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About LTD02

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  1. what makes a sub "sound good"

    really cool. animated the before and after with http://gifmaker.me
  2. Speaker acceleration, displacement and SPL

    i was highlighting the other half of the irony, where if the spl in the higher frequencies for a given average drive level is higher for the light driver, then the velocity is higher too, so the non-engineer who says that it "sounds faster" is actually right, at least in some sense.
  3. Speaker acceleration, displacement and SPL

    as you know... higher xmax subs tend to have a reduced top end frequency response in part because of inductance effects and in part because of increased moving mass. lower xmax subs tend to have an increasing top end frequency response. so without equalization, pro audio drivers will tend to sound faster at some average output level because...they are.
  4. Ideas for new ways to display data

    are you looking to determine output density for the subs that were measured or determining the output density in an ideally sized cab for each driver?
  5. Luke's basic amplifier tests

    the test signal is a constant sine wave, no? perhaps a 5-7 cycle tone burst would allow the amp to meet its spec?
  6. Luke's basic amplifier tests

    Not sure what to say Luke. The specs on the website and in the manual sure seem to indicate 1200 watts per side at 4R and specifically stated are voltage and current limits that exceed that spec. I'm sure you checked, but maybe worth double checking again for any limiter that may be engaged?
  7. Luke's basic amplifier tests

    the cc5500 was ~5300 watts both channels driven (bridged) through two drivers in series. the sp12000 was two channels each cranking 6148 watts for about 12,300 watts total through one driver per channel. the cc5500 hit 138.6db output. the sp12000 hit 139.0 output. those were the numbers that initially led me to conclude the ipal may be completely compressed out. but on second review and as others have pointed out the frequency was a little different. the low corner on the cab is right around there too, so it wasn't an apples to apples comparison.
  8. Luke's basic amplifier tests

    i wasn't suggesting that you hadn't done it or didn't know. i was just laying out my logic. on second thought, in this test, doubling the current and doubling the power are looking at the same thing. [they probably always are, but with amps and speakers frequently folks refer to the "watts" as the volts/dc r not the actual, and varying, impedance.] as for testing the same freq., that might make some sense as the contribution from the room (and possibly the sensitivity of the horn?) may be a little different at the two different frequencies. with that much power compression, i'd be worrying about cooking the drivers. don't want to see that!
  9. Luke's basic amplifier tests

    again, i'm a little foggy this morning, but i think you have to check the current for heating not the watts. 6148 w into 1.2 r is 86.5 v. 86.5 v divided by 1.2 r is 71 amps. one channel per driver so 71 amps through each driver. 5310 w into 4 r is 145.7 v. 145.7 v divided by 4 is 36 amps. drivers in series so 36 amps through each driver. with almost twice the amps, the spl at the listening position was 0.4db louder despite more than twice the watts, indicating almost total power compression past 36 amps. at least that is what i was thinking.
  10. Luke's basic amplifier tests

    neat. if i'm interpreting the result correctly, the ipal's can't handle the current and compressed out almost all the power gains afforded by the sp amp?
  11. since it was mentioned how much current the wall will allow and by extrapolation then the max power, that depends greatly on the "time current curve" of the breaker. they vary quite a bit. i just quickly searched on a ge 30 amp 240v breaker and was then cross-referenced to this link (ge industrial series ges-6112c available in amperages from 15-50, voltages from 120-240, and 60hz lines). it seems representative if not specific. http://apps.geindustrial.com/publibrary/checkout/GES-6122C?TNR=Time%20Current%20Curves%7CGES-6122C%7Cgeneric if the "bursts" that luke was drawing were less than one second in duration, the breaker may actually allow current to about 7 times its rating. for a 30 amp breaker that is obviously 210 amps. on a 240v line, that is 50,400 watts for a second. woohoo...
  12. Really nice work Josh. If you haven't, you might want to cross post to some of the boards that get a little more traffic, as this information will help save an awful lot of folks from failed projects. I ended up here because one of your measurements was posted at AVS and I specifically searched on it, otherwise I would not have known about it.
  13. JPC, DD, at it again w/LTD02 stirring the pot...

    my interest all along has been from the observation that spectrum lab isn't presenting what folks think they are seeing--the amplitude of the signal at each frequency isn't what is presented in spectrum lab (except in the case of pure sine waves). the fft is calculating average energy across the measurement window and displaying that as the "level". as a result, the "level" will display higher for low frequencies than for high frequencies even when the actual level of the signal itself is the same simply because a cycle of a low frequency fills a greater portion of the time window than does a high frequency. it starts out as zero-difference for sine waves, gets problematic with transient responses where the length of the signal is significantly less than the length of the measurement window, and it completely breaks down for impulse-like responses. most content is not characterized by sine waves, so the more accurate method of presenting the level of each frequency is to use some sort of adjustment. the log adjustment (3db/oct) of the rta seems as reasonable to me as anything, but by the nature of the fft there just isn't any way to present what we all would like to see--the level that each frequency is recorded on the disc.
  14. JPC, DD, at it again w/LTD02 stirring the pot...

    that's the same problem. the 3db/oct is the slope when using pink noise, log sine sweep, etc. with a transient, such as a door slam, the slope is even steeper. i'm not even sure if an fft can measure a full bandwidth transient. as a test, I created three test signals in audacity. all had the same amplitude. each was 3 cycles in length. then I measured their intensity in spectrum lab and measured significantly greater decline than 3db/oct. (appears to be closer to 30db/decade than 10db/decade). with constant sine waves, there is no rolloff with frequency (the blue dashed line is flat). so what is happening is the shorter the number of cycles, the steeper the slope of the rolloff (blue dashed line). with a single transient pulse, with equal level of output at all frequencies, the rolloff would be very dramatic, perhaps not all that different from what you presented.