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Upgrading my acoustical room treatments

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

  1. ToTo Man

    ToTo Man the band not the dog

    Following the success of treating my cupboard space I decided to make up some temporary corner bass traps to give an idea of the benefits from replacing my GIK TriTraps with bigger corner traps. I used my leftover RS45 and RS60 rockwool insulation slabs to make 60cm x 60cm squares and stacked these in the rear corners in front of my TriTraps to form two 60cm cubes. These traps are BIG, probably four times the footprint of the TriTraps!

    They have a decent effect on reducing decay times in the 40Hz-100Hz region. :) They do have one drawback though, - I now have +2dB more energy at 68Hz. I did a quick 'walk around' with my SPL meter and 68Hz seems to be in the height dimension, - it gets louder as you move nearer the floor. The level also changes depending on how you turn and tilt your head so I think it's my tangential length/height and width/height modes.

    Seeing a 60cm x 60cm stack in the flesh is an imposing sight, I'm not sure if I'm prepared to sacrifice this much floor space! :eek: The key question is just how much performance I'll lose by cutting these 60cm squares on the diagonal into wedges.

    PS - Ignore the high frequency response, - the measurements were done with both speakers playing at the same time, hence the comb filtering.

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    Last edited: Nov 29, 2021
    tuga likes this.
  2. ToTo Man

    ToTo Man the band not the dog

    I recently had the opportunity to home demo a modern floorstander, and thought it would be a good opportunity to measure it in exactly the same position as my Celestions to demonstrate the extent to which the room dictates the frequency response below the Schroeder value. The modern floorstander shall remain nameless, but suffice to say it's a very different design to the 66. I tried to match the positions of the speakers as closely as possible but it wasn't 100% identical because the modern floorstander is deeper and narrower, but I got it close enough for a valid comparison. If I could have matched the distances to the front wall perfectly then I suspect the responses from 70Hz-170Hz would have been an even closer match!

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  3. Tony L

    Tony L Administrator

    Massive difference from 1kHz upwards, just way, way brighter! Are you going to reveal what they are at any point? Based on entirely upon looking at a line on a graph I’d take the 66s all day long! Surprisingly little difference below 1kHz.
     
  4. Space is the Place

    Space is the Place pfm Member

    Interesting i have a suspended floor in my room and it causes the same sort null you have, i solved it for a while with a speaker that had a peak in the area where the null was, it worked fairly well without using room perfect room correction.
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  5. ToTo Man

    ToTo Man the band not the dog

    I was wondering when someone was going to point that out. It certainly took some acclimatising to coming from Dittons, plus a little help from my amp's tone controls! ;)

    Just to be clear I'm not looking to replace my Dittons. I've got these speakers in for review so I'd rather not divulge details yet. The purpose of the graph was to draw attention to the similarities below 250Hz, not the dissimilarities above 2kHz! :p
     
  6. ToTo Man

    ToTo Man the band not the dog

    I'm not sure my suspended wooden floor is the cause of the null at 150Hz because it fills in when I pull the speakers more than a metre away from the front wall (see graphs in this earlier post), but I suppose it could be caused by a combination of reflections.
     
    tuga likes this.
  7. Space is the Place

    Space is the Place pfm Member

    Well done for the amount of effort you've put into fixing your room and trying different placements, it's interesting how the relatively small movements of speakers effect the response so much. My front room system (mid-bass disappears never to return now i'm running smaller speaker in there) doesn't sound a good as the bedroom system, where i get some reinforcement from the walls.
     
    ToTo Man likes this.
  8. tuga

    tuga Legal Alien

    That peak is not real though, it's an artfact produced by the nearfield measurement of the woofer which John Atkinson prefers not to address:

    For published graphs, the loudspeaker's nearfield response is spliced to the farfield response in the 300Hz region. However, as pointed out in the Keele paper, the nearfield response assumes a 2-pi or half-space loading for the drive-units—close coupling to the room boundaries. This results in an apparent low-frequency boost in the resultant composite graph compared with a true anechoic response made of the same speaker. Given that a loudspeaker's woofer and port are always within a fraction of a wavelength from one boundary—the floor—and almost always less than one wavelength from three other boundaries—the walls and ceiling—below 100Hz or so, my experience has been that this does give a truer representation of a loudspeaker's real low-frequency performance than the anechoic response in all but extremely large rooms. Certainly, the loudspeakers I have auditioned that have true, flat anechoic extension to very low frequencies sound as if they have a somewhat exaggerated bass response—which is how they appear with a nearfield measurement.

    Measuring Loudspeakers, Part Three Page 6
    https://www.stereophile.com/content/measuring-loudspeakers-part-three-page-6
     
  9. Space is the Place

    Space is the Place pfm Member

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    Er... No the peak is real enough the above graph is the measure response in Larry Greenhill's listening room, fortunately it was flattened in my room other than a peak at 32 Hz.
    Below is the quasi anechoic response of the speaker, when i measured the Arrays because of the directivity of the horn i was amazed how flat and even they were in my room, (still the most refined, even speaker i've owned, at least with subtle room correction applied in the bass).

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  10. ToTo Man

    ToTo Man the band not the dog

    Four GIK Scopus bass traps custom-tuned to 42Hz arrived today. I've temporarily installed them on the back wall behind my listening seat but they will most likely go in the corners assuming they perform as hoped. (The lower panel you see in the corner at the moment is a '6A Alpha' which is essentially a broadband 'Monster' absorber with binary diffuser plate).

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    The Scopus appears to do what it says on the tin, absorb modal resonance at its tuning frequency (42Hz), thereby reducing the amplitude SPL and decay time at this frequency. It also completely fills in the null at 75Hz, which is an unexpected but very welcome bonus! However it also reduces a peak at 108Hz, which makes the scoop between 100Hz-200Hz even worse. I'm hoping that moving the traps into the corners will prevent this.

    Note the below measurements are NOT of my Celestion Dittons so cannot be directly compared to any of the previous measurements in this thread.

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    Last edited: Dec 15, 2021
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  11. ToTo Man

    ToTo Man the band not the dog

    Moving the Scopus into the corners restored output at 108Hz without sacrificing much performance at 43Hz, so this is where they are going to be staying for the moment. I've also stacked my 6A Alpha panels on top to make a rather imposing binary tower! :cool:

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  12. ToTo Man

    ToTo Man the band not the dog

    The 100cm x 100cm QRD N23 I ordered for my back wall arrived a couple of days ago and I was childishly eager to try it out! :)

    It's sitting on a 45cm x 110cm x 35cm (HxWxD) bench that's almost three times as deep as the diffuser, which isn't ideal for reflections, but I'll eventually replace it with a shallower bench.

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    I took three measurements, one with the diffuser aligned with the front of the bench, one with the diffuser in the middle of the bench, and one with the diffuser pushed all the way to the back of the bench. I also measured the bench on its own to obtain a baseline.

    The differences are interesting. From a FR perspective the best result is obtained with the diffuser at the back of the bench. I presume this is because there is greater distance to the listening seat which allows the diffused soundfield to develop more.

    I like the effect it has on the sound. My dad strummed his acoustic guitar in front of it and it sounded lovely, very harmonically rich and spacious compared to just a bare wall.

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    Last edited: Dec 20, 2021
    darrenyeats likes this.
  13. Somafunk

    Somafunk pfm Member

    Short of building a fully engineered listening room I doubt you’ll be able to improve what you currently have achieved, very impressive.
     
    darrenyeats and ToTo Man like this.
  14. Big Tabs

    Big Tabs looking backwards, going forwards

    I understand none of the graphs or measurements, but I do applaud the enthusiasm on display. Bravo.
     
    ToTo Man and darrenyeats like this.
  15. tuga

    tuga Legal Alien

    Unlike most room treatment gizmos, those traps look great!
     
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  16. ToTo Man

    ToTo Man the band not the dog

    The wood veneer is beautiful, the pics don't do it justice!

    I thought long and hard about choosing a finish that would suit my room best, flipping and flopping between all the options. In the end I chose Grey Elm veneer for the scatter plate. Beech looked a bit too much like 'office furniture' and Walnut looked a bit too dark for my room. The plain white and black finishes looked cheap!

    It took me even longer to settle on a fabric colour, in the end I chose Camira Cara 'Lerwick', which is just slightly darker than the wood so helps to highlight the binary pattern without looking too contrasty.

    I have to admit I chose the '2Da dots and dashes' binary pattern purely on looks. The '1D slatted' binary pattern would have provided a stronger diffusion effect but I didn't like the appearance as much! :D
     
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  17. ToTo Man

    ToTo Man the band not the dog

    Now that I have my room back to how it was pre-Christmas, I thought I should wrap up (this stage of) my acoustic treatment project by posting a measurement of my Dittons in their current position before I start moving them around in the quest of a better soundstage. This post can therefore be viewed as a continuation of post #121 before I switched speakers.

    The black trace is the last measurement I took of my Dittons in early December when I had one GIK 6A Alpha panel stood in front of each TriTrap stack in the rear corners.

    The red, blue and green traces show the effect of stacking two Scopus T42 tuned traps in front of each TriTrap stack in the rear corners with one 6A Alpha panel on top of the Scopus stack, plus the addition of a 100cm x 100cm N23 diffuser on the rear wall. The red, blue and green traces show the effect of aligning the diffuser with the front, middle and back of the bench, respectively.

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    And this is the response before and after EQ:
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  18. Tony L

    Tony L Administrator

    I’m struggling to understand this. Are the plots actually suggesting you are getting a boost at some frequencies from the additional treatment? I was only expecting to see cuts.
     
    tuga likes this.
  19. ToTo Man

    ToTo Man the band not the dog

    Yep, I wasn't expecting it either but apparently it's not uncommon. IIUI, the treatments disrupt/change the distance/path of reflections, so you can end up with deeper nulls and stronger peaks because you are absorbing or redirecting some of the reflections that were previously combining to keep certain peaks and nulls in check. I experienced this when I treated the side walls and again when I treated the front and rear walls. Purely from a FR perspective I reckon my room would measure better above 100Hz if I removed all treatments, but the low frequency overhang would be intolerable! I've also been told to expect the optimal listening position for flattest FR to change with the addition of treatments, but in the interest of consistency/continuity I've kept the mic position the same for all measurements (150cm or 39% from the rear wall).
     
    tuga and Tony L like this.
  20. darrenyeats

    darrenyeats pfm Member

    Another point, it seems you picked the Scopus that corresponded to your room dimenions, and not the frequency of the biggest measured peak. Am I right? - apologies for bringing it up only now, but it dawned on me after the fact.
     

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