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Upgrading my acoustical room treatments

Discussion in 'audio' started by ToTo Man, Sep 14, 2021.

  1. Si74

    Si74 pfm Member

    Incidentally have XTZ room analyzer kit and Cara room mapping software gathering dust, marvelous for showing the problems but requires a few years of study to interpret the results and solutions, a load of woodworking tools and experimentation and hours of labour which folks wanted veneered to match their speakers for less than a decent pair of interconnects. Only dealer tried them told me to quadruple the price but by the time they took their cut, was working for peanuts so gave it a miss. The along came GIK Europe, Not the end all and be all but mass manufactured at reasonable prices and doubt they have many unhappy customers?
     
    darrenyeats likes this.
  2. ToTo Man

    ToTo Man the band not the dog

    The plot thickens...

    I removed my side wall absorbers today that have been in situ since 2013, and I also removed the two absorbers that I put on the back wall behind my listening position a few weeks ago. My corner treatments remain installed.

    Removing the side and back wall treatments has had a huge effect, both on the measurements and my impression of the sound.

    As you'd expect, reverberation times have increased (evident on the RT60 and waterfall), as has the number of reflections above -20dB arriving at the listening position within 20ms (evident on the ETC). However, the frequency response has improved in some areas, or at least that's what my ears are telling me.

    [​IMG]

    How does it sound? Surprisingly nice!

    The presentation feels more enveloping, and the tonal balance from the upper-bass through mids and treble sounds more 'liquid' and 'dreamy'. The increased reverberation gives the treble shimmery ambience, which I rather like! However, the low end sounds a bit less controlled now. Another down side is presentation in general gets a bit confused during busy passages if there's lots of loud stuff going on.

    I don't know where this leaves me with regards to my room treatment strategy.... In an ideal world I'd like to reduce my reverberation times a lot in the low end, a little in the mids, but not at all in the highs, and do so using treatments that aren't going to bugger up the frequency response. Seen any flying pigs recently?...

    I've uploaded the REW mdat files to my Gearspace thread if you want to look at the ETCs and RT60s.
     
    Last edited: Oct 8, 2021
    tuga likes this.
  3. tuga

    tuga Legal Alien

    Perhaps you should try deflecting the early reflections towards the back wall using moveable screens (e.g. room dividers) positioned in the early reflection zones on the side walls, ideally in combination with diffusers on the back wall; you'll increase the arrival time and reduce the smearing of phantom images. I.
    Something like this:

    [​IMG]
    https://www.gikacoustics.com/product/freestand-acoustic-panel-gobo/
     
  4. ToTo Man

    ToTo Man the band not the dog

    The gobo looks like a regular thin absorption panel to me, so I'm not sure how it can be used to deflect the sound that hits it, or have I misunderstood what you mean?
     
  5. tuga

    tuga Legal Alien

    I used the photo more for shape illustration purposes. Partition screens from different manufacturers have different absorption coeficients and characteristics.
    The idea is to create a sort of Reflection-Free Zone as per D'Antonio whilst keeping some of the "livelyness" that you have experienced and liked when you removed the treatment, also cut down on the naked walls "glare" a bit.

    http://arqen.com/acoustics-101/room-setup-acoustic-treatment/#early-reflection-control
     
    ToTo Man likes this.
  6. tuga

    tuga Legal Alien

    AndyU and ToTo Man like this.
  7. cooky1257

    cooky1257 pfm Member

    ...and here's me awaiting feedback on the sound impressions from taming the 600/1khz peaks....
     
  8. tuga

    tuga Legal Alien

    It looks like the 600Hz peak is natural to the 66, not a room issue:

    [​IMG]
     
  9. tuga

    tuga Legal Alien

    I've superimpose the in-room and anechoic responses.

    [​IMG]
     
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  10. Tony L

    Tony L Administrator

    Interesting, as is a broad dip around 200Hz.
     
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  11. cooky1257

    cooky1257 pfm Member

    Neat tuga! That's rather close, all things considered and illustrates the way things go to pot below 200hz in rooms.
     
    darrenyeats and tuga like this.
  12. ToTo Man

    ToTo Man the band not the dog

    I've no idea how you did that, tuga, but it's amazing, - it must have taken you a lot of effort to align the scales?!

    I've often wondered how the 66's anechoic response was measured, i.e. at tweeter height or midrange height. However from the above graph it's now clear that it must be midrange height, because it isn't possible to get that nice, smooth lift around 5kHz if you measure at tweeter height, especially if you measure at only 1m metre distance, the lift turns into a dip because of MF/HF cancellation.
     
    tuga likes this.
  13. ToTo Man

    ToTo Man the band not the dog

    Removing the absorption treatments from the side wall midpoints was a fun experiment but I don't think it's the answer. Speech dialogue from my crappy built-in TV speakers has become less clear due to the increased reverberation times in the bass and mids. I'm going to re-install the side wall treatments, but move them further towards the front of the room so they're entirely in the speaker's first reflection zone, and see what effect this has.

    In the mean time, the following graphs show the reverberation times increasing as each stage of treatment was removed. Regardless of what I do next I think it would be worthwhile investing in some tuned membrane bass traps to reduce my reverberation times below 80Hz.

    [​IMG]

    [​IMG]
     
    tuga likes this.
  14. darrenyeats

    darrenyeats pfm Member

    The combined L/R RT60 without treatments is fine - the only issue I have is the big difference between L and R at 100Hz - not sure what's happening there. It's fairly even by frequency, and the bass RT60 is hardly worse than with treatments. The bass RT is typically a problem and far higher than the rest of FR, due to room modes. All such things are why I prioritise tuned bass traps over broadband traps.

    If you could keep the speakers well away from the side walls, no treatments probably would be okay. But since you can't, I'd treat first reflection points as you say (I do this). Is there any flutter echo without treatments (clap your hands and you'll know)?
     
    Last edited: Oct 10, 2021
    ToTo Man likes this.
  15. tuga

    tuga Legal Alien

    Perhaps the door next to the righ speaker?
     
    darrenyeats likes this.
  16. ToTo Man

    ToTo Man the band not the dog

    There is flutter echo, even with the treatment, but it's worse without it. The majority of the flutter echo is between the side walls. I bought some cheap inakustik EPS diffusors from Thomann years ago to use high up on the walls but they kept falling down! (My walls undulate so the velcro and double-sided foam tape didn't have enough pressure, and I didn't want to ruin the wallpaper with blobs of contact adhesive). I'm assuming the flutter echoes can be ameliorated with anything that breaks up the flat surface of the wall. My plan was to put tuned bass traps high up on the wall to deal with the modal ringing.
     
    Last edited: Oct 10, 2021
    darrenyeats likes this.
  17. Tony L

    Tony L Administrator

    You need records. Huge numbers of records. No flutter echo anywhere here. Except the bathroom, which I’ve yet to fill with records.

    PS Since getting the bathroom redone with a tiled floor it is a great reverb unit. I’d happily mic up an acoustic guitar in there!
     
    ToTo Man, Riotvan and darrenyeats like this.
  18. wylton

    wylton Naim and Mana member

    Don't give me ideas Tony, I have a serious overflow situation going on here!
     
    Riotvan, Tony L and darrenyeats like this.
  19. Riotvan

    Riotvan Snoofer in the Woofer

    I keep the brown note record collection in the bathroom, i’m practical like that.

    Enjoying this thread @ToTo Man fun read while i work on and fiddle with the acoustics in my own room. Just redid the side reflection panels with new frames and a nice fabric, next up are the corners but am waiting for the custom stands from Liedtke metal design before i tackle those.
     
    darrenyeats and ToTo Man like this.
  20. ToTo Man

    ToTo Man the band not the dog

    I moved the panel that was furthest back on the side wall forward into the first reflection zone of the nearside speaker. Positioning was dictated by the door handle, but a mirror test confirms the panel is perfectly placed for the nearside speaker. Likewise the panel to the right is perfectly placed for the farside speaker. I don't usually have such luck! Ideally I'd have liked to have replaced the 120mm thick absorbers with 170mm thick absorbers but I don't think it's going to be practical because the 120mm panel already restricts the ability to open the door to less than 90 degrees.

    [​IMG]

    Measurements show a reduction in RT60 as anticipated, but thankfully not by as much as I feared. It's quite a smooth reduction to 300ms across the frequency spectrum, pretty much a flat line from 100Hz upwards, and the left and right speakers appear to be much closer matched now below 100Hz. On the ETC, spikes at 4ms and 5.5ms been reduced by 6dB and 8dB, - the previous treatment placement did not catch these two reflections.

    [​IMG]

    The frequency is response objectively worse than when the side walls are bare, but this is something I may just have to live with. I haven't listened yet with the absorbers in this new arrangement, - the suspense is killing me! :D I was very surprised to see virtually no change in the FR at 600Hz, as this contradicts my findings in post 78 when I stood an absorber right next to the speaker.

    [​IMG]
     
    Last edited: Oct 10, 2021
    tuga likes this.

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