garyrc Posted May 30, 2006 Share Posted May 30, 2006 Hi -- I'm returning to the forums after a break of a few years. I'd like to use my Radio Shack meter to measure the response of my Klipschorns in my room, and to help tune the room. I saw the compensation chart Mike Lindsey posted when evaluating the K-77 v.s. another tweeter, I've looked at the response curves Radio Shack published on their meter (and later removed from the meter's manual), and I also measured the difference between the uncompensated and special Radio Shack Meter corrected tones used by Rives on their Test CD 2. They are all pretty different above about 5K Hz and sometimes call for compensation in opposite directions! Mike, where did you get your chart? Are there other compensation charts out there? Looking at Radio Shack's set of response curves, I'm guessing that "FREE FIELD", C weighting, on axis would be the nearest to appropriate for nearfield measurements, because I assume that the "RANDOM RESPONSE" curve droops (therefore calls for more compensation in the form of adding positive numbers to the reading) due to sound (reflections) entering the microphone at oblique angles. The compensation needed when "FREE FIELD" is used produces speaker / room curves with the least elevated treble. Here are three very different compensation charts. The first column is the compensation needed derived from the Radio Shack response graph for C wt. Free Field, as closely as I can read it with a magnifying glass, i.e., it is a mirror image of the graph at the 1/3 octave points from 5K up. The second column is the difference between the uncorrected and corrected Rives tones, and the third is Mike Lindsey's, from his post. I haven't pasted anything onto the forum before, so wish me luck -- i hope the columns stay straight. THREE CORRECTION CHARTS FOR THE RADIO SHACK METER <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /> 5K Hz to 16K Hz (approx. the usual K-77-F rage) (Apply the corrections shown to the raw readings with the Radio Shack meter) Radio Shack Chart Rives Mike FREE FIELD Correction Lindsey's 5K - 4 - 1.3 0 6.3K - 5 - 1.1 + 2 8K - 4.2 - 2.1 + 3 10K - 3 - 1.0 + 4.4 12.5K - 1.8 + 0.5 + 6.2 16K + 1.2 0 + 8.5 Any ideas on 1) Why these are so different, 2) How to best use the Radio Shack meter to measure speaker and room frequency response? Thanks Quote Link to comment Share on other sites More sharing options...
garyrc Posted May 30, 2006 Author Share Posted May 30, 2006 I see that the three correction charts I just posted have well scrambled columns. Apologies to all, particularly to Mike Lindsey, because his chart is misrepresented in the scrambled columns. For those who may be interested, I'll write the data out linearly. For the following 1/3 octave points of 5K, 6.3K, 8K, 10K, 12.5K, and 16K: My reading of Radio Shack's free field C wtd graph, the compensation needed would be -4 dB, -5 dB, -4.2 dB, -3 dB, -1.8 dB, +1.2 dB. The corrections I measured on the Rives CD for the RS Meter are -1.3dB, -1.1 dB, -2.1 dB, -1 dB, +0.5 dB, 0 dB. In Mike Lindsey's post, he recommends 0 dB, +2 dB, +3 dB, +4.4 dB, +6.2 dB, + 8.5 dB Quote Link to comment Share on other sites More sharing options...
3dzapper Posted May 30, 2006 Share Posted May 30, 2006 I thought I had a complete chart on my hard drive. It seems that all there is is lower frequencies.-( At 10Hz add 20dBs to the meter's readings and at ... 12Hz add 16.5dB16Hz add 11.5dB20Hz add 7.5dB25Hz add 5dB31.5Hz add 3dB40Hz add 2.5dB50Hz add 1.5dB63Hz add 1.5dB80Hz add 1.5dB100Hz add 2dB125Hz add .5dB So, we can add another column to the chaos. Rick Edit: And another: 10Hz +20.512.5Hz +16.516Hz +11.520Hz +7.525Hz +531.5Hz +340Hz +2.550Hz +1.563Hz +1.580Hz +1.5100Hz +2125Hz +0.5160Hz -0.5200Hz -0.5250Hz +0.5315Hz -0.5400Hz 0500Hz -0.5630Hz 0800Hz 01KHz 01.25Khz 01.6KHz -0.52Khz -1.52.5Khz -1.53.15Khz -1.54KHz -25KHz -26.3KHz -28KHz -210Khz -112.5KHz +0.516KHz 020KHz +1 Quote Link to comment Share on other sites More sharing options...
Marvel Posted May 30, 2006 Share Posted May 30, 2006 Sometimes it works better to use the pre formatted html tag. Makes it show up in courier, but it lines up that way. (watch it not work this time) THREE CORRECTION CHARTS FOR THE RADIO SHACK METER 5K Hz to 16K Hz (approx. the usual K-77-F rage) (Apply the corrections shown to the raw readings with the Radio Shack meter) ---------------------------------------------------------------------- Radio Shack Chart Rives Mike FREE FIELD Correction Lindsey's ---------------------------------------------------------------------- 5K - 4 - 1.3 0 6.3K - 5 - 1.1 + 2 8K - 4.2 - 2.1 + 3 10K - 3 - 1.0 + 4.4 12.5K - 1.8 + 0.5 + 6.2 16K + 1.2 0 + 8.5 Quote Link to comment Share on other sites More sharing options...
garyrc Posted June 1, 2006 Author Share Posted June 1, 2006 Thanks to 3dzapper and Marvel! 3dzapper, do you remember where you got your data? It agrees closely with my measurement of the amount and direction of comp applied by Rives -- exact agreement 10K and above, and within 0.9 dB from 5K through 8K --- probably normal measurement variation. The reason I don't like to use the Rives CD directly (instead of just noting with interest their degree of comp at their single frequency points), is that they use just a few single tones, rather than, say, 1/3 octave noise comprehensively covering the spectrum, with no gaps). Looking at the frequency curves PWK published in the mid 80s, for the entire Heritage line and more (Garrison reproduced them on this forum a few years ago), one can see that a single tone could be placed anywhere along a 7 to 10 dB peak / trough distance, and not be at all typical of its neighbors, or the mean elevation of that 1/3 octave. Since there is nothing magic about the center (as opposed to the average) of the 1/3 octaves, I can't figure out why Rives did that. Are there any other Radio Shack curves out there, particularly ones with a known source ? Can anyone recommend an adequate realtime analyzer for $500 to $1,000? I borrowed an old one that gave me outrageous elevations (up to 12 dB) above about 5K -- I don't believe it! Any experience with online software for FQ measurement? My goal is twofold: 1) to get nearfield and farfield response curves on my K-horns, Belle, and Heresy II surrounds (perverse curiosity, EQ temptations, and a desire to try the SMPTE curves for a small theatre) and 2) look at the response of the room at various listening positions, and make seat placement, diffuser, absorber, and trap adjustments. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted June 1, 2006 Share Posted June 1, 2006 IIRC I saved it from an AV forum. May well have originated at Rives. There is a free RTA or more sophisticated versions for a fee available at: http://trueaudio.com/ The RTA is calibrated for the Beheringer mic or with the updated versions, you can enter your calibration chart. Rick Quote Link to comment Share on other sites More sharing options...
rcarlton Posted June 1, 2006 Share Posted June 1, 2006 This is a more complete correction table: 10 -27.00 11 -24.15 12 -21.91 13 -20.13 14 -18.61 15 -17.33 16 -16.15 17 -14.92 18 -13.85 19 -13.01 20 -12.38 21 -11.66 22 -10.79 23 -10.00 24 -9.33 25 -8.80 26 -8.41 27 -7.99 28 -7.50 29 -6.99 30 -6.50 31 -6.03 32 -5.60 33 -5.23 34 -4.89 35 -4.58 36 -4.29 37 -4.04 38 -3.83 39 -3.64 40 -3.46 41 -3.31 42 -3.16 43 -3.01 44 -2.88 45 -2.74 46 -2.60 47 -2.46 48 -2.35 49 -2.26 50 -2.21 51 -2.18 52 -2.15 53 -2.11 54 -2.04 55 -1.98 56 -1.95 57 -1.92 58 -1.88 59 -1.84 60 -1.80 61 -1.77 62 -1.73 63 -1.71 64 -1.71 65 -1.72 66 -1.70 67 -1.67 68 -1.64 69 -1.60 70 -1.56 71 -1.52 72 -1.47 73 -1.41 74 -1.34 75 -1.26 76 -1.19 77 -1.12 78 -1.07 79 -1.02 80 -0.98 81 -0.94 82 -0.89 83 -0.85 84 -0.80 85 -0.75 86 -0.71 87 -0.66 88 -0.62 89 -0.59 90 -0.55 91 -0.52 92 -0.50 93 -0.47 94 -0.43 95 -0.40 96 -0.36 97 -0.34 98 -0.32 99 -0.30 100 -0.27 101 -0.25 102 -0.23 103 -0.20 104 -0.17 105 -0.14 106 -0.11 107 -0.07 108 -0.03 Quote Link to comment Share on other sites More sharing options...
rcarlton Posted June 1, 2006 Share Posted June 1, 2006 BTW Room EQ Wizard will work well for your needs. It is only free and works with your Radio Shack meter. It can be downloaded here. Quote Link to comment Share on other sites More sharing options...
Colin Posted June 1, 2006 Share Posted June 1, 2006 Despite its inaccuracies at the very lowest and highest notes of the musical range, the ubiquitous $40 analog Radio Shack (RS) sound pressure level (SPL) meter (cat.no.33-2050) was an inexpensive and invaluable tool for all tweaking audiophiles. With its <?xml:namespace prefix = v ns = "urn:schemas-microsoft-com:vml" /><?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><?xml:namespace prefix = w ns = "urn:schemas-microsoft-com:office:word" />frequency response is now corrected, blue dial added, the <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />SLM100 portable SPL meter now costs $70 and is available from ATI Audio.com (http://atiaudio.com/?fa=product&id=170). http://atiaudio.com/?fa=product&id=170#'> Quote Link to comment Share on other sites More sharing options...
NOSValves Posted June 2, 2006 Share Posted June 2, 2006 Get it here for $29 http://www.bswusa.com/proditem.asp?item=SLM100 Quote Link to comment Share on other sites More sharing options...
Mike Lindsey Posted June 2, 2006 Share Posted June 2, 2006 Just saw this thread. I'm not sure if I got it from my meter instructions, the AVS Forum or the HomeTheaterForum, but I can tell you I didn't make it up myself. I'm not that smart. [] I will try and find where I got that information. Mike Quote Link to comment Share on other sites More sharing options...
artto Posted June 2, 2006 Share Posted June 2, 2006 This makes a point that I've said before. Apparently few people still understand it. If we add the true response curve of mine, it also will be different from all the others and so on. With a true calibrated microphone we know EXACTLY what that specific microphone's response is, a calibrated graph and chart of the specific microphone you bought is supplied. While the RS SPL meter (and a few other bargains out there) have their usefulness providing general information about overall sound pressure levels or frequency response, they are NOT "instruments" appropriate for tweaking anything! Quote Link to comment Share on other sites More sharing options...
DrWho Posted June 3, 2006 Share Posted June 3, 2006 To expand on Artto, it only costs $100 to have a fully calibrated system....definetly something to consider. And then for another $200 you can have a full out ETF which is even better. Quote Link to comment Share on other sites More sharing options...
rcarlton Posted June 3, 2006 Share Posted June 3, 2006 Or for the $29 SPL meter that Craig found plus Room EQ Wizard (free) you would be set. REQ can also use the expensive calibrated microphone. Quote Link to comment Share on other sites More sharing options...
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