Dmitrydr: I'm not sure if I know the answer to your question as we have not tested an external mic. However, I can tell you this much:
1. The majority of the correction is for the C weighted circuitry. The remaining is for the fact that this C weighted circuitry is not quite right.
2. The external output of the RS meter is not weighted in any way and is just about flat up to around 2k. Above that the response is somewhat iradict and a better mic input would likely improve the response.
Hope that helps. |
Rives, if my understanding is correct, your CD is made for stock RS meter. Does it mean that it's not usable in case I'm using an external mike? |
Rives, thanks -- nice site by the way. I had two or three different adjustment factors for the RS meter. Your correction factors line up exactly with those Sean posted a few years ago. Now I finally know which to use. Now if I could only get my system down to 10 Hz ;-) |
Rives,
Thanks a bunch! Pp 3-4 should be required reading for all A'goners. I'm surprised a bit that the RS's treble peak is relatively low Q...it's a better mic than I thought.
Thanks again. Ern |
The full corrections are published in our instructions for use manual. If you go to our software page and download the instructions for our Test CD, there is a chart that gives the RS values. This was for the older 2050 analog meter. We have done preliminary work with the new 4050 meter and it appears to perform the same. Rives Software |
What are the corrections for above 1k (where it gets REALLY inaccurate!)?
Thanks. |
Pubul57,
You need to add the corrections at each frequency. So an 80db measured reading at 30hz is really 83db when corrected. |
Are the "corrections" for the RS Meter how much you need to add or susbtract to the meter reading or how far off the meter reading are? For example:
Does "30Hz +3" mean that a 80dB reading is really 83 or 77 |
Sean...Yes, analog (sorry analogue) meters can be guesstimated to fractional division resolution. When I was in college I had a professor who could read ten decimal places off a 4-inch circular slide rule that he kept in his shirt pocket. The 1 dB quantization of the digital meter represents "within 0.5dB" with no guesswork (or eyesight) required.
Fair enough...you take your boat. I'll hop on the jet. :) Ed |
El: The analogue meter offers pretty reasonable scaling and can easily be "guesstimated" to within a .25 - .33 dB on a steady state tone. When trying to chart something, a broad but shallow dip or peak can be quite evident to the ear. With only a 1 dB resolution on the digital meter, it could easily go un-noticed.
Other than that, i guess you take your boat and i'll take mine. Either way, with a stock RS meter, we are both paddling against the tide : ) Sean
> |
sean...The RS meter digital resolution is one dB which is probably better than you can read with a needle. As I mentioned, the digital display includes a bargraph display which shows dynamics, and is (IMHO) easier to follow than a needle. |
When I was in the market for a sound level meter I did some research on same and finally ended up getting the RS one. Not because with was the best but I had very little choice. Yes the next upgrade from RS is way too expensive to justify the cost for which it was going to be used. RS meter does the job well without putting a dent on your wallet.
I develeoped my own spread sheet ombining the RCA test disk that I own and the results I get are very much acceptable. |
http://www.prosoundweb.com/studyhall/lastudyhall/slm/slm.shtml
A good article from the ProSound community. |
Digital read-outs make it harder to follow subtle changes due to the lack of resolution between scaling calibrations. It is also harder to follow various dynamic trends with a digital read-out. As far as i know, both the RS analogue and digital meters share very close circuitry and neither are very accurate to begin with as they are delivered in stock form. Sean
> |
Edle, or anyone...Why not the digital version of the meter?
Except for the readout device (DVM vs Analog voltmeter) it's the same instrument. The digital unit has a bargraph display as well as the numeric readout, so it is easier to read in every way. For example, when balancing speakers of a multichannel system, it's a lot easier to remember "87" as the test tone moves from speaker to speaker, than to remember where the needle ended up. The price difference was $10, so I presume that is not the reason to recommend the analog version. Do we have another case of digiphobia here? |
I will be checking out the IVIE33 at CEDIA. I've contacted them and they said they will give demonstrations there. It does look pretty interesting. I have examined the audio toolbox. We considered it as substitute for our test kits, but upgradability, flexibility, and being able to program our BARE software into it was pretty limited. However, for a basic one piece unit it's pretty powerful and as I recall much less expensive than the Sencore unit. The Sencore is great--well made, near bulletproof, and priced accordingly. The one thing I don't like about the Sencore and Toolbox is lack of resolution--sure you can zoom in on a graph, but that's not terribly convenient. This is one other reason we chose a laptop based system--but then again--you need a laptop, which is more to buy and more to carry. |
Here is a link to the The Audio Toolbox Plus, a handheld audio and acoustic lab.
http://terrasonde.newmediaone.net/02/default.htm |
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Spend spend spend. IVIE 33, so cool you need gloves to hold it. |
The Radio Shack analog meter has a jack on the side for an external mike. When I owned a TACT RCS I used to put the TACT's mike on a tripod at ear level and plug the mike into the RS meter. It worked pretty well. For the "once in a while" casual hobbyist, the $50 or so for the RS meter and mods is likely sufficient. For a reviewer or serious hobbyist changing speakers regularly, it may pay to invest in better gear.
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Octopus: the link that you provided to Eric Wallin's DIY Audio website is where i snagged many of the mods that i did to my meters. If i can remember correctly, i think that i posted this site "way back" when we were discussing the inaccuracy of the meters and the correction factors to use. As Eric mentions on his website though, just playing with the parts in the meter will only change the linearity of the circuitry. The way that the microphone element is mounted and the low quality of the element itself are what hamper the performance beyond that point. This is kind of like having great backbone components ( preamp, amp, speakers, etc... ) and trying to compensate for a horrid source component. Granted, just getting the electronics to the point of increased linearity is a BIG step up, but addressing the problems with the mic will get you the rest of the way there without that much more hassle or expense. Sean > |
You can modify a RS analog meter to make it more accurate and extend the lf and hf responses. I've done it and it works great - and you probably won't need a more expensive spl meter.
See:
http://www.gti.net/wallin/rsmeter.htm
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Here are the corrections for the RS meter. Unfortunately, I only kept the #'s I was concerned with at the time. Use C weighting and the slow response:
20hz +7.5
25 +5
31.5 +3
40 +2.5
50 +1.5
63 +1.5
80 +1.5
100 +2
125 +0.5
160 -0.5
200 -0.5
250 +0.5
315 -0.5
400 0.0
500 -0.5
630 0.0
calib @ 1K 0.0 |
Here is a link to the Simpson analog meters. I use the model 886-2 with the 890-2 calibrator.
http://www.simpsonelectric.com/884-2.htm |
I purchased a few RS analogue SPL meters a while back while they were on sale with the intent of modifying them for a few friends. I haven't gotten around to doing any of them yet, but in stock form, i find these meters near useless in terms of accuracy. The problem is that there is SO much correction required that you end up having to chart your responses, add the correction factors to the figures you have and then recalculate what the true readings really are. People that take readings using the stock RS meter and then try to achieve flat response using those readings without adding the correction figures are really only achieving a different response that is not any flatter. This is due to the fact that they trust the readings that the meter produces yet the meters aren't accurate to begin with in terms of linear frequency response. By using Rives' disc, this takes some of the guesswork and math out of the equation, but should you not have his disc or want to take readings using other source materials at various frequencies, you're pretty much out of luck. As Rives mentioned though, there really is no "reasonably priced" alternative to the RS meter that shows demonstrably more accuracy or consistency from unit to unit. For those that do have one of these or something similar, one should remember that standing close enough to the meter to take readings or positioning the meter so that you can read it while standing away from it can REALLY throw things out of whack. This is primarily due to reflections from your body and / or the directivity of the mic element coming into play. Due to running into problems with this quite a bit, i've modified my meter for flat response electrically and connected this to a remote mic element that has a much wider & flatter frequency response. This allows one to mount a mic remotely and then stand a good distance away from it with the meter in hand. Due to the lack of reflections from your body, the readings are far more accurate using this approach. This is not to mention much easier also since you can position the meter itself for best visibility and ease of adjustment. With that in mind, i have to wonder how much of a market there would be for a product like what i've described above based on something similar to the RS meter ? Obviously, such a product would cost more money than the RS device itself, but how much, i don't know. Sean > |
There's really big gap in this area. You can go with Radio Shack for $30, or with something like Sencore for $2000+ (very accurate and very flexible). The Radio Shack does have non-linearities, but oddly enough it is very reproducible from unit to unit. We make a test CD that compensates for the non-linearities of this meter. |
Radioshack sound level meter - analog type(don't buy the digital type)....... |
