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Old 10th December 2018, 08:25 AM   #221
Armand is offline Armand  Norway
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According to the datasheet the ADXL1005 is 100g
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Old 11th December 2018, 06:18 AM   #222
Calvin is offline Calvin  Germany
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Hi,

yes it´s +-100g, which is more than one needs apart maybe freom some few ultra longstroke woofers doing maximum excursion @50Hz.
+-50g is more realistic I think.
Similar to an AD-Converter dynamic range was - and maybe still is- a major concern for the MEMs.
So You want one that offers just a slightly greater g-range than what is required maximally and You want the lowest noise figure for best resolution.
The ADXL1002 has a noise figure of 1/3 of the ADXL1005.
Also its sensitivity is roughly twice as high ... should improve signal handling at lower volume levels and keeping the acceleration signal out of the noise floor.
The +-100g ADXL1001 is also lower in noise figure.

jauu
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Old 15th December 2018, 10:11 PM   #223
bolserst is offline bolserst  United States
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Quote:
Originally Posted by Calvin View Post
… +-100g, which is more than one needs apart maybe freom some few ultra longstroke woofers doing maximum excursion @50Hz.
+-50g is more realistic I think.
Just curious, what woofers and how much power do you generally use for your MFB designs?
The reason I ask is that I easily exceeded 100G peaks with Peerless 10” and 12” woofers driven with 300W BASH plate amps using the ACH-01 sensor. Is it possible you are thinking of RMS rather than Peak acceleration?

I know I had posted these figures before somewhere so apologize for the repeat, but can’t seem to locate them.
The first compares SPL, excursion, and acceleration for a 15” woofer driven with 1500W and a 10” woofer driven with 200W.

As you mentioned, it is not at the lowest frequencies that you run into high Gs, but at the upper range of the subwoofer. This is because peak acceleration is proportional to peak excursion times the square of the frequency. The second attachment provides some acceleration trends lines for a range of peak excursions. For the 50Hz example you mention, with peak excursion of only 5mm you would already be bumping the 50G limit.

BTW, there is also an ADXL1003 currently available at Mouser which is +/-200G with 45µg/sqrt(hz) noise.
https://www.analog.com/media/en/tech...s/ADXL1003.pdf
https://www.mouser.com/datasheet/2/6...03-1503766.pdf
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File Type: png Gs-TC5400-XLS10_Compare.png (44.7 KB, 175 views)
File Type: png Gs-vs-Freq-vs-Xpeak.png (43.9 KB, 172 views)

Last edited by bolserst; 15th December 2018 at 10:16 PM.
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Old 16th December 2018, 12:43 AM   #224
Armand is offline Armand  Norway
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Attaced is measurements I did on a Peerless XLS 10" with 30V RMS (225W) at various frequencies.
At 47Hz I passed 50g and at 70Hz I had 69g. Above that I ran into problems with the coil rubbing into the magnet because I mounted the sensor on one side of the voice coil without any counter weight on the opposite side. The remaining THD is on the left of the table. 1,32% is down from 8,4% with the same signal without servo.
So 100g is absolutely something that can be neccesary. But I totally agree that if the design goal is less than 50g the ADXL1002 is a better choice.


The ADXL1001 seems to be the best option for 100g applications. It has better linearity with 0,1% vs 0,25% for the ADXL1005. The noise is also slightly better. But not that much smaller than the ADXL1005. The number is given with two different bandwiths in the two datasheets. 10kHz vs 20kHz for the ADXL1005.
It seems the old ACH-01 is still the noise king, but I am unsure how much noise affekts the system. The maximum linearity error of the ACH-01 is also 1% and its low frequency stability is not as good. I remember having oscillations around 1Hz. I guess we just have to try and see.
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Old 16th December 2018, 09:23 AM   #225
bentoronto is offline bentoronto  Canada
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Quote:
Originally Posted by bolserst View Post
...BTW, there is also an ADXL1003 currently available at Mouser which is +/-200G with 45µg/sqrt(hz) noise.
https://www.analog.com/media/en/tech...s/ADXL1003.pdf
The spec for that ADXL1003 says, "Linearity to ±0.2% of full-scale range". But if the full range is 400 G's, does that make the extent of linearity poor for small signals? With feedback, what's in the loop is the whole story; so noise and distortion introduced by the sensor have to be a whole lot better than the previously non-looped system the sensor is meant to fix.

Also, seems to have an 8-lead cable. I wonder if that is kind of heavy to work with a driver?

I wonder how the ACH-01 or the new accelerometers actually perform with increasing cone motion and what the failure mode sounds like?

Thanks.
B.
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Last edited by bentoronto; 16th December 2018 at 09:28 AM.
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Old 18th December 2018, 05:21 AM   #226
bolserst is offline bolserst  United States
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There certainly is much ambiguity in the linearity specification. The datasheet states that the testing was performed using 13kHz sine vibration, but does not indicate what G level was used. Ideally we would have a %THD vs G curve. Hands on testing or additional information from the manufacturer would be needed.

Linearity of mechanical sensors that I deal in my day job are always much better for small signals(sometimes an order of magnitude better) and gets poorer as you approach the specification extremes. I would anticipate the MEMS devices to behave similarly, but can’t say for sure.

The MEMS device weighs a mere 0.2g, compared to 3.5g for the ACH-01.
Only 3 wires would be needed for MFB use so weight should not be a concern.

The MEMS device has sensitivity scaled to a ratio of the supply voltage. Output will clip once the peak output range is exceeded. According to the datasheet the device is also toggled on/off in 500uS intervals until the G level falls back in range. That wouldn’t sound pretty.
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Old 18th December 2018, 05:22 AM   #227
bolserst is offline bolserst  United States
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Quote:
Originally Posted by Armand View Post
Attaced is measurements I did on a Peerless XLS 10" with 30V RMS (225W) at various frequencies. At 47Hz I passed 50g and at 70Hz I had 69g.
Thanks for sharing your measurements…a nice match with simulation from the values I calculated assuming free-air operation of the XLS10. Those are RMS values so the 69g would require 98g peak capability from the sensor, correct?
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Old 18th December 2018, 08:57 AM   #228
Calvin is offline Calvin  Germany
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Hi,

@bolserst
I can´t give a A to Q#223 about which woofer I use.
I´d like to use some of the TCsounds, but then TSound seems to have gone off market again.
There are too numerous longthrow sub drivers around to just fixate on a single one.

Overload behaviour certainly is one of the major concerns in a fedback system.
500µs togle intervall translates to 2kHz which should be easy to filter out and smooth with a lowpass.
And certainly the overload conditions won´t last for long ... it may repeat after a few tens ms but the overload condition itself may last alot shorter.

jauu
Calvin
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Old 20th December 2018, 09:03 AM   #229
esl 63 is offline esl 63
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I have used ordinary piezo tweeter chrystals with success.
Make sure to put an OP amp buffer close to the sensor since the piezo chrystal has high output impedance.
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Old 20th December 2018, 09:05 PM   #230
Armand is offline Armand  Norway
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Quote:
Originally Posted by bolserst View Post
Thanks for sharing your measurements…a nice match with simulation from the values I calculated assuming free-air operation of the XLS10. Those are RMS values so the 69g would require 98g peak capability from the sensor, correct?
It is 10 years since I did those measurements, but if I recall correctly the g's in the table are peak.
I hope I can find time in the coming year to test the new ADXL sensors and will of course post my findings here.
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