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just got Tannoy HPD385a in Academy I lockwood cabinets

Discussion in 'classic' started by Ayya Khema, Jul 19, 2017.

  1. ToTo Man

    ToTo Man the band not the dog

    It's interesting that all your plots show falling HF in near-field. If they truly measured like that then I think they would sound very rolled-off in far-field, which is the opposite of what you claim to be hearing. This would indeed make me suspect possible issues with your mic and/or sound card.

    All of the Tannoys I have measured all show a rising HF at 1 metre distance. I have measured with both an ECM8000 and UMIK-1 and results of both mics are comparable to within +/- 0.5dB.

    PS - The yellow line (stock XO) looks better to me, smoother across the mid frequencies. It's interesting that you prefer Amocom.
     
  2. Tony L

    Tony L Administrator

    The more I measure the more I fall into the measurements are only any use as the broadest brush tool. I find them utterly useless in this context to be honest as just having the mic a cm high, lower, right, left, up, down or whatever actually shifts the response more than the imperfections one is trying to read. You would not believe how much of my life I have wasted in recent years learning this! The horn on a Tannoy is very directional too, which really doesn't help when measuring. I'd forget nearfield measurement, it is just frustrating bollocks outside of an anechoic chamber.

    PS Anyone who doubts this just do a measurement from the listening seat of one speaker, then move the mic 2cm in any direction and do it again! A lot of the things we are inclined to interpret as issues with the compression driver, horn mouth, pair matching or whatever will have shifted by 2 or 3db!
     
  3. Ayya Khema

    Ayya Khema pfm Member

    yeah, to me I use the mics only for under the modal region to determine the best speaker position in relation to the bass which this is really mandatory. but over 5khz, I think its close to useless
     
  4. ToTo Man

    ToTo Man the band not the dog

    I agree that mic measurements can vary, but not extremely so in my experience. I find Tannoys to be more susceptible to this than other speakers, presumably due to the dual-concentric design, but I definitely would not expect a mic to turn a rising HF response into a declining HF response with just a few cm's shift in position!

    There are steps you can take to minimise the variability. Placement accuracy is critical. Whenever I measure how well matched any two loudspeakers are at 1m I ALWAYS keep the microphone in the same location and instead move the loudspeakers, making sure that they are placed in exactly the same spot as each other (down to a couple of mm's).

    If mic measurements were so flaky then room correction software that rely on mic measurements (e.g. Dirac) wouldn't be anywhere near as consistently effective.

    However it's also useful to remember that the two most powerful tools at your disposal are your own ears, and it's essential that you trust these above everything else! e.g. a difference of 1dB between 1kHz and 5kHz is likely to be much more audible to the ear than a difference of 2dB between 15kHz and 25kHz!
     
  5. cooky1257

    cooky1257 pfm Member

    That amocom plot looks to be missing any CD (5-6dB/octave boost above 3kHz)compensation on the HF, ie the HF looks like the frequency response of the horn without a crossover so am inclined to think it reflects a maximum energy maximum rolloff xover setting, I'd also check the polarity of the HF judging by that suckout around xover ...
     
  6. Ayya Khema

    Ayya Khema pfm Member

    oups, the last graph is my previous berkeley which was problematic to say the least
    my actual speaker measurement is at page 1
     
  7. tonymorris

    tonymorris New Member

    All but the very earliest Amocom XOs have the Roll-Off adjustment feature. This is an exact representation of the Tannoy design with various configurations of the 10R, 20R resistors and the 1.5uF capacitor. Sometimes there is a perception of a little brightness from brand new capacitors compared to ones which are very old of course. The Roll-Off feature is included to allow experimentation with high end treble if this is the case.
     

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