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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. My outside thermometer currently reads 2F/-17C. What's just as significant is that my indoor humidity meter reads 26%. I have a large humidifier running all the time, using on average two liters of water a day, otherwise it would be closer to 10%, a by-product of heating the house. Where the potential for moisture damage is concerned that's far more likely if you live in the tropics or near the ocean than if you live in a temperate climate.
  2. Condensation is more of a concern with amps. I've never run into a condensation problem with speakers, in temperatures that you never experience in the UK.
  3. Cold won't bother it, but thermal shock can. Let it get as warm as possible before using it.
  4. Doesn't it have a volume knob? Either reduces the voltage drive to the speaker, giving the same result. The only reason to use a power soak is when you have a valve amp that you want to over drive the power section on while keeping the volume low.
  5. That's a common misconception. The load on the output valves isn't the speaker, it's the output transformer. The impedance of the output transformer primary winding is a constant, therefore the speaker load doesn't affect current delivery. With direct coupled SS amps as the load goes down current goes up, because as the name infers the speaker load is directly coupled to the output devices. Using voltage to measure sensitivity doesn't favor a lower impedance speaker. For that matter one cannot measure sensitivity with anything other than a voltage source. One cannot hook up a meter to the amp output to read the amp power output, as no such meter exists. One may only read the voltage output. If one could read the power output it would render the sensitivity spec useless, because power output is different at every frequency. Voltage is used not only because it can be measured but also because it's constant no matter what the frequency.
  6. Speakers aren't driven by watts, they're driven by volts. While an 8 ohm speaker sensitivity is usually quantified as dB/1 watt/1 meter that's incorrect, because the amp power isn't a constant. It varies with the actual impedance load, which varies with frequency. If amplifiers were constant power devices every frequency would be at a different level. But they're not. An amp does provide constant voltage output at every frequency, no matter what the speaker impedance is at that frequency. Therefore the correct way to state sensitivity with an 8 ohm speaker is dB/2.83v/1 meter. If you add another identical speaker the amp output voltage remains the same, while sensitivity of the pair goes up 6dB compared to just the one. As to why sensitivity goes up by 6dB, output is dependent on cone displacement. When you double the displacement, which is cone area multiplied by excursion, you get a 6dB increase in output. In the case of adding a second identical speaker while maintaining the same voltage the cone area doubles, excursion remains the same for both, therefore displacement doubles and output goes up by 6dB.
  7. If you run two identical 8 ohm cabs (or whatever impedance) voltage sensitivity goes up by 6dB compared to one. That's what's responsible for the increase in output, not power. Power goes up because the halved impedance load doubles the current draw, but that's really anecdotal. You don't run two cabs to get more power out of the amp, you run them to take advantage of the sensitivity increase.
  8. Making that error impossible is reason enough why only Speakons should be used.
  9. That's fine. The trouble with your tech's advice is what does one do it they have a 2.67 ohm load as in the case of the OP? How does one match that exactly with the tap choices being 2 and 4 ohms? You can't. You may use either, though, and neither will bother the amp in the slightest. Amps aren't designed to operate into a precise impedance load because there's no such thing as a precise impedance load.
  10. Look at the impedance chart for a speaker and then reconsider that advice. This is a typical 8 ohm sealed speaker: This is a typical 8 ohm ported speaker: In neither case is the impedance 8 ohms at more than a few frequencies, so there is no way to exactly match the amp to the speaker. You use the tap that's equal to or higher than the speaker's rating, which is a nominal value, not an exact one.
  11. Yes. Valve amps have no minimum load. I remember running 4 ohm rated Fenders with 1 ohm loads with never an ill effect. They even handle a dead short. OTOH while you can run an SS amp with no speaker that will damage a valve amp. To protect against that Fenders have switched output jacks that short the output if there's no speaker plugged in.
  12. With an SS amp the rated impedance is minimum, with valve it's maximum. Using a 2.67 ohm load with a valve amp you'd probably be better off with the 4 ohm tap, but you're not going to have a problem with the 2 ohm tap. Using an 8 ohm load on the 2 ohm tap would be a different story.
  13. Amps don't send power, they send voltage. If two identical cabs are wired parallel to the amp each will receive the same voltage. Cabs consume power. When two identical cabs are wired parallel each will consume the same amount of power. A 300 watt amp can't provide two cabs with 300 watts each, it can only provide 150 watts to each without exceeding its rating at the given THD of the rating.
  14. Eminence has cabinet designs for most of their bass/pro-sound woofers posted on their website. In most cases they have two or more designs in various sizes, ported and sealed if the driver is suitable for both. Low frequency response charts and other details like impedance, excursion and maximum SPL charts. The only thing they don't show is how to build the cabinet.
  15. Assume the port is 4 inches diameter, which gives an area of 12.5 square inches. If the floor/wall is an inch away the area between the port circumference and the flat surface is 12.5 square inches, so not only is the port not blocked, it's not even constricted.
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