driver CTC on the order of 16 inches and a radiating plane on the order of 22 inches wide, and the 4kHz tones they're pushing with only 3.4 inch wavelengths, and one can hardly tell which is worse, the combing or the beaming.

[quote name='stevie' post='221527' date='Jun 18 2008, 11:47 AM']1 wavelength is way too much for interdriver spacing. Anyone who familiar with the laws of acoustics would know that where the time displacement between two low frequency drivers corresponds to one-half of one wavelength, the outputs of the two low frequency drivers will null. 180 degrees and all that. Spacing needs to be less than half a wavelength. Back to the Loudspeaker Cookbook for you. It's interesting that you use the term 'debate' here, because I have not seen you debating on any of the threads you have been involved in on this forum - merely pronouncing, and belittling others.[/quote]Stevie, the one compliment I will pay to you is that you remind me very much of the Honorable President of the United States, George W. Bush. Like he, everytime you open your mouth you somehow manage to stick your foot further down your throat than the time before. Your above statement is complete and utter gibberish. I'll let Alex point out why if he cares to, I have far more important things to attend to. Cutting my toenails is first on the list.

[quote name='lowhand_mike' post='221142' date='Jun 18 2008, 04:43 AM'] ha i just thought one was a backup. doh! bill i'm glad you mentioned about being able to have side by side configurations if you go one wavelenthg out of p[hase or what ever it was. i was wondering about that last night. as in why cant we actually still have speakers side by side but performing correctly?[/quote]You can, as seen in this pic of a typical PA line array cab The woofers are at either end of the cab, crossed over at 350 Hz to the mids that lie just inboard of them. Being closer together the mids can run to 1.5kHz, where they cross to the center mounted HF drivers. [quote name='alexclaber' post='221378' date='Jun 18 2008, 08:55 AM']Something I've noticed from modelling drivers in WinISD Pro is that the phase difference between models is rarely so huge as to cause cancellation if the cab tuning frequency is the same.[/quote] It's a bit more complicated than that, and while I'd rather not get even deeper into the science of it, time align also enters the equation. Phase response is the major culprit at low frequencies, and if the cabs are properly tuned to their drivers one would expect a 2x10 and a 1x15 fb to be off by at least 10 Hz. In the midbass phase response becomes moot, but when you hit the midrange time-align becomes critical. For the best known example research the (in) famous Eleanor Powell tap dancing fiasco that led to the development of the Altec A7 style of theater boxes. For the sake of simplicity I lump the phase response and time align issues into the same bundle, since time align is a phase issue as well, though from a different source.

[quote name='JonnyM' post='221059' date='Jun 17 2008, 08:16 PM']Can't resist posting these pics... [attachment=9739:1974_07_21.jpg] [attachment=9740:grateful..._sound_1.jpg] The backline IS the PA (the bass "rig" is the tallest stacks the right and left of the drums: 2 vertical stacks of 15's, 18 per stack... (I have an LMII and 2x10 Traveller and when I need to, I'll get another identical 2x10 to stack vertically... )[/quote] The Dead were probably the most technically literate band of all time. They did their homework for sure. Their most ingenious invention was to use two mics side by side, wired reverse-polarity. They'd sing into only one, but any foldback was equally received by both, where the reverse polarilty cancelled out the signal, allowing outragous levels with no feedback.

[quote name='stevie' post='220863' date='Jun 17 2008, 02:19 PM']Studio monitors from ATC, Quested and Dynaudio, by the way. And when these guys need four drivers, guess what?[/quote] Stevie, you'd have a lot more success arguing the fine points of loudspeaker design if you understood any of them. If you did you'd know that drivers may be placed on the horizontal plane if they are crossed over below the frequency that is 1 wavelength at their CTC spacing. Debating the laws of acoustics is a waste of my time, as being laws they are not subject to debate. I'm usually quite patient at explaining said laws and how they affect gear choices to those who have an interest in furthering their education. OTOH you strike me as one who clearly has already acquired all the knowledge he ever cares to, and that being the case please refrain from wasting any more of my time.

[quote name='stevie' post='220772' date='Jun 17 2008, 12:31 PM']What exactly is this "flawed standard"? Can you be more specific?[/quote] Foremost, placing drivers horizontally. For an example of how drivers should be placed investigate the circa 1950 PA installation in St. Paul's Cathedral in London, which was only recently upgraded because it worked so well for a half century plus despite being in the most difficult of environments. Assumption is Jim Marshall was not a parishoner.

[quote name='chris_b' post='220334' date='Jun 16 2008, 09:17 PM']At the risk of starting another argument here..... I repeat, it is my experience over the last 10 years that you can successfully run a 2x10 and a 1x15 together and it is my current experience (of 3 months) that I am successfully combining cabs from different manufacturers.[/quote]No one is saying that you cannot use different driver sizes or cabs from different manufacturers covering the same bandwidth and not have a useable result. OTOH if the goal is the best possible result that is obtained by either using identical drivers/cabinets or by using different size drivers in a sytem that has been engineered from the ground up to do so. Using the Chinese Restaurant Menu Method (as in pick one item from column A, one item from colunm is not sound audio practice.

[quote name='lowhand_mike' post='219952' date='Jun 16 2008, 10:57 AM']think bill means that as the "norm" for bass amps and indeed guitar amps was started back in the day as horizontal 2x10s and 4x10s when audio engineering was a little less refined it has been carried through,.[/quote] +1. The engineering used by the vast majority of musical instrument cabs has not changed significantly since the mid 1970s, and it was 30 years obsolete even then. If either Leo Fender or Jim Marshall had possessed beyond a rudimentary knowledge of audio theory in general and loudspeaker design in particular the vast majority of musical instrument speaker topologies introduced since 1955 would never have appeared in the first place. Fender was a machinest who didn't even play guitar or bass, and Marshall was a drummer. Their method of speaker design was 'stick some drivers in a box'. Unfortunately they set a flawed standard that still dominates the marketplace today.

[quote name='chris_b' post='219591' date='Jun 15 2008, 08:16 PM']2x10's have sat on top of 4x10's and 1x15's for years with no trouble[/quote] 'No trouble' is a matter of opinion. Mine is that of a bass player who also happens to be an audio engineer. As for specific examples, that would be the simultaneous using of any two cabs that don't have identical phase response. Since no two cabs that don't use identical drivers in identical alignments can have identical phase response that makes every use of non-identical cabs a specific example. I'm not saying they can't sound acceptable, but they would sound better properly matched. Amongst other things.[quote]Wow!! Dismissing the efforts of an entire billion dollar industry at a stroke... nice one![/quote] Just the instrument cab industry. The hi-fi, theater and PA guys got it right a half century ago, the instrument market segment is a wee bit slow on the uptake.

[quote name='bass_ferret' post='219442' date='Jun 15 2008, 03:55 PM']Bill may be assuming that you are using a crossover for these cabs but I suspect you are intending to put the full signal through both. As has been said many times putting the same signal through different cabs can produce unpredictable results and is likely to sound bad which ever way you stack them.[/quote] I'm assuming he is not using a crossover. Tens will naturally have a wider midrange dispersion angle and a higher frequency response than fifteens, so the caveat applies with or without being crossed. [quote]Then how come the workhorse rig for years was a Trace 4x10 on top of a Trace 1x15 both fed with the same signal from Trace Amp?[/quote]Because no manufacturer had, or has for that matter, any incentive to do better when they sell all the mediocre high profit margin junk they can crank out. And bassplayers are artists, not engineers, so by and large they just don't know any better.

[quote name='Youngatheart' post='219318' date='Jun 15 2008, 12:50 PM']Is there any reason why you can't stack a 1x15 on top of a 2x10. Trust me there is a sensible reason for me asking this [/quote] That puts the non-directional lows closer to ear level and the directional mids down below your knees. Perfectly OK if you're in the habit of playing whilst standing on your head.

[quote name='Mottlefeeder' post='217129' date='Jun 11 2008, 02:31 PM']I agree that bass players use EQ, but their initial stance is usually 'Can I hear it with the EQ flat first?'[/quote] Chances are they never do, since almost no amp around is actually flat. Most have some sort of pre-shaping built in. [quote]My personal view of EQ is that it is like a car accelerator pedal. If you have it at maximum all the time, then something is wrong[/quote]Quite right. The thing about EQ is that if you're using it correctly you should be cutting as much as you're boosting, and neither cutting nor boosting at anywhere near full capacity.

[quote name='rodl2005' post='216570' date='Jun 11 2008, 02:31 AM'][quote]"I had personal experience of this with a Peavey 115BW. I added a Peavey 2x10 and it sounded sh*t - much better with each individual cab, and whats more the 2x10 was actually deeper so I sold the 115 and got another 2x10."[/quote] IME this MAY've been due to the cabs/spkrs being outta phase. [/quote] Maybe, though I believe you are referring to polarity, which isn't the same thing. With reversed polarity the two cabs would be out of phase pretty much through their entire bandwidth. But even with like polarity two dissimilar cabs will be out of phase at some frequencies. That's because the phase response of every speaker varies with frequency. The only way to be sure that two speakers have identical phase responses, and therefore won't interfere with each other, is for them to be identical.