ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1] 2  All   Go Down

Author Topic: Smaart RTA 1dB/Octave HF Roll Off?  (Read 1087 times)

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1173
Smaart RTA 1dB/Octave HF Roll Off?
« on: October 12, 2017, 11:44:19 am »

In the outdoor test measurements below the microphone is on the ground 2 meters distant from the cabinet face also on the ground, the “tapped horn” mouth  exit center approximately 50 centimeters off  the ground, 11 meters from a house.

The Smaart Magnitude Response has been equalized for flat response from 30-100 Hz, the same signal measured using the RTA results in about a 3 dB drop from 30-100 Hz, with a less steep lower and upper roll off. The roll-offs are consistent over time, passing traffic and airplanes were mainly visible only above or below the pass-band.

The RTA’s comparative rolloff in an outdoor environment has me curious to the cause. Anyone familiar with the explanation?

Cheers,
Art
Logged

Frank Koenig

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 385
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #1 on: October 12, 2017, 02:15:37 pm »

Hi Art,

Sticking my neck out here, but at 2m measuring distance it seems you might be flirting with the near field. I wonder what happens if you go out to, say, 6m?

Have you looked at the impulse response to see hints of any inadvertent reflections (thinking of that house)? Unfortunately, Smaart does not give us direct control (or knowledge) of the measurement window it uses for the transfer function. This might be be easier to sort out using ARTA, or the like.

I think we agree that in the anechoic far field the RTA (with pink excitation) should agree with the (smoothed) magnitude of the transfer function. I look forward to the explanation.

--Frank

Logged
Yes, it is a giant stereo system!

Mark Wilkinson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 532
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #2 on: October 12, 2017, 05:18:55 pm »

Hi Art, interesting...........what's signal source?  And X-overs in play ?
Logged

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1173
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #3 on: October 15, 2017, 12:10:24 pm »

Hi Art,

1)Sticking my neck out here, but at 2m measuring distance it seems you might be flirting with the near field. I wonder what happens if you go out to, say, 6m?

2)Have you looked at the impulse response to see hints of any inadvertent reflections (thinking of that house)? Unfortunately, Smaart does not give us direct control (or knowledge) of the measurement window it uses for the transfer function. This might be be easier to sort out using ARTA, or the like.

3)I think we agree that in the anechoic far field the RTA (with pink excitation) should agree with the (smoothed) magnitude of the transfer function. I look forward to the explanation.

--Frank
1) My sub testing has shown the influence of reflected sound becomes worse as the distance is increased, and though 1 meter is too close, 2 meters is sufficiently "far field".

2)Not specifically, but coherency was 100% in the pass band. The house should  influence both RTA and magnitude response- in NM I found a convenient location out the shop door had something like +4 dB at 40 Hz compared to getting 25 feet away from the nearest building measuring at 2 meters.

3)Me too.
Logged

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1173
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #4 on: October 15, 2017, 12:20:38 pm »

Hi Art, interesting...........what's signal source?  And X-overs in play ?
Signal source was Smaart pink noise. Processing was a DriverackPA.
Without processing, it would be hard to notice the 3 dB drop in the raw response with all the usual peaks and dips, but since the sub's output was equalized flat, it became obvious.
Logged

Mark Wilkinson

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 532
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #5 on: October 16, 2017, 10:28:26 am »

Signal source was Smaart pink noise. Processing was a DriverackPA.
Without processing, it would be hard to notice the 3 dB drop in the raw response with all the usual peaks and dips, but since the sub's output was equalized flat, it became obvious.

Hi Art, if transfer's reference channel is straight from the soundcard (ie loopback), I don't have a clue.

But if you're getting reference from a mixer, maybe you have a mixer filter in play you don't mean to ? 

I screw that up every now and then.......
It's probably too simple to even mention to you, but since it could cause what you're seeing, I though i should....

Logged

Chris Tsanjoures

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 65
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #6 on: October 16, 2017, 11:30:50 am »

I'd be curious what the measurement looks like using Smaart's modern TF algorithm (try using the demo of v8). The v6 TF is effectively 24 FPPO. The under-the-hood mechanics of the TF engine from v7 forward uses a far more refined scheme of sample rate decimation and various FFT sizes to produce a measurement with different time and frequency resolution in the various frequency ranges - called MTW or Multi Time Window. MTW is effectively 80 FPPO.

You may also find adjusting the TF engine settings from Polar to Complex will give you a slightly different result depending on what you are looking for/what you are looking to ignore. In v6 I believe this is called Complex and Vector - though forgive me, it's been quite some time since I've opened that version.

Logged
I am employed by Rational Acoustics. Besides being a Product Manager for the Smaart Platform, I operate as a fully deployable Smaart Ninja (aka Instructor/System Guy).

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1173
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #7 on: October 16, 2017, 12:58:35 pm »

Hi Art, if transfer's reference channel is straight from the soundcard (ie loopback), I don't have a clue.

But if you're getting reference from a mixer, maybe you have a mixer filter in play you don't mean to ? 

I screw that up every now and then.......
It's probably too simple to even mention to you, but since it could cause what you're seeing, I though i should....
Mark,

Good point, but after I realized I could just use some simple adapters and a phantom PSU, stopped using an outboard mixer, so no mixer filters.
Logged

Art Welter

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1173
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #8 on: October 16, 2017, 01:31:14 pm »

I'd be curious what the measurement looks like using Smaart's modern TF algorithm (try using the demo of v8). The v6 TF is effectively 24 FPPO. The under-the-hood mechanics of the TF engine from v7 forward uses a far more refined scheme of sample rate decimation and various FFT sizes to produce a measurement with different time and frequency resolution in the various frequency ranges - called MTW or Multi Time Window. MTW is effectively 80 FPPO.

You may also find adjusting the TF engine settings from Polar to Complex will give you a slightly different result depending on what you are looking for/what you are looking to ignore. In v6 I believe this is called Complex and Vector - though forgive me, it's been quite some time since I've opened that version.
Chris,

Don't find any adjustment screen called "TF engine settings" or "Polar" or  "Complex". Was using the 32K FFT Size, which claims a 1.5 Hz frequency resolution.
What would  a higher effective FPPO rate have to do with the difference I displayed between the RTA and Magnitude response?

Having "upgraded" to OSX 10.6.8, the last available for my MacBook processor has downgraded the performance of Smaart considerably, using "Hide" will crash it.
Nothing higher than Smaart V6 will run on my laptop, so can't do the comparison you are curious about- you'll have to satisfy your curiosity yourself ;^).

Cheers,
Art



Logged

Chris Tsanjoures

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 65
Re: Smaart RTA 1dB/Octave HF Roll Off?
« Reply #9 on: October 16, 2017, 02:39:04 pm »

Chris,

Don't find any adjustment screen called "TF engine settings" or "Polar" or  "Complex". Was using the 32K FFT Size, which claims a 1.5 Hz frequency resolution.
What would  a higher effective FPPO rate have to do with the difference I displayed between the RTA and Magnitude response?

Having "upgraded" to OSX 10.6.8, the last available for my MacBook processor has downgraded the performance of Smaart considerably, using "Hide" will crash it.
Nothing higher than Smaart V6 will run on my laptop, so can't do the comparison you are curious about- you'll have to satisfy your curiosity yourself ;^).

Cheers,
Art

re: engine settings, this is in v8. Polar averaging is useful for getting a response that 'looks' more like it 'sounds' and since the RTA is most closely related to human hearing, I would think that polar averaging would make the two match pretty well. This is a moot point however, as you can't run v8 cause your computer is at 10.6, and I can't run v6 cause my computer is at 10.12!


With a higher frequency resolution, comes more data points. In the case of MTW, we have 1Hz resolution up to 140 Hz, and 1/48th octave resolution from 60Hz up - which is double the frequency resolution of v6. It could be possible there is information outside the window of v6 TF that is not showing, causing the de-correlation of the RTA to the TF.
Logged
I am employed by Rational Acoustics. Besides being a Product Manager for the Smaart Platform, I operate as a fully deployable Smaart Ninja (aka Instructor/System Guy).
Pages: [1] 2  All   Go Up
 


Page created in 0.044 seconds with 22 queries.