DIY speaker troubleshooting

Discussion in 'DIY' started by JustAnotherRando, Jul 29, 2019.

  1. JustAnotherRando

    JustAnotherRando My other bike is a Ferrari

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    My second DIY speaker attempt (after an Overnight Sensations kit) has been causing me some confusion.

    I've been using a Mark Audio driver that only became available in the past month- the Pluvia 7.2 HD, which is a replacement for the Alpair 7.3.

    Reasons for selecting these drivers were:
    • Full range to avoid thinking about crossovers
    • Availability of established plans online
    • Mark Audio is located locally (ironically, ordering them was very complicated)
    Plans are located on https://www.markaudio.com/Plans/itemlist/category/22-Alpair-7-Gold. So far I'm building enclosures out of foam core board, before deciding on a design for wood. Stuffing follows the recommend amount of polyfill plus some additional damping behind the drivers.

    My chain is RPi + SPDIF HAT -> Modi Mulitbit -> Loki -> Sys (for volume control) -> Akitika GT-102 -> Speakers.
    Measurements were done with a MiniDSP u-mik and REW, with measurements gated at 4.5ms (so anything under 200Hz should be ignored). 1/12 octave smoothing has been applied.

    The initial 8L bass reflex box which I tried sounded so anemic that I moved on to the Pensil MLTL design which sounds a lot better, but has too much treble. The treble reminds me of listening to an HD800S, and I can solve it exactly the same way- using a Loki with the treble knob turned down to the 10 o'clock position.

    The weird thing is, I tried measuring both the normal and the equalised output, and the graphs look practically the same. The same thing happened with the HD800S when I measured on the EARS- the sound is different, but the graphs are virtually indistinguishable. Green line is no EQ, red is EQ. So for starters, I am not quite sure what's going on here.

    [​IMG]

    Just to check my own sanity, I did an extreme EQ test with the treble knob turned all the way down, just to confirm that the Loki really was doing something. It's the orange line below:

    [​IMG]

    Can anyone suggest what to do about the treble? I'd prefer not to remain dependent on external or software EQ, so I'm wondering if modifications can be made to the enclosure design, to the electronics (perhaps figuring out a notch filter around that massive 13KHz peak?) or whether I have to look at different drivers entirely.

    Thanks.

    Edit: Any other advice is also welcome, this has been a a fun learning experience so far.
     
    Last edited: Jul 29, 2019
  2. dmckean44

    dmckean44 In a Sherwood S6040CP relationship

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    The Loki appears to be doing it's job. Setting to 8khz knob to 10'oclock will only lower the signal by 1 db or two. Lowering it all the way should only bring the signal down 12db.
     
  3. JustAnotherRando

    JustAnotherRando My other bike is a Ferrari

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    Yeah, I was just expecting to see something more dramatic on the graph that separates "ouch" from "this sounds okay".

    Overall, I am still less than enamoured of the results that I'm getting. Imaging and staging is really impressive to this speaker noob, but overall tonality even with EQ via the Loki isn't as pleasing as the previous OSMT kit build. I guess this is a good excuse to start looking into the electronics side of things with filtering, but I suspect I won't keep these drivers long.
     
  4. peef

    peef Friend

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    The peak shows up in the datasheet, too, so it is likely the driver's main breakup mode and not something to do with the enclosure. The easiest fix is probably to give them a listen off-axis as they're probably quite directional above a few kHz.

    Since you're running REW, I'd also peak at the HD/CSD plots for anything weird around 3-4k. Usually, you'll see a H3 peak at 1/3 of the main breakup frequency, and that might be more objectionable than the 13k peak itself.

    If you'd like to pursue the notch route, note that efficiency will take a hit. There are some interesting comments about the use of notch filters in Zaph's L18/27TBFC article-- it will probably involve trial and error. You might also want to experiment with a small resistor (<2R) in series with the driver to reduce Qes.
     
  5. JustAnotherRando

    JustAnotherRando My other bike is a Ferrari

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    Interestingly, I've been spending the evening listening to them about 20 degrees off axis. The treble problems pretty much go away, but at the same time imaging takes a big hit. I wasn't expecting this secondary effect at all.
     
  6. Parker

    Parker MOT: Soundsmith

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    I find Xsim to be invaluable when designing and modifying crossovers. Would easily help you tame the treble peak with very little modification:
     
  7. Poleepkwa

    Poleepkwa Friend

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    You could also try to angle them inwards, about 45 degrees.
     
  8. Wushuliu

    Wushuliu Acquaintance

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    What you're seeing and hearing is typical of Mark Audio drivers. It's the trade-off of using a full range driver. The treble peaks are really more like the natural break up of the driver being used in place of a tweeter; depending on one's setup and tastes or the driver - it can be unpleasant for the listener. If you are coming from Overnight Sensations/Typical Tweeter/Woofer speakers, it can be a bit of an adjustment. There are also these caveats:

    1. MA drivers typically need a good healthy amount of time to break in. Typically a 100+ hours. This is part of the design, not marketing. So they will mellow some over time. But that top end will never have the smooth delivery of a dedicated tweeter with a flat response.

    2. These are designed really for the 'girl and a guitar' or 'chamber music' crowd. From my experience they are not great for rock or anything that is heavily mixed/poorly mastered. Whether one wants to say it is because the drivers just aren't that great (because of frequency response/so-so distortion, IMD, etc) or because they need top notch source amplification, who knows - but the limitations need to be considered.

    3. He has multiple driver types and you need to do some homework to figure out which one suit your goals. The bigger the driver, the better the bass but also the earlier the break-up in upper frequencies. No free lunch. Remember the trade-off is a single driver able to do both low end AND high frequencies. You can excel at one or the other, but doing both means major compromises. That includes constructing an enclosure to maximize the response, which is *crucial* for full range drivers.

    I went through a Mark Audio phase and they definitely have their strong points, but unless you are really into midrange-centric/live performance/jazz/simple classical music - you may not like them.

    Personally if I was looking to build something simple and avoid a lot of crossover work I would get something like Scanspeak Discover 10F and do a very simple low cross to a woofer between 200-400hz or thereabout. Or even a Mark Audio Alpair 5, which is more like a tweeter, and do the same. Their frequency response are much more manageable and should be easier on the ear.

    Or build any one of the awesome kits at Meniscus Audio or Diysoundgroup.

    I haven't used Xsim, I only just learned about it. That looks like an excellent tool for designing crossovers.
     
  9. JustAnotherRando

    JustAnotherRando My other bike is a Ferrari

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    As an update, I recently sold off the drivers. I realised that I was trying to force myself to like them, and was resorting to patches like introducing EQ or exaggerated amounts of toe-in, or (the idea of) electronic components rather than building something that was fundamentally right to start with.

    I'd had several hundred hours of break-in on these (the Pluvia HDs are supposed to require less than most MA drivers). The sound was just so far away from what I wanted that these were never going to fit. They imaged a lot better than the OSMTs that I previously built, but the OSMTs sounded more tonally balanced.
     

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