iMM-6 and REW readings

Alex Smith

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Hello everybody,

I purchased an iMM-6 mic and was using REW or ARTA proggs but didn't get a line/curve in a graph for IEMs I was expecting. Instead I got something fur-tree like.

On one PC with built-in sound card I got the graph like in pic.1.
On another PC I had something with a lot of noise. See pic.2

What is the correct way of measuring FR for IEMs?
 

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Matthew J Poes

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Hello everybody,
I purchased an iMM-6 mic but using either REW or ARTA proggs but I don't have a line/curve in a graph for IEMs but something fur-tree like.

On one PC I get this graph with inbuilt soundcard.
On another PC I have it like this with a lot of noise.

How can I fix the problem?
I’m not totally sure what you are asking or what this is showing. The second graph with “noise” simply looks like an unsmoothed graph. Try adding smoothing.
 

Wayne A. Pflughaupt

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You can’t get a usable graph if it has a 200-300 dB + vertical axis span. Re-adjust the axis for 45-105 dB.

Regards,
Wayne
 

Alex Smith

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Thank you for fast responses.
I am absolutely new in this field.
Could anybody explain how I can get "smoothing" and re-adjust the axis for 45-105 dB?
Sorry for asking dumb questions.
The idea is to compare frequency responses for different In-Ear-Monitors.
 
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Matthew J Poes

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Thank you for fast responses.
I am absolutely new in this field.
Could anybody explain how I can get "smoothing" and re-adjust the axis for 45-105 dB?
Sorry for asking dumb questions.
The idea is to compare frequency responses for different In-Ear-Monitors.
You might want to look into how in ear monitors need to be measured to get accurate results. You can’t just stick a mic at the tip of the monitor and measure. I have the MiniDSP EARS and had worked with folks from large labs as well as fellow reviewers with proper gear to validate my measurements. My IEM measurements in particular were inaccurate. The problem goes beyond the typical response errors that we normally think of. Headphones and especially IEM’s interact with the head by setting off resonances, reflecting down an ear canal, and creating a seal in the ear canal. All of these impacts a bunch of response issues. Headphones always have a spike in the response and one of the things my EARS rig gets wrong is where that rise in the high frequencies is located. It’s not just the wrong level, which is correctable, it’s in the wrong place. It can’t be corrected and as such gives you an inaccurate sense of the response.

I’ve been playing around with solutions, but what I’ve learned is that you need an accurate ear simulator. For IRM’s you don’t need an accurate Pinna model, but you do need an accurate ear canal and head resonator chambers. Without that the response will be inaccauraye and uncorrectable. At this point I’m hoping to find a used ear simulator on eBay, because I haven’t found a cheap DIY solution.
 

Alex Smith

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You can’t just stick a mic at the tip of the monitor and measure.
I use a shell. I put IEMs to one side of the shell and the mic to the opposite side. It's almost air tight. It's similar to this
Is there a way to measure FR for headphones?
 
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Matthew J Poes

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No, it is not precisely accurate. But at least something. How do the manufacturers make the FR graphs of IEMs they sell?
This is actually getting at the issue I was trying to explain, and what has been a big lesson for me. When you say, “at least it’s soemthjng.” You are really getting at the common idea that it may not be exactly right but you can at least compare. That implies that the measurement is consistently in error. But it’s not and that’s the problem.

Imagine you want to track how fast a car is using a radar gun. But imagine that depending on the shape of the car you get a different reading. So the gun gives an erroneous reading that appears randomly wrong. Maybe you find out, as I’ve said here, that the shape is what causes the error, because cars are complex shapes, it’s not possible to correct for the shape error. That is what’s going on here. Because of the way the IEM interacts with the head and ear canal, there is no way to know ahead of time what kind of error it will get when you stick it into a non-accurate ear. So you can’t correct it.

Brent Butterworth has done a good job addressing the issues and his article is a good read. He also shows measurements compared to his rig which is basically a bare minimum of what is accurate.
https://www.soundstagesolo.com/index.php/features/152-is-minidsp-ears-the-death-of-headphone-measurement-or-its-savior

He uses this:
https://www.gras.dk/products/ear-simulator-kit/product/737-43ag

And the top labs would actually use this:
https://www.gras.dk/products/head-torso-simulators-kemar

https://www.gras.dk/products/product/722-43BB
This is the basic coupler you need to simulate and ear canal. That metal coupler is deceptive. It’s not just a metal tube. It’s dimensions are precise and inside it has a labeyth like chamber that creates resonances that match those or your ear, skull, cheek, etc. It doesn’t create chest resonances which are what he torso simulator adds and that primarily impacts lower frequencies.

So you can do what you are trying to do, but it’s important to know that the results will have a number of errors that can make even comparing the headphones to each other a problem. Depending on how they react to the non-standard loading. Worse yet, you really can’t use them to judge good or bad because you can’t actually see what is going on when they are loaded in your ear.

Sadly the price of entry is $5000 and it just goes up from there.
 

Alex Smith

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Worse yet, you really can’t use them to judge good or bad because you can’t actually see what is going on when they are loaded in your ear.
Quite dis-encouraging but OK. Then another question coming to my mind. What is the use of iMM-6?
 

Matthew J Poes

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Quite dis-encouraging but OK. Then another question coming to my mind. What is the use of iMM-6?
I understand Alex. It is discouraging to me as well. I am actively looking for inexpensive DIY solutions and will validate the accuracy of my method. If any of these ideas work out, I'll happily share publicly so you can do the same.

The iMM-6 is for acoustic measurement with a smart phone or tablet. It can be used with a laptop as well, but a UMM-6 is a better option for that. I have an iMM-6 and I use it when I need a somewhat accurate measurement in a room and I need high portability. Maybe I'm trying to assess the acoustics of an office and I am just running to check out the job before making a bid. Maybe I want to check SPL levels at a concert or event. Something like that. It really isn't designed for measuring headphones, though really there is no reason why it can't be used for that. The problem isn't the mic itself, its the pseudo-ear.
 

Alex Smith

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It is discouraging to me as well. I am actively looking for inexpensive DIY solutions and will validate the accuracy of my method. If any of these ideas work out, I'll happily share publicly so you can do the same.
Thanks, Matthew, I really appreciate your desire to help me out.
Could you explain how I can make the graph smooth and re-adjust the axis for 45-105 dB with REW?
 
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Matthew J Poes

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Wow, you've really been so cooperative. I appreciate that so much. :jump:
No problem. I won’t promise to make you a video every time you have a question, but we all always try to help out.

In this case I’ve been working on videos like this and your question was the kind that I suspected would be addressed best by a video. I plan to do more of these five minute videos around REW to help orient people with very specific questions.

Maybe i should call them 5 minutes with Matt!
 

Wayne A. Pflughaupt

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Alex Smith

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In this case I’ve been working on videos like this and your question was the kind that I suspected would be addressed best by a video.
You are an angel! :yes:
Matthew, do you mind if I share the link to this video you kindly made to two Russian audio forums? Most of the users there are good at English and I don't think there will be a problem comprehending the video.
 

Matthew J Poes

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You are an angel! :yes:
Matthew, do you mind if I share the link to this video you kindly made to two Russian audio forums? Most of the users there are good at English and I don't think there will be a problem comprehending the video.
Absolutely. Spread the word. We posted it to our front page. If these guys want more tell them to come join our forum. I plan to keep making more of these (and I’m open to topic ideas).
 
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