Dayton OmniMic Precision Measurement System - Page 25 - AVS Forum
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post #721 of 2090 Old 02-20-2011, 09:13 AM
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Well I did some measuring this morning. One of the tests was the “reverb” which is shown below. I do not think that is bad but I need to do some more reading up on it.

The second batch was the distortion. What I did here was to first go to the SPL tab and made sure I was reading close to 75db. I then went over to the distortion tab and grabbed a snip. I then increased the master volume by 5db and grabbed another one. My problem is, I have no idea if these are good bad or indifferent. When you use the distortion tab, you can mouse over any line and it shows readings (like shown in the help file), but you cannot click on the line to keep that little window of information available either through a snip or screen print.

I am not sure what program nyt was using to grab his distortion measurements with his TC’s but I wish this program had something like that. That program had information like THD=this, 2nd=this %, etc. Maybe it does and I missed it and if so, can someone point this out? Thanks.

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post #722 of 2090 Old 02-20-2011, 09:14 AM
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Last graph.

James
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post #723 of 2090 Old 02-20-2011, 09:42 AM
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"My problem is, I have no idea if these are good bad or indifferent."

not sure if its been said, so sorry if a dupe post. each 10db drop is about 30% and each 20db drop is about 10%, so a 40db drop from the main signal to the distortion level is about 10% of 10% or 1% distortion.

db drop.....distortion
10............31.6%
20............10.0%
30............3.16%
40............1.00%
50............0.316%
60............0.100%

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post #724 of 2090 Old 02-20-2011, 10:08 AM
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LT,

If has been said I probably missed it so thank you for posting or reposting it.

James
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post #725 of 2090 Old 02-20-2011, 11:53 AM
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I have question I would like to run by everyone.

I started out with a 75db signal using the SPL tab. Now I go and look at the 20HZ signal in the harmonics graph, my first one is reading at 75db (best as I can tell since I had to have the graphs in the 10 scale). I then go through every other graph after increasing the master volume on my Onkyo by 5 db. Each time the 20HZ reading appears to also increase by 5db.

So my question is, is it safe to believe that I am not getting any compressed output from my subs to the level I went to (specifically the 20HZ at 95dbspl). I hope I worded my question correctly.

Thanks, James
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post #726 of 2090 Old 02-20-2011, 12:40 PM
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"So my question is, is it safe to believe that I am not getting any compressed output from my subs to the level I went to (specifically the 20HZ at 95dbspl)."

i don't see any evidence of compression in the frequency sweeps that you have posted.

so, yes, it is safe to believe that you are not getting any compressed output at 20hz at 95db spl.

95db spl isn't really that high though. for full reference spl with full re-directed bass, you need about 121db spl at 20hz with no compression. ;-)

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post #727 of 2090 Old 02-20-2011, 12:48 PM
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LT,

Thanks for the response.

As long as my thinking was not wrong, I am not worried about the 95db spl being high right now. I can do some more sweeps at higher levels now that I know my thinking is correct and I move some things off on of my subs. My daughter has a little “office” behind the couch and some things of hers are on there and rattling at that volume.

Also, I will have to look and see if this Onkyo (885) redirects bass when running in “all channels” mode.

I will also be trying to figure out some of those distortion percentages soon.

Thanks again.

James
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post #728 of 2090 Old 02-20-2011, 01:08 PM
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no prob, at your test levels everything looks just fine from here. just enjoy.

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post #729 of 2090 Old 02-21-2011, 08:15 AM
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So if my calculations are correct (pretty big if there), I have 4.88 total THD at 20HZ at 95db (2nd-5th harm distortion).

I used the program on the page linked below and calculated each db drop to the 2-5th harmonic line, then added them all together.

http://www.sengpielaudio.com/calculator-thd.htm

James
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post #730 of 2090 Old 02-28-2011, 05:29 AM
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Quote:
Originally Posted by t6902wf View Post

When measuring SPL what response rating is best to use. With Meters I always thought C was preferred.

Also in the Peak Max Min window on the lower right how is peak different then Max?


Bill W. I am still wondering about this.

Peak is always higher then max.

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post #731 of 2090 Old 02-28-2011, 06:09 AM
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Min and max are averaged/damped values, corresponding to an average program level, as would be read on the meter.

Peak is a max peak value, which is basically absolute value of instantaneous pressure. The minimum "peak" value isn't given because it would be zero in all cases -- the signal always goes through zero pressure (changing from + to -).
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post #732 of 2090 Old 02-28-2011, 08:16 AM
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Quote:
Originally Posted by bwaslo View Post

Min and max are averaged/damped values, corresponding to an average program level, as would be read on the meter.

Peak is a max peak value, which is basically absolute value of instantaneous pressure. The minimum "peak" value isn't given because it would be zero in all cases -- the signal always goes through zero pressure (changing from + to -).

Thanks Bill, when measuring SPL what would be the most appropriate response weighting?

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post #733 of 2090 Old 02-28-2011, 10:13 AM
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Quote:
Originally Posted by t6902wf View Post

Thanks Bill, when measuring SPL what would be the most appropriate response weighting?

Depends on how much meter bounce you can tolerate. Probably "slow" when I use it, but nothing is standard. Music changes with time, so depends on how much you want to smooth through the peaks. Speakers and amps have to handle peaks.
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post #734 of 2090 Old 02-28-2011, 10:22 AM
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Quote:
Originally Posted by bwaslo View Post

Depends on how much meter bounce you can tolerate. Probably "slow" when I use it, but nothing is standard. Music changes with time, so depends on how much you want to smooth through the peaks. Speakers and amps have to handle peaks.

That's dampening. I meant weighting c, none?

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post #735 of 2090 Old 02-28-2011, 10:52 AM
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Quote:
Originally Posted by t6902wf View Post

That's dampening. I meant weighting c, none?

Oops. Sorry, misread. Usually, if any weighting is used it's "A" which is supposed to somewhat mimic human hearing response at least a little, so it is used as standard in lots of kinds of measurements (such as Sound Level Exposure). If you are looking at hifi gear, probably "none" most of the time.
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post #736 of 2090 Old 03-01-2011, 09:58 AM
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Quote:
Originally Posted by t6902wf View Post

That's dampening. I meant weighting c, none?

Try this link. http://www.noisemeters.com/help/faq/...-weighting.asp

Using most sound meters (like the Radio Shack for instance) it's recommended to use C weighting as it's the flattest response. Many meters tho (especially the Radio Shack...which I own and use) are not that accurate below about 80 Hz.

I don't know what the Omni manufacturers recommend tho.
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post #737 of 2090 Old 03-01-2011, 11:13 AM
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Quote:
Originally Posted by IceTBC View Post

Try this link. http://www.noisemeters.com/help/faq/...-weighting.asp

Using most sound meters (like the Radio Shack for instance) it's recommended to use C weighting as it's the flattest response. Many meters tho (especially the Radio Shack...which I own and use) are not that accurate below about 80 Hz.

I don't know what the Omni manufacturers recommend tho.

"none" is the flattest response. C and B are just there for continuity with regular meters. Usually, you use the weighting when you are looking at sound as a 'bad' thing: how annoying or damaging it may be, so that frequencies we are more sensitive to are weighted more. We hear 2kHz better than 20Hz, so 2kHz is weighted more strongly.
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post #738 of 2090 Old 03-01-2011, 03:13 PM
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Playback levels as defined by Dolby (I guess) in our HT systems are to be measured w/o weighting, correct?

Noah
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post #739 of 2090 Old 03-01-2011, 03:57 PM
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I don't know, you'd have to check with Dolby on that.
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post #740 of 2090 Old 03-03-2011, 05:22 PM
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Quote:
Originally Posted by FOH View Post

It comes with a 6' USB to Mini USB, I found this 15' replacement at Monoprice for 2 bucks.

I too was curious about the length limitations of the USB protocol.

The OmniMic actually uses the smaller micro 5pin:

http://www.monoprice.com/products/pr...seq=1&format=2
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post #741 of 2090 Old 03-03-2011, 05:37 PM
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You should be ok to 15'.
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post #742 of 2090 Old 03-12-2011, 07:58 AM
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Just a questions for users - seeing if everybody is satified
with there purchase of this product and any reqrets or concerns.
seems like pretty cool user friendly device from what I see
I think I will be ordering soon to take advantage of CDN$ and the fact I can
ship free to my inlaws who will be driving up from Florida in couple weeks

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post #743 of 2090 Old 03-12-2011, 11:12 AM
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I like it, it does have a couple little quirks, however,...I like it.

Here's a recent LF response taken at the LP (12'), of a nearly 20 year old, heavily modded (not in a good way) Velodyne driver, in a small sealed box, powered by an EP4000;



12th octave smoothing, pink noise and sweep averaged @ LP


Now, the following is a comparo of the same sub, naked (no eq) nearfield, and the same signal at the LP, no EQ, to illustrate onset of PVG, ~ 23hz;



Obviously, the thin red trace was taken about an inch from the driver, minimizing room interaction. Also, in the LP trace, nothing changes other than mic placement, same driver signal voltage and conditions.




Thanks
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post #744 of 2090 Old 03-13-2011, 10:25 PM
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I don't see anything unexpected.

Re the product, I love it.

Easy as pie freq response, and really handy to have real-time SPL/RTA to see what your program material is doing.

Noah
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post #745 of 2090 Old 03-14-2011, 09:04 AM
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Quote:
Originally Posted by noah katz View Post

I don't see anything unexpected.

Re the product, I love it.

Easy as pie freq response, and really handy to have real-time SPL/RTA to see what your program material is doing.

I would agree. Viewing a SPL meter, with simultaneous RTA functionality, while using the system during any type of program, allows a great deal of tangible and real-time correlation of specific mix elements.

I would love absolute control over the GUI, ie., like opening multiple windows and re-sizing each for task specific aspects.., as you would in some circumstances on-line.



Thanks

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post #746 of 2090 Old 03-16-2011, 01:41 PM
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thanks

put order in - will post up some graphs when set up but won't be
for few weeks till get hands on it

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post #747 of 2090 Old 03-16-2011, 05:53 PM
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I just got my OmniMic today and ran a few FRs and THD tests. Hope I am doing this right. LOL

Anyways, I ran the tests from the main listening position. My back subs are very close to the back seats, so I have them about 8db lower then the front subs. I did this for the flattest FR at all seats within 2db. I am sure my THD is a little higher then it should be because of this. Looks like the highest is about 3% THD.

Also, I really wish the OM could go down to 5hz. I know my subs start rolling off at 6-7hz. It would be nice to see the full FR and see how compression sets in at high SPLs.

Last, the BEST thing about the OM is the FR test. It is quick and repeats. This is great for adjusting the EQ on the fly. You see the changes right away.






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post #748 of 2090 Old 03-16-2011, 06:13 PM
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This may be a stupid question, but is this system better, much better than XTZ? I tried REW...but I just need something plug-n-play.
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post #749 of 2090 Old 03-17-2011, 09:30 AM
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I got my OmniMic last week, and have some fun playing with it.

But I have a stupid Newbie question: I can save an .frd file with the OmniMic and open it in REW to generate filters. But what about other information? For example, I can get a waterfall plot in Omni, but I have no idea how to save that data in a format that REW can open. I am able to save impulse response data as a text file, but REW won't open it.
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post #750 of 2090 Old 03-17-2011, 11:19 AM
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Yes I believe you export the frd file? I could be wrong in export but u did I'd and it worked great. Check for my minidsp omni mic eq thread

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