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OLD vs NEW radio shack meter comparisons

Discussion in 'Configuration & Setup' started by nelmr, Dec 23, 2010.

  1. nelmr

    nelmr Active Member

    UPDATE: See my other post below without the calibration files. These meters (at least mine) are virtually the same.

    So for those that claim the RS meter is a crapshot regarding bass below 30hz especially, you may be on to something. The following is both a 32 averaged high length FFT RTA graph and a sweep with both mics. I've used the calibration files for each respective rs meter found over at home theater shack. NOTE: those calibrations claim the old RS meter was even more off in bass than the new one. Yet other sources said the old one was better... hmm.. how does one know if each RS meter is the same from one produciton to the next (within the same overall version of the product).

    Any here are the graphs. I'll do some more tests without any calibration files to be able to see more clearly the differences between the old and the new.

    NOTE: My old meter is being quite hit-or-miss. Most of the time it works, but sometimes it stops working and I need to move the dial and/or selectors to jog it back into shape. It's been dropped a few times and is about 5 years old. This is why I got a new one that is more reliable.

    [​IMG]
    [​IMG]

    I calibrated both meters to be the same SPL (using 500-2000hz pink noise), though visually comparing the ballistic meters at the same time they are not exactly the same and vary by 1dB or so. Nevertheless, the overall SPL for the RTA chart not weighted for the NEW was 74dB. The Old was 86dB. Using C weighted this was 73 (new), 77 (old).

    So either the new meter and calibration file is right and I have a pretty flat calibration of the sub to the main (crossed at 60hz). Or the old meter and calibration file is right and I have a very bottom heavy sub calibration. Or... both are wrong.
     
  2. soundhound

    soundhound Well-Known Member

    The RS meters were deliberately rolled off in the bass region for reasons known only to the designers of the meters. What you are seeing is not meters being "off" from one to the next, but rather the bass rolloff design decisions from one generation of meter to the next. If you look at the graphs closely, you will note that they are remarkably consistent from one to the other; the only difference is that the slope of rolloff is different.

    Also, the RS meters have a calibration potentiometer which is accessible through a small hole on the side. Depending on the mood of the person who did the calibration somewhere in China that day, one meter could be calibrated differently than the next. If you had a calibration standard, you could do a good calibration of your meter. Additionally, the low frequency rolloff is very easy to defeat for somebody who is technically knowledgeable about circuits.

    The DIY mic you're making has no real restrictions on low frequency response; it is pretty flat down to 10Hz and below, with the only limitation being the LF rolloff designed into your sound card. For the measurement preamps I build, I usually choose a low frequency rolloff starting sub-1Hz, such as 0.3 Hz. This blocks the amplification of DC and keeps the circuit stable, but yields dead flat response to 10Hz.
     
  3. nelmr

    nelmr Active Member

    And here is the new vs old without calibration files and without employing c-weight correction from the software (REW has the option to use a calibartion file, c-weight, or no weight).

    I chose no weight and low and behold they are nearly identical :eek: . That goes against conventional wisdom that the two meters were different. Maybe they change the mic capsule they use over time. The one was made this year. The old one in 2003.

    NOTE: This graph has both RTA and sweep measurements.

    [​IMG]

    SPL measured 72dB with both.
     
  4. soundhound

    soundhound Well-Known Member

    Even those two are pretty consistent. The change in response that they can make in the electronics is much larger than the changes you will see with random production differences, or even mic capsule differences.

    At any rate, you should use the RS meter only for setting relative SPL levels of the speakers in your HT setup, and never to measure frequency response. The RTA program you have, and ones like TrueRTA are the right tool for that job, not a SPL meter.
     
  5. nelmr

    nelmr Active Member

    By saying maybe the changed the mic capsules (or anything else) from time to time I was referring to that perhaps explaining why there are so many different calibration files for the RS meter, why some tests show the old was more accurate in the bass, and vice versa.

    I was expecting a difference between these two mics judging by all the comments on forums and measurements done like this one. And there wasn't any. The old mic I have is the boxy one. The new one is the smaller softer edge one.
     
  6. Flint

    Flint "Do you know who I am?" Superstar

    The RS-Meters were designed for environmental SPL measurements, not precision audio amplitude response measurements. They offer either A-Weighted measurements (a measure of perceived loudness and potential hearing damage) and C-Weighted measurements (more for real SPLs with filtered bass where random environmental noise is often very high and could throw off the main audio range measurements).

    Here's a nice chart showing the measurement responses for the various weightings:

    [​IMG]

    Notice that the C-Weighting is at least 6dB below average at 20Hz and treble is even further off from that.

    This article goes into a detailed analysis of the RS Meters, including showing detailed accurate calibration measurements of the mic/system performance of the meters:

    http://www.audioxpress.com/magsdirx/ax/addenda/media/koya2811.pdf
     
  7. nelmr

    nelmr Active Member

    Flint, I understand the weighting. That article you link to is the same one I linked to in my post. On page 3 it clearly shows a difference between the old (bigger, boxy), and the new (smaller, smoother).

    I was expecting a similar difference as well. But there is none. They both have the same bass roll off characteristic. So I assume the change is roll off wasn't just as simple as the change of the look of the meter. It must have changed back when the meter was boxy. Either that or they have returned to the old characteristics in my 2010 model.
     
  8. Flint

    Flint "Do you know who I am?" Superstar

    Eh? What link? I've re=read this thread over and over and cannot see any link.

    That said, in my experience I have never gotten consistent and useful measurements from any general purpose SPL meter at frequencies below 30Hz, or so. Many are useles below 50Hz. Affordable SPL Meters were never really intended for this sort of application.
     
  9. nelmr

    nelmr Active Member

    The link is the word "one" in the following line of my 2nd post on this thread:

    I was expecting a difference between these two mics judging by all the comments on forums and measurements done like this one.

    I'm not going to keep using this meter for measurements. I'm building the DIY mic (already ordered the capsules). I just posted the differences between the meters I have and the calibration files available.
     
  10. Flint

    Flint "Do you know who I am?" Superstar

    Wow, I only see that as a link if I hover my mouse over the word. Otherwise it looks identical to all the other words. I wonder how many other links of yours I have missed? I'm not going to run my mouse over every word when I read your posts, so I guess I'll miss them.

    Just the same, I use my SPL Meters all the time to reference the levels in the room, trying to determine whether my ears are going to get damaged from tools and other items, and so on. It isn't easy to pull a PC out, plug in a mic, fire up the software, and calibrate the inputs when all I need is a quick level measurement. Also, I use my SPL Meters to calibrate TrueRTA so it measures real SPL levels fairly accurately.
     
  11. nelmr

    nelmr Active Member

    I was using the default skin for this forum (under board preferences in the user control panel) and didn't have any trouble seeing these links. I went changing to some others and if you are using the subsilver2 board skin, it appears that the hyperlink does not show (just a hint of blue compared to the normal text, but no underline), which could explain why you couldn't find the link, but if you click on the word one in the original post, or in quoted text of this post, it will work.

    I'll try to be more mindful of this when I post.
     
  12. soundhound

    soundhound Well-Known Member

    Eh, why are we even worrying about this? The RS meter is a cheap way for hobbyists to set the relative SPL of the speakers in a HT system. It is not intended to be even a relatively accurate measurement instrument. To get that, you need to spend a couple hundred at least.

    Frequency response measurements are the domain of RTA instruments, not the RadioShack SPL meters.
     

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