SPL Meter Correction Tables - Page 6

And another mic calibrating paper.
How Earthworks Measures Microphones, Khenkin (pdf document)
http://www.earthworksaudio.com/tech/...sures_mics.pdf

OK, all those analog meters on ebay look like the old RS meter. I've searched for a schematic on the ebay ones but came up empty. Anybody else with any luck. Oh, btw, the NADY (ASM-2) and Velleman (AVM2050) meters also fit that look-a-like category.

I have RS meter 33-2050. Do these files work with it? I use my meter with REW often. However, obviously, I don't believe it is completely accurate, because I don't know how to "load" or "import" or whatever these files. How do I apply these cal numbers to my meter? Do I "import" them as txt file? Please direct me to a post that explains how to apply these correction files, tables, or whatever you guys are calling them to my REW/RS SPL setup. I'm frustrated because I can't find the info anywhere.

If you have REW, go to Home Theater shack to the download section. They have updated numbers that you can download and save in REW so that the changes are done automatically.

Thanks very much. JohnPM posted on another thread and walked me through it. Thanks again.

Radio Shack "SPL" Meter Characteristics
As I wrote in another forum.
The June 2007 issue of Audio Xpress magazine has a 4 page article by Daisuke Koya:
"Radio Shack Sound Level Meter Characteristics"
Although I don't agree with his protocol, it's still interesting reading.

Is a link to the article available? I couldn't find one without signing up. Would be nice if you could link your comment to a readable article. Scanned would do as well.

EDIT:

Got it. Link

Quick question. Do I need to use correction values if im simply just using the RS SPL meter as a mic for Room EQ Wizard?

Did any of you calibrate your system using the receiver test tones and Radio Shack SPL Meter?

If so, did you calibrate everything at 75db, including the sub? Is it true that the SPL meter doesn't pick up low frequencies well so you need to calibrate the sub hotter (i.e. 85db or more?)

You can use a .cal file in REQ that automatically adds the correction values.




Yes, 75dB for receiver tones. To compensate for the meter being less sensitive at lower frequencies, adjust 1~3dB below 75dB if you want it even. If the meter says 75dB, you're at about 76~78dB.

And because of the meter is most accurate at the neutral point (70, 80, whatever you set it to), it might be easier to find the -5 point on your volume dial (may be -5, or 22, or wherever), and calibrate to 70dB.

What hz is the subwoofer setup noise in Avia?

I think it's 40~80Hz.

I haven't visited this thread in a looong time. However, the "corrected" sections that are on the Rives CD 2 disc are supposed to have been corrected for the RS #33-4050 meter. This is the meter that this thread is referring to.

The subsequent information in the latter half of this thread, should be updates. As you know, each meter has slightly different response characteristics. Remember that to make the correct measurements, the meter should be placed at the listening position (preferrably on a tripod - vibrations through your body will effect the low frequency response) and pointed straight up. Pointing it towards the front of the room (even slightly) will result in inaccurate measurements.

BTW, the "old" RS SPL meter, that I also have, is the #42-3019. There is also an even older model (real klunky looking), but it doesn't have a model number on it (except for a "No. 3110711" on a tag on the bottom of mine - labled "Realistic SPL").

That's an interesting article. My "old" model (the 42-3019) is apparently a slightly older version of the 33-2050 (Fig 2) pictured in the article, but it looks the same.

Here is a picture of my really old RS SPL meter:

I am quite confused. Are these the corrections that I should use when taking measurements with my SPL model 33-2055 SPL meter, C-weighted?

My onkyo HT-R510 is currently what I use to set up the sound, with its pink noise. I set up the SPL meter where I sit, set all the adjustments on it correctly and then turn up the volume (0-75, higher number = louder) on my amp until the Meter reads 75db. All amp settings are at 0db when I start. It starts with the left speaker and then goes all the way around. The left speaker is what as a reference to adjust the others. The Subwoofer reading has always been out of wack, never knew how to get that right. After I read through this though, seems like it should be set to 85db, correct? Also, what Hz is the onkyo test tones putting out, so that I can set the meter accurately according to the charts posted in this thread? Thanks in advance.

I have read the entire post and would like to achieve a more uniform and deeper low end from my subs. I have the analog rs meter, I do not have access to a laptop computer. Am then out of luck with the correction tables?

From one of the first posts on the SVS site FAQ

So find out what your subwoofer(s) are REALLY doing, and add the following numbers as appropriate to your SPL meter readings:

At 10Hz add 20dBs to the meter's readings and at ...

12Hz add 16.5dB
16Hz add 11.5dB
20Hz add 7.5dB
25Hz add 5dB
31.5Hz add 3dB
40Hz add 2.5dB
50Hz add 1.5dB
63Hz add 1.5dB
80Hz add 1.5dB
100Hz add 2dB
125Hz add .5dB

This excerpt is valid for the spl meter I own. Also in this thread they mention equalizers that will adjust at this low frequency. I think that possibly I can save the time and effort of selling my existing sub(s) for a new model and tweak what I already have to achieve a bit lower response. Two equalizers were mentioned a Rane and another brand. If the cost is less than a new sub which it should be that is the avenue to explore I think.

The chart above reads in part,
etc.

Does this mean if the meter is reading a steady 75db as compared to the other speakers it is actually 95db?
Or I have to add 20db at that frequence level?

If I could borrow/rent a lap top, I understand it is a free program that is then loaded with the correction values. Is the RS spl meter then connected to the laptop?

Could someone in layman's term explain to me what I need to do for accurate results?


I just calibrated my system. Set the meter to 70, set the volume on my receiver so the needle hovers around 0db. I then adjusted everything to the +5db setting. Supposedly I'm at 75db for my speakers, and my sub is 85db at my reference level.


What do I need for more accurate results?

All you need to do now is turn down your sub's volume so that the sub also reads at 75db. The +10db compensation for the sub is already taken care of by your amplifier/receiver, in other words your running your sub too hot.

Looks like my last post was one of the "lost" ones. I bought the RS 33-4050 yesterday and did a room test. I applied the dB adders from post #70 here. I generated an Excel file with results. Is there a way to change the x-axis of an Excel graph to log? I attached the file here, zipped because .xls won't upload.

 

MFW15_TestTones.zip 12.7880859375k . file

Under custom types you can set it up for log. Your's seemed to do the y-axis instead of the x-axis. Doublecheck your setup. HTH

I know there are a few of these out there but I made a really useful Excel sheet that is RS meter corrected, as most of these sheets do. But, you can remove or, put in any offsets you want for 3 different logs (3 full frequency sweeps). Mine is REALLY useful because it plots all 3 pages of logged sweeps on 1 graph for comparison. I have a notch filter in my receiver and I wanted a start graph line (before tweaking) for reference to make sure I am getting the results I want and not affecting other things. With my sheet you can record all your readings (start, change 1 and change 2) and see exactly what you did and if you got the results you were looking for. Good Luck and happy tweaking.

 

Frequency Response Graph (RS corrected).zip 7.1826171875k . file

I need a MIC for ROOMEQ....I know very little about them and wanted to get some recommendations. I thought maybe I'd look on ebay for one. Is there such a thing as a $20 MIC from a local guitar/music store and it be good enough for calibration purposes?

least expensive one I know of is the mic within the Radio Shack SPL meter ($40), but thats not the best for full range, but good enough for sub to speaker calibration. Typically, if you want something better, you are in the 120$ range. ECM8000 Behringer Mic $50 + XLR Mic cable $15 + Eurorack UB802 60$ (for phantom power).

If you want something for PEQ purposes, you will have to go the more expensive route. If you want something just to get subwoofer level matched to Speakers, you only really need the Radio Shack SPL meter.

Ok..I got the RS digital meter. I was just thinking I needed to use a microphone in order to use the REW program for room response. I'm just bored looking for a project itching to spend money on something.

For normal sub/speaker level matching, your meter will do fine.

If you want to take like 10hz-20khz sweeps, you want a mic like I listed (110$ overall though). RS Meter can do it, but it is not very accurate below 50hz and above 6khz. Using cal numbers is kind of gray area as well because those cal numbers arent for your exact RS meter, there are variances between meters.

The value of doing full sine sweeps would be to see that your room sucks acoustically just like 'everyone' else's (most likely). It will show you big problem areas and that you may want to invest (more money) in room treatments and bass PEQ. The values from 10-80hz will help immensely for pin-pointing PEQ settings.

Doing that sweep will lead to you spending quite a bit more money. Sometimes ignorance is bliss? HAHAHAHA. Its a long journey, my friend. But, it can be great fun in terms of balance between academics, hobby, and the all important "smile on one's face" at the end of the day.

So if we get the Behringer Mic and XLR cable and UD802/502 mixer, don't we still need an upgraded sound card?

I'm going this route to be able to do good full frequenncy sweeps but one thing I didn't figure on was the external sound card to connect the Mixer/Amp through. Do you use the RCA output/inputs of the UB802 connected to the laptop sound card? If so then the only one I've seen with RCA in/out was the SoundBlaster MP3+. IS there any others that have RCA ins/outs?

It works with my desktop's Creative Audigy 2ZS card. I do a 1/8" from the sound card Line IN to 1/4" Output of the mixer. The Behringer does a XLR between itself and the Mixer. My mixer does not use the RCA, it uses the 1/4 headphone adapters. I understand that Parts Express has updated their mixers, but I dont know the details of those updates.

To calibrate SPL level, I just hold the SPL meter for pink noise. Thats all I use my RS meter for now.