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Posts posted by 3ll3d00d

  1. Mmm, aliasing.  Too bad I can't boost the sample rate in VS.  But why not use pink noise filtered at 50 Hz?  Also, I don't see a white noise generator in REW.  Can you suggest a place to download a test sample?  Otherwise, I guess I'll have to make my own.


    Edit: I'm also concerned that white noise will have very poor SnR for ULF, and I can't seem to make the capture duration any longer than 1 minute.  (After all, the previous pink noise measurement largely failed to reveal my 5.5 Hz resonance.)

    there's no problem using pink noise, it's just easier to compare measurements when using white. 


    REW does have white noise in its generator, it's listed as "White PN" IIRC. There are a bunch of test signals in https://drive.google.com/open?id=0BxdmSMpV-t3GVzlJcnhYaDJhdmc, they're just REW generated though.


    It *looks* like it's filtered below 10 Hz, but I verified that the test signal extends below there.  As I said before, my suspended floor is pretty much a no-show in the single digits.  The PSD doesn't even show any activity at 5.5 Hz.  Though I've verified the existence of a very high Q floor-wobble resonance there.  The low teens response peaks at 12 Hz, but that's because my cal leaves the worst of the resonance at 11 Hz notched out.


    full band pink noise will contaminate the PSD reported by VS because any high(er) frequency vibration will be aliased into the reported results. Use 0-50Hz white noise instead, the signal itself is then a straight line in PSD so it's easy then to see the variation between measured and actual.

  3. I tried another one and got similar results, hacked together a multichannel wav with a sine wave at a different frequency for each channel and ran that through jriver then analysed it, result is a mono wav with a missing channel 4, i.e. no LFE channel in the output. I'm quite sure this used to work so will report over at jriver forum to see what is going on.


    edit: see https://yabb.jriver.com/interact/index.php/topic,111023.0.html  appears to be some random defect in this particular installation of jriver :|


    edit2: turns it out it is a bug in jriver - https://yabb.jriver.com/interact/index.php/topic,111023.msg767472.html#msg767472

  4. Any idea why your PvA looks so different from what JSS posted above?


    Yours appear to be higher resolution (longer window?) but looks smoother, so I don't think it's a resolution issue.  Indeed, the curve shape and levels both look quite a bit different.  Could the difference have to do with how the down-mixing is being done before analysis?

    dunno, I downmix using jriver as per http://www.avsforum.com/forum/113-subwoofers-bass-transducers/1333462-new-master-list-bass-movies-frequency-charts.html#post23468771


    I just doublechecked the settings, recreated the mono wav and ran it through speclab and my app. I get the same result each time.

  5. only in sketchup atm, trying to decide exactly how best to size it so it fits where I want it to go + I have to space to build it + tune is where I want + not really wasteful of sheets of wood. The design has been complicated somewhat by the fact I might now build a screen wall and hence put the sub in a different place as well

  6. 1. Level - This is measured by digitally bass-managing the 5.1 or 7.1 signal.  The Level is a composite number, and is calculated by the average of the [1] highest peak in dB (maximum 126dB for 5.1, 128dB for 7.1), [2] the average/RMS dB level of the track (125ms integration time) and [3] the RMS peak level (loudest single 1/8th of a second of the film) in dB.  Full modulation of the waveform is considered to be 0dBFS.  The ratings are as follows:


    5 Stars - >112.5dB composite

    4 Stars - >110dB composite

    3 Stars - >107.5dB composite

    2 Stars - >105dB composite

    1 Star - <105dB composite



    @maxmercy how do you calculate [2]? I don't understand how the integration time relates to a single dB level for the entire track. The time window sounds like it relates to the length of each slice in the spectrogram but then how do you turn that into a single number?

  7. let me know if you hit any issues, don't think anyone else has used it yet :) I could easily add some options to make it easier to use for this case though, for example 


    auto detecting files dropped into a certain directory

    providing some config option for tweaking the fft length

    providing a quicker way to see peak/average on one chart (rather than having to select peak then select average each time)

    • Like 1
  8. fwiw the vibration app I wrote does the same sort of analysis as speclab for the target curve function - http://www.avsforum.com/forum/155-diy-speakers-subs/2681865-rpi-based-diy-vibration-meter-3.html#post52214001- and the relevant bit of user guide is http://vibe.readthedocs.io/en/latest/uiguide.html#wav-upload


    It is currently tuned to produce output with ~1Hz resolution though, it decimates to 1kHz sample rate and then performs an analysis based on a 1024 point fft. Bit easier to use than speclab as you just drag and drop wav's into it, no options exposed to configure it though.

    • Like 1
  9. I don't know what you are doing in Hornresp, but for the frequencies that you are interested in, that port is definitely not "far away" from the driver.  

     it seems like that feature adjusts spl of one source by an inverse square law sized amount which I suppose is where the "surprising" result comes from as I'm thinking of "what will happen in a room" and the model is not. 

  10. I don't know what you are doing in Hornresp, but for the frequencies that you are interested in, that port is definitely not "far away" from the driver.  It's less than 1/4 wavelength at the port resonance, which is what will give you trouble if anything.  Depending on how strong it is, you might want to try to knock down the port resonance with a PEQ.

    that's what I thought (that the port is not far away in wavelength terms) but it seems like that setting has a relatively strong effect (in terms of making the port dominate output if you move the port closer to the listener). This makes me think that that setting doesn't do what I think it does (wouldn't be the first time in hornresp), It's described pretty plainly as


    The distance from the port outlet to the listener can be adjusted if necessary using the length difference parameter. A positive value for path length difference increases the listener distance.

    The path length difference is the distance from the port outlet to the listener minus the distance from the direct radiator diaphragm to the listener. The difference is positive when the distance from the port outlet to the listener is greater than the distance from the direct radiator diaphragm to the listener.


    Example of the effect - http://imgur.com/s3IwddN

  11. came up with this so far




    ~205L net with a 304cm2 by 110cm port, 1kW and a 15Hz LR4 puts excursion at ~10mm and velocity at 20m/s. Going longer doesn't seem to add much in this size enclosure so this seems a reasonable balance to me, port resonance is ~135Hz so outside the realm of my LPF.


    My main doubt is whether having the port that far away from the driver makes bad things happen, adding the centre to centre distance to the path difference in hornresp properly trashes the combined output. Any idea if this is an issue in reality (in a room)?


    btw, is there a reason to go with the 4 or 8ohm option other than the load presented to the amp? they seem to model pretty similarly.

  12. here's a quick model of the b&c 21, set voltage to limit velocity to ~20m/s. I imagine the port would be bigger ideally but space constraints probably mean not possible (and actual SPL probably means I won't compress to much anyway)




    seems like the 18 has same shape at the low end but results in less output higher up. What is the advantage of the 21 over the 18 in this situation?

  13. Do the NF subs fire into the sofa?  If so, how close are they?  I wonder if the strong ULF tactile effects you are witnessing require drivers that fire very close to the furniture?  FWIW, one of my original two subs had the driver firing into the sofa when it was situated near-field.  I often found it to too much, to the point of being distracting, in the mid-bass frequencies.  I still preferred having the deep bass and ULF frequencies reproduced at the front.


     yes they do, they are right up against the rear of the sofa. From what I've seen (on other threads), this is the standard position for such a sub. I don't have that much room behind the sub so I can't say how far away you have to be before the effect really tails off. I roll this sub off quite steeply (2nd order NT low pass) around 45-50Hz, mainly because I find it negatively impacts SQ when running higher (the notes get thicker/duller) though also because the measured vibration hands over to the main subs nicely around about this point. As measured, a relatively smooth (with a slightly upwards incline as you go up in frequency) measured acceleration curve seems to feel good to me, not distracting or unnatural at all. The current subs roll off around 15Hz though as they lack the excursion to go further safely so I can't crank that ULF end without thinking I'm going to destroy them :)

  14. Well based on your replies and the fact it's your money I vote for trying the UXL's nearfield and trying a pro woofer up front. :D


    How much is the 21DS115-4 compared to the 18SW115? It could work in that much space.

    About £450 for the 21, £400 for the 18 (similar for the faitalpro). Net cost is less than zero though as i have a uxl-18 to sell as well as a dual infinity 1260.
  15. If you have your acceleration measurement system working, maybe you can compare acceleration measurements between your floor and furniture separately.  I don't know that pounding on the floor will tell you much about how inert it is unless you are pounding it with something real heavy.


    just for a quick test, I measured the floor while playing my white noise calibration signal at a fairly loud level & normalised the measurement against background noise (i.e. sensor on same floor but with no signal playing)


    top graph is NF only at ~5cm away and ~20cm away




    this is same but with both front and NF playing





    scale is in dB La which puts 0dB at 1 µm/s2


    so you can see there is some increase in vibration on the floor but more at higher frequencies than low. Not sure if this tells us anything but might as well use this app I've written!

  16. Is this true for the entire subwoofer range, including ULF?  Or is it only true for a particular part of the range?  If you believe this is true for ULF, is it possible that you are just feeling the relatively higher levels of harmonic distortion?  Also, unless your NF subs are dual-opposed, how do you know you aren't just feeling vibration transmitted directly from the subs to your seat through the floor?

    the NF dominates below 40Hz in my room & my measurements do not indicate harmonic distortion is an issue. The delivery mechanism is via the seat, it's not via the floor (as far as I can tell at least, my floor seems really quite inert no matter how hard you pound it).
    I think crowsons would be tricky and/or expensive to accommodate in my room (I have a quite large bespoke L shaped sofa) unfortunately.
  17. What is it that you are trying to improve most with the change? More headroom overall? More tactile sensation in the deepest bass? More impact in the upper bass? Just bored and can't leave well enough alone?

    It's not headroom and it's not really "just bored..." though there is an element of that for sure. Basically I want to get my L and R a bit wider apart and also a bit more symmetrical with respect to adjacent room boundaries, I think this will bring some, relatively marginal, improvement to the system but it's not enough to warrant rebuilding a bunch of speakers. Nevertheless I still want to do that (there is another, also fairly marginal, non audio reason to do so) so then it's a question of what other changes could be made to make it worthwhile.


    so this leaves us with "More tactile sensation in the deepest bass? More impact in the upper bass?" . I would like to achieve the former for sure, particularly more tactile sensation per dB spl. I am unsure about the latter, of course that would be great to achieve but I can't say the system is lacking as is so it is not something I need to "fix" per se. I've never tried a pro style (sub)woofer though so I am curious as to whether I would hear/feel a marked difference in SQ in that range when compared to my UXL. That alone makes it an interesting one thing to try out (even if it means I end up changing again next year).

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