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Bill Fitzmaurice

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About Bill Fitzmaurice

  • Birthday 27/11/1949

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    New Hampshire, USA

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  1. Standing waves are a low frequency issue, not midrange. Adiabatic process has nothing to do with how damping and stuffing work. That's also old school theory that tried to use thermodynamics to explain how damping and stuffing functioned before the actual acoustical processes were understood.
  2. To simplify, all cabs need damping for smoother mids. Sealed cabs that sound boomy may be improved with more than just being lined, some may require being fully filled to adequately tame the boom.
  3. That's old school theory, long ago abandoned. Modern speakers are too small for standing waves to arise. If they were large enough for that to happen the wavelengths would be too long to be broken up by stuffing. The air mass with sufficient stuffing density doesn't seem larger to the driver. That said, the effects of both damping and stuffing are real, easily measured, and with sufficiently advanced speaker modeling software predictable.
  4. Cabs should be lined with either open cell urethane foam, rigid fiberglass board insulation, or polyester furniture upholstery batting, 2 to 4 cm thick. Sealed cabs may benefit from being totally filled with pillow stuffing, not foam, and absolutely not fiberglass building insulation. That depends on details about the drivers that you're probably unable to find if you have a store bought speaker. If you're building a cab with plans from a professional designer they should tell you what should be used. One can rightfully infer that if they make no mention of it that they're not from a professional.
  5. Pass band is where the speaker primarily operates. For instance, with a four string you wouldn't care about port velocity below 40Hz, as there's nothing there at sufficient levels to excite it. Full excursion is at the voltage required to reach xmax at the peak above Fb. Not at Fb of course, as that's where excursion is at a minimum. What you don't care about is velocity at maximum Pe voltage, unless you have one of those rare drivers that doesn't reach xmax well below maximum Pe.
  6. Why 4 ohms? It won't go any louder or work any better than 8 ohms. The only reason for a 4 ohm cab is to use only one with a valve amp that has no 8 ohm tap.
  7. In theory you want no more than 20 M/s within the speaker pass band at full excursion, but temper that with knowing most of the power from the electric bass is an octave up from the fundamental frequency of the note you're playing.
  8. I can supply a crossover schematic that will work much better than what you can buy, at a lower price, but it won't do you any good if you don't know how to assemble it.
  9. Impedance is not affected by using a tweeter and a woofer. Below the crossover frequency the impedance of the woofer is what the amp sees, above the crossover frequency the impedance of the tweeter is what the amp sees. Now, for the bad news. You don't have crossovers, you have first order high pass filters. That means high frequencies that the woofer can't reproduce are going to them, while the protection of the tweeters is almost non-existent. I'd get rid of what you have and replace them with these: https://www.bluearan.co.uk/index.php?id=EMIPXB2-3K5&browsemode=category If you have any electronic chops you could make your own for perhaps half the cost of a pre-made. While you're at it the cab appears to be bare inside. It should be lined with an inch or so of open cell foam or polyester batting.
  10. The speaker impedance ratings for valves is the maximum, that for SS is the minimum. Use the tap on a valve head that's equal to or more than the speaker impedance, use a total speaker load on an SS amp that's equal to or greater than the amp rating.
  11. No, as the 115 will reach its limits long before the 4x10. The increased sensitivity realized from using the two cabs may give a better result than just the one, but it also may not. Without question the best cab to use with the 410SVT is another 410SVT, if you actually need more than the one.
  12. Bass. That's the reason for the port, which MM incorrectly called a reflex horn, that what RH stands for. It would be of zero benefit for guitar. That doesn't mean guitar players might not have used them, but if so they were lugging around a lot larger cab than they needed to.
  13. That's a common misconception, even among those who really should know better. The size of the driver does not determine how low the speaker will go. A dozen or so other factors, Thiele/Small parameters, along with the cabinet design do. A 115 might go lower than a 410 but it also might not. That would be revealed by the measured SPL charts for the cabs in question, if there were any, but sadly there are not. In any event, Hartke lists the low frequency response limit of both the 4.5xl and 115 xl as 30Hz, although they don't say if that's down 3dB, 6dB, 10dB or more from the base line sensitivity, which is another bit of critical information.
  14. Then you'll end up with a 115 that can't keep up with the 410, so whatever additional low end it might have, and that's not much best case, won't be of any benefit. If you had a clean slate what you should do is find the 8 ohm cab that sounds the best to you, and if one wasn't enough add a second. +1. Your stage rig drives the stage, the PA drives the room. No one needs more than a 4x10 or 2x15, unless it's to impress the kiddies in the audience.
  15. That is a rack version, contained within a case. You may be able to find the manufacture date from the serial number. https://www.bassic.de/attachments/ampeg-dating-pdf.106974/
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