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Speaker/Room Measurement Witchcraftery

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

  1. tuga

    tuga European

    Or take the speakers outdoors?
    herb likes this.
  2. March Audio

    March Audio Trade: March Audio

    Of course :)
  3. John Phillips

    John Phillips pfm Member

    I have REW and a UMIK-1. I occasionally venture into measuring my room/loudspeakers to learn something. I have read the thread with interest but I wonder if there are simpler but still useful things that one can do.

    I have personally found it useful to set up REW to generate noise [1] and then use the RTA (real-time analysis) tool while moving loudspeakers around in real time to observe how the frequency response changes at the listening position. I find I can moderate the peaks and troughs in the low frequency region to a useful extent, and this is noticeable in things like bass-heavy movie scores.

    I am never going to get anywhere close to a perfect response this way. However the human ear-brain system adapts and I have found that I can make a useful improvement without aiming for technical perfection.

    [1] White PN noise for the RTA tool in "Spectrum" mode (which is what I prefer) or Pink PN noise for the RTA tool in one of the "RTA" modes (EDIT: Pink PN noise is safer for the tweeter).
    Last edited: Feb 28, 2019
    tuga, Sibbers and AndyU like this.
  4. Purité Audio

    Purité Audio Trade: Purite Audio

    Wouldn’t it be more convenient to ‘virtually’ move your speakers/listening position in the room simulation feature?
  5. camverton

    camverton pfm Member

    Indeed, and whilst the room sim is a useful tool it won’t be as accurate as the method you use. The room sim cannot take into account openings, odd shaped rooms, furnishings etc etc. In the last analysis, whilst measuring is a fantastically useful tool, it is only that when used with listening with one’s dear old ears and to one’s own taste!
  6. JohnPM

    JohnPM Member

    White noise puts more energy in the tweeters, keep the levels down if you use that.
    John Phillips and camverton like this.
  7. John Phillips

    John Phillips pfm Member

    Indeed. That's a very welcome reminder.

    In the generator I applied the custom high cut filter at 1 kHz (a couple of octaves below the mid/tweeter crossover frequency) and set a maximum level of 80 dB SPL. Positioning a loudspeaker this way seems primarily to impact frequency response below the room's Schroeder frequency (typically 250 Hz, AIUI) and also a little in the two octaves above. So protecting the tweeter (and my ears) is always a good idea.
  8. John Phillips

    John Phillips pfm Member

    Yes. The final proof is in what you hear. In that respect I have been interested in discovering how much room equalization is "good enough" for my ears. I am quite sure "ruler flat" is not necessary to enjoy good sound and, more important, good music. My own experience is that simple improvements with the help of excellent tools like REW work very well without needing to buy more "stuff" to equalize the room to within an inch of its life.

    And my room is indeed quite asymmetrical acoustically. A fairly plain wall (with a sofa) to the left. Two doors, a fireplace and bookshelves to the right. Playing with REW's room simulator does show some features recognizable in measurements but didn't help me much (I may still have a lot to learn, though). But putting in the final loudspeaker positions from testing with noise and RTA did show a surprising degree of frequency response smoothing, although not quite in the way I was expecting.
  9. Purité Audio

    Purité Audio Trade: Purite Audio

    You could measure, reposition re-measure and overlay the plots, you don’t really want a’flat’ in room response nearly every domestic user prefers the 10dB downward slope.
  10. John Phillips

    John Phillips pfm Member

    The simulation of my room is quite busy with features, some of which correspond to measured and/or audible features and some that don't (or maybe I just don't understand yet). Plugging numbers into the simulator after positioning the loudspeakers using the noise + RTA method does indicate tentatively what matters in the simulation and what to ignore. I would not understand that from just believing my interpretation the simulation without the practical evidence.
  11. Purité Audio

    Purité Audio Trade: Purite Audio

    The main axial modes are mostly responsible below a few hundred hertz.
    darrenyeats likes this.
  12. ToTo Man

    ToTo Man the band not the dog

    I realise that measuring will answer my question, but before I put my back out doing so, for a loudspeaker system that uses a passive bass radiator to extend low frequency response, such as the Celestion Ditton 66, which driver should be used as the position in the REW Simulator, the active woofer or the passive radiator? I'm presuming its the active woofer, since it's the driver that's contributing most to the output?

    Also, if I wanted to (very roughly) measure the contribution of the passive radiator to the system's response, can I simply measure the system's response whilst blocking the movement of the passive radiator with my hand, and then compare this against the normal response?
  13. tuga

    tuga European

    The REW simulator is too generic. It doesn't take into account doors, windows, furnishing, has no option for irregularly-shapped rooms and doesn't really recreate the response of your particular speaker model.
    I use the same technique as you with RTA/Pink Noise and find it very effective.

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