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Speaker/Room Measurement Witchcraftery

Discussion in 'audio' started by S-Man, Apr 8, 2018.

  1. Ayya Khema

    Ayya Khema pfm Member

    imd happens with 2 ways with small woofers like 5 or 6.5 inch. bigger 2 way like tannoy eaton, devore 096, or even bigger jbl will stll have imd but only at high spl.
  2. Purité Audio

    Purité Audio Trade: Purite Audio

    Where on earth do you read this tosh?
  3. mattgbell

    mattgbell Weird owl

    Intermodulation distortion is a form of non-linear distortion produced by summed or difference tones. Here's a definition from Wolfgang Klippel.

    "A nonlinear system generates new spectral components which are not in the stimulus. In addition to harmonics, the fundamental components interact with each other and generate difference-tone and summed-tone components in the output signal (see figure below). In the time domain the intermodulation causes a variation of the phase (instantaneous frequency) or an amplitude modulation of the envelope. Loudspeakers and other electro-acoustical transducers generate significant intermodulation distortions in the audio band which have a significant impact on the perceived sound quality. The inductance nonlinearity L(x) produces low harmonic distortions at low frequencies but generates wide-band intermodulation which rise to significant values (30 %) at higher frequencies. Intermodulation distortion can easily be detected by using a two-tone signal with varying frequencies of the excitation tones (“bass tone sweep” or “voice tone sweep”)."
    S-Man likes this.
  4. S-Man

    S-Man Kinkless Tetrode Admirer

    Why on earth do you post this tosh?
    tuga likes this.
  5. Elephantears

    Elephantears Trunkated Aesthete

    I've heard music in S-Man's room. It definitely isn't dead. Just goes to show the limits of judging by a few graphs.
  6. March Audio

    March Audio Trade: March Audio

    No I don't consider it dead either, I consider it an appropriate reverberation time. My point was referring to smans comments about studios essentially being dead. His RT is in the middle of the EBU studio recommendations.

    You are wrong. The graphs are extremely informative and tell me how that aspect will sound. Having said it isn't dead, that room does have a low RT. However compared to a room such as one with wood floors and little soft furnishings you might well say it was dead.

    Can You define dead and how you quantified it?
    tuga likes this.
  7. March Audio

    March Audio Trade: March Audio

    Has anyone got any measurements that show this effect because it sounds like a generalisation. Drivers will suffer IMD but this description sounds more like doppler related issues.

    Edit. I can measure a driver today and see what we get.
  8. March Audio

    March Audio Trade: March Audio

    Aahhh so basically time alignment. OK with you now. Time alignment requires more than xo alignment, the acoustic centres need to be aligned. Otherwise you need to use a linear phase DSP XO where you can rotate the filters.

    As shown below with the impulse step response, your speakers aren't actually time aligned.

    My step isnt perfect, needs some further work. Also I didnt time align the front and rear subs individually. However ther drivers are mostly in line.

    My dsp XO speakers

    non aligned example


    Aligned example



    Narrow tweeter impulse followed by wider mid/bass, followed by wider sub unit

    Last edited: Feb 11, 2019
    Emlin likes this.
  9. S-Man

    S-Man Kinkless Tetrode Admirer

    That's a reasonable description.
    The bass drivers (3 per side) are directly underneath the mid driver. SInce I listen at tweeter level I suppose the bass units are slightly further away due to the height.
    The mid/treble is down to the designer of the CAOW1s. I cannot affect this. They are the best sounding speakers I have yet tried with the ZRBs (ESL57QA, ESL63, Gale 401, LS3/5A, JR149, H3PSR, LS50) and IMO preferable to Kii3s - the main difference being the superior bass of the ZRB/CAOW1.

    Rolloff at 50Hz might be your idea of "proper".

    Gale 401s are significantly improved by using them with the ZRBs. You don't know what you're missing.
  10. Purité Audio

    Purité Audio Trade: Purite Audio

  11. S-Man

    S-Man Kinkless Tetrode Admirer

    I wonder what that Kii3 measurement would look like at the ~4m listening position in my room (with the terrible lf decay problems ;))?
  12. tuga

    tuga pfm Member

    Not sure about driver size but wide bandwith and increased IMD makes sense; measurements here:

    March Audio likes this.
  13. March Audio

    March Audio Trade: March Audio

    The long decaying modes won't affect the step response measurement.

    Those room mode problems are absolutely typical of untreated rooms.
  14. March Audio

    March Audio Trade: March Audio

  15. Purité Audio

    Purité Audio Trade: Purite Audio

    When I measured them to traditional actives , ATC in this case both speakers in the exact same position, the Kiis measurements were much tidier, much tighter FR, but they are phase coherent have a perfect step response, cardioid , sophisticated boundary filters etc.
  16. S-Man

    S-Man Kinkless Tetrode Admirer

    So it seems that the Kiis measure better than my speakers, but they don't sound as good.
    In particular, there is the anomaly that the Kiis sounded mediocre when cold, but after a few hours warm up (which could be relevant/important because the amps are inside the boxes) they sounded very good.
    The problem is that drive units are notoriously difficult to model (stiffness of the surround due to age, temperature, signal-history, & inductance nonlinearity etc.) and therefore DSP correction can be a hit and miss affair.
  17. darrenyeats

    darrenyeats pfm Member

    Martin Colloms found the passive 50s distort a lot less below 500Hz.

    E.g. 3rd harmonic distortion:
    ATC 50 (passive), 85dB 100Hz 0.03%
    Kii Three, 86dB 125Hz 0.35%

    If active 50s are "traditional" - and therefore passive 50s must be "olde time" in your book - give me traditional please.
  18. Purité Audio

    Purité Audio Trade: Purite Audio

    I have ATCs sound fantastic soffit mounted in a fully treated studio, but obviously because you can’t really adjust them, I found it difficult to know where to place them, measurement in the various positions didn’t really help, pulling them away introduced cancellations.
    https://www.dropbox.com/s/by1wfspl8f7wfyt/HiFi Critic Kii 3 Nov 2018.pdf?dl=0
    Do you have his ATC review it would be interesting to compare.

  19. Purité Audio

    Purité Audio Trade: Purite Audio

    Sound quality doesn’t appear to alter at all here, very odd.
  20. AndyU

    AndyU pfm Member

    Here’s Colloms’ review of the passive 50s.


    And here’s one from Absolute Sound that’s just come out of the active 50 ASLTs. The reviewer bought them.


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