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post #28351 of 31063 Old 03-14-2015, 04:31 AM
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Ok, now that i have the Dayton Audio omnimic and software... what do i do and look out for?

Here's what I am thinking..

1. Look at the freq resp graph when everything is silent.. basically see how quiet the room is..

- Results, for freq 500hz and up, it's below 20dB... but it starts to go up below 500hz to about 40dB... i wonder if the 'mic' has a problem, because in the room it's dead silent to me... it's the quietest place i have been to... in fact, it's so eerily quiet that i wonder if i am hearing my own brain think... so, can someone confirm that what i see on the graph is accurate or that my mic is completely off??? The reason i asked is it's strange that below 500hz, it's up by 20dB... at 40 dB you would think you're hearing a lot of stuff...

2. Is the dayton audio mic even accurate down low in the bass dept? I see my chart pretty good down to like 5hz (which is impossible)...

3. What is a good bass decay chart look like? or, in fact, how is a good freq resp chart looks like... where do i see examples of you guy's rooms? When you measure your freq response, do you use all 7.1 speakers on?

Basically, i have the software/measuring device ,not sure what to measure... and look out for... and how to compare it to what??

ps: I have thus far done everything by 'ear'.... what i like, what i don't like, adjust as appropriate.. first measurement of the freq resp, i found the chart pretty smooth down to 20hz.. looks like our own 'ear' is a pretty good instrument itself!
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post #28352 of 31063 Old 03-14-2015, 07:06 AM
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Quote:
Originally Posted by coolgeek View Post
Ok, now that i have the Dayton Audio omnimic and software... what do i do and look out for?

Here's what I am thinking..

1. Look at the freq resp graph when everything is silent.. basically see how quiet the room is..

- Results, for freq 500hz and up, it's below 20dB... but it starts to go up below 500hz to about 40dB... i wonder if the 'mic' has a problem, because in the room it's dead silent to me... it's the quietest place i have been to... in fact, it's so eerily quiet that i wonder if i am hearing my own brain think... so, can someone confirm that what i see on the graph is accurate or that my mic is completely off??? The reason i asked is it's strange that below 500hz, it's up by 20dB... at 40 dB you would think you're hearing a lot of stuff...

2. Is the dayton audio mic even accurate down low in the bass dept? I see my chart pretty good down to like 5hz (which is impossible)...

3. What is a good bass decay chart look like? or, in fact, how is a good freq resp chart looks like... where do i see examples of you guy's rooms? When you measure your freq response, do you use all 7.1 speakers on?

Basically, i have the software/measuring device ,not sure what to measure... and look out for... and how to compare it to what??

ps: I have thus far done everything by 'ear'.... what i like, what i don't like, adjust as appropriate.. first measurement of the freq resp, i found the chart pretty smooth down to 20hz.. looks like our own 'ear' is a pretty good instrument itself!
40db noise floor is about the most you can expect out of a USB mic. I have a phantom power mic that can go lower (EMM-6 + Q502USB), but to go really low, you need a more expensive "type 1" mic.
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post #28353 of 31063 Old 03-14-2015, 09:26 AM
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Originally Posted by rcohen View Post
40db noise floor is about the most you can expect out of a USB mic. I have a phantom power mic that can go lower (EMM-6 + Q502USB), but to go really low, you need a more expensive "type 1" mic.
Oh, ok, so, there's no use measuring my noise floor then?

Also, how high does the mike I have go in terms of dB? Does it go to 120dB? or, 100 dB? basically what would be the accurate range of the omnimic from Dayton audio? also, what range in frequency? Should i ignore everything under 20hz, 15 hz? etc?
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post #28354 of 31063 Old 03-14-2015, 09:52 AM
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Originally Posted by coolgeek View Post
Oh, ok, so, there's no use measuring my noise floor then?

Also, how high does the mike I have go in terms of dB? Does it go to 120dB? or, 100 dB? basically what would be the accurate range of the omnimic from Dayton audio? also, what range in frequency? Should i ignore everything under 20hz, 15 hz? etc?
I always assumed they were okay up to clipping, but I don't really know.
I would expect the frequency response to be accurate within the range of the calibration file.
For corrected frequencies where the mic is less sensitive, I think the main issue is that you lose SNR.
For example, if the mic is -10db at 15z, the noise will have to get boosted by 10db, along with the rest.

Does Dayton specify this stuff anywhere?
With Cross Spectrum, I see that they will provide the measured noise floor of the mic with a deluxe calibration.
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post #28355 of 31063 Old 03-14-2015, 10:22 AM
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Originally Posted by coolgeek View Post
Oh, ok, so, there's no use measuring my noise floor then?

Also, how high does the mike I have go in terms of dB? Does it go to 120dB? or, 100 dB? basically what would be the accurate range of the omnimic from Dayton audio? also, what range in frequency? Should i ignore everything under 20hz, 15 hz? etc?
Noise floor is what it is ... . That ^ (bold) is irrelevant but it is probably accurate into the 120's. You should just take some frequency response sweeps from the main LP and see what you have. Point the mic at the ceiling and keep it above reflective chair seat backs (recline them). AFAIR the Frequency Response Sweeps are Track 2 on the Omnimic test disk.

Here is a Omnimic FR measurement taken by desertdome at the 2014 215RT GTG.
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post #28356 of 31063 Old 03-14-2015, 12:01 PM
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CG,

RMK! is right, track two on the disc is the stereo sweep, tracks 6 and 12 are the left and right short sine sweeps. Those are what you want to use to really see what is going on between your two main speakers. Track two is ok, but you might see comb filtering between the two speakers, so I always use the 6 and 12 tracks for looking into my responses. Do you have the OM DVD as well? That lets you run sweeps on a full 5.1 system....I really wish it was 7.1 but oh well.

If you have the v2 omnimic, it should be good down to below where your OS will already be dropping off for sure. The calibrated mics you can get from spectrum are typically good down to 5hz. The OM is fine to around 10hz.

AFA what to look for. Pay good attention to the impulse resonse below the Freq response window to see how good your room treatments are and if you are getting any bad reflections. You should see a good blip at 1ms with a little correction as it comes back, then the line should be flat from there on out. If you see any major issues past 2ms, you need to diffuse or absorb a reflection of some sort. The Freq response, this is entirely personal preference but I like a response that slowly slopes down from 10hz all the way up to 20khz, at around a 10dB total slope. This naturally sounds the best to my ears, and many others.

Other folks tend to like the audyssey target curve which is basically a dead flat line across the entire FR. Harman did a study that showed this in fact was not preferred by most, but if there are drastic issues in the room, flat can very well sound better than a garbled all-over-the-place response.

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post #28357 of 31063 Old 03-14-2015, 12:03 PM
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Originally Posted by rcohen View Post
I always assumed they were okay up to clipping, but I don't really know.
I would expect the frequency response to be accurate within the range of the calibration file.
For corrected frequencies where the mic is less sensitive, I think the main issue is that you lose SNR.
For example, if the mic is -10db at 15z, the noise will have to get boosted by 10db, along with the rest.

Does Dayton specify this stuff anywhere?
With Cross Spectrum, I see that they will provide the measured noise floor of the mic with a deluxe calibration.
I have not seen Dayton specify anything anywhere. If anyone have the right information, I would love to know it. For example, this list of info is important:

1. SPL range that is accurate (ie, from lowest to highest).
2. Frequency range that is accurate, say from 10, 15 or 20hz up? till where?


Quote:
Originally Posted by RMK! View Post
Noise floor is what it is ... . That ^ (bold) is irrelevant but it is probably accurate into the 120's. You should just take some frequency response sweeps from the main LP and see what you have. Point the mic at the ceiling and keep it above reflective chair seat backs (recline them). AFAIR the Frequency Response Sweeps are Track 2 on the Omnimic test disk.

Here is a Omnimic FR measurement taken by desertdome at the 2014 215RT GTG.
I know the noise floor is what it is.. but still would be nice to know exactly what my room's noise floor is

Thanks for the information RMK! So, follow up questions, why point the mic up? I would never have thought of that, for instance.. shouldn't i point it at the front? like how we are seating and looking at the front?

The example sweep you provided, what sort of smoothing is that? 1/12? 1/24? this is another confusing variable, what sort of variables should i set in the software?

And last but not least, what is a good bass decay rate? does anyone have a good example of a graph by omnimic?

Maybe someone ought to create a thread on 'freq resp' charts for their respective rooms so that ppl can compare and learn...
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post #28358 of 31063 Old 03-14-2015, 12:12 PM
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Originally Posted by beastaudio View Post
CG,

RMK! is right, track two on the disc is the stereo sweep, tracks 6 and 12 are the left and right short sine sweeps. Those are what you want to use to really see what is going on between your two main speakers. Track two is ok, but you might see comb filtering between the two speakers, so I always use the 6 and 12 tracks for looking into my responses. Do you have the OM DVD as well? That lets you run sweeps on a full 5.1 system....I really wish it was 7.1 but oh well.

If you have the v2 omnimic, it should be good down to below where your OS will already be dropping off for sure. The calibrated mics you can get from spectrum are typically good down to 5hz. The OM is fine to around 10hz.

AFA what to look for. Pay good attention to the impulse resonse below the Freq response window to see how good your room treatments are and if you are getting any bad reflections. You should see a good blip at 1ms with a little correction as it comes back, then the line should be flat from there on out. If you see any major issues past 2ms, you need to diffuse or absorb a reflection of some sort. The Freq response, this is entirely personal preference but I like a response that slowly slopes down from 10hz all the way up to 20khz, at around a 10dB total slope. This naturally sounds the best to my ears, and many others.

Other folks tend to like the audyssey target curve which is basically a dead flat line across the entire FR. Harman did a study that showed this in fact was not preferred by most, but if there are drastic issues in the room, flat can very well sound better than a garbled all-over-the-place response.
Beast, thanks for the info.. very helpful indeed... but some of them are confusing:

1. What do you mean let's you sweep for 5.1? I am assuming it was sweeping for all my speakers in place.. i set my AVR to 7.1, so all speakers are blasting away.. I have the v2 and their dvd that comes with the soundtracks. Even if the tracks are stereo, or mono, wouldn't the avr up-mix it to all channels? I am using a DSP mode like THX Theater. Are you saying I should switch the mode on my avr to stereo?

2. What's an impulse response? I never understood that... the only thing i knew what was going on in the software is the 'freq resp' and the 'bass decay' tabs... the rest is a bit blur to me.. what they are used for and how to read them...

3. As for audyssey.. i totally hate that curve.. i have used audyssey, and have decided it's not for me.. thus, my personally setting up the speaker by EAR first... right now, i wan to see what it is that i like, and see if there's anything else to squeeze out of in terms of getting the best out of my system.

4. Last question, what volume do you guys do the sweep at? And what is reference? is it 75dB or 85dB?
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post #28359 of 31063 Old 03-14-2015, 02:48 PM
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Originally Posted by coolgeek View Post
Beast, thanks for the info.. very helpful indeed... but some of them are confusing:

1. What do you mean let's you sweep for 5.1? I am assuming it was sweeping for all my speakers in place.. i set my AVR to 7.1, so all speakers are blasting away.. I have the v2 and their dvd that comes with the soundtracks. Even if the tracks are stereo, or mono, wouldn't the avr up-mix it to all channels? I am using a DSP mode like THX Theater. Are you saying I should switch the mode on my avr to stereo?

The Dvd allows for you to select all 5.1 channels to run sweeps. The v1 omnimic would only do stereo, so just your left and right. I typically run the fronts with my AVR set to stereo if just using the 2 channel CD, and on Dolby DSU upmixing for the 5.1 dvd. When running sweeps, you really want just a single speaker making noise, and with the DVD, that is exactly what you get my selecting which specific speaker you want to see. For 7.1, I have taken sweeps by switching out the inputs for side surround and putting it to the rears just to get a base-line, but that is getting a little technical as the distance and trim levels are obviously off since you are using the side surround's info, but on the rears. Another important thing is to remember to switch em back I have forgotten that before.....

2. What's an impulse response? I never understood that... the only thing i knew what was going on in the software is the 'freq resp' and the 'bass decay' tabs... the rest is a bit blur to me.. what they are used for and how to read them...

Under the Freq response tab's main window where you see the full 5hz-20khz response, there is a little black and Red squiggly line. That is your impulse response. OM takes this the same time you are running normal sweeps. You want the initial blip to spike, settle, and then stay smooth all the way out. If there is another smaller spike past the 1ms initial blip, you have a reflection somewhere (side wall, ceiling etc.) making the sound arrive at the mic more than once. These reflection will need to be tamed and you will see a better impulse response at that point.

3. As for audyssey.. i totally hate that curve.. i have used audyssey, and have decided it's not for me.. thus, my personally setting up the speaker by EAR first... right now, i wan to see what it is that i like, and see if there's anything else to squeeze out of in terms of getting the best out of my system.

I like you style there. I have been getting back into Audyssey a little bit lately, but I was running clean, absolutely NO eq other than the room treatment method and good speaker placement/toe-in and such for quite some time.

4. Last question, what volume do you guys do the sweep at? And what is reference? is it 75dB or 85dB?
Information answered above for 1-3. for question 4, I typically run sweeps at -10 ref on the master volume.

Check out my thread in my signature the "master measurement thread" to see some more good info. I update it every once in a while when I make any major change, but I have waterfalls, different methods of sweeping and such in there Cheers! and have fun!
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post #28360 of 31063 Old 03-15-2015, 09:15 AM
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I have not seen Dayton specify anything anywhere. If anyone have the right information, I would love to know it. For example, this list of info is important:

1. SPL range that is accurate (ie, from lowest to highest).
2. Frequency range that is accurate, say from 10, 15 or 20hz up? till where?




I know the noise floor is what it is.. but still would be nice to know exactly what my room's noise floor is

Thanks for the information RMK! So, follow up questions, why point the mic up? I would never have thought of that, for instance.. shouldn't i point it at the front? like how we are seating and looking at the front?

Because that is the consensus on the way to measure. If for example the R&L are playing the test signal, where should you aim the mic?

The example sweep you provided, what sort of smoothing is that? 1/12? 1/24? this is another confusing variable, what sort of variables should i set in the software?

Quote:
That measurement was taken 1/12th and that is generally the recommended level
And last but not least, what is a good bass decay rate? does anyone have a good example of a graph by omnimic?

Maybe someone ought to create a thread on 'freq resp' charts for their respective rooms so that ppl can compare and learn...
Quote:
Appropriate ... there is no specific rate except fast when necessary with no overhang or ringing. Some LFE sounds require some extension and others need to stop on a dime depending upon the effect. It's all about getting it to sound appropriate (not easy with those long waves )
As always, Beast provided some good tips. Have fun with it but don't get to hung up on the numbers. In the end, it's all about what you hear/like (but you know that ).

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Last edited by RMK!; 03-15-2015 at 09:20 AM.
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Hopefully someone in Florida can take advantage of this!
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post #28362 of 31063 Old 03-15-2015, 09:50 AM
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Information answered above for 1-3. for question 4, I typically run sweeps at -10 ref on the master volume.

Check out my thread in my signature the "master measurement thread" to see some more good info. I update it every once in a while when I make any major change, but I have waterfalls, different methods of sweeping and such in there Cheers! and have fun!
Beast,

Thanks... that's very helpful indeed... i guess it's time to go play around a bit...

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As always, Beast provided some good tips. Have fun with it but don't get to hung up on the numbers. In the end, it's all about what you hear/like (but you know that ).
Right as always!!

I am pretty old school... (code word for non-techie)

So, up to this point, it's all been done without Auto-EQ, or looking at numbers... I am almost 100% satisfied right now. In fact, the sound has far exceeded my own expectations... so, pretty happy.

However, since I have the Omnimic, I am curious to see what sort of graph that I ended up with, and if I can even fine tune it further... this will take a lot of playing around I think... but it's all fun!
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Hopefully someone in Florida can take advantage of this!
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Where is the amp mounted on the S2?
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Where is the amp mounted on the S2?
Probably at the back same as the S1. Could not find an image for the S2.


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Originally Posted by coolgeek View Post
Ok, now that i have the Dayton Audio omnimic and software... what do i do and look out for?

Here's what I am thinking..

1. Look at the freq resp graph when everything is silent.. basically see how quiet the room is..
The Frequency Response tab can only be used with Omnimic sweeps. The noise shown when no sweeps are playing isn't accurately indicative of the noise floor. When nothing is playing, you need to use the SPL/Spectrum tab to see the actual noise floor. However, the Omnimic self noise swamps any attempts at seeing the actual noise floor except in the bass region. My Earthworks M30BX has a noise floor of 22 dB and is better suited for noise floor measurements. For a noise rating or noise criteria measurement of the background noise, you need to use ARTA with a low noise microphone (see page 150ff in the manual). NC20 (noise criteria 20) is the recommended level by some home theater designers. Here is a chart showing that NC20 still allows for a noise floor of over 50 dB at 63 Hz.



Quote:
So, follow up questions, why point the mic up? I would never have thought of that, for instance.. shouldn't i point it at the front? like how we are seating and looking at the front?
You point the microphone at the speakers if using the default calibration file. If pointing the microphone up you need to manually make a calibration adjustment based off the rolloff shown in the manual.



Regarding measuring for 7.1, I always use track 6 (Left Channel, Short Sine Sweep) and the Order Channels feature in JRiver to quickly move the track through all speakers to take measurements. It only takes a minute to measure all the channels. If measuring with a receiver in the signal path I just use the HDMI output from the laptop into the receiver and still playback through JRiver.
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Thanks!
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post #28369 of 31063 Old 03-16-2015, 08:26 AM
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Originally Posted by desertdome View Post
The Frequency Response tab can only be used with Omnimic sweeps. The noise shown when no sweeps are playing isn't accurately indicative of the noise floor. When nothing is playing, you need to use the SPL/Spectrum tab to see the actual noise floor. However, the Omnimic self noise swamps any attempts at seeing the actual noise floor except in the bass region. My Earthworks M30BX has a noise floor of 22 dB and is better suited for noise floor measurements. For a noise rating or noise criteria measurement of the background noise, you need to use ARTA with a low noise microphone (see page 150ff in the manual). NC20 (noise criteria 20) is the recommended level by some home theater designers. Here is a chart showing that NC20 still allows for a noise floor of over 50 dB at 63 Hz.




You point the microphone at the speakers if using the default calibration file. If pointing the microphone up you need to manually make a calibration adjustment based off the rolloff shown in the manual.



Regarding measuring for 7.1, I always use track 6 (Left Channel, Short Sine Sweep) and the Order Channels feature in JRiver to quickly move the track through all speakers to take measurements. It only takes a minute to measure all the channels. If measuring with a receiver in the signal path I just use the HDMI output from the laptop into the receiver and still playback through JRiver.
DesertDome, as usual, you truly know your engineering stuff...

And where does one go about obtaining one of these very low noise floor, high quality USB mic? What can I do with the Omnimic I have then? (it's calibrated).. if I can't trust it to measure correctly, then wouldn't all my measurements with it goes out the window? Do you happen to know the dB range of that mic in terms of accuracy?

ps: I noticed the chart you presented loses about 5dB from 5Khz to 20khz... is that a good thing or should a flatter one be better?
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post #28370 of 31063 Old 03-16-2015, 08:32 AM
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And where does one go about obtaining one of these very low noise floor, high quality USB mic?
I don't think there is a low noise floor USB mic. Mine isn't USB.

Quote:
What can I do with the Omnimic I have then? (it's calibrated).. if I can't trust it to measure correctly, then wouldn't all my measurements with it goes out the window?
Measurements are always taken at louder levels than the noise floor in the room. This means you can trust the measurement. Just use your Omnimic and don't worry about it.

Quote:
Do you happen to know the dB range of that mic in terms of accuracy?
9Hz to 30kHz ±1/-3dB

By the way, the Omnimic can be used with REW software, too.
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post #28371 of 31063 Old 03-16-2015, 08:35 AM
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Originally Posted by coolgeek View Post
DesertDome, as usual, you truly know your engineering stuff...

And where does one go about obtaining one of these very low noise floor, high quality USB mic? What can I do with the Omnimic I have then? (it's calibrated).. if I can't trust it to measure correctly, then wouldn't all my measurements with it goes out the window? Do you happen to know the dB range of that mic in terms of accuracy?

ps: I noticed the chart you presented loses about 5dB from 5Khz to 20khz... is that a good thing or should a flatter one be better?
In blind tests it has been shown that the majority of people prefer a rolling off just like you see in DD's graph. I am not that way. I actually like a flat response up to around 8khz and then RISING above that. These are NOT harsh frequencies, they add air/sizzle etc. I've tried EQing the response to look like DD's many times and it sounds dead to me.

I probably just need to get used to it, but I can't. My ears crave some sparkle.
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post #28372 of 31063 Old 03-16-2015, 09:24 AM
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Originally Posted by carp View Post
In blind tests it has been shown that the majority of people prefer a rolling off just like you see in DD's graph. I am not that way. I actually like a flat response up to around 8khz and then RISING above that. These are NOT harsh frequencies, they add air/sizzle etc. I've tried EQing the response to look like DD's many times and it sounds dead to me.

I probably just need to get used to it, but I can't. My ears crave some sparkle.
"DD's graph" is the actual "Mic facing upward compared to mic facing forward" graph from the Omnimic manual and isn't an actual room sweep. The point is don't face the mic upward and then use its measurement (unless you have adjusted your omnimic calibration file) to try to flatten or have a rising response in the high frequencies.
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post #28373 of 31063 Old 03-16-2015, 09:34 AM
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Desertdome,

I've not been able to find much solid information on the direction of the omnimic mattering? Isn't that kind of the point of the name? omnidirectional?

The manual says the omnimic should be pretty much omnidirectional in measuring accurately, with the variance being a 3dB difference at 13kHz between pointing up vs pointing the mic to the speaker.

Is that not what you've experienced. I can't say I've ever noticed much difference between holding it different ways if the tip stays in the same place.

http://www.daytonaudio.com/OmniMicV4/hs230.htm

From the link:

Quote:

Omnimic is a small capsule, narrow tip measurement
microphone and its response is essentially omnidirectional at most frequencies.
At very high frequencies, there is about 3dB reduction in response at 13kHz, as
can be easily determined by making a set of comparative measurements with the
mic pointing at and then perpendicular to a high frequency speaker.
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post #28374 of 31063 Old 03-16-2015, 09:36 AM
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Originally Posted by desertdome View Post
"DD's graph" is the actual "Mic facing upward compared to mic facing forward" graph from the Omnimic manual and isn't an actual room sweep. The point is don't face the mic upward and then use its measurement (unless you have adjusted your omnimic calibration file) to try to flatten or have a rising response in the high frequencies.
Gotcha. It does look like the curve that they say most people prefer though.
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post #28375 of 31063 Old 03-16-2015, 10:15 AM
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Quote:
Originally Posted by desertdome View Post
I don't think there is a low noise floor USB mic. Mine isn't USB.


Measurements are always taken at louder levels than the noise floor in the room. This means you can trust the measurement. Just use your Omnimic and don't worry about it.


9Hz to 30kHz ±1/-3dB

By the way, the Omnimic can be used with REW software, too.
Gonna download REW then... lots of stuff to play with... thanks for all the 'beginner's help btw... else, i'll be looking at charts with no idea what to do with them or trust them...

Quote:
Originally Posted by carp View Post
In blind tests it has been shown that the majority of people prefer a rolling off just like you see in DD's graph. I am not that way. I actually like a flat response up to around 8khz and then RISING above that. These are NOT harsh frequencies, they add air/sizzle etc. I've tried EQing the response to look like DD's many times and it sounds dead to me.

I probably just need to get used to it, but I can't. My ears crave some sparkle.
Currently mine slopes down a bit like that.. but maybe not 6dB down... I'll see if I like it flat to 20hz...

I don't find it dead at all though... i put a lot of diffusers around the room,... i think if you feel it's dead, it might not necessarily be the 'slope' but rather too much absorbers... In my room construction, i went thru many phases.. first phase is to cover the entire room (most places with at least 2-4 inches of rockwool (ceiling is all 4 inches))... I with all the rockwool exposed, i tried listening to some songs.. the room was DEAD... then when i started covering up the rockwool with wood, the sound became better and better... and when i added diffusors on side walls and back walls, the sound became really good... lively.. and quiet at the same time.. basically when a singer pause, you can hear her/him breathe.. when playing gravity, it can be dead silent, and as the astronaut speaks, the levels became ever so slowly louder.. it's palpable...

Anyways, I'll be playing with the slope over the next weeks...
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post #28376 of 31063 Old 03-16-2015, 10:27 AM
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Quote:
Originally Posted by Archaea View Post
Desertdome,

I've not been able to find much solid information on the direction of the omnimic mattering? Isn't that kind of the point of the name? omnidirectional?

The manual says the omnimic should be pretty much omnidirectional in measuring accurately, with the variance being a 3dB difference at 13kHz between pointing up vs pointing the mic to the speaker.

Is that not what you've experienced. I can't say I've ever noticed much difference between holding it different ways if the tip stays in the same place.

http://www.daytonaudio.com/OmniMicV4/hs230.htm

From the link:
Almost all microphones are omni directional. However, when a microphone is also measuring the reflections in the room, the response changes. There is what is called a free field measurement and a diffuse field measurement. Free field is typical of a close mic measurement and is what the Omnimic was originally developed for - making measurements of speaker drivers to design crossovers. The further you get away from the source, the more you are in the diffuse field. A free field measurement is taken without any reflections and a diffuse field measurement is a measurement taken in a reverberant room. Since most are taking measurements from the listening position, they are taking measurements in the diffuse field. In this case, the microphone is experiencing the rolloff shown by the vertical Omnimic graph even if the microphone is pointing at the speaker. Depending on the speaker and room, the microphone can vary in its upper frequency rolloff between a horizontal or vertical mic, but it still exists. For this reason I usually use a diffuse field calibration when doing any room EQ. The Omnimic comes with a free field calibration file, though.

Summary - The closer you are to the speaker, the more difference there will be between vertical and horizontal microphone placement. The further you are from the speaker, the more similarity there will be between the vertical and horizontal microphone placement with the tendency of the measurement to be be that of a a vertical placement. When I say "vertical placement" I just mean the rolloff in the measurement more closely tracks a vertical or diffuse field calibration.

The gating used also effects the rolloff. In the Omnimic software this is changed by selecting "blended" or specifying "only to" a certain time limit on the Frequency response tab. Remember the Bill Fitzmaurice DR250's? We were using a gated semi free field measurement to determine SPL. A diffuse field measurement, by using "only to" and setting a longer window or using the RTA would have more accurately showed us the much higher SPL at the higher frequencies. A frequency sweep in the Frequency Response tab cannot be used to level match SPL between two speakers.

Because it is so hard to ascertain what is really accurate in the upper frequencies when measured at the listening position, I like to design a room correction target in Audiolense that matches the actual measurement.

It wasn't until I got my iSEMcon microphone that included free field and diffuse field calibrations and comparing to real measurements that I started realizing this.

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post #28377 of 31063 Old 03-16-2015, 10:54 AM
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Originally Posted by coolgeek View Post
Gonna download REW then... lots of stuff to play with... thanks for all the 'beginner's help btw... else, i'll be looking at charts with no idea what to do with them or trust them...



Currently mine slopes down a bit like that.. but maybe not 6dB down... I'll see if I like it flat to 20hz...

I don't find it dead at all though... i put a lot of diffusers around the room,... i think if you feel it's dead, it might not necessarily be the 'slope' but rather too much absorbers... In my room construction, i went thru many phases.. first phase is to cover the entire room (most places with at least 2-4 inches of rockwool (ceiling is all 4 inches))... I with all the rockwool exposed, i tried listening to some songs.. the room was DEAD... then when i started covering up the rockwool with wood, the sound became better and better... and when i added diffusors on side walls and back walls, the sound became really good... lively.. and quiet at the same time.. basically when a singer pause, you can hear her/him breathe.. when playing gravity, it can be dead silent, and as the astronaut speaks, the levels became ever so slowly louder.. it's palpable...

Anyways, I'll be playing with the slope over the next weeks...
Mic aiming issues aside ( ) a dead room is well .... dead. I don't have all surfaces covered for a reason and it ain't the cost of doing it. I wanted to get rid of slap echo's but still maintain some reflections. I never think I need more treatments but I do think that for music and that live feeling, less sidewall absorption might be a good idea. How that would effect movie watching (primarily dialog clarity) would be my main concern. I think Carp removed some first reflection side wall absorption panels and is happy with the result. How that looks in FR graphs is another story and that's why I don't measure much anymore. Now that I have been at this hobby for 12+ years it's much better to go by what I hear.

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post #28378 of 31063 Old 03-16-2015, 11:51 AM
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Mic aiming issues aside ( ) a dead room is well .... dead. I don't have all surfaces covered for a reason and it ain't the cost of doing it. I wanted to get rid of slap echo's but still maintain some reflections. I never think I need more treatments but I do think that for music and that live feeling, less sidewall absorption might be a good idea. How that would effect movie watching (primarily dialog clarity) would be my main concern. I think Carp removed some first reflection side wall absorption panels and is happy with the result. How that looks in FR graphs is another story and that's why I don't measure much anymore. Now that I have been at this hobby for 12+ years it's much better to go by what I hear.
Exactly...!!!

Our ears is what matters! The measurements comes after... (like see what you ear).
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post #28379 of 31063 Old 03-17-2015, 03:48 AM
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Oh Nooooooooooooooo!!!

Disaster Struck!!

My Orbit Shifter appears to be in trouble... it's giving me the silent treatment!

Ok, here's the problem.. while testing... it suddenly went dead silent.. it doesn't appear to be clipping.. the clip lights aren't on... i wasn't playing too loud.. nothing it couldn't handle.. in fact, my dial was at -8 and on the receiver 0 gain...

Actually, it acted up a bit before it completely went silent.. while playing, the 'signal lights' went off... i thought it was in protection mode, but the protect light (red) wasn't on... the clipping (orange light) wasn't on either...

Just the 'Signal' light was gone... the 'power light' is on all the time..

Basically, it did this a few times... off and on.. and now, it won't turn on anymore.. i mean, there is no signal light at all..

Do you guys think the AMP is done? Or, could it be the woofer?

Also, on a separate note: How close to the walls can you put the 'mouth opening'? if it's too close, can the air go back into the mouth and destroy the driver?? i mean, do we need a lot of clearing?
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post #28380 of 31063 Old 03-17-2015, 04:50 AM
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^^Check the Mute button.


The top switch/button labeled "MUTE" or "SW1" is available for troubleshooting or setup as a simple MUTE function. This should be set to the IN position for use (OUT mutes the signal to the amplifier module). It is packed with the switch depressed (IN), but can be occasionally pressed while handling or unpacking. This mute switch takes effect AFTER the signal LED
http://www.seaton-sound-forum.com/po...-hp-f2-5999706

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