An rpi based DIY Vibration meter - Page 4 - AVS Forum | Home Theater Discussions And Reviews
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post #91 of 321 Old 03-10-2017, 10:59 AM - Thread Starter
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I think I'm going to adopt the ISO (1631?) reference acceleration and convert the graphs to dB, this places 0dB at 1 micro m/s^2 which means 140dB is 10m/s^2 (i.e. about 1G)

main reason is that it simplifies the plotting of a normalised curve (for technical reasons...)
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post #92 of 321 Old 03-10-2017, 05:59 PM
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Quote:
Originally Posted by 3ll3d00d View Post
I think I'm going to adopt the ISO (1631?) reference acceleration and convert the graphs to dB, this places 0dB at 1 micro m/s^2 which means 140dB is 10m/s^2 (i.e. about 1G)

main reason is that it simplifies the plotting of a normalised curve (for technical reasons...)
Makes sense...get everything in db...easier to speak the same language across different metrics.

Do you have a link for this ISO reference?
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post #93 of 321 Old 03-10-2017, 11:24 PM
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A small side note, no need to reference things to 140 db. That is way to high unless the reference used is less. Anything over 128 db. from the subs is clipping somewhere with movies and clean output was a goal of the thread. You can have a 100 subs but, the movies were only meant to be so loud and ear protection should not get loss in all of this. The goal is to keep our hearing and enjoy it.
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post #94 of 321 Old 03-10-2017, 11:33 PM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
Makes sense...get everything in db...easier to speak the same language across different metrics.

Do you have a link for this ISO reference?
It is mentioned in http://www.acoustic-glossary.co.uk/d...m#acceleration and http://www.diracdelta.co.uk/science/...l#.WMOn6WmnxnE

If you Google acceleration reference db then you get lots of hits including that "measuring vibration" b&k pdf.
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post #95 of 321 Old 03-10-2017, 11:36 PM - Thread Starter
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Quote:
Originally Posted by derrickdj1 View Post
A small side note, no need to reference things to 140 db. That is way to high unless the reference used is less. Anything over 128 db. from the subs is clipping somewhere with movies and clean output was a goal of the thread. You can have a 100 subs but, the movies were only meant to be so loud and ear protection should not get loss in all of this. The goal is to keep our hearing and enjoy it.
SPL dB (which is referenced against 20 micro Pa) and La dB (which is referenced against 1 micro m/s2) are two completely different scales so 140 in one means nothing to the other. I'm sure we can (will) arrive at a view on what dB constitutes reference though.

Last edited by 3ll3d00d; 03-11-2017 at 01:25 AM.
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post #96 of 321 Old 03-11-2017, 01:49 AM
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Quote:
Originally Posted by 3ll3d00d View Post
SPL dB (which is referenced against 20 micro Pa) and La dB (which is referenced against 1 micro m/s2) are two completely different scales so 140 in one means nothing to the other. I'm sure we can (will) arrive at a view on what dB constitutes reference though.

Matt, your work for this ULF and Vibsensor thread is appreciated at the highest levels. I am just putting a caution for us to keep things real and relevant. We have to all admit, we are approaching levels found by many sources harmful to our hearing and need to keep things in perspective. I plan on doing dual UM18 boxes this summer but, it will be a lateral move since I don't need more spl. It no longers matters what increase in db. that the project may net. I hope this is not coming off wrong. I am all for people making a better system but, caution extreme spl for regular use.

Pesonally, I would love to hear how the perception is at 160 db clean. I can do the upper 130s but, the room can't take it for to long. So, I'm near the limit without having to do some major mods.

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post #97 of 321 Old 03-11-2017, 04:36 AM - Thread Starter
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for sure, I don't go anywhere near those levels myself. Just remember it's not an arcade game, you don't need the highest score!
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post #98 of 321 Old 03-11-2017, 04:46 AM
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3, have you done a comparison of your vibe psd compared to the vibsensor psd?

I'd love to see how they compare with each other.
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post #99 of 321 Old 03-11-2017, 08:10 AM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
3, have you done a comparison of your vibe psd compared to the vibsensor psd?
there is an example in this post, I'll repeat in more detail at some point.

seems like weighing down VS produces similar results <25-30Hz but IMV VS is not useful for >30Hz.
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post #100 of 321 Old 03-11-2017, 01:29 PM - Thread Starter
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got a basic normalisation function going, for example a simple x y z view



and then with the z axis selected as the reference (so it becomes a flat line)



it's a bit limited atm as it is done client side and relies on measurements being taken at the same sample rate (will expand that later)

next step is to allow target curves to be set then you will be able to pick a target curve and use that as the reference curve
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post #101 of 321 Old 03-11-2017, 04:07 PM - Thread Starter
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example showing the calculated summed response



and using the sum as the reference to indicate how each axis contributes to that sum (though perhaps this should show the x and y scaled accordingly)

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post #102 of 321 Old 03-12-2017, 12:00 AM
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Are the accelerometers calibrated in terms of sensitivity? I assume you need that in order for us to compare measurements or discuss them on absolute terms.

Last edited by awediophile; 03-12-2017 at 12:03 AM. Reason: clarification
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post #103 of 321 Old 03-12-2017, 01:24 AM - Thread Starter
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Originally Posted by awediophile View Post
Are the accelerometers calibrated in terms of sensitivity? I assume you need that in order for us to compare measurements or discuss them on absolute terms.
yes they are for sensitivity

there are register slots for sensor specific offsets that you can overwrite. This involves running a calibration routine (placing the device as close to perfectly level as possible, measuring the output over some period of time to calculate new offsets). I get the impression it's important if you're building a quadcopter but not so much for this purpose. I will add that to the app at some point though.
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post #104 of 321 Old 03-13-2017, 01:52 PM
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Quote:
Originally Posted by 3ll3d00d View Post
yes they are for sensitivity

there are register slots for sensor specific offsets that you can overwrite. This involves running a calibration routine (placing the device as close to perfectly level as possible, measuring the output over some period of time to calculate new offsets). I get the impression it's important if you're building a quadcopter but not so much for this purpose. I will add that to the app at some point though.
I see. Thinking about it, gravity actually should make a good reference.

Also to your earlier concern about removing the affect of gravity from measurements. If your sensor is stable against rotations, then gravity should be very easy to ignore. It will just be a DC component in the measurement.
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post #105 of 321 Old 03-13-2017, 02:44 PM - Thread Starter
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Quote:
Originally Posted by awediophile View Post
Also to your earlier concern about removing the affect of gravity from measurements. If your sensor is stable against rotations, then gravity should be very easy to ignore. It will just be a DC component in the measurement.
yes that's what I'm doing atm
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post #106 of 321 Old 03-14-2017, 04:56 PM
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Quote:
Originally Posted by 3ll3d00d View Post
example showing the calculated summed response



and using the sum as the reference to indicate how each axis contributes to that sum (though perhaps this should show the x and y scaled accordingly)

That sum line is awesome! Brings a lot of insight that was hard to see before. For example, that dip in x, y, and z between 20 and 30hz, when summed, is actually flat.

The question is...does it subjectively feel 'flat' or a 'dip' in that range?

Also, how did you calculate the sum? I'd like to try in Excel...
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post #107 of 321 Old 03-15-2017, 01:09 AM - Thread Starter
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Quote:
Originally Posted by dominguez1 View Post
That sum line is awesome! Brings a lot of insight that was hard to see before. For example, that dip in x, y, and z between 20 and 30hz, when summed, is actually flat.

The question is...does it subjectively feel 'flat' or a 'dip' in that range?

Also, how did you calculate the sum? I'd like to try in Excel...
my perception of my setup is that it's pretty "smooth", i.e. it doesn't feel like any particular frequency is emphasised. So yes, the sum looks more like what I think I feel.

Note that the sum is for spectrum only, I don't believe it can be applied to PSD (or at least I've never seen PSDs summed anyway, only acceleration). It's just the root sum of the squares with an additional weighting factor for x & y as per some research doc I posted in one of the other threads.

Code:
# calculate the sum of the squares with an additional weighting for x and y
Psum = (((Pxx * 2.2) ** 2) + ((Pxy * 2.4) ** 2) + (Pxz ** 2)) ** 0.5
Note that ** 2 means squared and ** 0.5 means square root
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post #108 of 321 Old 03-15-2017, 12:35 PM
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Quote:
Originally Posted by 3ll3d00d View Post
my perception of my setup is that it's pretty "smooth", i.e. it doesn't feel like any particular frequency is emphasised. So yes, the sum looks more like what I think I feel.

Note that the sum is for spectrum only, I don't believe it can be applied to PSD (or at least I've never seen PSDs summed anyway, only acceleration). It's just the root sum of the squares with an additional weighting factor for x & y as per some research doc I posted in one of the other threads.

Code:
# calculate the sum of the squares with an additional weighting for x and y
Psum = (((Pxx * 2.2) ** 2) + ((Pxy * 2.4) ** 2) + (Pxz ** 2)) ** 0.5
Note that ** 2 means squared and ** 0.5 means square root
Cool...thanks for the equation.

I keep forgetting that this is not PSD, but acceleration.

I referenced this in this post in the ULF thread a while back, but here is some info on Peak Ground Acceleration and perception:

https://en.wikipedia.org/wiki/Peak_ground_acceleration

Do you see anything applicable in here that can make acceleration/vibration more relatable?
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post #109 of 321 Old 03-15-2017, 02:08 PM - Thread Starter
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We could probably calculate a value like that and see what we measure in our setups. I'm not sure how it relates though as the subjective assessment is based on the whole earth moving (NB: I have never been in an earthquake so no idea what it feels like, I find it hard to relate that to a home cinema setup though)
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post #110 of 321 Old 03-23-2017, 01:11 AM - Thread Starter
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switched to a different chart lib which is much faster to render & added the normalisation options (NB: build not published yet)

quick demo below

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post #111 of 321 Old 03-27-2017, 02:26 PM - Thread Starter
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added a time series view

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post #112 of 321 Old 03-29-2017, 03:01 PM - Thread Starter
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added a simple target curve editor, need to hook this into the measurements for normalisation use next

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post #113 of 321 Old 04-02-2017, 02:34 PM - Thread Starter
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added the ability to use a wav as a target curve, example showing EoT



also faffed around for ages attempting to get a constant Q filter going but failed (well technically succeeded but it didn't achieve what I wanted so...)
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post #114 of 321 Old 04-07-2017, 03:23 PM - Thread Starter
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bought the target curve into the analysis screen so you can measure a scene and then normalise the measured response vs the on disk content. This is just some random measurement compared against EoT though.

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post #115 of 321 Old 04-08-2017, 03:50 AM - Thread Starter
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a better example, 2 sensors placed at different seats and using EoT as the test signal

usual vibsensor style view against time, suggests it is a bit noisy (wasn't especially careful with securing the sensor tbh) but seems sane



now looking at the frequency response, using the summed vibration to keep the graph simple & comparing the two seats. They look pretty similar except one seat falls away at the low end



pick one as the reference so we can really concentrate on the differences, now we can really see that one seat is feeling it much more than the other and this seat is the one that is closer to the sub. This suggests a need for more subs to produce a more even response across the area & also illustrates how quickly TR falls away as the sub gets further away.



next add the source track as a target curve (means get the track as a wav and drag it onto the target screen)



you can now add this to the analysis screen, for now you have to manually adjust the level so in this case I set it so the curves meet at the 30Hz tone. We can already see my room adds a random spike at ~40Hz that is non existent in the content and in fact this is my room mode so we can see how a room mode adds TR as well

(NB: the glitch over on the right appears to be some sort of rendering bug on chrome on linux, doesn't happen on windows)



finally set EoT as the reference series so we can see how we track the source, this makes it clear how much one seat is hotter than the other and the extent to which we're falling behind the curve.

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post #116 of 321 Old 04-13-2017, 04:55 AM - Thread Starter
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pushed a new release to https://github.com/3ll3d00d/vibe/releases/tag/0.3.1 containing all the above features

the windows exe is a bit big (200M) but my time > disk space I'm afraid
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post #117 of 321 Old 05-01-2017, 02:38 PM
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post #118 of 321 Old 05-01-2017, 02:42 PM - Thread Starter
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Quote:
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I get this error on windows 10,
I should change that message, it's not an error Open your browser and go to http://localhost:8080, you want the target option (menu at the top)
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post #119 of 321 Old 05-01-2017, 02:49 PM
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I should change that message, it's not an error Open your browser and go to http://localhost:8080, you want the target option (menu at the top)
OK i got it working. thank you
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post #120 of 321 Old 05-01-2017, 02:52 PM
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o that sucks, i wish it could handle bigger files,

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