Home Theater Forum and Systems banner
1 - 16 of 16 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #4 ·
Thanks Wayne, I will try to make a cal. file by useing the notepad method. The cal. sheet i got is not
generic as it comes with a serial number - same as my mic. I alredy wrote Beyerdynamic to send me
the cal file not only the paper, but got no answer...

to John:
thanks for the link - its a really nice program. I changed the colour of the graph but my only problem is now
how to set the amplitude values? My sheed comes with an dB FS scale goning form 0 to plus or minus and there
are no minus values in the program - can you help me? I read the help but dident find something.


again thanks to you all - I really appriciate this!
 

·
Premium Member
Joined
·
1,562 Posts
I also have the MM1 and Beyerdynamic customer service at the germany website supplied the file for me. It just takes a couple of days.

The calibration covers 60 - 20k Hz so the LF end is not provided. Mine extends very flat down to about 20 Hz and assume that is very typical.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #6 ·
now I got the sulution - I called the service of Beyerdynamic and one day after I got the cal. file.

thanks for your help everyone!
 

·
Registered
Joined
·
66 Posts
I just found out about this mic. Before I take the plunge, I wanted to ask whether anybody has a handle on whether Beyer calibrates each individual mic in the manufacturing process (made in China?) or whether they have a one-size-fits-all calibration file for a "typical" mic that they give anyone who asks. This is what I suspect, but can't prove, the other company "B" does with its measurement mic. I can't imagine that for $200 Beyer calibrates each mic on the assembly line but what a pleasant surprise it would be if that were the case. Maybe I'm dreaming.
 

·
Premium Member
Joined
·
1,562 Posts
I just found out about this mic. Before I take the plunge, I wanted to ask whether anybody has a handle on whether Beyer calibrates each individual mic in the manufacturing process (made in China?) or whether they have a one-size-fits-all calibration file for a "typical" mic that they give anyone who asks. This is what I suspect, but can't prove, the other company "B" does with its measurement mic. I can't imagine that for $200 Beyer calibrates each mic on the assembly line but what a pleasant surprise it would be if that were the case. Maybe I'm dreaming.
Yes, each mic is individually calibrated by Beyerdynamic.
Before I purchased I had them supply a sampling of several calibrations and they had the expected variation for an inexpensive mic.

On request they will supply the cal file for your particular serial number. The cal file only goes down to 60 Hz though so it is not helpful for low frequency usage.

Also my MM-1 calibration with its cal file did not compare well to my Dayton EMM-6 with its cal file from Cross-Spectrum Labs. My measurements are very repeatable and there is a 2 dB difference at higher frequencies. The chart below shows the difference of measurements using the MM-1 compared to measurements using the EMM-6. These are repeatable speaker measurements using the respective calibration files. If both mic calibration files were accurate the line would be flat at zero dB.

Text Line Font Design Parallel


Everyone here has great faith in CSL calibrations and they go down to 5 Hz. I have no way of evaluating which is really correct, but am using the EMM-6/CSL based on the large amount of favorable information here at HTS. [Someday I will have CSL calibrate my MM-1 and also my Behringer ECM8000]

I really favor the design and construction of the MM-1. It has higher sensitivity and lower noise than my other 2 mics. Its smaller barrel also marginally reduces the directional sensitivity at the high frequencies. This will be my main mic after I have CSL calibrate it.
 

·
Registered
Joined
·
66 Posts
Thanks for the info. Someone posted some calibration data for an MM1 on Facebook, so after I posted I saw that the Beyer curve only goes down to 50 Hz. I would prefer curves that go down to 20, so I think you just saved me $200. I suspect the MM1 uses the same Panasonic electret capsule with the plastic diaphragm as all of the other cheap "calibration" mics.

my MM-1 calibration with its cal file did not compare well to my Dayton EMM-6 with its cal file from Cross-Spectrum Labs. My measurements are very repeatable and there is a 2 dB difference at higher frequencies. The chart below shows the difference of measurements using the MM-1 compared to measurements using the EMM-6. These are repeatable speaker measurements using the respective calibration files. If both mic calibration files were accurate the line would be flat at zero dB.

Read more: http://www.hometheatershack.com/for...alibration-beyerdyamic-mm1.html#ixzz2W0yIsmnO
I face the same dilemma. I hve two ECM-8000s, each calibrated by Cross Spectrum and by Kim Girardin. There are significant differences at the extremes of the band to be sure. The quandary is, which calibration is more accurate?

If you don't mind my saying so, have you checked the IR windows of your graphs? There appears to be a great deal of ripple in them, possibly caused by first reflections?
 

·
Registered
Joined
·
66 Posts
OK, now I remember the procedure for checking calibrations.

Pick two or more mics that you have had calibrated. Perform a sweep on these mics. To each sweep, apply the calibration curve for that mic from calibration service "A" and the curve from calibration service "B". Export the measurement for each mic as its own text file.

Import the data from these text files into a spreadsheet program. Even though you are looking at two different mics, in a perfect world, once the calibration curves are applied they should look like the same mic. If the calibration curve for each mic were perfect, in theory the two mics' curves should match. Does that make sense? In your spreadsheet program you could then calculate the (hopefully minor) differences between the mics and then the RSS of the differences for the calibration services you are comparing, or create a pretty graph of the differences..
 

·
Premium Member
Joined
·
1,562 Posts
Yes, That makes sense. That is basically what was done for the chart above. All the steps were done within REW however, no need for a spreadsheet.

In my case.
I took 3 measurements with each mic with its calibration file applied. I was careful to control my room noise floor to its lowest level.
> The 6 measurements were all RTA forever averages over approximately a 18"h x 36"w vertical window centered on my LP. This measurement method is repeatable to approximately ±0.75 dB.
> The 3 measurements in each set were then averaged together. This further reduces the variability of the process.
> The SPL levels of the 2 averages were then closely matched manually.
> The A/B math function was then applied to the 2 averages; A = MM-1 and B = EMM-6.
> No smoothing was applied to the 1/48 octave measurements (or the averages) until the final A/B plot which was smoothed to 1/6 octave.

The resulting chart shows the relative SPL reading of the MM-1 as it relates to the reading of the EMM-6 under similar circumstances.

This is not as accurate a process as a good lab calibration would be. I would expect the variability at CSL to be more like ±0.15 dB over this same 60-22k Hz range. This home brew procedure is plenty good enough however to conclude there is about a 2 dB difference in the output these 2 calibrated mic's at the high frequencies however.

As you noted this says nothing directly as to which, if either of them, is accurate. We need to surmise that based on other information.
 

·
Registered
Joined
·
66 Posts
I chose one of my externally-performed calibration sources as the standard, then averaged my two mics together with calibrations from that source. I made the determination of which calibration source to use by examining the two mics' curves together with calibrations from each source, to see which curves matched more closely. I'm happy now and figure I'm within 1/2 dB of true flatness, and no longer lust for a $2,000 DPA 4007 or an ACO Pacific, and won't be getting a Beyer or an Earthworks or any of those mics. I would get a Beyer if the curve went to 20 Hz.

Send me a PM if you want more information.
 

·
Premium Member
Joined
·
1,562 Posts
I think I understand your measurements and comparisons, but don't follow the logic of how this helps to determine accuracy. We have 5 unknowns for accuracy; The measuring signal, 2 mics and 2 calibration curves. No matter how we combine the cal curves with the mics and compare them I don't see how that helps.

We can relatively easily can determine "repeatability and reproducibility" of a measurement system by performing a "Gage R&R" test. This will determine the scatter in the gaging system and provide us the sigma and other statistics of measurement system variability.

For "accuracy" however it is my understanding the only practical option for a certified lab is to use a gaging processes with very low sigma as shown by the "Gage R&R" test and compare the subject mic to one closely traceable to NTIS standards. We would then still have the variability in accuracy as a result of the R&R's of any measuring systems used in the traceable chain to the NTIS standard.

It seems to me to that Herb at CSL is knowledgeable and skilled in lab practices and standards. He has been open and forthcoming in the how he handles the service of providing low cost calibrations that are as accurate as possible at CSL's price level. They are one step removed from a true NTIS traceable calibration, but it appears every effort is made to keep standards as high as possible given the pricing level.

I have no helpful information regarding the calibrations done by the mic manufacturers. From all the various problems reported here my confidence is not high for those sources. I assume the manufacture/assembly of the mic is the main business focus and the calibration is a relatively recent sideline service for customers (Dayton, MINIDSP, etc). Their calibration equipment and expertise may still be very limited. This may not be correct, but it seems more likely to me that CSL calibrations are more accurate and we at least have information as to what they are doing.
 

·
Registered
Joined
·
66 Posts
Well, the idea of averaging the two calibrations together didn't work out in practice, so forget it.

I had my mics calibrated by two independent services. There is quite a bit of divergence between the two measurements. Which is the more accurate? That is the question facing me.

If I take a mic and apply a perfect calibration curve to it, the result should, in theory, be a ruler-flat curve. If the cals from both services were perfect, two curves, one with each cal. applied, should both be ruler flat. In other words, ideally there would be no divergence between the cals from each service. All I have to go by are the sweeps I generate here which, of course, are not flat, so the best I can do is compare the two cal. curves to these (repeatable) sweeps -- one for each mic. Again, in a perfect world, the sweeps of the two mics, with callibration curves applied, should match exactly. Not being a perfect world, they should be very close. My technique is to see which combination of mic + calibration curve from which vendor matches most closesly. Make sense?

I should be able to take any mic, not necessarily a "calibration mic",have it calibrated, apply the cal. curve, and have it match any other mic with its cal. curve.

Let's see if I can explain this with a syllogism:

Two mics, 1 and 2.
Two calibration services: A and B

mic 1 + curve A = 1A
mic 1 + curve B = 1B
mic 2 + curve A = 2A
mic 2 + curve B = 2B

In theory:

1A should = flat
1B should = flat
2A should = flat
2B should = flat

therefore

1A should = 2A (the two mics should match).
1B should = 2B (the two mics should match).

It not being a perfect world, the question arises, which combinations match most closely?

If 1A and 2A match more closely than 1B and 2B, then A's calibration is truer than "B".
 

·
Premium Member
Joined
·
1,562 Posts
Okay, I see now you have 2 mics that are each calibrated at 2 labs. For "accuracy" we now have 7 unknowns; The signal, the 2 mics and the, 4 calibration curves. Again, any combination of these does not lend any insight into "accuracy".

The process you describe does give a very narrow insight into the gage R&R of the labs. If the lab's R&R is very good, every mic calibration, done by any lab calibration person, done at any time, will provide a very consistent result. That is, pick up any mic with its cal file from that lab and we would get the same measurement result for a given signal (again within the distribution established by the "gage R&R" for the calibration process).

I agree that if we have any evidence that the lab "gage R&R" is not good, as is the case with the recent MINIDSP postings, that automatically leads us to less confidence regarding their "accuracy". Several different answers cannot all be accurate, but maybe one of them is.

On the other hand just because a lab has good "Gage R&R" it does not tell us anything about its accuracy. It can very consistent, but very consistently wrong for accuracy.

It would be nice to be able to see a labs quarterly gage R&R results of their calibration process. It would be even better to see that and the annual result of the NTIS calibration for their reference mic. With both of those we can be confident in our measurement at the level defined by the stacked Gage R&R's of the chain of measurement tracing back to the NTIS standards.

No lab is likely to provide complete visibility to these items to the general public. When purchasing a NTIS traceable calibration a notation to the reference mic's NTIS calibration date is provided, but if the actual data and history is desired that may not be provided unless you are an important enough customer. I have rarely been able to see a good set of historical "gage R&R" data from a lab even when representing a significant customer. It is not easy to keep up with that process and it often exposed issues that the lab does not want to share. Also, all labs have problems due to "special causes" from time to time. These are things that disrupt the normal calibration process. If they are minor they may go undetected for some time. If they are gross then they are usually detected quickly. Labs can have good gage R&R and good tracible accuracy and still have frequent "special causes" that also disrupt the accuracy.

In summary; you have seen more variability from 2 CSL calibrated mic's than the same 2 mics calibrated at another lab. That gives you pause. I now understand that, and would share the same concern if that was the only information available to me. Based on the all the information I have seen so far though, CSL still seems to be the best choice for me. I am not willing to spend more money and also do the research needed find a better lab. If the other lab you used is low cost, I would be interested in more information about them.

Everyone's situation is different and what seems right for me isn't necessarily for right for someone else's situation. SLM, calibrated SLM, uncalibrated mic, factory calibrated mic, CSL calibrated mic, certified lab calibrated mic, Professional measurement mic and so on, all have their proper application. I guess I was just nitpicking over the idea that we can somehow determine "accuracy" of our mic or a given lab.
 

·
Registered
Joined
·
66 Posts
you have seen more variability from 2 CSL calibrated mic's than the same 2 mics calibrated at another lab
It would be more accurate to say that the variability between the two labs gives me pause.

No lab will give 100% accuracy; that I understand. I'm interested in which one is closer to "true".

One wonders if a high-end lab such as B&K keeps gage R&R data. I kind of doubt it.
 
1 - 16 of 16 Posts
Top