Basstrap - Jon Risch

Discussion in 'DIY Discussion' started by scott_01, Oct 26, 2008.

  1. scott_01

    andyoz

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    That's a shame. I busted up my leg a few years ago and couldn't drive/walk for 6-weeks. I felt basically useless as a consultant during that time as mobility is really important.
     
    andyoz, Dec 5, 2008
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  2. scott_01

    andyoz

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    Scott,

    Can you extract the 1/3rd octave Reverberation Time vs frequency from your measurements? Post the plots for the various config's if you can :)
     
    andyoz, Dec 5, 2008
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  3. scott_01

    Tenson Moderator

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    I've had M.E. for about 6-years now. Legally that doesn't stop me driving but I know damn well that my awareness and reactions are crap a lot of the time because of it. Not to mention the lack of energy to go running around the country. That's why I like to work from home and set my own hours building kit.
     
    Tenson, Dec 5, 2008
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  4. scott_01

    scott_01

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    Andy

    I'd love to. But to be honest I'm a total amateur in this area and I don't know how to at the moment. I guess a bit more reading is required. I'll get them up when I do though.
     
    scott_01, Dec 5, 2008
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  5. scott_01

    andyoz

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    I know Acoustisoft can do it. Just read up on how to display the RT60 curves.

    RT60 is actually less useful a measurement at low-frequencies (particularly in small rooms). Google the term "Shroeder frequency" to see what I mean. RT60 can still be useful to get a feel for what treatments are doing at low-frequencies though.
     
    andyoz, Dec 5, 2008
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  6. scott_01

    Tenson Moderator

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    I tend to use waterfall for low frequency analysis and RT60 and ETF (where the program got its name) for mid and highs.

    In my room RT60 is completely useless below about 200Hz. However, I have found I get more reliable results on RT60 by changing the ETF default settings to start 'counting' from more like 20ms after the direct sound rather than 50ms which is default. It seems more sensible for a domestic size room.
     
    Last edited by a moderator: Dec 17, 2008
    Tenson, Dec 6, 2008
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  7. scott_01

    andyoz

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    Yeah Simon,

    RT60 can be "slightly" useful in well damped rooms to get a snapshot of the before and after treatment scenarios. But as an absolute measure, it's a bit meaningless. When assess LF treatments, we normally have a quick look at the RT60 plots first and then delve into the waterfall plots. The waterfalls can sometimes throw too much narrow band detail at you making it hard to see the woods for the trees.
     
    andyoz, Dec 6, 2008
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  8. scott_01

    andyoz

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    Simon, just saw your plots.

    Have you experimented with the RT20 and RT30 readouts. It's hard to get useful results using RT60 in real life.
     
    andyoz, Dec 6, 2008
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  9. scott_01

    Tenson Moderator

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    They tend to give the same shape but just reduce the time frame. I do the measurements around 90dB and use an MLS test signal which the computer is able to deconvolve below the noise floor to a degree. So I am able to get around -50 to -60dB range.

    I don't know if it s just me but I also find ETF unreliable. Sometimes the RT60 measurements are way off. Other times they are fine. I notice that on the ones that are odd I can see slight ripples in the impulse response just before the start. Its a tad buggy I think.
     
    Tenson, Dec 6, 2008
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  10. scott_01

    scott_01

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    I know how to do it now Andy. I'm going to be busy for the next week or so so I'll be off here until then. I'll post them when I can. I'd be grateful if you can talk me through what they show.

    I've actually got Acoustisoft RplusD. It's effectively ETF with some more functionality. I think some of the bugs have been worked out. It definitely has a different user interface. To access the RT60 plots you have to opt for 'large room measurements'. Some ETF users can upgrade for free, visit the site for info.

    I'd agree that the software has it's flaws but overall it's pretty user friendly. Mind you I don't have anything to compare it with.

    I should also stress to others reading this or contemplating their own room treatment that, even with the cost of the ETF and all the materials; I'm more than happy with how cost effective this has been in terms of a sound quality upgrade.

    You don't need to be a genius at either acoustics or DIY to get decent results. A relatively small amount of money, some time and some effort deliver a really satisfying result. Also If you get stuck and think you need some 'expert' help then I'm sure the folks above would be more than willing to help out with some advice.
     
    scott_01, Dec 8, 2008
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  11. scott_01

    andyoz

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    It doesn't take much for RT60's to become eratic, even with MLS. Best to concentrate on the RT30.

    For music, it can actually be argued that the EDT (early decay time) is the most representative of what you actually hear in the listening room. The EDT is the rate of decay over the first 10dB of decay (extrapolated out to a full 60dB decay).

    For time varying signals like music, you rarely get to hear the full 60dB decay and the first 10dB decay is probably more important...becomes more of an issue with much bigger rooms though. A room where the EDT adn RT60 vary wildly can throw a few anomolies up that can be "hidden" by the RT60 measurements alone. You siftware should allow you to extract the EDT as well as RT.
     
    andyoz, Dec 8, 2008
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  12. scott_01

    scott_01

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    This took me a while, the shots are in the same order as the measurements shown in the last posts:

    1. No treatment


    [​IMG]

    2. All corners treated

    [​IMG]

    3. Doubled up treatment behind the speakers only

    [​IMG]

    4. Doubled up behind the speakers and fireplace treated too


    [​IMG]

    As I understand it the RT/60 time is a measurement of how long a particular frequency takes to decay by 60db.
     
    scott_01, Dec 14, 2008
    #32
  13. scott_01

    Tenson Moderator

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    I think the measurements are faulty. They are changing way too wildly. Also at some points it seems to be reading '0' decay time. That is really quite strange. Like on the first and second graph there is no decay at all between about 76Hz and 292Hz, then on the third one it is over one and a half seconds.

    Try doing the same measurement 3 or 4 times and see if it gives inconsistent results.

    If it does, please post pictures of the RT60 time on each repeat of the measurement and also a copy of each impulse response.
     
    Tenson, Dec 15, 2008
    #33
  14. scott_01

    scott_01

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    I didn't think they looked right but I can't seem to get them to look any better so up they went. Although no expert I can understand how a decay time of 0 is probably not realistic :D.

    Any ideas why this happened, other than the fact that the measurement is faulty?

    Does the generation of accurate RT60 depend on the particular type of test being run? For example MLS / Sweep / Hybrid etc?

    I can't face taking everything down and measuring again TBH. I've got a couple of other things to try on the treatment side.

    I've just got a new amp and will be hearing some new speakers tomorrow. Then I'll be moving the rack from between the speakers which should help further, so I'll leave as is for the moment, not least so I can hear the new kit against my old in a more representative way.

    Thanks for the advice everyone.
     
    scott_01, Dec 15, 2008
    #34
  15. scott_01

    andyoz

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    Yikes, something seriously wrong with those plots...
     
    andyoz, Dec 15, 2008
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  16. scott_01

    Tenson Moderator

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    It looks like a similar problem to what I was having, only worse. I got R+D after what you said Scott, but I still waiting for the replacement measurement mic to arrive so I will see how it works later on.
     
    Tenson, Dec 15, 2008
    #36
  17. scott_01

    andyoz

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    It's a slight worry that the program puts out RT results that are so weird. What does the heading RT60: 50ms - 150ms refer to??

    It must not be very user friendly..:confused:
     
    andyoz, Dec 16, 2008
    #37
  18. scott_01

    scott_01

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    User friendly? In interface terms I'd say yes. Its easy to set up and get basic measurements.

    Totally reliable and accurate? Well after those RT60 plots I'd have to say that is up in the air isn't it?

    I hope this doesn't invalidate all previous measurements. Were I being scientific then I know that it would and I'd start again. It's a good job I'm not becuase the thought of taking all the stuff down and doing it again makes me want to weep.

    I've e-mailed Doug Plum the writer to see what his take on this is. Hopefully he can see what I've done wrong or what is wrong with the settings / software. I'll post what he says.

    Laters
     
    scott_01, Dec 16, 2008
    #38
  19. scott_01

    andyoz

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    I'd be interested to know what the problem is.
     
    andyoz, Dec 16, 2008
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  20. scott_01

    scott_01

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    Thread from the dead

    Mainly becuase I've been looking at answering the 'Where to start' one on here and forgot that I'd looked at this.

    The problem with my RT60 plots was my selection of too long a time period when generating them:

    The writer of R+D (Doug Plumb) says...

    'The zeroed parts of the RT60 measurement are that way because there was too much noise at those frequencies to get good readings. Change your time limits and re-calculate.'

    I'll see if I've still got the measurements and do them again.
     
    scott_01, Aug 31, 2009
    #40
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