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Old 06-12-2013   #151
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Sweeps and REW (RoomEQ) would be a good idea when I think about it ^^

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Old 06-12-2013   #152
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Default Re: Sound Deadening (CLD) Testing

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Originally Posted by Jazzi View Post
It seems like using a sweep would be better than individual tones because time domain is important too. The maximum steady-state amplitude of a resonance is interesting, but without taking time into consideration, you cannot see how quickly the resonance builds or decays (how quickly the motion is transformed into heat, and thus how effective the damping is).

Room EQ Wizard for example generates its own sweep and will calculate just about anything you could ever want. Each sweep is quick and the program and makes comparison of multiple trial runs (or multiple test products) very easy. Among a ton of other stuff, the program will find the frequency, amplitude, and duration of all resonances for you. That's the interesting stuff, isn't it?

Also, your non-treated system having a single dominant resonance is not unexpected.

-J

(I love this project by the way!)
Hey, I'll pm you later today, I ran through a bunch of things today with omnimic, all with sweeps, but until I can satisfy a few problems I have with using the mic (mostly related to isolating it from the sound coming from the actual speakers) its just playing around. I'll post some snapshots of what I got though. The tones are ONLY for the accelerometer, although there will be some time domain stuff going on there too, with phase comparisons between the speakers, and the accelerometer.


I totally expected the single resonance, and for it to be big when un-treated. But, both the frequency response graph I posted and the video of response from the accelerometer on the scope was with with the metal treated. It has 30% coverage right now with a CLD sheet, in the center of the metal. The CLD currently on there has the second thickest constraining layer of all the samples I have.

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Old 06-12-2013   #153
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Default Re: Sound Deadening (CLD) Testing

These ones are also treated, the same as before, 30% coverage.












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Old 06-12-2013   #154
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Default Re: Sound Deadening (CLD) Testing

I am not familiar with the Omnimic. What signal does it use? I see tone burst mentioned on one of the graphs. The scale of the frequency response makes it a little hard to see, but that resonant peak near 100hz is much more sharp than the result of any of my tests. My experiment had the sheet metal suspended on string though, not firmly clamped to an enclosure from all edges.

You are having problems isolating the microphone from the speakers? It looks like the rear half of the speakers are open to air and might contribute noise to your measurement. However it looks like your mic is vesy close to the sheet metal so the high signal to noise ratio should overwhelm any interference from the rear wave of the speaker since it is relatively very far away.

Maybe the signal from the speaker is being passed through the sheet metal and picked up by the microphone in addition to the re-radiation from the sheet metal. That could skew the results dramatically.

So, why not forgo the mic and use the accelerometer exclusively? If you can hook it up to the scope, it should have enough voltage to drive a preamp and be captured by your computer and analyzed by any software you choose. I assume this would be the most direct way to measure the vibrations of the sheet metal without any acoustic interference.
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Old 06-12-2013   #155
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Default Re: Sound Deadening (CLD) Testing

For all measurements above, it uses sine sweeps, short sweeps for the freq response, impulse response, and waterfall, longer sweeps for the energy time curve and bass reverberation decay, and long bass sweeps for the bass decay.

The accelerometer will put out 3 volts when I move to a battery to lower the noise level, I hadn't yet looked into whether or not it will work with my sound card. The other probably seems to be sensitivity. In order for it to read anything but the peak, it needs to have some eq, to allow it to read the low intensity areas while preventing clipping at the resonance peak. With the program for the scope, that would be built in, but I'm not sure if that can be done with Omnimic or REW. Of course, if the resonant frequency changes dramatically enough, that built in EQ could also cause a problem with accurate measurements.


As for the speakers interfering with the mic, even with as close as the mic is, they still mess with the results. I held some pillows over the speakers today while running sweeps, and it definitely affected measurements, and I wasn't doing a very good job of muffling the speakers on the outside. I might have my wife help grab some shots tomorrow without and with pillows, since I need two sets of hands. I have an idea on how to isolate them better, but it requires more wood, which has to wait until I get paid next friday. Then I can see if the sound coming through the sheet metal is enough to skew the results.




Edit) Just talked to my dad, hes working on the program right now and will be testing certain parts of it tomorrow. He is basically working on a program that would run the scope, output the signal to measure, compare phase between the signal (at the speakers) and the accelerometer output, and the intensity between the two, all while logging everything into access. It would then be put into excel and graphed however I wanted. He encouraged trying to work on getting the mic to work better as well, just as a sort of checks and balances system, basically saying that if one varies wildly from the other, something is wrong with the test.

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Last edited by TOOSTUBBORN2FAIL; 06-12-2013 at 10:59 PM..
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Old 06-13-2013   #156
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Default Re: Sound Deadening (CLD) Testing

Hello, guys.

Looks like its going to be a very interesting test, but I would like to add my $0.02 to possibly make it even better.
First of all, it is good to see that at least one of the Russian suppliers has made it to US car audio market (STP that is).
In Russia, most of vibration damping material marketed for car audio take its origin from construction industry. And they share measurement techniques.

It is well known that damping properties are frequency ant temperature dependent. Less known that eficiency also depends on metal thickness and vibration mode shape.

TOOSTUBBORN2FAIL, your test setup looks overly complicated and prone to systematic errors:
1. steel panel has square shape. This shape is not the best if we want to measure damping in wide frequency range because vibration mode shapes wil be different and will effect results in almost unpredictable way.
2. Panel clamping has low reproducibility and possible high level of damping, which in turn will mask damping of CLD.
3. I don't see clear raw data processing strategy and all these transient measurements are completely uneccesary.

I would strongly recommend to reconfigure test according to Oberst beam method
1. You would need to cut you panel into stripes (length depends on the stripe thickness, but 1:100 ratio would be a good starting point). Stripe shape is good because it has primerely lateral mode shapes of different wave length. Mode shapes uniformity will help with results consistency in wide frequency range.
2. Clamp the stripe vertically by the top end in really rigid vice.
3. Put the accelerometer at the bottom end of the stripe
4. Excite stripe vibration is some way (sweep tone, white noise, even hit with the metal bar at different stripe points - it all works!)
5. Record spectrum response (holding max. achieved levels).
6. Display spectrum in linear scale for frequency
7. Identify resonances (you only can measure damping at resonances)
8. Identify resonance frequencies - Call it F0 (it is good if CLD has more added stifness rather than added mass, i.e. treated stripe frequency goes up)
9. Identify frequency range where response is -3 dB from max resonance response - call it delta_f
10. Calculate Q factor of the system.

Using this method you wil be able to measure damping in wide freq. range (which is really imposrtant for CLD effective envelope evaluation)

P.S. May be I'm too obviouse here with this explanation, but I really wish you all the success with this test and looking forward to see some reasonable (and usable) test results.

Regards,
Andrey.

Last edited by ansuser; 06-13-2013 at 09:46 AM.. Reason: Spell check
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Old 06-13-2013   #157
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Default Re: Sound Deadening (CLD) Testing

Quote:
Originally Posted by ansuser View Post
Hello, guys.

Looks like its going to be a very interesting test, but I would like to add my $0.02 to possibly make it even better.
First of all, it is good to see that at least one of the Russian suppliers has made it to US car audio market (STP that is).
In Russia, most of vibration damping material marketed for car audio take its origin from construction industry. And they share measurement techniques.

It is well known that damping properties are frequency ant temperature dependent. Less known that eficiency also depends on metal thickness and vibration mode shape.

TOOSTUBBORN2FAIL, your test setup looks overly complicated and prone to systematic errors:
1. steel panel has square shape. This shape is not the best if we want to measure damping in wide frequency range because vibration mode shapes wil be different and will effect results in almost unpredictable way.
2. Panel clamping has low reproducibility and possible high level of damping, which in turn will mask damping of CLD.
3. I don't see clear raw data processing strategy and all these transient measurements are completely uneccesary.

I would strongly recommend to reconfigure test according to Oberst beam method
1. You would need to cut you panel into stripes (length depends on the stripe thickness, but 1:100 ratio would be a good starting point). Stripe shape is good because it has primerely lateral mode shapes of different wave length. Mode shapes uniformity will help with results consistency in wide frequency range.
2. Clamp the stripe vertically by the top end in really rigid vice.
3. Put the accelerometer at the bottom end of the stripe
4. Excite stripe vibration is some way (sweep tone, white noise, even hit with the metal bar at different stripe points - it all works!)
5. Record spectrum response (holding max. achieved levels).
6. Display spectrum in linear scale for frequency
7. Identify resonances (you only can measure damping at resonances)
8. Identify resonance frequencies - Call it F0 (it is good if CLD has more added stifness rather than added mass, i.e. treated stripe frequency goes up)
9. Identify frequency range where response is -3 dB from max resonance response - call it delta_f
10. Calculate Q factor of the system.

Using this method you wil be able to measure damping in wide freq. range (which is really imposrtant for CLD effective envelope evaluation)

P.S. May be I'm too obviouse here with this explanation, but I really wish you all the success with this test and looking forward to see some reasonable (and usable) test results.

Regards,
Andrey.
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Old 06-13-2013   #158
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Default Re: Sound Deadening (CLD) Testing

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Old 06-13-2013   #159
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Default Re: Sound Deadening (CLD) Testing

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Old 06-13-2013   #160
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Default Re: Sound Deadening (CLD) Testing

Quote:
Originally Posted by ansuser View Post
Hello, guys.

Looks like its going to be a very interesting test, but I would like to add my $0.02 to possibly make it even better.
First of all, it is good to see that at least one of the Russian suppliers has made it to US car audio market (STP that is).
In Russia, most of vibration damping material marketed for car audio take its origin from construction industry. And they share measurement techniques.

It is well known that damping properties are frequency ant temperature dependent. Less known that eficiency also depends on metal thickness and vibration mode shape.

TOOSTUBBORN2FAIL, your test setup looks overly complicated and prone to systematic errors:
1. steel panel has square shape. This shape is not the best if we want to measure damping in wide frequency range because vibration mode shapes wil be different and will effect results in almost unpredictable way.
2. Panel clamping has low reproducibility and possible high level of damping, which in turn will mask damping of CLD.

I did notice this, and have been working on a work around for this but haven't been able to test it yet.

3. I don't see clear raw data processing strategy and all these transient measurements are completely uneccesary.

I would strongly recommend to reconfigure test according to Oberst beam method
1. You would need to cut you panel into stripes (length depends on the stripe thickness, but 1:100 ratio would be a good starting point). Stripe shape is good because it has primerely lateral mode shapes of different wave length. Mode shapes uniformity will help with results consistency in wide frequency range.
2. Clamp the stripe vertically by the top end in really rigid vice.
3. Put the accelerometer at the bottom end of the stripe
4. Excite stripe vibration is some way (sweep tone, white noise, even hit with the metal bar at different stripe points - it all works!)

The paper linked suggests using non contacting electromagnetic transducers for vibration generation, stating that it significantly reduces the accuracy of the results if the test sample is contacted by the method of vibration generation. It also suggests the same for the measurement, suggesting that an accelerometer can be used, but that it would degrade the results.

5. Record spectrum response (holding max. achieved levels).
6. Display spectrum in linear scale for frequency
7. Identify resonances (you only can measure damping at resonances)
8. Identify resonance frequencies - Call it F0 (it is good if CLD has more added stifness rather than added mass, i.e. treated stripe frequency goes up)
9. Identify frequency range where response is -3 dB from max resonance response - call it delta_f
10. Calculate Q factor of the system.

I've seen a lot of studies stating that the half power bandwidth method of calculating damping ratio can be significantly inaccurate, often significantly overstating the damping ratio. There is a correction for it, but I have not been able to find somewhere where I don't have to purchase it (and unfortunately, I don't have any additional budget right now).

Using this method you wil be able to measure damping in wide freq. range (which is really imposrtant for CLD effective envelope evaluation)

P.S. May be I'm too obviouse here with this explanation, but I really wish you all the success with this test and looking forward to see some reasonable (and usable) test results.

Regards,
Andrey.
In the beginning, I really wanted to pursue this method, but the more I looked into it, the more it became priced out of my range for reliable results. Granted, I admit, there are still some issues with my setup, but as a comparative comparison, I will make sure all possible fixes are made before final testing and results are obtained.

Damping ratio can also be calculated by comparing the phase shift between the exciter and the substrate, which is what I'm working on now.

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Old 06-21-2013   #161
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Default Re: Sound Deadening (CLD) Testing

This product is sold on amazon, they have a thinner version also, maybe if you call them they can send aome free samples to test




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Old 06-22-2013   #162
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Default Re: Sound Deadening (CLD) Testing

Alrojoca, thanks for the info, email has been sent, and I'll make a follow up call monday afternoon.



The testing program is done, just waiting until tuesday when my dad is back in town to load it onto my computer. That means this week I'll be testing the repeatability of the test system, then moving forward with tests next weekend. I'm hoping to be able to post the first full scale test by the following monday.



I had an interested experience last night when removing the deadener from the test panel. So everyone knows, the material I used was SDS' CLD sheet, approximately 30% coverage. Obviously, most people have seen his video on his website, and that is an accurate idea of what the metal SOUNDED like before and after deadener was applied. However, I needed to remove the deadener last night, so I tried to pull it off. I ended up getting the aluminum layer off, while most of the butyl stayed put. Guess what, the metal sheet now SOUNDS almost as it did before any deadening was in place. Now, I haven't measured, and that's something I plan to do, but its pretty compelling evidence that the butyl by itself its not doing much, and that constraining layer construction and thickness is one of the most important factors in how this stuff works.

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Old 06-22-2013   #163
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Default Re: Sound Deadening (CLD) Testing

Thanks for the update. I emailed Knu again to see if they had any interest, as I never heard back. Still no response. I might just have to order a sheet of each of their products.

Interesting observation regarding the effects of the butyl thickness vs aluminum thickness.
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Old 06-22-2013   #164
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Default Re: Sound Deadening (CLD) Testing

Ya, I hadn't heard anything back either.


The SDS tile was a monster to get off. Had to use channel locks to grip it past a certain point, and the constraining layer came off in pieces. Hit myself in the stomach a few times with the channel locks pulling towards me when the aluminum tore.

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Old 06-22-2013   #165
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Default Re: Sound Deadening (CLD) Testing

As I'm finishing this quarter's differential equations and materials science classes, your project is becoming more and more fascinating! After studying mass/spring/damping systems and stress/strain behavior of materials for the past few months, I'm able to see with a new clarity what is happening. Maybe I can contribute a little better now.


Quote:
Originally Posted by TOOSTUBBORN2FAIL View Post
Damping ratio can also be calculated by comparing the phase shift between the exciter and the substrate, which is what I'm working on now.
Is this still the method you are using to measure damping factor?

This method works because the damping material resists the change in velocity of the substrate, so the system's displacement becomes out of phase with the external force. This difference in phase builds up over many cycles (over some amount of time) to a maximum steady-state value, and if the external force is removed the displacement of the system will also take time to decay down to some insignificant amplitude. If the frequency of the external force is changing "fast" enough, the difference in phase between the system and the force will not have enough time to react and establish a meaningful value. What I mean is, this process does not happen instantaneously and cannot be measured with this assumption. So pink noise is not a useful signal for this measurement, and a "fast" sweep is not either. My guess is a stepped change in frequency or a very "slow" sweep would be best for this method.

But how "slow" is slow enough? If adding the time for one cycle of each frequency from 1hz to 600hz (the upper limit of your accelerometer), it would take about 7 seconds (thank you wolframalpha). So if your sweep was continuous and increased logarithmically in frequency similar to what REW does, you could have around 4-8 cycles near each frequency along the way (or many more if you start the sweep at 10hz instead of 1hz).

All that aside, how are you going to measure the absolute phase of the external force? The two speakers you're using, the enclosure volume both in front and behind the woofers, the airspace coupling them to the substrate, the group delay of the system and who knows what else seems to make that impossible. If you were to replace the external force with something more directly coupled to the substrate like an electromagnet, that might make this method easier to use. But that line of thinking is moving towards the Oberst Beam method that you responded to a few pages back.

I don't know if anyone else finds this fascinating (doubtful), but I suddenly do! I wish you the best man, and kudos for taking on such a great project. I hope your experiment yields some interesting results.

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Old 06-22-2013   #166
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Default Re: Sound Deadening (CLD) Testing

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Originally Posted by TOOSTUBBORN2FAIL View Post
.....However, I needed to remove the deadener last night, so I tried to pull it off. I ended up getting the aluminum layer off, while most of the butyl stayed put. Guess what, the metal sheet now SOUNDS almost as it did before any deadening was in place. Now, I haven't measured, and that's something I plan to do, but its pretty compelling evidence that the butyl by itself its not doing much, and that constraining layer construction and thickness is one of the most important factors in how this stuff works.
More evidence that constrained-layer-damping tiles are more effective and worth the money compared to home improvement store alternatives

As anuser mentioned a few pages back the constraining layer stiffness, the adhesive stiffness, and the viscoelastic layer thickness are all very relevant to damping performance. You can record the thickness of the aluminum backings as a relative measure of stiffness, and you can record the thickness of the viscoelastic + adhesive layers too as part of your data.

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Old 06-22-2013   #167
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Default Re: Sound Deadening (CLD) Testing

Jazzi, that's exactly the idea behind measuring phase of both. And that was my worry, was how to best measure phase of the exciting force. I haven't yet figured out how to work that it, and it probably wont get fully worked out, which is why I'll also have decay plots. But if it can be relative, it may work in the context of a product comparison. As for how to deal with frequencies with enough cycles to let the phase differences to its maximum value, we will be using tones, very close together. Thinking 1/24th octave. Basically, any tone (and amplitude) I want can be entered into Access, and the program will read that and create the tone. Then it will record the results and log them in another Access file, which can then be imported into excel for any graphing and math needed.


I definitely plan to measure and include comparisons of the constraining layer thickness, butyl thickness, and weight. Basically I'll have 1"x1" samples for measurements, controlled heat (oven), realistic heat (car roof through summer), and the 5.5"x5.5" samples for vibration testing.

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Old 06-22-2013   #168
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Default Re: Sound Deadening (CLD) Testing

I was thinking more about finding the absolute phase of the external force and that path just looks nasty and full of uncertainties.

Instead, leverage the relative measurements like you mentioned. How about calibrating your system by running one (or several) untreated pieces of sheet metal and using these measurements as a control. Then you can subtract the control data from your product data to see the change in phase relative to no treatments. The change in phase between control and products should only be an increase (positive values) corresponding to an increase in damping, or an increase in performance. This works out nicely in my mind's eye anyways.

I hope your family is doing well.
Enjoy what is left of the weekend!

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Old 06-22-2013   #169
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Default Re: Sound Deadening (CLD) Testing

That's exactly what I started thinking about, and why I want to run a number of consistency checks as well. As long as consistency between batches is good, then the relative damping will be shown for this system.


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Old 06-23-2013   #170
 
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Default Re: Sound Deadening (CLD) Testing

TOOSTUBBORN,

Have you looked at the paper I referenced from the Navy testing damping properties for ship hulls? If you haven't you will find some valuable references / ideas.

You mention some issues you are having. Keep in mind there is no possible way to eliminate all the imperfections in a test setting. Actually the best way to test this would be to take a stripped out car body and apply the products one at a time. Then shoot a sweep tone at it from underneath and measure the response inside the body with a super flat reference mic.

With that in mind your setup is a good start. You mention decoupling the sound from the speakers in relation to the microphone. You should be able to do this with some minor changes to your test box. You would then create a baseline waveform that you subtract out from all the samples tests so whatever "spillage" from the speakers to the mic are removed from all the test runs.. There are a variety of ways to subtract the common baseline waveform.

I am happy to help build text boxes, provide test tone sweeps, baseline testing, audio advice, accelerometer issues, etc. Let me know what is bogging you down if you want and I will try to help you with a solution. I do it for a living.

Question - have you considered using a transducer for measuring the results? Or as an extra data set? Depending on the device it should have a negligible effect on the results and it would be the same on each sample. The accelerometer is currently being used for this but there may be more suitable transducers for this application. I am not sure but will look into it if you like.

Keep at it.

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Old 06-23-2013   #171
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Default Re: Sound Deadening (CLD) Testing

Thanks for the input Greg.

I have read though most of the file you linked, and to be honest, I'll need a couple more reads before I get everything down. Some of the math is definitely over my head. My dad also has it, but hasn't had a chance to look it over. He's been trying to get permits for his reverse osmosis setup and acid neutralization for his shop, but its hard when local officials have no idea what in the world those things are. It took 2 months to get the furnaces and evaporator ok'd, and he still needs to add a cooling system for the evaporator.

I hadn't actually though about making the baseline run and subtracting it from the results, but I was planning on making baseline runs without the metal in place to see what the differences were, so that wouldn't be hard to do.

I haven't looked past the accelerometer mostly due to cost. When I first started this, I had a little more money to spare, but rent went up where were at, and the job my wife had lined up fell through. I am in the running for a supervisor position which could give more options for testing (due to the raise), but being that I'm by far the youngest of the candidates, it could come down to office politics.

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Old 06-23-2013   #172
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Default Re: Sound Deadening (CLD) Testing

Just to try it, I measured response with the mic, without the metal, and with the metal (butyl rubber still on it). I also took a measurement including phase, with and without. For without metal measurements, the clamping ring was still bolted and torqued, just not with the metal.

Without metal

With metal

Without metal with phase

With metal with phase

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Old 06-23-2013   #173
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Default

Interesting that there's practically no phase shift in the usable range of the 'with metal' plot...

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Old 06-24-2013   #174
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Default Re: Sound Deadening (CLD) Testing

I thought so too, but im not 100% confident with the phase measurements with the metal on. It seemed to struggle to measure phase with the metal, but had no problems without it. Im going to repeat the tests today and see what I get.

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Old 06-24-2013   #175
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Default Re: Sound Deadening (CLD) Testing

What do you think the measurements with no metal will show you?

Wouldn't it be more interesting comparing bare metal to treated metal?

Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
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