SPL Meter Correction Tables - Page 5

Question for sonny, why is the correction -27dB at 10Hz when, on your site, the old analog meter using the old cal file showed very good agreement with your calibrated mic at 10Hz? The old cal file uses -20dB at 10Hz, correct? If your calibrated mic matched the old analog meter at 10Hz using a cal factor of -20dB wouldn't -20dB be correct?

Is this a merger of your new low frequency data for the old analog meter with the old cal file at higher frequencies or did you actually measure the old analog meter versus your calibration standard out to 20kHz?

This is for the old Radio Shack analog meter. I took Sonnie's low frequency data out to 100Hz, Ilkka's mid-frequency data from 110Hz to 660Hz, the old calibration data from 800Hz to 8000Hz and data from a guy named Salas from 10000Hz to 20000Hz and merged them. I then did a spline fit and came up with the following set of correction factors:

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
110 -0.21
120 -0.19
130 -0.16
140 -0.13
150 -0.10
160 -0.08
170 -0.07
180 -0.05
190 -0.04
200 -0.03
210 -0.02
220 -0.01
230 0.00
240 0.00
250 0.01
260 0.01
270 0.02
280 0.02
290 0.02
300 0.02
310 0.02
320 0.02
330 0.01
340 0.01
350 0.01
360 0.01
370 0.00
380 0.00
390 0.00
400 -0.01
410 -0.01
420 -0.01
430 -0.01
440 -0.01
450 -0.01
460 -0.01
470 -0.01
480 -0.01
490 -0.01
500 -0.01
510 0.00
520 0.00
530 0.01
540 0.02
550 0.02
560 0.03
570 0.03
580 0.04
590 0.04
600 0.05
610 0.05
620 0.06
630 0.06
640 0.07
650 0.07
660 0.08
670 0.08
680 0.08
690 0.08
700 0.07
710 0.07
720 0.06
730 0.06
740 0.05
750 0.04
760 0.03
770 0.02
780 0.01
790 0.01
800 0.00
810 -0.01
820 -0.01
830 -0.01
840 -0.02
850 -0.02
860 -0.02
870 -0.02
880 -0.02
890 -0.02
900 -0.02
910 -0.02
920 -0.02
930 -0.01
940 -0.01
950 -0.01
960 -0.01
970 -0.01
980 0.00
990 0.00
1000 0.00
1100 0.01
1200 0.00
1300 0.00
1400 0.02
1500 0.04
1600 0.08
1700 0.13
1800 0.19
1900 0.26
2000 0.34
2100 0.42
2200 0.51
2300 0.60
2400 0.70
2500 0.81
2600 0.91
2700 1.02
2800 1.13
2900 1.24
3000 1.34
3100 1.45
3200 1.55
3300 1.65
3400 1.74
3500 1.83
3600 1.92
3700 2.01
3800 2.09
3900 2.16
4000 2.24
4100 2.31
4200 2.37
4300 2.43
4400 2.49
4500 2.55
4600 2.60
4700 2.65
4800 2.69
4900 2.73
5000 2.76
5100 2.80
5200 2.83
5300 2.85
5400 2.87
5500 2.89
5600 2.90
5700 2.91
5800 2.91
5900 2.92
6000 2.91
6100 2.91
6200 2.90
6300 2.88
6400 2.86
6500 2.84
6600 2.81
6700 2.78
6800 2.75
6900 2.71
7000 2.66
7100 2.62
7200 2.56
7300 2.51
7400 2.45
7500 2.38
7600 2.32
7700 2.24
7800 2.17
7900 2.09
8000 2.00
8100 1.91
8200 1.82
8300 1.72
8400 1.62
8500 1.51
8600 1.40
8700 1.29
8800 1.18
8900 1.07
9000 0.95
9100 0.83
9200 0.71
9300 0.58
9400 0.46
9500 0.33
9600 0.21
9700 0.08
9800 -0.05
9900 -0.17
10000 -0.30
11000 -1.50
12000 -2.50
13000 -3.51
14000 -4.60
15000 -5.74
16000 -6.93
17000 -8.16
18000 -9.43
19000 -10.71
20000 -12.00

Can someone who took data with this meter and a calibrated microphone through the entire spectrum verify if this is close?

Here is an image from a SMAART session using a Meyer HD1 as the speaker, with a DPA 4006 calibrated mic which is almost razor flat against the Rat Shack digital meter. I made this today.

Hello, maybe im thinking or trying to hard with my RS SPL and Rives disc. Im not sure if i have the old or new analog RS SPL or if the old is analog and new would be digital??? So if someone could plz help with what #,s i would need to +- to/from my samples i have taken. Im using an RS Analog SPL bought it 4 months ago and the Rives disk tracks 32-62. A simple wich post here (Name/Date posted) #'s to use would be fine to. Thanx for any help and sorry if i seemed confused I am Edit= OK searched alot more now i know i got the NEW anolog meter 33-4050 so is there any correction tables needed for this or has Rives realy done all the compensation needed if i use tracks 32-62 ?

I was wondering how accurate or inaccurate the newer digital RS meters are in the higher frequencies. I know they are pretty close in the bass region.

But I ask because this is the result I got with REW from my Ascend 340SE center channel (I had the receiver in DPL II Movie) + sub, with the meter on a tripod in the LP aiming diagonally up, as well as aimed forward (attached).

In my room I do have absorber panels on the left/right sides, and I have a large 3~4" thick floor cushion that I put on top of the large square coffee table.

Any idea why the frequency response looks like this in the highs?

I'm glad you asked that . Here is a similar graph of my left main speaker (a Phase Technology Velocity series tower), measured at the listener position & height with RS digital meter pointing almost vertical.
http://www.avsforum.com/avs-vb/attac...id=73756&stc=1

What's happening? I believe the "hairy" appearance of the graph at midrange to high frequencies (all frequencies greater than about 300 Hz) is due to comb filtering effects. If you zoom in on any part of the frequency scale, you will see the "hair" is actually narrow, deep minima (or "nulls") at many distinct frequencies. The nulls occur when, at a particular frequency and room location, the amplitudes of the direct sound wave (from the speaker) and all the reflected sound waves (from the walls or even from furniture in the room) sum to zero, or close to zero.

I don't think the "comb filtering" at high frequencies is as annoying to our ears as the graph might suggest. That's partly because each null occurs within a very narrow frequency range, and partly because the nulls are due to reflected sound that is time-delayed (at the listener position) relative to the direct wave. The time delay makes the reflected waves less audible than the earlier direct wave. (That's why we're told to concentrate on treating "early reflections" in room acoustic treatments; the early reflections affect our perception of the sound more than the later reflections.)

Notice that your graph appears flatter than mine below 200 Hz, and significantly flatter below 100 Hz. That may well be the result of the room treatments (absorber panels and cushion): I haven't gotten started with room treatments yet.

The next graph presents some evidence that the comb filtering is due to "reflections" that arrive later than the direct sound from the speakers (if my interpretation of the data is correct). This is a graph of exactly the same measurement as before (same speaker, microphone position, and REW data set); the only change is that I reduced the pre-ref and post-ref time domain widths (under Impulse Response controls) from the standard -125 ms to +500 ms, to a range of only -3 ms to +3 ms, which (I think) eliminates even "early" reflections.
http://www.avsforum.com/avs-vb/attac...id=73757&stc=1

The broad peak at 6kHz, followed by a steady rolloff toward higher frequency (in all the graphs being considered here), may be due to the non-flat frequency response of the RS meter. The frequency response corrections that we're using apply only to the low bass region, so we don't know what the RS meter frequency response looks like in the top two or three octaves.

Suppose you want to measure the "inherent" or "room effect free" frequency response of a speaker over the full 20 Hz - 20 kHz range? I believe there are some inexpensive microphone models with relatively flat response and known correction curve from 20 Hz to 20 kHz. But how can the "room effects" on the measurement be minimized? In addition to the time domain narrowing trick (that I already described), the ratio of the direct to reflected sound can be increased by placing the microphone close to the speaker, rather than at the listener position. In fact, the microphone can be placed very close to each driver or "port" on the speaker, and a "near-field" measurement can be done for each driver or port. I've seen these types of "near-field" measurements in audio magazines.

For example, here are some measurements from a recent Stereophile review of a speaker with several drivers and ports, the Monitor Audio RS6 (see the color curves in Fig. 3):
http://stereophile.com/floorloudspea...or/index3.html
And here is a picture of the speaker being reviewed:
http://stereophile.com/floorloudspea...tor/index.html

Anyone else have thoughts or information on doing "full-range" (20 Hz - 20 kHz) speaker measurements at home? This topic may have been discussed at some point on the Speaker (rather than Subwoofer) forum, but I haven't tried a search yet.

Sonic icons,

Thanks for the response.

My response under 200hz is due to bass traps I have in the room, as well as the BFD eq I apply to my sub.

Another trick to get rid of the extreme zig zags is smoothing, like going from NONE to 1/12 or 1/6, or even 1/3.

I posted further measurements here:
http://www.hometheatershack.com/forums/22634-post9.html
With full frequency response, the sub+speakers with bass traps but BFD disabled, and more from the bass region.

Anyway, other feedback I've heard is that the RS meter isn't accurate above 4~8KHz. Like you said, I'd need a better mic to get accurate readings for anything other than the bass region.

I commented about the accuracy of the analog RS Meter compared to a better microphone a little in a different thread. As you can see, my RS meter was inaccurate in the same range as you see in your graph. I took mine at very near field to minimize the comb filtering...

Even if you add 3db to the graph on the right, it still is significantly different. The two should be identical below 2khz for your reference.

http://www.avsforum.com/avs-vb/attac...chmentid=61543

I thought having a RS analog meter #33-2050 which I purchased many years would be all that I would ever need to set up my speakers. That is until I read every message in this thread.

If I'm just concerned about setting proper volume levels in a 5.1 spkr system (versus making absolute measurements of individual spkrs), is it that significant that the RS meter falls off at low freqs? Let's presume all 5 main spkrs are the same & I want to adjust the volume so that they all are equal. Since I am adjusting the spkr sound levels relative to one another, would the meter readings I get be "accurate" for this purpose?

Is there any standard for the spkr test signal that most receivers generate? For example, let's say it is limited in range from 100Hz to 5KHz, then would the poor linearity of the RS meter should be a moot point?

I just got a subwoofer a couple weeks ago so I brought out the RS meter. That's when I started reading all these postings & figured there would be more to setting up the sub than I had planned on. FWIW, I just looked at the Owner's Manual and the response curve for C weighting if flat from about 1.5KHz all the way down to 20Hz. My manual is dated 1993 and the meter is about that old.

The posted correction tables indicate the meter is off about 1dB or less in the 80Hz to 100Hz range of crossover freqs that I've been playing with.

1) Do you think I should just use the meter as is for my application?
2) Any possibility that my meter is so old that it was made to tighter specs than newer ones of the same model, since the response graph indicates flat to 20Hz ?
3) Should I get a new model analog meter?
4) Should I modify my existing meter & swap capacitors as per this thread?

Any comments would be appreciated.
Thanks in advance,
Mike

As long as you make sure your batteries are fresh, you should be okay. If your meter is anything like the newer analogs (digitals are separate, newer ones are much more accurate in the bass range), then it's approximately 2dB off in most of the range played in test tones to set up the subwoofer. This means that if the meter says 75dB, it's actually about 77dB. The roll-off is steeper the lower you go, so after a certain point between 30~40Hz or so, you'd have to add 3dB+, down to 6~7dB in the 20s, etc.

Basically, don't worry about it.

cyberbri,

Thanks for the reply. My initial thought was I better modify my meter or use a correction table, which would be easy. But there seems to be basically 2 different tables that keep getting mentioned. Then I figured since I'm not really too concerned about anything below about 80Hz, I should not get too anal about setting spkr levels.

Thanks again.
Mike

Not concerned about anything below 80Hz? Do you not have a subwoofer?

If this has been answered already I apologize and ask to be pointed to my answer. I have a digital RS SPL meter, but from what I have seen the correction numbers are for the analog meter. Do the same numbers apply to the digital meter or is it accurate enough not to need correction numbers?

Thank you

I guess I should re-phrase that. At this point I am trying to figure out the best crossover freq & level for the subwoofer. So I am concentrating on the range from 80Hz to 100Hz and trying to make sure it's relatively flat at the crossover freq. So I'm playing with that first. Do I want response flat down to 20Hz? Sure I do. I may be wrong & will gladly stand corrected, but I figured the crossover settings should be adjusted first, or at least roughed in.

Sorry for the confusing comment.
Mike

The newer digital meters are much more accurate, to within 1/2dB ~ 1dB for most of the bass range.

I use one, and calibrate for music to 0~1dB over, and for movies 2~3dB over my speakers (with the sub eq'd very flat first).

Not at all. Yeah, the speaker placement, listening position, and phase setting on the sub will all effect the frequency response from below the xo to nearly 200Hz. Which is why Avia is nice - it has frequency sweeps from 200Hz down to 20Hz for each of the 5 channels, which are fed through the receiver's bass management so you can measure response.

Does this mean that I don't need to apply any correction numbers to what the meter reads for my sub?

None, or 1dB at the most. So if you are calibrating your speakers to 75dB, getting your sub to 74dB~75dB is probably about even. But unless you have super-flat response, the meter will probably jump around at least 3~4dB. Just take the mean or average from the sub reading.

http://www.hometheatershack.com/newrsdigital.cal

Go to Sonnie Parker's site (above) and there you will find the correction values for the digital meter - (which DOES require a bit of correction in the very lowest region.)

Thank you guys, now I need to re-calculate my sweep numbers, I was using the old correction numbers for the analog meter.

Yes, below 30Hz. Which calibration test tones probably don't even get near...

10 -7.29
11 -6.85
12 -6.35
13 -5.70
14 -5.10
15 -4.60
16 -4.30
17 -4.00
18 -3.70
19 -3.55
20 -3.25
21 -3.15
22 -3.00
23 -2.90
24 -2.80
25 -2.65
26 -2.58
27 -2.45
28 -2.25
29 -2.09
30 -2.01
31 -1.91
32 -1.80
33 -1.71
34 -1.55
35 -1.40
36 -1.27
37 -1.15
38 -1.07
39 -1.00
40 -0.98
41 -0.93
42 -0.86
43 -0.75
44 -0.69
45 -0.63
46 -0.59
47 -0.55
48 -0.50
49 -0.49
50 -0.46
51 -0.46
52 -0.45
53 -0.46
54 -0.47
55 -0.47
56 -0.48
57 -0.49
58 -0.50
59 -0.51
60 -0.53
61 -0.55
62 -0.57
63 -0.59
64 -0.61
65 -0.63
66 -0.65
67 -0.67
68 -0.68
69 -0.72
70 -0.75
71 -0.77
72 -0.79
73 -0.79
74 -0.80
75 -0.82
76 -0.83
77 -0.84
78 -0.86
79 -0.85
80 -0.86
81 -0.87
82 -0.88
83 -0.91
84 -0.94
85 -0.94
86 -0.93
87 -0.92
88 -0.92
89 -0.91
90 -0.90
91 -0.89
92 -0.88
93 -0.87
94 -0.86
95 -0.85
96 -0.84
97 -0.83
98 -0.83
99 -0.82
100 -0.82
101 -0.81
102 -0.80
103 -0.78
104 -0.76
105 -0.73

Sorry couldn't get a smaller pic to work! Are these the correct #'s to add to my raw #'s using the 33-4050. Also any fast link to full #'s from 10-20k please. I see #'s for the OLD RS but having trouble finding full chart for the NEW rs analog. Thanks

I have the Avia disc but find it difficult to watch the RS meter and the TV simultaneously to correlate the readings with what frequency the sweep is currently moving past. Do you record the Avia sweeps using software so you can analyze them properly?

No, if I'm using Avia, I'm either holding it in front of my head, or have it on a tripod on the couch. I can dart my eyes back and forth reasonably fast enough, and I can always rewind if I want to see a section again.


But I also use Room EQ Wizard, a free computer program, in conjunction with my SPL meter, to do instant (10 seconds or so) sweeps and have graphs made automatically like this:

cyberbri, is Room Eq simple to use? Do I just download it, connect my laptop to my receiver and my spl meter to my laptop? IF so, that would be so much easier then doing the sweeps manually.

Yes, it's that easy. There might be some hiccups initially when you try to set it up, and initial setup does take a while because you have to measure your sound card's response, etc., but once you have it down, it's very easy. I can set it up now in about 3 minutes, including getting the meter and tripod out and hooking up all the wires. Sweeps take about 10 seconds each.


Here's the best place to ask REW questions:
http://www.hometheatershack.com/forums/bfd-rew-forum/

Here's where to download the program:
http://www.hometheatershack.com/roomeq/

Here's the setup guide, hosted on hometheatershack:
http://www.hometheatershack.com/room...tml/index.html

Thanks cyberbri, I will look into it.

Sorry if I missed the response but I believe someone asked about using the Scosche SPL meter that seems to be available from Wal-Mart for about $20. Any opinions on this meter - will it do the job of setting speaker levels on a surround sound system? I don't need to balance all sorts of frequencies, just set sound levels.

An interesting mic calibrating paper.

ARTA Chamber for the Lower End Microphone Calibration (english version - pdf 352kB)
http://www.fesb.hr/~mateljan/arta/Ap...r-Rev03Eng.pdf
home page
http://www.fesb.hr/~mateljan/arta/index.htm