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Thread: Room Acoustics - Understanding the Measurements - Next Steps

  1. #1
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    Room Acoustics - Understanding the Measurements - Next Steps

    Hello everyone,

    i thought id share some of my measurements and gather some Feedback. Also i would like know what Options i can take to lower the 29.2Hz resonance as the "off the shelf" Absorbers dont do anything down there. I use 8 GIK Soffit Traps and some other devices (ceiling, curtain etc...)

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    Smoothing 1/3

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    Time (I still have to find a way to fix the reflection)

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    The very deep bass rises cause the most challanges

    The room is 5.97m in length, 4.25m width and 2.4m in height.

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    Cheers

    Florian
    Last edited by Florian; 10-09-2016 at 10:00 AM. Reason: Additional Information

  2. #2
    Addicted to Best! RayDunzl's Avatar
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    Since no one else has responded, I will. I do in-room measurements often.

    Figure 1: Frequency response:
    Looks reasonable, no big peaks or dips to contend with are obvious at the 1/3 smoothing selected. However, you might want to use no smoothing in the low bass as to not lose the detail in that area.

    Figure 2: Impulse Response:
    Why is the first millisecond so hashy? It is far from ideal. I use room correction, but even my uncorrected IR looks similar to my "best example" - first two milliseconds:

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    The apparent levels of the later reflections may be accentuated by the lack of a strong peak in the initial response in the measurement.


    Here is a longer IR from a couple of days later which shows the major reflections in my room using dipoles:

    1 ms: probably reflections off the top of the couch where the microphone is
    7 ms: the backwave off the wall behind the speakers
    27 ms: double room-length bounce

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    If the initial peak on mine were more smeared out (like yours appears) the highest peak would be of lower amplitude and the relative amplitude of the reflections would be higher.

    Figure 3: Waterfall Decay time

    Your concern about the 20Hz area...

    You might want to take a measurement without much input from the speakers, just the ambient noise levels. The lowest frequencies can have quite a high SPL, and while not being particularly audible, are quite measurable.

    Here is a Waterfall for my room, with the excitation sweep at -60dB - you can see a little waterfall at, say, 4kHz, but the rest of the sweep would be below the level of ambient noise in the room (or measurement system) so it isn't even seen here:



    The point being - it may not be so much a lack of decay (at 20hz), but just mostly ambient noise that you see in the low frequencies of your waterfall. I have a 18hz bump when the AC is on, and plenty of other LF content intruding from the outside world.

    So, how much of that 20Hz in yours is always there, and how much of it is lack of decay from your test tone?

    I'm not saying my room is noisy - all I hear is a little muted computer fan noise, but the measurement microphones are quite sensitive. Right now, 2am., 35.6dB A-weighted, 44.5dB C-weighted, 50.9dB Z or unweighted


    Figure 4: The System
    Very nice. I simply must do something better with mine... one of these days...

    ---

    Sorry if these are not the responses you would have liked to have seen, but, at least it is a reply, based on my recent measuring escapades.
    Last edited by RayDunzl; 10-10-2016 at 02:33 PM.
    I'll be back later...


    System: Equitech 1.5RQ - OpenDRC-DI w/AcourateDRC - DAC2 - Krell KCT and FPB 350mcx - MartinLogan reQuest

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    Addicted to Best! YashN's Avatar
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    I don't think there's a big pb at 29Hz, but there are two troughs higher that could be problematic. Usually, bass traps in room corners help with standing waves.

    Otherwise, it looks like a quite smooth response.
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    Member Sponsor [WBF Founding Member] FrantzM's Avatar
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    Hi Florian

    I side with Ray on the low bass issue. As it is, your room response is extremely good and beg to be left alone . I know we, audiophiles are constantly looking to improve our systems but ... what you have here is remarkable.
    Apogee Grand?
    Frantz
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    Addicted to Best! Rodney Gold's Avatar
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    As it is right now , what is "wrong" with the bass?

    You need some DSP eq to remove low bass massive peak issues . no physical treatment will be effective.

    Troughs , unless very broad are not anywhere as audible as a peak is . pull down the peaks and if its a bit bass light , apply a house curve. you cannot cure steep troughs with boost..dont even try .. shallow dips can be "fixed"

    Im not sure of your path , but if its puter based , download a trial version of J river and use their DSP studio parametric to mess with low bass eq , , you can hear as you tweak , equalizer APO is also a nice freebie option for computer based stuff

    If you are not running off a computer, and you use analog sources you will have to use an external unit which will digitise all your delicious analogness and then convert it back to analog .. you have to balance any possible deterioration of the signal with much better reproduction

    Alternatively , albeit it sounds counter intuitive , use multiple subs and apply DSP to them ONLY...
    Or you could just move the listening chair to get out of nulls and peaks... tho whats best for bass might not be best for the rest
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    VIP/Donor [VIP/Donor] microstrip's Avatar
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    IMHO the 1/3 octave smoothing hides the useful information in the bass - 1/12 or 1/24 is needed bellow 200 Hz before debating peaks. Perhaps it is a good time to remember we had an excellent WBF thread written by Amir some years ago, Acoustic-Measurements-Understanding-Time-and-Frequencyhttp://www.whatsbestforum.com/showth...-and-Frequency.

    In my longer room (31') the second eigenvalue was around 35 Hz with corresponding very long decays at this frequency and I managed to improve it significantly, both in subjective listening and measurements, building very large bass tuned traps - see http://www.whatsbestforum.com/showth...l=1#post133862. As I had plenty of space behind the speakers, they are hidden by curtains. I am in the process of building a second one covering the whole back wall.
    DCS Vivaldi 2.0 stack, Soundlab A1 Px's while waiting for the XLF successor, EMT927, SME3012R, ARC Phono 3, Lamm ML1.2 Ref, Lamm L2ref, Stealth Dream speaker , Crystal Dreamline ICs, TA XL digital, TA XL gen V power cables, CenterStage footers and Nordost Qkore8's!

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    Since no one else has responded, I will. I do in-room measurements often.

    Thank you :-)

    Looks reasonable, no big peaks or dips to contend with are obvious at the 1/3 smoothing selected. However, you might want to use no smoothing in the low bass as to not lose the detail in that area.

    I did select 1/6 and higher where it does move out a little more but still within the +-5db realm. I will upload another set once i am home from work. The sound is very nice. If i move in 30cm steps towards the back wall, it gets quite a bit more busy.

    Figure 2: Impulse Response:
    Why is the first millisecond so hashy? It is far from ideal. I use room correction, but even my uncorrected IR looks similar to my "best example" - first two milliseconds:

    Good question, i can influence this in a big way depending on how far i sit back. I assume this is from the reflection points and my listening chair, as i place the microphone on top of my chair. Maybe i should move that out of the way.

    Figure 3: Waterfall Decay time

    Your concern about the 20Hz area...

    You might want to take a measurement without much input from the speakers, just the ambient noise levels. The lowest frequencies can have quite a high SPL, and while not being particularly audible, are quite measurable.

    I will take a measurement to see the noise in the room. I never caught that :-)

    Figure 4:The System
    Very nice. I simply must do something better with mine... one of these days...

    Thanks, it did take a lot of work.

    ---

    Sorry if these are not the responses you would have liked to have seen, but, at least it is a reply, based on my recent measuring escapades.[/QUOTE]

    Thats actually a really good response and i learned something. Thanks!

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    Quote Originally Posted by YashN View Post
    I don't think there's a big pb at 29Hz, but there are two troughs higher that could be problematic. Usually, bass traps in room corners help with standing waves.

    Otherwise, it looks like a quite smooth response.
    Its about +-5db, even at 1/6 smoothing. I use 8 full size bass traps from GIK (Soffit) but their value in the very low bass frequencies is close to none.

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    Quote Originally Posted by FrantzM View Post
    Hi Florian

    I side with Ray on the low bass issue. As it is, your room response is extremely good and beg to be left alone . I know we, audiophiles are constantly looking to improve our systems but ... what you have here is remarkable.
    Apogee Grand?
    Thank you, besides the long decay at the deep frequencies i am quite happy with it. Yes, its an Apogee Grand. Its been my speaker since more than 10 years :-)

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    Quote Originally Posted by Rodney Gold View Post
    As it is right now , what is "wrong" with the bass?

    You need some DSP eq to remove low bass massive peak issues . no physical treatment will be effective.

    Troughs , unless very broad are not anywhere as audible as a peak is . pull down the peaks and if its a bit bass light , apply a house curve. you cannot cure steep troughs with boost..dont even try .. shallow dips can be "fixed"

    Im not sure of your path , but if its puter based , download a trial version of J river and use their DSP studio parametric to mess with low bass eq , , you can hear as you tweak , equalizer APO is also a nice freebie option for computer based stuff

    If you are not running off a computer, and you use analog sources you will have to use an external unit which will digitise all your delicious analogness and then convert it back to analog .. you have to balance any possible deterioration of the signal with much better reproduction

    Alternatively , albeit it sounds counter intuitive , use multiple subs and apply DSP to them ONLY...
    Or you could just move the listening chair to get out of nulls and peaks... tho whats best for bass might not be best for the rest
    Thanks for your post, i do stream from JRIVER as well but am more into Analog. I use a Lyngdorf RP-1 which corrects 7% at the listening position. The chair is placed already at the best measuring location, if i move forward or backward the bass just gets more bumpy :-)

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