Dayton OmniMic Precision Measurement System - Page 27

Alright, I fall into that small category of users that needs everything explained for my own sanity and so I can sleep at night

I did some measurements today but they look way different then my REW and I feel semi-confident about them. What is the best way to measure just my sub frequency response at listening position?

From what I've seen playing with this app using track #3 with the frequency response set to sine sweep plots the best sub graphs but it isn't what the PDF states to do and I am constantly getting the message I am using the wrong track. When I plot out bass response using the Bass Decay tab and use track #4 my graph is almost flat and I know it isn't right. Is there any way to do just a regular sweep and have it plot out the results without me constantly having to hit the pause button? The issue I have with this I sometimes hit it too soon or too late and it screws up the graph and it doesn't look the same from one run to the next.

So for the sake of others too afraid to ask, what is the best method to plot out just subs using the Omnimic?

You need to use the tracks as described in the instructions. Results generated without matching the correct tracks and measurements have no value.

The screens are telling you "wrong track" for a reason.

Use the arrows to reduce the response display to show 10 - 200 hz, and select "no smoothing". Use the sine sweep track ( I think track 2) with the frequency response chart, There shouldn't be any need to use pause - if you want to hold a reading for reference against new settings, use the "average" button. I'm working off memory, but I think those are the correct button and track names,

I usually use track 2, sine sweep, window from 10-100 (or 200) and 1/6 and another at 1/24. I go down to 10 even though the mic only goes to 12HZ.

Also, if you do not want to pause the screen, just go and save it as an fdr and then it will "unpause" itself.

James

Too make the sound less annoying and get just the sub's response, I set the receiver to DPLIIx; the mono signal means only the center channel speaker has significant volume.

I then disconnect it.

The results seem fine, even though I get a "wrong track" message, presumably because the top 7 octaves of response are missing.

Thanks guys, good advice from all.

Noah - When you say "I then disconnect it" are you stating that you disconnect your center speaker all together or do you just disable it in the receiver as not even having one?

I really need to get some banana plugs to make my life easier

I disconnect it; I do have banana plugs

Attached are my graphs at my main LP. I am a little surprised by these and not sure what to even think other than maybe I messed something up

I took these with the MIC attached to a MIC stand, used track #2, set my receiver to "pure" which is the front 2 speakers but I have them hooked up to an external amp so nothing played out of them except the my 2 SW's. I set the range as recommended (10-200hz) and I set it to sine sweep.




These were semi-rushed so I am going to take some more measurements at the throat of my sub ports and other listening spots to see what the graphs look like. My only question regarding this is if my crossover is set to 80hz, why would the MIC be measuring anything unless it was background nose in the room (possible, the EP4000 fan is not too far away)?

Sorry for the big pics, I wanted to show how I set up the app for verification and yes I know there is a snapshot feature

Bill,

Probably a silly question but what is the Pa representing in the O'scope measurement? I understand it is the amplitude but is type of voltage measurement? I checked the help file but did not see and was wondering since I grabbed some of these while testing my subs. Thanks.

James

Pascals (units of acoustic pressure)

Thank you.

James

Bill,

Would I also be able to see a clipped or distorted signal with this o'scope? Thanks.

James

Clipping - probably not, unless the speakers are unusually linear in phase response. The problem is that clipping creates high frequency harmonics, and if the speaker isn't rather precisely linear phase the harmonic energy will get shifted to different parts of the fundamental frequency waveform. For instance, a clipped amplifier should clip sinewave peaks but non-linear phase will move the uglies from the peak to elsewhere on the wave which would not be so visually identifiable. To see clipping you want to look before speakers get into the action, using an electrical (not acoustical) oscilloscope.

Bill,

Sounds good, thank you very much again.

James

I am look for this sulotion for years!
thanks dude!

Bill,

I know that 12HZ is the lowest reading we can get with the Omni graphs but is that the lowest signal sent when using pseudo noise, sine sweep etc? Thanks.

James

No, there is energy below 12Hz. Period of the sweep or noise is 680msec, so that there will be energy down to about 1.5Hz.

Thanks Bill.

James

That's assuming the CD player and amp go that low, of course!

If you use no smoothing the graphs go to 10 Hz.

Never tried that one Noah.

James

From all my searching on the web, the Dayton Audio Omnimic (OM) measurement system appears to be a very capable system. The fact that Bill Waslo - the creator of Praxis - is the developer gives me confidence. Also, ease of use is a priority for me - and this appears to be an OM strength. I read many post at AVSforum & PE Tech Talk forums; just have some lingering questions:
1. Are there any independant professional comparisons or reviews; specifically has Kal Rubinson completed a review, per indications from this thread?
2. Would like to confirm that OM does NOT need a soundcard to function.
3. Assume OM works with Windows 7; am planning on purchasing a new laptop.
4. Is a boom style mic stand recommended, or just a conventional vertical mic stand? Any recommendations on which stand to purchase?
5. If I also purchase a Woofer Tester WT3 from Parts Express, will I need any other components for a complete measurement system? It appears that the outputs from OM & WT3 can be exported into Jeff Bagby's Speaker Design Software, providing a speaker design capability - please confirm.
6. I also want to be able to measure individual drivers; I am very pleased that OM has a CSD measurement function (although I determined this not from looking at the online brochure, but through posts on Tech Talk forum).
Thanks for your consideration.

1. Not yet. Will happen when I can get to it.
2. True.
3. Probably. Look at the help stuff.
4. Always recommended.
5. Dunno.
6. OK.

I have OM on a net book and a laptop. Both are running windows 7. IMHO net books lack the horsepower even with memory upgrade and I had to disable some programs to keep it from stalling. I just got a new laptop with widi and you can steam the graphs to any HDMI display. Handy for HT acoustic testing and sharing results with others.

im very interested in this, but before I order I wanted to ask one thing.

Has the 60hz bump [people were saying pssible ground issue], been isolated and fixed? I tried reading through the pages, but got through quite a bit without any resolution.

This looks very promising, as im looking to see what other room acoustics treatment may be benificial for my bass null. Plus for subwoofr placement, as I plan on getting a second epik empire, and it gets tricky with two subs im told. Thanks for the help.

EDIT: Nevermind. Found the answer. It is indeed found and resolved. I hope this is easy to learn and understand. All I really will be using this for is subwoofer placement. [nulls and peaks]

It will work great for that.

I had a defective 60hz unit and it was replaced.

Seeking advice. I don't need the most flexible, sophisticated measuring system out there, I'd just like to do some measurements in my room to evaluate sub placements, room treatments, etc. I don't have a cal file for any of my current mics and am unwilling to spend many hours learning software and getting pieces of equipment to work properly. So REW does not look good to me. I am considering XTZ or OmniMic. I feel confident with Kal's review of XTZ but have also heard that this "new kid on the block" (coincidentally for the same price) may offer advantages. I'd like some unbiased input as to the plus/minuses of these two for the casual user. Advice? Does it matter? TIA

So I just looked up the info on XTZ and found this statement interesting:

"Finds room modes/nodes and calculates (using advanced algorithms), then suggests acoustically optimum countermeasures"

I haven't seen anything in OM that suggests "optimum counter measures".

I also noted that the claimed lower end of the measurement range is a bit higher than the OM.

Just placed the order.

Is there any easy guide someone has written on how to accurately find the problem areas where one should place bass traps? Or how to calibrate your speakers and sub to a certain dB before taking measurements; not sure how to do this without actually using audyssey, which I would assume I cant use as I should turn audyssey off 1st.

Are there any Test tones available for testing each channel? If not, what are the options available to test each channel for full spectrum, without disconnecting the speakers not in use.

KE