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Bill Fitzmaurice

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Everything posted by Bill Fitzmaurice

  1. By posting in a zombie thread on a totally unrelated topic you appear to be a spambot, as that's typical of what they do, especially when it's their first post. You also greatly reduce the chances of someone who may be of assistance seeing your question. Someone who has the schematic you need may have no reason to read a three year old thread about RMS versus peak watts.
  2. Did you happen to read the subject of this thread? And why did you double post? Trying to live up to your username?
  3. It's probably not their impedance, as most electronic devices have a high input impedance and low output impedance. It's their input sensitivities and operating levels that can vary widely.
  4. I think you've got that backwards. The load input impedance should be at least ten times the impedance of the source. This goes into greater detail than most of use need to know: http://whirlwindusa.com/support/tech-articles/high-and-low-impedance-signals/ The gist of it says ' In order to preserve signal level and frequency response, it's important to drive equipment with a source signal that is lower in impedance than the destination equipment's input impedance. If the input impedance of a device is not significantly higher than the source impedance, the signal will be reduced or “loaded down” and its signal to noise ratio and frequency response will suffer. ' It depends. On a console the mic channel needs an additional gain stage because low-Z mics have very low output compared to a a high-Z guitar or bass pickup. But both have lower output than a low-Z line level signal.
  5. Impedance matching usually doesn't make that much difference. What causes problems is level matching. Something made to work with a low level input signal isn't going to be happy if you plug in something with a high level output signal, and vice versa.
  6. The input impedance of amps and devices is going to be similar. The output impedance and output level of passives versus actives is different, as is the input sensitivity, output impedance and output level of other devices, depending on where they're supposed to go in the signal chain. You just have to experiment as to which works where.
  7. It's not the instrument, it's the pickups. Passives have a loss of highs when the instrument volume is turned down, actives don't. It's one of the downsides inherent to passives.
  8. It's more complicated than that, because watts vary with current, current varies with impedance, and impedance varies with frequency. With equal dB level output you can be pushing 200w at 50Hz but only 40w at 70Hz. Voltage delivery is a constant into any load impedance, so by all rights both amps and speakers should be rated for maximum voltage, but someone decided on watts back in the 1920s and we've been stuck with it ever since.
  9. It means they're trying to bamboozle you with phony specs. Power handing should always be RMS watts (even though there's technically no such thing as RMS watts, but that's a different discussion). That's probably what the 1,100 watt figure refers to. Not that it matters all that much, because that figure is thermal, while what counts is mechanical power handling. You'll sooner find Waldo than that number.
  10. It's not ported in the usual fashion. The rear chamber is sealed. There's a down firing driver you can't see operating into a vented chamber, making it a 4th order band pass. There's no mention if the forward firing drivers share the same chamber as the down firing driver. If they do that further complicates the design process to get the best possible result. The commentary in the video leads me to believe that it's more of a seat of the pants design than a high tech design, but that can work too.
  11. They don't need thicker plywood, they need bracing. A single brace connecting the middles of two opposing panels has the same effect as making the panels twice as thick, with far less weight. More braces make things even better. There are three ways that manufacturers cheap out on speakers. One is to use inexpensive drivers, the other two are insufficient or even non-existent bracing and wadding. All three they get away with because you can't see it without taking the cab apart. They have less low end than ported, which can seem tighter, especially in comparison with ported cabs that are too small, which results in boomy response.
  12. There's more than one way to make a dual chamber bass reflex. For that matter there's more than one way to make just about any alignment.
  13. With 1/4" outputs it's better to use both, because being originally intended for telephone switchboards they don't have high current capacity, so with more than 200w amps it's prudent to split the current to two sets of connectors. That's not a concern with the far higher current capacity of Speakons.
  14. That pretty much describes a double chamber bass reflex box. The oldest example of that design that I recall was in 'Designing, Building and Testing Your Own Speaker System', by David B, Weems, first edition 1981. I doubt that Weems invented that alignment, so it probably dates back further than that.
  15. If you want to see how little there is in the way of new speaker technology read 'Elements of Acoustical Engineering' by Harry Olson, 1957. http://cyrille.pinton.free.fr/electroac/lectures_utiles/son/Olson.pdf The only major item missing is the use of Thiele/Small parameters, which came along eight years later. Most of what's contained in the 1957 printing was contained in the 1940 first edition. The math (or maths, if you prefer) hasn't changed. What has changed is the hardware, which has allowed significant reductions in enclosure size and increases in output, although much of the alteration in driver technology is tied to amplifier technology. When 20 watts was the largest amp available speaker power handling mattered little, while speaker sensitivity mattered a lot.
  16. Assuming the amp jacks are parallel wired, which nearly all are, the two options are electrically identical.
  17. I've yet to see a technical description or a picture of the innards that shows what it is. It may be a double bass reflex with a passive radiator connecting the two rear chambers as opposed to a port, but that's purely a guess without any evidence to back it up. There's no defying physics, nor much new under the sun for that matter. All reflex cabs reduce cone excursion. While most do so only at the tuned frequency of the box it's possible to have more than one tuning frequency, as in a double bass reflex, to reduce excursion at more than one frequency.
  18. My 2x12 '65 Fender Bassman sounded good at bedroom levels too, but being loaded with guitar drivers, as most bass cabs were back in the day, War Volume was more of a skirmish than a battle.
  19. The source doesn't matter, and an interface isn't necessarily required. The issue is that the output of an iPod is probably at line level, about a volt. The output of passive pickups is closer to 1/10 volt, so an iPad could overload the input stage. That normally would only cause the sound to be very distorted, but if one's not careful it could pop something in the amp. If anything valves are less likely to suffer damage from a high level source.
  20. You're right, 35 liters isn't fantastic for bass. It's barely marginal, and assuming you didn't account for the space taken up by the ports it's not even that large. I'd move on.
  21. A 12" driver doesn't mean it's good for bass. If it's really optimized for guitar the xmax will be too short and Fs too high.
  22. It's not likely A, which you see in valve amps of no more than 20w.
  23. It does depend on the amp. Where the DI out taps the signal isn't the same with all amps.
  24. The minimum protection required is a full inch of polystyrene foam beneath heavy cardboard.
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