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Thread: Help with 4312's

  1. #76
    RIP 2011 Zilch's Avatar
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    If I'm reading your results correctly, groundplane max and min are 89.5 and 83.5, i.e., +/- 3 dB, better than any results I've ever obtained measuring LF conventionally. The technique is credited to Mark Gander at JBL in Stereophile 28:1, January, 2005, P. 68.

    I'd call it most excellent work, Old_4312. May we have a summary of your findings, then, regarding LF measurements? Some readers may not get what's going on otherwise.

    Also, tell us about the measurement software you're using, please.

    Tip: See D'Appolito Chapter 4 regarding loudspeaker measurement microphones.

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    Hello everyone!
    Originally posted by Zilch:
    May we have a summary of your findings, then, regarding LF measurements? Some readers may not get what's going on otherwise.
    I learned so much from these tests, I'm not sure where to start with a summary.
    I'll do the best I can-forgive me if I get longwinded.
    Lessons learned:
    1. Unless you perform nearfield testing, it is impractical, if not sometimes impossible to do meaningful LF testing of loudspeakers in a less than perfect acoustic space, unless your objective is to see the result of the marriage of those speakers to that space.
    2. All boundaries have an impact on LF response of a loudspeaker.
    3. When 2 or more boundaries are acting on a loudspeaker system,
    their effect is cumilative. If these boundaries are far enough apart, they can introduce more than one large dip in frequency response.
    If they are identical, they will create a significant dip in response, as much as a 20 db loss. If the half wave length frequencies of the two are close in frequency, they actually can widen the "Q" of the dip, effecting even a wider number of bass frequencies.
    Check out the "4312 outside" response graph, and compare it to the skyward test and the 1 meter floor/ground boundary tests, which are both one boundary tests only. The "4312 outside" test shows the effect of two similar, but not identical boundaries workin' my poor 4312 over. That's one whopper of a dip there! This is pretty much what I'm seeing in my kinda sortof treated room.
    *Note* Be sure and observe the difference in db's per line. In some tests, the difference is 3db per section, others it is 6db.
    4. Groundplane testing in a wide open environment, with no vertical structures closer than 40', yields acceptable LF response measurements.
    The closest boundary in my case was 43 feet.
    5. The null points and depth of bass loss in db's, caused by room boundaries, are not fixed parameters. They actually vary in frequency and depth depending upon the distance and position of the microphone/listener from the loudspeaker. Refer to the 2 floor/ground boundary tests in my last posts.
    The only difference in these 2 tests, is the distance of the mic in relationship to the speaker. Everything else is the same.
    Changing microphone/listening positions can have a significant effect on measured/perceived bass response.
    6. No one room boundary appears to be more or less important than another.
    Addressing one or two acoustic problems in a room, does not a accurate listening/monitoring room make!
    7.It takes much planning, considerable construction, and a great big wad of cash to even get close to published frequency response curves or "grade A" studio quality monitoring to happen in an enclosed room.
    To quote Seinfeld: "Good luck with ALL THAT!!"
    Unless you're able to address and correct every boundary problem in a room, including floor and ceiling, don't expect perfect bass response.
    Carefully placed bass traps, the removal of right angles,etc.. is not enough to get the "Holy Grail".
    Whew!! I think I may have rambled too much there.
    I did apologize for getting long winded, right?
    I think that's the gist of it.
    If anyone has questions, I'll do my best to answer them.
    Zilch or others here in the forum can probably do that better than I can...
    One last lesson: If you have a loudspeaker or acoustics problem, this is a great place to come for help!!!
    It sure helped me to see the light of day!
    In the next post, I'll describe the software, "ETF5. " I've been using for the tests. It's a great, affordable piece of software. It does have limitations and certain hardware requirements, though.More on that later.
    Thanks everyone!

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    Exclamation

    Hello everyone!
    Per Zilch's request, here's some info on the software, ETF 5.XXX, I've been using for these tests.
    If you want to download it, it's available as a demo or full version from www.etfacoustic.com
    The demo is the same as the full version except:1. You can't save files with it, and 2. It will only perform 2 analysis per launch.
    If you need more than 2, all you have to do is re-launch it and start over
    ---not reboot.
    It does however, have a sequential test function (by clicking the red arrow at the right of the analysis screen's toolbar),once an analysis has been run.(This also works in the demo.)
    You can then click the "play" button for manual one shot updates, where the program will repeat the noise burst, then display the result, or you can set it to loop mode, and it will consecutively repeat the noise bursts and display any changes made in the measurement as you change speaker/mic positioning, eq changes etc..., just like a real RTA.
    What I like most about the program, is that it calibrates itself, so you don't have to burn up brain cells calculating the differences in decibels between two noise signals across the freq. range, or go through the task of trying to calibrate a hardware RTA to its own signal, dealing with crest factor and all that crap.
    To use the program, you must have a full duplex soundcard.
    Also, if the soundcard has a DSP mixer, and direct monitoring capability,
    you have to mute the monitoring of inputs one and two, before you make the soundcard connections,or you will get a loop, which might damage the soundcard. It doesn't mention this in the manual-so beware!
    When you read how the soundcard is wired up for this thing, you'll understand why;Channel one output is connected to channel one input, and ditto for channel two, for initial soundcard tests.
    Then, the channel 2 output is disconnected from the #2 input and connects to the signal path feeding the speaker, and the channel 2 input receives a line level microphone signal measuring the speaker.
    This allows the program to calibrate itself to it's signal, and any variances in soundcard freq.response. If you look at the graphs I posted, that line at the top, is the reference noise signal + innerchannel soundcard freq. deviations.
    For me, the trickiest part of the program was learning to always set the gating function up right. Too short a gate time, and low frequences aren't displayed, too long a gate time will add too much room noise. Around 49 ms seem to work the best for low freq.response measurements.
    The manual is pretty thorough, and explains everything fairly well.
    The software also offers impulse testing, with either graph display or waterfall displays for identifying speaker or room resonances.
    *The soundcard must pass the initial soundcard impulse tests with flying colors to utilize the impulse testing feature.*
    The more spurious noise and ringing your soundcard generates, the harder it is to discern resonance from soundcard artifacts. The manual explains this quite well. My 20 bit Layla barely squeaks by, but that's possibly due to driver issues, since it seems to works best with DirectX7 and it's own ASIO drivers.
    Newer, high end soundcards will not likely have any problems.
    I don't know what type of drivers this software uses.
    Acoustisoft may have soundcard recommendations.
    The only thing I don't like about the program, is that you can't custom select the frequency co-ordinates. You have to choose from a predefined selection from a drop down dialog box. If you're trying to zero in on a specific freq. range, that can get a little annoying--especially if the db range changes per range selection.
    Once you do the initial soundcard testing, it's not necessary to repeat that test everytime you launch the program. If you're using the demo version, this soundcard test will eat up one your two allowed analysis.
    If your soundcard will allow you to save sessions or setups, it's good idea to save 1 setup just for ETF5, after the soundcard is wired up and all the levels adjusted.
    If you're using the demo, don't forget about the sequential RTA option!
    If you need to make constant adjustments while observing the result, that's the way to go.
    I believe the cost of one license is 40 bucks...that info is available at the website.
    The software can also perform even more advanced testing such as psychological testing(for speaker placement), PSD testing(for noisy environments), and IMD and HD distortion tests as well--but these are available only as individually purchased plug-ins.
    One little trick: I've been capturing snapshots of tests by using the print screen key, and then pasting the clipboard in a jpeg editor/viewer.
    That's not the same as saving a test, then reloading it into the program and continuing to work with it, but it's a simple way to store a specific one time result.
    That's about it for my ramblings on the subject.
    The manual explains all the rest.
    Hope this has been helpful.
    I've received so much help here, I hope I've given a little back!
    Later everyone!

  4. #79
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    I think the site is actually www.acoustisoft.com - 'looks interesting!

    John

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    oops!

    Hello everyone!
    I goofed on the url, originally.
    I corrected the link in the original post.
    The url works now.Actually, both listed url's will work.
    Thanks,Johnaec for bringing this to my attention!
    Hope this didn't cause too many problems...
    I'll watch my fingers a little closer next time.
    Later everyone!

  6. #81
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    Shamefull!!

    You did all this with FREE software?

    [How embarassing.... ]

  7. #82
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    Hello!
    Except for the one limitation, it's a great piece of software.
    After I buy the "Testing Loudspeakers" book, I plan on buying a license.
    There are advantages to saving and reloading analysis files for further scrutiny.
    One license is cheaper than a one day Goldline 31 band RTA/AKG ref. mic rental--and I'd rather use the ETF5.
    Later everyone!

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