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Multi-Way Conventional loudspeakers with crossovers

Need help interpreting measurements
Need help interpreting measurements
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Old 29th January 2018, 07:25 PM   #1
montana1 is offline montana1  United States
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Default Need help interpreting measurements

Hi To All,
I finally took the plunge and bought a measurement mic (Umik1) and after some setup headaches, I was finally able to capture my very first measurement. Everything is set up using Room EQ Wizard. My lack of understanding is where do I gate the IR given the attached screenshots. All the examples I have seen, there is a logical spot to gate the measurement around 4-5 ms. Any explanations will help in understanding what I'm looking at or what I should be looking for.

Best Regards,
Rich
Attached Images
File Type: jpg ss18w-8434FR-screenshot.jpg (83.4 KB, 354 views)
File Type: jpg SS18W-8434IR-screenshot.jpg (56.8 KB, 349 views)
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Old 29th January 2018, 08:10 PM   #2
eriksquires is offline eriksquires  United States
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That is actually a really clean impulse!

The goal is really to get the most USEFUL FR plot. If you are designing a 2-way, you want to gate low enough that your smoothing is below the expected crossover point.

As D'Appolito points out, we can kind of play with this by adjusting the distance as well. I mean, we normally use 1m, but there's no law that forces us to do this. It's a convention. If you have too much noise still, get closer!

Best,


E
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Old 29th January 2018, 09:36 PM   #3
Draki is offline Draki  Macedonia
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In "impulse" graph, click the "limits" icon and set "Left s" to -0.002 and "Right s" to 0.008 (typical).

You may also want to set the "limits" in the SPL graph to 20 - 20.000 Hz and phase to 720 deg (top) and -180 deg (bottom), this to give you a more standardized look.

And, in "IR Windows" try this: check the "Add frequency dependent window" and select 6 cycles, and then hit "Apply windows". Select 1/48 smoothing. This will smooth the measured curve but still with plenty of useful data.

You can always revert back to whatever your current settings are.

Last edited by Draki; 29th January 2018 at 09:45 PM.
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Old 30th January 2018, 01:20 AM   #4
montana1 is offline montana1  United States
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Thanks Erik,
I have been following Jeff Bagby's paper on 'Accurate In-Room Response Measurements Down To 10 Hz.' His method is to get close as possible and still remain in far field. Thus 3-5 times the radiating diameter of driver being measured and at list twice the baffle width away in order to pick up baffle step correctly. So, In my case baffle width is 10 inches and radiating diameter of driver is 5.25 inches. Armed with that information, I setup up mic 22 inches from driver on tweeter axis (2 way floor stander) and elevated to 66.5 inches from floor. I'm measuring in a very large room with vaulted ceiling. Let me know if I'm overlooking anything. My issues right now are trying to get my head around REW. The Umik1 mic is plug and play but the software is not.

Best,
Rich
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Old 30th January 2018, 01:28 AM   #5
montana1 is offline montana1  United States
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Thanks Draki,
That is exactly the kind of expert information I'm looking for. Anything that moves the learning curve ahead is much appreciated. I will re-visit measurements tomorrow using the settings that you recommended. I found that zooming in close to the IR helps to see the arrival of early reflections. Do you also set a gate time in the right window along with the 6 cycle setting?

Best,
Rich
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Old 30th January 2018, 02:21 AM   #6
wintermute is offline wintermute  Australia
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Need help interpreting measurements
As Eric said it's a very clean impulse! Usually what I look for is the first prominent bump (indicating first reflection) in the IR

Below shows different gating for the same impulse (with the fourth being 1/8th octave smoothed.

The measurement was taken at 66cm distance outside.

You can see the first reflection around 4.5ms, the first graph shows the gate set a bit before this which gives the cleanest high frequency response. The next three show moving the gating out and subsequently increasing "hairiness" of the resulting measurement. I'm not sure if the software you are using allows you to move the gate window in real time (I'm using holm impulse and it does). I normally look for the first obvious anomily in the response and then play around + or - around that.

The last graph is using 1/8th octave smoothing for comparison.

Tony.
Attached Images
File Type: png gate1.png (56.1 KB, 310 views)
File Type: png gate2.png (56.3 KB, 298 views)
File Type: png gate3.png (56.6 KB, 294 views)
File Type: png gate4.png (58.0 KB, 89 views)
File Type: png one_eighth.png (55.2 KB, 96 views)
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Old 30th January 2018, 03:22 AM   #7
montana1 is offline montana1  United States
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Thanks Tony,
Your detailed explanation helps immensely. The graphs you attached are very helpful. Question: can a person just use smoothing techniques rather then gating if near field measurements will be spliced in anyway? Is their advantages to one method or the other?

Best Regards,
Rich
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Old 30th January 2018, 03:54 AM   #8
AllenB is offline AllenB  Australia
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You should be able to see where in the impulse response the speaker ends and the room begins, with the cabinet somewhere in the middle. It depends what you are working on at the time. Smoothing would be questionable.
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Old 30th January 2018, 04:05 AM   #9
mkane77g is offline mkane77g  United States
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Need help interpreting measurements
Nice. Heck, I can't even figure out how to get mine set up to take a measurement.
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Old 30th January 2018, 05:37 AM   #10
montana1 is offline montana1  United States
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AllenB,
Thanks so much for pointing me in the right direction! I did notice if I zoomed in on the IR there is brief space that is blank before the first reflection arrives. That I would assume is the cabinet effect you mentioned. I'm sure there will be many more questions along this journey. Fun stuff though.

Best,
Rich
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